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FERTILISERS AND MANURES

FERTILISERS AND
MANURES

BY A. D. HALL, M.A., F.R.S.

DIRECTOR OF THE ROTHAMSTED EXPERIMENTAL STATION ; FOREIGN MEMBER
OF THE ROYAL ACADEMY OF AGRICULTURE IN SWEDEN

NEW YORK
E. P. BUTTON AND COMPANY

1912

DEDICATED TO

SIR CHARLES LAWES-WITTEWRONGE, Baronet

OF ROTHAMSTED

WHO HAS SHOWN IN OTHER FIELDS

THE DISTINCTION AND IMAGINATION

WHICH MARKED HIS FATHER'S WORK

FOR AGRICULTURE

First Edition ...... June 1909

Reprinted . , • . . June 1910

Reprinted ...... May 1912

PREFACE

The use of some form of fertiliser is becoming more
and more a mark of modern agriculture. Though many
farmers, and among them some of our best, still pro-
fess to scorn all artificial manures and pin their faith
on the dung made by their stock, they none the less
are buying the elements of fertility — nitrogen, phos-
phoric acid, and potash — in the cakes and other feeding
stuffs which they bring from some outside source and con-
sume on their farms. It is the continual introduction
of plant food from outside which distinguishes modern
intensive methods of cultivation from the old farming.
Prior to a period which roughly coincides with the
foundation of the Royal Agricultural Society of Eng-
land in 1838, the farmer, living on the inherent capital
of the soil, was forced into a conservative system of
cultivation, which by restoring in the dung the greater
part of what had been taken from the soil by the crops,
would reduce the losses from his land to a point where
they would be more or less balanced by the natural re-
cuperative processes at work in the soil. In consequence
the level of production was low, and it was the discovery
and introduction of artificial fertilisers and feeding
stuffs — nitrate of soda, guano, the phosphates, cotton
cake, maize, etc., — which enabled the British farmer to
raise his output per acre by at least 50 per cent,
during the reign of the late Queen. It is true that all

vi PREFACE

intensive farming in the United Kingdom received a
great set-back in the 'eighties and 'nineties, when the
continued opening up of new areas of virgin soil and
the fall in freights filled the country with corn and meat
at prices below our cost of production under the condi-
tions then prevailing, because declining prices cannot be
met by more intensive methods, but only by a reduction
in the expenditure. However, we are steadily recover-
ing from that position : the supply of rich virgin soil is
not without a limit nor are its riches inexhaustible ; the
cost of production has begun to rise in the new
countries, already we see the American farmer is in
his turn being compelled to resort to fertilisers; and
with each rise in prices the intensive farmer can
recoup himself for an increased outlay. The future,
too, lies with intensive farming ; every year the
ratio of the cultivable land to the population of the
world shrinks ; every year science puts fresh resources in
the hands of the farmer. In the United Kingdom for
some time the stream may still run backwards and the
more expensive forms of arable cultivation continue to
be replaced by grass which demands no outlay, because
as long as ours is the one market open to the competi-
tion of all other countries selling agricultural produce,
prices are still liable to such wreckage as frightens the
home grower out of the business ; still, in the end, what-
ever agriculture survives in this country will be forced
into more and more intensive methods by the increasing
scarcity of the land. As it is, the specialist farmers
in Great Britain — the potato growers, the market
gardeners, the hop growers — have reached a pitch of
cultivation which is hardly to be paralleled elsewhere.
Intensive farming implies the use of fertilisers ; still

PREFACE vii

more it implies, or should imply, skill and knowledge in
using them.

If this book is to have any justification for its exist-
ence, it will be by helping men to a greater skill and
knowledge in the use of their fertilisers and manure.
There is no lack of books which give an account of
the origin and composition of fertilisers : my object is
rather to make the reader understand their mode of
action and their relation to particular crops and soils.
For it is only by understanding the why and the how
that a farmer can properly adjust his manures to his
soil and his style of farming ; he must to some extent
reason the scheme out for himself, he cannot simply
be told.

The scientific man is always being asked to arrange
his experiments to demonstrate the best way of grow-
ing this or that crop, by the best being implied the
cheapest : farming visitors to Rothamsted are often
inclined to suggest that the plots, if interesting, are
not " practical." After sixty years of work they rather
expect to see the absolutely cheapest form of manur-
ing each crop set out once and for all. But in
practical farming there is no "best" way of doing
things ; the mere fact that the weather of the coming
season is unknown makes it impossible to specify the
absolutely right course either in cultivation or in manur-
ing. The question even of the best manure for a given
crop is complicated by the manner in which every farm
differs somewhat from every other, not merely in its soil
and climate, for these matter less than is commonly
supposed, but in its object and management. One
man aims at crops, another man gets his money
back by his stock; one man has only to pay 15s.

viii ' PREFACE

an acre rent, another has to get twice as much out of
his land before he touches a profit ; one man's markets
are such that he can repay himself for an outlay of £^
an acre for fertilisers on his root area, whereas another
man could not afford 20s. ; no one recipe can be
handed out to suit all these different men.

The object, then, of the scientific man should be to
lay down principles which the practical man in his
turn must learn to apply to his own conditions ; success
is only possible when he too does some thinking.
Furthermore, the object of experiments should be to
provide knowledge that can be thus applied to other
conditions, and an experiment is practical just in so far
as it carries out its avowed object, which is to lead
men into a sound and fruitful way of thinking on
the question at issue.

It is in this respect — the elucidation of general
principles — that the Rothamsted experiments have
proved so exceedingly valuable ; though initially laid
out to test certain definite questions about the
nutrition of crops, the answers to which have long
since been absorbed into farming practice, the design
was so sound and the continuity of the record has
been so rigorously maintained that the results now
afford an instructive commentary on the whole
range of the science of crop production. We have by
no means come to the end of the lessons the Rotham-
sted experiments can teach : every new theory, each
extension of our knowledge, finds an unsuspected
criticism or an illustration in the records that are still
accumulating.

I have in consequence throughout this book used
very freely the results of the Rothamsted experi-

PREFACE ix

merits; and if the conclusions I have drawn do not
always square with popular opinion, I have none the
less set them out in the hope that other experimenters
would thereby be led to check or revise them.
Agricultural chemistry is still cumbered with a good
many a priori deductions resting upon a very slender
foundation — first approximations to the truth which fail
because they do not take all the factors into account ;
it is about many of these opinions that the Rothamsted
results suggest scepticism.

The book is intended for farmers and for the
senior students and teachers in our agricultural schools.
I have therefore kept the language as non-technical
as possible, though some elementary knowledge of
chemistry has to be assumed. If sometimes, as in
Chapter X., I may seem to have gone rather far in
the discussion of theoretical questions, it is in pursuance
of my main idea that it is only by thinking about the
rationale of manuring we can arrive at right practice.
And as the book is intended for those who are using
or going to use fertilisers, I have not troubled to say
much about their manufacture, nor have I dealt at all
with their analysis : these are both technical matters
outside the business of the farmer.

I have meant this to be a companion to my book,
The Soil ; they are both written for the same audience,
and on similar lines. I hope later to complete the series
by a third book, dealing with the chemistry of the grow-
ing plant.

A good deal of the material in the book has already
been utilised and in part published in a course of
Cantor Lectures delivered before the Society of Arts
in 1906, and again in a course of lectures delivered

X PREFACE

at Cornell University to the Graduate School of
Agriculture of the United States Department of Agri-
culture in July 1908. In this way, much of the sub-
stance of Chapters II., III., IV., V., and VI. has already
been printed in the Journal of the Society of Arts, the
greater part of Chapter VI I. has appeared in the
Journal of the Board of Agriculture, and Chapter X.,
the last of my American lectures, was printed in
Science.

I have drawn so freely upon my friends for informa-
tion, that it seems invidious to single out for thanks
some more than others : but I owe much to Dr E. J.
Russell of this Laboratory, who has read and criticised
parts of the text ; to Dr J. A. Voelcker, who has so
often placed the results of his wide experience at my
disposal ; to Mr H, Voss of the Anglo-Continental
Guano Co., and to Mr T. Elborough of the Lawes
Chemical Manure Co., who have furnished me with
many facts and figures respecting the trade in ferti-
lisers ; and once again, to Mr G. T. Dunkley of the
Rothamsted Laboratory, who has been indefatigable in
verifying references and in securing the accuracy of the
many figures and tables the book contains.

A. D. HALL.

The Rothamsted Experimental Station,
Harpenden, December 1908.

CONTENTS

CHAPTER I

INTRODUCTORY

Early Notices of Manures and Manuring — The Growth
of the Theory of Nutrition of Plants — Priestley, de
Saussure, Boussingault, Liebig, Lawes and Gilbert,
Hellriegel and Wilfarth — The Introduction of Com-
mercial Fertilisers — General Outline of the Process of
Nutrition of Plants — The Constituents of the Soil — Mode
of Entry of Food into the Plant — Nature and Function
of a Fertiliser . ....

CHAPTER n

FERTILISERS CONTAINING NITROGEN

The Importance of Nitrogen — Evidence that Plants cannot
utilise the Free Nitrogen of the Atmosphere — Ammonia
and Nitric Acid in the Atmosphere — Origin of the
World's Stock of Combined Nitrogen — Nitrogen-fixing
Bacteria — Fixation of Atmospheric Nitrogen to form
Calcium Cyanamide — Fixation of Atmospheric Nitrogen
in the Electric Arc ; Manufacture of Nitrate of Lime —
Nitrate of Soda : Nature and Origin — Properties of
Nitrate of Soda : Use as a Fertiliser — Value of the Soda
Base — Injurious Effects of Nitrate of Soda upon the
Texture of the Soil — Sulphate of Ammonia : Sources
and Production — Changes undergone by Sulphate of
Ammonia in the Soil — Acidity of Soil induced by
Sulphate of Ammonia — Relative Value of Nitrate of
Soda and Sulphate of Ammonia — Other Nitrogenous
Fertilisers : Soot, Shoddy, Fur and Feather Waste,
Hoofs and Horns — Slow Action of such Manures —
Seaweed . . . . . -25

xii CONTENTS

CHAPTER III

THE FUNCTION AND COMPARATIVE VALUE OF
NITROGENOUS MANURES

Nitrogen promotes the Vegetative Activity of the Plant — p^<^"
Growth proportional to Nitrogen Supply — With Excess
of Nitrogen Maturity is deferred and the Proportion of
Straw to Grain is increased — Variation of Composition
of Crop with Nitrogen Supply — Susceptibility of Plants
to Disease when supplied with Excess of Nitrogen —
Crops requiring Large Quantities of Nitrogen — Relative
Availability of Nitrogenous Manures — Nitrate of Soda
V. Sulphate of Ammonia — Question to be decided by
the Nature of the Soil — Residues left by the Different
Nitrogenous Manures — Greater Value attached by
Farmers to Manures containing Nitrogen in Organic
Combination . . . . . . yj

CHAPTER IV

PHOSPHATIC MANURES

The Phosphates of Calcium — The Early Use of Bones as
Manure — Preparation of Bone Meal and Steamed Bone
Flour — Dissolved Bones and Bone Compounds — The
Discovery of Mineral Phosphates, Coprolites, Phos-
phorite, Phosphatic Guanos, Rock Phosphates — The
Invention of Superphosphate, Lawes and Liebig — The
Manufacture of Superphosphate — -The Manufacture of
Basic Slag — Nature of the Phosphoric Acid Compounds
in Basic Slag, their Solubility in Dilute Acid Solutions —
Basic Superphosphate — Wiborg Phosphate — Wolter
Phosphate ....... 103

CHAPTER V

THE FUNCTION AND USE OF PHOSPHATIC
FERTILISERS

Ripening Effect of Phosphoric Acid — Most manifest in wet
Seasons— Effect of Phosphoric Acid in stimulating the
Formation of Roots and Adventitiotis Shoots — Associa-
tion of Phosphoric Acid with the Intake of Nitrogen by the
Plant — Solvents to determine the Relative Availability
of Phosphatic Fertilisers — Relative Value of Phosphatic
Fertilisers determined by the Soil — Soils appropriate to

CONTENTS xili

Superphosphate — Fate of Superphosphate applied to ^''^^
the Soil — Soils appropriate to Basic Slag — Neutral
Phosphatic Manures for Light Soils — Comparison of
Bone Meal with other Phosphatic Fertilisers . .136

CHAPTER VI

THE POTASSIC FERTILISERS

Early Use of Wood Ashes — The Stassfurt Deposits — Manu-
facture and Composition of Commercial Potash Fertilisers
— The Retention of Potash by the Soil — The Function
of Potash in the Nutrition of the Plant — Dependence of
Carbohydrate Formation upon Potash, as illustrated in
the Barley and Mangold Crops — The Action of Nitrate
of Soda upon Insoluble Potash Compounds in the Soil —
Potash Fertilisers as promoting the Growth of Legu-
minous Plants — Effects of Potash Starvation upon
Vegetation — Potash as a Preventive of Fungoid Disease
— Potash as prolonging the Growth of the Plant —
Destruction of the Tilth of Clay Soils by Potash Salts —
Soils deficient in Potash . . . , .158

CHAPTER Vn

FARMYARD MANURE

Variable Composition of Farmyard Manure — The Fate of the
Constituents of Food during Digestion and Excretion —
Composition of Urine and Fasces of Farm Animals —
Fermentation Changes taking place during the Making
of Dung — The Breakdown of the Nitrogenous Bodies
and of the Carbohydrates — Gases found in the Dunghill
— Losses of Nitrogen during the making of Farmyard
Manure — Preservatives used to minimise the Losses
during Dung-making — Composition of Farmyard Manure
— Cake-fed v. Ordinary Manure — Long and Short
Manure — London Dung — The Value of Fresh Manure —
The Fertilising Value of Farmyard Manure — Recovery
of its Nitrogen in the Crop — Long Duration of the Action
of Farmyard Manure — Farmyard Manure as a Carrier
of Weeds or Disease — The Physical Effects of Farmyard
Manure upon the Soil — The Improvement in Texture
and Water- retaining Power — Value of Farmyard Manure
as a Mulch on Grass Land — Farmyard Manure best
utilised for the Root Crop or Grass Land — Value of
Farmyard Manure : Cost of making One Ton . . 178

«V CONTENTS

CHAPTER VIII

PERUVIAN GUANO AND OTHER MIXED
FERTILISERS

Origin of the Deposits of Guano — Variation in Composition p*^°«
with Age — Compounds of Nitrogen present in Peruvian
Guano — Ichaboe and Damaraland Guanos — Fish
Guano — Meat Guano — Dried Blood — Greaves — Rape
Dust and other Cake Residues — Manures derived from
Faecal Matter — Sewage Sludges .... 229

CHAPTER IX

MATERIALS OF INDIRECT FERTILISING VALUE

Lime — Early Use of Lime — White and Grey Limes — Lime
Ashes — Marl — Chalk — Ground Limestone — Indications
of the Lack of Lime in the Soil — Action of Lime upon
the Soil — Improvement of Texture — Promotion of the
Oxidation of nitrogenous Residues in the Soil — Increase
in the Availability of Phosphoric Acid and Potash —
General Action of Soluble Salts on the Soil — Gas
Lime — Gypsum — Salt — Sulphate and Carbonate of
Magnesia — Sulphate of Iron ; Supposed Connection of
Iron in the Soil with the Colour of Fruit and Flowers —
Manganese Salts — Silicates — Green Manuring — Folding
Catch Crops on the Land ..... 249

CHAPTER X

THEORIES OF FERTILISER ACTION

Liebig's Ash Theory — Part played by the Soil in the Nutrition
of the Crop — Ville's Theory of Dominants — Liebig's
Law of the Minimum — Law of diminishing Returns —
Limiting Factors in Plant Growth — Is the Composition
of the Soil Water unaffected by Fertilisers ? — Attack of
the Plant's Roots upon Insoluble Fertilisers — The Part
played by Carbon Dioxide in the Soil — Excretion of
Toxic Substances from Plant Roots — Rotations as a
Substitute for Fertilisers — Unexplained Factors in the
Nutrition Problem ...... 276

CONTENTS XV

CHAPTER XI

SYSTEMS OF MANURING CROPS

High and Low Farming — Fertilising Constituents removed P'^o"
in Meat and Corn — Losses of Nitrogen increased when
Land is in high Condition — Manures for Wheat —
Barley: Importance of Quality — Oats — Root Crops:
Swedes, Mangolds, Potatoes — Importance of Farmyard
Manure for Root Crops — Leguminous Crops : Beans,
Clover, Lucerne, Sainfoin — Value of Potassic Fertilisers —
Grass Land — Effect of Manures in changing the Botanical
Character of the Herbage — Land laid up for Hay —
Manures for Poor Pastures — Hops — Fruit — Garden
Manures — Manures for Tropical and Semi-Tropical
Crops : Sugar Cane, Tobacco, Cotton, Tea . . 300

CHAPTER Xn

THE VALUATION AND PURCHASE OF
FERTILISERS

Valuation on the Unit System — The current Market Price
of the Unit of Nitrogen — Phosphate of Lime and Potash
— Variations in Unit Values due to Market Fluctuations
— Valuation of Fertilisers before Purchase — The
Fertilisers and Feeding Stuffs Act ; Obligations of the
Vendor — Sampling Consignments of Fertilisers — Mixed
V. Unmixed Fertilisers — Incompatibles — Residues of
Fertilisers after the Growth of one or more Crops —
Valuation of unexhausted Residues derived from the
Consumption of purchased Feeding Stuffs . . 340

CHAPTER XHI

THE CONDUCT OF EXPERIMENTS WITH
FERTILISERS

Magnitude of Experimental Error mvolved in Field Experi-
ments— Choice of Land for Field Experiments — Size
and Shape of Plots — Machines for sowing Fertilisers —
Should Farmers conduct Experiments upon their own
Land? ....... 359

Index . .078

LIST OF ILLUSTRATIONS

FIO. FACE PAGE

1. Water Cultures of Barley . . . . .17

2. Deflocculating Action of Nitrate of Soda on Clay Soils . 55

3. Curves showing the effect of Phosphoric Acid in

hastening the formation of Grain of Barley, and the
Migration of Nitrogen to the Grain . . .137

4. Effect of Excess of Nitrogen, with and v/ithout Potash, on

the Leaves of Mangolds . . . .174

5. Relation between Cost of Production and Returns with

varying quantities of Manure .... 284

6. Diagrammatic Section of Manure Distributor — Seed

Drill Type ■■■■■■ 373

7. Diagrammatic Section of Manure Distributor, with

Revolving Drum Feed ..... 373

8. Diagrammatic Section of Manure Distributor — Endless

Chain Feed Type ..... 374

9. Broadcast Manure Sower with Revolving Discs for
Distribution » . . t . t

374

FERTILISERS AND MANURES

CHAPTER I

INTRODUCTORY

Early Notices of Manures and Manuring — History of the Theory
of Nutrition of Plants — Priestley, de Saussure, BoussingaulL
Liebig, Lawes and Gilbert, Hellriegel and Wilfarth — The
Introduction of Commercial Fertilisers — General Outline of
the Process of Nutrition of Plants — The Constituents of the
Soil — Mode of Entry of Food into the Plant — Nature and
Function of a Fertiliser.

The word " manure," when first met with in English,
possessed a much wider significance than it does
to-day. Of the same origin as manoeuvre, it meant,
primarily, to work by hand, and it is used in that sense
by Defoe in Robinson Crusoe — " The land which I had
manured or dug"; but it also took on the extended
meaning of any process or material by which the land
could be ameliorated. In the seventeenth and early
eighteenth centuries this latter sense alone began to
prevail ; agricultural writers enumerated chalk, lime,
marl, burnt clay, etc., as manures, and began to speak
of the operations of cultivation as tillages or husbandry ;
and more recently the tendency has been to restrict
the employment of the term even further, confining
it to the natural substances possessing a direct fertilising

A

2 INTRODUCTORY [chap.

value. Farmyard manure is the typical "manure";
marl or chalk would no longer be regarded as manure,
because they do not feed the plant directly; while
substances like basic slag or nitrate of soda, which
simply supply one or other element in the nutrition
of a plant, should be termed " fertilisers " rather than
artificial manures. The distinction is not, however,
very clearly drawn, and manure and fertiliser are gener-
ally and unconsciously used as interchangeable terms,
as indeed they will be in this book.

It is impossible to assign a period to the discovery
of the fertilising properties of the excrement of animals :
agriculture must be almost coeval with the human race ;
and that tissue of experience and observation which
reaches us as the tradition of farming — the stock-in-
trade of the practical man — began to form long before
letters existed by which it could be recorded. At any
rate, when in Rom. an times we began to get some
record of agricultural practices, we find that not only
was the value of dung recognised, but that the virtues
of certain other manures, such as marl, had been
established. Even the fertilising effect of a crop of
vetches or lupins upon the succeeding wheat crop was
sufficiently well known to be related, not only by pro-
fessed agricultural writers like Varro and Columella, but
also by a poet like Virgil. But to whatever point the
knowledge of manures had reached in the time of the
Romans, for a long time it made no further advances
and bade fair to be utterly lost with the irruption of
the barbarians. When the new peoples emerge again
in Europe, after the great movements of the races, we
mostly find them practising the Germanic common
field system of agriculture, with its rotation of wheat,
beans or barley, and fallow, followed up by general
grazing over the whole area — a system which lends no

I.] EARLY niSTORY OF MANURES 3

encouragement to the use of substances like manures
for the improvement of the land.

Doubtless the old traditions did not perish in the
Romance countries, but as before were handed down
from one generation to another ; as long as corn and
wine continued to be cultivated the immemorial pre-
cepts concerning their management would linger about
the country side and be treasured in the memories of
the workers in the fields. But during the Dark Ages
this kind of knowledge sank below the level of what-
ever literature was being written ; it had to diffuse
slowly from the remains of Roman civilisation among
the invading peoples, and it is only by chance that we
get any record of what the countryman did or thought.
In many English tenures we find that the flocks of the
tenants had to be folded on the lord's land at night,
the manure thus brought being one of his most valued
privileges ; while in Walter de Henley's Husbandrie, the
great mediaeval treatise on the duties of a land agent,
we find instructions for the preservation of dung by
the use of litter and marl. The manure thus obtained
was to be stored in a heap and preferably applied to
sandy land. From mediaeval times also we derive such
maxims as the Flemish proverb,

Point de fourrage, point des betail.
Point des betail, point de fumier,
Point de fumier, point de fourrage.

When, with the general resurrection of learning at the
Renaissance, we once more get books on agriculture,
we find that either old tradition or the experience of
men of an enquiring turn of mind, who had been
trying all sorts of things on their land, had already
built up a certain knowledge of manures and manuring.
The value of marl and chalk, of woollen rags and ashes,
was certainly known in the sixteenth century; men

4 INTRODUCTORY [chap.

had even begun to reason a little on the mode of action
of manures. For example, Bernard Palissy the potter,
in his Recepte Veritable, published in 1563, not only
recommends the use of marl and lime, but can assign a
reason for the value of ashes, and shows that the rich-
ness of farmyard manure resides in the portion soluble
in water : — " Et ainsi la paille estant bruslee dedans
le champ, elle seruira d'autant de fumier, parce que
elle laissera la mesme substance qu'ell auoit attiree
de la terre ... ; " and again, " au lieu ou ledit pilot de
fumier aura repose quelque temps, ils n'y laisseront
rien dudit fumier, avis le jetteront deca et dela, mais
au lieu ou il aura repose quelque temps, tu verras
qu'apres que la ble qui aura este seme sera grand, il
sera in cest endroit plus espes, plus haut, plus verd et
plus droit. Par la tu peux aisement cognoistre que ce
n'est pas le fumier qui a cause cela, car le labourer le
jette autre part ; mais c'est que quand ledit fumier estoit
au champ par pilots, les pluyes qui sont suruenues, ont
passe a travers des dits pilots, et sont descendu a travers
du fumier jusqu'a la terre, et en passant, ont dissout et
emporte certains parties du sol qui estoit audit fumier."

If, then, by the sixteenth century we find written
evidence of the knowledge of the fertilising properties
not only of dung but of other waste substances, we
may safely push back the original discovery of the
properties of these bodies to a much more remote epoch,
if such a term as discovery can properly be applied.
Just as happens to-day, this or that man tried an
experiment or noticed the result of an accident which
caused him to report well of the action of some sub-
stance on his crops ; his opinion would often be
mistaken and often, again, it would be forgotten ; but
occasionally it would be repeated and find confirmation,
until it acquired the wide circulation and staying power

I.] SCIENCE AND TRADITION 5

of a farming tradition and passed more or less into the
common routine. Even at the present time there are
many beliefs and practices more or less current among
farmers, which science has neither verified nor disproved,
and which may either be examples of sound observation
or only imperfect generalisations. Such opinions
require to be examined with the utmost care and open-
mindedness, for even when correct they are of no final
use to agriculture until they have been explained and
absorbed into the general stream of scientific knowledge.
The value of many fertilisers must have been observed
and lost sight of over and over again, because of the
lack of any general theory to serve as a touchstone and
discriminate between the true and the false reports.
So, despite the experience that was accumulating
respecting the fertilising value of this or that substance,
no real progress towards a theory of manuring was
made until the close of the eighteenth and the
beginning of the nineteenth century.

Before the development of a science of chemistry it
was naturally impossible to form any idea of how a
plant came to grow ; while the nature of the plant
itself, of the air, water, and earth were equally unknown,
no correct opinion could be reached as to how the latter
gave rise to the former. In spite of Palissy's very
sound conclusions as to the salts plants draw from the
ground, Van Helmont described an experiment to
show that a tree is made out of water alone. Jethro
Tull, arguing from his hoeing experiments, concluded
that manures were unnecessary : for the soil, if only
stirred up enough and exposed to the air, will provide
all that the plant requires. Even so late as 1810 we find
Thaer writing that there is no doubt that the fallow
absorbs or attracts the fertilising properties of the
atmosphere.

6 INTRODUCTORY [chap.

The true theory of the nutrition of the plant begins
very soon after the discovery of the composition of the
air. "Thus, Priestley observed that plants possessed
the faculty of purifying air vitiated by combustion or
by the respiration of animals ; and he having discovered
oxygen, it was found that the bubbles which Bonnet
had shown to be emitted from the surface of leaves
immersed in water consisted chiefly of that gas. Ingen-
housz demonstrated that the action of light was essential
to the development of these phenomena, and Sennebier
proved that the oxygen evolved resulted from the
decomposition of the carbonic acid taken up."

Following up these results, de Saussure demonstrated
with as much quantitative accuracy as was then possible
that the oxygen which was split off by the leaf was
contained in the carbonic acid, and that the gain in
weight of the plant was practically represented by
its carbon ; combined with the elements of water to
make up such carbo-hydrates as sugar and starch.
De Saussure further arrived at very clear ideas as to
the source and value of the ash constituents of
plants : the nitrogen, which he also pointed out
as an invariable constituent of plants, he considered
to be either derived from the ammonia in the
atmosphere or the organic matters in the soil. Sir
Humphrey Davy, in his lectures before the Board
of Agriculture from 1802 to 1813, practically adopted
de Saussure's views, and emphasised the importance
of the ash constituents, which could come neither
from the air nor water, as he yet thought it necessary
to demonstrate.

Though Davy made no advances towards ascertain-
ing the relative importance of these substances, and
was by no means certain that the plant derived all
its carbon from the atmosphere, his lectures did

I.] THEORIES OF PLANT NUTRITION 7

much to pave the way for the adoption of a sound
theory.

Thaer, about the same period, was still attributing the
chief share in the nutrition of the plant to the organic
juices, or, as we should say, to the humus in the soil,
which substance he showed to contain hydrogen, nitrogen,
sulphur, and phosphorus. Though knowledge of the
composition of plants, soils, and manures continued to
accumulate, as seen in the work of Sprengel and
Schubler, the next step forward was due to Boussingault,
who was the first man to undertake field experiments on
a practical scale. Farming his own land at Bechelbronne,
Alsace, from 1834 onwards, he systematically weighed
crops and manure and analysed both so as to obtain a
balance-sheet showing the quantities of carbon and nitro-
gen added in manure and removed in the crops. He
thus in 1838 demonstrated on a working scale the
enormous amounts of carbon w^hich are assimilated by
the plant from the atmosphere — far greater quantities
than the humus in the soil could continue to supply.
Boussingault's experiments led him to conclude that the
plant derives its nitrogen from the soil, though he also
showed that in certain rotations more nitrogen is
removed in the crop than is supplied in the manure.

But it is to the great Liebig that we must attribute
the chief impulse which agricultural chemistry has
received ; though he made little original contribution
himself to the theory, adopting in the main the con-
clusions that arose from the work of Priestley, Ingen-
housz, Sennebier, and de Saussure, he was the man who
drove home to the minds, both of scientific men and of
farmers, the true theory of plant nutrition.

In his report to the British Association, published
in 1840, and his Chemical Letters , he laid down the
general principle that the carbon compounds, which

8 INTRODUCTORY [chap.

constitute more than 95 per cent, of the dry matter of
the plant, are derived by the plant from the atmosphere,
and that if the plant be supplied with the 2 per cent,
or so of mineral constituents which are found in its ash,
it will then draw upon the atmosphere for all the other
materials the crop ultimately contains.

Coming at a time when much intellectual interest
was directed towards agriculture, and backed by his great
scientific reputation and his commanding personality,
Liebig's views aroused instant and general attention ;
they became the foundation both of practical experi-
ment and scientific research, and were the starting-point
of a controversy the echoes of which are but now dying
down. In several respects Liebig's views required
modification ; he seemed to consider all the ash con-
stituents were of equal importance, and even that one
base like soda could replace any similar one like potash ;
he regarded the composition of the plant's ash as deter-
mining its proper fertiliser — a point which will be con-
sidered later ; and he misapprehended the part played
by nitrogen compounds in manuring. At that time,
owing to imperfections in the methods of analysis, very
exaggerated ideas were current as to the amount of
ammonia naturally present in the atmosphere : the
rain was believed to bring down 30 or 40 lb. per acre
per annum of combined nitrogen instead of the 3 or 4 lb.,
which we now know to be contributed to the soil, and
to this source Liebig was disposed to look for the
nitrogen in the plant. He stated that manures contain-
ing nitrogen certainly stimulated growth, because they
fermented and increased the proportion of ammonia in
the air round the plant ; but in the main nitrogenous
manures were unnecessary, for full crops could be grown
if only the constituents removed in the ash were annually
returned to the soil.

I.] ROTHAMSTED 9

In particular, these views on the nutrition of plants
and the part played by the nitrogenous nianures, did
not commend themselves to John Bennet Lawes, a
young Hertfordshire landlord who had recently come
into possession of the family estate of Rothamsted, near
St Albans, and had already begun to try manurial
experiments on a small scale. In 1843 the experiments
took more systematic form and Lawes obtained the
services of Joseph Henry Gilbert, a chemist who had
worked under Liebig at Giessen, to conduct them,
thus inaugurating the field trials which have continued
without a break to the present day. The immediate
result of the Rothamsted experiments was to demon-
strate the necessity of a supply of combined nitrogen,
the yield being in fact roughly proportional to the
amount of combined nitrogen added as manure. If
only the mineral constituents of the ash were supplied,
the crop fell away rapidly as soon as the reserves of active
nitrogen in the soil had become exhausted. Lawes,
Gilbert, and Pugh further repeated, with great exacti-
tude, a series of laboratory experiments initiated by
Boussingault, and demonstrated that the ordinary plants
of the farm were incapable of utilising the free nitrogen
of the atmosphere, but only took up nitrogen in a
combined form from the soil or the manure. Lawes
and Gilbert were fiercely attacked by Liebig ; but as far
as his views can be extracted from his writings, there
was no very great difference between the opinions held
by the rival parties. Liebig laid the chief stress on
the need for the mineral manures, whereas the latter
investigators were more concerned to demonstrate the
importance of nitrogen. Liebig also seems to have
thought that the leafy crops, like clover or roots — the
so-called restorative crops — could gather nitrogen from
the atmosphere and dispense with any supply in

lo INTRODUCTORY [chap.

manure. But in addition to establishing the value of
nitrogenous manures, the Rothamsted experiments also
settled in a practical fashion the question of which of
the ash constituents were indispensable to the plant
and were necessary constituents of a complete manure.
The fundamental necessity of phosphoric acid and
potash, and the non-essential nature of soda, magnesia,
and silica as manure constituents were soon established,
and the experiments began at once to bear fruit in the
way the various artificial manures, then being discovered
and put on the market, were utilised by farmers.
Contemporaneously the methods of pot cultures in weak
solutions of known salts were evolved, and in the hands
of Boussingault, Knop, Stohmann, and others, demon-
strated with all the precision of a laboratory process
that of the elements found in the plant, only compounds
of nitrogen, phosphoric and sulphuric acids among
acids, and potash and lime with a trace of iron among
bases, are absolutely essential to the nutrition of the
plant.

There was, however, still one point which remained
somewhat unintelligible — the gain in combined nitrogen
which seemed to take place when certain crops of the
leguminous order were grown. Cases were recorded
where more nitrogen was found in the crop than was
supplied in the manure, and yet the soil on which the
crop had been grown itself showed an increase of
nitrogen.

Boussingault, in his earliest investigations, had shown
that in certain rotations which included clover or lucerne
more nitrogen was removed in the crop than had been
supplied in the manure, and many of the Rothamsted
results could only be explained on the assumption that
the roots of such crops ranged exceptionally deep and
drew upon stores of subsoil nitrogen unavailable for other

I.] NITROGEN AND VEGETATION ii

plants, thus leaving the upper soil the richer for their
prowth, since the roots and stubble, in which this subsoil
nitrogen has been accumulated, decay near the surface.
It was not until 1886 that these difficulties were cleared
up by the discovery of Hellriegel and Wilfarth that
leguminous plants do fix the atmospheric nitrogen by
the help of certain bacteria living in symbiosis upon the
root of the leguminous plant. The leguminous plant,
however, will also feed upon combined nitrogen in the
soil like any other plant, and the failure of Lawes and
Gilbert to detect any nitrogen fixation in their labora-
tory experiments with beans and clover, was due to the
great care to shut out any intrusion of foreign matter
during the experiments, thus preventing the leguminous
plants from becoming inoculated with the bacteria
causing fixation. In a measure, the discovery of
Hellriegel and Wilfarth, which has formed the starting-
point of much further research, may be taken to have
justified some of Liebig's arguments, although the
mechanism by which the nitrogen fixation is brought
about — by bacteria living in concert with the higher
plant — would have been entirely foreign to his way of
looking at things, just as it was to Lawes and Gilbert,
who thus unhappily missed the clue which would have
rendered intelligible many of their results.

It has been already indicated how impossible it is to
recover the date of the original discovery of the
fertilising value of the substances we now call artificial
manures ; only by an occasional allusion in the older
books can we find that particular materials were in
common use at the period of the writer. Blithe's
English Improver, published in 1653, mentions the
value of rags, wool, marrow bones or fish bones, horn
shavings, soot, and wood ashes ; and Evelyn, writing a
few years later, adds also blood, hair, feathers, hoofs,

12 INTRODUCTORY [chap.

skin, fish, malt dust, and meal of decayed corn, so that
a knowledge of the value of these materials must have
been widespread.

William Ellis, a Hertfordshire farmer who wrote in
1732, enumerates a long list of "hand manures," the
use of which he regarded as characteristic of Hertford-
shire farming in his day. These include soot, wood
ashes, woollen rags, horn shavings, hoofs, hair, coney
clippings, oil cake, and malt dust ; and the regular part
they evidently played in the farming of that district
show that they must have been known and used for a
long time previous to Ellis's writings. Throughout the
eighteenth century we hear of the same materials, and
also of bones, which Ellis does not mention, though
their value is stated by several of the seventeenth
century writers. Early in the nineteenth century we
begin to hear of guano from Peru, though the first
importation did not take place until 1840.

The importation of nitrate of soda from Chile had
begun a year or two before ; its value as manure was
for a time in doubt, though as early as 1669 Sir Kenelm
Digby had recounted an experiment to show how much
barley plants were benefited by watering with a weak
solution of nitre, and Evelyn in 1675 ^^^ written: "I
firmly believe that were saltpetre to be obtained in
plenty, we should need but few other composts to
meliorate our ground."

The employment of ammoniacal salts seems to have
begun entirely upon theoretical grounds ; de Saussure
had attributed the nitrogen of vegetation to the
ammonia in the atmosphere, and in this he* was
followed by Liebig; fortunately, about the same time,
the manufacture of coal-gas gave to the world a cheap
source of ammonium salts. Lawes had already been
trying them before Liebig's paper of 1840, and wher]

I.] INTRODUCTION OF ARTIFICIAL FERTILISERS 13

the Rothamsted experiments were definitely started in
1843, a mixture of muriate and sulphate of ammonia
became their standard nitrogenous manure.

The use of mineral phosphates as manure begins
with Lawes' superphosphate patents in 1842, although
no mineral phosphates were available on a large scale
until Henslow's discovery of the coprolite beds of
Cambridgeshire in 1845, soon after which time Lawes
and others took them up as material for the manu-
facture of superphosphates. Putting aside the various
methods adopted for the utilisation of slaughter-house
refuse, etc., no further novel manurial substances can be
said to have been introduced until the development of
the Stassfurt potash deposits, which began about i860,
and the discovery of basic slag in 1879, which has been
followed in the last few years by various processes for
bringing atmospheric nitrogen into a combined form.

Since the nutrition of the plant is the object with
which all manures are employed, it will be necessary
at the outset to obtain some knowledge of how a plant
feeds under the simplest possible conditions without
any of the disturbing effects introduced by the many
complex processes going on in the soil.

If we take any living plant and reduce it to its
elements, we find but a small range of substances ;
water forms the greatest portion of the plant, the rest
is almost wholly composed of compounds of carbon
with hydrogen and oxygen, approximately in the
proportions which make up water. Of the dry matter
of the plant at least half is carbon ; oxygen and hydro-
gen constitute most of the remainder; then a certain
restricted number of other elements are present in much
smaller quantities. Nitrogen constitutes about 2 per
cent, of the dry matter ; the other substances, which are
found in the ash when the plant is burnt, make up a

14 INTRODUCTORY [chap.

further 2 per cent, or so. These ash constituents com-
prise sulphur, phosphorus, silicon, and chlorine, among
the non-metals ; potassium, sodium, calcium, magnesium,
and a little iron and manganese, among the metals.
Traces of other metals occur from time to time in the
ashes of plants growing on soils which happen to
contain them, but they are unessential and may in this
connection be neglected.

Carbon, then, is the main element in the plant's
economy, and we know that it is obtained by the plant
from the carbonic acid in the atmosphere through the
agency of the living cells in the leaf, which contain
green chlorophyll. The carbonic acid is taken in
through the small openings in the skin of the leaf, the
stomata ; it is decomposed by the chlorophyll-containing
cells, and the carbon is retained in combination with
the elements of water, so that it is first identifiable as
sugar and then as starch ; at the same time oxygen is
returned to the atmosphere. This decomposition is
one that necessitates an external supply of energy,
which is found to be derived from the light incident
upon the leaf, the process stopping in darkness, and
for low illuminations becoming proportional to the
amount of light falling upon the leaf.

The conditions affecting this process of photo-
synthesis— the fundamental reaction of the whole plant-
world — have been subjected to considerable examina-
tion of late. In the method adopted by H. T. Brown,
the leaf, which may still be attached to the plant, is
enclosed in a flat air-tight box with glass sides, through
which sweeps a rapid but measured current of air. The
issuing air which has passed over the leaf is led into
an apparatus for the determination of the carbonic
acid (and, if need be, of the water) it contains ; at the
same time a parallel experiment without the leaf

!•]

ASSIMILATION

J5

measures the proportion of carbonic acid and water
in the incoming air. Thus the amount of carbonic acid
absorbed, and therefore decomposed, in a given time
by a leaf, whose area can be afterwards measured, is
directly determined, and such factors as illumination and
temperature can be varied at will. The energetics of
the process have been worked out by Brown and
Escombe, from whose paper the following examples
have been selected : —

Table I.— Utilisation of the Energy incident on a Green
Leaf. (Brown and Escombe.)

E

E

nergy in Calories per sq. cm. of Leaf,

'C

c O

per minute.

i^

s-2

£ c

-c ^

-c

^m

? oJ

0 rf

3 >,

t. 5

^^^.

Plant.

"S ^

■^ ^

•JS J

■^ '^

'5 •—

-^ rt S

^ o

"S 5

?S|

^0

5||

8

S 5...
5 ~
§1

[-. >- ^
^^ 0 ►-'

S-r 5

e; cS 0

c.c.

grnis.

Polygonum

3-7£8

I -054

0-1942

0-1256

0-0031

O-IO4I

0-0184

(Juno 19)

Tropoeolum

I -498

0-141

0-0889

0-0622

0-0012

0-OI39

0-0471

(September 4)

Helianthus

2-134

1-259

0-2569

0-1762

o-ooi 7

0.1243

0-0502

(August 7)

These experiments show that the leaf of a plant
is not to be regarded as a very efficient machine for
the decomposition of carbonic acid, since in no case was
more than i-66 per cent, of the total energy incident
on the leaf used for photo-synthesis, so that even dull,
diffuse daylight can amply provide a growing plant
with the energy it wants for assimilation. The process,
however, is limited by many factors, any one of which
may fix a minimum rate at which assimilation will take

1 6 INTRODUCTORY [chaP.

place, however favourable the other conditions are.
Temperature, the supply of water, the proportion of
carbonic acid in the air, the number and area of the
stomatic openings, are all limiting factors of this kind,
as also is the supply of other nutriment to the plant.

Though the compounds of carbon with hydrogen
and oxygen make up so much of the solid matter of
the plant, the remaining substances, comparatively
small in amount as they are, are still all-important to
the process of growth. The part they respectively play
and their mode of entry can best be illustrated by the
method of water cultures, of which Fig. i shows an
example. By this method the roots of young seedling
plants are just allowed to dip into a large jar of water
in which salts of the elements found in the plant are
dissolved. A complete solution might be made up as
follows : —

Grammes per litre.

Calcium Nitrate 07

Potassium Phosphate o-6

Potassium Chloride ..... o-8
Magnesium Sulphate 0-3

with a trace of ferric chloride.

This will contain all the elements, except silicon,
normally found in plant ashes, and under such condi-
tions the plant will grow and go through its whole
cycle of life, assimilating freely, producing large quanti-
ties of dry matter, setting flowers, and ripening healthy
seed. Certain precautions have to be taken, but if the
right conditions are assured, the growth of a plant in
a water culture is perfectly normal, and may be taken,
as far as the plant is concerned, as representing the
course of its nutrition in the field. The advantage of
the method lies in the fact that it is possible to vary
the composition of the nutrient solution by omitting in
turn from successive jars each of the salts used in

Fig. I.— Water Cultures of Barley.

1. Complete Manure. 4. No Potash.

2. No Nitrogen. 5. No Lime.

3. No Phosphoric Acid. 6. No Magnesia.

'To face vaae 17.

I.] NUTRITION OF THE PLANT 17

making up the complete solution, thus obtaining media
for the plant containing no nitrogen, no phosphorus, no
potassium, etc., the other constituents found in the
plant being present in each case. The result of one
such series of experiments is shown in Fig. i, which
illustrates that when, e.g., nitrates are omitted from the
culture solution, the plant is quite unable to grow
after it has used up the material in the seed, however
freely it may have been provided with potassium,
magnesium, etc The net result of such experiments,
in agreement with the one shown in the photograph,
is that a plant must obtain by means of its root
nitrogen in combination, phosphorus, sulphur, potas-
sium, magnesium, calcium, and a little iron — all of
which constituents are indispensable to the growth
of the plant and cannot be omitted from the
culture solutions. Sodium, silicon, and probably chlo-
rine, though invariable constituents of the ash, are
not necessary and can be dispensed with. From
these water culture experiments we arrive, then, at
the conclusion that the plant must draw certain
elements, in quantities which are small compared
with the weight of the crop but are nevertheless
indispensable, out of the soil by means of its roots, the
rest of the plant being built up from air and water.
These water culture experiments may also be made
to lead to another conclusion, which we first of all
owe to de Saussure — that the nutrient substances
must first of all be dissolved or capable of going into
solution before they can feed the plant. The growing
plant contains 80 per cent, or more of water, but this
amount bears but a small proportion to the total
quantity of water which passes through the plant
during the whole period of growth. There exists,
in fact, a continual •' transpiration current " through

1 8 INTRODUCTORY [chap.

the plant, of water which enters by the root hairs and
is eventually evaporated from the leaves and other
growing surfaces of the plant. It has been shown
that under the normal conditions the plant transpires
from 200 to 500 pounds of water for every pound of
dry matter that is simultaneously produced ; the lower
number being nearer the factor prevailing in our humid
atmosphere, and the higher one holding for drier coun-
tries. With this water enter the nutrient constituents
of the soil and of fertilisers applied to it ; but the
process by which they enter is rather more complex
than one of the simple intake of a solution.

The passage of the dissolved substances into the
plant takes place by the purely physical process
of osmosis, the walls of the root hairs (which con-
sist of single elongated cells) acting as membranes
through which water or salts will pass independently,
according to the relative concentration of the solu-
tions inside or outside the cell. Should the cell sap
be more concentrated than the soil water outside,
pure water will pass through the wall until a certain
osmotic pressure (causing turgor in the plant) is
reached, which varies with the concentration. If, on
the contrary, the soil water became more concentrated
than the cell sap, water will leave the cell, the plant
will become flaccid, and even die if the withdrawal of
water be too great. It is in this way that plants
become " scorched " or " burnt " by too concentrated
solutions of any kind of soluble salts, such as are formed
when a little soluble manure, salt, etc., falls upon the
surface of a leaf

Not only will water pass in or out of the cell, but
an equilibrium will be attained between the cell sap and
the external soil water for each constituent present in
the latter. If, for example, sodium or potassium chlorides

I.] ENTR Y OF PLANT FOOD 19

be present in solution in the external soil water, both
will continue to diffuse through the cell wall until their
respective concentrations are the same within and
without the cell. If now the potassium compounds
be withdrawn from the solution within the cell by
the living protoplasm in order to take part in the
various vital processes requiring potassium, there
will be a fresh influx of potassium until the old equi-
librium within and without is restored. It is in this
way that the apparent selective action of a plant
takes place ; as a rule, sodium compounds are more
abundant in soil water than salts of potassium, yet
the ash of the plant will be found much richer in
potassium than in sodium. Similarly, again, the ash
of any particular plant will maintain a fairly constant
composition although grown on soils of widely differing
character. The selective power resides in the living
cells themselves ; all substances dissolved in the soil
water diffuse through the walls of the root hairs into
the plant, but will not continue to accumulate therein
unless they are utilised and withdrawn from solution
by the protoplasm.

Further, it is not necessary to consider that the
plant takes up the various salts presented to it as
wholes ; the process of diffusion until equilibrium is
attained, of withdrawal by the protoplasm and con-
sequent renewal of the process of diffusion, takes
place for each acid or base independently of the
others. As a rule, a plant growing in a nutrient
medium containing nitrates as sources of nitrogen, will
withdraw an excess of acid and render the solution
alkaline, but cases also occur when the medium
becomes acid during growth because the plant takes
more base than acid. According to modern views of
solution, we must regard the soil water as a highly

20

INTRODUCTORY

[CHAP.

ionised solution, and each particular kind of ion
establishes its own conditions of equilibrium within
and without the cell.

The soil, however, is not to be regarded merely as
an inert medium to anchor the plant and convey the
manure to it when convenient, but is itself an enormous
potential reserve of plant food.

We may take, by way of an example, the
Rothamsted soil. On the one hand, it is neither
richer nor poorer than the majority of British soils
and has no abnormal characteristics, so that it repre-
sents a very fair average type ; on the other hand,
there is no other soil about which so much knowledge
has been accumulated.

Table II.— Analysis of the Soil of Broadbalk Field,
Rothamsted, Unmanured for 50 Years.

Per cent.

Lb. per
Acre.

Loss on ignition

Containing Carbon ....

„ Nitrogen
Matter soluble in Hydrochloric Acid .
Containing Soda ....

„ Potash ....

„ Magnesia

„ Lime ....

„ Alumina

„ Oxide of Iron

„ Phosphoric Acid .

„ Sulphuric Acid

,, Carbonic Acid
Undissolved Siliceous Matter

4-20

12-53
83-27

0-89

O-IO

o-o6

0-27

0-36
2-49
4-49
3-40

0>II

0-05
I -30

22,250
2,500

1,500
6,750
9,000

62,250
112,250

85,000
2,750
1,250

32,500

The accompanying analysis shows, as usual, that
the greater part of the soil consists of insoluble
siliceous matter, of which no account need be taken ;
there is, further, a certain amount of organic material,
important as containing a store of nitrogen which may

I.] AMOUNT OF PLANT FOOD IN SOIL 21

eventually reach the plant. In addition, we have
various salts going into solution in the acids used
for the analytical process, and these include pre-
cisely the substances that have already been indi-
cated as constituents of the ash of plants — amongst
metals, calcium, magnesium, potassium, sodium, with
iron and aluminium in quite disproportionate amounts;
sulphuric and phosphoric acids, chlorine and silica
supply the non-metals. Read as percentages some
of these amounts seem small enough, but they repre-
sent enormous quantities of material in the soil, as
will be realised when they are correlated with the
fact that the layer of soil at Rothamsted, nine inches
deep, which is taken for analysis, weighs, over the area
of one acre, rather more than two and a half million
pounds. Translating, then, the percentages into pounds
per acre, o-i per cent, of nitrogen becomes 2500 lb.,
o-ii of phosphoric acid becomes 2750 lb., and the
potash rises to 6750 lb. ; also, these quantities are in
the surface soil only, without considering the lower
layers into which the plant roots penetrate freely.
A comparison of the materials in the soil with those
taken away by ordinary crops at once leads to results
which seem paradoxical ; the stock of plant food in
the soil is so much greater than any requirements
of the crop that further additions of the same stuff
in the shape of fertilisers would seem to be needless.
The accompanying table (III.) shows the amounts
of various materials per acre which are on the average
drawn from the soil by various crops at Rothamsted.

Roughly speaking, an average soil contains enough
plant food for a hundred full crops, yet without fresh
additions of plant food as manures the production will
shrink in a very few years to one-third or one-fourth of
the average full crop. Once, however, the yield has

22

INTRODUCTORY

[CKAP'

reached this lower level, it will remain for an indefinite
period comparatively stationary, affected only by the
fluctuations due to season. At Rothamsted, for example,
wheat has now been grown year after year on the same
land for sixty-five seasons, and one plot has received
no manure throughout the whole period. In the first

Table III, — Soil Constituents contained in Average
Crops.

Wheat.

Barley.

Swedes.

Mangolds.

Hay.

Tons.

Tons.

Tons.

Tons.

Tons.

Crop

2-2

2-0

I6-I

30-1

1-5

Lb.

Lb.

Lb.

Lb.

Lb.

Nitrogen .

50

49

98

149

49

Soda

2-6

5.0

32-0

II8-7

9-2

Potash

28-8

35-7

79-7

30O-7

50-9

Magnesia .

7-1

6.9

9-2

42-5

14-4

Lime . .

9-2

9-2

42.4

42-9

32-1

Phosphoric Acid

2I-I

20.7

21-7

£2-9

12.3

Sulphur .

7.8

6-1

17-8

14-0

5-7

Chlorine .

2-5

4-1

I5-I

83-1

14.6

Silica

96.9

68-6

6.7

17-9

56-9

few years the crop declined steadily, but since then little
or no further drop has been seen. The yield remains
at about I2| bushels per acre for each successive ten
years' average, and has considerably overtopped that
amount during recent favourable seasons. This yield,
however, of 12 J bushels of corn per acre, is only about
a third of that obtained on the adjacent plots receiving
manure every year during the same period.

These facts lead to a new point of view : it is not
merely the amount of this or that plant food present in
the soil which must be taken into account but also
their mode of combination. The material may be
present in the soil and soluble in the acid used for
analysis, but yet may be beyond the reach of the plant

I.] DORMANT AND AVAILABLE PLANT FOOD 23

in a locked-up or dormant condition. The plant can
only obtain substances which have been previously dis-
solved in the water contained by soils in the field, hence
plant food in the soil is only available for the plant in
so far as it can pass into solution.

Accepting, then, the fact that the soil contains a vast
store of all the elements necessary to its nutrition but
in forms of low availability, it remains to ascertain
which of the substances are normally likely to fall below
the current requirements of the crop. This is a ques-
tion that, can only be solved by field experiments, and
though the answer will vary with each crop and each
soil yet certain general principles at once become
evident and upon them the whole idea of a fertiliser is
based. For example, field experiments at once show
that certain elements indispensable to the plant, as seen
from water culture experiments, need not be supplied
to the crop in the field, since the soil is practically
always able to provide a sufficiency. Calcium,
magnesium, iron, sulphur, chlorine, and silicon fall into
this class ; to judge by field experiments alone there
are only three elements required for the nutrition of the
crop — nitrogen, phosphorus, and potassium — and this
means that soils can usually supply the elements
necessary to the plant in sufficient quantities, except in
these three cases. Fertilisers, then, are designed to
supply deficiencies in the soil, and for all practical
purposes are to be regarded as consisting of compounds
of nitrogen, phosphoric acid, and potash, either singly or
together. They may also contain magnesia, lime, or
sulphuric acid, but these, though equally necessary to
the plant, are not counted, since the unaided soil may
be trusted to furnish the crop with them.

To summarise the position we have reached : a
fertiliser must contain one or more of the three sub-

24 INTRODUCTORY [chap. 1.

stances, nitrogen, phosphoric acid, and potash, which
alone among the various elements necessary to the
nutrition of the plant cannot be supplied by cultivated
soils in amounts sufficient for profitable crop production.
The soils do contain these substances in comparatively
enormous quantities, but the distinguishing feature of a
fertiliser which makes it effective when supplied in
quantities comparable with those removed by the crop,
is its " availability."

A distinction is often drawn between natural and
artificial manures ; properly speaking, the latter should
include only such materials as are the results of some
manufacturing process, e.g., sulphate of ammonia, super-
phosphate and basic slag. But practically speaking, any
concentrated fertiliser that is brought on to the farm in
bags, though its origin be as natural as the sea birds*
excrement constituting "guano," or the ground seeds
known as " rape dust," gets called an artificial manure,
in contradistinction to the farmyard manure which is
the normal product of the farm. In all the published
reports dealing with the Rothamsted experiments it has
been customary to distinguish such substances as are
found in the ash of a plant — the phosphates, the sul-
phates, and chlorides of the alkalis or alkaline earths —
as "mineral manures"; the compounds containing nitro-
gen are regarded as distinct, since they are ultimately of
organic origin, even when they consist of such obviously
mineral substances as nitrate of soda or chloride of
ammonia. The term "cinereals" has also been pro-
posed in place of mineral manures or ash constituents ;
none of the terms are satisfactory, but since attempts
at corrected terminology only result in increased con-
fusion, the term " mineral manures," however imperfect,
will continue to be used throughout this book for
fertilising substances containing no nitrogen.

CHAPTER II

FERTILISERS CONTAINING NITROGEN

The Importance of Nitrogen — Evidence that Plants cannot utilise
the Free Nitrogen of the Atmosphere — Ammonia and Nitric
Acid in the Atmosphere — Origin of the World's Stock of
Combined Nitrogen — Nitrogen-fixing Bacteria — Fixation of
Atmospheric Nitrogen to form Calcium Cyanamide — Fixation
of Atmospheric Nitrogen in the Electric Arc ; Manufacture of
Nitrate of Lime — Nitrate of Soda: Nature and Origin —
Properties of Nitrate of Soda : Use as a Fertiliser — Value of
the Soda Base — Injurious Effects of Nitrate of Soda upon the
Texture of the Soil — Sulphate of Ammonia : Sources and
Production — Changes undergone by Sulphate of Ammonia in
the Soil — Acidity of Soil induced by Sulphate of Ammonia —
Relative Value of Nitrate of Soda and Sulphate of Ammonia
— Other Nitrogenous Fertilisers : Soot, Shoddy, Fur and
Feather Waste, Hoofs and Horns — Slow Action of such
Manures — Seaweed.

Amongst the elements of the nutrition of the plant
the first place must be given to nitrogen ; not only does
it cost more per pound to the farmer than do the other
necessary elements, but as a fertiliser applied to ordinary
soils it seems to have a more direct and immediate
effect upon the plant ; furthermore, it differs from the
others in that plants live habitually in contact with a
vast unusable store of it. Since plants live in an
atmosphere four-fifths of which consists of elementary
nitrogen, it is perhaps necessary to justify a little the

26 FERTILISERS CONTAINING NITROGEN [chap. ll.

Statement made in the previous chapter, that they only
obtain the nitrogen they require in a combined form by
means of their roots. The form that the demonstration
has taken may be seen in the water culture experiment
which has already been illustrated ; in the absence of
combined nitrogen, the development of the plant is very
small. The same is true for cultures in sand, which re-
produce more closely the natural conditions, and many
experiments have been performed with the greatest
care with plants thus growing in artificial soils supplied
with a known amount of nitrogen. When the plants
have come to the full term of their growth, the nitrogen
they contain is found to be exactly balanced by the
amount of the same element which has been removed
from the soil. Among these experiments, a most
elaborate series were carried out at Rothamsted in
1857-58, and were generally regarded as definitely
settling the question against the fixation of nitrogen
by the plant itself

The experiments were made with wheat, barley,
oats, clover, beans, peas, and buckwheat, and the trials
were repeated, in the one case with no manure in the
pots, and in the other with the supply of a small
quantity of sulphate of ammonia. The soils employed
were made up from either ignited pumice or ignited
soil, and the glass shades under which the plants were
grown rested in the groove of a stoneware vessel, mercury
being used as a lute. The air, previously passed
through sulphuric acid and sodium carbonate solution
and washed, was forced into the apparatus, so as to
always maintain a greater pressure inside than out,
thus minimising all danger of unwashed air leaking in ;
carbonic acid was also introduced as required. Under
these rigorous conditions the following results were
obtained : —

Tari.k IV.— Summary of the Results of Exf'eriments made at
rotuamsted to determine whether plants assimilate
Free Nitrogen.

Nitroireu. — Giaui.

Ill Seed

and
Manure
if any.

lu

Plants,

Pot, and

Soil.

Gain or
Loss.

WITH NO COJIBINED NITROGEN SUPPLIED BEYOND THAT
IN THE SEED SOWN.

Gramineae

Leguminosas

Other Plants .

1857-

1858

1858J

1857

1858

Wheat .

Barley

Barley

o-oo8o
0-0056
0-0056

0-0072
0-0072

0-C082

Wheat .

0-0078

0-0081

Barley
Oats .

0-0057
0-0063

0-0058
0-0056

Wheat .
Oats .

0-0078
0-0064

0-0078
0-0063

Beans

0-0796

0-0791

Beans
Peas .

0-0750
0-01S8

0-0757
00167

Buckwheat

0-0200

0-0182

- o oooS
+ 0-0016
+ 0-0026

+ 0-0003
+ 0-0001

- 0-0007

-0-000 1
-0-000;

+ 0-0007
-0-0021

-0-0018

0-90
1-29
1-46

1-04
1-02
0-89

I -00
0-98

0-99

I -01

089

0-91

with combined nitrogen SUPPLIED.

Leguminosse -[

Other Plants .

1857-

1858

1858J

i858{

18:8

iS;8

Wheat
Wheat
Barley ,
Barley .

Wheat ,
P)arley
Oats .

Wheat
Barley
Oats .

Peas .
Clover

Beans
Buckwheat

0-0329

0-0383

0-0329

0-0331

0-0326

0-0328

0-0268

0-0337

0-0548

0-0536

0-0496

0-0404

0-0312

0-0216

0-0268

0.0274

0-0257

0-0242

c-0260

0-0198

0-0227

00211

0-0712

00665

0-07 1 1

0-0655

0-030S

0-0292

+ 0-0054

+ 0-0002
+ 0-0002
+ 0-0069

-0-00I2
-0-0032
-0-0096

+ 0-0006
-0-0015
- 0-0062

-o-ooi6
-0-0047

-0-0056
-o-ooi6

I-I6

I -or

I -01
1-25

o-qS
o-i,4
o-u^

1-02

0-94
0-76

0-93
0-93

0-92
0-95

28 FERTILISERS CONTAINING NITROGEN [chap.

And if objection be made that such plants were
enfeebled by the unnatural conditions, so that they
had lost their power to bring nitrogen into combina-
tion— to " fix " it, in current language — there are many
other types of experiment which render such criticism
invalid. For example, Hellriegel performed a long
series of experiments with different plants, which

Table V. — Barley (Hellriegel and Wilfarth).

Nitrogen Supplied.

Dry Matter Produced,

o

0-028

0-056

0-II2
0-336

0-5I

3-0

5-6

10-8

29-3

showed, up to a point, that the amount of growth was
very closely proportional to the amount of nitrogen
supplied in a combined form, when there was a suffici-
ency of the other elements of plant food present.
This would not be the case were the plant able to get
any nitrogen for itself from the atmosphere. Again, to
meet an early objection of Liebig and his followers that
the Rothamsted crops, which seemed unable to draw
upon the nitrogen of the air though freely supplied
with phosphoric acid and potash, failed to do so because
they had not got the necessary initial development of
leaf, to one plot there was supplied a very small amount
of active nitrogenous manure, just to give the young
plant a good start, whereupon it might be able to
continue to feed upon the atmospheric nitrogen. But,
as Table VI. shows, the small addition of nitrogen only
produced a small increase of crop, very fairly propor-
tional to the much larger increase produced by a normal
application of the same fertiliser. If, then, the yield of

II.] GROWTH PROPORTIONAL TO NITROGEN 29

most of our field crops is, until some other limiting
factor comes into play, proportional to the amount ot
combined nitrogen they receive, it is necessary to con-
clude that they have drawn none from the atmosphere.
It is indeed true that the atmosphere does contribute a
small amount of nitrogen for the use of the plant under
ordinary conditions, because traces of both ammonia

Table VI.— Rothamsted Mangolds (1876-1902).

Roots

Increase

per

per lb.

Acre.

otN.

Tons.

Tons.

Superphosphate

and Sulphate

of Potash .

4-53

Do.

do.

+ 7-8 lb. N.

5-93

0.17

Do.

do.

+ 86 „ .

14-03

O-II

Do.

do.

+ 93-8 „ •

14-60

0-107

and nitric acid are found in the air and are washed
out by the falling rain. Table VII. shows the average
amount of nitrogen as nitric acid and ammonia brought
down in the rain falling at Rothamsted for the thirteen
years between ist September 18S8 and 30th August
1901, together with the corresponding results obtained
at a few other places where observations have been
made for any long period. It will be seen that the
Rothamsted results are considerably lower than those
obtained at the Paris, Copenhagen, or Florence stations,
though they do not notably dififer, as regards the total
amount of nitrogen falling per acre, from those obtained
at the two tropical stations in the West Indies. The
high results are probably due to the proximity of towns,
because the majority of other determinations, not
quoted here because they have only been continued for
one or two years, agree more nearly with the Rotham-
sted figures. It may thus be assumed that ordinary

FERTILISERS CONTAINING NITROGEN [chap.

land receives about 4 to 5 lb. per acre per annum of
combined nitrogen from the atmosphere, an amount
which only forms a small fraction of the requirements
of the crop : —

Table VII. — Nitkogen as Ammonia and Nitric Acid
IN Rain.

Locality.

Date.

Rain-
fall.

NiTKOGKN.

Per MilHon.

Pfr Arre
P';r aununi.

.2

01 0

< S

s

<

0 .

s
<

0 .
^1^

"a
0
H

Rothnmsted .
Copenhagen .
Montsouris
Florence .
Barbados
British Guiana

18S8-1901
1880-18S5
1876-1900
1869-1875
1885-1897
I S 90- 1 900

27-25
21-95

21-^2

3S-3I

63-95

102-41

0-440
1.97

2-13
1-004
0-084
0.055

0-183

0-473

c-66

0-57
0.268
0-078

2.71
9.27

10-37
8.70

1.22
1. 17

I-I3

2.21
3-22
3-09

3-88
1.82

3-84
11.48

13-59

11-79

5.10

2-99

The tenacity with which in the face of such evidence
the opinion has been held that the leaf of the plant can
obtain nitrogen as well as carbon from the atmosphere,
is due to the difficulty of explaining how the world's
original stock of combined nitrogen can have arisen.
Assuming the world to have cooled down from the
state of incandescent gas, it must have started with all
its nitrogen in the free gaseous state ; yet as we see it
to-day, the whole stock of combined nitrogen is of
organic origin.

The circulatory process through which combined
nitrogen passes is very plain. Animals only use the
highly organised compounds like the proteins ; these
they break down during their vital processes to simpler
compounds like urea and the amides, which in turn are

[I.] ORIGIN OF Nil ROGEN IN VEGETATION 31

taken by plants and built up once more into the protein
complexes. The nitrogen, however, only circulates
from one form of combination to another, with
occasional losses when a compound is broken down
as far as elementary nitrogen ; there is never any
bringing of fresh elementary nitrogen into the account.
The stocks of combined nitrogen that have been handed
down from past ages all speak of the same organic
circulation, never of fixation. Coal is but the debris of
an extinct vegetation ; nitrate of soda represents the
glorified result of the same decay processes which give
rise to nitrate of potash in India and nitrate of lime in
the old nitre beds. Virgin soils with their vast stores
of nitrogenous humus are often looked upon as having
gained nitrogen by the accumulation of long epochs of
vegetable growth ; but if plants cannot fix nitrogen there
can have been no gain, however long the growth, but
only a circulation of the pre-existing combined stock-
At first sight there seem to exist no processes which can
either bring about the original combination or renew
the stock from time to time. Inorganic agencies are
certainly trifling, because nitrogen is a difficult element
to bring into combination, so great an initial expenditure
of energy is required to separate the atoms in the
gaseous molecule. Electric sparks will effect a com-
bination of nitrogen and oxygen, and lightning flashes
through the air have been invoked to account for the
trace of nitric acid to be found in the atmosphere and
in rain water. Again, it has been supposed that during
the evaporation of water there is always a slight com-
bination of nitrogen with the elements of water to form
ammonium nitrite, but more recent and refined experi-
ments are against the existence of any such reaction.

There has, however, of late years been discovered
one vital process capable of fixing nitrogen, which has

32 FERTILISERS CONTAINING NITROGEN [chap.

probably been operative since the beginning of life on
the earth, and this power is the property of certain
groups of bacteria only. The history of nitrogen-fixing
bacteria began some thirty years ago with the resolu-
tion by Hellriegel and Wilfarth of the great outstanding
difficulty in the theory that plants only make use of
combined nitrogen. Though the demonstration in the
laboratory of this opinion seemed perfect, and though
in the main it was corroborated by field experiments,
there was one group of plants — peas, beans, clover, and
their allies — which seemed to derive little or no benefit
from nitrogenous fertilisers, and yet actually left the
land richer in nitrogen after their growth, although in
the crop removed there was an exceptional amount of
nitrogen. That beans or vetches or lupins were the
best preparation for a wheat crop was a commonplace
of Roman agriculture, and the same observation became
afterwards enshrined in that most fundamental of
rotations, the Norfolk four-course system, in which
wheat follows clover or beans. Hellriegel and Wilfarth
found that leguminous plants did gather nitrogen from
the atmosphere, and could, therefore, become wholly
independent of nitrogenous manures ; but this only
took place when, by infection from the soil, certain
characteristic nodules were formed upon the roots.
These nodules were found to be colonies of a particular
bacterium which seems to live symbiotically on the host
plant, furnishing it with nitrogenous matter and deriving
from it the carbohydate required for the fixation of
nitrogen. As the fixation of nitrogen is a chemical
process analogous to going uphill, it requires a supply
of energy from outside, which external source of energy
the bacteria obtain by the oxidation of carbohydrate
in some form or other. The particular bacterium living
in symbiosis with the leguminous plants is highly

n.] NITROGEN FIXED BY LEGUMINOUS PLANTS 33

specialised and has not been transferred to other non-
leguminous plants ; only with some difficulty has it also
been made to grow and to fix nitrogen when living
alone and no longer in association with its host But
with increasing knowledge of the methods of handling
this organism, it seems probable that by cultivation
we shall be able to obtain races showing variations in
their power of fixing nitrogen, though how long they
will retain this greater or lesser virulence after inocula-
tion back to the leguminous plant is still uncertain.

The leguminous plants form, then, by their associa-
tion with nitrogen-fixing bacteria, one considerable
natural source of combined nitrogen, and how effective
they can be in accumulating fertilising matter in the
soil may be judged from the accompanying table
(VIII.) showing the results of one of the Rothamsted
experiments upon crops grown in rotation.

Table VIII.— Effect of Ci-Over on Succeeding Crops.

Manuring

for

Swede Crop

only.

CO

>
0

0

Wheat, 1S95.

Boots, 1896.

Barley, 1S97.

<3

Isi

£ I >

= T30

S °

=■=0

^5

Increase
line to
Clover.

Mineral
manure

Complete
manure

Cwt-s.

59-7
76.7

Lb.
4,220

4i547

Lb.
5,180

5>209

Per
cent.

+ 22.7
+ 14-6

Cwts.
I79-I
379-8

Cwts.

244-5
388.8

Per

cent.

+ 36-5
+ 2.4

Lb.
2,103

3.595

Lb.

3,991
4.913

Per

cent.

+ 89-8

+ 367

On this field (Agdell) the rotation begins with a crop
of Swede turnips, which is manured, in one case with
mineral manures, in the other with a complete fertiliser.
Following the Swedes comes barley without manure,
then the field is divided, and on one portion clover is
grown, while the other is bare fallowed and carries no

34 FERTILISERS CONTAINING NITROGEN [cHAP.

crop throughout the year. A crop of wheat, still un-
manured, completes the rotation. In the table the
yield on the portions which have grown clover is com-
pared with that on the portions without crop ; it will
be seen that although a crop of nearly three tons of
clover hay has been taken away from the one portion,
the wheat which follows it is 23 per cent, better than on
the portion where no clover had been grown in the
previous year. Nor is the benefit due to the clover
exhausted by the wheat crop, for it is seen to persist in
the root crop following the wheat and in the barley
which comes a year later still.

The only practical limitation to the gathering of
nitrogen by this method lies in the difficulty that is
found in growing leguminous crops frequently on the
same land. Although the Rothamsted experiments
have demonstrated that it is possible to grow wheat
year after year for more than half a century and
maintain the yield if the appropriate manures are
employed, on few soils can clover be grown with success
more frequently than once in four and even once in
seven years. As the farmer says, the land becomes
"clover sick," and though the clover seed germinates
and grows for a time, the constitution of the plant is so
weak that it almost inevitably succumbs during the
winter to an attack of fungoid or other disease. The
determining cause of this weakness of constitution
which lies at the back of "clover sickness" is still
unknown, but preventing as it does the more extended
use of these nitrogen-collecting crops it would be of
real economic importance to find the cause and a
remedy.

More recently, however, other bacteria have been
discovered in the soil which are capable of fixing free
atmospheric nitrogen without association with any

II.) NITROGEN FIXED BY BACTERIA 35

host plant, provided they are supplied with some carbo-
hydrate, by the oxidation of which they derive the
energy necessary to bring the nitrogen into combination.
Of these bacteria the best known and probably the
most effective is a large organism, discovered by
Beijerinck in Holland, and called by him Azotobacter
chroococcum. It is widely distributed in cultivated soils
both in Europe and America, and although the author
failed to detect it in the arid soils from the high veldt
or the Karoo in South Africa similar though perhaps
slightly varying bacteria were obtained from cultivated
soils from tropical East Africa, Egypt, India, Russia,
Western America and Canada, Sarawak, and Monte
Video. It appears to be only active when there is some
calcium carbonate in the soil, possibly because in its
oxidising reaction certain acids are produced which must
be neutralised before its activity will continue. Roughly
speaking, its action is to oxidise carbohydrates to
carbon dioxide and water, forming as bye-products
certain organic acids, and some dark brown humus
(whence the name "chroococcum"), and incidentally
bringing a certain amount of nitrogen into combination,
not more, however, under the most favourable laboratory
conditions than i to 2 per cent, of the carbohydrate
consumed. It is, however, extremely probable that we
may look to this organism and its allies as the origin
of the continued accumulation of nitrogen in such rich
virgin soils as the black soils of the Russian Steppes or
of Manitoba. As long as these lands were uncultivated,
the annual fall of the leaf and dying down of the summer
vegetation furnished the conditions necessary for the
activity of the Azotobacter, The carbohydrate-containing
material thus returned to the soil provided the organism
with its necessary food supply, by the oxidation of which
it gained energy to fix the atmospheric nitrogen. In

36 FERTILISERS CONTAINING NITROGEN [chap.

cultivated soils where the crop is removed the action is
almost brought to a standstill, as may be seen in the
steady loss of nitrogen from the arable soils at
Rothamsted during the fifty years they have been
cropped without any extraneous nitrogen supply. Only
when land is laid down to grass is there a sufficient
amount of carbohydrate debris returned to the soil to
enable the Azotobacter to fix a measurable quantity of
nitrogen. A good example of the natural accumulation
of combined nitrogen may be seen in two pieces of
land at Rothamsted, which for the last twenty-five
years have been allowed to run wild and assume a
natural prairie condition of self-sown weeds and grasses,
that are never taken away but left to rot where they die
down. Samples of the soil had been taken at the
beginning of the period, and by comparing them with
more recently taken samples it has been possible to
detect a very considerable fixation of nitrogen,
amounting in the most favourable case to nearly fifty
pounds of nitrogen per acre per annum. The second
similar piece of land shows a much lower result, and this
is correlated with the lack of carbonate of lime in the
soil of this plot and a corresponding absence of the
Azotobacter organism.

It is too early yet to speculate freely on the
work of the various nitrogen-fixing bacteria ; we may,
however, confidently attribute to their action both the
current stock of combined nitrogen in the world and
the main source of its renewal in the future.

Attempts have already been made to raise the
nitrogen-fixing bacteria artificially, particularly those
associated with leguminous plants, and by introducing
them into soil that is lacking or poorly supplied with
them, to render it capable of self-enrichment in this
most natural manner. Such cultures are, in fact, sold

II.] SOIL INOCULATION 37

*

commercially at the present time and have in some
cases been somewhat unscrupulously boomed as
dispensing with the need for nitrogenous fertilisers.
Undoubtedly cases may be quoted where the use of
these pure cultures of nodule-forming bacteria has
been of great service, generally on newly-reclaimed
soils, which have thus become for the first time capable
of carrying a leguminous crop. But in old cultivated
soils the organism is already present, and sufficient
evidence is not yet forthcoming to show that the new
introductions have had any effect ; certainly the results
obtained in the British Isles are almost wholly negative.
Doubtless the useful soil bacteria will be domesticated,
improved, and made more effective, just as our flocks
and herds have been tamed and developed, while the
useless ones will be stamped out as vermin ; but at the
present time we cannot be satisfied that any improved
race of bacteria introduced artificially into the soil has
managed to persist and get a real footing in face of the
competition of the enormous natural bacterial flora
already existing there. So the picture of the farmer
carrying the manure for a field in his waistcoat pocket and
applying it with a hypodermic syringe, is still a vision
of the future.

These natural processes for the recuperation of our
stock of combined nitrogen have, during the last year
or two, been supplemented by one or two manufacturing
processes of great interest in themselves, which are on
the point of becoming factors of importance in the
fertiliser market.

Speaking broadly, there are two ways of bringing
free nitrogen gas into combination : first, at extremely
high temperatures, such as are attained in the electric
arc or sparks, nitrogen will combine with oxygen to
form various oxides from which nitric acid will eventually

38 FERTILISERS CONTAINING NITROGEN [chap.

result by solution in water; secondly, nitrogen will
combine with a few metals and allied bodies, again at
high temperatures, to yield substances which under the
action of water give rise to ammonia. It is this latter
method which was first developed on a commercial
scale by Frank and Caro in Berlin. They did not
exactly start with a metal, but with calcium carbide,
the substance now so well known as the source of
acetylene for illumination. This body, Frank and
Caro found, would combine readily with nitrogen gas
at quite moderate temperatures, and the resulting sub-
stance, calcium cyanamide, nitrolim, or kalk-stickstoff,
as it is called, will decompose under the action of water,
yielding its nitrogen as ammonia and the calcium and
carbon as calcium carbonate. An Italian company,
which was the first to take up the patents for the
manufacture of calcium cyanamide, has established its
factory alongside one of the great producers of calcium
carbide at Piano d'Orte in the hills above Rome, where
water-power can be obtained for the cheap generation
of electricity, and other works are being erected in
Norway, in Savoy, and in America, where suitable
water-power can be obtained. On theoretical grounds,
one electrical horse-power per annum should bring
about the fixation of 772 kilogrammes of nitrogen ; in
practice 300 to 330 have been attained. In the manu-
facturing process the calcium carbide is first roughly
ground and then heated in iron tubes through which a
current of nitrogen gas is passed. The calcium carbide,
which itself results from the reaction of a mixture of
chalk and coke in the electric furnace, must either be
purchased or manufactured by a preliminary process.
The two reactions of forming the carbide and uniting
it with nitrogen can indeed be carried out simultaneously,
but this method has been abandoned in practice. The

11.] CHEMICAL FIXATION OF NITROGEN 39

nitrogen gas is obtained by passing a current of air
over red-hot copper, the copper oxide formed being
afterwards reduced to the metallic state again by sending
over it a current of coal-gas while it is still hot. More
recently a process of obtaining nitrogen by fractional
distillation from liquefied air has been employed. The
resulting calcium cyanamide is a very fine dark grey
powder, light and rather difficult to sow alone because
it floats so readily in the air.

Since the product also contains about 20 per cent.
of free lime, it readily absorbs water from the atmo-
sphere, the first change that takes place being the
slaking of the quicklime. At the same time the cyan-
amide begins to decompose slowly into ammonia and
calcium carbonate in eventual accordance with the
equation

CaCN2 + 3H20 = 2NH3 4-CaC03,

so that some loss of ammonia may take place if the
manure is left lying about exposed in a loose condi-
tion to the atmosphere. In bags, however, it may be
stored without any sensible loss.

With superheated steam the reaction takes place
more rapidly, and with acids or acid manures salts of cal-
cium and ammonium are formed, preceded of course by
an active interaction between the free lime and the
acid. The same reaction may be expected to take
place when calcium cyanamide is applied to the soil :
it should change slowly into ammonia, which will be
arrested by the soil, and calcium carbonate. It has
been shown, however, by Lohnis, that the reaction with
water alone is slow and not particularly effective, but
that in practice certain soil bacteria bring about the
change.

Commercial cyanamide contains as much as 20

40 FERTILISERS CONTAINING NITROGEN [chap.

per cent, of nitrogen, the theoretical substance being
CaCNg with 35 per cent, of nitrogen. As a fertiliser,
calcium cyanamide has been subjected to a series
of sufficiently conclusive trials which show that on most
soils it is almost but not quite as effective as sul-
phate of ammonia supplying an equal amount of
nitrogen. For example, Table IX. shows the results of
four trials at Rothamsted in 1905, mangolds and
barley being the crops under experiment. On soils
poor in lime, doubtless the cyanamide would give

Table IX. — Rothamsted Experiments with Calcium Cyanamide,

1905.

Barley.

Mangolds.

Grain.

Straw.

Calcium Cyanamide
Sulphate of Ammonia .

Bushels.
34-3
37-5

Cwts.

19

24

Tons.
22-0

23-5

Tons.
II-I
lO-O

Tons.
28-9
27-9

comparatively better results, because then the carbonate
of lime, which is the bye-product of the decomposition
taking place in the soil, would itself be of considerable
value. The Rothamsted soil, however, contains sufifiicient
carbonate of lime to minimise the effect of this factor.
The chief drawback to the practical employment of
calcium cyanamide as a manure is its light, blow-away
character, and the injurious effect upon germinating seeds
of the ammonia and other gases given off when it is
first applied to the soil. It has, therefore, to be sown
on the land alone, and it should be incorporated with
the soil a week or so before any seed is sown. For
similar reasons it should not be used as a top dressing
unless mixed with earth beforehand, though recent
experiments suggest that this objection has been

II.] CALCIUM CYAN AM IDE 41

exaggerated. It is best to mix the cy anamide witli
superphosphate before application to the land ; in most
cases when cyanamide is used phosphates will also be
required, and a mixture of cyanamide with from five to
ten times its weight of superphosphate can be con-
veniently made and forms a good fertiliser for barley
or turnips. The mixture should be made on the
floor of the manure shed at least a day before the
manure has to be sown ; if the cyanamide is care-
fully handled and covered with superphosphate, it
can be mixed without creating an unbearable dust.
With the slaking of the lime a good deal of heat is
developed and the manure begins to steam, but a
sprinkling from a watering pot will help to keep the
heat down without rendering the mixture in any way
difficult to handle. The heap should be turned over
two or three times to secure a good mixture, and left
until the next day to cool off. It remains in a nice
friable condition and undergoes practically no further
change if it cannot be sown at once. No unpleasant
gases are given off during the mixing; the samples
of cyanamide first made contained some unchanged
calcium carbide which gave off acetylene on wetting,
but this is now avoided in the manufacturing process.

Two methods have been adopted to obviate the
dustiness ; in one the product is treated with a small
proportion of heavy shale or coal oil, in the other just
sufficient treatment with steam is applied to convert
the quicklime into slaked lime, and give the material
a more granular form. This latter process has the
further advantage of decomposing any traces of calcium
carbide and phosphide that may be present in the
original material. A slightly different product con-
taining calcium cyanamide is manufactured by a firm
in Westeregeln, under the patents of F. Polzenius, by

42 FERTILISERS CONTAINING NITROGEN [chap.

heating a mixture of calcium carbide and chloride in a
stream of pure nitrogen at about 750° C. The product,
known as stickstoff-kalk, is a black powder containing
over 20 per cent, of nitrogen and about 10 per cent, of
calcium chloride, together with a considerable amount
of free lime. As a manure stickstoff-kalk behaves in all
essential respects like the kalk-stickstoff oi v^YiXoh a more
detailed description has been given.

The other method of bringing nitrogen into com-
bination— that of effecting its union with oxygen at
the temperature of the electric arc — has received con-
siderable attention, and forms the base of at least two
working processes. It will be remembered that when
Sir William Crookes in 1898, in his British Association
address, warned the world of the rapidly progressive
exhaustion of its supplies of combined nitrogen, it was
to the union of nitrogen with oxygen that he looked
for the future supply of combined nitrogen for the
wheat crop, and he showed experimentally how the
two gases would burn together at a very high tempera-
ture. Not enough heat, however, is given out by the
flame to bring more gas up to the ignition point, hence
the flame is only continuous as long as external energy
is poured in.

Calculating from the best results Lord Rayleigh
had obtained in bringing nitrogen and oxygen into
combination by the electric spark, Crookes decided that
if electricity could be generated at one-seventeenth of
a penny per Board of Trade unit, as it was expected
would be the case at Niagara, then nitrate of soda
could be made artificially at about £^ per ton.

Such an electrical process was installed at Niagara
by Bradley and Lovejoy, who produced a number of
arcs between platinum poles with a continuous current
zX a potential of 10,000 volts. The oxides of nitrogen

II.] ELECTRICAL FIXATION OF NITROGEN 43

generated were converted into nitric and nitrous acids
by steam and more oxygen, and a mixture of sodium
nitrite and nitrate was prepared for agricultural pur-
poses. The installation, however, only ran for fifteen
months, for though considerable amounts of nitric
acid were produced, technical difficulties in maintaining
the apparatus in working order proved insuperable.
More recently a working process has been devised by
Berkeland and is running on a commercial scale at
Notodden in Norway. In the Berkeland-Eyde process
an alternating current at about 5000 volts is set to form
an arc between U-shaped copper electrodes, which are
hollow and kept cool by a current of water within.
The electrodes are placed equatorially between the
poles of a powerful electro-magnet, which has the
effect of causing the arc to spread out into a broad
flat flame. Though the temperature of the arc-flame
is calculated to be 2600° C, it is not particularly
luminous; it may be looked at directly from a yard's
distance.

Through the furnace in which this special arc is
generated about 15,000 litres of air are blown per
minute at gentle pressure and the issuing air contains
about I per cent, of nitric oxide and is at a temperature
of 600° to 700° C. It is cooled and then passes into
two oxidising chambers, where the combination of the
nitric oxide with the oxygen of the uncombined air
takes place, after which it passes into a series of five
condensing towers. Down the fourth tower, which
is filled with broken quartz, water trickles and picks
up enough of the nitrous gases to become 5 per
cent, nitric acid at the bottom ; this is pumped up
and trickles down the third tower, the process being
repeated until the liquid leaving the bottom of the
first tower contains 50 per cent, of nitric acid. In the

44 FERTILISERS CONTAINING NITROGEN [chap.

fifth and last tower the absorbing liquid is milk of lime,
and the resulting mixture of solution of calcium nitrite
and nitrate is treated with enough of the previously-
formed nitric acid to convert it wholly into nitrate,
the nitrous fumes evolved being led back into the oxi-
dising chambers. The product is then concentrated
until it solidifies as a material containing about 13
per cent, of nitrogen, or 75 per cent, of pure calcium
nitrate.

The present factory has three electric furnaces
installed, each employing 500 kilowatts, and the pro-
duction amounts to about 150 kilogrammes of nitrogen
fixed per kilowatt year.

Berkeland calculates that the cost of manufacturing
calcium nitrate containing 13 per cent, of nitrogen
is about £/\. per ton, and that it can be sold at a
profit at ;;^8 a ton, which would be equivalent to nitrate
of soda at about ;^io a ton. The present large factory
at Notodden has been putting calcium nitrate on the
market for two years or more, the rate of pro-
duction now being about 20,000 tons per annum.
When the extensions to the factory are completed it
is expected the output will amount to nearly 3000 tons
per month. As a fertiliser there cannot be the least
doubt that nitrate of lime will be just as valuable,
nitrogen for nitrogen, as nitrate of soda. At Rotham-
sted a chemically prepared nitrate of lime has been
used for two or three years for a special purpose on one
of the mangold plots, and it has given exactly equal
results to the nitrate of soda plot alongside. Many
field experiments have also been carried out with the
electrical product in Norway during the last year or
two, and have shown that the new material can be
strictly valued against nitrate of soda on the basis of
the nitrogen it contains. Indeed, on some soils it

11.] NITRATE OF SODA 45

is likely to be more valuable, because, as will be
shown later, part at least of the lime base will be
left behind in the soil as calcium carbonate. This
will be an advantage in peaty soils, and will also save
clay soils from the peculiar wetness and stickiness
which results from the employment of much nitrate
of soda. The present price is about ^8, 8s. per ton at
the British ports.

Turning now from the atmospheric nitrogen and
the various possibilities of utilising it to the purely
nitrogenous fertilisers that are available, we can begin
by dividing them into two classes, the quick and the
slow acting, in the first of which we have practically only
nitrate of soda, sulphate of ammonia, cyanamide, and
nitrate of lime. Our acquaintance however with the two
latter is too limited as yet to enable us to do more than
predict that they will fall into line with sulphate of
ammonia and nitrate of soda respectively. Nitrate of
soda has now been in use in this country for something
like seventy years, the Chilian deposits having been
first discovered about the time of Darwin's voyage
round the world in the Beagle. As nitre had long
been known to possess great manurial value, the
exportation of nitrate of soda to Europe was at once
suggested, and in 1830 it appears that a trial ship-
ment was made of 18,700 quintals of about 100 lb.
each. By 1838, the date of the first volume of the
Journal of the Royal Agricultural Society^ it was being
tried experimentally by a good many landlords and
farmers in this country. The production grew rapidly,
and reached its maximum in 1899, when 1,344,550 tons
were consumed ; since then the output has declined a
little, owing to combination between the producers.
At the present time the United Kingdom takes about
one-twelfth of the total production, Belgium an equal

46 FERTILISERS CONTAINING NITROGEN [chap.

share, France and the United States about one-sixth
each, and Germany rather more than one-third of the
whole. Opinions differ greatly as to the approaching
exhaustion of the Chilian deposits ; various estimates
set their probable life at from twenty to forty years,
but doubtless long before exhaustion sets in the
poorer grounds, now being neglected as containing
less than the paying amount of nitrate, will be exploited,
provided always that the artificial nitrate of lime does
not render the whole industry unprofitable.

As to the origin of the nitrate of soda deposits there
are two theories, to understand which some description
of the mode of occurrence is necessary. The chief
deposit lies in the province of Tarapaca, in Chile, on
an elevated plain, about 3000 feet above sea level, known
as the Pampa of Tamarugal, which stretches for a breadth
of some thirty or forty miles from the Corderillas on
the eastward to a low range of foothills separating it
from the sea. The climate is intensely dry, rain falling
only every two or three years, and then in quantities so
small as to evaporate rapidly. The special nitrate-bearing
deposit or caliche occurs a few feet below the surface,
and in it the nitrate is associated with earthy matters,
gypsum, common salt, and sulphates of sodium and
potassium. The generally accepted theory regards the
plain as an ancient sea-bed elevated by one of the
volcanic movements common on that coast, and then
desiccated. The nitrate of soda is set down to the
oxidation of immense masses of seaweed present in the
original sea, the salt of which has provided the necessary
sodium base. The chief argument in support of this
supposition is the presence of a small amount of sodium
iodate in the crude caliche, seaweed being known to
contain iodine. But such a theory is as impossible on
chemical grounds as it is untenable geologically. It

11.] FORMATION OF NITRATE OF SODA 4?

involves, in the first place, an extravagant amount of
seaweed, and our knowledge of the nitrification process
is quite opposed to the idea that it would take place in
a rapidly concentrating medium containing common
salt. Nor have we any reason to suppose that salt
would supply a base for nitrification ; even if its hydro-
chloric acid could be turned out the liberated acid
would at once suspend the process. And again, if the
iodates are to be taken as indicating seaweed, why
are not bromates also present in the caliche, since
both bromine and iodine are associated in seaweed.

A much more probable theory is that the deposit
represents the saline residues of fresh-water streams
flowing off the Corderillas, containing nitrates and
other salts derived from old rich soils or rocks on the
heights. The evaporation of such waters for a long
period of progressive desiccation would result in the
accumulation of the dissolved salts in the dry region
over which the waters formerly spread when the rainfall
was greater. The occurrence of iodine cannot be
explained until more is known as to the amount of
this element present in the waters and soils of the
Corderillas.

The only other deposits of nitrate of soda v\^hich
assume any economic importance are those which
occur in Upper Egypt, where certain shale beds of
Eocene age, out-cropping on both sides of the Nile
between Qena and Assouan, contain enough sodium
nitrate to make the clay worth carriage as a manure
known locally as " tafia." Analyses of a series of these
shales by F. Hughes show an average of ^-y per
cent, of nitrate of soda associated with lo-i per cent, of
sodium chloride, and 5-4 per cent, of sodium sulphate.
The material is disseminated throughout the whole
bulk of the clay ; and as this is not permeabk to any

48 FERTILISERS CONTAINING NITROGEN [cHAP.

extent by water, the nitrate can hardly be due to
infiltration, but must have been formed in situ — a
conclusion which is much strengthened by the fact
brought out by Hughes' analysis that small quantities
of nitrogenous organic matter, ammonia and nitrites
are also present in the extract from the clay.

In all probability the nitrates in these shales repre-
sent the results of nitrification of a mass of organic
matter originally contained in the deposit, but until
further data have been accumulated as to the depth to
which the nitrates extend, and their replacement or
not by unoxidised organic nitrogen compounds at
depths beyond the access of atmospheric oxygen, it is
impossible to say whether we are dealing with recent
or with what might be termed fossil nitrification, or
again whether there has been any concentration of the
salts in the surface layer analysed.

In any case, these Egyptian deposits give a clue to
the possible origin of the Chile beds by washing from
similar strata (and the Corderillas consist of rocks of
recent age) into a rainless area, where the salts are
accumulated by evaporation. The two deposits present
this common difficulty : that the deposit is nitrate of soda
instead of nitrate of lime — the usual product of nitrification
in soil ; again, both are associated with a preponderance
of sulphates over chlorides, a fact which seems to put
any marine origin out of the question. We are, how-
ever, dealing with typically arid conditions, and in all
parts of the world sodium salts are characteristically
abundant in the soils and rocks of areas of small rainfall ;
indeed, sodium carbonate is always found in such cases,
and this would form the base for nitrification. At the
same time, similar oxidising processes to those which
give rise to nitrates would convert the sulphur of the
organic matter to sulphates. But to settle the problem

II. J PREPARATION OF NITRATE OF SODA 49

of the origin of the Chile deposits of nitrate of soda, an
examination is required of the salts in the rocks of the
Corderillas, the drainage from which would find its way
into the plain of Tamarugal.

The nitrate of soda is found in a deposit named
caliche, of which it constitutes from 60 per cent, down to
17 per cent, lower grades not being at present worked.
In the caliche it is associated with sodium chloride,
sulphates of calcium, sodium, and potassium, and a
varying proportion of insoluble earthy matter. The
caliche is not found on the surface, but is covered by
various earthy and gypseous deposits to the depth of 2
to 10 feet. After the deposit has been broken up by
blasting, the caliche is removed to the works, broken up
and lixiviated in large vats heated by steam. The
saturated solution is led into tanks in which the nitrate
of soda deposits on cooling, further crops being
obtained from the mother liquors by continuing the
treatment. After draining and drying the nitrate is
made up into 2-cwt. bags for export. A further
product of the nitrate process is iodine, because the
caliche always contains a small quantity of sodium
iodate. The nitrate of soda thus obtained is a coarsely
crystalline powder, varying in colour from a slight
brown or pink shade to a grey-white, containing 95 to
96 per cent, of pure sodium nitrate, the remainder being
made up of moisture, sodium chloride, and traces of
sulphates of sodium, magnesium, and calcium.

A sample of the crystals after drying in the sun had
the following composition : —

Sodium Nitrate .

94-164

Magnesium Chloride

0-289

Potassium Nitrate

. 1763

Calcium Sulphate

0-102

Sodium Chloride .

0-933

Insoluble matter .

0-138

Sodium Iodate

O-OIO

Water .

2-IOO

Potassium Perchlorate

0-282

lOO-OO

Magnesium Sulphate

0-219

D

50 FERTILISERS CONTAINING NITROGEN [chap.

The salt is very soluble in water and is deliquescent,
so that it will gradually absorb enough water to liquefy
when exposed to the damp air of an English winter in
a manure shed. The salt is poisonous in quantity, awd
both horses and stock have not infrequently been killed
by licking nitrate of soda or the bags in which it has
been stored. Nitrate of soda contains as much as 56
per cent, of oxygen and accelerates the combustion of
such bodies as wood or coal with almost explosive
violence, one accident at least has been recorded from
this source of danger. Nitrate of soda is not only
soluble in water, but it is not in any way retained by
the soil, so that it must wash through into the drains or
subsoil when percolation is going on. For this reason
it should only be applied as a top dressing when the
crop is growing. Like all other saline bodies which
form a strong solution with water, nitrate of soda will
scorch and destroy any green tissue with which it is left
in contact ; it withdraws water from the cells and kills
them by plasmolysis (see p. 18). Hence in sowing
nitrate of soda on a crop like cabbage, a certain amount
of care should be taken not to let the salt lodge in
the crown of the plant.

Nitrate of soda may be mixed with other manures
except superphosphates and dissolved bones, the acid of
which gradually liberates nitric acid, so that such a
mixture should be sown immediately after it has been
made.

Nitrate of soda is always sold by the producers with
a guarantee of 95 per cent, pure, which guarantee
should also be obtained by the farmer, for the material
should be sold exactly as it is imported. It usually
contains about 96 per cent, of pure sodium nitrate,
which is equivalent to 15-7 per cent, of nitrogen or 19-1
per cent, of ammonia.

II.] IMPURITIES IN NITRATE OF SODA 51

Sodium perchlorate is sometimes present in small
quantities as an impurity ; this has a very injurious
effect upon vegetation, but the instances of damage due
to this cause are uncommon. Adulteration of nitrate of
soda has become rare nowadays ; in the past (and to a
certain extent still) it was mixed with common salt, a
substance which it resembles in colour and crystalline
appearance. In the manufacture of gunpowder it is
customary to make potassium nitrate by mixing sodium
nitrate with potassium chloride and crystallising out the
less soluble nitre. The mother liquors contain sodium
chloride (common salt) with small quantities of the
more valuable potassium nitrate, and when evaporated
down yield what is sometimes known as " gunpowder
salt." On occasion this material has been sold at a
fraudulent price as " nitrate of salt," and credited with
being a combination of nitrate of soda and salt, more
valuable than either for such crops as mangolds.

As there is no occasion for any admixture with
nitrate of soda, the farmer should always insist on
buying the unmixed substance of standard purity.

As a manure, nitrate of soda is of course treated as
a source of nitrogen. It is not sufficiently realised how
valuable the soda base may be. This is not because
soda is in any way necessary to the nutrition of the plant,
but because of the action of any soluble salt upon the
insoluble potash compounds in the soil. The potash of
the soil is due to the partial weathering of double
silicates like felspar into clay, which is not to be
regarded as pure kaolinite, AlgOg 2Si02 sHgO, but as
containing a certain proportion of zeolitic bodies inter-
mediate between felspar and kaolinite — hydrated double
silicates containing potash, soda, magnesia, and lime
combined with alumina and silica. Any soluble salt,
and particularly a soluble soda salt, will react with

52 FERTILISERS CONTAINING NITROGEN [chap.

these zeolites and exchange bases to an extent depend-
ing upon the relative masses of the two bodies ; hence
nitrate of soda acts on the clay in the soil and brings a
little potash into solution. To such an extent does this
action take place that in practice a dressing of nitrate
of soda on any but the lightest soils will dispense with
the necessity of a specific potash manuring, even for
potash-loving crops.

This is well illustrated in the Rothamsted experi-
ments (see Table X.) upon mangolds, if we compare the
yields on the plots receiving equivalent amounts of
nitrogen as nitrate of soda, sulphate of ammonia, and
rape cake, both with and without potash. The table
refers to the season of 1900, the twenty-fifth year of
that series of experiments, when it might be sup-
posed the potash in the soils of the plots receiving no
potash in the manure must have become thoroughly
exhausted : —

Table X.— Effect of Soda in Nitrate of Soda, Mangolds,
Rothamsted, 1900.

Plot.

With
Nitrate

of
Soda.

With
Sulphate

of
Ammonia.

With
Rape Cake.

6

5

Superphosphate and Potash .
Superphosphate only

Tons.
29.6
28.3

Tons.
28-2
I2'0

Tons.

29-4
14.9

The plots receiving potash all give about the same
yield, whatever the source of nitrogen; but on plots 5,
without potash, the yield is only maintained on the
nitrate of soda plot ; on the other two the plant is
neither supplied with potash by the manure, nor is the
soil forced to yield some of its stored-up potash as it is
by the nitrate of soda, whereupon the yield declines by

II.]

ACTION OF SODA IN NITRATE OF SODA

53

one-half or more. For twenty-five years, then, the use
of nitrate of soda alone has enabled the soil to supply
a mangold crop with the large amount of potash it
wants, though the store of potash in the soil apparently
soon becomes exhausted when a manure is used which
cannot bring it into solution. With other crops the
same results are obtained, though the lack of potash
does not become manifest so quickly as in the case of
mangolds. For example, we may compare the yield of
barley (Table XI.) for successive ten-year periods, the
yield of each plot being calculated as a percentage of
that on the completely manured plot receiving nitrate
of soda, to eliminate seasonal influences.

Table XL— Barley Grain, Hoosfield

Rothamsted

• I

^

^

ii to

V. t~

t. 00

f- Oi

t- 0

g M

C3 CO

CS 00

03 00

cj c>

Plot.

>.lj

^^

^3

^S

>.^

o o

0 i)

■=>&

oco

0 Oi

r-i CO

rt 00

r-i CO

^^

^— '

'^

^^

'-'

4N

Nitrate, Superphosphate,

and Potash .

lOOO

1 00-0

lOO-O

lOO-O

lOO-O

2N

Nitrate and Superphos-

phate ....

98-0

IOO-2

99'S

ios-7

1 01 -4

4A

Ammonia, Superphosphate,

and Potash .

92-4

93-7

97-2

1007

ico-8

2A

Ammonia and Superphos-

phate , • . .

91.4

97-8

96-0

908

77-8

It will be seen that when the manure contains
potash the ammonium salts yield practically the same
crops as nitrate of soda. When the nitrogenous
manure is nitrate of soda, the omission of potash
causes no diminution in the yield ; but with ammonium
salts and no potash the crop after the third decade
becomes unable to satisfy its potash requirements
from the soil alone, and the yield declines. In other
words, nitrate of soda has dispensed with the necessity

54 FERTILISERS CONTAINING NITROGEN [chap.

of a potash dressing, which after a time becomes
necessary when sulphate of ammonia is the nitrogenous
manure.

One of the most characteristic effects of the use
of nitrate of soda as a manure, either repeatedly or in
any quantity, is its deleterious action upon the texture
of a heavy soil ; farmers have repeatedly observed
that where nitrate of soda has been applied the
land remains very wet and poaches badly if it is at
all disturbed before it has dried. Market gardeners
in particular, who manure heavily with nitrate of
soda, have found this destruction of the tilth a
serious drawback to its use. The cause has usually
been put down to the hygroscopic character of nitrate
of soda ; since the salt itself readily attracts moisture
from the air and will even liquefy spontaneously, it
is considered that it keeps the land moist for the
same reason. But the extra amount of moisture that
could be held in the soil by a few hundredweights of
nitrate of soda would be wholly imperceptible when
distributed through the hundred tons or more which
the top inch of soil weighs per acre, even if the
application of nitrate of soda persisted near the
surface and were not quickly washed down in the
soil. Some of the Rothamsted plots in the mangold
field, where very large amounts of nitrate of soda
have been applied year after year for the last fifty
years, show this deterioration of tilth in very marked
fashion, the land being intolerably sticky after rain
and drying into hard intractable clods, so much so
that it is very difficult to secure a plant of roots unless
the season is favourable. Determinations, however,
of moisture in the surface soil do not show any sensible
difference between these plots of bad texture and those
v/orking more kindly, so that we must put aside the

Fig. 2. — Deflocculating Action of Nitrate of Soda on Clay Soils,

he jars contain water in which equal amounts of clay soil had been suspended and
allowed to settle for forty-eight hours. The soil in the left-hand jar had been
taken from a plot regularly receiving nitrate of soda.

II.] ACTION OF NITRATE OF SODA ON CLAY SOILS 55

idea that there is any direct attraction of water by
nitrate of soda remaining in the soil. The explanation
appears to be more complex. When a plant is feeding
upon a neutral salt like nitrate of soda, it takes up
rather more of the nitric acid than of the soda, leaving
behind in the soil some of the soda combined with
carbonic acid excreted from the root. Water cultures
in which plants are grown with nitrate of soda will
actually become alkaline to test-paper from this cause.
Now, a very small quantity of a free alkali, like carbonate
of soda, has an altogether disproportionate effect upon
clay ; the clay is deflocculated — i.e., the little aggregates
of very fine particles which cause the clay to crumble
down when dry and to allow water to drain through
it, are immediately resolved into their finest state of
division, and all the characteristic properties of clay are
accentuated. Deflocculation is effected mechanically
whenever clay is puddled or worked in a wet con-
dition, and all the features of puddled clay, which
is both retentive of water and impermeable by it,
which shrinks greatly in drying and then holds together
with extreme tenacity, are found in these soils when the
deflocculation has been brought about by a little dissolved
alkali. The fact that such deflocculation has taken
place may be illustrated by a very simple experiment.
Fig. 2 shows two large jars, each containing 3
litres of distilled water, in which has been shaken up
I gramme of the Rothamsted clay loam, in the one
case from a plot manured with nitrate of soda, in
the other, from the adjoining plot receiving ammonium
salts. It is obvious how much greater is the amount
of material remaining suspended in the jar con-
taining soil manured with nitrate of soda, which
means that this latter soil had been previously
brought into a more fine-grained and less flocculated

56 FERTILISERS CONTAINING NITROGEN [CHAP.

condition. Collateral evidence is furnished by some
of the other Rothamsted plots ; for example, when
the tile drains beneath the wheat plots run, the water
percolating from below the nitrate of soda plot is
always slightly turbid with fine suspended clay material,
while the water from the other plots is clear. This
removal of the finest material from the nitrated plot
has been so persistent during the fifty years or so of
experiment on this field, that the mechanical analysis of
the soil now shows a smaller proportion of clay, which
removal has only been possible because of the defloc-
culation brought about by the nitrate of soda manuring.
Again, the soil of the plots receiving nitrate of
soda is found to be losing carbonate of lime to the
water percolating through it at a lower rate than the
soil of the unmanured plot ; this is because the pro-
duction of a free base by the plant's own growth has,
to a certain extent, saved the carbonate of lime in the
soil from attack. The following table (XII.) shows the

Table XII. — Calcium Carbonate in Broadbalk Wheat Soils.
First Depth (i to 9 Inches).

Plot.

Per cent, in
Fine Dry Soil.

Loss
per Acre

per
annum.

Lb.

1865.

1904.

3
9

7

2

Unmanured

Complete Minerals and 275 lb. Nitrate
of Soda

Complete Minerals, and 400 lb. Am-
monium Salts .....

Dung

4-54
4-24
3-82

4-20

3-29

3-36
2.25

3-28

800

564
lOIO

590

annual average rate of loss of carbonate of lime for the
last forty years from some of the chief plots of the
Broadbalk field ; it will be seen that the nitrate of
soda has reduced the loss of carbonate of lime from the

II.] NITRATE OF SODA USED ALONE 57

soil by between 200 and 300 lb. per acre per annum,
this quantity representing the base it has itself sup-
plied. The bad texture of the land induced by the
use of nitrate of soda is not easily removed ; lime is
of no service in this case, because it only adds another
alkali ; a better remedy is to be found in the simultaneous
application of an acid manure like superphosphate.
Better still, when an active nitrogenous manure is
needed, instead of nitrate of soda alone a mixture of
sulphate of ammonia with nitrate of soda might be
employed ; for, as will be seen later, sulphate of
ammonia acts on soil like an acid, hence a mixture
of the two manures ought to make a better source of
nitrogen than either alone.

Amongst farmers a certain amount of prejudice
against nitrate of soda still lingers ; it is described as
a " stimulant," even as a " scourge," and is regarded as
producing a crop to the detriment of the fertility of the
land. To a certain extent it is true of nitrate of soda,
as of an}' other fertiliser containing only a single con-
stituent of a plant food, that its continued use alone
must increase the draft upon the other nutritive elements
in the soil, in this case phosphoric acid and potash.
Nitrate of soda, also, is such an active source of nitrogen
and nitrogen is so dominant a factor in producing growth
that large crops can often be grown for a time by the
help of nitrate of soda alone. But so far from nitrate
of soda being specially harmful in this way, the Rotham-
sted experiments show that the yield of any crop is
maintained with nitrate of soda alone better than with
any other single manure. For example, the produce of
mangolds with nitrate of soda alone averages 10^ tons
for twenty-seven years, as against 10 tons with rape
cake alone, and under 6 tons with ammonium salts
alone. But, of course, the true answer to such criticism

58 FERTILISERS CONTAINING NITROGEN [CHAP

is that nitrate of soda requires to be used with phos-
phates and potash in order to make up a complete
fertiliser, and that only in this way can the fertility of
the soil be maintained. As has already been seen,
potash can generally be omitted in practice, but
phosphates must be added except in the special cases
when only a nitrogenous manure is needed, as in top
dressings for wheat. The prejudice against nitrate of
soda is probably really due to its injurious effect upon
the tilth ; if it is used in large quantities or repeatedly,
not only does the humus content run down but the land
begins to work badly, so that poor crops result, although
the land has not been particularly exhausted of plant food.

As a fertiliser the special value of nitrate of soda
lies in its immediate availability ; no change has to take
place before it passes into the plant ; in consequence, it
has a very immediate effect in early spring, when the
land is still so cold that the production of nitrates by
bacterial processes is almost suspended however rich
the soil. As an aid to the rapid production of spring
vegetables, or to give a start to a field of spring corn
dwindling in the cold east winds, or to push a crop
through an insect attack, nitrate of soda is without a
rival.

The great rival of nitrate of soda is at present
sulphate of ammonia, of which over 200,000 tons are
annually produced in this country. The source of
origin is coal, which contains about 1-5 to 2 per cent, of
nitrogen derived from the original vegetable matter
giving rise to the coal. When coal is subjected to any
destructive distillation by heat, as in the process of
gas-making or even when it is burnt, about 15 per
cent, of its nitrogen is given off as ammonia, which may
be recovered from the gases by simply washing them
with water. The ammoniacal gas liquor thus produced

II.]

SULPHATE OF AMMONIA

59

is redistilled into sulphuric acid and sulphate of
ammonia is crystallised out; the resulting commercial
salt contains about 20-5 per cent, of nitrogen. Not only
gas works, but blast furnaces, coke ovens, shale oil
works, etc., are now arranged to recover this valuable
product of the coal, and the accompanying table shows
the current output from each of these sources : —

Table XIII.— Production of Sulphate of Ammonia in the
United Kingdom.

SCMlIVft.

1901.

1000.

1899.

Gas works ....
Iron works , «
Shale works . «
Coke, etc., works

Tons.

148,500
16,000
36,500
19,000

Tons.
142,000
17,000
37.000
17,000

Tons.
134,000
18,000
38,500
15,000

Total production .

220,000

213,000

205,500

Exports ....
Home consumption .

150,203
69,797

145,285
67,715

140,371
65,129

Average price

;^io, IIS. 4d.

;^ii, 2s. od.

;^ii, 5s. lod.

In the early days of the industry hydrochloric acid
was sometimes employed, in which case ammonium
chloride (muriate of ammonia) was obtained, but the
only salt now prepared as a manure is the sulphate.

Sulphate of ammonia, when pure, is a white crystal-
line salt freely soluble in water ; the commercial article
varies somewhat in colour, being generally grey or
yellow from a trace of tarry matter ; in some cases it is
distinctly blue, owing to the presence of a little ferro-
cyanide, derived from the cyanides always present in
coal-gas. The pure salt contains 21-2 per cent, of
nitrogen, and as the commercial article is generally of

6o FERTILISERS CONTAINING NITROGEN [chap.

about 95 per cent, purity, it is usually guaranteed to
contain 20-2 per cent, of nitrogen, or 24-5 per cent, of
ammonia. Adulterations are infrequent and can
readily be detected, because sulphate of ammonia is
the cheapest substance which is wholly volatile. A
handful of sulphate of ammonia placed on a fire shovel
and heated to redness over a fire should leave no
appreciable residue. Samples of the salt are occasion-
ally found containing ammonium sulphocyanide (thio-
cyanate), a substance actively injurious to vegetation.
Its presence can be readily detected by adding to a
solution of the salt a little ferric chloride, with which a
sulphocyanide produces an intense red coloration. Like
all salts of ammonia, the sulphate reacts with lime and
even with carbonate of lime, giving off free ammonia as
a gas. For this reason sulphate of ammonia should
never be mixed with lime or with basic slag, which
contains a certain amount of free lime, lest a loss of
nitrogen should ensue. A lightly calcareous soil in dry
weather may induce a similar loss of free ammonia.

As a nitrogenous manure sulphate of ammonia is
practically as effective, nitrogen for nitrogen, as nitrate
of soda ; it is also to all intents and purposes as rapid
in its action, because the process of nitrification, which
generally precedes the utilisation of the ammonia by the
plant, takes place very rapidly in suitable soils. The
fact is well illustrated in the following table (XIV.),
showing the composition of the water draining from one
of the Rothamsted wheat plots to which a mixture of
sulphate and chloride of ammonia had been supplied on
25th October, followed the next day by heavy rain, so
that on the 27th the drains began to run. It will be
seen that at this early date the ammonia had not been
wholly caught up by the soil, so that a little found its
way into the drains; at the same time, however, the

II.] NITRIFICATION OF SULPHATE OF AMMONIA 6i

proportion of nitrate has been enormously increased,
due to immediate nitrification, and the later runnings
of the drains in November and December show that the
ammonium salts were being rapidly oxidised and re-
moved from the soil as nitrates.

Table XIV.— Broadbalk Wheat Field, Rothamsted. Nitrogen
AND Chlorine in Drainage Water from Plot 15. Parts
per Million.

§5

C3 ^

52§

Year.

Month.

Nitrogei
Ammun

5

III

1880

October 10

None

8-2

22-7

37 -o

1880

October 27, 6-30 A.M.

9-0

13-5

146-4

9.2

: 1880

October 27, i P.M. .

6-5

12.9

II 6.6

ii-i

! 1880

October 28

2-5

1 6-7

95-3

17-5

1880

October 29 . . .

1-5

i6-9

80.8

20-9

: 1880

November 15, 16

None

50-8

54-2

93-7

I 1880

November 19, 26

None

34-6

47.6

72.7

: 1880

December 22, 29, 30 .

None

21.7

23-2

93-5

I88I

February 2, 8, 10

None

22.9

19.4

ii8-o

When applied to the soil sulphate of ammonia is
very rapidly and completely absorbed ; the instance
quoted above (Table XIV.) being one of the very few
cases when ammonium salts have been found in the
waters draining from the Rothamsted wheat field,
however recent the application of ammonium salts
had been. The sulphuric acid or chlorine is found
at once in the drainage water, but combined with
calcium and magnesium derived from the soil. It is
commonly supposed that the reaction taking place is
one of double decomposition with the calcium carbonate
in the soil —

CaC0, + (NH4),S0, = (NH,).,C03 + CaS0„

the ammonium carbonate beinsf held without further

62 FERTILISERS CONTAINING NITROGEN [CHAP.

change by the humus in the soil. But experiments
with pure kaolin and samples of natural humus — peats
of various age and origin — show that the reaction which
takes place is one of double decomposition whereby
ammonium displaces calcium and magnesium in clay
and humus. With kaolin and clays the reaction
takes place with the double hydrated silicates or
zeolites, with humus with certain natural calcium com-
pounds of the insoluble complex organic humic acids
produced during decay. A certain amount of the
ammonia is also taken up at once by soil bacteria and
converted into more organised and insoluble forms like
proteins.

It is the calcium carbonate in the soil that finally
suffers loss, because before nitrification takes place the
ammonium compounds just described have to be
decomposed by calcium carbonate with the produc-
tion of ammonium carbonate, which alone can be
attacked by the nitrification organisms.

Referring again to the analyses of the Rothamsted
wheat soils, p. 56, it will be seen that the long con-
tinued use of ammonium salts has reduced the proportion
of calcium carbonate below that of the unmanured plots
by amounts which are approximately those to be
expected if interaction between the salts and the calcium
carbonate had taken place according to the equation set
out above.

The Rothamsted wheat soils started with sufficient
calcium carbonate to withstand this loss, but on soils
initially poor in calcium carbonate its removal by
sulphate of ammonia soon induces a condition approach-
ing actual sterility. The best example is afforded by
the experimental plots on the farm of the Royal
Agricultural Society at Woburn, where through the con-
tinued . use of ammonium salts as manure, the soil

II.] ACIDITY CAUSED BY AMMONIUM SALTS 63

refuses to grow barley any longer, though the former
fertility is at once restored by the application of a
dressing of lime. The soil of the plots receiving
ammonium salts is actually acid to litmus paper, and a
similar condition prevails on some of the grass plots
at Rothamsted, where the soil, unlike that of the
wheat field, is deficient in calcium carbonate. At
Woburn the soil is a light sandy loam which con-
tained in 1876, when the experiments began, only
0-074 per cent, of calcium carbonate. For many years
the wheat and barley plots manured with ammonium
salts gave as good returns as those receiving an equal
amount of nitrogen as nitrate of soda. Towards 1895
it became every year more difficult to obtain a plant
of barley on the plots receiving ammonium salts, the
soil was noticed to be acid to litmus paper, and certain
special weeds, spurry in particular, invaded the plots.
The plots were then divided, and on one portion 2
tons per acre of lime were applied, whereupon the
soil recovered its healthy condition and the crop was
restored.

Table XV. shows the result on the crop of 1904
of the dressing of lime applied in December 1897,
and also the destruction of the crop where the
soil had remained acid through the use of ammonium
salts.

The effect of sulphate of ammonia upon wheat at
Woburn is not so marked as upon barley, probably
because of the deeper rooting habit and more robust
constitution of the wheat plant.

The acidity of the soil where the ammonium salts
have been used is due to the attack of various moulds
and other micro-fungi upon the ammonium salts ; they
seize upon the nitrogen for their own nutrition, and set
free the acids with which the ammonia was combined. If

64 FERTILISERS CONTAINING NITROGEN [chaP.

there is no calcium carbonate present to neutralise the
acids, they combine with the calcium of the humus and
set free humic acid, which accumulates from year to year,
until, with the small amount of mineral acid from the
salts that is also left free, the acidity becomes consider-
able enough to be detected. But the injury to the
crop seems to be less due to the direct effect of the

Table XV.— Woburn. Yield of Barley, 1904.

Bushels per Acre.

No Lime.

After
Liming.

Ammonium Salts alone (41 lb. N. per acre) .
Nitrate of Soda alone (41 lb. N. per acre) .
Minerals + Ammonium Salts (4 1 lb. N. per acre) .
Minerals + Nitrate of Soda (41 lb. N. per acre) .

0-7

1-8
247

14-3
23-9

acids upon the plant than to the way the acidity tends
to suspend the normal bacterial activities of the soil, as,
for example, the process of nitrification, and to replace
them by the growth of moulds and fungi. In the acid
grass soils at Rothamsted, for example, nitrification
is almost at a standstill, the organisms are very few
in number, and the plant is chiefly feeding on the
unchanged ammonia of the manure.

Although under ordinary farming conditions an
actually acid reaction is not likely to arise through the
use of sulphate of ammonia, the experiments at Woburn
and Rothamsted clearly indicate that it is not a desirable
source of nitrogen for soils which are deficient in
calcium carbonate. The reaction of ammonium salts
with the soil, resulting in the withdrawing of the
ammonia from solution, gives a clue to the difference
in both the yield and the character of the crop when

II.] NITRATE OF SODA— SULPHATE OF AMMONIA 65

grown with sulphate of ammonia and nitrate of soda
respectively. On the grass plots at Rothamsted, for
example, where the manuring has now been repeated
year after year for fifty years, very distinct types of
herbage have associated themselves with the two
manures. Putting aside the prevalence of sorrel as
due to the acid conditions, the characteristic grasses on
the plots receiving ammonium salts possess a shallow-
rooted habit, e.g., sheep's fescue and sweet vernal grass,
while the nitrate of soda has favoured deeply rooting

Table XVI.— Ammonium Salts v. Nitrate of Soda, Rothamsted.

Average Yield.

Wheat
(22 years).

Barley
(51 years).

Mangolds
(i;7 years).

Complete Manure :—
Nitrogen as Nitrate
„ „ Ammonia

Bushels.

28-7
23-4

Bushels.

43-5
42.1

Tons.

I8-OI
14-86

grasses like the soft brome. Actual examination of
the subsoil shows that the roots have penetrated much
deeper on the nitrate of soda than on the ammonia
plots, the roots having followed the soluble nitrate
down into the soil in the one case, whereas in the other
they remain near the surface where the nitrogenous
material has been accumulated. We may apply the
clue thus obtained to interpret the comparative results
given by the two manures on other crops ; wheat, for
example, a deep-rooted crop, may be contrasted with
barley, which feeds near the surface, but agrees again
with mangolds, another deep-rooted crop.

It will be seen that with the deep-rooting crops,
wheat and mangolds, nitrogen in nitrate of soda gives

66 FERTILISERS CONTAINING NITROGEN [chap.

a better return than an equivalent amount of nitrogen
in ammonium salts, although no other disturbing
factors, such as lack of potash or lime, intervene in the
cases quoted ; with barley, however, the yield is sensibly
equal from the two manures. At the time of harvest,
the crop grown with ammonium salts is always a little
the riper ; in the case of barley, this is of distinct value,
for it results in a more uniform product of higher quality.
Taking an average of fourteen years' valuations of the
barleys grown on the Rothamsted plots, the corn grown
with minerals and ammonium salts was valued at 104-3,
while the produce from minerals and nitrate of soda was
set at 100-3, ^^id that from the plot receiving farmyard
manure at 96-4 only, 100 being the average price of
barley for the year. These figures are calculated from
the cash valuations put on the various barleys every
year. With the mangolds again, it is seen that the
plants manured with nitrate continue to grow long
after those manured with ammonium salts have so
completed their season's growth that the leaves are
beginning to turn yellow and flaccid. All these
differences are explained by the deeper rooting habit
induced by the nitrate ; the plant is less affected by
the drought and the changes of temperature incident
to autumn, growth is more prolonged, with the cor-
ollary of a larger yield but a later and less uniform
maturity.

One other factor may also contribute to the general
superiority of nitrate of soda. It must not be forgotten
that when a nitrogenous manure reaches the soil there
will be competition for it between the plant's roots and
the mass of living organisms present in the soil, nearly
all of which required combined nitrogen for their own
development. Some of these organisms, like the
nitrification bacteria, are wholly useful. Others cause

11.] IVET AND DRV SEASONS 67

permanent loss by liberating some of the nitrogen in
the form of gas, but the majority simply withdraw the
soluble nitrogen for a time from circulation, building it
up in their own tissues. The immediate result is,
however, a lessened availability of the manure, and this
loss will fall far more upon ammonium compounds than
upon nitrates, which are not so generally utilisable by
the organisms found in the soil.

It is generally assumed that since nitrate of soda is
not retained by the soil, while ammonium salts are,
the former is a manure better suited to dry seasons and
climates, whereas under wetter conditions there is less
danger of the latter washing out of the soil. This view,
however, forgets that if the ammonium salts are to feed
the plant they must be nitrified, and that the calcium
nitrate produced is just as likely to be washed down in
a wet season. Indeed, the Rothamsted results do not
bear out the popular idea. In exceptionally dry seasons
there may be some advantage from the use of nitrate
of soda because of the deep-rooted habit it induces,
but the advantage is still more pronounced in seasons
of excessive wet. Taking an average of the wet seasons
against the dry, the ammonium salts do better in the
latter. Probably the nitrification of the ammonium salts
is checked in wet seasons when the temperature is low,
when also aeration is deficient through the repeated
saturation of the soil.

In addition to the definite compounds which have
just been described, a very large number of waste
products from some industrial or manufacturing pro-
cess dealing with material containing nitrogen are
employed as nitrogenous manures. For example,
almost all animal products contain nitrogen, hence the
residues from slaughter-houses, fish-curing sheds, and
other processes concerned in the preparation of food.

68 FERTILISERS CONTAINING NITROGEN [chap.

which are not utilisable in other ways, are available for
manure. Again, all industries dealing with wool, silk,
hair, feathers, skins, give rise to highly nitrogenous
waste material, and other residues of vegetable origin
occur from time to time.

From their origin and mode of preparation it follows
that these substances must be of very variable composi-
tion : again, the supply is apt to be irregular and
limited, so that their use is somewhat local and confined
to particular classes of farmers.

Most of the manures of organic origin will contain
phosphoric acid as well as nitrogen, but as a matter
of convenience some of them may be treated as purely
nitrogenous fertilisers, leaving others to be dealt with
among the compound substances.

Of these waste materials the most generally used
is soot ; its value, which is due as much to its physical
effects upon the soil as to its fertilising constituents,
has been known for the last three centuries at least.
It has already been pointed out that coal contains one
per cent, or more of nitrogen ; in a fire some of this
is evolved as ammonia when the coal is heated, and if
it escapes combustion in the higher levels of the fire it
is afterwards partially arrested by the particles of carbon
constituting soot, which possess an exceptional power of
condensing gases upon their surface. In the main soot
is only an impure form of carbon ; its fertilising value
is due to the small and variable proportion of ammonia
it has thus absorbed from the gases in the chimney.
The percentage of nitrogen present may be as low as
0-5, in exceptional cases it may rise to 6, 3-2 being the
mean of a large number of analyses.

Since the nitrogen is present in the form of
ammonia, soot as a fertiliser may be regarded as one
of the ammonium salts ; its action, however, is pro-

II.] SOOT 69

foundly modified by its physical condition. In the first
place, the dark colour of soot makes it a very effective
absorbant of the sun's rays, so that in sunlight the tem-
perature of land which has been darkened by a sprinkling
of soot will rise two or three degrees above that of
the same land uncoloured. And as the radiation from
such darkened soil at low temperatures is not increased
in the same proportion, there is no corresponding loss
of heat at night from the sooted land to discount its
higher temperature by day. Soot is most commonly
used by farmers as a top dressing for wheat and other
spring corn ; these crops are particularly responsive
to a small application of active nitrogenous manure
in the early months of the year when the soil is cold
and the oxidation of its nitrogenous residues is slow,
hence part of the value of the soot. At the same time,
the increased temperature of the soil induced by the
black colour of the soot is particularly valuable in
forwarding the growth both of the plant itself and of
the bacteria which are rendering available the reserves
of plant food in soil.

Soot also helps materially to lighten the texture of
heavy soils, and on that account is much valued by
market gardeners in districts like Evesham, where the
land is somewhat clayey and retentive.

Soot is also very distasteful to the slugs and small
snails which often do great damage to cereal and other
crops in their earlier stages.

Soot is usually sold by the bushel, which weighs
about 28 lbs., and the lighter the soot is per bushel
the more it is valued, because this indicates its purity
and freedom from ashes or other admixture. This is
probably the best test the farmer can apply, for soot
being bought locally no guarantee can be obtained as
to its composition, nor could one very well be given,

^o FERTILISERS CONTAINING NITROGEN [chap.

so small and irregular are the parcels from which any
bulk of soot is made up.

Another group of substances which practically are
purely nitrogenous manures are the shoddies and kindred
products derived from textile industries and other trades
dealing with silk, wool, hair, fur, or skin. Properly
speaking, shoddy should consist of the short, broken
fragments of wool which are rejected in the various
processes for preparing woollen fabrics because they
are not long enough to make up into yarn, but now
the term is applied more generally to any form of
waste from silk or wool manufacturing which is no
longer profitable to work up for cloth. The material
is thus extremely valuable in composition ; pure wool
contains over 17 per cent, of nitrogen, pure silk about
as much, and at one end of the scale of shoddies come
materials like carpet waste, cloth clippings, and gun wad
waste, which are nearly pure and may contain as much
as 14 per cent, of nitrogen. Less valuable, because of
the greater admixture of dirt, are wool combings, flock
dust, and other cloth wastes where cotton is also used,
these may have 5 to 10 per cent, of nitrogen ; while lower
still come the manufacturing dust from textile factories,
the sweepings of workshops, etc., in which the nitrogen
may fall as low as 3 per cent.

Closely allied to such shoddies are hair and fur
waste, skin waste, rabbit flick (ears, tail, feet, etc., and
other fragments of rabbit skins), feathers, ground hoofs,
horn shavings, and leather dust.

In all these materials the nitrogen exists in very
complex compounds of carbon, insoluble in water, and
requiring to pass through several stages of bacterial
decomposition before they reach the plant. In conse-
quence of their very variable composition and character
it is impossible to make any general statements about

II]

NITROGENOUS WASTE MATERIALS

71

their action as manures, though certain principles may
be laid down. In the main they are slow and lasting
manures, akin in this respect to the more resistant
constituents of farmyard manure, but the rapidity of
their action will depend to a very large extent upon
the fineness of their division and to the warmth and
the amount of cultivation the soil receives. Fine
woollen material like flock dust, rabbit hair, and small
feathers decays with some rapidity in the soil, and give
a very considerable return in the season of their applica-
tion, as may be seen from the following table of results
obtained at Rothamsted with a fine flock dust shoddy
containing i2-6 per cent, of nitrogen. In the table
(XVII.) the results of four years' experiments with
different crops are reduced to a common standard, the
unmanured plot each year being reckoned as 100, and
the effect of the manure is shown for the four successive
crops following the application : —

Table XVII.— Value of Residues from Previous Applications
OF Shoddy. Rothamsted,

Un-
manured.

Shoddy,
same year.

Shoddy,

previous

year.

Shoddy,
2 years
before.

Shoddy,
3 years
before.

Swedes
Barley
Mangolds
Wheat .
Swedes

Mean .

100
100

100
100
100

I43-I
i66-9
140.8
177-2
130-7

139-9
136-9

147-3
146-9

I2I-9

io7'5
126-6

II0-4
loS-l

100

152

142

119

109

Many of the coarser materials, rags, hair, skin,
may be found in the soil apparently but little changed
for a year or two after their application ; while such
coarse and tough material as crushed hoofs and leather
waste must change with extreme slowness, and can be

72 FERTILISERS CONTAINING NITROGEN [chap.

of little service except in such cases as vine borders,
where the prime cost is not of very great moment but
the land has to remain without further manuring for
many years. The presence of oil in a sample of shoddy
is generally regarded as detrimental, since it hinders
the access of water and so delays the decomposition of
the nitrogenous material. But considering how rapidly
all oils and fats are attacked by bacteria, it is doubtful
if this objection is valid, and actual experiments are
lacking.

The value of woollen rags as manure has long been
known. Blithe wrote in 1653 * "Coarse wool, nippings,
and tarry pitch marks, a little whereof will do an acre of
land, there is great virtue in them. I believe one load
hereof will exceedingly well manure half an acre," and
at the beginning of the nineteenth century Arthur
Young recommended them for dry, gravelly, and chalky
soils. At the present day, though shoddy is used to
some extent in general farming in the neighbourhood
of cloth-manufacturing districts, and though a certain
amount is worked up into compound manures, it is
mainly consumed by the hop and fruit growers. Such
farmers are dealing with a perennial crop, the quality of
which is important ; in consequence they prefer a nitro-
genous manure which will come into action steadily and
continuously throughout the season, rather than an
active one which will at any time induce a sudden rush
of growth. As the plant continues on the same ground
year after year, the residues of slow-acting manures
which are not recovered in the first crop accumulate in
the soil. Eventually the land becomes stored with
manurial residues, which come into action — i.e., decay
and nitrify — pari passu with the growth of the plant,
because both the plant and the soil bacteria are similarly
affected by the variations in such factors as warmth and

II.] SHODDY 73

ir.oisture. The result of the continuous and steady
feeding of the plant in this fashion is an equable
development, which is found to give rise to high
quality in the product.

Hop and fruit growers, in fact, regard shoddy as the
best substitute for farmyard manure, of which they are
rarely able to make, or even to buy, as much as they
require ; for fruit, indeed, shoddy is often regarded as
preferable to farmyard manure, because it results in
healthier growth. The organic matter present in
shoddy is of value in improving the texture and water-
retaining power of the soil, and i to 2 tons, according
to the nitrogen it contains, are regarded as a fair
equivalent for 20 tons of farmyard manure, though the
latter will supply considerably more non-nitrogenous
organic matter. Shoddy is only suitable for arable
land, and should preferably be applied in the early
winter and ploughed or dug in as soon after it has
been spread as possible, in order to start the decay
processes.

The inevitable irregularity in the composition of
shoddy, even in the output from week to week from
a single factory, renders its sale on any exact basis
a matter of some difficulty. It is, indeed, a very
unsatisfactory task to obtain a sample of a few pounds
which will properly represent the bulk of a consign-
ment, and the difficulties are renewed in the laboratory
when the large sample has to be reduced to a few
grammes for analysis. When, therefore, shoddy is bought
and sold on a guarantee, a somewhat wide margin of
variation must be allowed ; a large bulk is, perhaps,
best purchased on the basis of a given price per unit of
nitrogen, samples being drawn from each consignment
on arrival and a mean taken of their analyses in order
to fix the price. While nothing but an analysis will

74 FERTILISERS CONTAINING NITROGEN [chap.

afford a definite idea of the quality of a shoddy, some
opinion can be formed by tearing a small sample to
pieces and trying each portion in a gas or candle flame.
Wool, silk, hair, and all nitrogenous materials, frizzle
up and burn slowly with an unpleasant smell ; cotton,
linen, and similar substances of no fertilising value, burn
quickly with a clear flame, since they consist when pure
of cellulose. Or the mass may be digested by gentle
heating with a strong solution of caustic soda or potash,
in which the wool and kindred substances will dissolve,
leaving untouched the cellulose and dirt. But analysis
forms the only real basis for determining the richness of
the material, added to which the farmer must exercise his
own judgment about its fineness and the possibility of
getting it properly distributed throughout the soil.

Woollen shoddies are sometimes treated with
sulphuric acid, with a view of starting the decomposi-
tion of the nitrogen compounds and so rendering them
more quickly available. Shoddy thus treated is also
used as a source of nitrogen in making various com-
pound and mixed manures. Evidence is, however,
lacking that the sulphuric acid does quicken the decay
of the shoddy, and on any soils but those rich in calcium
carbonate the introduction of so much free sulphuric
acid is not advisable.

It would be difficult to enumerate all the bodies
which from time to time get applied to the land as
nitrogenous manures : tallow chandlers' waste or
" greaves " is a residue containing from 3 to 9 per
cent, of nitrogen, according to its origin, and a little
phosphoric acid ; it is often, however, comparatively
high in price, because the better qualities are saleable as
poultry food.

Spent hops, and kiln or malt dust (the rootlets of
the germinated barley which are broken off when the

II]

SEA WEED

75

malt is dried) are sometimes available, and the latter is
a valuable and active manure if it can be obtained
cheaply.

In the neighbourhood of the sea other materials can
sometimes be obtained ; sprats or herrings, when a glut
renders such fish unsaleable, mussels, and starfish or
" five fingers " collected from the oyster beds, are all
used in the Kentish hop gardens, and the two latter
supply carbonate of lime as well as nitrogen. Off the
south and west coasts, and in the Channel Islands,
seaweed forms the staple manure, being collected after
heavy weather and laid up in heaps to dry and rot. On
the heaviest soils it is sometimes ploughed in immedi-
ately after gathering, just as " long " dung is used on
clays to open up the soil. The following analyses
(Table XVIII.) show the composition of three different
kinds of seaweed used for manure in Jersey : —

Table XVIII. — Analyses of Seaweed. Russell.

Fucus.

Laminaria.

Sea Grass.

Water

Organic matter ....
Containing Nitrogen . . ,

Ash

Containing Phosphoric Acid

„ Potash

„ Sand

30-5
51-3
1.56

l8-2

0-50

4-5
0-86

52.8

30-0

0-7

17-2

0-43

37

0-54

22-6

59.1
0-52

18.3
0-62
0-56

2-8

Thus, even the poorest of these samples is in its
wet condition about as rich as the ordinary farmyard
manure, while the fucus would be valued as highly as
£2 a ton.

These results are probably above the average ; a
number of samples of Fucus from the North Sea gave
only 0-3 to 0-4 per cent, of nitrogen, and o-i to 02 per

76 FERTILISERS CONTAINING NITROGEN [chap. ii.

cent, of phosphoric acid, while species of Laminaria
from the same locality contained from 0-15 to 0-5 of
nitrogen, and 0-2 to 0-3 of phosphoric acid.

It is needless to continue the enumeration of the
substances which from time to time are employed as
manures : leather in the form of dust, turnings and
shavings of horn, meat and cheese that have been
condemned for food, all find their way from time to
time either to the manure manufacturer or to the land.

The only general rule one can apply to such
residues is to buy them on their approximate nitrogen
content, paying a low unit price because of their slow-
ness of action, and also to take into account the
comparative fineness of division and ease of spreading.
Even the most resistant material, such as leather or
horn, will decay if it is only freely enough divided and
disseminated through the soil

CHAPTER III

THE FUNCTION AND COMPARATIVE VALUE OF
NITROGENOUS MANURES

Nitrogen promotes the Vegetative Activity of the Plant — Growth
proportional to Nitrogen Supply — With Excess of Nitrogen
Maturity is deferred and the Proportion of Straw to Grain is
increased — Variation of Composition of Crop with Nitrogen
Supply — Susceptibility of Plants to Disease when supplied
with Excess of Nitrogen — Crops requiring Large Quantities
of Nitrogen — Relative Availability of Nitrogenous Manures —
Nitrate of Soda v. Sulphate of Ammonia — Question to be
decided by the Nature of the Soil — Residues left by the
Different Nitrogenous Manures — Greater Value attached by
Farmers to Manures containing Nitrogen in Organic Com-
bination.

Before passing on to a comparison of the values ot
the different nitrogenous manures, it is necessary to
consider how far nitrogen exerts on the plant a specific
effect that shows itself whenever there is either an excess
or defect of the constituent in the soil. To answer
this question properly, we should require to know what
is the physiological function of nitrogen in the nutrition
of the plant, and though we are still far from any full-
ness of knowledge, certain general conclusions may be
drawn both from field experiments and from the experi-
ence of the farm. In the first place, nitrogen is mainly
concerned with the vegetative growth of the plant, with
the formation of leaf and stem that are the necessary

77

78 NITROGENOUS MANURES [chap.

preliminaries to complete development. A deficiency of
nitrogen results in a stunted general growth, in which
the grain or seed bears a high proportion to the whole
weight of the crop; the plant on analysis, however,
shows no marked lack of nitrogen as compared with the
other constituents. These other bodies, phosphoric
acid, potash, etc., in whatever excess they may be
present in the soil, are only taken up by the plant as it
can use them — i.e., in quantities proportionate to the
growth, which in its turn is proportionate to the
nitrogen supply. As the amount of available nitrogen
is increased, the development of leaf and shoot increases,
their green colour deepens, and maturity becomes
more and more deferred, so that a crop grown on
land over-rich in nitrogen always tends to be late
and badly ripened, and to show a profusion of leaf —
characters which, in the case of a grain crop, often
result in lodging before harvest.

But the fact that the primary growth of the plant is
up to certain limits almost proportional to the supply
of nitrogen, so that an application of nitrogenous
manure has a quickly visible effect, not only makes it
the leading constituent of a fertiliser, but is apt to give
it a fictitious importance in the farmer's eyes.

On most of our cultivated soils, when the cropping is
continued and manure withheld to a point when there
begins to be a serious falling off in the yield through
lack of plant food, it is the want of available nitrogen
rather than of phosphoric acid and potash which
determines the yield ; in other words, the soil is much
more rapidly exhausted of its available nitrogen than
of its available phosphoric acid and especially of its
available potash. Thus, while each of these three con-
stituents of plant food is equally indispensable to the
plant, good crops can often be grown by the aid of a

III.] IMPORTANCE OF NITROGENOUS MANURES 79

nitrogenous manure alone, and in nearly all cases by a
mixture of nitrogenous and phosphatic manures. The
special value of nitrogen in this connection is well seen
in the Rothamsted experiments ; on the wheat field, for
example, we may compare the yield of the unmanured
plot with that receiving nitrogen alone and minerals
alone, and again that which receives nitrogen and
phosphoric acid against that which receives nitrogen,
phosphoric acid, and potash.

From Table XIX. it will be seen that plot 5, which
is nitrogen starved but which receives an excess of all
the other elements of nutrition, only yields 1-9 bushels

Table XIX.— Average Yield of Wheat. Broadbalk,
Rothamsted. 56 years (1852-1907).

Plot.

Grain.

Straw.

3

5

10

II

13

Unmanured

Mineral Manures only, no Nitrogen
Nitrogen only, no Minerals .

,, and Phosphates

„ Phosphates, and Potash .

Bushels.
12-9

14-8

20-5

237

31-6

Cwts.
IO-5

12-3

18.7

22-8

31-9

more grain than the unmanured plot ; whereas plot 10,
which receives an excess of nitrogen but has had to
rely solely upon the original reserves of minerals in
the soil, has produced on the average 7-6 bushels of
corn more than the unmanured plot. The minerals only
increased the yield by 14-7 per cent, but nitrogen by 59
per cent, and these differences would have been much
more pronounced had they been calculated on the
results of the first year or two of the experiments only,
instead of over a period so long that the mineral reserves
of the soil are also highly exhausted. It is this greater
relative deficiency of available nitrogen than of available

8o

NITROGENOUS MANURES

[CHAP.

potash or phosphoric acid in the soil which makes the
nitrogenous compounds the most important manures in
practice, though in the formation of this opinion some-
thing also must be set down to the fact than an applica-
tion of nitrogenous manure always shows itself in the
richer green colour and increased vigour of the plant,
whereas the effect of phosphatic manures is generally
only to be ascertained from the weight of the ripe
product like the grain.

Another result of the amount of mineral reserves in
the soil is that crops such as wheat or mangolds, which
are chiefly dependent upon an external supply of nitro-
gen, give yields that are roughly proportional to the
amount of nitrogen supplied as long as it is not large ;
there, however, soon comes a point when the law of
diminishing returns comes into play and the return
for each further addition of nitrogen falls off rapidly.
The following table (XX.) taken from the Rothamsted

Table XX. — Wheat with Increasing Amounts of Nitrogen.
Broadbalk, Rothamsted. (Average, 1852-1864.)

Plot.

Manures.

11

a m

1-H ,,

Grain.

0 ^

Bushels.

Wt. per
Bushel.

5
6

7

8

16

Minerals only
+ 43 lb. N, .
+ 86 „ .
+ 129 „ .

+ 172 „ .

Lb.
3009
4829
6601
7234
7713

1820

1772

633

479

18.3
28-6
37-1
39-0
39-5

58-2
58-9
58-7
58-2
58-0

16-6
27.1
38-1
42.7
46-6

62-0
58-9
54-6
Si-3
47-9

experiments, illustrates this in regard to wheat ; there
are five plots each receiving the same phosphoric acid
and potash, in excess of the crops' requirements, but
the supply of nitrogen increases by regular steps from
none to 172 lb. per acre.

in.] YIELD WITH INCREASING NITROGEN 8i

Considering the total produce as a measure of the
growth, it will be seen that the increase produced by
the second 43 lb. of nitrogen is almost as great as that
due to the first, but that the third application gives a
smaller, and the fourth a still smaller increase.

As the nitrogen increases the character of the
development changes, the extra growth is seen more in
the straw — z>., in the vegetative parts of the plant — than
in the grain ; the fourth addition of 43 lb. nitrogen only
increases the yield of grain by half a bushel, but the
straw is greater by 3-9 cvvts. The proportion which the
grain bears to the straw — 62 per cent, when no nitrogen
is used — drops with each increment of nitrogen, and falls
to 48 per cent, when 172 lb. of nitrogen per acre are
applied. An excess of nitrogen also tells upon the
quality of the grain, as judged by the size of the berry
and the weight per bushel. The weight per bushel
increases for the first application of nitrogen, but after
that it becomes less and less with each increment;
other results from the same field show a parallel varia-
tion for the weight of a hundred grains and for the
average market value of the corn from the different
plots.

When dealing with barley, an exactly similar state
of things prevails : the proportion the grain bears to
the straw decreases with each addition of nitrogen ;
while as regards the quality of the grain, the weight per
bushel falls, the percentage of nitrogen increases, and
the barley takes on all the appearances that are summed
up as " coarse." This is due to the fact that the glume
and pale, vegetative parts, are pushed on out of propor-
tion to the endosperm, so that the berry is light and
appears thick-skinned ; at the same time the colouring
matter is increased, though this is more apparent in the
ear than in the grain.

82

NITROGENOUS MANURES

[chap.

These differences may be illustrated by one of the
Rothamsted experiments in 1905, where barley was
grown on one plot with 283 lb. of nitrogen in the form
of wool dust, on the neighbouring plot with the residue
of the same amount of shoddy that had been applied
the year before to a Swede crop, and on a third plot
with no nitrogen. The results are shown in Table XXI.

Table XXL— Effect of Excessive Nitrogen on Barley.
Rothamsted, 1905.

Weight

per
Bushel.

Grain

to

100 Straw.

Offal Com

to 100

Dressed Grain.

Nitrogen.

No nitrogen .

Shoddy, previous year .

Shoddy, same year

Lb.

58-0
57-3
55-1

1 10-4
96-6
72.8

5-9
12.5

34-9

Per cent.

1. 61

1.79
2-42

This is an extreme case, but it illustrates the effect
of an excess of nitrogen in producing a disproportionate
amount of straw and a thin, light, nitrogenous barley.
Of course some nitrogen is necessary in order to obtain
a good-sized berry ; the long series of Rothamsted
experiments all show that high quality cannot be
secured by merely growing barley on land exhausted
of nitrogen : it is the excess, especially the relative
excess when the mineral constituents are deficient,
that leads to inferior grain.

Although these results show that the quality, and
therefore the composition, of the grain is affected by the
amount of nitrogen supplied to the crop, it is really
astonishing to find how small are the changes brought
about by extreme differences in the manuring.

To begin with, the plant reacts against variations in
the composition of the soil and tends to keep its own
composition constant ; when also the time comes for the

III.]

EFFECT OF SEASON AND MANURING

83

grain to be formed from the reserve materials already
stored up in the plant, another attempt is made to turn
out a standard product.

Even on the Rothamsted plots, where the differences
in the supply of nutrients are extreme and have been
accumulating for fifty years, the composition of the
grain changes more from one season to another than
it does in passing from plot to plot. Table XX 1 1,, for
example, shows the percentage of nitrogen in the
wheat grain and straw, from several plots differing in
their nitrogen supply in two sharply contrasting
seasons.

Table XXII.— Composition of Wheat Grain and Straw as

AFFECTED BY MANURING AND SEASON, BROADBALK FiELD,

Rothamsted (1852 and 1863).

2

3

7

10

11

Dung.

-a

a

N.

P.,Og
K2O.

N.
only.

N.

P0O5.

Weight per bushel, lb. ■ [f^^-^
Weight of 100 grains, gms.-^ „§
Grain to 100 Straw . . i \^^^
Nitrogen in Dry Grain, % -j g§
Nitrogen in Dry Straw, % | ^g^^

58-2
63.1

3-46

5-35

49.6
67-5

2 -02

1-52

0-46
0-25

56-6
62.7

2-88
5 -02

53-9

70-4

2 -08
1-65

0-57
0-33

:6.o
62.6

3'08
4-79

41-9
59-4

2'29

1-53

0-87
0.36

55-9
62-6

3-26

4-Si

47-3

74-3

2-48
1.70

0-89

0-35

55-6
62.5

2-94
4-76

47-8

70-4

1-95
1-79

0-46
0-44

Of course very great differences in " quality " may
be entirely passed over in a crude chemical analysis
which merely determines the amount of such ultimate
constituents as nitrogen, phosphoric acid, etc. For
example, high nitrogen content is generally associated

NITROGENOUS MANURES

[chap

with good quality in wheat ; yet the flour made from
the grain of the plots on the Broadbalk field, which
received the highest amount of nitrogen, gives rise to
such a loose, unstable dough that it can hardly be
formed into anything resembling a loaf.

Table XXI 1 1, shows the percentages of nitrogen in
the grain and in the flour made from the grain grown
in 1903 on certain of the Rothamsted plots, which vary
greatly as regards their nitrogen supply.

Table XXIII.— Nitrogen in Wheat Grain and Flour.
Broadbalk, Rothamsted, 1903.

Plot.

Manuring.

Nitrogea

applied

per Acre.

Nitrogen
in Grain.

Nitrogen
in Flour.

3
6

7
8

10
2

Unmanured .
Complete Manure

)) )) • •

Nitrogen only
Farmyard Manure

Lb.
0

43

86
129

86
200 (?)

Per cent.
1-844
1.923

2-195
2-332
2-II3

2.462

Per cent.
1-462
1-575
1-738
1-785
1-736
2-0x4

The variations in the nitrogen content of the flour
are extreme, ranging from 1-462 for the unmanured
plot to 2-014 for the dunged plot. The increased
nitrogen thus obtained did not, however, result in the
stronger flour which is associated with a higher nitrogen
content when wheat is grown under more normal
conditions, the loaves made from the grain of Plots 2 to
10 being very greatly inferior to that made from the
grain of the unmanured plot. This only shows that
such a characteristic as the strength of wheat — the
quality, as the practical man would term it — is as a rule
due to some more subtle combinations than are measured
in ordinary analysis. In this case strength is not to be
measured by the nitrogen content, though the two
often vary together.

III.] NITROGENOUS MANURES AND COMPOSITION 85

When dealing with root crops like Swedes and
mangolds, the effect of large quantities of nitrogen
may be seen to some extent in an increased production
of leaf in relation to the root, especially in the case of
Swedes, but the variation thus induced is not great.
The root or bulb is to be regarded as a vegetative
part of the plant just as much as the leaf; the true
physiological maturity does not set in until the second
season, when the production of the seed takes place.
The Rothamsted mangold plots afford a good illustra-
tion, and Table XXIV. shows the production of root
and leaf and the relation betv/een them for several
plots which vary in the amount of nitrogen supplied,
in 1900, a year when a very uniform plant was obtained.

Table XXIV. — Effect of increasing Nitrogen Supply on
Ratio of Root to Leaf. Rothamsted.

Plot.

Nitrogen
supplied,

lb.
per acre.

Mangolds, 1900.

Swedes, 1908.

Root.

Tons.

Leaf.
Tons.

Root
Leaf

Root.
Tons.

Leaf.
Tons.

Root
Leaf

40

4A
4AC

0

86

184

8-75
28-95
43-20

I-IO

3-25
6-30

8-0
8-9
6-9

4-07
1 1 -48
11.65

I'SI

5-63

10.94

2-7

2-0
I'l

The proportion of leaf is a little greater with the
excessive dressings of nitrogen applied to the last two
plots, but ^he variations are not great nor closely
parallel to the supply of nitrogen. When Swede turnips
were sown on the same plots in 1908 the increase of
leaf with the greater nitrogen supply was much more
manifest, as is shown in the last three columns of the
table.

The effect of the large amounts of nitrogen upon
the vegetative development of the plant is more dis-

86

NITROGENOUS MANURES

[chap.

tinctly seen in a prolongation of growth far into the
autumn ; on the plots receiving little or no nitrogen
the leaves turn yellow and begin to fall in early October,
when the mangolds on the high nitrogen plots are still
putting out fresh growths of green leaves and showing
no signs of entering into a resting period. It is hardly
possible to illustrate this effect by figures, but analysis
of the mangolds from these plots demonstrate the
preponderance in the roots grown with excess of
nitrogen of such unelaborated materials as the nitrates,
amides, and reducing sugars, associated also with a
higher proportion of water.

Table XXV. — Composition of Barn Field Mangolds, 1902.

Plot.

S <" 2
8)Sg

§ §3

60
0 bJO

■a d

Glucose
xlOO.
-f-Cane
Sugar.

Nitrogen. 1

1

Total.

As
Amide.

As

Nitrate.

40
4A
20

2A

4AC

4C,

Aug.

28/03

Lb.
0

86
200
286
184

I98

15-62
12-98
1373

12-47
12-78

11.74

io-8o
8-49
8-86
7-78
8-11

7-II

0-20
0-32
0-30
0-19
0-19

o-i6

1-85
3-77
3-39
2-44

2-34
2-25

O-II92
0-1336
0-1388
0-1902
O-1615

0-1507

0-0263
0-0320
0-0427
0-0651
0-0514

0-0331

0-0020
0-0023
0-0158
0-0148
0-0153

0.0155

In November the roots grown with excess of
nitrogen approximate in composition to normally
manured roots taken in August, when still growing
vigorously.

One of the most important effects upon plants of
an excess of nitrogen is their increased susceptibility
to fungoid attacks of all kinds; for example, rust is
always much more abundant upon wheat which has
been heavily manured with nitrogen, just as it appears

III.] EXCESS OF NITROGEN AND DISEASE 87

on normally manured wheat whenever the character
of the season has been such as to induce a specially
rapid production of nitrates while the plant was making
its growth, as when great heat and moisture come
together in May. In seasons when rust is prevalent
the high nitrogen plots at Rothamsted are always
markedly the more rusty, and can easily be picked out
by their colour; the grass plots are also marked by
their special rusts ; and, again, such a characteristic
grass fungus as Epichiloe typhijia is generally common
enough on the high nitrogen plots but absent from the
others. But susceptibility to disease brought about
by an excess of nitrogen is perhaps most strikingly seen
at Rothamsted on the mangold plots, though the man-
gold is a plant which, as a rule, suffers but little from
fungoid attacks. In September, however, the leaves of
the mangolds at Rothamsted that receive an excess of
nitrogen begin to be attacked by a leaf spot fungus,
Uromyces betae, which develops rapidly until on the
worst plots all the larger leaves turn brown and present
a burnt-up appearance, because the spots of destroyed
leaf tissue have become so numerous as to run together.
Where the application of nitrogen has been less heavy
but is still high, the severity of the attack is diminished,
while the fungus is entirely absent from the leaves of
the normally manured plots, although they are in close
proximity and equally exposed to infection. The
association of high nitrogenous manuring with suscepti-
bility to disease may be seen in all plants ; it is often
very manifest in greenhouses where crops are grown
in specially rich soil, nitrifying very rapidly owing to
the high temperature prevailing. The dark green
aspect of the leaves of such plants is generally evidence
of the excessive amounts of nitrogen they are receiving,
and it is well known that if any fungoid disease makes

88 NITROGENOUS MANURES [chap.

its appearance it is very difficult to keep in check and
often destroys the whole crop with great rapidity ; as,
for example, has been the case with the leaf spot fungus
Cercosporium inelonis, which has of late years proved so
destructive to cucumbers grown under glass.

Various attempts have been made to get a little
nearer to the cause of this association of high nitro-
genous manuring with susceptiblity to disease. In the
first place, certain physical differences can be traced
in the tissues of the plants; just as high nitrogen
results in a weakness of straw in cereals, due to a
long-jointed soft stem, so the cuticle of the leaf and
the cell walls of the leaf tissue are measurably thinner
when the plant has been grown with an excess of
nitrogen. The cause is, however, more probably to be
found in some alteration in the composition of the cell
sap, which renders it a better medium for the growth
of the fungus in question. It has been found, for
example, that spores of the Uromyces betae will grow
freely upon a bruised surface of the mangold leaves
grown with excess of nitrogen, but make no headway
when sown upon a similarly bruised surface of the leaf
of a normally manured plant

The softness of tissue that is induced by large
applications of nitrogenous manure — most markedly by
nitrate of soda, because of its immediate availability —
is recognised in other ways ; for example, cabbages and
similar vegetables grown rapidly with nitrate of soda
are preferable for immediate consumption because of
their tenderness, but in the market they bear a bad
reputation, because the same softness of tissue leads
to rapid wilting and a faded appearance when the
vegetables have been cut for some time and have
experienced the usual amount of rough handling in
transit.

III.] DOMINANT FERTILISERS 89

When various crops are considered in relation to
manures, they are found to show considerable differences
in their response to the individual elements of nutrition,
differences which are only to be ascertained by trial,
but which are not determined by the greater or less
amount of the fertilising ingredient in question taken
up from the soil. For example, Ville introduced the
idea that for each plant there is a " dominant " element
of fertility, and if the requirements of the plant in this
respect are satisfied it is generally capable of obtaining
the other necessary constituents from the soil. For
wheat, grass, and mangolds, nitrogen is the dominant ;
under ordinary conditions of farming if the wheat crop
is well supplied with nitrogen it is waste of money
to give it any phosphatic manure or potash salts,
because neither will result in any adequate increase
of crop, supposing the soil to show no abnormal
deficiencies. Without pushing the idea too far, it may
generally be recognised that when the land is in good
condition most of our crops require a special, rather
than a general manuring; the plant, owing to some
peculiarity in its habit of growth, finds a particular
difficulty to obtain one of the constituents of its nutri-
ment from the soil ; if that weak spot is repaired by
the manure employed, the soil will furnish the other
essentials for growth. For example, wheat and barley,
cereals that are so similar in their general character,
demand entirely distinct treatment ; under ordinary
farming conditions, wheat, as we have stated above,
requires an active nitrogenous manure and little else;
barley requires comparatively little nitrogen, but is very
responsive to a supply of phosphates.

This contrast between wheat and barley is due to
the differences in the time and growth of the two
plants : wheat is generally grown in the autumn after

90 NITROGENOUS MANURES [chap.

a single ploughing, and this light preliminary prepara-
tion of the soil is not followed up by any further
cultivation except rolling, and possibly a single hoeing.
The winter rainfall not only washes away much of the
nitrate that may have been present in the soil at the
end of the summer, but it also tends to set the soil down
into a close mass, in which aeration may become defec-
tive. The main growth of the crop takes place also
during the early spring months when low temperatures
prevail ; and all these causes work together to reduce
the rate of decay and nitrification, and so keep the soil
poorly supplied with nitrates. In consequence, wheat is
specially responsive to an early supply of some active
compound of nitrogen, such as nitrate of soda or sul-
phate of ammonia. But apart from this difficulty in
obtaining nitrogen, wheat possesses a very extensive root
system and also has a comparatively prolonged period
of growth, by which means it is able to satisfy its
requirements for potash and phosphoric acid, even on
comparatively poor land.

Barley, on the other hand, is a comparatively shallow-
rooted crop, occupying therefore a much more restricted
layer of soil, and possessing but a short period of growth ;
it has not the same opportunity as wheat to search for
phosphates, and thus becomes specially dependent upon
an artificial supply. Barley, further, makes its chief
growth at rather a later date in the spring than
wheat does; the land receives a spring cultivation
before the barley is sown and the tilth is not destroyed
by the winter rains. Thus the nitrification of the
natural reserves of the soil can count for much more
in the nutrition of barley, and in consequence external
supplies of nitrogen are rarely required.

Swede turnips afford another example of a crop
comparatively indifferent to nitrogenous manuring,

III.] NITROGEN REQUIRED— HABIT OF GROWTH 91

although large amounts of nitrogen, 100 to 150 lb.
per acre, are taken up from the soil. The turnip
is a shallow-rooted crop possessing a considerable
development of small fibrous roots, but which are
confined to a surface layer of restricted depth ; as a
rule, the crop is grown with a moderate dressing of
farmyard manure and 4 to 5 cwts. per acre of phosphates.
When farmyard manure is not used, \ cwt. per acre
of sulphate of ammonia or its equivalent is found to
be enough nitrogenous manure ; and in the south and
east of England even that is sometimes omitted when
the land is in good heart. But the land receives a very
thorough preparation during the spring months before
the seed is sown, so that the fine seed-bed has already
been enriched by an accumulation of nitrates, the pro-
duction of which has been greatly stimulated by the
working and aeration of the soil. The seed is not
sown until the end of May or early June, by which
time temperatures are high and nitrification very
active, and the growth of the crop is accompanied by
continual hoeing and working of the land between
the rows. There thus continues to be produced in a
rich soil sufficient nitrates for the requirements of the
crop, and large external supplies in the manure are
unnecessary. Mangolds, on the contrary, are a much
deeper rooted plant, are sown earlier and generally on
stronger soils less adapted to rapid nitrification, and
are found by experience to require a far greater
supply of nitrogenous manure.

One of the most important questions to be settled
in connection with nitrogenous manures is their relative
availability and rapidity of action. It has already been
stated that the nitrates are both soluble and can be
taken up without further change by the plant; the
ammonium salts as a rule require to be nitrified, but

92 NITROGENOUS MANURES [chap.

this action is speedy in normal soils, whereas the
organic compounds of nitrogen have to undergo
several successive processes of bacterial breaking down
before they reach the plant, so that some of them, like
straw and the residues of protein digestion, may remain
for a very long period in the soil before their nitrogen
becomes converted into nitrate.

It is important for the farmer to know what return
he may expect from a given nitrogenous manure in the
year of its application, and whether the nitrogen which
is not recovered by the first crop may be expected to
become available in the next or following seasons. It
is necessary even to put a money value upon the
residues left behind in the soil after the first crop has
been grown with the manure, because a tenant leaving
his farm is entitled to compensation for the unexhausted
fertility he has thus added to the soil but has had no
opportunity of cropping out.

A large number of investigations have been made
as to the relative value of nitrogen combined as nitrate
of soda and sulphate of ammonia; but it has already
been explained in the preceding chapter that the
comparative effect of nitrogen from these two sources
will be determined by a variety of external conditions,
such as the crop under consideration, the amount of
calcium carbonate in the soil, the supply of potash,
dormant or available, and the effect of the manures
upon the tilth of the soil ; in consequence, no general
answer is possible that will apply to all cases. From
the Rothamsted experiments it is found that nitrate
of soda affords the better source of nitrogen for wheat,
grass, and mangolds, the superiority amounting on the
average to about ten per cent. ; but that, for barley,
potatoes, and turnips, the two manures are of equal
value, nitrogen for nitrogen.

III.] AVAILABILITY OF NITROGENOUS MANURES 93

While these results might not be exactly borne out
on other soils, it will be within the limits of ordinary
error to conclude that, for equal amounts of nitrogen,
nitrate of soda possesses a slightly greater value than
sulphate of ammonia, but that the choice between the
two should be dictated by the relative price of the
nitrogen per unit, the nature of the crop, and the
amount of carbonate of lime in the soil. Since sulphate
of ammonia contains approximately 20 per cent, of
nitrogen against 15 per cent, in nitrate of soda, the
relative prices of the two manures ought to be in the
ratio of 3 to 4; if sulphate of ammonia is £\2 per
ton, nitrate of soda, to yield an equivalent value of
nitrogen, ought not to cost more than £(^ per ton ; if
nitrate of soda is £\o per ton, the equivalent value of
sulphate of ammonia would be ;;^I3, 6s. 8d. per ton.
For mangolds, nitrate of soda should certainly be
chosen, unless the advantage in price is largely on
the side of the sulphate of ammonia, because of the
great value of the soda base in rendering available
the dormant potash so much required by the mangold.
On soils short of lime, and especially if they have any
tendency to become acid, nitrate of soda will always be
preferable ; and again, when extra large quantities of
nitrogenous fertilisers are to be used, as is sometimes
the case in market-garden work. For barley, sulphate
of ammonia is preferable, because of the better quality
it produces ; on the light soils also it should have the
preference, provided they are properly supplied with
carbonate of lime.

But undoubtedly the best plan is to use a mixture
of the two fertilisers ; there is then nitrate for the
immediate use of the crop, and yet no great excess of
salt remains, with the risk of its being washed down
below the range of the plant's roots in the soil water ;

04

NITROGENOUS MANURES

[chap.

the nitrification of the ammonia continues the supply
of nitrate at a later stage, and the injurious effects
upon the soil of the two manures, nitrate of soda as
a producer of alkali, and sulphate of ammonia as causing
acidity, neutralise one another.

Several of the organic compounds of nitrogen, such
as those contained in Peruvian guano, rape cake, and
dried blood, are almost as active sources of nitrogen as
the salts of ammonia, especially when used continuously,
so that the residues left in any one year are available
for succeeding crops. For example, the Rothamsted
barley plots receive equal weights of nitrogen as
nitrate of soda, sulphate of ammonia, and rape cake ;
and as the following table shows, the returns from the
rape cake are but little below those from the other two
manures.

Table XXVI.— Nitrogenous Manures with Minerals.
Average Yield of Barley (1852-1901). Rothamsted.

Plot.

Manuring.

Grain.

Straw.

4A

4N
4C

Ammonium Salts = 43 lb. N. .
Nitrate of Soda - 43 lb. N. .
Rape Cake = 49 lb. N. .

Bushels.
42.1
43-6
41-0

Cwts.

25-0

27-4
24.5

These results do not, however, show how much
return from the given manure is obtained in the year
of application, but from other of the Rothamsted plots
we learn that on such a soil neither nitrate of soda nor
ammonium salts leave any appreciable residue behind.
On the wheat field, two of the plots receive in alternate
years either 400 lb. of ammonium salts or a mixture of
complete mineral manures ; so that in any year there is
one plot with the ammonium salts and the residue of
the previous year's minerals, and another with mineral

III.] RESIDUES LEFT BY NITROGENOUS MANURES gj

manures and a residue of ammonium salts. The results
are set out in Table XXVII., the basis of comparison
being a third plot, which receives both the ammonium
salts and the mineral salts in the same year, and a
fourth plot, which never receives any ammonium salts,
but the minerals every year.

Table XXVII.— Residual Effect of Manures.

ROTHAMSTED. WHEAT (1852-I902).

Plot.

Manuring.

Grain.

Straw.

Bushels.

Cwts.

7

400 lb. Ammonium Salts and

Minerals. ....

32-9

33-0

17

400 lb. Ammonium Salts and

Mineral Residues .

30-4

29-5

18

Minerals + Residues of 400 lb.

Ammonium Salts .

15-3

I3-I

5

Minerals only ....

14-9

12-2

Thus the residue from the ammonium salts applied
in the previous year only raises the yield by 0-4 bushel
of grain and 0-9 cwt. of straw above the yield of the
plot which never receives any nitrogen, whereas the
application of fresh ammonium salts on Plot 7 causes
an increase of 18 bushels of grain and 20-8 cwt. of
straw. On the other hand Plot 17, with the residues of
mineral manures applied in the previous year, only falls
behind Plot 7 to which they had been applied in the
same year, by 2-5 bushels of grain, and 3-5 cwt. of straw.

A very similar experiment is included among the
Woburn plots, the only difference being that there the
minerals are put on every year, and that the trials are
also repeated with nitrate of soda.

Table XXVIII. shows the average results for the
five years, 1882-86, from which it will be seen that the
ammonium salts left behind considerable residues which

96

NITROGENOUS MANURES

[chap.

were of service to the succeeding crop, while little
benefit was derived from the preceding year's application
of nitrate of soda. With barley the residues from both
manures were more pronounced.

Table XXVIII.— Effect of Nitrate of Soda and Ammonium
Salts applied in the Previous Year. Woburn (1882-1886).

Plot.

4
ia

93

Maunring.

Wheat.

Minerals only .

Minerals + Residue of Ammonium

Salts ......

Minerals + Ammonium Salts .
Minerals + Residue of Nitrate of

Soda

Minerals + Nitrate of Soda

Bushels.
18.3

20-4

42.8
I7.I

40-9

Barley.

Bushels.
24-6

37-0
55-5

34-5
59-9

This essential difference in the results at Rotham-
sted and Woburn arises from two causes ; in the first
place, the soil at Woburn is very deficient in carbonate
of lime, indeed at a later date than the period from
which the figures in the table are quoted the soil of the
barley plots had become so acid that the crop would no
longer grow. Under these conditions nitrification will
be very slow and some of the ammonium salts will be
retained unchanged in the soil until the following season,
instead of nitrifying and so getting into a form that
will wash through the soil. Thus the ammonium salts
will leave a much greater residue than the nitrate ;
that the latter has any effect in the following season
must be set down to the texture of the fine sandy
loam at Woburn, which admits of a much greater capil-
lary rise of the soil water than is possible in the close
Rothamsted soil, with the result that some of the
nitrates which have been washed down during the
winter are brought back to the surface.

III.] AVAILABILITY OF NITROGENOUS MANURES 97

In the main, however, it will be safer to regard the
fertilising effect of both sulphate of ammonia and nitrate
of soda as confined to the season of their application ;
the only residues they leave behind being due to the
increased root and stubble left in the land and the
extra nitrogen in the crop, some of which, e.g., the
nitrogen in the straw or the roots grown, does remain
on the farm as a permanent addition to the stock of
fertility.

Wagner of Darmstadt has made a very extensive
series of comparisons of various nitrogenous manures
based upon experiments in pots, and from them has
compiled the following table, showing the comparative
recovery in the crop of 100 of nitrogen supplied in each
fertiliser.

Table XXIX. — Return in Crop for 100 Nitrogen applied and
Relative Value when Nitrate of Soda = 100. Wagner.

Nitrate of Soda , .

82

100

Ammonium Salts

77

94

Peruvian Guano ,

71

87

Green Plants .

63

77

Horn Meal , ,

61

74

Dried Blood .

60

73

Castor Cake .

60

73

Wool Dust

21

26

Cow Dung «

18

22

Leather Meal .

13

16

These results are, however, based upon the results of
pot experiments, which, because of the rapid variations
of temperature and the comparative concentration of
manures employed, are always somewhat unfair to
organic manures, especially to the bulky ones coming
at the lower end of the scale.

Experiments have been carried out of late years at
Rothamsted to examine the question from a slightly
different point of view by means of field plots. The

G

98

NITROGENOUS MANURES

[chap.

scheme of experiment is to take four plots for each
manure ; one receives the manure in any particular year,
while the others remain unmanured except for the
residues that may remain from a similar application
that had been made one, two, and three years pre-
viously, a fifth plot continuously unmanured being
employed as a check.

The experiments have not been in progress long
enough to enable exact results to be obtained, especially
as regards the residues remaining in the second or
third year after the application, but the following
figures show the kind of return which may be antici-
pated. In order to eliminate the effect of season and
crop, the increase given by a residue is always compared
with the increase brought about by a fresh application of
the same manure, which increase is reckoned as lOO.

Table XXX.— Increased Yield due to residues of Nitrogenous
Manures compared with Increase produced in First Year.
Rothamsted.

Year of
Application.

Second Year.

Third Year.

Dung . . .
Wool Waste
Peruvian Guano .
Rape Cake

lOO
TOO
100

loo

46

79
12

9

37
38

12

2

Thus rape cake, a manure which we have seen to
be comparatively active, leaves behind for the following
year a very small residue, having only 9 per cent, of
the effect of a fresh application of manure ; whereas a
wool shoddy increases the crop in the second year by as
much as 79 per cent, of the increase produced by a fresh
application of the same manure, and even after two
crops have been removed the residue is still one-third
as effective as a fresh application.

III.] RECO VER V OF NITROGEN IN CROP 99

From many of the Rothamsted experiments it is
possible to calculate how much of the manure applied
year after year has been eventually recovered in the
crop ; with the mangold crop it will be shown later that
(Table LXIII.) 78 per cent, of the nitrogen applied as
nitrate of soda was recovered in the crop, the percentage
falling to 71 for rape cake, 57 for ammonium salts, and
only 31 per cent, for dung. When manures were
applied to plots which were also enriched with dung the
recovery was less in all cases, the usual law of diminish-
ing.returns coming into play.

It cannot be said that the conclusions which may be
drawn from these results as to the relative availability
of different compounds of nitrogen are in any way
endorsed by their price in the market, or by the general
opinions of farmers. From the experimental point of
view the value of the different compounds of nitrogen,
unit for unit, ought to be proportional to their avail-
ability ; a slow-acting manure not only involves a delay
in realising the capital that has been put into the land,
but much of the residue is never recovered at all. Not-
withstanding this the farmer has a strong preference, to
which credit must be given as founded upon experience,
for the organic sources of nitrogen ; furthermore, prices
fluctuate in accordance with accidents of supply that
are quite independent of agriculture. For example,
the relative value of nitrogen in nitrate of soda and
sulphate of ammonia, which may be regarded as
equally valuable in farming opinion, has fluctuated
widely of late years ; on occasion the nitrogen in
sulphate of ammonia has been the dearer of the two,
while at other times it has been so much the cheaper
that the price per ton of sulphate of ammonia, with
20-21 per cent, of nitrogen, has fallen below that of
nitrate of soda with 15-16 per cent, of nitrogen. The

lOO NITROGENOUS MANURES [CHAt.

unit of nitrogen in dried blood is always expensive,
because of the limited supply of this material and the
special value to manure manufacturers it possesses for
compounding purposes ; in rape cake, nitrogen is also
greatly above the average price, because of the compara-
tively short supply of this manure. Again, in Peruvian
guano the unit of nitrogen always costs more than in
the average run of manures, whereas in fish and meat
guanos it ranges at almost the same price as in sulphate
of ammonia. Finally, in all the shoddies and waste
materials of that nature the price of the unit of nitrogen
is extremely variable, a large proportion being made up
by the cost of carriage of so bulky a material, but, as a
rule, it will not be more than one-half of the price asked
for nitrogen in its more available forms. At the time of
writing, the unit of nitrogen in Peruvian guanos costs
about 1 8s. and rather more in dried blood and rape dust,
in fish guano about 17s., in nitrate of soda about i6s.,
in meat guano about 14s., and in sulphate of ammonia
about 13s., while shoddies can be obtained in which it
costs as little as 6s.

Putting aside shoddy, it is thus seen that the
farmer is prepared to pay more for nitrogen in any
form of organic combination than in its inorganic salts,
though all the experimental evidence goes to show that
the latter give the larger and speedier returns in the
crop.

What, then, is the origin of this strong prejudice
of the farmer in favour of an organic source of nitrogen,
the prejudice which is further seen in the common
description of nitrate of soda and sulphate of ammonia
as stimulants or even " scourges " of the soil, rather than
plant foods ? Of course, no purely nitrogenous sub-
stance is a complete manure ; cropping with one alone
must eventually exhaust the land of phosphoric acid or

III.] VALUE OF ORGANIC MANURES loi

potash ; but, as has already been shown, the reserves of
such materials in the soil are so large that long-
continued cropping would be needed to deplete them
seriously.

Some other source must be found for the farmer's
prejudice, and its true cause is probably the manner in
which organic manures improve the tilth of the soil by
maintaining the stock of humus, whereas sulphate of
ammonia, and particularly nitrate of soda, injure it.
The importance of this factor of tilth will be more
realised when we remember that nearly the whole of the
farmer's labour in spring is directed towards obtaining
a fine seed-bed for such crops as barley and roots.
Furthermore, if the weather conditions are adverse to
the start of the crop, the eventual yield will depend
more upon the condition of the seed-bed than upon any
other factor.

The potent effect of organic manures in promoting
a good tilth is very clearly shown by the Rothamsted
experiments upon mangolds, where the nitrogenous
manures are nitrate of soda, sulphate of ammonia, and
rape cake respectively. In a good season the nitrate of
soda is the most effective manure ; but taking an average
over the whole period, rape cake shows a great superi-
ority, simply because of the difficulty of jetting a full
plant upon the other plots. Though all the plots are
cultivated in the same way and at the same time, the
condition of the soil has become so bad where purely
inorganic manures have been used, that only in favour-
able seasons is what a farmer would call a good plant
obtained on the nitrate and the ammonia plots, whereas
the rape cake plot starts regularly enough. On three
occasions the plant has completely failed on the
ammonia and nitrate plots. Even in the other years
there are great deficiencies, as shown by the average

I02

NITROGENOUS MANURES [chap. in.

number of plants counted on each plot, which is set out
in Table XXXI.

Table XXXI.— Effect of Manures upon the Number of Roots.

ROTHAMSTED MANGOLDS, 1876-1902.

Plot.

4C
4A

4N

Manures

Complete Minerals with Rape
Cake

Complete Minerals with Am-
monium Salts .

Complete Minerals with Ni-
trate of Soda

Average Crop
per acre.

Tons.
21-3
14.9
1 8-0

Average Number
of Boots
per acre.

Number.

17,474
14,802
14.130

In ordinary farming the effect upon the soil is never
likely to become so pronounced as in these experiments
at Rothamsted, but without a doubt a considerable
element in the extra value which the farmer sets on
organic nitrogen must be put down to its improvement
of the texture of the soil, a factor the farmer rightly
regards as of the first importance.

CHAPTER IV

PHOSPHATIC MANURES

TheThosphates of Calcium — The Early Use of Bones as Manure —
Preparation of Bone Meal and Steamed Bone Flour — Dis-
solved Bones and Bone Compounds — The Discovery of
Mineral Phosphates, Coprolites, Phosphorite, Phosphatic
Guanos, Rock Phosphates — The Invention of Superphosphate,
Lawes and Liebig — The Manufacture of Superphosphate —
The Manufacture of Basic Slag — Nature of the Phosphoric
Acid Compounds in Basic Slag : their Solubility in Dilute
Acid Solutions — Basic Superphosphate — Wiborg Phosphate —
Wolter Phosphate.

Although the fertilising effect of bones, in common
with most other substances of animal origin, had been
known in an empirical way for a very long time, the
efficacy was generally put down to the oil they con-
tained, and it was only at the close of the eighteenth
century that attention became fixed on the phosphoric
acid.

Lord Dundonald, in his Treatise on the Connection of
Agriculture with Chemistry, published in 1795, had
arrived at a very sound perception of the case. When
treating of phosphate of lime, he writes that it "is
contained in animal matters, such as bone, urine, shells,
etc., in some sorts of limestone, and in vegetable sub-
stances, particularly in the gluten, or the vegeto-animal
part of wheat and other grain. It is a saline compound,
very insoluble. There is reason to believe a very

104 PHOSPHATIC MANURES [chap.

considerable proportion of this nearly insoluble salt is
contained in most fertile soils. . . . These alkaline
phosphates (potash and soda) will be found to promote
vegetation in a very great degree, the substance of
which they are composed, viz., alkaline salts and
phosphoric acid, are found in the ashes of most
vegetables." Again, Kirwan writes in 1796 about the
constituents of plants : " Phosphorated calx is found in
greatest quantity in wheat, where it contributes to the
formation of animal gluten. . . . Hence the excellence
of bone ashes as a manure for wheat. . . ." Finally,
de Saussure, in his Recherches Chimiques sur la Vegeta-
tion, published in 1804, writes : " Le phosphate de chaux
contenu dans un animal, ne fait peut-etre pas la cinq
centieme partie de son poids : personne ne doute
cependent qu ce sel ne soit essential a la constitution
de ses os. J'ai trouve ce meme sel dans les cendres de
tous les v^getaux ou je I'ai recherche, et nous n'avons
aucune raison pour affirmer qu'ils puissent exister sans
lui." This opinion was repeated by Davy, and adopted
and disseminated by Liebig, by which time various
other experimenters had reached the conclusion that
the mineral and not the organic matter contained in
bones was their chief fertilising constituent.

Since all the phosphatic manures which possess any
practical importance are phosphates of calcium, it is
necessary to discuss these compounds a little before
proceeding further. The phosphatic material which is
most widely disseminated, occurring in all the primitive
crystalline rocks and occasionally found massive, is the
true crystalline mineral apatite, Ca5(POj3F, in which
the flourine atom may be wholly or partially replaced
by chlorine. This is a definite crystalline compound,
the undoubted source of all the other compounds of
phosphoric acid, but being very hard and difficult of

IV. J THE PHOSPHATES OF CALCIUM 105

solution in acids it is little used in manure-making.
The typical phosphate of lime, which is regarded as
the starting-point for the manures, is the tricalcium
phosphate CagPgOg, which is supposed to exist in bone
ash and in the natural uncrystalline phosphate rock,
such as is mined in Algeria or Florida. It is, however,
doubtful if such a phosphate really exists in any stable
condition ; it has been shown that bone ash and such
phosphates, when treated with water, continue to yield a
little phosphoric acid to solution and become more and
more basic ; crystals of the composition CagPgOg do not
exist, nor can a substance corresponding to this formula
be precipitated. This, however, is an academic ques-
tion ; in all dealings with manures tri-calcium phosphate
is supposed to exist, and whatever the actual compound
in the manure may be, the quantity of phosphoric acid
is always expressed as if it were combined as tri-calcium
phosphate. Thus 310 parts of calcium phosphate are
equivalent to 142 parts of phosphoric acid, hence what-
ever the percentage of phosphoric acid found by analysis

it is multiplied by 2- 18 {=' — ) and expressed as

percentage of tri-calcium phosphate. This puts all
phosphatic manures on an equal basis and enables a
comparison to be made of one against the other, just as
would the percentages of phosphoric acid which are really
obtained by analysis, but which are not in favour with
manufacturers because, being so much smaller numbers,
they seem to give the manure too poor a showing.

When a solution of phosphoric acid, such as is
obtained by treating any of the natural phosphates with
sulphuric or hydrochloric acid, is precipitated with lime
water, a salt of the composition CaHPO^, di-calcium
hydrogen phosphate, is obtained, and this is a perfectly
stable and definite compound. It sometimes comes on

io6 PHOSPHATIC MANURES [chap.

the market as precipitated phosphate ; it is also known
as retrograde or reverted phosphate, because it arises
when the soluble compound next to be described,
"superphosphate," passes into the insoluble condition.
When tri-calcium phosphate is treated with such an
amount of sulphuric acid as is required to combine with
two out of the three lime radicles in the molecule, a
mixture is obtained of gypsum and of soluble mono-
calcium phosphate, CaH^PgOg, which is known as
superphosphate. Some uncertainty may still be
supposed to exist as to the exact identity of this
compound, but in practice a readily soluble mixture of
phosphoric acid and lime in something like these pro-
portions does get formed, and the reactions of this
solution are explained accurately enough by the formula
CaH^PgOg. Soluble phosphoric acid itself, H3PO4, also
exists, and some is always supposed to be present in a
free state in superphosphate.

It has already been mentioned that by the continued
treatment of ordinary insoluble phosphates with water
a more and more basic phosphate is formed, to which
Warington gave the formula (Cag P208)2Ca(OH)2 ; and a
definite phosphate of this type, Ca^PgOg or 4CaO, PgOg,
has been isolated in crystals from basic slag and may be
supposed to mark the compound of lime and phosphoric
acid which is stable at high temperatures. It is this
tetra-calcium phosphate which is supposed to constitute
the greater part of the phosphoric acid compounds of
basic slag, but little is really known of its existence.

Of the phosphatic manures, the earliest and for a
long time the only ones to be employed on a large
scale were those derived from bones. It would be
impossible to attribute the discovery of the fertilising
value of bones to any individual ; in common with all
other waste materials of animal origin, they were prob-

IV.] BONES 107

ably tried and appreciated by numbers of people in
all ages and countries; they are mentioned by Blithe
in 1653, Evelyn in 1674, and Worlidge in 1668, and by
the close of the eighteenth century their use was
becoming common in the neighbourhood of all the
great towns. Arthur Young mentions the use of the
waste from the making of knife-handles near Sheffield,
and again enumerates bones as one of the substances
the Hertfordshire farmers were in the habit of bringing
back from London when their carts had been delivering
hay or grain, A Mr St Leger writes to Dr Hunter
of York (edition of Evelyn's Terra published in 1778):
" I also dressed an acre of grass ground with bones in
October 1774, and rolled them in. The succeeding
crop of hay was an exceeding good one. However, I
have found from repeated experience that upon grass
ground this kind of manure exerts itself more power-
fully the second year than the first. It must be obvious
to every person, that the bones should be well broken
before they can be equally spread upon the land. No
pieces should exceed the size of marbles ... At
Sheffield it has now become a trade to grind bones for
the use of the farmer."

It was in the early years of the nineteenth century,
however, that the demand began to grow ; and it received
a considerable impetus from the introduction, probably
first of all in Yorkshire, of machines for reducing the
bone into half- or quarter-inch fragments, or even into
powder. By 181 5 the home supply was proving insuffi-
cient, and bones began to be imported from the Continent
in rapidly increasing quantities until nearly 30,000 tons
per annum were brought in, chiefly from Europe — a
demand which is said to have resulted in the ransacking
of many of the battlefields. In this connection a
characteristic outburst of Liebig's has often been

io8 PHOSPHATIC MANURES [chap.

quoted : " England is robbing all other countries of
their fertility. Already in her eagerness for bones,
she has turned up the battlefields of Leipsic, and
Waterloo, and of the Crimea : already from the cata-
combs of Sicily she has carried away the skeletons of
many successive generations. Annually she removes
from the shores of other countries to her own the
manurial equivalent of three million and a half of men,
whom she takes from us the means of supporting, and
squanders down her sewers to the sea. Like a vampire
she hangs upon the neck of Europe, nay, of the whole
world, and sucks the heart blood from nations without
a thought of justice towards them, without a shadow of
lasting advantage to herself ! "

For a time the importations fell off, but with the
growth of the artificial manure trade and the opening up
of India and South America as sources, the amounts
introduced increased enormously, though since the
discovery of basic slag and the cheapening of mineral
phosphates, they have been falling greatly again for
the last fifteen or twenty years. In 1906 the imports
amounted to 42,600 tons, the home production being
estimated at about 60,000 tons, so that they still form
a very important part of the fertiliser trade, even if they
no longer retain their old pre-eminence.

Bones are but rarely used for manure in their raw
condition as they are received from the collectors ; in
nearly all cases they are put through one or more
steaming processes. The raw bone consists of a
mineral framework, amounting to 70 per cent, or
so of the dry bone and consisting in the main of
phosphate of lime, which, together with a little carbonate
of lime, is left behind when the bone is burnt, as in bone
ash. The whole of the mineral framework is permeated
by cartilage consisting of nitrogenous compounds —

IV ] BONE MANURES lOQ

collagen, chondro-mucoid, etc. — which are insoluble in
acids and are left behind in a soft tough condition if the
bone be put to soak for some time in weak acid. Mixed
with the cartilage is a certain amount of fat, and the
first treatment the bones receive is to steam them
under a pressure of 15 to 20 lb. in order to melt and
remove the fat, which is sold as tallow or used for soap-
making forthwith. In some cases the fat is extracted
even more thoroughly by the action of benzene. The
boiled or steamed bones thus obtained contain 4 to 5
per cent, of nitrogen and 43 to 50 per cent, of calcium
phosphate, and are ready for conversion into manure.
They are sometimes merely crushed into ^-inch or ^-inch
bones, though there is no longer much demand for
material so coarse ; more generally they are ground
down into "bone meal." A really fine powder is,
however, rarely obtained, because the cartilage inter-
feres materially with the disintegration unless special
methods are employed. It is this crushed material
which is also treated with sulphuric acid for the
manufacture of "dissolved" or " vitriolised " bones.
In factories making glue the cleaner bones are picked
out, and, after the fat extraction, they are broken up
and steamed afresh at a much higher pressure and
temperature, 50 to 60 lb. to the square inch, by which
process the collagen takes up water and becomes con-
verted into gelatine, which dissolves. The solution
is concentrated and allowed to set, when it becomes
glue : the bone residue, which now contains only i
to 1-5 per cent, of nitrogen but 55 to 60 per cent, of
calcium phosphate, is ground and sold as " steamed
bone flour." Owing to the removal of the cartilage,
this material can be ground finely, and forms a dry
friable powder very convenient for use as a manure.
The coarser kinds of bone meal are converted into

no PHOSPHATIC MANURES [chap.

dissolved bones by being mixed with enough sulphuric
acid (see p. 124) to convert about half the phosphates into
a soluble condition ; steamed bone meal is also often
treated with acid, but the product is not regarded by the
trade as dissolved bones, but should be called soluble
bone compound or some other name not implying that
it has been made from unchanged bones and acid only.

There are thus four classes of bone fertilisers — (i)
the bone itself deprived of fat and crushed into the
state of -l-inch or ^-inch bones or bone meal ; (2)
steamed bone flour, from which most of the nitrogenous
material has been removed ; (3) dissolved bone con-
sisting of No. I treated with acid ; (4) bone compound,
generally consisting of No. 2 treated with acid and
perhaps fortified with nitrogen from some extraneous
source. Table XXXII. shows a number of typical
analyses of these substances.

Bone meal, by far the most abundant of these
products, is a somewhat gritty powder with a strong
and distinctive smell, which should not contain less
than 45 per cent of calcium phosphate. The per-
centage of nitrogen is more variable : good fresh
English samples sometimes show 5, but 4 per cent,
is good, and Indian samples which have been much
weathered and are a little decayed fall to 3 or even
lower; this nitrogen is not present in a very active
form, the cartilage being slow to decompose in the
soil. Of the phosphates in bones about one-half can
be dissolved on shaking up i gramme of the bone meal
with I litre of i per cent, citric acid solution, which
would show that the phosphoric acid is easily available.
However, there is plenty of experimental evidence that
bone meal is rather slow acting as a source of phosphoric
acid, probably because of its comparative coarseness
and the consequent small surface of the manure

IV.]

nONE MANURES

ttt

particles offered to the solvent action of the soil water ;
and it is the appreciation of this fact, and the rise of
other phosphatic manures like basic slag, which have
caused the decline in recent years of the popularity of

Table XXXII.— Composition

OF Bones and Bone Manures.

a

1

0 .

0.-3

0

phoric
cid.

■alent to

alcium

ipliate.

g

§0

3-r —

§<1

— V 0

Oh

H^^

P^

|g£

Raw Bones : —

Not degreased .

4-45

20'14

43-98

...

...

11 * •

5<3I

22-00

48-03

...

,, , ,

4-o6

23-36

51-01

...

Bone Meal:—

Fat extracted

4-94

22-81

49-80

...

...

11 • •

5-17

22-46

49-03

...

Steamed . .

4-59

22-09

48-23

11 • , .

4-5°

21-48

46-92

Indian

3-35

23-19

50-62

11 ...

3-6

22-6

49-35

Steamed Bone :—

Meal ....

0-93

29-02

63-36

..-•

Flour.

1-34

28-27

61-72

...

...

„ . . . .

104

31-5

68-76

...

Solu

ble.

Insol

uble.

Dissolved Bones :—
From raw bone .

2-92

5-59

12-2

11-57

25-25 1

i» 11 • •

3-21

5-10

11-64

12-23

26-69 j

i» )» • •

3-44

4-84

10-54

II -06

24-12 i

>» II • •

2-96

6-91

15-0S

10-40

21-93 1

«» 11 • •

3-47

7-84

17-13

9-44

20-62 i

„ boiled bone

1-33

4-58

9-99

8.28

17-90

II 11 •

1.42

8.96

19-55

3-83

8-38 j

Bone Compound .

0-82

8-5

18-55

5..

11-35

bone meal. It was, however, bones in their even coarser
form — merely roughly broken, sometimes by hand on
the farm — which built up the fertility of much English
land, as, for instance, the famous dairy pastures of
Cheshire, which were made during the early years

112 PHOSPHATIC MANURES [chap.

of the nineteenth century. Large dressings of bones
were employed — a ton or more per acre — and the
application was expected to last for twenty years,
little return being obtained during the first year or
two ; for this reason the landlord contributed freely
to the cost of boning, even if he did not pay for it
entirely. The pastures improved steadily after the
dressing of bones ; in particular, such a growth of
white clover was encouraged that farmers began to
suspect the manure contained clover seed, a supposition
which was repeated fifty years or more later when basic
slag first began to be used on clay pastures. At one
time bones and bone meal were subject to a good deal
of adulteration, often of the most flagrant description ;
nowadays, however, there is very little admixture of
foreign substances with bone meal. Occasionally mineral
phosphates may be used to raise the percentage of phos-
phoric acid, or the bone meal may be represented as
richer than it is, but these frauds are at once detected
on analysis, which indeed should never be omitted
because of the natural variations in the material.

If bone meal is still somewhat overvalued on account
of the long experience farmers have had of its value,
on the other hand, steamed bone flour hardly gets
justice done to it. Its deficiency in nitrogen is regarded
as a defect, but when steamed bone flour is considered
merely as a phosphatic manure, its finer grinding and
freedom from cartilage render it more available than
bone meal ever can be. The experiments of the High-
land and Agricultural Society during 1 890-1 have shown
it to be about the most suitable of all the phosphatic
manures for the turnip crop on light soils which are too
poor in lime for superphosphate and too short of water
for basic slag. For the sands and gravels, a neutral
easily soluble manure like steamed bone flour is the best

IV.] DISSOLVED BONES 113

form of applying phosphates; a mixture of steamed
bone flour and superphosphate left for a few days
in the mixing shed and then broken down again
is also very useful on such land.

Dissolved bones also represents a manure which at
one time had a much greater vogue than it possesses
at the present day, when it is no longer admitted
that superphosphate made from bone possesses any
superiority over the same compound made from
mineral phosphates, except in so far as the bone
manure also contains nitrogen. Dissolved bones or
bone superphosphate generally contains from 35 to 40
per cent, of phosphate, of which from 12 to 18 will
usually be in a soluble condition ; while the nitrogen
amounts to about 3 per cent.

Dissolved bones forms a brown mass generally
somewhat damp and sticky, and not rubbing down
into a convenient powder for sowing; it is, in fact,
impossible to get it into a dry friable condition
without some admixture of " dryers " like gypsum,
which are not considered as admissible. The trade
in dissolved bones usually proceeds on a guarantee
that it contains pure bones and sulphuric acid only,
though it is difficult to demonstrate that such a
product possesses any intrinsic superiority over any
other manure mixture compounded so as to show
the same composition. Such mixtures are furnished
by the bone compounds and bone manures, which
are often mineral superphosphates mixed with more
or less superphosphate made from steamed bone
flour, with a little extra nitrogen derived from dried
blood, fine shoddy, or even sulphate of ammonia.
Such compounds are useful enough if they are cheap ;
before purchase they should be valued on the basis of
their analysis and judged accordingly^

H

114 PHOSPHATIC MANURES [chap.

Mineral Phosphates.

With the recognition that the fertiHsing value of
bones lay in the phosphate of lime they contained,
which we may conclude had become the accepted
opinion about 1840, attention began to be directed to
mineral sources of phosphate of lime, — apatite and
phosphorite, the existence of which had long been
known to mineralogists. Acting on an analysis of
Proust's, Professor Daubeny and Captain Widdrington
made an expedition in 1843 to Estremadura to find a
bed of phosphatic rock there reported. They dis-
covered the deposit and secured enough of it for a few
field experiments in England in the following year,
but difficulties of transport prevented anything more
than small quantities being exported until a much later
period. The immediate demand for such material was
satisfied by the discovery in 1845 by Professor Henslow
of the bed of coprolites lying at the base of the Green-
sand near Cambridge.

These coprolites — small rounded nodules of impure
phosphate of lime, mixed with fragments of bone and
shell, shark's teeth, etc. — were at one time regarded as
fossilised dung, but are now considered to be pebbles of
carbonate of lime in which the carbonic acid has been
replaced by phosphoric acid by long contact with
material containing organic matter. They occur at
various horizons in the newer secondary and tertiary
rocks, e.g., at the base of the Upper Greensand and at the
base of the Gault, and in the Crag, where it rests upon
the London Clay. Shortly after their discovery these
deposits began to be worked for coprolites at various
places in Suffolk, near Cambridge, and at Potton in
Bedfordshire. The output reached 50,000 tons or so
in the early eighties of the last century, but then rapidly

IV.] cor ROUTES AND ROCK PHOSPHA TE 115

declined owing to the opening up of so many cheaper
foreign deposits, and has of late }'ears entirely ceased.
The coprolites formed hard dark-coloured nodules, which
were ground down to a grey powder containing from 50
to 60 per cent, of calcium phosphate, about 10 per cent,
of calcium carbonate, and 3 per cent, of calcium fluoride.
Though occasionally applied directly to the land in a
ground form, they were almost wholly used in the
manufacture of superphosphate.

Another phosphatic material which is practically
mineral and at one time entered into competition
with coprolites and bone phosphates as material for the
manufacture of superphosphate, consists of these guano
deposits in which the nitrogen has been wholly removed
or nearly so by the action of rain. Such deposits are
found in the West Indies (Aruba, Navassa, Sombrero,
Curacao), the Pacific (Baker, Abrolhos, Christmas, and
Ocean Islands), Bolivia (Mejillones), and one or two
other places 'of less importance. The action of the
weather, particularly where the climate is not absol-
utely rainless, is always removing the nitrogenous
compounds from guano, so that the proportion of
phosphoric acid tends to increase, until even among
the Peruvian deposits a guano is found on Lobos
Island containing little more than 2 per cent, of
nitrogen and 60 per cent, of phosjDhate of lime. In
some of the other deposits that have been enumerated,
Christmas Island for example, the nitrogen has entirely
disappeared and a phosphate rock is left behind which
can only be termed a guano in virtue of its origin.
These purely phosphatic deposits, many of which are
now exhausted or no longer pay to work, have been so
much mineralised that they are not sold as guanos but
are employed for the manufacture of superphosphate.
However, the Lobos phosphatic guano is still exten-

ri6 PHOSPHATIC MANURES [chap.

sively imported, and being naturally soft and in a fine
state of division, it can be applied without treatment to
the land, and forms one of the most valuable of the
neutral phosphates that are so well adapted to light
soils. With the exception of the Peruvian deposits and
those from the Pacific — Christmas and Ocean Islands,
practically none of the other deposits are now worked.

While some of these "crust guanos," as they were
termed, contained high percentages of phosphoric acid,
the presence of oxides of iron and aluminium in
quantity seriously interfered with the use of the Aruba
and Navassa rock as material for superphosphate making.

More akin to the English coprolites were the phos-
phates obtained from France, Germany, and Belgium,
where they occur in the secondary and tertiary forma-
tions on a more important scale than do the similar
deposits in England. Of these materials the most
important were the Lahn phosphates, extensively
worked for some time after their discovery in 1864, the
Belgian phosphates worked near Mons, with 45 to 60
per cent, of phosphate of lime, and the Somme phos-
phates, of which extensive deposits were found in the
north of France, and formed an important source of
supply to the manure market about 1890.

The Lahn phosphates fell out of favour because of
the large amount of iron and alumina they contained,
the Belgian phosphates became of too low grade, but
the Somme phosphates remained valuable because they
contained in the better grades 70 per cent, or so of
phosphate of lime, and only i to 2 per cent, of oxides
of iron and alumina. They also yielded a very dry and
friable superphosphate, and were useful for mixing
with the Florida phosphates before treatment with acid.
These coprolitic phosphates, however, attain their
greatest development in Florida, Tennessee, and South

IV.] ROCK PHOSPHATES 117

Carolina. There in many places the subsoil is a sandy-
deposit full of coprolitic pebbles, which can readily be
separated by screens or washing ; the beds of the rivers
and creeks, again, are wholly composed of the same
pebbles, which are recovered by dredging. The land
phosphate contains some oxide of iron and alumina, and
is chiefly sold in the United States, but the river
deposits have been particularly valued in Great Britain
for superphosphate making, because though they only
contained about 60 per cent, of phosphate of lime they
were specially free from iron and alumina. About
1 50,000 tons per annum used to be imported, but of late
years the supply has been falling off. The various
phosphate deposits in North America yielded in 1901
nearly 1,600,000 tons, of which more than half was
exported to Europe.

Just as it is impossible to draw a line between the
recently formed true guanos and the weathered deposits
which have practically become phosphate rock, so again
no real distinction can be made between the guanos and
coprolites of known origin and the phosphate-bearing
strata which are to be found in many countries and at
all geological horizons. Many of these may have
originated in guano beds, others are coprolitic, others
again are due to solution of phosphate of lime, originally
diffused through a great mass of rock, and its concentra-
tion in a single layer. In all cases, however, the material
has been of animal origin, whatever processes of solution
and redeposition it may have suffered since. In the older
rocks the phosphate has often become crystalline, forming
the hard mineral known as apatite, which is mined on a
small scale in Canada and Norway. The Estremadura
deposits were perhaps the first of the rock phosphates
to be described, though they were not much worked
until the seventies of the last century.

ii8 PnOSPHATIC MANURES [chap.

All these phosphate deposits are now yielding to
the competition of the great deposits of phosphate
rock which have been discovered in Northern Africa
and are now being exported in immense quantities
from Algeria and Tunis. The phosphate bed appears
to stretch right across the continent, but Morocco has,
naturally, not been explored, while the Egyptian rocks
as yet examined are hardly rich enough in phosphoric
acid for export, though immense beds exist containing
40 to 50 per cent, of tricalcium phosphate. The most
important of the phosphate mines in North Africa occur
in the province of Constantino in the district of Tebessa,
from whence they extend into Tunis, near Gafsa. The
rock is generally at the base of the Eocene system, and
occurs in strata that may be 2J or 3 metres thick and
contain as much as 60 per cent, of calcium phosphate,
which may be raised to 70 per cent, by picking
over. These African phosphates contain but little iron
and alumina, and are rapidly becoming the chief
material for the manufacture of superphosphate in this
country.

The mineral phosphates have been but little
employed directly as manures, though there is plenty
of evidence that when they are really finely ground
they are effective enough on soils retaining plenty of
water, and particularly on those of a peaty nature.
Recent experiments also indicate that such ground
mineral phosphates are most available when used
with ammonium sulphate, which, as already explained,
acts as a physiologically acid manure and helps to
bring the phosphoric acid into solution. In the main,
however, the mineral phosphates are used for the
manufacture of superphosphate, practically the only
manure which contains phosphoric acid at all readily
soluble in water.

IV.] SUPERPHOSPHATE 119

Superphosphate.

In the early years of the nineteenth century, long
prior to the introduction of superphosphate as a
manure, the existence of a soluble phosphate of lime
produced by the action of sulphuric acid upon bone ash
was a matter of common chemical knowledge, and the
composition of this and the other phosphates had been
studied accurately by Berzelius. The application of
this knowledge to agriculture and the introduction of
superphosphate as an artificial manure began about
1840. The first published suggestion of the kind is
due to Liebig, in 1840, in his Report to the British
Association, which was published in the September
of that year as TJie Chemistry of Agriculture and
Physiology. Writing of bones as a manure and the
necessity of their being finely divided, he goes on : —
" The most easy and practical mode of effecting their
division is to pour over the bones, in a state of fine
powder, half of their weight of sulphuric acid, diluted
with three or four parts of water ; and after they have
been digested for some time to add 100 parts of water,
and sprinkle this mixture over the field before the
plough. In a few seconds the free acids unite with the
bases contained in the earth, and a neutral salt is
formed in a very fine state of division. Experiments
instituted on a soil formed from a Grauwacke, for the
purpose of ascertaining the action of manures thus
prepared, have distinctly shown that neither corn nor
kitchen garden plants suffer injurious effects in conse-
quence, but that, on the contrary, they thrive with much
more vigour." Liebig then adds : — " In the manu-
factories of glue, many hundred tons of a solution of
phosphates in muriatic acid are yearly thrown away as
being useless. ... It would be important to examine

I20 PHOSPHATIC MANURES [chap.

whether this solution might not be substituted for the
bones."

In 1 841, a Mr Fleming of Barrochan had made an
experiment with about three-quarters of a pound of
dissolved bones, and in 1842 the Highland and Agri-
cultural Society offered a prize for an experiment with
bones dissolved in sulphuric acid. In January 1842,
Professor Johnston, in his published lectures, suggested
the use for purposes of manure of acid or soluble
phosphate of lime, made by adding sulphuric acid to
burnt bones or bone ash: — '^ Acid or biphosphate of
lime. — When burned bones are reduced to powder, and
digested in sulphuric acid (oil of vitriol) diluted with
once or twice its weight of water, the acid combines
with a portion of the lime, and forms sulphate of lime
(gypsum), while the remainder of the lime and the
whole of the phosphoric acid are dissolved. The
solution, therefore, contains an acid phosphate of lime,
or one in which the phosphoric acid exists in much
larger quantity than in the earth of bones. "If the
mixture of gypsum and acid phosphate above described
be largely diluted with water, it will form a most
valuable liquid manure, especially for grass land and for
crops of rising corn. In this liquid state, the phosphoric
acid will diffuse itself easily and perfectly throughout
the soil, and there will speedily lose its acid character
by combining with one or other of the basic substances,
almost always present in every variety of land." Mr
Hannam in Yorkshire, in 1843, claimed to have been
the first to carry out this experiment with burnt bones
and acid.

All these experiments, however, had in reality been
anticipated by Mr J. B. Lawes, to whom, in May 1842,
was granted a patent for making superphosphate, from
the specification of which the following extract has

IV.] EARL Y HISTOR Y OF SUPERPHOSPHA TE 121

been made ; — " Whereas bones, bone ash, and bone
dust and other phosphoritic substances have been
heretofore employed as manures, but ahvays, to the best
of my knowledge, in a chemically undecomposed state,
whereby their action on the soils to which they have
been applied has been tardy and imperfect. And
whereas it is in particular well known that in the case
of a large proportion of the soils of this country, the
application of bone dust is of no utility in producing
crops of turnips on account of the slow decomposition of
the bone dust in the soil, and the consequent exposure
of the young plant for a long period to the ravages of
the turnip fly. Now, the first of my said improvements
consists in decomposing, in manner following, the said
bones, bone ash, bone dust, and other phosphoritic
substances. Previous to using them for the purposes
of manure, I mix with the bones, bone ash, or bone
dust, or with apatite or phosphorite, or any other
substance containing phosphoric acid, a quantity of
sulphuric acid just sufficient to; set free as much
phosphoric acid as will hold in solution the unde-
composed phosphate of lime."

Subsequently, on becoming acquainted with Liebig's
published suggestion, Lawes amended his patent by
disclaiming all references to bone and bone products,
and confining it to "apatite and phosphorite, and
other substances containing phosphoric acid." Follow-
ing on his patent, Lawes began the manufacture of
superphosphate on a commercial scale, establishing a
factory at Deptford and using for the purpose at first
bone ash and later the crag coprolites from Suffolk, to
which Henslow's paper in 1845 had attracted attention.
The first advertisement appears in the Gardetier's
Chronicle and Agricultural Gazette in 1843, the price
being 4s. 6d. per bushel. From the dates of Liebig's

122 PHOSPHATIC MANURES [chap.

book and Lawes' patent, Liebig has generally been
regarded as the inventor of superphosphate, and even
though Lawes was able to take out a patent for making
it from mineral phosphates instead of from bones, the
idea is generally set down to Liebig. Owing, however,
to actions for infringement of his patent brought by
Lawes in 1853, the steps leading up to Lawes' patent
are on record, and it is seen that he arrived at the idea
of making superphosphate and had tried it experi-
mentally on a considerable scale, prior to Liebig's
publication.

In his proof of evidence, Lawes, after describing his
fitting up of a laboratory and taking over the Rothamsted
estate in 1834, stated that during 1836, 1837, and 1838,
he used considerable quantities of bone dust on his
farm for the purpose of manuring his turnip crops, and
finding that it produced no good effects, and knowing
that upon other soils its properties as a manure were
very great, he commenced a series of experiments
with bones and mineral phosphate of lime decomposed
by sulphuric and other acids, applied to the most
important agricultural plants of the farm. These
experiments were in 1839 conducted on a small scale
by plants in pots and by manuring a certain number
of plants in a field. The result of these small experi-
ments was most remarkable with turnips, and he
in 1840 used the superphosphate on half an acre or
more of that crop. In 1841 the results were so far
advanced that he used about 20 tons of superphosphate.
He was prepared to have taken out a patent in 1841,
but was persuaded by his friends not to do so, as they
objected to his embarking in any mercantile or business
occupation (Lawes was then only twenty-six years of
age). Lawes further stated that he had not noticed
Liebig's recommendation until after the date of his

IV.] EARLY HISTORY OF SUPERPHOSPHATE 123

patent, whereupon he disclaimed the use of bone
substances included therein. He also declared that he
began his manufacture with bone ash, apatite and
phosphorite being unobtainable commercially, though
in 1843 he imported several tons of the Spanish
phosphorite from Estremadura, and early in 1845 began
his enquiries if coprolites could be obtained cheaply
from the Eastern counties. Gilbert also gave evidence
that the manufacture and use of superphosphate on
a large scale prior to the date of the patent were
matters of common knowledge at Rothamsted when
he came there in 1843. Putting aside the fact that
Lawes was the iirst man to make superphosphate a
practical possibility, there is thus no doubt that
he arrived at the idea of the importance of a soluble
phosphatic manure quite independently of Liebig,
and had tested the idea on a working scale before
taking out his patent. The only other point of
interest in this early history of superphosphates is that
Sir James Murray of Dublin took out a patent a few
weeks before Lawes, in which he suggested as manure
phosphoric acid prepared by treating phosphorite with
sulphuric acid Murray's object, however, was to
generate carbonic acid in the ground, and his patent is
for a means of " mechanically fixing and solidifying
mineral acids " — sulphuric, muriatic, nitric, and phos-
phoric— by mixing them with absorbent matter like
bran, sawdust, peat, etc., the phosphoric acid thus
coming in incidentally only, and not for its own
nutritive value to plants. A few years later, to avoid
any question of priority that might arise, Lawes
purchased Murray's patent, and amended it by dis-
claiming everything but the manufacture of a manure
by the treatment of phosphorite with acid.

The early superphosphate thus manufactured by

124 PHOSPHATIC MANURES [chap.

Lawes and sold at about £'j a ton, was a mixture of
soluble and insoluble phosphate derived from coprolites
or from guanos, mixed with animal substances and am-
moniacal salts, resembling, in fact, dissolved bones and
very much the kind of thing nowadays sold as soluble
bone compound. Way in 1851 gives analyses ranging
from 3-24 to 0-I2 per cent, of nitrogen, soluble phosphate
of lime from 18-5 down to i-6 per cent., insoluble from
28-3 down to o-o6 per cent. By 1862 the manufacture
had risen to 150,000 to 200,000 tons per annum ; in 1907
about 700,000 to 800,000 tons were made in the United
Kingdom, of which about 120,000 tons were exported.

In the manufacture of superphosphate, the finely-
ground materials, graded and mixed after analysis so as
to produce superphosphate of the desired quality, are
mixed with sufificient dilute oil of vitriol, containing
about 60 per cent of pure acid, to bring about the
following reaction :-—

Ca3P208 + 2H2S04 + 4H20 = CaH^PgOg + sCaSO^, 2H2O.

At the same time, an excess of acid must also be em-
ployed to convert into sulphates the carbonate, fluoride,
and chloride of calcium present. The mixing is per-
formed mechanically, a considerable rise of temperature
ensues, and there is an evolution of water vapour, car-
bonic, hydrochloric, and hydrofluoric acids ; the two latter,
besides causing a waste of sulphuric acid, are trouble-
some to the manufacturer, because they must be con-
densed, and not allowed to escape into the atmosphere.
After mixing, the hot damp mass is dropped into a
lower chamber where the reaction completes itself, and
the whole solidifies as the gypsum combines with the
remaining water. The mass is easily friable, and is
dug out, crushed, and put into store. At one time
artificial drying had to be employed, in order to obtain

IV.] COMPOSITION OF SUPERPHOSPHATE 125

a really dry product that would run easily through a
drill, but all necessity for that process has passed away
since high grade phosphates containing but little iron
or alumina have been available. The more gypsum the
finished " super " contains, the drier and more friable
the powder, hence the former value of Somme phosphate
for mixing purposes, because its impurity was almost
wholly calcium carbonate. The objection of the super-
phosphate maker to oxides of iron and aluminium in
the raw material arises from two sources — the bad
mechanical condition of the resulting compound and
its tendency to revert. In calculating the amount of
sulphuric acid to use, a little calcium phosphate is
always left undecomposed, because free phosphoric
and sulphuric acids would injure the mechanical con-
dition of the fertiliser. This phosphate of lime left
unattacked will always slowly combine with some of
the acid phosphate to form two molecules of the
intermediate di-calcium phosphate, which is thus known
as reverted or retrograde phosphate —

CaH^PaOg + CagPgOg = 2Ca2H2P208.

Since this last compound is insoluble in water, freshly
made superphosphate always contains a little more
phosphoric acid soluble in water than it does after it
has been stored for some time, and as in England this
fertiliser is valued only on the basis of its water soluble
phosphoric acid, to this extent it deteriorates on storage.
The deterioration is more pronounced when the
raw material contains oxides of iron and aluminium,
because both of these substances will slowly react with
acid phosphate to form insoluble phosphates of iron or
aluminium. Even if these oxides have been attacked
by the sulphuric acid to form ferric or aluminium
sulphates, or if the iron and aluminium were originally

126 PHOSPHATIC MANURES [chaP.

present as phosphates, which by treatment with the
acid give rise to sulphates of these metals and free
phosphoric acid, reversion will still take place at the
lower temperatures. A mixture of ferric sulphate and
phosphoric acid is not stable, but will always partly go
back to ferric phosphate and sulphuric acid, the final
state of equilibrium which is attained being one with a
large proportion of insoluble ferric phosphate. It is
for this reason that so much stress is laid in the United
Kingdom on raw phosphates being free from iron and
aluminium ; on the Continent, where reverted phosphate
(estimated by solubility in ammonium citrate or 2 per
cent, solution of citric acid) is ranked as almost the
equal of water soluble phosphate, there is not the same
objection to the use of such materials.

Superphosphate as manufactured nowadays is a grey
friable powder, which is made in various grades contain-
ing 26, 30, 35 and 40 per cent, of phosphate made soluble
or 12, 14, 16, and 18 respectively of phosphoric acid,
together with about 2 per cent, of insoluble phosphate.
The 26 per cent, super has for long been the standard
article and is still the most generally manufactured,
because a good dry product can be made from the
raw phosphates most readily available, whereas the
higher grades require selected materials if the result
is to be dry. They were, in fact, chiefly made for
export, but since they are now, owing to the better
quality of the raw phosphates available, just as cheap
per unit of phosphoric acid as the lower grades, there is
every reason for saving carriage by their purchase.

The chief phosphates at present employed for
superphosphate-making are those from North Africa
— Tocqueville, Gafsa, Tebessa, and Algerian — Florida
hard rock and pebble, Christmas Island phosphate, and
the Aruba and Carolina deposits. The material is ground

IV.] BASIC SLAC^ 127

until 80 per cent, passes through a sieve with 100
meshes to the inch, the African phosphates being much
easier to grind than those from Florida, and then it is
mixed with about 70 per cent, of chamber acid of a
specific gravity 1-52, according to the composition of
the rock. The mass takes a day or two to cool, is
disintegrated and thrown into heaps, after which it
must be crushed again before it is bagged. About
half a ton of acid is used in making a ton of super.

The next great development in regard to phos-
phatic manures came from a very unexpected source —
the introduction of basic slag as a waste product in
steel-making. A great many ores of iron, notably those
found in the Cleveland district of North Yorkshire,
contain considerable quantities of phosphates, and in
the process of smelting in the ordinary blast furnace
much of the phosphorus passes into the iron. As far
as the product of the blast furnace goes — the cast iron
— the presence of phosphorus does no particular harm,
but as soon as the cast iron has to be converted into
steel it becomes highly objectionable. With the general
introduction of mild steel, obtained cheaply by the
Bessemer process of blowing air through the molten
cast iron until all the carbon and silicon are burnt out of
it, and then adding just enough of an iron rich in carbon
to get back to the proportion of carbon and iron which
forms steel, the Middlesborough iron made from the
Cleveland ores was at a serious disadvantage, since it
contained a considerable amount of phosphorus which
could not be removed in the Bessemer process. After
much research two chemists, Thomas and Gilchrist,
invented a process for removing the phosphorus in the
Bessemer process, and so obtained a phosphorus free
steel from the impure Middlesborough iron. Their
plan was to line the " converter," the great vessel con-

128 PHOSPHATIC MANURES [chap.

taining the molten iron through which the blast of
air was forced, with a " basic " lining composed of lime
and magnesia, instead of the previous acid lining of
bricks composed mainly of silica. Lime was also added
to the converter, and when the oxidation due to the
blast of air takes place in the molten metal, in presence
of the lime the phosphorus oxidises as well as the carbon
and silicon, because the resulting phosphoric acid is
at once taken up by the bases present and so removed
from the action, instead of being immediately reduced
again by the molten iron. Under these conditions the
resulting slag, or molten impurities derived from the
iron, which is " basic " from the excess of lime instead
of " acid " as usual from excess of silica, contains con-
siderable quantities of phosphoric acid, ranging from
12 up to as much as 23 per cent. At the present time
the Bessemer has largely been replaced by the " open
hearth " process of making steel, but as the principle
is the same — the oxidation of the impurities in the
iron by a current of air — it can similarly be carried
out in the presence of lime with the production of a
"basic slag" containing phosphoric acid.

For some time after Thomas and Gilchrist had intro-
duced their process in 1879, ^^o use was made of the basic
ilag, though it was known to contain so much phosphoric
acid, and it accumulated in the usual mounds near the
steel furnaces. Various methods were tried for extract-
ing the phosphoric acid or bringing it into a soluble
form, though without any success ; but early in the
'eighties it began to be found that the only thing
necessary to make the basic slag available as a manure
was to grind it to an extremely fine powder. In this
country the value of fine ground basic slag was first
brought to light by Wrightson and Munro in 1885,
who carried out a series of experiments, on a chalk

IV.] BASIC SLAG 129

soil in Wiltshire and a heavy clay in Durham with
basic slag finely ground on the one hand and on the
other dissolved by treatment with sulphuric acid, com-
pared with superphosphate and other forms of undis-
solved phosphate. The results were highly favourable
and showed that the slag was comparable with super-
phosphate as a source of phosphoric acid to the crop,
being much superior to the other insoluble phosphates
tried. About the same time as Wrightson and Munro's
experiments, basic slag, which was known in Germany as
Thomas slag or Thomas phosphate, after one of the
inventors, attracted considerable attention there ; many
experiments were made with it and turned out so success-
ful that it rapidly grew into considerable demand for
agricultural purposes. Indeed, so much more quickly
was basic slag taken up in Germany, that a considerable
export trade from Great Britain at once grew up, and
even at the present day of the 300,000 tons annually
made in Great Britain, about 150,000 tons are exported
to Germany.

Basic slag, basic cinder, or Thomas phosphate
powder (the two latter names are little used in the
United Kingdom nowadays) comes into the market
as a dense black powder, so finely ground that four-fifths
of it will pass through a fine brass wire sieve carrying
100 meshes to the inch, which is found to pass only
particles having a smaller diameter than 0-2 mm. A
small but varying amount of free quicklime is present ;
from 2 to 10 per cent, may be obtained from fresh
samples by careful extraction with pure carbon dioxide
free water. Both free iron and magnetic oxide of iron
are present, and can be separated from the bulk by
means of a magnet ; this test, together with the presence
of free lime, the density of the material, and the evolu-
tion of a little sulphuretted hydrogen on treatment with

I

130

PHOSPHATIC MANURES

[chap.

an acid, make it easy to distinguish between basic slag
and made-up imitations in which the phosphates are
derived from ground phosphate rock.

Table XXXIII. shows an analysis of the material,
in which the most striking feature will be seen to be
the large amount of lime and magnesia present —
more than would normally combine with the phos-
phoric acid, even when allowance has been made for
any lime that is free or that may be supposed to be

Table XXXIII.— Analysis of Basic Slag
(Stead and Ribsdale).

Lime ......

41.58

Magnesia

6'i4

Alumina

2-57

Peroxide of Iron

8-54

Protoxide of Iron .

13-62

„ IVIanganese .

3-79

,, Vanadium

1.29

Silica

7-38

Sulphur \
Calcium/

0-23

0-3I

Sulphuric Anhydride

0-12

Phosphoric Acid .

14.36

99-93

combined with the silica. The analysis alone suggests
that basic slag does not contain the usual tri-calcium
phosphate, and its behaviour in the soil and the ready
availability of the phosphoric acid strengthen the view
that it contains some other compound of phosphoric
acid. For example, basic slag is found to be readily
attacked by a solution of carbon dioxide or other very
weak acid ; a much larger proportion of phosphoric
acid goes into solution than would be the case with
an equally fine ground sample of tri-calcium phosphate
containing the same amount of phosphoric acid. Nearly

1V.5 COMPOSITION OF BASIC SLAG 131

the whole of the phosphoric acid in basic slag also goes
into solution when it is shaken with an alkaline solution
of ammonium citrate, in which tri-calcium phosphate
is not very soluble. The analysis of certain flat square
plate crystals, occasionally found in cavities in the balls
of slag, proved them to consist of a tetra-basic phos-
phate of calcium of the formula (CaO^PgOg, the mole-
cule of phosphorus pentoxide being combined with four
molecules of lime instead of with three as in ordinary
calcium phosphate. To this tetra-basic phosphate of
lime the properties of basic slag have usually been
ascribed, it is supposed to be readily acted upon by
carbon dioxide with the formation of calcium carbonate
and di-calcium phosphate, and as this latter phosphate
is readily soluble in water containing carbonic acid, the
availability of the basic slag is accounted for.

But it is by no means certain that this association
of tetra-calcium phosphate with basic slag is correct.
In the first place, the detailed analysis of the basic slag
hardly bears out this view ; there is more lime than is
necessary to make up tetra-calcium phosphate even
when every allowance is made for silica and sulphur,
and the amount of free lime that can be determined
is not sufficient to make up the balance. Moreover,
the crystals of tetra-calcic phosphate are only to be
found in basic slags made from irons poor in silicon ;
the usual crystals found in the basic slag cavities are
long hexagonal needles, pale green or blue in colour,
of which considerable quantities can be picked out from
the cindery portions of the slag. The appearance also
of a fractured surface of the ordinary molten parts of the
slag would agree much better with a structure built up
of such prismatic crystals than of the flat crystals of tetra-
calcium phosphate. The prismatic crystals, according to
Stead, consist of a double silicate and phosphate of lime

132 PHOSPHATIC MANURES [chap.

of the composition (CaO)5Po05Si02, and contain about
29 per cent, of phosphoric acid, 1 1 per cent, of silica,
and 56 per cent, of lime. Moreover, when separated
from the mass of the cinder, finely ground, and attacked
with water charged with carbon dioxide or with very
dilute citric acid, the phosphoric acid they contain shows
approximately the same solubility as that of the phos-
phoric acid in an ordinary sample of basic slag, whereas
the crystals of tetra-basic phosphate of lime are markedly
less soluble. On the whole, it seems more probable that
the typical phosphoric acid compound of basic slag is
this (CaO)5P206Si02 — and not the tetra-calcium phos-
phate, (CaO)^?^©^, especially as there is plenty of other
evidence to show how large a part silica will play in
bringing phosphoric acid into a soluble state.

Whatever may be the form of combination of the
phosphoric acid in basic slag, it is undoubtedly easily
attackable by the soil water, so that it is more available
to the plant than any of the forms of tri-calcium
phosphate, though as a rule it falls below superphos-
phate. In this availability the fineness of grinding is
a very important factor, and all samples should be
carefully tested ; at least 90 per cent, of the material
should pass through the standard wire sieve of 100
meshes to the inch. The content in phosphoric acid
varies with the amount of phosphorus present in the
iron employed in the steel-making process ; of late years
basic slags have been on the whole richer than they
were in the earlier years of its manufacture, and it is
possible to obtain material containing 23 per cent, of
phosphoric acid (equivalent to 50 per cent, of tri-calcium
phosphate). Lower grade material is more common,
but has been shown to be equally valuable when
quantities containing equal amounts of phosphoric acid
are compared ; consequently basic slag should always

IV.] MANUFACTURED PHOSPHATES 133

be bought on the basis of an analysis. For a long time
it was customary in Germany to estimate only the
phosphoric acid in the slag which could be dissolved
by shaking the material for a specified time with
an alkaline solution of ammonium citrate, and to value
the slag on such a basis, the idea being that the solvent
differentiated between the available tetra-calcium phos-
phate which dissolved, and other compounds of phos-
phorus and phosphoric acid with iron, which possessed
no fertilising value and did not dissolve in the reagent.
Ammonium citrate as a solvent has, however, been
replaced by a 2 per cent solution of citric acid, and in
the United Kingdom the vendor of basic slag is now
compelled to give a guarantee of the percentage of
phosphoric acid that is dissolved when 5 grms. of the
slag are shaken in a litre bottle for half an hour with
500 c.c. of a solution containing 10 grms. of citric acid.
Though this method gives no absolute separation
between the different phosphates in the slag, it affords
a sufficiently good practical means of estimating what
are easily soluble and therefore of fertilising value.

A few other manufactured phosphates find their way
into commerce, though none of them have much agricul-
tural importance as compared with superphosphate and
basic slag. Basic superphosphate is a form of precipi-
tated calcium phosphate introduced in 1901 by John
Hughes and made by mixing ordinary superphosphates
with sufficient lime to neutralise all the free acid and
convert the superphosphate into di-calcium phosphate,
leaving in addition a small proportion of free lime.
The material is very finely ground and forms a light
white very bulky powder, which remains dry and works
readily through any manure-sowing machine. On
analysis it shows a little over 12 per cent, of phosphoric
acid and about 4 per cent, of free lime, and as the phos-

134 PHOSPHATIC MANURES [chap

phoric acid is almost wholly combined as di-calcium
phosphate, it is to that extent soluble in the dilute citric
acid solution above described. The fine state of division
of this manure and the form of combination in which
the phosphoric acid exists render it very available to
the plant, so that it is a good phosphatic manure for
use on light soils deficient in lime, though it may be
doubted whether a mode of manufacture which first
involves solution of the phosphoric acid by means of
sulphuric acid and then neutralisation and precipitation
by lime is not essentially uneconomical.

Small quantities of various forms of precipitated
phosphate come on the market from time to time :
these are bye-products in the manufacture of gelatine,
when the bones are treated with hydrochloric or
sulphuric acid to dissolve out all the earthy matter, and
the resulting solution of phosphoric acid is neutralised
with milk of lime. When the initial solution has been
effected by sulphuric acid the product is sometimes sold
as "phosphatic gypsum," since it consists largely of
gypsum formed by the reaction of the sulphuric acid
and the lime. These fertilisers are very good sources
of phosphoric acid, which is combined in them in the
form of di-calcium phosphate ; they form excellent
phosphatic fertilisers for light soils, being easily avail-
able and neutral.

Wiborg PJwsphate is the product of the heating of
apatite, occurring as a waste material mixed with
felspar in the preparation of certain Swedish iron ores,
with sodium carbonate in the proportions of 30 soda
to 100 apatite containing 17 per cent, of felspar. The
result is a phosphate to which Nilson ascribes the formula
2NaoO. loCaO. 3P2O5, which is completely soluble in
ammonium citrate solution and has proved to be
particularly valuable on the peaty soils poor in phos-

IV.] MANUFACTURED PHOSPHATES 135

phoric acid of the island of Gothland, though it is not so
effective as basic slag containing an equivalent amount
of phosphoric acid. While extensively used in Sweden,
it does not find its way into this country.

Wolter Phosphate is made by melting together in a
regenerative furnace 100 parts of powdered phosphorite,
70 parts of acid sodium sulphate, 20 parts of carbonate
of lime, 22 parts of sand and 6 or 7 parts of coke, the
molten material being run into water and then finely
powdered. The resulting phosphate is almost wholly
soluble in dilute citric acid and has proved in experi-
ments to be more assimilable by the plant than
phosphoric acid in basic slag, and almost equivalent
to phosphoric acid in superphosphate. At present the
cheapness of basic slag and superphosphate prevent
any wide distribution of fertilisers of the type of Wiborg
and Wolter phosphates, though they may be remunera-
tive in a locality where some waste phosphatic material
is available.

CHAPTER V

THE FUNCTION AND USE OF PHOSPHATIC
FERTILISERS

Ripening Effect of Phosphoric Acid — Most manifest in wet
Seasons — Effect of Phosphoric Acid in stimulating the
Formation of Roots and adventitious Shoots — Association of
Phosphoric Acid with the Intake of Nitrogen by the Plant —
Solvents to determine the relative Availability of Phosphatic
Fertilisers — Relative Value of Phosphatic Fertilisers deter-
mined by the Soil — Soils appropriate to Superphosphate —
Fate of Superphosphate applied to the Soil — Soils appropriate
to Basic Slag — Neutral Phosphatic Manures for light Soils —
Comparison of Bone Meal with other Phosphatic Fertilisers.

Before considering the question of the relative fertilis-
ing value of the different phosphatic manures and their
application in practice, it will be necessary to get some
idea of the function of phosphoric acid in the nutrition
of the plant.

Just as nitrogen delays maturity by promoting
growth, phosphoric acid has an opposite effect ; it is in
some way closely bound up with grain formation, being
always found in greater proportions in the reproductive
parts of the plant than elsewhere. This ripening action
is very clearly seen in the Rothamsted experiments on
barley ; the plots without phosphoric acid being as a
rule about a week behind those which receive this
fertiliser.

This effect is brought out in the diagrams, Fig. 3,

136

80%

6096

40%

20
2 &4

2&4
1&3
1&3

July 4

__j

•

, -''

,-'''

■ TT^)

/ J

,-'-''

N. ofwhole

content present

in the Grain.

' of Grain
in Plant.

25

Fig.

Aug.l

Curves showing the effect of Phosphoric Acid in hastening the formation
of Grain of Barley, and the Migration of Nitrogen to the Grain.
2 and 4 with Phosphoric Acid, i and 3 without Phosphoric
Acid.

[7'o jacc page 137.

CHAP, v.] RIPENING ACTION OF PHOSPHORIC ACID 137

which show the results of certain determinations made
upon barley cut at regular intervals during the develop-
ment of the grain from some of the Rothamsted barley
plots in 1904.

The two lower curves show the rate of the formation
of the grain week by week, calculated as percentages of
the weight of the whole plant, for the two plots which
receive phosphoric acid and for the corresponding plots
without, both series being similarly treated as regards
nitrogen and potash. It will be seen that the formation
of grain begins earlier where phosphatic fertilisers have
been used, and even at the end is more complete.
Similarly, the two upper curves show the migration of
the nitrogen to the grain, again calculated as percent-
ages of the nitrogen of the whole plant, and, as before,
the movement of nitrogen begins at an earlier date, and
is more completely carried out when there is plenty of
phosphoric acid.

Table XXXIV.— Effect of Phosphoric Acid and Potash upon
Barley at Rothamsted. Wet and Dry Year compared.

Grain,
Bushel3.

Grain to
100 Straw.

Nitrogen
per cent.
in Grain.

1893.

1894.

1893.

1894.

1893.

1894.

Ammonium Salts alone .

Ammonium Salts and
Superphosphate .

Ammonium Salts and
Potash ....

Ammonium Salts, Super-
phosphate, and Potash .

II.6
I8-I
16.8
30-8

10-4

34-9
17-8
41-4

85-3

lOI-O

S5-9

102-2

67-5
77-0
73-8
77-7

2-19
2-13
2-17

2-08

1-65
I '60
I -61
1-44

As might be expected, this ripening effect of phos-
phoric acid will be particularly seen in a wet year when
the crop is late to harvest. Table XXXIV. will illus-
trate the point : it gives the yield and other particulars

138

PHOSPHATIC FERTILISERS

[chap.

of one series of the Rothamsted barley plots in 1893, a
specially dry season, and in 1894, vvhich was almost
equally wet.

The phosphoric acid increases the proportion of grain
to straw, and decreases the nitrogen content of the grain,
and it will be noticed that this latter effect is more
marked in the wet season of 1894. Even on the yield
itself the phosphoric acid had the greater effect in the
wet season.

Exactly the same result can be observed in the
wheat crop, as may be seen in Table XXXV., which
gives the yield of grain and straw in 1879, the wettest
year in the Rothamsted records, and in 1893, which was
characterised by an extremely dry hot spring and
summer.

Table XXXV.— Effect of Phosphoric Acid and Potash on the
Development of Wheat. Bkoadbalk Field, Rothamsted.

Grain,
Bushels.

Straw,
Cwts.

Weight per
Bushel, lb.

Grain to
100 Straw.

WET SEASO^

r, 1879.

Unmanured . . .
Nitrogen only .
Nitrogen and PgOg .
Nitrogen, PaOg, and KgO .

4-5

4-3

ii-i

16.0

6.7

8.5

i8.o

27.2

51-8
50-8

54-6
57-8

42-8
33-6

36-2
35-2

DRY SEASON

, 1S93.

Uiinmnured . , .
Nitrogen only . . .
Nitrogen and PgOg .
Nitrogen, PgOg, and K„0 .

10.7

8.4

7*7
1 5-4

5-6
5-6
6.2
9-7

62.5
59-1
56-4
62.6

II 0-3
84-4
67-3
98-0

In the wet year the use of phosphoric acid in-
creases the yield from 4-3 bushels with nitrogen only
to IM bushels with nitrogen and phosphoric acid, the

v.] ■ ACTION OF PHOSPHORIC ACID 139

proportion of grain to straw being raised from 33 6 to
36-2. In the dry year the phosphoric acid so hurried
on the premature ripening of the grain that the yield
declined from 8-4 to y-y bushels, and the proportion the
grain bore to the straw similarly fell from 84-4 to 67-3
per 100 of straw.

The action of phosphoric acid on the plant is not
confined to its ripening effect ; it stimulates the early
development of the young seedling to a remarkable
extent. Farmers are well acquainted with the good
start that any crop gets when manured with super-
phosphate ; indeed, it is often used merely to secure a
better plant, though with little expectation of otherwise
increasing the yield. More than sixty years ago this
had been noticed by the late Sir John Lawes ; and in
one of his earliest papers on " Turnip Culture " in 1847,
he writes : " Whether or not superphosphate of lime owes
much of its effect to its chemical actions in the soil, it is
certainly true that it causes a much enhanced develop-
ment of the underground collective apparatus of the
plant, especially of lateral and fibrous root." For this
statement he was vigorously attacked by Liebig, but
some experiments, which are still in progress, show that it
was the result of sound observation and that in some
way or other phosphoric acid does stimulate the root
development of the young plant Barley seedlings, for
example, grown in water cultures without, or with a
minimal amount of, phosphoric acid develop practically
no root, whereas when they are nitrogen or potash
starved the root growth will be proportional to that
of the rest of the plant. Both in the field and in
pot experiments the phosphoric acid has a great effect
in promoting the formation of adventitious buds,
so leading to the tillering of the plant. To what
extent this stimulus to root growth is brought about

I40 PHOSPHATIC FERTILISERS [chap.

by other sources of phosphoric acid and under diverse
conditions of soil, has not yet been worked out,
but there can be little doubt but that it explains why
a phosphatic manuring has such a valuable effect in
establishing the plant, even if the gross yield is not
ultimately much enhanced.

It may also go to explain the extraordinary results
of quite small dressings of phosphoric acid upon soils in
Southern Australia, where a manuring with half a
cwt. per acre or even less of superphosphate has been
found sometimes to double the yield of cereals. On
analysis the soils are not rich, but they show no such
signal deficiency in phosphoric acid as would account
for the action of the manure ; it seems much more
likely that in a semi-arid country where the whole
success of the crop depends on the roots getting quickly
down to the cooler and moister subsoil, the stimulating
action of the phosphoric acid upon the young roots
becomes of the greatest value. In this connection it
may be noted that the two crops which most respond to
phosphatic manuring, turnips and barley, are both
possessed of shallow roots, confined to a comparatively
limited layer of soil ; whereas, under ordinary farming
conditions, wheat responds very little to phosphoric acid
and mangolds hardly at all, both being deep-rooted
plants. But even for mangolds farmers are accustomed
to use superphosphate, because they have found by
experience it is of great assistance in securing a plant.

It has sometimes been stated that phosphoric acid is
associated with the assimilation of nitrogen by the
plant, and particularly with its migration from the stem
or roots into the seed, the opinion being probably
founded on the fact that the nucleo-proteins, so char-
acteristic of the reproductive parts of plants, contain
phosphorus. This opinion is not, however, borne out

v.] PHOSPHORIC ACID AND NITROGEN IN CROP 141

by the examination of a large number of analyses of
barley grain from the Rothamsted plots ; when phos-
phoric acid is deficient the intake of nitrogen is not
proportionally reduced ; in fact, the grain grown on the
plots receiving no phosphoric acid is the richest in
nitrogen.

This point may be further elucidated from some
experiments upon wheat made at Rothamsted in 1907;
a large number of ears of wheat were marked just as
they came into flower, in order to secure that all should
be as nearly as possible the same age at starting. A
number of these heads were gathered every third day,
and the grain was extracted and analysed, so as to trace
any progressive changes in composition as the grain
formed and ripened. Table XXXVI. shows the ratio
of nitrogen to phosphoric acid in such grain from three
of the Rothamsted plots — from the unmanured Plot 3,
where all the elements of nutrition and particularly nitro-
gen are lacking ; from Plot 10, where there is an excess
of nitrogen and a great deficiency of phosphoric acid ;
and from an adjoining plot under ordinary farming
conditions, where phosphoric acid will be relatively
abundant. It will be seen that on any plot the ratio
of nitrogen to phosphoric acid remains pretty constant
throughout the whole development of the grain, but
that a different ratio exists for each plot. From this
we may conclude that the material which the plant on
any particular plot moves from its straw and root to
form into grain is the same throughout the development
of the grain, but that each plant, according to the soil
and manure conditions under which it is growing,
builds up a type of grain of a composition special to
itself It is true that the nitrogen and phosphoric acid
move into the grain pari passu, and in that sense the
phosphoric acid might be regarded as a carrier of the

142

PHOSPHATIC FERTILISERS

[chap.

nitrogen, but then the starch also migrates in an equally
constant ratio to the nitrogen compounds, though no
such association is claimed between nitrogen and starch.
Both actually and relatively the nitrogen is highest in
the grain from Plot lo, where the plant is phosphoric
acid starved.

Table XXXVI.— Development of Wheat Grain, 1907.

Date.

Plot 3.

Ui) manured.

Plot ao.

Nitrogen only.

Normal
Manuring.

Nitrogen

per cent.

in Dry

Grain.

Ratio of
Nitrogen
to P2O5.

Nitrogen

per cent.

in Dry

Grain.

Ratio of
Nitrogen
to P2O5.

Nitrogen

per cent.

in Dry

Grain.

Ratio of

Nitrogen
to P2O5.

July 16 .
„ 19 .

„ 22 .
., 25 .
„ 28 .
„ 31 •

Aug. 3 .
,, 6 .

„ 9 .
„ 12 .

., 15 .
„ 18 .
1. 21 .
„ 24 .
„ 27 .
„ 30 .

2.68
2-41
2.46
2-17
2-12
2 -06

1.86

1.83

1.80
1.72

1-86
1-79
1-85
1.78

2-15
2-15

2-12
2.00
2.05
2-22
1.87
2-04
1.89

1-86
2.28
1.96
2.06
1.99

2-6l

2-45

2-13
2-IO
2.1 1
1-92

1-85
I-S8
1-83
1-83
1-88
1.90

...

2-35

2-32
2-25

2-53

2-32
2-27
2-50

2-45
2-41
2.17
2-29
2.38

2-27
2-20
2-05
1-97
1-84
1.35
1-89
1-88
2.03
1.98
2-05

I-9I
1-88
1-91
1.85
1.82

2-00
I.8I
1.82
I.9I
1.85
1-98

The phosphatic manures are practically all com-
pounds of phosphoric acid with lime, and, as is well
known, four distinct combinations exist and are found
in commerce. Only one, the dihydrogen calcium
phosphate, the characteristic constituent of super-
phosphate, is to any degree soluble in water; the
others give rise to extremely dilute solutions of phos-
phoric acid, too dilute, as has been shown by experiment
to nourish a plant properly, with however large a volume

v.] SOLUBTTJTY OF PHOSPHATES 143

of the solution it may be in contact. Yet insoluble as di-,
tri-, and tetra-basic phosphate of lime are, when they are
sufficiently finely divided and well incorporated with the
soil so as to be in contact with the roots, they are all
effective in supplying the plant with phosphoric acid.
It will be shown later (p. 290) that the carbonic acid
excreted by the roots of the plants is the chief agent
in producing a solution in the soil water capable of
attacking these insoluble phosphates ; acid humus and
ammonium sulphate, which gives rise to free acid in
soils, also assist in rendering them available to the
plant.

Since only one of the commercial phosphates is
freely soluble in water, yet all of them have to enter
into solution before they can be utilised by the plant,
the question of their relative availability is not easy to
settle, and a variety of solvents have been proposed for
its determination in the laboratory. In Germany, for
example, basic slag was formerly valued, not on the total
amount of phosphoric acid it contains, but on the
amount that is soluble in a strong ammoniacal solution
of ammonium citrate, the idea being that this reagent
discriminates between the tri-calcium phosphate, which
is insoluble, and the di- and tetra-calcium phosphates,
which will dissolve in the medium. Instead of the
ammonium citrate, a 2 per cent, solution of citric acid
is now employed, and i per cent, and o-i per cent.
solutions have also been proposed by various chemists
for the valuation of phosphatic fertilisers. None of
these solvents, however, really draws a sharp distinc-
tion between the different phosphates, which are all
soluble up to a certain point, when an equilibrium is
established between the phosphoric acid in solution and
that remaining undissolved. If the first solution formed
is replaced by a fresh portion of the solvent, more

144

PHOSPHATIC FERTILISERS

[chap.

phosphoric acid will come into solution ; in fact, all the
phosphates can be eventually completely dissolved
away by the solvents in question. The following table
(XXXVII.) shows the amount of phosphoric acid
extracted by a i per cent, solution of citric acid from
one of the Broadbalk soils manured for fifty years with
superphosphate, the extraction being repeated with fresh
solvent as soon as one portion had been saturated and
then removed : —

Table XXXVII.— ioo Grms. Broadbalk Soil (Plot 7), with
I Litre i per cent. Solution of Citric Acid.

First Extraction

56'i mg. PgOj dissolved

Second ,,

22-8 „ „

Third „

8-9 ,,

Fourth „

6-5 „

Fifth „

4-4 » ,,

Sixth „

4-4 „ »

Very similar results have been obtained when
manures are treated in the same manner, and they
may be taken to show that a single extraction of any
solvent of the kind proposed does not dissolve the
whole of a particular compound of phosphoric acid,
which may be thereupon reckoned as distinct in kind
from the rest of the phosphates left unattacked. This
mode of attack with weak solvents should be regarded
as affording only empirical figures to assist the analyst
in forming a judgment of the manure; and the condi-
tions of making the solution, such as time, shaking,
relative amounts of solvent and substance, must be
strictly defined. Furthermore, the only solvent which
has any a priori justification is a solution of carbon
dioxide, such as does the work in the soil ; the acids of
the cell sap, to resemble which citric acid was taken,
have been shown to experience no direct contact with
the soil particles.

v.]

SOLUBILITY OF PHOSPHATES

145

The kind of information which is yielded by the
attack of dilute solvents may be seen in Table XXXVIIL,
which shows some of the results obtained by J. K. S.
Dixon when certain phosphates of similar character
were shaken with a 2 per cent, solution of citric acid.
The results agree in the main with practical experience
and with the field trials which have been made upon

Table XXXVIIL — Relative Solubility of various
Phosphatic Manures (Dixon).

PoOs dissolved

by 2 per cent.

Manure.

Nitrogen.

Total P2O6.

Citric Acid
Solution as
per cent, of
total P2O5.

Per cent.

Per cent.

Steamed Bone Meal

1-86

29-07

64-29

Steamed Bone Flour .

1.07

29-14

70-55

English Bone Meal .

5-17

22-46

56-67

Indian „ » • < •

3-35

23-19

52-29

Peruvian Guano . .

1-40

27-28

66-05

)> )> ♦ . »

3-26

21-36

85-95

)) »t ...

8.II

13-13

95-73

these materials ; the phosphoric acid of bone meal is less
soluble than that of steamed bone flour, and the Indian
bones which have long been dried and exposed show a
lower solubility than do the fresh English bones. The
phosphatic guano and the steamed bone flour show
much the same solubility of their phosphoric acid, but
the younger the guano is, as indicated by the increased
percentage of nitrogen, the greater is the solubility of
the contained phosphoric acid. It will be explained
later that as the guano ages and loses its nitrogen the
phosphates pass more and more into tri-calcium phos-
phate, and eventually by solution and redeposition
become much the same material as a rock phosphate.
But while it would thus be possible by the use of one

K

146 PHOSPHATIC FERTILISERS [cHAP.

of these weak acid solvents to arrange the various
phosphates in a scale of decreasing solubility, and argue
from that as to their availability to the plant, the order
of the table would not represent their relative value in
practice.

In considering the action of the various phosphatic
manures in the field, the most important factor to be
taken into account is the soil, for the relative value of
the fertilisers will change entirely with different types
of soil. For example, the choice between super-
phosphate and basic slag or bone meal, as a phos-
phatic manure, must be determined, not by their
comparative solubility, but by the amount of calcium
carbonate and the wetness or dryness of the soil to
which the fertiliser is to be applied. A very large
number of experiments have been made to institute
a comparison between these fertilisers, but without
resulting in any very general information, just because
the question is really settled by those external soil
factors which are generally unrecorded. On certain
soils one or other of these manures will always give
the best results, on other soils their effects may be so
much alike that the choice between them can be
settled by price alone or by any consideration of
convenience that may enter. For example, in one
of the Rothamsted experiments one series of plots
receive superphosphate, another series basic slag, and
a third bone meal, in quantities supplying the same
phosphoric acid to each, the plots being otherwise
treated alike as regards nitrogen and potash. If we
abstract the results which refer to the yields in the
year of the application of each manure and reduce
them to a common standard each year by taking the
yields of the unmanured plot as loo, we obtain the
relat've figures in Table XXXIX.

v.] RELATIVE VALUE OF VARIOUS PHOSPHATES 147

It will be seen that the phosphates have produced a
greater effect upon Swedes and barley than upon the
deeper rooting and more slowly growing mangolds and
wheat, but that on the whole the three fertilisers are
equally valuable as sources of phosphoric acid on the
Rothamsted soil. The soil of the Little Hoos field, in
which the experiment is being conducted, contains a

Table XXXIX.— Relative Yield from various Phosphates
(Rothamsted). Unmanured = 100.

Crop.

Superphosphate.

Basic Slag.

Bone Meal.

!

Swedes .
Barley . .

Mangolds .

Wheat

Swedes

120
119
114
106
132

1X6
121
105
108
109

126

no

III
117
131

Means .

118

112

119

reasonable working quantity of carbonate of lime; it
is also fairly heavy and cool, so that it retains sufficient
moisture to give the phosphates of basic slag and bone
meal an opportunity of coming into solution.

Without attempting any detailed review of the
numerous experiments upon phosphatic fertilisers, we
may yet draw certain general conclusions from them.

On nearly all normal soils superphosphate is the
most effective phosphatic fertiliser when equal amounts
of phosphoric acid are compared. The exceptions are
the light sands and gravels very deficient in carbonate
of lime, peaty soils where the humus is of the sour acid
type and all other soils that have developed an acid
reaction. On the peaty soils of the fen country
superphosphate is the fertiliser most valued, but
there the humus is of the " mild " type, consisting

148 PHOSPHATIC FERTILISERS [chap.

of calcium humate, with which the superphosphate
reacts.

When superphosphate is applied to the soil, the
soluble phosphoric acid it contains is rapidly repre-
cipitated ; to some extent the clay provides the
necessary base, but on most soils the calcium carbonate
takes the chief part in the reaction, with the pro-
duction of di-calcium phosphate. As this precipita-
tion takes place all throughout the soil, the phosphate
is very finely divided and thoroughly disseminated,
hence the great effectiveness of superphosphate.
Though di-calcium phosphate, like tri-calcium phos-
phate itself, is probably eventually converted in the soil
into a compound approaching the composition of tetra-
calcium phosphate, it remains effective as a fertiliser
because of the fine state of division in which it
continues to exist.

How thorough is the precipitation of the phos-
phoric acid within the soil may be seen from Dyer's
examination of the soils from the Broadbalk wheat
field, which had been receiving 3I cwts. per acre of
high grade super for fifty years previously. He found
that though the surface soil to the depth of 9 inches
had been enormously enriched in phosphoric acid
soluble in i per cent, solution of citric acid, the subsoil
below had practically gained none, so complete had been
the precipitation in the layer stirred by the plough.
Again, the drainage waters from these plots show a
most trifling amount of phosphoric acid, so that losses
by washing out must be negligible. Still more cogent
evidence of the retention of phosphoric acid by the soil
has been obtained more recently by applying the method
of successive extractions with a i per cent solution of
citric acid, until the phosphoric acid going into solution
has fallen to the low constant figure indicating the

V.J RETENTION OF PHOSPHORIC ACID BY SOIL 149

solubility, not of the recently added, but of the original
soil phosphates. About five extractions remove the
phosphoric acid down to this point, further extractions
remove very little more, and the sum of the phosphoric
acid dissolved in these five extractions approximates
very closely to the surplus of phosphoric acid supplied
as superphosphate over that removed in the crop.

Table XL.— Phosphoric Acid soluble in Five Extractions with
I PER cent. Citric Acid, compared with that in Manure
AND Crop (Rothamsted).

Phosphoric Acid, lb. per acre.

Supplied in
Manure.

Kemoved in

Crop.

Surplus in
Sou.

Dissolved by
1 per cent.
Citric Acid.

Broadbalk, Plot 3 •
.. 5 •
11 II 7 •
„ 8 ,
Hoos, Plot I .
,- 2 .
.. „ 4 .

3960
3810
3810

3390
3390

550

790

1370

1520

555
1200
1240

-550
3170
2440
2290

-555
2190
2150

565
3000

2470

2055
400

2315
2000

This shows that phosphoric acid supplied as super-
phosphate remains in the surface soil, and in a form
that is readily soluble in such weak acids as a dilute
solution of citric acid or the natural solution of carbon
dioxide occurring in the soil. Doubtless the result
would be modified if the soil were not well provided
with calcium carbonate, in which case more insoluble
phosphates of iron and alumina would be formed. It
is a fair conclusion to draw from these results that
superphosphate and indeed all phosphatic manures,
may be applied to the land much earlier than is usually
the case ; because there is not the least fear of their
washing out, and it is all-important to get them well

ISO PHOSPHATIC FERTILISERS [chap.

disseminated through the soil. For the turnip crop there
may perhaps be some advantage in drilling the manure
with the seed, so important is it to have the young
roots stimulated by an abundance of phosphoric acid
close at hand, but with other crops much of the benefit
of phosphatic manures is often lost because they are
applied when the land has already begun to run short of
water. Fine grinding and early application are the two
great factors in making phosphatic manures available.

The essential condition that should dictate the choice
of superphosphate as a fertiliser, is the presence of
sufficient carbonate of lime in the soil to ensure the
precipitation of the soluble phosphoric acid as a calcium
compound. On acid soils, on some clays, and on many
sands and gravels, there is such a deficiency of carbonate
of lime that the phosphoric acid becomes precipitated
as iron or aluminium phosphate, which possess a much
lower solubility in the soil water and are therefore
less available to the plant. But on the great majority
of our British soils experience has shown that the
extra price of the unit of phosphoric acid in its soluble
form in superphosphate is more than justified by its
superior effectiveness, which is due to the rapidity with
which it becomes disseminated in a finely divided
condition in the soil immediately near the roots of the
crop.

On many of the heavier clays, which are in general
deficient in phosphates, though superphosphate is a
valuable fertiliser, especially if lime has been applied to
the soil previously, basic slag is really the more effective
manure when quantities costing the same money are
compared. In the first place, basic slag is so much
cheaper that nearly twice as much phosphoric acid can
be bought at the same cost, and on heavy soils well
provided with moisture or on peaty soils its effectiveness,

v.] PHOSPHATES APPROPRIATE TO SOILS 151

unit for unit, is not much less than that of the phos-
phoric acid in superphosphate, especially when it has
been put on early and has had plenty of time to
saturate the soil water and to be disseminated within
the soil by solution and reprecipitation.

Moreover, the lime contained in the basic slag is
itself of considerable value ; it supplies what is often a
much-needed base, and on old grass land in particular
its effect in bringing the soil potash into solution and
in promoting the oxidation of the nitrogenous reserves
in the soil is very marked ; on tillage land also the
lime is of assistance in improving the texture of the
soil. When such soils are poor in carbonate of
lime there is always some danger of "finger-and-toe"
in the turnips, and if once this disease has appeared
superphosphate should no longer be used, but basic
slag should take its place. The spread of the disease
is promoted by any acid manure like superphosphate ;
the free lime of basic slag, on the contrary, tends to
render the soil unfit for the survival of the spores. Thus
the choice between superphosphate and basic slag
should in the main be determined by the soil ; the
more calcareous and loamy the soil, the more effective
is superphosphate, but heavy soils and land poor in
carbonate of lime respond better to basic slag, and on
wet sour soils no other phosphatic manure should
be used.

In this country there is rather a prejudice against
the use of basic slag on the lighter soils — the sands, and
gravels, which are yet too poor in carbonate of lime to
be fitted for superphosphate. They are generally
regarded as too dry to allow the basic slag to be effec-
tive, but in view of the value that basic slag has been
found to possess on the light sandy soils of Eastern
Germany, where, too, the rainfall is less than that of

152 PHOSPHATIC FERTILISERS [chap.

England, the popular opinion seems to be founded on
a misapprehension. It has probably arisen from the
fact that on the poor sandy grass pastures basic slag
never shows the extraordinary effect it does on the
poor clay pastures. This is due, not to the ineffective-
ness of the phosphoric acid in the basic slag, but to the
lack in the sandy soil of both potash and of humus to be
set in action by the lime contributed by the basic slag.
The great outburst of white clover which often follows
the application of basic slag to a clay pasture is
mainly promoted by the potash liberated from the soil.
As a source of phosphoric acid for tillage land basic
slag is probably little less effective on a light than a
heavy soil, but it should be applied early and well
worked in.

On such light land, however, there is a very general
preference for some of the forms of insoluble phosphate
that are found by experience to be readily attacked
by the soil water and available to the plant ; phosphatic
guano, steamed bone flour, basic superphosphate, and
precipitated phosphate are all of the type that is valu-
able on such soils. Very effective phosphatic fertilisers
for light soils deficient in carbonate of lime, and there-
fore requiring a neutral manure, may be made by mix-
ing about two parts of superphosphate with one of
steamed bone flour, phosphatic guano, bone meal, or
basic slag itself. If the mixture be left in a heap for a
time in the manure shed the superphosphate will react
with the tri-calcium phosphate of the bone or guano
to produce a di-calcium or precipitated phosphate ; and
though the mass cakes a little when the reaction is
complete, it can easily be broken down into the original
fine powder. This is probably the cheapest way of
obtaining an easily available neutral phosphate for use
on light arable land where superphosphate is unsuitable

v.]

BONE MEAL

153

because of the lack of carbonate of lime. Otherwise
the choice between these different phosphates is very
much one of price, since, phosphoric acid for phosphoric
acid, they have proved to be about equally effective.

Raw bones or bone meal, though the price has been
at a low level for some years, still seems to be rated too
highly, the nitrogen of the phosphoric acid it contains
being over-valued if we take into account the low
availability which field experiments indicate it possesses.
Most of the experiments go to show bone meal to be so
slow in its action that excessive amounts have to be
applied and locked up in the soil if any immediately
appreciable result is to be obtained.

For example, Table XLI. shows the results of one
series of experiments carried out by the Highland and

Table XLI.-

-Returns from Bone Meal and other Phosphatic
Manures.

1878.

1879.

1880.

1881.

Swedes.

Barley,

Unmanured.

Total

Produce.

Seeds Hay,
Unmanured.

Oats,
Manured.

Total
Produce.

Ground Coprolites .
Bone Meal
Phosphatic Guano .
jround Coprolites,

dissolved
Bone Meal, dissolved
No Phosphate

Tons.
150
13-4
15.4

15-8
I3-I

Lb.

5844
6052
6016

5964
6364
5955

Cwts.
38.5
41-5
33'8

41-3
44-3
33*5

Lb.

5911
66S6
6726

7696
7460
7132

Agricultural Society, wherein bone meal was less
effective than fertilisers of the superphosphate class,
not only in the year of its application but afterwards
also, when further crops were grown without the
application of fresh manure. It is probably on grass

rS4 PHOSPHATIC FERTILISERS [chap.

land that bone meal answers best, for there the fine
roots of the grasses can come into very intimate contact
with the fragments of the fertiliser.

The reason of the comparative ineffectiveness of
bone meal is not far to seek : owing to the toughness
of the cartilage structure of the bone, it is a matter of
difficulty to reduce it to a really fine state of division
— at any rate the bone meal of commerce is a com-
paratively coarse powder. Now, it has already been
pointed out that a tri-calcic phosphate, such as exists in
bones, is very far from insoluble in water charged with
carbon dioxide, but, as with all sparingly soluble salts,
the rate of solution will be proportional, other things
being equal, to the amount of surface the substance
exposes to attack, and for a given weight of material this
increases in the same proportion as the average diameter
of the particle decreases. In consequence, fineness of
grinding is perhaps the most important factor in deter-
mining the value of the insoluble phosphatic manures,
upon it more than even upon the chemical composition
depends the availability of the fertiliser to the plant.
Bone meal is slow-acting and ineffective, because it is
coarse ; nor is the phosphoric acid brought into solution
more readily in the second year than in the first,
because the coarse condition still persists. The availa-
bility of a phosphatic fertiliser might even be reckoned
as the product of two factors : a solubility factor depending
upon its chemical composition, and a second factor —
the area of surface of unit weight of the material.

If bone meal has been overrated, on the other hand
steamed bone flour has not received the credit it
deserves. In the first place, analysts have rather warned
the farmer against steamed bone flour, as representing
in some way a spurious bone meal from which the
nitrogen had been illicitly extracted. The warning would

v.] BONE FERTILISERS 155

be needful enough if the steamed bone flour were in any
way being passed off as bone meal, but provided it is
sold on its own basis as a material containing nearly
sixty per cent, of tri-calcic phosphate and one per cent,
or so of nitrogen, it is a better manure than bone meal.
The fine grinding of the steamed bone flour allows the
phosphates to pass into solution, while the extra
nitrogen of the raw bone is so slow in its action, that as
a rule it would pay the farmer to buy steamed bone
flour instead of bone meal and to make up this deficiency
by the addition of a more active nitrogenous material.

Just as the long-standing knowledge of the effect of
bones has given rise to a certain prejudice in their
favour, which is reflected in the fact that they realise
a rather higher price than their content in nitrogen and
phosphoric acid would justify, something of the same
tradition exists on the side of dissolved bones and bone
superphosphate. There is no experimental evidence to
lead one to expect that a mixture of superphosphate
and sulphate of ammonia will not give as good results
as dissolved bones containing the same amount of
nitrogen and phosphoric acid ; indeed, the former mixture
will probably be more effective, because it is finer and in
better mechanical condition. And yet dissolved bones
is generally much the dearer fertiliser : for example, at
the time of writing, the price of dissolved bones in
London is £^, 5s. per ton, and it contains 275 per cent,
of nitrogen and 15 per cent, of phosphoric acid. To
supply 275 units of nitrogen, 2| cwts. of sulphate of
ammonia containing 20 per cent, of nitrogen will be
required, and this costs 32s. ; to supply 15 units of phos-
phoric acid i\ tons of superphosphate with 12 per cent,
of phosphoric acid would be wanted, and this would cost
£1, 2s. 6di. For 32 +62-6 = 94s. 6d., therefore, the same
amount of nitrogen and phosphoric acid could be

IS6 PHOSPHATIC FERTILISERS [chap.

purchased as are contained in the ton of dissolved
bones, and the phosphoric acid would be wholly soluble
instead of partially, as in the bone manure ; there is a
saving of los. 6d. a ton, against which would only
have to be offset the greater carriage on the extra
8 cwts. the mixture weighs.

This, of course, is only an example of the general
fact that the longer a fertiliser has been known, and the
greater the number of people who have had experience
of its value and learnt how it can be profitably employed,
the better will be its standing in the market, and the
higher its price per unit of nitrogen, phosphoric
acid, etc.

It has already been stated that finely-ground rock
phosphates are occasionally employed as fertilisers
without any treatment with acid. In America they
are often obtainable very cheaply in comparison with
superphosphate and are ground to an extremely fine
powder, so that on the basis of equal money value they
give more favourable results on many soils than the
acid phosphates. In Britain they have proved most
effective on wet and peaty soils ; they require a soil
containing plenty of organic matter to generate a
comparatively strong solution of carbon dioxide in the
soil water, in which they must become dissolved. For
the same reason their action is forwarded by the
ploughing in of green crops or by the use of sulphate
of ammonia as a source of nitrogen, but on the generality
of soils they form but ao ineffective source of phosphoric
acid.

It will thus be seen that it is impossible to arrange
the phosphatic fertilisers in a scale of value depending
upon the relative availability of the phosphoric acid
they contain, for this availability is mainly determined
by the soil, and will vary for the same manure from

v.] BONE FERTILISERS 157

soil to soil. In order to make a proper choice, the
farmer ought, first of all, to know how much carbonate
of lime his soil contains, and in the light of his know-
ledge of that factor and of the general character and
climate of the soil, he will decide first whether he
requires a basic, acid, or a neutral phosphate, and then
which is the cheapest inside the selected class.

CHAPTER VI

THE POTASSIC FERTILISERS

Early Use of Wood Ashes — The Stassfurt Deposits — Manufacture
and Composition of commercial Potash Fertilisers — The
Retention of Potash by the Soil — The Function of Potash in
the Nutrition of the Plant — Dependence of Carbohydrate
Formation upon Potash, as illustrated in the Barley and Man-
gold Crops — The Action of Nitrate of Soda upon insoluble
Potash Compounds in the Soil — Potash Fertilisers as promot-
ing the Growth of Leguminous Plants— Efifects of Potash
Starvation upon Vegetation — Potash as a Preventive of
Fungoid Disease — Potash as prolonging the Growth of the
Plant— Destruction of the Tilth of Clay Soils by Potash Salts
— Soils deficient in Potash.

Although the water cultures already described,
coupled with the results of the Rothamsted experiments
even in their early years, showed that of the alkali
metals found in the plant's ash only potassium was
indispensable, for a long time the salts of potash could
not be obtained in quantities or at a price appropriate
to agricultural requirements. Almost the only source
of potash was the crude carbonate or " potashes," which
was obtained by dissolving the soluble salts found in
wood ashes ; and though this was to a small extent
supplemented by the nitrate of potash or saltpetre
obtained from India, and by a certain amount of
sulphate of potash obtained from " kelp " — the ashes of
seaweed — no widespread use could be made of potash

158

CHAP. VI.] tVOOD ASHES I59

salts in farming until the opening up of the great
Stassfurt deposits in Germany. The fertilising value
of wood ashes had long been known, and' in the south-
east of England it had been customary for the hop-
growers to organise a regular system of collection of
the ashes of their cottagers, who burned little besides
wood, but such a supply was only local and early
exhausted.

William Ellis, again, writing in 1750, states that "at
Long Marston, in Bucks, is a potash kiln, where they
make ashes from bean straw for the most part, and sell a
vat of them, which contains 32 five-bushel sacks, which
dresses one acre for fourteen shillings, to be shovelled
out of a cart or waggon, and throwed over grass land in
this month (July) or at any time till Candlemass."

In 1 86 1, the output of potash salts began from
Stassfurt and rapidly grew, until in 1900 no less than
1,158,000 tons were being used for agricultural purposes
alone.

The German potash deposits are situated near the
Harz mountains, and centre round the old town of
Stassfurt, where for a very long time common salt
had been manufactured from natural brine springs.
A boring made in 1858 proved the presence of rock-
salt at a little more than 1000 feet below the surface,
but found above the rock-salt a layer of minerals con-
taining potash and magnesia salts, which were at first
regarded as worthless but have since become the most
valuable substances in the mine, because they constitute
the only known source of potash on a large scale. The
deposits occur between the D3'as and' Trias formations,
and are, therefore, of much the same age as the salt-
beds of Cheshire and Worcestershire, and like them
they represent the result of the drying up in a hot
climate of a great lake or sea, which retained some con-

i6o THE POT AS SIC FERTILISERS [chap.

nection with the ocean so as to admit of the constant
inflow of fresh sea water. It has been shown that all
the various minerals — salts of sodium, potassium,
magnesium, and calcium — which occur in these deposits,
are formed at different stages in the concentration and
drying up of a solution originally of the composition of
sea water, and the sequence of their deposition has led
to the estimation that a period of about 13,000 years
was necessary for the formation of the bed. The
sequence of deposits varies somewhat from shaft to
shaft, especially where the influx of water in the past
has effected some rearrangement in the salts ; but in
the main, after passing through 600 to 800 feet of red
sandstone, limestone, etc., a bed of gypsum is first
reached, underneath which is a bed of very pure,
"younger" rock-salt, which in its turn gives place to a
bed of anhydrite (anhydrous sulphate of lime) with
some gypsum. Below the anhydrite comes a bed of
tough impervious salt clay, which has acted as a water-
proof layer and prevented the solution of the highly
soluble potash and magnesium salts immediately below ;
at the top is a layer 50 to 130 feet thick of carnallite,
a crude double chloride of potassium and magnesium
which is the main source of the manufactured salts.
Below the carnallite comes the " kieserite " region, where
this mineral, a crude sulphate of magnesia, predominates,
and below it again comes a " polyhalite " region, char-
acterised by the prevalence of this complex sulphate of
potash, lime, and magnesia. The polyhalite overlies
the " older " rock salt, 2000 feet or more in thickness,
interspersed with and underlaid by layers of anhydrite,
before the limiting bituminous sandstones are reached.
It will be noticed that the bottom layer of anhydrite
represents the least soluble salt in sea water ; above it
comes the sodium chloride in bulk ; while at the top are

VI.] THE STASSFURT DEPOSITS i6i

gathered together the magnesiurn and potassium salts,
which would be the last to remain in solution. The
manufacturing is extremely simple in principle ; the
salts of the potash region, chiefly carnallite, are mixed
and brought into solution, from which products of
various grades of purity can be obtained by evaporation.
In this way are obtained the sulphates and muriates of
potash of commerce, but the substances chiefly used in
agriculture are certain crude salts contained by grinding
suitable mixtures of the original material as mined. Of
these the best known in this country is kainit, a mineral
which, properly speaking, only occurs in some of the
mines where water had formerly access, but which
commercially represents a mixture of sulphates and
chlorides — chiefly sulphates, of sodium, potassium, and
magnesium, containing a little over 12 per cent, of
potash.

A crude "hard salt" or "sylvinit," consisting chiefly
of chlorides, but equally containing 12 per cent, of
potash, is put upon the market rather more cheaply
than the kainit, and for most purposes will serve equally
well. Owing to the rapid exhaustion of the true kainit
deposits, this material is now taking the place of
kainit in the manure market. In Germany a crude
"carnallite" of still lower grade, containing only about
9 per cent, of potash, is used, but its hygroscopic nature
and low concentration prevent its export to any distance.
Table XL II. shows the analyses of the chief Stassfurt
products, of which only i, 3, 4, and 6 come to this
country in any quantity.

The Stassfurt salts are white or grey or pink (owing
to the presence of a little iron as impurity) gritty
powders, which dissolve readily and almost entirely, and
are, as a rule, more or less deliquescent. Potassium
chloride, and particularly magnesium chloride, are very

L

l62

THE POT AS SIC FERTILISERS

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VI.] OTHER SOURCES OF POTASH 163

soluble and greedy of moisture ; and as both chlorides
and magnesium are present in all but the purest grades
of sulphate of potash, the salts used for manurial
purposes are always somewhat deliquescent.

These salts constitute practically the only sources of
potash for manurial purposes ; wood ashes are a little
used occasionally, a small amount of sulphate of potash
is derived from kelp, and the ashes which form the final
waste product in beet sugar refining are used for the
carbonate of potash they contain ; but the whole amount
is trifling compared with the increasing output of the
Stassfurt mines.

Attempts have been made from time to time to
utilise as fertilisers various minerals which occur in large
quantities and contain considerable amounts of potash ;
for example, orthoclase felspar, KgAlgO^, 6Si02, with 17
per cent, of potash, and leucite, KgAlgO^, 2Si02, with
22 per cent, of potash. In some cases these minerals
have been simply reduced to a very fine powder, in
others they have been heated with lime or soda salts
in order to bring the potash into a more soluble form.
Though the results show that the potash can thus
be rendered comparatively available for the plant,
the great cheapness of the completely soluble Stassfurt
salts has prevented any general adoption of the
processes.

The question of which of these salts it is advisable
to apply as a manure has excited a good deal of
attention, but cannot be said to have reached any
very definite settlement, probably because the problem
is complicated by a secondary action of the salts on the
texture of the soil, which will be discussed later. But,
speaking generally, it may be said that for grass and
mangolds, and wherever the salts can be put on in the
winter months so as to allow the magnesium chloride

I64 THE POTASSIC FERTILISERS [chap.

to be washed away, kainit and the crude salts are as
effective, potash for potash, as the concentrated salts in^
which the unit of potash is more expensive. But foj
potatoes, malting barley, and similar crops where qualit
is of moment, especially when the manure is put
near the time of seeding, sulphate of potash is advisable,
especially upon heavy soils.

Muriate of potash has often been shown to yield a
greater weight of potatoes than sulphate, though the
tubers are more watery, and this result has been
associated with the chlorine, which is supposed to
assist in the migration of starch about the plant, but
the facts are by no means certain as yet.

All the compounds of potash found in these fertilisers
are freely soluble in water, so that some danger of loss
by washing out might be apprehended when the
manures are applied in the winter. As early, however,
as 1850, Way found that ordinary soils possessed con-
siderable powers of reacting with potash salts to produce
insoluble potassium compounds, the chlorine or sulphuric
acid of the salt remaining in solution combined with
calcium and other bases derived from the soil. The
absorptive power was found to be greatest with soils
rich in clay and humus, and the retention of the
potash is chiefly effected by interaction with the zeolitic
double silicates of the clay, potassium being exchanged
for calcium, magnesium, or sodium in the zeolite. To
a certain extent a similar exchange of calcium for
potassium takes place in the humus, a comparatively
insoluble potassium humate being precipitated and
calcium sulphate or chloride going into solution.

When experiments are made in the laboratory, by
treating a soil with a weak solution of potassium
sulphate or chloride, the removal of the potassium
from solution is never complete ; the extent of the

VI.] RETENTION OF POTASH BY SOIL 165

removal will in any case depend upon the relative
masses of the potassium salt and the zeolite, so that
it is practically complete when a few hundred pounds
of fertiliser are applied to the great weight of soil
which represents an acre. Voelcker's analyses of the
drainage waters collected below the various plots at
Rothamsted showed that the amount of potash in the
water flowing from the drain below the unmanured
plot was 1-7 parts per million, and was only increased
to 2-9, 3-3, 4-4, and 5-4 parts respectively on other plots
which are annually manured with 300 lb. per acre of
potassium sulphate. Dyer's examination, also, of the
soils from the same Broadbalk wheat field show that,
of the potash applied as manure during fifty years and
not removed in the crops grown during the same
period, about one-half was still to be found in the top
9 inches of soil, much of it in such a combination
as to be soluble in i per cent, solution of citric acid,
while further quantities of the applied potash, also
soluble in the weak citric acid, were to be found
in the second and third 9-inch layers of soil. Thus,
from the point of view of practice, no loss of potash
need be apprehended through its application in the
winter before the crop is occupying the land, except
on the lightest sands where clay and humus are
lacking.

To understand the use of potassic fertilisers in the
ordinary routine of farming, it is necessary to enquire
into the function of potassium in the nutrition of the
plant, for the water culture experiments hitherto
quoted only demonstrate that it is one of the indis-
pensable elements.

Further enquiry goes to show that in some way
potash is an essential part of the mechanism of the
process of assimilation ; when it is deficient the manu-

i66 THE POTASSIC FERTILISERS [chap

facture of carbohydrates, like starch, sugar, and cellulose,
is greatly reduced, and in practice it is the crops rich in
carbohydrate which are most dependent upon a full
supply of potash. Reed observed that starch grains
were not formed in the cells of a green alga immersed
in a culture fluid containing no potash, and that
those originally present in the chlorophyll gradually
disintegrated and disappeared. Some earlier experi-
ments of Hellriegel and Wilfarth illustrate the depend-
ence of starch formation on potash even more clearly.
They started a series of water cultures, in one of which
the supply of nitrogen increased in successive jars from
nothing to the full amount required for the plant ; the
other constituents were fully supplied in every jar. In
a second series, the phosphoric acid supply was similarly
varied, and in a third series the potash. As would be
expected, in each series the amount of dry matter grown
was roughly proportional to the supply of the constituent
which was in defect. Further, when nitrogen or
phosphoric acid was lacking the formation of grain
was small, but, as far as might be, the grains produced
were perfect ; a larger number of grains, but not bigger
ones, being found as the supply of nitrogen or phosphoric
acid increased. Hence the weight of a single grain was
fairly constant whether there was much or little nitrogen
and phosphoric acid. But when potash was lacking the
individual grains were small and undeveloped, and the
average weight of each grain increased with each
addition of potash. In the absence of potash the
assimilation process was at a standstill, hence the
grains could not be filled with the starch which is
their main constituent. The following table (XLIII.)
shows the total dry matter, the percentage of grain,
and the weight of a single grain in each experiment
of the three series : —

VI.]

GROWTH OF BARLEY

167

Table XLIFI.— Growth of Barlev with increasing Amounts op
Nitrogen, Phosphoric Acid, and Potash (Hellriegel and
Wilfarth).

NITROGEN SERIES— OTHER CONSTITUENTS IN EXCESS.

Nitrogen

Dry Weight of

Com.

Weight of One

supplied.

Produce.

Grain.

Mg.

Grms.

Per cent.

Mg.

0

0-7

II-9

19-5

56

4.9

37-9

27-0

112

IO-8

38-0

33-0

168

17-5

42-6

32-0

280

2I-2

38-7

31-5

PHOSPHORIC ACm SERIES— OTHER CONSTITUENTS IN EXCESS.

Phosphoric Acid

Dry Weight of

Corn.

Weight of One

supplied.

Produce.

Grain.

Mg.

Grms.

Per cent.

Mg.

0

1-9

...

14.2

8-3

22-4

27

28-4

12-6

31-8

29

56-8

19-5

38-4

38

85-2

19.5

41-6

34

II3-6

20-2

43-8

41

142

18.7

41-3

38

213

17-8

40-1

30

2 84

31-3

43-4

34

POTASH SERIES— OTHER CONSTITUENTS IN EXCESS.

Potash

Dry Weight of

Com.

Weight of One

supplied.

Produce.

Grain.

Mg.

Grms.

Per cent.

Mg.

0

2-3

23-5

5-4

4"8

5-0

47-0

9-0

21.5

9-5

70-5

II-6

27-2

I3-0

94 -o

15-3

30-I

17.0

I88-0

21-2

38-5

260

282-0

29-8

42-8

34-0

i68

THE POT AS SIC FERTILISERS

fCHAP.

The Rothamsted results with barley are less striking,
because of the large amount of potash originally in the
soil; it is only during the later years, as has already
been explained, that any deficiency of potash has been
manifest on the plots that do not receive this fertiliser.
Still, as shown in the following table (XLIV.), which
gives average results for the fourteen years 1 889-1902,
the use of potash has increased both the weight per
bushel and the weight of the individual grains : —

Table XLIV.— Rothamsted Barley (14 years,

1889-1902).

Plot.

Manuring.

Weighti
[per Bushel.

Weight
of 100 Grains.

lA

2A

3A
4A

Nitrogen only

Nitrogen and Phosphoric Acid
Nitrogen and Potash .
Nitrogen, Phosphoric Acid,
and Potash

Lb.

52-3
52-2

53-3
53-8

Grms.

4-03
3-86
4.14

4-21

The effect of potash manuring on the production of a
carbohydrate, in this case sugar, is most manifest on the
mangold crop. If Nos. 4 and 5 of the Rothamsted
mangold plots which receive the same supply of nitrogen
and phosphoric acid are compared, it will be found that
in a good year they produce approximately the same
weight of leaf; indeed, the similarity would be still closer
if the comparison were made when the leaves were in
full activity, and not at the end of the growing season.
One plot (4), however, receives a dressing of potash
salts, but not the other (5), and the plot with potash
produces nearly two and a half times the weight ot
roots grown upon the other plot without potash. Now
the difference in dry weight is almost wholly due to sugar
and other carbohydrates, which were manufactured in
the leaf and then passed on to the root for storage ; yet

VI.]

EFFECT OF POTASH ON MANGOLDS

169

the two plots possessed practically the same leaf
development, working under identical conditions of
illumination, carbon dioxide, and water supply. But
in one case the photo-synthetical process had been
limited by the want of potash ; all the machinery was
there and the power was in excess, but the machinery
was running idle for the lack of one necessary link — in
this case the potash : —

Table XLV.— Effect of Potash on the Produce of Mangolds
at rothamsted, 1900.

Plot.

Manure.

Leaf
per acre.

Roots
per acre.

Sugar
per acre.

5A
4A

Ammonium Salts and Superphos-
phate .....

Ammonium Salts, Superphosphate,
and Potash . . • .

Tons.
2'95
3-25

Tons.
12 00
28-95

Tons.
0-797
2-223

The effect of potash upon the mangold crop is also
to be seen upon the plots where dung is also supplied,
as shown in Table XLVI. : —

Table XLVI.— Rothamsted Mangolds (12 years, 1895-1906).

Manuring.

No Potash.

+Phosphate3
and Potash.

Dung only ......

„ and Nitrate of Soda . .

„ and Ammonium Salts

„ and Rape Cake ....
Dung, Rape Cake, and Ammonium Salts

Tons.
l8-6

277
21-8
24.9
24.2

Tons.

19-5
26-8
25-9
28.6
29.9

Here it will be seen that potash increased the crop
in every case, except where nitrate of soda had been
used as the nitrogenous cross dressing, in which case
the soda liberates so much potash from the soil that

I70 THE POTASSIC FERTILISERS [chap.

specific application of potassic manures is unnecessary.
In the earlier years of this experiment only phosphates
had been added to the dung and nitrogenous manures,
but had produced no increase ; we may conclude, there-
fore, that in the series quoted it was the potash alone
that had been active. This result is the more striking,
in that dung itself contains a large proportion of
potash, yet the use of 14 tons of dung per acre year
after year, beginning in 1856, has still been unable to
supply the mangold crop with all the potash it needed.

Both in this series of plots and that in which the
mangolds receive no dung, the value of potassic manur-
ings is small where nitrate of soda is the source of
nitrogen. This is not only because the sodium can be
made to do some of the work usually done by potassium
in the plant, but also because it is able to attack the
compounds of potash in the soil (the Rothamsted soil
contains an enormous reserve of insoluble potash), and
bring it into solution so that it becomes available for
the plant.

This can be illustrated by the results obtained on
the Rothamsted mangold field in 1900 (a good year);
Table XLVII. shows the yield of roots and leaves, and
the potash and soda removed from the soil by the crop,
both with and without potash, when the nitrogenous
manures were ammonium salts and nitrate of soda
respectively.

It will be seen that on Plot 5N, without any potash
but where nitrate of soda is used, the yield of roots and
leaves is almost as great as that obtained on 6N where
potash salts are also added, and is more than double that
given by the corresponding plot without potash, 5 A, but
which receives its nitrogen as ammonium salts. The
amount of potash taken from the soil by the crop on Plot
5N is 927 lb. against 596 lb. on 5 A, the increase repre-

vi.l SOIL POTASH RENDERED SOLUBLE BY SODA 171

senting the attack of the soda salt upon the insoluble
potash in the soil, but it will be seen that the potash thus
present in the crop by no means came up to the quantity
removed by the crops on 6A and 6N, where an excess of
potash had been applied in the manure. Since, also, the
sum of the two alkalis, potash and soda together, in

Table XLVII.— Potash and Soda contained in
Mangolds. Rothamsted, 1900.

Plot.

Roots.

Leaves.

Potash.

Soda.

Tons.

Tons.

Lb.

Lb.

5A

Ammonium Salts and

Superphosphate .

I2-00

2-95

59-6

56-9

6A

Ammonium Salts, Super-

phosphate, and Potash .

28-20

3 -60

306-6

67-0

■^N

Nitrate of Soda and Super-

phosphate

28-35

3-85

92.7

251-6

6N

Nitrate of Soda, Super-

phosphate, and Potash .

29-65

3-60

220-9

1606

the crops on 5N, 6 A, and 6N is nearly the same, it may
be concluded that on 6A and 6N the plant was taking
up a much greater amount of potash than it needed,
due to the excess of this constituent in the soil and
manure.

Next to their effect upon carbohydrate-making
crops, the most striking action of potassic manures is
their value in promoting the growth of clover and all
leguminous crops. The function of potash here may be
still that of prom^tinga^milatiDn, because the bacteria
which fix mtrogenin the nodules on the roots of the
leguminous plants must be supplied with carbohydrate
by the plant in order to obtain, by its oxidation, the
energy requisite for the fixation of nitrogen. There is
evidence to show that the fixation of nitrogen by these
organisms is promoted by a supply of carbohydrate ; but

/

172

THE POTASSIC FERTILISERS

[chap.

whatever may be the explanation it is found in practice
that the growth of clover, etc., is very much promoted
by a free supply of potash, and this is very manifest
upon sands and gravelly soils usually poor in potash.

This effect may be very strikingly seen when the
fertiliser is applied to grass land carrying a mixed
herbage, for the potash encourages the leguminous
plants until the aspect of the vegetation may be
entirely changed. On the Rothamsted grass land,
which is mown for hay every year, one plot gets a
complete mineral manure — phosphates and sulphates
of potash, soda, and magnesia ; the adjoining plot
receives the same phosphoric acid, magnesia, and soda,
but no potash, while a third plot gets the phosphates
alone. The Table XLVIII. shows the comparative
yield and the composition of the herbage by weight : —

Table XLVIII.— Rothamsted Hay Crop, without and with
Potash.

Plot.

Manuring.

Dry Hay.

Composition of Herbage
in 1902.

1856

to

1902.

1893

to

1902.

Grasses.

Legu-
minous
Plants.

Weeds.

7
8

4

3

Complete Mineral

Manure .

Do. without

Potash .
Superphosphate

only
Unmanured

Cwts.

38-8

28.1

23-3
21.9

' Cwts.

36.5
21.6

17-8
iS-9

Per cent.
20-3

28-8

54-4
34-3

Per cent.
55-3

22 I

15-4
7-5

Per cent.

24.4

49-1

30.2
58-2

On the plots receiving a mineral manure including
potash half the vegetation now consists of leguminous
plants, but in the absence of potash the proportion is

Vi.l EFFECT OF POTASH UPON GRASS LAND 173

only 22 per cent, and 15 per cent, the higher proportion
being where magnesia and soda, which attack the potash
reserves in the soil, are applied. It should be noticed
that the large amount of phosphoric acid received by
these two latter plots does not result in any great
stimulus to the leguminous plants, which constitute 7-5
per cent, of the herbage of the unmanured plot. Where
nitrogen is applied and potash omitted, no leguminous
plants are to be found.

On these grass plots another very striking effect of
potash manuring is also very manifest, which confirms,
on a large scale, the experiment of Hellriegel and
Wilfarth's already quoted. On the potash-starved plots
the grasses fail to a large extent to develop any seed,
and the heads are soft and barren, presumably because
of the deficiency in carbohydrate formation. For the
same cause the straw, not only of the grasses, but also
on the similarly manured wheat and barley plots, is
always weak and brittle when potash is wanting. The
plants of the potash-starved plots at Rothamsted are
also characterised by certain other appearances, which
to a less degree are to be observed in nature where the
soil is naturally poor in potash, as on many peaty and
sandy lands. The grass has a dull colour, partly due
to a deficiency of chlorophyll and its substitution by
a certain amount of a red colouring matter along the
stems, and partly because the tops of the grass blades
show a great tendency to die off for an inch or two and
leave a brown withered end. When in 1908 the man-
golds on the Barn field were replaced by Swede turnips,
they grew with considerable vigour and remained per-
fectly healthy on the potash-starved plots, except that
the leaves in the autumn showed a flecked appearance,
especially towards the margins, where a good deal of
the leaf tissue had a yellow brown papery look which

174 THE POT AS SIC FERTILISERS [chap.

marked off the whole plot very distinctly, especially
after the first frosts had taken place.

There is abundant experimental evidence to show
that potash makes the plant more resistant to the
attacks of fungoid diseases. It has already been
explained how susceptible the use of nitrogenous
manures renders the mangolds on certain of the
Rothamsted plots to the attack of a leaf spot fungus
— Uromyces betae. The attack is, however, much less
severe on the plots receiving an abundant supply of
potash ; there the plant remains healthy even though
the nitrogen is in excess. The photograph, Fig. 4,
shows two typical roots taken in 1902 from plots with
and without potash, both receiving the same large
dressing of nitrogenous manures.

Just in the same way, the wheat on the potash-
starved plots is always subject to rust, even in a good
season when very little is to be seen on the other plots
normally manured. The grass also on potash-starved
plots is attacked by various fungi ; hence it may be
taken as a general rule, that crops which do not receive
their full supply of potash will be correspondingly sus-
ceptible to disease.

It is not possible to say whether this is due to
any specific alteration in the composition of the cell
contents or to a general lack of vigour, but the latter
is probable, because an excess of potash tends to pro-
long the vegetative growth of the plant and to delay
maturity. Plants receiving potash are always a little
the greener, especially late in the season, and this is
not always an advantage, as may be seen from the
fact that the barleys grown on the plots receiving
potash at Rothamsted, show a somewhat darker and
less attractive colour than those grown without potash.
That potash tends to prolong growth may also be

'O

l-

C

« -ti

>

z z

«*- ^^_

z'

o o

e

^ to

n

<U <D

^

X X

H

^

W W

Z

<

cd o

VI.] POTASH MOST EFFECTIVE IN DR Y SEASONS 175

inferred from the fact that its effect upon the yield is
always most pronounced in dry seasons.

Referring again to Table XXXIV., it will be seen
that in the dry season of 1893, the yield of barley
(grown also with ammonium salts and superphosphate)
was increased by a dressing of potash from i8-i to 30-8
bushels per acre, whereas in the wet season of 1894 the
increase was only from 34-9 to 41-4 bushels per acre.

Similarly with the wheat (Table XXXV., p. 139),
in the wet season the application of potash only
increased the yield of grain from ii-i to i6-o bushels,
and the weight from 54-6 to 57-8 lb. per bushel ; whereas
in the dry season the yield was increased from 77 to
16-4 bushels (more than double), while the weight was
raised from 56-4 to 62-6 lb. per bushel. That the bad
results in the dry year were due to a premature ripen-
ing of the plant, which was deferred by the potash, is
seen from the fact that with potash the ratio of grain
to straw was 98, whereas without potash it only reached
67-3, in which case the migration of materials from the
straw to the grain is clearly incomplete. But though
in such cases of grain crops the use of potash prolongs
the development of the plant and defers maturity,
apparently an opposite effect is produced upon root
crops. On the Rothamsted field, for example, where
potash is used, the mangold leaves will begin to turn
yellow and fall, indicating that the plant has finished
its season's growth, long before any such appearance
is seen on the potash-starved plots alongside, where
a tuft of dark green and apparently growing leaves
persists until the plant is cut off by the frosts. Similar
appearances, though in a less pronounced degree, can
be seen on ordinary crops in light soils, whenever a
strip has been left to show the action of potash in the
manure.

176 THE POT AS SIC FERTILISERS [chap.

The apparent contradiction may be explained on
physiological grounds ; with the root crops ripeness
does not represent the completion of a migration process
of material previously stored up, such as takes place
from straw to grain, but marks the completion of the
work of the leaves in manufacturing carbohydrate and
passing it on to the root for storage. It has already
been shown (Table XLV.) that in the absence of
potash the leaves cannot carry on the assimilation
process properly, and probably they continue green
instead of ripening off because their function of storing
up material in the root has not been completed.

From time to time field experiments have been
reported which show a reduced yield for the use of
potassic salts, and while in many cases the results
might be put down to experimental error, the cases
are too numerous to be entirely covered by such an
explanation.

A clue to this apparent depressing effect of potash
is provided by the appearance of the soil on certain
of the experimental plots at Rothamsted, as on the
Barn field, where considerable amounts of potash salts
are applied every year. The behaviour of the soil,
which lies extremely wet and sticky after rain, and dries
with a hard glazed surface, shows that the clay particles
must have become thoroughly deflocculated, just as they
are on the plots receiving nitrate of soda (p. 55).

This deflocculating effect of the potash salts, which
in themselves would flocculate clay particles, is due to
a prior interaction between the potassium salt and the
calcium carbonate in the soil, resulting in the formation
of a certain amount of potassium carbonate, the defloc-
culating powers of which have already been recognised.

The destruction of tilth of the soil brought about in
this way may easily give rise to an irregular stand and so

VI.] SOILS REQUIRING POTASH MANURES 177

account for an inferior plant and a reduced yield on the
plots receiving potash salts ; the author has observed
a case on heavy land where the application of a rather
excessive amount of kainit so altered the texture of the
soil, that the draught of ploughs upon it was perceptibly
increased, and the crop suffered to a marked degree.

The examples that have been given to illustrate
the specific action of potash must, however, be used
with some caution as a guide to the manuring of
crops under ordinary conditions of farming. They are
extreme cases, drawn mostly from the later years of
the Rothamsted experiments, when the exhaustion of
the available potash in the soil had become very pro-
nounced through the continuous cropping with the help
of a manure containing all the other elements of
fertility except potash. Except on special soils and
with the specially potash-loving crops, it is not usual
to find in this country that the use of a dressing of
potash salts has any visible effect on the yield, so large
is the stock of potash in the soil, and so well is it
conserved by the ordinary systems of cropping.

On the lighter soils, the sands and the gravels,
potash is most likely to be deficient, and the ill-effects
arising from its absence are intensified by the dryness
of these soils. Even on such soils, potash manures will
rarely be found remunerative for cereal crops ; for
mangolds and potatoes, and to a less extent for turnips,
they are necessary ; while grass land can hardly be
maintained in a satisfactory character without potash
at regular intervals. On the stronger soils, potash is
a remunerative manure for mangolds, and occasionally
for land laid up for hay ; but in general, the use of
nitrate of soda as a source of nitrogen will liberate
enough of the locked-up potash in the soil for the needs
of the crop.

M

CHAPTER VII

FARMYARD MANURE

Variable Composition of Farmyard Manure — The Fate of the
Constituents of Food during Digestion and Excretion —
Composition of Urine and Fasces of Farm Animals —
Fermentation Changes taking place during the Making of
Dung — The Breakdown of the Nitrogenous Bodies and of
the Carbohydrates — Gases found in the Dunghill — Losses of
Nitrogen during the making of Farmyard Manure — Pre-
servatives used to minimise the Losses during Dung-making —
Composition of Farmyard Manure — Cake-fed v. Ordinary
Manure — Long and Short Manure — London Dung — The
Value of Fresh Manure — The Fertilising Value of Farmyard
Manure — Recovery of its Nitrogen in the Crop — Long
Duration of the Action of Farmyard Manure — Farmyard
Manure as a Carrier of Weeds or Disease — The Physical
Effects of Farmyard Manure upon the Soil — The Improvement
in Texture and Water-retaining Power — Value of Farmyard
Manure as a Mulch on Grass Land — Farmyard Manure best
utilised for the Root Crop or Grass Land — Value of Farmyard
Manure : Cost of making One Ton.

Farmyard manure, foldyard manure, yard manure, and
dung are all terms employed in various parts ol the
country for the same more or less decomposed mixture
of the excreta of domestic animals with the straw or
other litter that is used in the yards or stalls to absorb
the liquid portions and keep the animal clean. Probably
it would be more correct to retain dung as a name for
the excreta alone, and farmyard manure for the product
that leaves the yards, but it is impossible in practice to
observe any such distinction. It follows, from its origin,

178

CHAP. vii.J PROCESS OF DIGESTION 179

that the composition of farmyard manure must be far
from constant, varying with the nature of the animal
making the dung, the kind and amount of food it
receives, the proportion between excreta and litter,
the nature of the litter, and the extent and character of
the decomposition which has taken place in the manure
itself. The composition of the excreta being the largest
of these factors, it will be necessary first of all to trace
the effect of the process of digestion on the various
manurial substances in the food — compounds of nitrogen,
phosphoric acid, and potash. Animals that are not
increasing in weight, such as working horses or full-
grown cattle simply being maintained in store condition,
excrete the whole of the nitrogen, phosphoric acid,
and potash they receive in a liquid or solid form,
the carbohydrates and fat of the food being mostly
got rid of as gases. But the fate of the manurial
constituents varies according as they are present in the
food as digestible or indigestible compounds ; for
example, part of the proteins of the food withstand
the action of the digestive ferments, and are excreted
unchanged in the fceces, but to a much greater extent
they are broken down into soluble compounds which
pass into the blood and eventually are excreted as
urea, uric acid, etc., in the urine. Similarly, for the
phosphoric acid and the potash in the food, whatever
is digestible is excreted in the urine in some simpler
combination, whatever resists digestion passes out
unchanged in the solid excreta. Hence a great
difference in the manurial value of the two portions of
the excreta ; the compounds in the urine — urea, uric
acid, soluble phosphates, and potash salts — are either
ready for the nutrition of plants or require but slight
further changes to become so ; whereas in the solid
dung the materials have several stages of decomposition

i8o

FARMYARD MANURE

[chap

to go through before they can reach the plant, and
having already shown themselves able to resist the
attack of the animal's digestive ferments they are
correspondingly unaffected by the ordinary decay
processes in the soil. The proportion the digestible
bear to the indigestible constituents of a food varies
with the nature and even with the mechanical condition
of the material, also with the kind and age of the
animal ; roughly speaking, the richer the food the
greater the proportion that is digestible — ^.^..decorticated
cotton cake contains 7 per cent, of nitrogen, of which
87 per cent, is digestible and finds its way into the
urine, while hay contains about 1-5 per cent, of nitrogen,
of which only 50 to 60 per cent, is digestible.

When the animal consuming the food is growing or
fattening or yielding milk, a certain proportion of the
manurial constituents in the food is retained, the
proportion varying with the nature both of the food
and the animal. Cows in milk and young growing
animals take the greatest toll from their foods, animals
in the later stages of fattening the least. If, for
example, 100 lb. of linseed cake be fed to milch cows
and oxen nearly fat respectively, the manurial con-
stituents contained in the cake will be distributed in
each case as shown in Table XLIX.

Table XLIX. — Nitrogen Retained and Digested.

In
100 lb.
Cake.

Fattening Oxen.

Milch Cowa.

In
Meat.

In
Urine.

lu

Psece*.

In

Milk.

In
Urine.

In
Faeces.

Nitrogen

Phosphoric Acid .
Potash .

4-75

2-0

1-4

0-2I
0-14
0-02

3-88
0-09

I-IO

0-66
1-77

0-28

I-?2 2-75
0-5 0-07
0-14 1-05

0.66
1-43
0-21

VII.]

COMPOSITION OF EXCRETA

i8i

It is thus impossible to state the composition of the
excreta of the various farm animals except within
certain wide limits, owing to the variations induced by
the food and the age of the animal. Table L. shows
certain average results which will serve to characterise
the different animals.

Table L.— Composition of

Urine and Excreta.

Animal.

Excreta.

Water.

Nitrogen.

Phosphoric
Acid.

Potash.

Horse . • <
Cow . . 1
Sheep . . \
Pigs . . {

solid
liquid

solid
liquid

solid
liquid

solid
liquid

75-0
90 -o

86-0
91.5

57-6
86.5

76-0
97.6

0-56
1-52

0-44
1-05

0-72
I-3I

048
0-50

0-35
trace

0-12

trace
0-44

O-OI

0-58
0-14

O-I

0-92

0-04
1-36

0-36
0-70

It will be seen that the urine of sheep and horses is
much more concentrated than that of cattle and pigs ;
similarly, the solid excreta of the two former are also
the drier. It is this greater dryness and richness
which causes the gardener to describe horse manure as
"hotter" than that produced by either cows or pigs;
bacterial changes take place in it much more rapidly, a
greater amount of ammonia is produced, and the rise
of temperature is more pronounced.

The next factor which enters into the composition
of the dung is the nature of the litter on which the
animals are placed ; from time to time, especially among
small holders, various materials, such as bracken fern,
hop bine, leaves, even manufacturing refuse like spent tan
and sawdust, are used ; but on a large scale only two —
straw and to a less extent peat moss litter, get employed.

l82

FARMYARD MANURE

[chap.

The litter has a twofold function : it absorbs the urine
and other liquid portions, and it provides both organic
matter and nitrogen for the resulting manure. The
cereal straws contain about 0-5 per cent, of nitrogen,
0-2 per cent, of phosphoric acid, and i-o per cent, of
potash, the variations in composition between individual
samples of any one kind of straw being as great as
the variation between average samples of wheat, oat,
and barley straw. Speaking generally, straw grown in

Table LL— Composition of

Litter.

Water.

Organic

Matter.

Ash.

Nitrogen.

P205.

K^O.

I. Wheat Straw (W^et

Season)

17-8

76-2

6-0

0-38

0-19

0-77

2. Wheat Straw (Dry

Season)

15-6

78.9

5-5

0-2 1

0.17

I-OO

3. Oat Straw

16.5

77-9

5-6

0-4

0-28

0-97

4. Barley Straw .

20-0

74.6

5-4

0.27

o-i8

0-45

5. Bracken . ,

13-6

81.7

4-7

1.44

0-20

O-II

6. Hop Bine ,

18.7

77-3

3-95

0.28

0-07

O-IO

7. Peat Moss ,

31-8

47-6

20-6

0.83

O-IO

0.17

the north of England and Scotland is richer than straw
grown in the south and east of England, because the
vegetative growth has been more prolonged and the
migration of food materials from the straw into the
corn has not been quite so thorough. Straw will absorb
from two to three times its weight of water, and again
the variation in absorbing power between different
samples of the same kind of straw is greater than that
between different kinds of straw. In practice wheat
straw is the most highly esteemed, as cleaner and
wearing better under the feet of the animals than any
other kind of straw. Oat straw comes next, and is often
almost as good as wheat straw ; barley straw is least
liked, as it is often brittle and dusty.

VII.]

FUNCTION OF LITTER

1S3

Peat moss litter consists of humified vegetable
matter, being derived from the upper layers of a peat
bog, where the material still retains a good deal of its
original structure ; it forms a brown, spongy, fibrous
mass consisting almost wholly of organic matter. It
will absorb a greater amount of water than will an
equal amount of straw, up to about ten times its own
weight of water. Peat moss is also remarkable for its
power of absorbing ammonia even from the atmosphere,
so that a stable littered with peat moss will remain
sweet for a comparatively long time. Table LI I. shows
the result of an experiment in which two similar
stables carrying the same stock were littered — the one

Table LII. — Ammonia in Stable per Million of Air.

Litter.

1st
day.

2nd
day.

3rd
day.

4th
day.

5th
day.

6th
day.

inh

day.

Straw . .
Peat Moss

•0012
0

•0028
0

•0045
0

•0081
0

•0153
trace

•0168
•001

•017

with straw, the other with peat moss, and the amount
of ammonia in the air was determined every day.
As will be seen, the peat moss proved a much
more efficient absorber of the ammonia produced than
the straw. The peat moss itself usually contains a
higher proportion of nitrogen than straw does, hence
the manure it makes appears to be correspondingly
richer, and this difference is often increased by its
longer retention in the stalls. But the peat moss
itself is very slow to decay, especially in dry soils,
so that it is doubtful whether its extra content in
nitrogen is of much value ; direct experiments, however,
are lacking to compare the relative value of manure
made from the same amount of feeding stuffs with peat
moss and straw respectively. Peat moss manure is

i84 FARMYARD MANURE [chap.

always short, and is less easy to handle in consequence,
but it requires no making and can be applied straight
from the yards even to the lightest of soils.

However the farmyard manure has been made, it
thus starts with a mixture of excrement, urine, and
litter, which become more or less consolidated and
mixed together by the trampling of the animals. Other
changes, however, intervene very rapidly, and these in
the main are brought about by bacteria, which for
convenience may be divided into two groups, one acting
on the cellulose and other carbon compounds of the
straw that make up the bulk of the manure, and the
other acting on the nitrogenous compounds that do not
weigh so much but supply the main fertilising properties
of the dung.

Among the more important of the organisms dealing
with nitrogenous material are those which attack the
urea in the urine and by adding to it the elements of
water give rise to a carbonate of ammonia, which very
readily dissociates into free ammonia and carbonic acid
— both gases, and therefore capable of escaping into
the atmosphere.

CO(NH2)2 + 2H20 = (NHJ2CO3 = 2NH3 + CO2 + H2O

There exists more than one organism bringing
about this change, but the best known is a small coccus
known as Micrococcus urecB, which is widely disseminated
in the air and dust, and is naturally extremely abundant
in such places as stables and cattle stalls, where it is
always giving rise to ammonia. This change into
ammonium carbonate is an extremely rapid one; in
the liquid draining from a yard or a manure heap, or
even in the liquid manure tank, little or no urea can be
detected, so complete has been the change to ammonia.
As long as the liquid containing the ammonium car-

VII.] CHANGES IN THE COMPOSITION OF DUNG 185

bonate is protected from evaporation, no loss of nitrogen
will result, but the more surface it exposes to the air
and the higher the temperature, the greater will be the
amount of ammonia passing off in a gaseous condition.
Thus thin films of urine on the floors, walls, or even on
the surface of loose straw, easily lose nitrogen by the
fermentation of the urea and subsequent volatilisation
of the ammonia; the smell of a stable arises in this way
and is clear evidence of the escape of ammonia. As
will be brought out more clearly later, this volatilisation
of ammonia causes most of the loss of nitrogen that
takes place in making dung.

The ammonium carbonate is itself subject to change
and even to loss by other actions than evaporation :
there are always present in the manure heap various
bacteria which can oxidise ammonia into free nitrogen
gas and water ; in consequence dung which is allowed
to lie about loosely grows poorer in nitrogen from this
cause as well as through volatilisation of ammonia.
Though the action has been recognised as taking place
in practice, little is known of the specific bacteria which
set free gaseous nitrogen in this way, a process which
is often called " denitrification," though the term is
better restricted to the change whereby nitrates are
reduced to nitrogen gas. Nor have the conditions
favourable to this change been closely investigated ; it
is, however, certain that rapid oxidation such as is
brought about by a loose condition of the manure or by
turning it, will be accompanied by some destruction of
ammonia. It is also favoured by the presence of soluble
carbohydrates — i.e.^ easily oxidisable material — and it is
materially reduced, if not suspended, as soon as these
substances have been used up.

Another group of bacteria which are extremely
abundant in fresh faeces are the so-called putrefactive

r86 FARMYARD MANURE [chap.

bacteria which break down the proteins into simpler
compounds such as amino-acids, amides, and finally
ammonia. Some of these bacteria, like B. coli communis,
are abundant in the large intestine of herbivorous
animals, and of course continue their work in the excreta
after ejection. Without discussing them individually,
their function is to convert the insoluble nitrogenous
bodies of the straw (those of the faeces are more difficult
of attack because they have already resisted the actions
of digestion) into soluble bodies akin to ammonia and
therefore more nearly utilisable by the plant. Thus,
with a certain amount of loss as free nitrogen, the trend
of the bacterial actions taking place in the fresh farm-
yard manure is to break down the complex insoluble
compounds of nitrogen to more and more simple ones,
ammonia being the final term. At the same time, there
is always a reverse change going on ; as the bacteria
themselves multiply, they seize upon the active soluble
forms of nitrogen and convert them into insoluble
proteins in their body tissues. Which action is pre-
dominant will depend on the stage that has been
reached in the dung-making process — i.e.^ on the supply
of carbohydrate, air, water, and other variable factors —
but after the first rapid production of ammonium com-
pounds, the longer the dung is stored the more the
ammonia returns to a protein form.

So far we have been considering only changes in
the nitrogenous material of the excreta and the litter,
since nitrogen is the chief fertilising constituent of the
manure, but the most characteristic change in dung-
making is the destruction of the straw and its con-
version into dark brown "humus," which in the end
retains none of the structure of the original straw.
There are a number of organisms to be found commonly
in the air and dust which readily attack such carbo-

VII.] CHEMICAL CHANGES DURING DUNG-MAKING 187

hydrate material as straw affords, and in the presence
of oxygen burn it up completely into carbon dioxide,
water, and inorganic ash. Such organisms, however,
do not play a very large part in manure-making,
because oxygen soon gets excluded from the mass ;
the work is taken up instead by other bacteria
capable of working in the absence of oxygen. Two
of these only have been as yet studied in any
detail ; they both rapidly attack carbohydrates like
cellulose, and give rise to carbon dioxide, marsh
gas or hydrogen respectively, certain fatty acids, of
which butyric is the chief, and the indefinite brown
acid substance known as "humus," which is richer in
carbon than the original carbohydrate. The evolution
of such gases can easily be demonstrated during the
making of dung, either by laboratory experiments or
by an analysis of the gases extracted from a dunghill.

Table LI 1 1, shows the gases extracted from a fresh
dunghill by Deherain during one of his experiments at
Grignon.

When the first sample was taken, the dungheap was
still in process of formation, and was in too dry a
condition. The hydrogen fermentation was most
prominent at this stage, and hydrogen and carbon
dioxide were the most prominent gases. On that
day the liquid manure was pumped up over the
whole mass, and fermentation became more active, as
seen by the very high temperatures reached on the
24th, when the formation of hydrogen had diminished,
while that of marsh gas had increased greatly. The
analyses on 30th August show the result of having
again let the heap get dry ; the top and middle were
full of air, as may be seen from the large proportions
of nitrogen and the presence of some oxygen; the
percentage of carbon dioxide had also become so

1 88

FARMYARD MANURE

[chap.

low that losses of ammonia would take place by
volatilisation, especially as the temperature was high.
The later analyses, taken when the heap was well
consolidated and kept moist, show that a steady

Table LI 1 1. —Composition of Gases in Dunghill (Deherain).

Date,

OS

si,

int

pies
.aken.

a

i
0

i

a

1899.

•s^

^^i«

Ot

«.2

fe-

£

•0

s

-^3

wl

a

up

0

w"

iS

Metres.

"C.

Aug. 22 .

2.00

middle

52

54-3

o-o

7-8

23-5

14-4

,. 23.

2-00

middle

52

58-0

...

14.2

II-8

i6-o

r top

71

50-0

• ••

17-4

3-1

29-5

„ 24.

2-30

\ middle

67

68-0

...

23-9

7-4

0-7

y bottom

63

49.0

...

40.8

3-9

6.0

„ 26.

2-30

bottom

60

51-0

...

46.6

2-4

O'O

r top

60

7.2

7-0

0-0

...

85-8

„ 30.

2.50

A middle

65

14-5

4-7

1-3

...

79-5

y bottom

60

50-8

0-0

49-2

...

o-o

[ top
^. middle
[ bottom

66

42.7

I'l

52-4

.„

9-8

Sept. 20 .

2-50

65

49-5

48-3

...

2-2

52

47-8

51-2

I-O

f top

55

54-0

0.5

43-0

...

2-0

Oct. 4 .

2.50

J. middle

65

42.7

56.1

...

O-O

[ bottom

40

48-3

517

0-0

anaerobic fermentation of carbohydrates into equal
volumes of carbon dioxide and marsh gas was then
going on, while the evolution of hydrogen had stopped.
From these and the other analyses executed by
Deherain, it may be learnt that the main anaerobic
fermentation which takes place when the straw and
other materials are fresh, is that which gives rise to
hydrogen and carbon dioxide ; if the heap gets too
dry and air penetrates, an aerobic fermentation begins,
which gives rise to carbon dioxide only ; but at the

Vii.]CBEMICAL CHANGES DURING DUNG-MAKING 189

same time the proportion of this gas falls to such an
extent because of its dilution with the air, that
ammonia can be lost by volatilisation. By consolidat-
ing the heap and pumping the liquid over it afresh,
the anaerobic fermentation rapidly sets in again and
the proportion of carbon dioxide is restored, thus
checking the dissociation and volatilisation of the
ammonium carbonate. After the first outburst of
fermentation, the evolution of hydrogen ceases and
the marsh-gas fermentation takes its place.

A considerable proportion, amounting to one-quarter
or more, of the dry matter of the original dung is lost
during this process of humification, by the conversion
of carbohydrates into carbon dioxide, marsh gas or
hydrogen, and water. The various acids which are
also produced are neutralised by the liquid part of
the manure, which is alkaline from the presence of
ammonium and potassium carbonates resulting from
the fermentation of the nitrogenous constituents and
salts of the urine ; the dark brown liquid to be seen
draining from a dunghill is a solution of the humus
formed in this alkaline liquid.

The changes going on during the making and
storage of farmyard manure are thus exceedingly
complex ; it is in the early stages that the bacterial
actions are most rapid, and they fall chiefly upon
the soluble nitrogenous compounds like urea. At this
time the greatest losses of nitrogen take place both by
volatilisation of ammonia and by evolution of nitrogen
gas, and so active is the oxidation that the temperature
of the mass rises continually. If the rate of oxidation
b2 promoted by occasionally turning over the mass, as
in preparing a hot bed or a mushroom heap, the rise
in temperature is much increased ; at the same time
the losses of nitrogen rise rapidly, and the amides and

tgo FARMYARD MANURE [chap.

ammonium carbonate disappear more quickly. What
the gardener calls " taking the fire " out of the manure,
means so reducing the free ammonia that the material
is no longer injurious to a plant's roots, though it still
remains rich in nitrogen and organic matter capable of
further decay. As soon as the first violent reactions are
over, especially after the mass has become consolidated
by trampling and the oxygen in the entangled air has
been used up, the rate of change slows down consider-
ably ; it now consists mainly in the attack of the
anaerobic organisms upon the carbohydrate material.
The long strawy dung begins to change to " short " or
rotten manure, and this change may continue slowly for
years, until all trace of structure is entirely gone and
only a brown pulp is left. During this second change
but little loss is experienced by the nitrogenous
compounds ; if the mass is kept tightly pressed and
moist enough to exclude air, there will be no loss
of fertilising constituents, only a gradual decline of
weight as some of the carbon compounds are con-
verted into gases. Of course, as the manure gets
older and shorter it becomes richer in nitrogen ; this
apparent increase is, however, simply due to the loss of
non-nitrogenous carbon compounds, whence it follows
that the nitrogen, which does not waste, always bulks
larger and larger in the residue. But though there is
no loss in nitrogen in these later stages, the more active
compounds, such as ammonia and the easily decom-
posable amides, become converted by bacterial action
into carbon compounds which take longer to reach the
plant when the manure finally gets in the soil.

Thus, during the making and storage of farmyard
manure there are a large variety of bacterial actions
at work, some running in an opposite sense to others,
and it will depend on such external conditions as the

S\\:\CHEM1CAL CHANGES DURING DUNG-MAKING 191

supply of air and water which class of action pre-
dominates at any given time. Putrefactive bacteria are
resolving proteins into simpler compounds of nitrogen
and ultimately into ammonia ; oxidising bacteria (some-
times called denitrifying bacteria) set free nitrogen
gas ; meantime the bacteria engaged in the destruction
of cellulose and the formation of humus are always
building proteins or bodies akin to them out of the
previously produced amides and ammonia.

One other change sometimes takes place when the
manure is allowed to get too loose and dry — instead of
bacteria, fungi begin to develop very rapidly until the
whole mass becomes permeated with the mycelium.
The masses of manure begin to look white and dusty,
a condition which the practical man describes as " fire
fanged." It is generally agreed that such manure is
seriously deteriorated, but no analyses are available.

With these general facts in mind it will be possible
to interpret the experiments which have been made to
ascertain what part of the fertilising materials contained
in foods consumed by animals is recovered in the dung
and what losses occur during the making and storage of
farmyard manure. In the first place, it can be shown
that there is no loss of nitrogen in the gaseous form due
to the animal ; the nitrogen contained in the urine and
faeces is equal to the nitrogen in the food, less whatever
may have been retained by the animal in its bodily
increase. Numerous feeding experiments demonstrate
this point ; the following example from Kellner's
researches may be taken as an illustration.

An ox was fed on a daily ration of 2 kg. of gluten
meal, 2 kg. of starch meal, 4 kg. of dried sugar-beet
slices, 5 kg. of hay, and i kg. of chaff, containing in all
388-8 grms. of nitrogen. About 18-5 kg. of dung was
excreted containing 15-36 per cent of dry matter and

192 FARMYARD MANURE [chaP.

100-9 grms. of nitrogen, and about 13 kg. of urine
containing 2-03 per cent, of nitrogen, equal to 265-5
grms, of nitrogen. The ox was putting on weight, and
retained from the food 714-5 grms. of carbon and 22-5
grms. of nitrogen. Thus of the nitrogen supplied 68-2
per cent, was excreted in the urine, 25-4 per cent in the
faeces, and about 6 per cent, was retained by the animal.
To attain such a result, however, it is necessary to
collect the urine and fseces as they are voided, and to
preserve them or analyse them before any fermentation
and evaporation of ammonia can take place.

Assuming the animal itself to cause no loss of
nitrogen other than that retained in the increased live
weight, a number of experiments have been made to
ascertain the losses in making farmyard manure under
ordinary working conditions.

For example, Maercker and Schneidewind, at Leuch-
stadt, in 1896-7 tied up twenty-four three-year-old
steers from i6th June to 29th October 1896 — 136 days
— during which their average increase of live weight
was 306 lb. The food consisted of lucerne hay, chaff,
barley straw, dried sugar beet pulp, decorticated cotton
cake, and bran, and they were littered on wheat straw.

Twelve of the beasts were tied up in a deep, carefully
cemented box or pit, from which no losses by drainage
could take place, and the dung was not disturbed but
kept trampled down until the end of the trial. The
second twelve were fed in an ordinary stall, and the
dung and litter were removed every other day to one
or other of two heaps in the yard alternately, one of
these being covered by a roof, and the other open to the
weather. At the end of the feeding experiment the
three lots of dung were carefully sampled and analysed,
with the results set out in Table LIV. below.

In a second experiment, fourteen steers were fed in

VII.]

LOSS OF NITROGEN

193

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194 FARM YARD MANURE [chap.

the deep pit from 6th November 1896 to 21st February
1897, when the dung made was cleared out, sampled,
and analysed. The experiment was then resumed until
2 1st May, after which the dung was left in the box for
another month, until 17th to i8th June, without any
beasts to keep it trodden down, the weather being
meantime very hot. The results appear under items 4
and 5 in Table LIV. It will be seen from this that the
loss of nitrogen was much greater during the second
series, which only differed from the first in the fact that
the dung lay without trampling for a month during the
summer.

Taking these results as a whole, it is seen that, even
with the most careful management, the loss in making
the dung amounts to 13 per cent, of the total nitrogen
supplied in the food, in addition to 6 per cent, or so
which the animals retain. This loss increases with
great rapidity if the conditions are less favourable ; the
minimum is only attained if the dung be kept trampled
beneath the animals in a deep box, for if it be left to
itself for a time, or if it be made in a shallow stall and
thrown out daily into a heap, as is often the practice,
the loss rises to between 30 and 40 per cent.

In connection with the first-mentioned experiment,
Maercker and Schneidewind made determinations of
the state in which the nitrogen exists in the dung,
whether it was soluble and therefore active, or msoluble
and comparatively inactive. From the known digesti-
bility of the foods consumed, it was possible to calculate
what proportion of the nitrogen in each food left the
body in a digested condition as urea and kindred
bodies dissolved in the urine, and what proportion
consisted of undigested and insoluble compounds in
the faeces. Maercker and Schneidewind found not only
that the loss had fallen upon the active nitrogen — i.e.t

VII.] LOSSES DURING DUNG-MAKING 195

that urea had been transformed into ammonium
carbonate and volatilised, or broken up with loss of
free nitrogen — but also that some of the active nitrogen
had been converted into an insoluble form, as though
the bacteria swarming in the dung had seized upon the
active nitrogen and converted it into the insoluble
material of their own substance. Of course, this with-
drawal of nitrogen from the active into the insoluble
form still further reduces the value of the dung as a
whole.

In France, experiments were carried out on the
same question by MM. Miintz and Girard, with
omnibus horses, cows, and sheep. They showed that
with horses and milking cows, where the manure was
removed every day, the loss of nitrogen amounted to
from 30 to 35 per cent, of the total nitrogen contained
in the food. With sheep the losses were still higher.
Liberal littering and immediate treading of the excreta
into it by the animal greatly reduced this loss. The
results are given in Table LV, It is apparent that, on
the whole, the proportion of the nitrogen recovered in
the manure is about one-half of that supplied in the food.

Further experiments with sheep show that the loss
was greatest with no litter, and could be reduced by
using an excess, or particularly by using peat moss or
earth.

Loss
per cent,

(No Litter . . 590

Litter. . . 50-2
T ■ i

Litter. . . 44-2 f On Straw . 50-2

Abundant Litter 40-8 ! i5heep.| ^^ ^^^^^^ ^ ■>

Experiments of the same kind have also been
carried out on the farm of the Royal Agricultural
Society at Woburn for some years, and the results
obtained in 1899, 1900, and 1901, are given in Table LVI.

Loss
per ceut.

Horses!^" S^^^^ • 58o

Peat Moss 44-1

1 96

FARMYARD MANURE

[chap.

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VII.]

LOSS OF NITROGEN

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198

FARMYARD MANURE

[chap.

The animals were fed in deep boxes with cemented
bottoms and sides, and tlie dung was not removed
until the feeding experiment had concluded ; it was then
weighed and samples taken for analysis. The manure
was then, in the early winter, made up in a heap in the
open on ground beaten down hard and covered
thoroughly with earth. No liquid appeared to drain
away, and in the spring the heap was again weighed
and sampled before application to the land for the root
crop. Here, again, the loss of nitrogen in making the
dung under the best conditions varied from 13 to 18
per cent, while the making into a heap and storage
brought up the loss to 33-37 per cent.

Wood, at Cambridge, has also estimated the losses
involved during the making and storage of farmyard

Table LVII.— Loss of Nitrogen in making Manure (Wood).

Retained

by

Animal.

Lost.

Recovered in
Dung.

During
Making.

During

Storage.

When
Made.

After
Storage.

DRY MATTER.

Roots and Hay only
Roots and Hay with Cake

2-6
5-0

38-8
35-0

l6-2

18.6

58-6
6o-o

42-4
41-4

nitrogen.

Roots and Hay only
Roots and Hay with Cake

8-0
9-0

16-8
12-5

IO-6
26-9

75-2
78-5

64-6
51-6

manure. In his experiments four heifers were tied up
and fed, one pair on mangolds, hay, and straw alone,
the other pair on the same foods with the addition of
decorticated cotton cake. The feeding went on for

vilI

LOSSES DURING DUNG-MAKING

199

84 days in boxes with well-rammed clay floors, the
dung was not disturbed but was kept trampled down by
the animals; this is taken as the period of "making"
the dung, and at the end samples were drawn by cutting
out sections. The dung was now left without moving
for six months, May to November, and again sampled
as it was taken out — this constitutes the storage period.
Table LVII. shows the fate of 100 lb. of dry matter and
nitrogen respectively fed to the animals.

In an experiment made by Russell and Goodwin
at the Wye Agricultural College, the beasts were fed
upon roots, hay, and linseed cake, a comparison being
made between linseed cake poor and rich in oil respec-
tively. The feeding lasted for twelve weeks and the litter
was composed of a bottom layer of peat moss, to which
straw was added at the rate of 28 lb. per week. Table
LVII I. shows the results obtained.

Table LVIII.-

-Loss

OF Nitrogen

IN MAKING Manure

(Russell).

Nitrogen supplied.

Nitrogen
recovered.

Nitrogen
lost.

|3

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Lb.

Lb.

Lb.

Lb.

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Cake poor in

Oil .

43-83

11-77 4-35

3-07

28-6

20-9

7-38

14-9

2.

Cake rich in

Oil .

33-29

10-19 4-35

2-04

22-1

i6- 9

6.69

14.4

The dung was sampled immediately the experiment
was over, while the manure was still tight under the
feet of the animals ; the experiment also took place
during the winter months, yet the loss still amounted
to nearly 15 per cent, of the total nitrogen. It is note-
worthy that all the experiments quoted show practically
this same loss of 15 per cent, for the first stage of

200 FARMYARD MANURE [CHAP.

the dung-making process under the best conditions.
Not only does the loss fall upon the active compounds
of nitrogen, but a still further amount is converted
into more slowly acting bodies. For example,
in experiment i there were 43-83 lb. of digestible
nitrogen fed, of which the animal only retained 3-07 ;
the remainder, 40-76 lb., was excreted as urea, but only
28-6 lb. of ammoniacal and amide nitrogen were found
in the dung, so that besides the loss of 7-38 lb. another
4-78 lb. had been transformed into proteins and other
insoluble compounds.

It will be seen that in all cases the losses fall most
heavily on the rich dung made by animals receiving
concentrated foods ; they also fall almost entirely on
the most valuable part of the manure — the urea and
ammonia compounds arising from the digestible por-
tions of the food. It is also clear that these losses are
avoided when the food is consumed upon the land, as
by sheep folded on the arable, milch cows grazing or
beasts fattened with cake upon the summer grass.

Of course, in all these considerations no account has
been taken of such preventable losses as those which
too often occur through the escape of the liquid portions
of the manure in a leaky yard or into the drains,
or by the washing of rain through the dung heap. Such
losses are very great and fall on the most valuable
substances in the manure — the soluble ammonia and
potash compounds which occur in the liquid portion.

In order to minimise these losses of nitrogen, a
number of substances have been suggested, which, when
strewn about the cattle stalls and mixed with the fresh
dung, would either combine with the ammonia and
prevent its volatilisation, or by reducing the bacterial
actions would hinder its formation. These preserva-
tives fall into two classes : those designed merely to

VII.] PRESER VA TIVES IN D UNG-MAKING 201

fix the ammonia, and the true antiseptics which will
check the production of either ammonia or free nitro-
gen gas. Of the first class of substances, the oldest
proposal was to use gypsum, which would react with
the ammonium carbonate and form the non-volatile
ammonium sulphate.

(NH4)2C03 + CaS04, 2H2O = (NH4)2S04-l-CaC03+ 2H2O.

The drawback to the use of gypsum lies in the large
quantities that are required ; the reaction represented
by the above equation is really a reversible one, so
that only part of the ammonium carbonate is trans-
formed into sulphate, the amount being proportional
to the excess of gypsum present. As also the gypsum
is an insoluble salt, far more than the calculated quan-
tity will be required for an efficient fixation of the
ammonia. Again, the urine contains nearly all its
potash in the form of potassium carbonate, and this
also will react with gypsum, increasing the quantity
that must be used before the ammonia is fixed.

From the above equation, about 1 1 lb. of gypsum
would be required for each ton of dung, but at least
ten times as much as this would be necessary in practice,
or a hundredweight of gypsum, costing 2s. for
each ton of farmyard manure made. Besides the
question of cost, another great drawback to the use
of gypsum lies in the fact that the calcium sulphate
is itself liable to bacterial change ; during the storage
of the dung it is reduced by anaerobic bacteria to the
state of calcium sulphide, which afterwards acts injuri-
ously on plant life when the farmyard manure is
applied to the soil.

Another suggestion has been to use kainit, because
it is composed of salts of magnesium and potassium
which will to a certain extent be transformed intp

202 FARMYARD MANURE [chap.

carbonates and fix the ammonia as chloride or sulphate.
Here, again, the quantity required is very large, though
the soluble nature of the kainit enables it to be utilised
more thoroughly. But of this class of substances the
most effective is superphosphate ; the acid calcium
phosphate it contains reacts with the ammonium car-
bonate to form a double ammonium calcium salt,
insoluble indeed, but readily becoming available for
the plant. The same objections, however, apply to
superphosphate as to gypsum ; uneconomical quantities
are required if the fixation of the ammonia is to be
complete, the superphosphate itself contains gypsum
which becomes reduced to the injurious calcium sul-
phide, and again the acid superphosphate is found to
be harmful to the feet of the animals treading down
the litter among which it is strewn.

Sulphuric acid itself has been tried, as also peat
moss impregnated with small quantities of the same
acid, but neither have proved successful for the reasons
indicated above.

As to antiseptics proper, soluble fluorides and even
carbon bi-sulphide have been tried, but the saving
effected in the nitrogen is never sufficient to pay for
the cost of the material and the trouble of applying
it. Schneidewind, in the course of his experiments at
Leuchstadt, found that the only practical means of
reducing the losses of nitrogen, was to place a layer
of old well-rotted farmyard manure as a basis for the
new manure heap ; this had a distinctly beneficial effect
and always resulted in smaller losses of nitrogen,
probably because of the constant evolution of carbonic
acid from the layer of old manure.

Turning now to the composition of farmyard manure,
the average of a large number of analyses at Rotham-
sted shows that it contains about three-quarters of its

VII.] COMPOSITION OF FARMYARD MANURE 203

weight of water, about two-thirds of i per cent, of
nitrogen, one-quarter of i per cent, of phosphoric acid,
and one-third of i per cent, of potash, or per ton about
15 lb. of nitrogen, 5 lb. of phosphoric acid, and 7 lb.
of potash. The composition, however, will vary very
greatly, both with the nature and feeding of the animals,
and the treatment and storage the manure receives.

The influence of the feeding is well illustrated in
a series of analyses of two lots of dung, made in

Table LIX.— Percentage Composition of Farmyard Manure

MADE at RoTHAMSTED FROM ROOTS AND HaY ONLY, OR

FROM Roots and Hay with Cake.

;S

if

g .a

|« 5
■c a

as

II

.2 a

1904

23-6

0-577

0-046

0-067

0-464

1904

24-03

0-716

0-079

0-096

0-541

1905

29.5

0-462

0-040

0-047

0-375

1905

31-3

0-698

0-182

0-055

0-461

1906

22-0

0-466

0-022

0-033

0-411

1906

24-3

0-690

0-097

0-049

0-544

1907

25-3

0-589

0-125

0-053

0-411

1907

25-5

0-815

0-377

0033

0-405

Roots and Hay

only ,
Cake-fed

Roots and Hay

only .
Cake-fed

Roots and Hay
only . .
Cake-fed

Roots and Hay

only .
Cake-fed

(Made into
Mixen and
stored.

Do.

Do.

Not
stored.

adjoining boxes by bullocks receiving in the one case
roots and hay only, and in the other a fattening ration
of cake in addition to the roots and hay. The two lots
of dung were generally made up into separate mixens
out of doors, and sampled a month or two later, when
they were carted out to the land ; in one case they
were sampled as they left the boxes. Table LIX.
shows the analytical results, not only as regards the

204

FARMYARD MANURE

[chap.

total nitrogen, but also that present as salts of ammonia,
and as amido-compounds easily changing into ammonia
It will be seen that the cake-fed dung is always
considerably richer in nitrogen, the average percentage
being 0-73 as against 0-523, a superiority of nearly 40
per cent. Moreover, the extra nitrogen in the cake-
fed dung is mostly in the highly available forms, the
ammonia, urea, and amido-compounds which represent
the digestible nitrogen of the cake ; the insoluble nitro-
Table LX.— Crop Returns from the above Manures.

Year of
Application.

Second
Tear.

Third
Year.

Mean of 4.

Mean of 4.

Mean of 3.

Unmanured Plot ....
16 tons per acre Root and Hay Dung
16 tons per acre Cake-fed Dung

lOO
132
183

100
131
137

100
112

118

gen in the cake-fed dung is only 0-488, as against 0-415
in the dung made from roots and hay, a superiority of
less than 18 per cent. That the superiority of the
cake-fed dung as regards the soluble nitrogen com-
pounds is not even more pronounced, is due to the
change back from ammonia into proteins effected by
bacteria during storage ; in 1907, when the dung was
sampled as it left the yard, both lots contained practically
the same proportion of insoluble nitrogen, and both pos-
sessed an exceptional amount of ammonia, which, how-
ever, was three times as much in the cake-fed as in the
other manure. These differences in composition are
clearly reflected in the crops grown with equal quan-
tities of the two manures, the weights of which are
summarised and reduced to a common standard (the
yield of the unmanured plots being taken as 100) in
Table LX. The crops grown in these trials were

Vii.] VARIABLE COMPOSITION OF MANURE 205

Swedes, barley, mangolds, and wheat in rotation, and
after the two kinds of dung had been applied in a given
year, no other manure was used on those plots for the
next three years. In the first year the increase in
yield produced by the cake-fed dung was 83 per cent.,
as compared with an increase of 32 per cent, produced
by the root and hay dung ; in the following year the
residue left by the cake-fed dung produced an increase
of 37 per cent., as against 31 per cent, from the residue
of the other manure ; in the third year the increases
produced by the residues still remaining were 18 and
12 per cent, respectively. The great difference in the
value of the two manures comes in the first year, for
though the superiority of the cake-fed dung may still
be seen in the second and third year, it is almost covered
by the experimental error.

The analyses in Table LXI. show the change in
composition which results from the storage of farmyard

Table LXI. — Composition of Farmyard Manure from

VARIOUS SOURCES.

Water.

Nitrogen.

Phosphoric
Acid.

Potash.

I. Fresh long Straw

66.I7

0-544

0.318

0-673

2. No. I after rotting

75-4

0-597

0-454

0-491

3. Very old and short from a

mushroom bed .

53-14

0'8o

0-63

0-67

6. Very old J "^^^^ \

75-0

0-39

o-l8

0-45

75-0

0-50

0-26

0-53

79-0

0-58

0-30

0-50

7. Rothamsted average .

76-0

0-64

0*23

0-32

8. Fresh Liquid Manure .

98-02

0-044

0-051

0-355

9. Old

99-13

0-026

0-0x4

0-22

manure ; it will be seen that old short dung contains a
higher proportion of fertilising constituents (z>., when
reckoned in the dry matter, because the amount of
water present at any time is a matter of accident)

2o6 FARMYARD MANURE [chap.

than fresh dung, if it has been at all properly managed.
We have already seen that though considerable losses
of nitrogen take place during the rotting down of the
manure, the losses of non-nitrogenous organic matter
are greater still, so that the manure becomes concen-
trated in nitrogen and still more so in phosphoric acid
and potash. The active compounds of nitrogen, how-
ever, like ammonium carbonate, grow less as the manure
ages, since they are constantly being converted into
insoluble protein-like bodies making up the bacteria
themselves. These of course, die and decay, giving
rise again to soluble nitrogenous compounds, but the
tendency is on the whole in the other direction, so that
the older the manure the poorer it becomes in ammonia
and kindred bodies. Hence old short dung is both
slower in its action and less caustic to germinating
seedlings or the fresh delicate rootlets of tender plants ;
it can in consequence be used with more safety in the
spring in potato drills or immediately beneath the seeds
of Swedes and mangolds, particularly on a light soil. A
few analyses of liquid manure are also given, though it
is subject to such variations in the amount of rain-water
that gets mixed with it and the degree to which its
■constituents are held back by the litter, that little can
be deduced from these results as to the composition of
any other sample. It will be seen, however, that the
fertilising constituents are chiefly nitrogen and potash,
both in an active form ; hence it forms a very valuable
manure for grass land.

Table LXII. shows a series of analyses made by B.
Dyer of stable manure from London, such as is used in
very large quantities by farmers and market gardeners,
whose distance from London does not render the freight
too great. The most noticeable thing in the five last
analyses is the very low proportion of nitrogen that

VII.] COMPOSITION OF LONDON STABLE MANURE 207

remains soluble ; the frequency with which the stables
are cleaned out in London, the open nature of the
heaps, and the many turnings to which the manure is
subjected in collection and transit, all result in extreme
aeration and a rapid fermentation with a corresponding
loss of ammonia. The last three samples had been
stored for eight or nine months on the farm ; usually no
great care is taken to consolidate such heaps, so that the

Table LXIL— Composition of London Stable Manure
(B. Dyer).

Peat
Moss.

Straw.

Mixed Peat Moss and Straw.

Fresh.

After Storage.

1

2

1

2

3

Water .
Organic Matter
Nitrogen, soluble .
Nitrogen, insoluble
Phosphoric Acid ■
Potash .

77.8
i8-o
o-Si
0-37
0.37
102

70-0
24-3

O-IO

0-52
0-48
0.59

76.1

19-3
o-o8
0-46
0-33
0-45

62 -0
26.4
o-oS
0-62
0.45
0-58

53-8

17-5
0'06
0-58
0.49
0-58

6i'9
22 -o
o-o8
0.68
0-56
0.65

52-9

23-0
O-IO

0-79
0-66
o-8o

rotting down process goes on rapidly. In the above
cases Dr Dyer calculates that the loss in organic matter
had been about 40 per cent, and in nitrogen from 15
to 20 per cent, during the storage.

From a consideration of the origin of the losses of
nitrogen which take place during the making of dung,
and of the above analyses, a good deal of guidance can
be obtained as to the practical management of farmyard
manure, which remains the fundamental fertiliser in the
ordinary course of farming in this country. In the first
place, since it is clear that the most valuable part of the
manure resides in the liquid, far more care should be
taken to preserve this than is usually the case. Whether
the dung is made in boxes or in yards, there should be

2o8 FARMYARD MANURE [chap.

sufficient depth to allow the manure to accumulate
under the animal for the whole winter if need be, and
the floors should be rammed with clay to render them
water-tight. Yards, in particular, should be constructed
so that the accumulated manure is not above the general
ground line outside, in which case there will always be
a gradual soaking away of the liquid. On the other
hand, yards made thus below the general ground level
are apt to flood in heavy rain, so that the excess of
liquid containing the soluble part of the manure has to
be run off to waste by means of a drain ; this can,
however, be avoided by cutting drains outside to keep
land water from running into the yard, and by seeing
that all the surrounding sheds are properly provided
with guttering. For real economy of litter, part at least
of the yard should be covered ; if the whole yard is
covered a certain amount of care is necessary to prevent
the dung from getting at times too dry. Only just
enough litter should be used to soak up the urine, and
in order to prevent the liquid working up to the surface
with the trampling, the floor of the yard should run
down to a slight hollow, filled at first with something
stiff like bean haulm or coarse peat moss, in which the
excess of liquid may collect. Above all, the manure
should be kept tightly trampled ; the greatest amount of
loss takes place when the urine falls on a thin layer of
loose strawy litter. The yards and boxes should be
deep enough to carry the animals through the whole
winter, so that they need not be cleaned out except
when dung is wanted to go straight on the land. A
box, for example, 8 ft. by lo ft. in area, with an avail-
able depth of 3 ft. would hold about 9 cubic yards, or 8
tons of dung when well trodden down. This would
accommodate two beasts, each receiving 10 lb. of straw
in food and 12 lb. in litter per diem, for four months.

VII.] MANAGEMENT OF FARMYARD MANURE 209

As far as possible manure made in the spring should
be left undisturbed until the autumn, it may then be
carted out on to the stubbles and ploughed in where
potatoes or roots are to be taken in the following
spring. Even on the lightest soils the land will be
more benefited thus than if the manure is made up
into a mixen and only put on immediately before the
roots are grown. Sometimes, of course, a potato grower
must have a supply of well-rotted manure to put in the
drills immediately before planting ; this can often be
got from the lower layers of the earliest used boxes or
yards, since a mixen should be avoided as much as
possible. The principle to keep in mind is that every
disturbance of farmyard manure results in loss, and that
the shorter the time which elapses between the dropping
of the dung and its application to the land, the less this
loss of fertilising material will become.

In considering the value of farmyard manure as a
fertiliser one has to keep in mind that it is an essential
product of the farm, and that it must constitute the
main source of manure for the land under the conditions
of ordinary mixed farming, where artificial manures will
only be used as supplements and not as rivals. It is
only in certain special cases, such as potato or hop
growing, where the ordinary course of farming does not
supply as much farmyard manure as is wanted, that the
question has to be decided whether artificial manures
or dung from the towns shall be purchased, or again
whether stock shall be fattened solely with the view of
making manure.

As a fertiliser, the chief value of farmyard manure
lies in the fact that it contains all the elements of a
plant's nutrition — nitrogen, phosphoric acid, and potash
— though for a well-balanced manure the phosphoric
acid is comparatively deficient. Moreover, the nitrogen

O

2IO

FARMYARD MANURE

[chap.

is present in various forms of combination, varying from
the rapidly acting ammonia compounds down to some
of the undigested residues which will remain for a very
long period in the soil before becoming available for the
plant. In consequence dung is a lasting manure, which
accumulates in the soil to build up what a farmer calls
"high condition" — the state of affairs which prevails
when the reserves of manure in the soil are steadily
and continuously passing into the available condition
in sufficient amount for the needs of the crop, so that
there is no necessity for freshly applied active manure
— a state of affairs which results in healthy growth
and good quality. But however marked the farmer's
preference is for such lasting manures, the delay in
realising the capital they represent means a certain
amount of loss ; besides which, some of the constituents
of farmyard manure are so slowly acting as to be hardly
recoverable during the lifetime of the tenant. The
imperfect recovery of the nitrogen from large dressings
of farmyard manure is illustrated in Table LXIII.,

Table LXIII. — Mangolds. Relation between the Nitrogen
Recovered in Crop and that Supplied in Manure
(Rothamsted.)

Plots.

Manure.

2 "

S 0
la

Nitrogen.

cm
■" 0

S30

a

2

■2 ^ a

.9 S

Kg

4N
4A
4C
lO

Nitrate of Soda, 550 lb,
Ammoiiium Salts, 400 lb.
Rape Cake, 2000 lb.
Farmyard Manure, 14 tons

Tons.

17-95
15-12
20-95
17-44

Per
cent.
0-164

0-I45
0-1^8
0-162

Lb.

67-2
4Q-3
69-4
63-3

Lb.

86

86

98

200

Per
cent.
78-1
57-3
70-9
31-6

Vil] RECO VER V OF NITROGEN IN MANURE 1 1 1

which shows the nitrogen removed in the mangold crops
at Rothamsted when grown with farmyard manure and
other sources of nitrogen.

In this case 78 per cent, of the nitrogen applied as
nitrate of soda is recovered in the crop, and 71 per cent.
of that applied as rape cake, while only 32 per cent, of
that which was estimated to be included in the dung
has come back in the crop. This low figure is partly
due to the fact that the dung was put on year after year
in considerable quantities (14 tons per acre) ; hence all

Table LXIV.— Fate of Nitrogen in Farmyard Manure,
APPLIED TO Wheat (Rothamsted).

Plot.

Manuring.

Nitrogen in Soil

9 inches deep,

1S93.

Approximate

supply of Nitrogen

in Manure in

50 years.

Approximate re-
moval of Nitrogen
in Crops, 50 years
(1S44-1S93).

Surplus of Nitrogen
over Plot 8,

unaccounted for in
Crop or Soil.

Per cent.

Pounds
per acre.

3
2

Unmanured .
Farmyard Manure

0-0992

0-2207

2570
5150

Lb.
10,000

Lb.

850

2600

Lb.
5670

the wasteful processes are increased and there is also a
great accumulation of nitrogenous material in the soil.
How great the waste may become is seen by comparing
the nitrogen supplied to one of the permanent wheat
plots at Rothamsted, which receives 14 tons of farmyard
manure per acre every year, with the nitrogen stored up
in the soil and that removed in the crop. Table LXIV.
shows that only 26 per cent, was recovered in fifty
years, and that nearly 57 per cent, has been lost, since
it is accounted for neither in the crop nor in the soil at
the end of the period.

These, however, are extreme cases ; on referring to
the crops grown with the rich and poor dung on p. 204,

2t2 ' P ARM YARD MANURE [chap

where four crops in rotation are grown after each
application of farmyard manure, out of 207 lb. "of
nitrogen supplied as dung made from roots and hay
alone 144 lb, were recovered in the three following
years, and of 257 lb, supplied as cake-fed dung 158 lb.
were similarly recovered.

The extremely lasting character of those nitrogenous
compounds in farmyard manure which are not recovered
in the first year is illustrated in an exceptional manner
in the Rothamsted experiments. On the grass land,
for example, one plot received 14 tons of dung per
acre per annum for eight years (1856-63) and then was
left unmanured. Table LXV. shows that it has con-
tinued to give a larger crop than the unmanured plot
alongside for more than forty years. The table shows
that in the first year after the application of farmyard
manure had been stopped the plot with the residues of
the previous eight years' manuring gave double the yield
of the unmanured plot ; in the following year the yield
was still double ; but from that time its superiority has
slowly declined, though for the last ten years it has
still amounted to 1 5 per cent.

A similar experiment was made on the barley plots,
one of which received 14 tons per acre of farmyard
manure for twenty years from 1852 to 1871, and has
since been left unmanured. Table LXVI. shows the
yield from this plot, from the unmanured plot, and from
the plot which has continued to receive 14 tons of
farmyard manure every year, for the years immediately
following the discontinuance of the dung and for
successive five-year periods since. It will be seen
that though the yield has fallen continuously to about
40 per cent, of that of the continuously dunged plot,
it still remains more than double that of the wholly
unmanured plot.

ni.]

PRODUCE OF HA V PER ACRE

213

Cc!

0

z

&

0

K

Ui

m

li<

0

0!i

0

0

7.

/-\

0

-u

M

tA

C/3

H

r3

Q

^

2:

•<

Oi

f-

^— '

m

Dj

0

V,

u.

D

^

Q

M

(k:

{I.

u

0

<

05 S"

t. 0

ro

0

.a ■*

CO

u-j

0

>.3

0 rX

J Ov

0

«

0

"-^

^

m >"

M 0

.Q a>

N

0

0

>.-o

ij '^

VO

0

0

0

ss

N

N

*"*

'"'

u

^"^

C4

0

05^

>

I2

'i-

0

>>'i)

J t^

0

M

0

CO

CO

"

'^

d

0

1- I-

0
.0 M

02
<

r^

0

^3

ij t^

CO

w-i

0

of

CO

N

Q

*^

'"'

"^

D

H

13 .
0 0

05 0

00

0

0

ce«

►4 00

M

rj

0

S. '-'

c<

w

02

CO

0

0 .

>-)

J3 0^

00

00

Ck

M

0

ee»

J CO

VO

E[^

0

0

0 rl

02

w

0

N

"^

H

0

^_;^

Lb.
4804

1

Hi

0

00

8

CO 00

0
1

VO

.

VO

•

VO

IT)

00

.

<1

CO

,

in

kJ

«3 ^«

>- IJ

E^

b ?^

_>»

«

^

X^

s

>>"w

3

1^

00 TJ

0

00 -d

0

2

_ 1)

3

_ i>

3

3

a
08

3 e

.5

c

3 c

.s

S

c 2
J2 S

8

0

0

S c

-o

§ c

T)

-0 =

-0 =

t. _

3

>-> -

3

C3 -^

C

C

E

>,^

>>CO

C 00

E

c 00

rt

c

S "

B

bn

D

b.

D

^

0

N

to

«

CO

S

214

FARMYARD MANURE

[chap.

In considering the results of these last two experi-
ments, it must be remembered that such a long duration
of the residues of farmyard manure would not be per-
ceptible in practice : they only become apparent when
the soils are cropped to a state of exhaustion that would
never be met with in ordinary farming experience.

Table LXVI,— Total Produce per acre of Barley Plots,
SHOWING Residual Effects of Dung.

C3

2 .1

•gi?

►> 6

>>•-* *

fc-^-l

ofe-g

ii

Relation to Produce 1

IM r-1 £

g°

of Plot 7-2

f\

reckoned as 100.

n

2 CI

0

Q

p ^

Plot r-2.

Plot 7-1.

Plot 1-0.

Plot 7-2.

Plot 7-1.

Plot 1-0.

Mean.

Lb.

Lb.

Lb.

Lb.

Lb.

Lb.

1852-1871

5933

2454

100

41

1872

5202

4870

1282

100

94

25

1873

6561

5165

1570

100

79

24

1874

7943

5675

1922

100

71

24

1875

5825

3955

1448

100

68

25

1876

6166

4010

1561

ICO

65

25

Mean.

1877-1881

6167

3305

1528

TOO

54

25

1882-1886

6546

3494

1529

100

53

23

1887-1891

5334

2664

1379

100

50

26

1892-1896

6477

3101

1508

100

48

23

1897-1901

5349

2251

II41

100

42

21

1 902- 1 906

6223

2485

1 301

100

40

21

Since only a portion — and that not the largest — of the
nitrogen of farmyard manure is readily available, if it is
the only manure supplied the crop in a good season
is often unable to obtain nitrogen rapidly enough, even
though very large quantities are lying dormant in the
soil. As an example, we may take the Rothamsted

VII.]

SLOW AVAILABILITY OF MANURE

215

mangold crops for the years 1900 and 1907, when crops
considerably above the average were grown, and com-
pare the yields obtained when farmyard manure was
used alone, with that given by a purely artificial dressing
containing nitrate of soda and by farmyard manure
supplemented by nitrate of soda : —

Table LXVII.— Yield of Mangolds at Rothamsted, 1900 and 1907.
Roots only.

Year.

Farmyard

Manure

+PhosphoricAcid

and Potasli

= 200 lb. N.

Nitrate of Soda

+ Phosphoric Acid

and Potash

= 861b. N.

Farmyard

Manure

= :;L)0 1b. N.

+Nitrat«of Soda

= 86 lb. N.

Farmyard

Manure

= 200 lb. N.

+ Nitrate of Soda

+ Phosphoric Acid

and Potash

= 86 1b. N.

1900
1907

Tons.
28-0
26-5

Tons.

33-1
32-8

Tons.

41-3
41-4

Tons.
41-8

42-1

The farmyard manure, though it contains about 200
lb. of nitrogen, cannot provide the rapidly growing
mangolds with as much nitrogen as does the nitrate of
soda containing 86 lb. of nitrogen, since it only grew
27-2 tons of mangolds against 33 tons with nitrate of
soda, and this notwithstanding the great accumulation
in the soil of the residues of thirty years' previous
manuring with dung. That only the nitrogen was
concerned in these differences is seen from the fact
that both the plots received the same phosphoric acid
and potasK The crop had by no means reached its
limit, for an addition of nitrate of soda to the dung
increased the crop to 41-4 tons ; and here, again, only the
nitrogen is concerned, because, on a further plot where
phosphoric acid and potash were added to the combina-
tion of dung and nitrate of soda, there was but a very
slight additional increase of crop.

From other experiments it has been repeatedly

2i6 FARMYARD MANURE [chap.

demonstrated that where the grower is aiming at a very
large crop it is more economical to attain this by using
dung and a mixture of active artificial fertilisers than
by increasing the amount of dung ; 20 loads of dung,
with I to 2 cwt. of nitrate of soda and 3 cwt, of super-
phosphate costing about 30s., will generally be more
effective than 40 loads of dung, of which the second 20
loads cannot be charged at less than £a^ or £^.

Farmyard manure has frequently been blamed for
carrying the seeds of disease and of weeds which have
passed through the animals making the dung in an
unchanged condition and thus contaminate the land for
other crops. When bullocks have been fed with Swedes
affected with " finger-and-toe " and the uneaten frag-
ments of the roots have been thrown among the litter,
the spores of the disease have been found to live un-
harmed through the making and rotting of the manure,
so that fresh land may thus become infected when the
dung is carried on to it. Similarly, when hop bines are
used as litter, the spores of the hop mildew are not
destroyed ; but no other cases of transmission of disease
have been investigated. As regards weeds, farmyard
manure is very commonly employed for root crops, in
which case the usual cultivations will keep down any
weeds whose seeds are in the dung, and when the dung
is put on grass land the weed seeds stand little chance
of establishing themselves.

The value of farmyard manure to the land is by
no means confined to its fertilising action ; its physical
effects upon the texture and water-holding powers of
the soil are equally important ; indeed, for some crops,
and particularly in droughty seasons, these factors
count for more than fertilisers towards ensuring a good
yield. The farmyard manure, as it rots down in the
soil, goes to restore the stock of humus, which otherwise

VII.] PHYSICAL EFFECTS OF MANURE 217

is always tending to oxidise and diminish, and the
humus, considered merely from the physical side,
contributes largely to the fertility of the soil. In the
first place, it improves the texture of all soils ; to sands
it gives cohesion and water-retaining power, while by
loosely binding together the finest particles of clay soils
it renders them more porous and friable. When a piece
of old grass land, even on the stiffest of soils, has been
ploughed up it is easy to see the beneficial effect of
the humus that has been accumulated ; after the winter
the plough slice will crumble naturally so as to harrow
down at once to a mellow seed-bed, whereas a neigh-
bouring piece of the same soil that has long been under
arable cultivation will only show a number of harsh
intractable clods. The importance of a good seed-bed
to the future well-being and ultimate yield of the crop
can hardly be exaggerated ; it is the basis of all good
farming ; so that even when the fertilising properties of
farmyard manure have been replaced by artificial
manures, some other means, such as the ploughing-in
of green crops, must be resorted to in order to maintain
the stock of humus. Of course, the value of humus —
and in this respect of farmyard manure — will vary on
different soils and with different crops ; cereals, for
example, are comparatively unaffected by its absence,
as may be seen by the manner in which Mr Prout
grows cereals almost continuously on his strong soil
with artificial fertilisers only, but root crops are very
dependent on a mellow seed-bed. This may be seen on
the Rothamsted plots ; the wheat which has now been
grown on the same land for sixty-five years, comes as
well and yields as big crops on the plots receiving only
artificial manures as it does on the plot receiving dung,
but on the mangold field the result is different. Where
artificial manures containing no organic matter have

2i8 ^ FARMYARD MANURE [chap.

been supplied, the tilth is bad, and in trying seasons,
when drought succeeds heavy rain soon after sowing,
the plant obtained is so imperfect as to reduce the yield
considerably. If the conditions are favourable to
germination and the plant once becomes established,
then, as we have previously seen in Table LXVII., the
plot manured with minerals and nitrate of soda will
grow a bigger crop than that receiving dung ; but this
superiority is masked in many seasons by the defective
plant resulting from the bad texture of the soil. Table
LXVII I. shows the proportion the number of roots on
each plot bears to the possible number, as calculated

Table LXVII I.— Number of Mangold Plants as Percentages of
THE Possible. Average of 7 years, 1901-1907.

Farmyard
Manure, etc.

Mii:erals and
Nitrate of Soda.

Minerals and
Rape Cake.

69

62

83

from the width of the rows and the distance apart at
which they are singled, for three plots, one of which
receives farmyard manure, minerals and nitrate of soda,
another only the minerals and nitrate of soda, and the
third, minerals and rape cake, as an organic source of
nitrogen.

These are average figures for a period which includes
several years when a very good plant was obtained all
over the field, and only one of the occasional years
when the plant failed entirely on the plots receiving no
organic manure. It is noticeable that the plot receiving
rape cake (2000 lb. every year) is actually better as
regards the number of plants it carries than the dunged
plot, because the repeated dressings of an organic
manure like rape cake supply enough humus to maintain

VII.]

PH YSICAL EFFECTS OF MANURE

219

the texture without getting the soil too open — a defect
which is now beginning to overtake the plot that has
been so continuously treated with large amounts of
farmyard manure.

A soil which has been enriched in humus by
repeated applications of farmyard manure will resist
drought better than one in which the humus is low ;
the difference is seen, not so much in the greater amount
of moisture present in the soil containing humus, as
in the way it will absorb a large amount of water

Table LXIX. — Percentages of Water in Rothamsted Soils.

Depth.

Broadbalk Wheat.

H008 Barley.

Unmanured.

Dunged.

Unmanured.

Dunged.

Inches.

0 to 9

9 ., 18
18 „ 27

i6'0
19-8
23.3

19-3
I7-0
18-4

I7-0
22-5
22-1

20-7

17-7
18.3

temporarily during heavy rainfall and then let it work
more slowly down into the soil, thus keeping it longer
within reach of the crop. Good examples are afforded
by the Rothamsted plots ; samples of soil were taken
from the wheat land on 13th September 1904; on
the previous day 0-262 inch of rain had fallen, but
for nine days before there had been little or no rain.
The portions of the plots from which the samples were
drawn had been fallowed through the summer, so that
the drying effect of the crop is eliminated. Samples
were also taken from the barley plots on 3rd October
of the same year; 0-456 inch of rain had fallen on the
30th September, before which there had been fifteen
days of fine weather. Table LXIX. shows the water
in the soil of the unmanured and the continuously

220 FARMYARD MANURE [chap.

dunged plots respectively, calculated as percentages of
the fine earth from which the stones had been sifted.

It is thus seen that in both cases the dunged soil,
rich in humus, had retained more of the comparatively-
recent rainfall near the surface, so that the top soil was
moister, while the subsoil was drier. The difference in
favour of the surface soil is about 3- 5 per cent, which
on that soil would amount to about 30 tons per acre, or
approximately 0-3 inch of rain. It is thus seen that
the surface soil of the dunged plot had retained
practically the whole of the preceding rainfall : and the
greater dryness of the subsoil is due to the way the
soil has kept back the small rainfalls, which have
evaporated instead of being passed on to the subsoil, as
happens on the unmanured plots. The same fact is
illustrated by the behaviour of the drains, which lie
below the centre of each of the wheat plots at a depth
of 30 inches ; below the dunged plot the drain very
rarely runs — only after an exceptionally heavy and
long-continued fall ; whereas the drain below the
unmanured plot runs two or three times every winter.
Putting aside the greater drying effect of the much
larger crop on the dunged plot, the difference is mainly
due to the way the surface soil rich in humus absorbs
more of the water at first, and then lets the excess
percolate so much more slowly that the descending
layer of over-saturation, which causes the drain to run,
rarely or never forms.

The water-retaining power of the dung may also be
seen in the superior yield of the dunged plots in
markedly dry seasons. Table LXX. shows a com-
parison of the yield on Plot 2, receiving 14 tons of
dung, and Plot 7, receiving a complete artificial manure,
for the years 1879, which was exceptionally wet and
cold, and for 1893, which was hot and dry throughout

VII.J

PHYSICAL EFFECTS OF MANURE

221

the growing period of the plant. The rainfall for
this period, ?>., for the four months March to June,
was 13 inches in 1879 and only 2-9 inches in 1893.
The average yield on the dunged plot is about
3 bushels more than on Plot 7, but in the dry year its
superiority amounted to 14 bushels, whereas in the very

Table LXX.— Effect of Farmyard Manure in Dry and Wet
Seasons. Wheat. (Rothamsted.)

Plot.

1879
(Wet).

1S93
(Dry).

Average,
51 years.

2

7

Bushels.
16-0
16-25

Bushels.

34-25
20-25

Bushels.

35-7
32-9

wet year the two plots sank to the same low level. In a
bad season the bacterial changes, which render the plant
food in dung available for the crop, go on very slowly.

It has been suggested that farmyard manure may
have an effect upon the water-content of the soil by
reducing the surface tension of water with which
it comes in contact. If the surface tension of the
soil water were thus reduced, it would be less readily
lifted to the surface and therefore less available to
shallow-rooted plants, but more conserved in the lower
layers of the soil. Although an extract of dung
possesses a lower surface tension than pure water, the
facts concerning its behaviour in the soil are very
obscure as yet, and the figures just quoted as to the
relative distribution of moisture under dunged and
unmanured plots lend no support to the theory.

The application of farmyard manure to grass land,
not only has a fertilising and water-retaining effect, but
is also valuable from the way it acts as a mulch and
affords the springing grass in the early months of the

22i FARMYARD MANURE [chap.

year some protection from cold and drying winds. At
Rothamsted on the permanent grass plots it is often
noticed that the plots which receive applications of
farmyard manure once in every four years start a little
earlier and make a quicker growth than the others.
This mulching effect partly accounts. for the great value
attached to dung as a dressing for permanent grass
land on open chalky soils, as in Wiltshire, where
it is customary to reserve all the farmyard manure
for the grass and farm the arable land entirely with
artificial manures, aided by the folding off of catch
crops. Such a practice is wasteful of the farmyard
manure as a fertiliser, for the loss of nitrogen from
a layer spread loosely over the ground until it decays is
considerable, but the waste is tolerated in view of the
gain to the physical or mechanical condition of the
land.

In ordinary mixed farming undoubtedly the best
way of utilising farmyard manure is to apply it to the
root crops, and especially to mangolds and potatoes.
Swedes require much less nitrogen than do the other
root crops. They also require a firm but fine tilth ; in
consequence, not more than lo to 12 tons of dung
per acre should be given for Swedes and it should be
applied in the autumn, in order that it may become
well rotted down before the spring cultivation begins.
But up to 20 tons of dung per acre can be profitably
employed for mangolds and potatoes, and it can if
necessary be applied immediately before sowing. Any
surplus dung, after the requirements of the root crops
have been satisfied, is probably best given to the young
seeds in the early winter, to act both as a fertiliser
and as a mulch. The seeds benefit greatly, and at the
same time much of the added fertility is retained for
the corn crop that follows ; manuring the young seeds

VII.] COST OF FARMYARD MANURE 223

is certainly preferable to the very general custom of
manuring the old ley before it is ploughed up for wheat
or oats. A certain amount of the farmyard manure
made on the farm should, however, always be reserved
for the meadow land, especially on light soils and on
land comparatively newly laid down to grass. Of
course dung would be wasted on rich grazing land ; it
is the thin light soils that are cut for hay, or grass land
that has only been laid down for a few years and
has had no time to accumulate a stock of humus,
which are most benefited by an occasional dressing
of farmyard manure — once in every four or five
years.

What price should be set! upon a ton of farmyard
manure is a question often asked, but no general answer
is possible, so much depends upon the other conditions
prevailing upon the farm. As a rule, farmyard manure
is part of the normal output of the farm ; the farmer has
only to make it and use it to the best advantage, he
is not concerned with the question of whether it would
be cheaper to replace it with an equivalent amount of
some other fertiliser. There are, however, occasions
when the problem does arise of whether it is cheaper
to make farmyard manure, to buy it, or to attempt
to replace it by artificials ; for example, the men who
are farming specially for potatoes or hops often fatten
bullocks or pigs solely for the sake of the manure thus
made, and are content to lose money on the live stock
because of the value of the dung. Since farmyard
manure made in this way is often a very expensive
Particle, it is important to try and put some monetary
value on it, so that the farmer may attain a clearer idea
of the profit or loss attached to the keeping of live
stock as manure makers. It is, of course, possible to
treat farmyard manure like any other fertiliser and

224 FARMYARD MANURE [chap.

value it on the unit system (see p. 348), the result of
which would be somewhat as follows : —
Farmyard manure contains —

0'6 per cent. Nitrogen at 12s. . ,= £072,

0-3 per cent. Phosphoric Acid at 3s. . = o oil

0-5 per cent. Potash at 4s. . . = 020

Value per ton . = ;^o 10 i

Much weight cannot, however, be attached to such a
valuation, because the unit values are taken from con-
centrated manures and do not apply to dung ; for
example, nitrogen in waste materials like shoddy can
often be obtained at half the price paid for it in
sulphate of ammonia or nitrate of soda, and considering
the slow availability of much of the nitrogen in dung its
unit value should be much below 12s. On the other hand,
the organic matter supplied in the farmyard manure is
not valued ; yet it is for the effect of this organic matter
on the texture of the soil that farmyard manure is most
generally required. The cost of handling farmyard
manure, which is so much greater than it is for an
equivalent amount of artificial fertiliser, should also be
taken into comparison but cannot well be estimated,
because it will vary on each farm.

While it is thus practically impossible to value farm-
yard manure on its composition, a proper system of
book-keeping will show what it costs to make, in a
manner that is independent of the profit and loss
upon the live stock. In this way a farmer can form
for himself a clear idea of the economics of dung-making
as compared with the purchase of either town manure or
artificial fertilisers. The most valid principle on which
a cost can be worked out, and one which does justice
equally to the live stock and to the manure, is to

VII.] COST OF FARMYARD MANURE 42$

charge the dung with the cost of the Htter and with
the manure value of all the foods consumed in the
yards or boxes. These manure values are what the
valuer would allow to an outgoing tenant for the
fertilising material which he brought on to the farm
during the last year of his tenancy and which he leaves
behind in the form of dung. Of course the valuer
does not allow compensation for the roots, hay, and
straw grown on the farm ; these, however, must be
reckoned in making up the cost of the dung.

The manure value of any food (see p. 356) is based
upon its composition and represents the value at current
market rates of whatever part of the food has a fertilis-
ing value and may be supposed to find its way into the
manure ; the values employed below are those recom-
mended by the Central Chamber of Agriculture for
adoption in farm valuations and have been obtained by
the method to be shortly described. To arrive at the
cost of the dung the manure values of all the food con-
sumed must be taken and added to the whole cost of
the litter, whether straw or peat moss ; the sum is then
divided by the amount of manure ascertained to have
been made. In Table LXXI. this principle is applied to
the data obtained from some of the feeding experiments
already quoted (pp. 196-9), and also to two cases extracted
from the accounts of an ordinary farm. The first
column gives the nature of the food and the second its
manure value per ton ; the remaining double columns
give for each food the amount consumed in the experi-
ment and its manure value. The cost of the litter is
set out below, and, added to the manure values, gives
the total cost of the manure made in each case, the
amount of which is also shown. Working on these
lines we learn that farmyard manure costs from 5s. to
I2S. a ton to make on the farm, without taking into

P

226

FARMYARD MANURE

[chap.

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Total cost

Quantity dung made
Cost oer ton

Foods.

Peas

Mangolds
Swedes .
Decorticated

li

cotton cake .
Linseed cake .
Oats

Barley .
Maize meal ,
Bran
Straw
Hay
Litter :—

& •

in 0

<D 4->

Vii.l COST OF FARMYARD MANURE 227

account any profit or loss on the live stock, because
this latter question is so much dependent upon the turn
of the market and the skill of the dealer. It is neces-
sary to discriminate and to keep distinct the two
operations — the making of dung and the fattening of
the cattle — so that a conclusion can be reached as to the
profitableness of each separately. Of course in making
out the charges against the cattle, the whole cost of
the cake, etc, which they consume must not be put down,
but only that part of it which is not debited to the dung
as manure value ; e.g., if a ton of linseed cake cost £^^
only £6, 2s. should be charged against the stock for
food, because £i, i8s., its manure value, would be
charged to the manure.

To make this clearer, we can draw up a balance-
sheet for the feeding of two of the heifers already
mentioned : —

Table LXXfl.— Cambridge, No. 2.

Dr.

Purchase price of 2 Heifers 30 o

6 tons of Mangolds at 5s. .

\ ton of Hay at 45s.

6 cwts. of Decorticated

Cotton Cake at £^
Attendance, 12 weeks at

6d

Balance, being profit

Total

£ S. D.

Cr. & s.

D.

30 0 0

Manurevalue of Mangolds 015

0

I 10 0

I 2 6

11 Hay . 0 7
„ Cake . 0 16

6
10

280

(Charged to Dung)
Sale price of Heifers . 34 0

0

060

0 12 10

35 19 4

Total . . 35 19

4

Thus the feeding has resulted in a small profit of
1 2s. lod., and at the same time, as was shown in Table
LXXI., 5 J tons of farmyard manure were made at a cost
of I IS. 8d. per ton, or if the heifers are considered to have
been fattened solely for the purposes of making dung
and the two accounts are combined by crediting the
I2S. lod. profit to the dung, the latter has cost about
9s. 4d. per ton,

228 FARMYARD MANURE [chap. vii.

This figure, about los. per ton for farmyard manure,
is considerably higher than the usual estimate attached
to dung for purposes of valuation or of drawing up the
the balance-sheet of a manurial experiment ; it does,
however, represent what it will cost the potato or hop
grower who sets out to keep cattle solely for the purpose
of making dung. It is for him to decide whether he can
secure sufficient profit from the cattle themselves to
make it worth while to buy farmyard manure at such
a price. A big cake bill is indeed a great source of loss
on many farms ; unless the cattle themselves pay for
their food, the increased richness of the dung due to the
purchased food will not produce a very remunerative
increase in the crops.

CHAPTER VIII

PERUVIAN GUANO AND OTHER MIXED
FERTILISERS

Origin of the Deposits of Guano — Variation in Composition with
Age — Compounds of Nitrogen present in Peruvian Guano
— Ichaboe and Damaraland Guanos — Fish Guano — Meat
Guano — Dried Blood — Greaves — Rape Dust and other Cake
Residues— Manures derived from Faecal Matter— Sewage
Sludges.

The term "guano" (Spanish kuano = dung) is properly
restricted to a fertilising material consisting almost
wholly of the excreta of sea birds, which has accumu-
lated upon certain oceanic islands where rain rarely
falls. The original guano came from islands off the
coast of Peru between the 7th and 20th degrees of
south latitude, and this "Peruvian Guano" still forms
the bulk of our importations, although since the time
of the first introduction of guano, other deposits, formed
under similar conditions of climate and situation, have
been opened up. All these deposits, being of similar
origin, possess many features in common. The islands,
small and uninhabited, are the resort for breeding
purposes of enormous ilocks of pelicans, albatrosses, and
other oceanic birds, which resort to land only in their
breeding season. On the favoured spots they nest very
closely, and the young birds after they are hatched are
fed for a month or more with great quantities of fish

2^9

230

PERUVIAN GUANO, ETC.

[chap

brought by the parent birds. In addition to the excreta
the deposit will thus also contain many carcases of
young birds dying from some cause or other, fragments
of fish, feathers, seaweed, and even sand and stones
originally swallowed by the parent birds. When the
birds leave the island the tropical sun and the intense
dryness of the atmosphere rapidly desiccate the
accumulated materials and prevent any change or loss
by fermentation.

The excreta of the birds, which is the starting-point,
is highly nitrogenous, consisting very largely of uric
acid, together with a fair amount of phosphoric acid
derived from the fish, which is the exclusive diet of the
birds. An old analysis of a white Peruvian deposit,
consisting mainly of recently deposited excreta, showed
as much as 18-3 per cent, of nitrogen and only 9-2 per
cent, of phosphoric acid.

Table LXXIII. — Analysis of Freshly-deposited Guano.

Water

Organic Matter and Ammonium Salts
Containing Nitrogen .
Phosphoric Acid ....

Lime . . ....

Alkaline Salts ....

Sand

10-9
65-63
(18-32)
9-20
6 -08
6-43
1.76

Dry as is the climate a certain amount of change
still goes on ; the uric acid is fermented to urea and to
ammonium salts, some of which are volatilised, while
the occasional rains dissolve out both the ammonium
compounds and soluble phosphates and the alkalis. As
a result, the composition of guano deposits is extremely
variable, both in the different strata of one deposit
and still more in passing from island to island. The
older a deposit is, and the greater the washing it has

VIII.] IMPORTATIONS OF GUANO 231

received, the more will it have lost nitrogen and the
richer will it have grown in phosphoric acid, until from
the material described above deposits are formed con-
taining little or nothing beyond phosphate of lime.

The analyses (Table LXXVII.) will show how great
is the range in quality that thus results.

Peruvian Guano. — Peruvian guano is derived from
three groups of islands off the coast of Peru, of which
the most important, Chinchas, is a little south of Callao.
The fertilising value of the deposit was known long
prior to the Spanish occupation of the country, in many
parts of which crops could only be obtained by the aid
of guano.

A. von Humboldt was the first European to call
attention to the use of guano ; he brought samples
home with him about 1804, at which time he found
some fifty vessels annually employed in carrying guano
from the Chinchas Islands for use in Peru.

The exportation to Europe, however, did not begin
until nearly forty years later, the first crops being landed
in Liverpool early in 1840. The success of the manure
was rapid and the exportation soon assumed consider-
able dimensions, as much as 283,300 tons reaching the
United Kingdom in 1845. For some time the annual
consumption remained at a very high figure, but
financial troubles, the war between Peru and Chili, the
exhaustion of the richest deposits, and difficulties
induced by adulteration and the natural variation in the
composition of the cargoes, led to a slackening in the
demand. During the last few years the exportation
has been at the rate of about 60,000 to 70,000 tons per
annum, of which the United Kingdom consumed about
one-half.

During the earlier years Peruvian guano was derived
from the Chinchas Islands only, and was an exceedingly

232 PERUVIAN GUANO, ETC. [chap.

rich deposit, containing 1 1 to 15 per cent, of nitrogen ;
but as that deposit became exhausted, the other islands
producing a poorer material were in turn drawn upon.
Of recent years it has been found that new deposits have
accumulated on the Chinchas Islands to such an extent as
to justify fresh workings, and accordingly a guano with
a very high percentage of nitrogen is again obtainable.
Another of the islands, Ballestas, has latterly been
yielding a very rich guano with more than 12 per
cent, of nitrogen and about an equal amount of
phosphoric acid, and now it is expected that material
of this class will always be available.

It is difficult to form an adequate idea of the
enormous bird population of these islands and the
amount of food consumed during the breeding season, but
a recent commission which visited the islands estimated
the current production of fresh guano as 10,000 tons per
annum. Thus, freshly deposited guano is light grey in
colour and contains about 16 per cent, of nitrogen, with
9 of phosphoric acid, the usual brown colour coming as
the material ages and undergoes some decomposition.
A law has been recently passed ensuring a four-
months close season during the breeding of the birds,
and the Peruvian Government have recently forbidden
the working of the deposits during this close season in
order to ensure as little disturbance as possible. The
guano islands are now, in fact, being regularly " farmed,"
and the exportations will consist of the previous years'
rich deposit, together with a certain amount of the older
accumulated stock.

The bulk of the imports, however, consists of
material containing from 5 to 8 per cent, of nitrogen,
and each consignment is sold on the basis of an analysis
of a sample drawn by the officials of the Dock Company
as the vessel unloads. Another class of material has

VIII.] COMPOSITION OF PERUVIAN GUANO

233

latterly been exported in large quantities ; it consists
of the phosphatic guanos derived from the Lobos
Islands, containing as much as 60 per cent, of calcium
phosphate and only from 2 to 3 per cent, of nitrogen.
In addition to these cargoes of varying composition
which are sold in the condition in which they arrive,
the importers make up a mixture to a standard com-
position with about 7 per cent, of nitrogen, which is
sold as equalised Peruvian guano.

Peruvian guano, as imported, is a loose dry powder,
grey in the richer samples and becoming browner as it
grows more phosphatic. As a rule, it is friable and
may be sown by any manure distributor, but there
are found in it occasional fragments of slaty rock,
with a number of half-decayed feathers in the richer
specimens. It possesses a strong and characteristically
ammoniacal smell and an alkaline reaction due to the
presence of ammonium carbonate.

The following detailed analysis, Table LXXIV.,

Table LXXIV.— Analysis of Chinchas Guano,

1897.

Nitrogen as Nitrate

0-32

„ as Ammonium Salts , .

3-94

„ as Uric Acid

8-85

„ in other Organic Forms . t

2-98

Total Nitrogen

16.09

Phosphoric Acid soluble in Water .

2-63

„ soluble in Ammonium Citrate

6-29

„ insoluble „

•37

Total Phosphoric Acid, all soluble in I per cent.

Citric Acid solution

9-29

equivalent to Tri-calcium Phosphate .

20-28

shows the composition of a sample of the Chinchas
deposit ; it will be seen that the nitrogen is mainly
present in compounds soluble in water — uric acid, a
little urea, guanine, and ammonium salts, with a trace
of nitric acid. The phosphoric acid is also largely

234 PERUVIAN GUANO, ETC. [chap.

soluble in water, being combined with the ammonia
and the potash and soda also present in small
quantities.

Similar detailed analyses are not available for
poorer grades, but it may be taken as a general
rule that the lower the percentage of nitrogen, the
less of it will be found in a soluble form, and the
more insoluble will the phosphoric acid compounds
have become, so that the richest guanos are also
the most readily available for the plant. It is also
characteristic of a good guano, and to this much of its
value as a choice fertiliser is due, that the compounds
of nitrogen present are very varied and require differ-
ent series of bacterial changes in the soil before they
become available, so that the crop is fed steadily and
continuously.

It is this property and the fact that guano is naturally
a well-balanced manure, rich in phosphates as well as
nitrogen, and containing also a small proportion of
potash, which makes guano so popular. It is essentially
a safe manure, applicable to all crops, and not requiring
the skill in its adjustment to the land or the crop which
is necessary with the more active single manures like
nitrate of soda, etc. Again, coming into action con-
tinuously and equably, it is more calculated to yield
produce of high quality than more concentrated
manures ; it is therefore specially suited for fruit and
similar valuable crops. As a natural consequence of
these advantages the good Peruvian guanos are always
somewhat dearer than other manures when valued on
a unit basis, the extra price representing partly the
value of this natural blending and partly the long
farming tradition of the excellence of guano, which was
the earliest of the concentrated manures to find a large
sale in this country.

VIII.] ADULTERATIONS OF GUANO 235

Few fertilisers have been subjected to a greater
amount of sophistication and adulteration than has
Peruvian guano, but since the passing of the Fertilisers
and Feeding Stuffs Act, and the better organisation
of its sale from a single distributing centre, there
has been but little fraud. It should always be found
on receipt to be in the sealed bags of i^- cwt. in which
it is distributed, and, as with all manures of variable
composition, the guarantee should be checked by
analysis, so as to ensure the delivery has been made
from the specified cargo. Deliberate adulterations with
sand or dirt can generally be detected by the incinera-
tion of a sample, the incombustible residue should be
white, and show but few signs of red oxide of iron.

A certain arnount of Peruvian guano is treated with
sulphuric acid, so as to convert the ammonium carbonate
into non-volatile ammonium sulphate, and also to render
a larger proportion of the phosphoric acid soluble. In
this way is obtained " dissolved Peruvian guano," which
is made to contain about 6 per cent of nitrogen and 10
per cent, of phosphoric acid, of which 9 per cent, is
soluble in water. The use of acid adds to the value
of the guano, and not only will it store and travel
with less risk of deterioration through volatilisation of
ammonium carbonate, but the increased solubility of the
phosphates present, and their consequent activity, makes
the whole a better balanced manure.

Compared with the Peruvian, the other deposits of
guano which can be classed as nitrogenous are com-
paratively unimportant, and only those from Ichaboe
Island and Damaraland on the south-west coast of
Africa have of late been articles of commerce in this
country.

The Damaraland deposits are apparently exhausted,
while shipments of Ichaboe guano only come inter-

236 PERUVIAN GUANO, ETC. [chap.

mittently, when the requirements of Cape Colony
have been satisfied.

Ichaboe guano only represents the deposit of a
single year, it is thus very fresh and distinguished by
the undecomposed feathers it contains. With about 8
per cent, of nitrogen, it is usually proportionally less
rich in phosphoric acid than a similar grade of Peruvian
guano would be. It usually also contains more sand.

On the many other oceanic islands where guano has
been deposited, the occasional rains or heavy dews have
been sufficient to remove the soluble nitrogen com-
pounds and even in time the organic nitrogen bodies,
which in the presence of moisture have been able to
decay and break down into soluble material, leaving
behind a residue consisting mainly of phosphate of
lime. In other cases chemical reactions have taken
place with the calcium carbonate of the coral rock on
which the deposit happened to be formed, resulting in
the production of a calcium phosphate, containing some-
times rather a large proportion of iron and alumina.
These phosphates, at one time of importance in the
manufacture of superphosphates, will be dealt with
under phosphatic manures.

Besides the true guanos derived from bird drop-
pings and the closely allied bat guanos, small deposits
of which are found in caves in America and South
Africa but which possess no commercial importance, a
good many other substances containing nitrogen and
phosphoric acid are called guano, though they have no
proper claim to the title. For example, the residues
from various processes dealing with fish {e.g., in the
preparation of cod liver oil, the curing of herrings, the
tinning of sardines, etc.), are dried and reduced to a
powder, which is sold as " fish guano " ; and again, meat
residues, such as accumulate in the manufacture of meat

VIII.] PISH GUANO 111

extracts, are similarly dried and disintegrated for sale
as " meat guano " ; even some forms of dried sewage
sludge masquerade under the name of guano.

Fish guano is manufactured in many places where
any considerable fish waste is available. The oil is
extracted by heat and pressure, and the remaining
material is dried and disintegrated as finely as possible.
Considering the very varied origin of fish guano, its
composition is remarkably constant : the nitrogen
varies between 6 and 9 per cent, the phosphoric acid
represents from 13 to 20 per cent, of tri-calcic phos-
phate. The fineness of grinding is less uniform ; two
classes of fish guano are found : in one of them the
material is reduced to a light fluffy powder, the other
is denser and contains pieces of hard bone up to a
quarter of an inch in diameter. This coarsely ground
material must be less available, at any rate as regards
the phosphates. Fish guanos generally contain a
distinct amount of oil which has not been removed
in the manufacture ; it has been suggested that more
than 3 per cent, should be regarded as detrimental
to the value, but this opinion — that the presence of oil
delays the decomposition of such manures — has really
never been demonstrated.

Fish guano is a comparatively active nitrogenous
manure, since some of the compounds it contains are
soluble in water and are rapidly decomposed by bac-
teria ; the main constituents are, however, proteins and
gelatinoids which resist attack to a greater or less
degree. In consequence fish guano shares with the
true guanos the property of continuing to yield
nitrogen available to the plant throughout the whole
growing season, though the range of compounds in fish
guano must be regarded as a little less active than
those in Peruvian guano. Fish guano has for many

238 PERUVIAN GUANO, ETC. [chap.

years been a favourite manure among hop growers ;
it is also occasionally used for root crops when farm-
yard manure is not available. It should be applied
early in the year, when the land is first worked, and
it should be dug or ploughed into the land as soon as
sown, otherwise rooks and other birds will eat it as
long as they are allowed to do so. Like all manures
of this class, it is injurious to germinating seeds or the
tender rootlets of growing plants, until it has been in
the soil for a short time and the first active fermenta-
tion is over.

Meat guano is prepared from all kinds of slaughter-
house refuse in much the same way as fish guano — the
waste of carcases, condemned imported meat, tallow
boilers refuse, the residues obtained in making meat
extracts, and so forth, are heated and pressed to
remove fat, and the residue is then finely ground.
Material of this class, though more often after treatment
with acid or other admixture, is known in America
as " tankage." In some cases a good deal of bone is
mixed with the material before grinding, and the
resulting " guano " approximates to bone meal ; in other
cases the nitrogenous material predominates. Thus
the nitrogen may be as high as 12-13 per cent., in
which case there is little or no phosphate of lime
present; whereas at the other end of the scale come
mixtures with 4 to 5 per cent, of nitrogen and 35 to 40
per cent, of phosphate of lime. A good representative
example, manufactured by the Liebeg Company under
the name of Fray Bentos Guano, contained 7 per cent,
of nitrogen and 30 per cent, of phosphate of lime, all
in a fine friable condition, dry, and suitable for sowing.

In its action and uses meat is very similar to fish
guano, and all that has been said about the time and
manner of application of the one, equally applies to

VIII.] MEAT RESIDUES 239

the other. On the whole, the hop growers appear to
prefer fish to meat guano, but this is probably only
due to the greater regularity of the supply of fish guano
and its more uniform composition. There is no evi-
dence of the relative superiority of one over the other
which should deter anyone from buying whichever of
the two shows the lower price per unit of nitrogen and
phosphoric acid. The price of the better grades of
meat guano is raised to a certain extent by the fact
that it can also be used as a cattle, and especially as
a poultry food, in which case the nitrogen compounds
always command a higher price than when they can
only be employed as manure.

As with fish guano, meat guano should be ploughed
in pretty quickly after it is sown ; birds find both
manures very palatable, and the rooks in particular will
carry off large amounts if left on the surface.

Drkd blood is a product of the slaughter-houses,
which in its origin is closely allied to the meat guanos,
differing from them in the absence of bone and in
the nature of the proteins supplying the nitrogen. As
will be seen from its analysis, it is a rich fertiliser and
a very active one, because of the readiness with which
its nitrogen compounds are broken down into ammonia.

Dried blood, however, comes but little on the
market and is rarely purchased by the farmer. The
total production is small and it is practically all taken
up by the manure manufacturers, who, because of its
richness in organic nitrogen and its good mechanical
texture, find it valuable for mixing with other manures,
when it is desired to raise the percentage of nitrogen
in a compound manure.

Greaves may be regarded as a low grade of meat
guano ; properly speaking it is the waste from tallow-
making, and consists of the scraps of cartilage and bone

246 PEkUVlAN GUANO, ETC. [cHAP.

which remain after the fat has been melted down and
expressed as far as possible. The resulting waste
material is still very fatty, and contains anything from
1-5 up to 6 per cent, or even more of nitrogen, with
phosphates varying from 5 to I2 per cent, of phos-
phate of lime. As a rule, the mechanical condition of
greaves is bad and much against its proper distribution
in the soil ; the price is also often higher than its
nitrogen content would warrant, because reasonably
clean samples can be used as poultry food. The
amount of fat present is again possibly detrimental to
its availability. Since greaves is extremely variable
in its composition, according to the kind of material
which happens to be treated at the factory from day
to day, it is difficult to buy any large bulk on a
guarantee, just as is the case with shoddy. It is
difficult also to judge a consignment from a small
sample, so that, as with shoddy, it is best to fix the
price on the agreed unit value for nitrogen, taking the
mean of several analyses from the bulk.

Rape dust and other cake residues. — In the manu-
facture of oil cake the oil-bearing seeds are subjected
to great hydraulic pressure, either in bags or in metallic
moulds which permit of the escape of the oil. The
pressure is increased, aided sometimes by a little heat,
until as much oil as possible has been obtained, there
being left behind a cake consisting of the other parts
of the seed, the proteins, carbohydrates, fibre, etc.,
together with a certain amount of oil which cannot
be expressed. The remaining cake is usually a valu-
able cattle food and is sold as such. In crushing
rape seed, however, the resulting cake is apt to be
very impure ; rape seed not only contains a large
proportion of impurities, but often also a good deal
of wild mustard seed, from which, when the cake is

VIII.] RAPE DUST 241

used as food, mustard oil is generated in the stomach
to a dangerous extent. It thus becomes the custom
only to use the purer grades of rape cake for cattle
feeding ; in the other cases the cake is ground to
powder and sold for manure. More recently a method
of extracting the ground rape seed with carbon
bisulphide, in which the oil is soluble and can be
recovered by distilling off the solvent, has been gener-
ally adopted, because the whole of the oil in the seed
is obtained in this way. The residue, which is really
improved by the complete removal of the oil, is only
used for manure.

Rape dust, as the ground rape cake is termed, has
long been valued as a manure; William Ellis in 1735
speaks of oil cake with approval as one of the Hertford-
shire " hand dressings " for corn, and at the time of the
beginning of scientific agriculture in the second quarter
of the last century we find that the use of rape dust
had become pretty general throughout the eastern
counties.

Rape dust contains about 5 per cent of nitrogen,
with such small quantities of phosphoric acid and potash
that it must in the main be treated as a nitrogenous
manure. In its action it may be classed with the fish
and meat guanos previously described, in that decom-
position and nitrification is set up pretty rapidly and
continues throughout the whole season. It has been
largely used in the Rothamsted experiments, and the
results with barley and mangolds (Tables XXVI., XXX.,
and LXIII.) show that, nitrogen for nitrogen, it is
almost as effective as nitrate of soda or sulphate of
ammonia. In these cases, however, the manure is
applied year after year to the same land, so that the
residues unused in the year of application accumulate
for the benefit of the crop in future years, other

Q

242 PERUVIAN GUANO, ETC. [chap.

experiments, however, show that it is active enough
to produce nearly its full effect in the first season.
The organic matter rape dust supplies has a bene-
ficial effect upon the tilth of the soil ; on the Rotham-
sted mangold field, as has been pointed out earlier
(p. 218), the best results as regards the proportion of a
full plant obtained are yielded by the plot manured
with rape cake. In general farming rape cake has been
found a very suitable source of nitrogen for the barley
crop ; it is highly esteemed by hop growers, though
of late years its comparatively high price per unit of
nitrogen has much diminished its consumption in Kent
and Sussex. It is also valued by fruit growers, but it
is supposed to make a bad top dressing for grass, and,
like all manures of its class, it should not in its fresh
condition be put in contact with germinating seeds or
young plants, probably because of the fungi and moulds
with which it becomes permeated in the soil.

Other cake residues of a similar character come on
the market from time to time in the shape of damaged
cargoes of cotton, linseed, or other cakes, that have been
spoilt for food by getting damp and heating or by the
access of sea water. They may be judged on the same
basis as rape cake and their value estimated from their
analysis.

Castor cake or pomace, the residue left after castor
oil has been expressed from the seeds, has no value for
food, but makes a good fertiliser of the same class as
rape cake. It is not often available in this country, as
the castor oil is generally expressed before exportation ;
in India and other tropical countries, however, it forms
a very valuable source of manurial nitrogen, because
organic compounds of nitrogen are particularly desirable
in tropical soils, which so rapidly lose their humus under
cultivation.

VIII.] MANURES DERI VED FROM HUMAN EXCRETA 243

Manures derived from Human Excreta.

Since the process of digestion in man does not
essentially differ from that of animals, the greater part,
and in the case of adults the whole, of the nitrogen*
phosphoric acid, and potash, contained in human food
is excreted in the urine and fseces. We have already
seen that when plants are grown to feed animals, the
nutrient constituents drawn from the soil are for the
most part returned to the land ; the only fertilising

Table LXXV.— Composition of Human Excreta.

Faeces.

tJrine.

Per cent.

Lb.

per annum.

Per cent.

Lb.

Per annum.

Water .
On:;;anic mitter
Ash

Nitrogen
Phosphoric Acid
Potash .

77-2

19-8

3-0

I-O

i-i

0-25

I -04

1-3

0-3

96-3
2.4

1-3
0-6
0-17

0-2

3-2
3-4

constituents which leave the farm permanently are the
corn, the wool, and the fat stock for the use of man.
Even of these the husk of the grain, the wool, the bones
and hair find their way back to the land eventually, but
under modern conditions the permanently valuable con-
stituents of human food which pass into the excreta
are then wasted agriculturally by being washed away
into the rivers and sea. In the gross the waste is
enormous ; the only difficulty of preventing the loss lies
in the fact that most of the methods for rendering
serviceable the wasted material cost more than an equal
amount of fertiliser from some other extraneous source.
Wolff and Lehmann have estimated (Table LXXV.)

244 PERUVIAN GUANO, ETC. [chap.

the average composition of human excreta, and for
the average yearly output of each individual, from
which it will be seen that neither urine nor faeces are
particularly rich fertilisers.

These are mean figures for all ages, and the weights
of nitrogen and phosphoric acid excreted per annum
are calculated upon a somewhat different basis ; for
adults the quantities should be at least half as large
again. But taking high average figures, an adult only
excretes during a year about 12 lb. of nitrogen, 7 of
phosphoric acid, and 5 of potash, worth respectively
about 7s. 6d., 2s., and is., or los. 6d. a year in all when
converted into a marketable fertiliser. Though for a
large population the total waste may thus seem to be
enormous, los. 6d. per head is yet but a small amount
to be set against the expense of dealing with such
a quantity of low grade material so difficult to
handle.

Many attempts have naturally been made to utilise
the fertilising material contained in human excreta ; on
the crowded lands of China it is applied fresh to the soil
and is daily fetched by hand from the cities for that
purpose, but such a mode of dealing with night soil is
only possible with an excessively low standard of living.
In the towns of Flanders and the north of France it
was the custom to collect the excreta in large tanks,
and after fermentation, to cart them out in a liquid form
to the fields, though modern views on public health are
rapidly getting rid of such practices. Almost the only
method of getting human excreta back to the land
cheaply and inoffensively is in houses or small com-
munities where the " earth closet " system prevails.
There the excreta are mixed with dry sifted earth,
which deodorises them quickly and completely, the
mixture is removed daily to a heap under cover, and

VIII.] MANURES DERIVED FROM NIGHT SOIL 245

in a very short time, the faecal solids, paper, etc., are so
completely broken down by bacterial decay that the
soil can be spread upon the land and used for growing
crops.

In some towns attempts have been made to manu-
facture a concentrated fertiliser by collecting human
excreta without any admixture and evaporating off the
water, sometimes with the addition of a little acid to
fix the ammonia arising from the urea, sometimes with
powdered turf, etc., to give the finished material a
better mechanical texture. In Rochdale, one of the towns
where such a system prevails, the houses are provided
with external pan closets and the faeces are collected
at short intervals for conveyance to the manure works.
The following analysis shows the composition of the
resulting manure —

Water ....

. 13-9

Organic matter .

. 637

Containing Nitrogen

6-74

Phosphoric Acid

3-12

Potash ....

2-l6

Insoluble Ash .

3-45

The almost universal prevalence of a water-borne
system of dealing with excreta puts an end to all such
systems and intensifies the difficulty of saving the
fertilising constituents of human food for the land
again, because of the enormously increased dilution
they have experienced ; the sewage from towns with
water-closets only contains on the average about 2-2
parts of nitrogen per 100,000. Where the conditions
are favourable and the community has at hand a
sufficient area of light, permeable land which can be
cheaply graded and adapted to irrigation, then the
sewage waters, either with or without a preliminary

246 PERUVIAN GUANO, ETC. [chap.

treatment to get rid of suspended matter, can be
profitably utilised in raising crops. But light land,
permitting of free percolation, is necessary, and it must
not be overloaded with sewage but allowed intervals
for aeration and oxidation, or else the surface becomes
sealed with a layer of organic matter difficult to break
down and both percolation and purification cease. An
acre of land is not capable of dealing with the sewage
of many more than one hundred people. This is hardly
the occasion to discuss the various processes now in
vogue for the purification of sewage by bacterial action
or by land filtration, but at one point they do touch the
manure question by turning out " sewage sludges "
which possess a certain fertilising value. In many
of the processes the raw sewage is first submitted to
some process of chemical precipitation to effect the
removal of the suspended matter and obtain a clear
effluent, which can be purified by bacterial filter beds
or by application to the land. As precipitating agents,
lime, alum, and sulphate of iron are commonly employed,
alone or together, the object being to produce a bulky
colloidal precipitate which will entangle and drag down
the flocculent organic matter of the sewage. After
mixing with the precipitant, the sewage is left in tanks
to settle, the clear liquid is passed on for further treat-
ment, and the remaining sludge is freed from excess of
water by passing through some form of pressure filter.
The resulting press cakes are either disposed of locally
in the wet state or, in one case at least, dried and sold
as a manure under the name of " native guano." It is
obvious that any such precipitating process with either
lime or the sulphates of alumina and iron, can only take
out of the sewage such nitrogenous bodies as proteins,
leaving the greater part — the amides and ammonium
salts, still in solution. Thus the sludge will only con-

VIII.]

SEWAGE SLUDGES

247

tain the smaller and least valuable portion of the
nitrogenous material, also the phosphates but not the
potash of the sewage. Table LXXVl. gives a series of
analyses of such sludges, made for the Royal Commis-
sion on Sewage Disposal in 1906, which may be taken
as typical of this class of material : —

Table LXXVL— Composition of Sewage Sludges.

1

2

3

4

Water ....

lO'I

31-2

40-6

3-55

Organic matter, etc. .

49.8

24-9

i6-8

38-23

Nitrogen ....

2-32

0-94

0-55

1-65

Phosphoric Acid

2-27

o-8o

1-42

1-25

Lime

2-34

24-6

24-45

8-40

Potash ....

traces

traces

traces

traces

Insoluble matter

23-27

7 -06

5-57

28-28

Of these sewage sludges No. i represents the
material sold as "native guano," 2 and 3 are lime
sludges, while for 4 the precipitant had chiefly been
sulphates of iron and alumina. It will be seen that in
no case is the material possessed of much fertilising
value, for not only are the percentages of nitrogen and
phosphoric acid low, but they must be combined in
extremely inactive forms. Field trials show that the
action of these sludges as manures is very small, below
that of equivalent amounts of nitrogen and phosphoric
acid in commercial fertilisers, so small in fact to be
negligible unless the material is applied in very large
quantity. Indeed, we can only conclude that these
sludges possess little or no value as fertilisers, though
they may be valuable for the lime they contain, especi-
ally on light sandy land where they will also add some
water-retaining humus and improve the texture of the
soil.

248

PERUVIAN GUANO, ETC. [chap. viii.

Table LXXVIL— Composition of Guanos and Kindred
Fertilisers.

a

0

0

«

0 .

St, «

A

^

.a -a

S.S,A

^

0

§0

>2§

1

0

g

A

d tv ja

Ph

^

^HP.

Peruvian Guano

Ballestas, 1902 .

I2'24

11-36

24-76

fi

Macabi, 1902 .

IO-57

13-90

30-30

II

Guanape, 1902 .

7-75

I8-S9

34-00

.••

*..

>i

Lobos, 1902 .

2-86

29-52

64-35

ti

„ 1902 .

I-50

31-63

68-95

....

II

1906 .

8-4

13-17

28-70

2"8S

II

„ 1906 .

4.9

21-22

46-25

3-51

II

„ 1906 .

2-37

2I.6l

47-12

2.90

)>

Equalised .

7-8

II — 14

25—30

2—3

...

Ichaboe .

.

8-64

12-14

28-09

2-47

...

))

• • .

8-22

14-3

31-3

2.0

...

Damaraland

« . •

6.83

14.63

31-89

Fish Meals .

•

8-97

8.87

19-34

4.96

11 *

•

8^8

10-14

22-11

8.48

„ (from
)> •

)» •

>) •

herring refuse) .

8.78
9-29
6-26
6.15

6-59
7-70
5-96
5-26

14-37
16-79
12.99
11-47

...

16.46

Meat Meals .

• • . .

12-3

0-92

2-0

f) •

•

6-51
6-36

13-22
14-32

28-82
31-27

)i •

.

5-82

12-80

27-94

» •

• •

5-6i

11-35

24-77

...

...

Greaves ,

.

6-22

4-19

2.6l

5-48

2-l8

2-56

11-96

4-75
5-50

Dried Blood

• • • •

9-65

0-83

1-82

Rape Dust (Homco) .

4-84

1-7

3-8

"

• • • •

5 -08

1-58

3-44

Damaged Cotton Cake

4-78

1-73

3-77

2-77

Castor Cake

•

^■"

1.83

3-99

1.04

CHAPTER IX

MATERIALS OF INDIRECT FERTILISING VALUE

Lime — Early Use of Lime — White and Grey Limes — Lime
Ashes — Marl — Chalk — Ground Limestone — Indications of the
Lack of Lime in the Soil — Action of Lime upon the Soil —
Improvement of Texture — Promotion of the Oxidation of
Nitrogenous Residues in the Soil — Increase in the Availability
of Phosphoric Acid and Potash — General Action of Soluble
Salts on the Soil — Gas Lime — Gypsum — Salt — Sulphate and
Carbonate of Magnesia — Sulphate of Iron ; Supposed Connec-
tion of Iron in the Soil with the Colour of Fruit and Flowers
— Manganese Salts — Silicates — Green Manuring — Folding
Catch Crops on the Land.

There are several substances commonly used by
farmers as manures, which produce desirable effects
upon the crops, although they are not themselves plant
foods and only act indirectly on the soil, either by
making it more amenable to cultivation or by bringing
into action the stored-up reserves in the soil.

Such substances are lime, gypsum, salt, all of which
contain elements present in the plant, though they also
exist in the soil in quantities sufficient for the nutrition
of the crop ; they are valuable as soluble salts for their
indirect effect in making soluble other more important
plant foods in the soil.

Lime. — When the value of lime became known it
is impossible to ascertain, but we find that the use of
both lime and marl was recognised among the Romans.

2SO MATERIALS OF INDIRECT VALUE [chap.

For example, Pliny writes : — " There is another way
of nourishing earth by earth, which has been found out
in Britain and Gaul. It is thought that there is a
greater degree of fruitfulness in this kind than in any
other. It is a certain richness of earth, like the kernels
in animal bodies, that are increased by fatness. " The
principal of those, reckoned the fat kinds, is the
white ; of this there are many. One very acrid, that
has already been mentioned. Another kind of the
white is like a soft clay. It is found at a great depth ;
the pits very frequently dug an hundred feet down,
narrow at the mouth ; but the vein, as in metals,
widening within. This is chiefly used in Britain. It
remains eighty years ; nor is there an instance of any
man laying it twice on the same field. "The Hedui
and Pictones manure their fields with lime, which is
likewise found very good for olives and vines. All
marl ought to be laid upon ploughed land, that
its virtue may be the easier sucked in by the soil. A
little dung should be laid on with it, particularly with
that kind that at first is too hard, and does not dissolve
well enough to nourish plants. Besides, of whatever
kind it is, it hurts the soil, by its being new, and does
not render it fertile till after the first year."

The regular use of some form of lime or chalk was
part of the accepted routine of farming as early as we
possess any records of British agriculture, and among
the manures it figures in all books of the sixteenth and
seventeenth centuries. In fact "the black and the
white," dung and lime, were the only manures employed
by the great mass of farmers until well into the
nineteenth century.

Lime itself, or quicklime, is obtained by the " burning "
of any form of calcium carbonate, which occurs as
limestone [either pure in the Mountain Limestone of

IX.] VARIETIES OF LIME 251

Derbyshire and North Yorkshire, or argillaceous in the
Lias] as chalk, and even as shell sand, on the Cornish
and other coasts. The so-called " burning " consists in
driving off by heat the carbonic acid contained in the
calcium carbonate. The resulting lime, known some-
times as quicklime, stone lime, cob lime, lime shells,
etc., combines with great readiness with water, developing
much heat and falling down into a fine powder termed
" slaked lime," and this slaked lime will then combine
with the carbonic acid present in the atmosphere to
reconstruct the original carbonate of lime. Thus when
lime is applied to the soil it very rapidly becomes
carbonate and the effects of " liming " are really due to
carbonate of lime.

The quality of lime varies considerably, according
as it has been made from a pure limestone or from the
impure forms containing some admixture of clay and
sand. In the former case the result is a white, " fat,"
lime which swells considerably on slaking and falls
into a very fine powder ; the other grey or thin limes
do not slake so readily nor swell much, they also
contain a smaller proportion of free lime and are less
valuable for agricultural purposes. In some parts of
the country the limestone is dolomitic and contains
considerable proportions of magnesium carbonate, but
the limes arising from it are not regarded with so much
favour by farmers.

Lime ashes, which are to be had cheaply in the
neighbourhood of the kilns, consist of the waste
accumulating in burning the lime and are therefore
mixtures of lime in a powder with the ashes of the
coal employed. The percentage of lime may vary from
20 to 60 according to circumstances, so that the value
of each lot must be judged by its apparent cleanliness
and freedom from clinker.

252 MATERIALS OF INDIRECT VALUE [cHAP.

Since lime becomes calcium carbonate in the soil,
obviously the same results would be obtained by
applying the latter material, the main advantage in the
use of lime lies in the very fine state of division into
which it falls on slaking and the consequent good
admixture with the soil that is effected.

Such a finely divided calcium carbonate is provided
in many parts of the country by the calcareous marls
which occur in beds sufficiently near the surface to
admit of working, as in the New Red Sandstone
formations in Cheshire, Worcester, etc., or the shell
marls which occur in Norfolk, A true marl is a clay
containing a variable percentage of calcium carbonate>
it is specially valuable on sandy or peaty soils, not only
for its calcareous matter but also for the clay, which
improves the texture of the soil.

In many parts of the country, where the superficial
formations resting upon the Chalk are \ devoid of
carbonate of lime, it was formerly the custom to sink
bell pits into the chalk rock, haul it up in baskets and
spread it upon the surface. In Hertfordshire, for
example, this chalking was part of the regular routine
of farming from the earliest times of which we have
records, and from the analyses of the Rothamsted soils
it has been ascertained that by the repetition of the
process a hundred tons per acre or more must have
been applied before the beginning of the nineteenth
century, there being now present in the soil from
2 to 5 per cent, of carbonate of lime, all of artificial
origin. Chalk was also formerly carried for con-
siderable distances on to the clay formations — the
London Clay, the Gault Clay, and the Weald Clay —
that are contiguous, but the increased cost of labour
has put an end to this practice.

None of the other British limestones are sufficiently

IX.] C ROUND LIME AND LIMESTONE 253

soft to allow of their direct application to the land with
any prospect of their reduction to a fine state by the
action of the weather, but of late years, since many of
the lime works have established grinding plants, it has
been possible to obtain both limestone and chalk in a
finely ground condition. In certain parts of the country
precipitated carbonate of lime in a very fine state of
division is to be obtained from water works which
soften their hard calcareous water by the use of lime,
and this forms valuable material for all land in need of
lime. Ground quicklime is also manufactured and forms
a very convenient means of applying small quantities of
lime to the soil ; unfortunately the ground lime avail-
able is generally grey or cement lime, so that at its
higher price and with its lower proportion of pure lime
it is often more profitable to buy a larger quantity of
ordinary lime. When the practice of liming was more
general it was customary to apply very large amounts,
4 to 6 or 8 tons per acre (100 to 200 bushels) at long
intervals, but this is likely to act injuriously by causing
too rapid oxidation in the soil at first, and a better plan
is to put on I ton or so of ordinary lime every time the
turnip crop comes round in rotation, or 5 to 10 cwt. of
ground lime to each crop for which artificial manures
are applied. A heavy dressing of lime is also supposed
to affect the processes of nitrification detrimentally for
some time after its application.

Lime, chalk, or ground limestone, in whatever form
it is used, should always be applied to the land as early
in the winter as may be convenient, on arable land
before ploughing.

The question of whether lime is required as a regular
part of the routine of farming on a given soil can only
be decided by an analysis of the soil ; any soil contain-
ing less than i per cent, of calcium carbonate will be

^54 MATERIALS OF INDIRECT VALUE [chap.

benefited by liming, and when the percentage falls
to \ per cent, lime becomes a necessity to enable the
manures to exert their proper action.

Many clays and sands are in this latter condition ;
and although the absence of lime may often be con-
cluded from the appearance of the vegetation, every
farmer ought to get a determination made of the
amount of carbonate of lime in his soil, because the
whole scheme of manuring should depend on whether
the soil is properly supplied with a base.

In arable land the presence of the small sorrel
{Rumex acetosella), corn marigold {Chrysanthemtini
segetuni), Spurrey {Spergula arvensis)^ and the growth
of foxglove {Digitalis purpurea) and bracken {Pteris
aquilind) on the waste places are pretty sure signs of
the absence of lime, while the pastures on such soils are
generally very deficient in leguminous herbage. If a
little soil when covered with dilute hydrochloric acid
shows no visible effervescence, the proportion of
carbonate of lime must be below what is desirable for
the healthy growth of vegetation. Nor must it be
supposed that the use of artificial manures, such as
superphosphate of lime, or bones which are phosphate
of lime, or gypsum which is sulphate of lime, will
obviate the necessity of liming. Lime or its carbonate
are needed in the soil to supply a free base, and in
the compounds mentioned it is already saturated with a
fixed acid ; in fact, in superphosphate of lime there is an
excess of acid, so that this fertiliser reduces the amount
of carbonate of lime in the soil. Gas lime is again of
very little service in this connection, since the base has
already been largely combined with various compounds
of sulphur, and still remains so after these sulphur
compounds have been oxidised by exposure of the gas
lime for some time. The following table (LXXVIII.)

IX.j

ACTION OF LIME

255

shows analyses of " grey " and " white " limes made from
chalk : —

Table LXXVIII.— Analysis of Lime.

White Lime.

Grey Lime.

Caustic Lime . . •
Carbonate of Lime . .
Magnesia ....
Oxide of Iron .
Alumina ....
Silica as Soluble Silicates.
Insoluble residue . ,
Water, Alkalis, etc .

90-20
2-40

0-35
0-52
1-70

2 -60

0-25
1.98

74 -DO

2-66

0.38

I -GO

7 -60
8 -60
0.94
4-82

Total ,

roO'OO

lOO-OO

Lime is best applied to the stubbles in the autumn
before ploughing in preparation for a root crop ; if
ground lime is used it may be sown broadcast with any
form of manure distributor, choosing a quiet morning
while the dew is still on the surface.

Stone lime should be distributed in small heaps,
covered with a little earth and left for a week or two to
slake, under which conditions it will fall into a fine
powder. The heaps are then broken down and thrown
abroad before ploughing.

The action of lime is partly physical, affecting the
texture of the soil, and partly chemical, setting free the
dormant reserves of plant food.

On the strong soils the physical action of lime is
most manifest ; it acts by flocculating the finest clay
particles, causing them to aggregate into temporarily
larger units, and so making the soil effectively of coarser
texture. The soil thus becomes less retentive of
moisture ; percolation is increased, making the limed
land dryer and warmer, so that it admits of cultivation
earlier in the spring and is far more friable when dry.

2S6 MATERIALS OF INDIRECT VALUE [CHAP.

In dry seasons the clay will crack less and the crop
will keep on growing longer, because the improved
texture of the soil admits of a better supply of subsoil
water to the plant by surface tension.

It is difficult to exaggerate the improvement that
lime effects in the dryness and workability of strong
soils, which in many cases would not be fit for arable
cultivation had they not been so treated. It has
already been mentioned that on the Rothamsted
estate the custom of chalking has added from 2 to
5 per cent, of carbonate of lime to the surface soil,
which is otherwise non-calcareous ; but on one of the
fields, formerly under experiment, the treatment had
never been carried out. This field, Geescroft, formerly
carried experimental crops of oats and beans, but during
the rainy seasons about 1879 the land lay so persis-
tently wet in the spring that on several occasions a
tilth could not be obtained in time for sowing, and the
land had to lie fallow, until at last cultivation was
abandoned and the field was allowed to fall down into
grass. Even now the herbage is very inferior and
shows the wet character of the soil by the prevalence
of Aira ccsspitosa ; yet in situation, drainage, and
mechanical composition this soil is in no respects
different from that of the other Rothamsted fields.
The essential factor which has caused all the difference
in the character of the two soils is the absence of calcium
carbonate from the Geescroft field, which for some reason
had escaped the chalking given to the other fields. The
physical improvement of a clay soil by lime is not appar-
ent at once but grows from year to year after the applica-
tion of the lime ; the flocculating action is really not due
to the lime itself but to the soluble calcium bicarbonate
which arises from the action of water and carbonic acid
upon the calcium carbonate formed from the lime.

IX.] ACTION OF LIME 257

On the lighter soils — the sands and gravels — lime
exerts a good effect by forming a weak cementing agent
and increasing the cohesion of the particles. As a rule,
however, it is not wise to apply quicklime in any
quantities to very light open soils, because oxidation of
the organic matter is pushed on too rapidly. Either
chalk or marl, or some form of calcium carbonate should
be used, or the quicklime should only be applied in
small quantities.

From the chemical side the great value of carbonate
of lime in the soil lies in its power of maintaining
the neutral reaction necessary to the development
of those bacteria which oxidise the organic compounds
in the soil to the state of plant food. In the absence of
lime, organic matter by its decay gives rise to various
acid bodies which may be grouped as humic acid, and
the acidity thus produced inhibits the action of many of
the valuable groups of bacteria, such as the Azotobacter
which fix nitrogen, and the nitrifying bacteria which
convert ammonia into nitrates. It has been shown that
in soils that are acid through the accumulation of humic
acid, nitrification is at a standstill and bacterial life gener-
ally is repressed in favour of the growth of moulds and
micro-fungi, which compete actively with the crop for
the plant food in the soil.

On all land which has been enriched by the
residues of past manuring or by the debris of previous
vegetation, lime is very necessary to promote the
oxidation of the nitrogen compounds and the formation
of nitrates for the crop ; consequently it is on bog or
peaty land, on old turf or reclaimed forest land, or on
old gardens, that liming exercises its maximum effect.
The following figures (Table LXXIX.) show the com-
parative crops on limed and unlimed plots, otherwise
manured alike, in an old hop garden at Farnham,

258

MATERIALS OF INDIRECT VALUE [chap.

Surrey, which had been heavily dressed with organic
manures for many years previously : —

Table LXXIX.— Effect of Lime upon Hop Soils.

Artificial Manures.

Year.

With 1 ton Lime
per acre.

With no Lime.

1895

100

70

1896

100

84

1897

100

80

1900

ICO

81

1 901

100

90

Because of the wide fluctuations due to season the
yield each year has been calculated on a basis of the
limed plot = 100, showing that, on the average, liming
has increased the return by 19 per cent.

It is on soils with a tendency to sourness that
liming is of the greatest value, for in such cases dung
or any other organic manure only tends to aggravate
the evil. This is very well illustrated by the action of
lime upon the grass plots at Rothamsted, where 2000
lb. per acre of ground lime was applied to half of the
plots in January 1903, with the results shown in Table
LXXX. ; the yield of the limed half of the plot in each
year has been compared with the yield of the unlimed
portion taken as 100.

It will be seen that the increased yield due to
liming is most manifest on plots 4/2, 9, and ii/i,
where the soil had become acid through the long-
continued use of ammonium salts. It should also be
noticed that the action of lime is slow, and is more
manifest in the third and fourth year after its applica-
tion than in the first and second.

It has already been stated that moulds and other

IX.]

ACTION OF LIME

259

micro-fungi are favoured by an acid reaction in the
soil, consequently we find that various fungoid diseases
of plants are specially prevalent on soils devoid of
calcium carbonate, a notable example being the slime
fungus, PlasiiiodiopJiora brassiccB, which causes " finger-
and-toe," " club root," or " anbury " in turnips, cabbages,

Table LXXX.— Effect of Lime upon Rothamsted Grass Plots
(Unlimed = ioo).

Plot.

1903.

1904.

1905.

1906.

1907.

3

Unmanured .

154

134

119

98

119

4/2

Super, and Am. -salts

124

III

134

118

113

7

Complete Minerals

105

100

106

120

no

8

Minerals ; no Potash .

93

90

103

93

no

9

As 7, +Am.-salts .

121

no

142

128

106

ii/r

As 7, +extra Am. -salts .

115

103

206

120

167

10

As 8, +Am.-salt5 .

120

III

128

112

104

and similar plants. This disease does not occur on cal-
careous soils and can be obviated on soils where it does
prevail by a thorough liming, best applied both after
the removal of one turnip crop and again immediately
before another is sown. As long an interval as possible
should elapse between the two cruciferous crops to
enable the spores of the disease to die off in the
soil, now rendered faintly alkaline. The finger-and-
toe fungus is not the only one thus affected by lim.e,
but it is the one known on the widest scale ; speaking
generally, calcareous so'Is are always the healthiest for
crops.

But the nitrogenous compounds in the soil are not
the only ones rendered more available by the presence
of carbonate of lime ; both phosphoric acid and potash
are thereby kept or brought into a more soluble form.
When soluble phosphates are applied to the land they
are precipitated either as di-calcium phosphate, ferric

26o MATERIALS OF INDIRECT VALUE [chap.

phosphate, or aluminium phosphate ; and on soils
containing any reasonable amount of calcium carbonate
the former will predominate, the two latter on the sands
and clays where calcium carbonate is lacking. Now the
effective solubility of the two latter phosphates in the
soil water is very much below that of the precipitated
calcium phosphate, consequently their phosphoric acid
is much slower in reaching the plant, which may remain
short of this necessary constituent even though large
amounts have been applied to the soil. Similarly a
soil may contain considerable amounts of phosphoric
acid, which in the absence of lime is combined with
ferric oxide or alumina so as to be in a highly
insoluble condition; for example, a soil derived from
the marlstone has been known to contain 0-84 per cent,
of phosphoric acid but yet show great response to
phosphatic manures, because at the same time it con-
tained 28-16 per cent, of ferric oxide and no calcium
carbonate. Applications of lime or calcium carbonate
are of great value on these soils because they form a
certain amount of calcium phosphate by interaction with
the iron or aluminium phosphates, and so increase the
proportion of phosphoric acid in the soil water.

The action of lime upon the potash compounds in
the soil is equally marked ; as the soil water carries
down the dissolved calcium bi-carbonate it attacks the
zeolitic double silicates in the clay and some of their
soluble bases, potash among them, change place with
the lime and come into solution. Thus lime is precipi-
tated and potash is found in the soil water. The action
is the converse of that which takes place when potash
salts are applied as manures ; whatever base is in excess
in the water reaching the soil will turn the others out
and be precipitated in the solid zeolite. When potash
salts are applied to the land the strong solution thus

IX.] ACTION OF LIME 261

formed attacks the zeolites and replaces calcium by-
potassium, thus the potash is precipitated and lime
salts go into the drainage water ; when lime is applied
to the land the process is reversed and potash goes into
solution as bicarbonate.

This may again be seen in the results quoted in
Table LXXX. of the application of lime to the
Rothamsted grass plots : on Plot 8, where potash
had not been used previous to the application of
the lime there is little or no increase of yield, because
there were no reserves of potash to be set free. That
lime acts in this fashion may also be inferred from
its beneficial effect upon clovers and other leguminous
plants in a mixed herbage, or by the remarkable
power of basic slag to promote the growth of white
clover in a pasture where it was formerly dormant
Other phosphatic manures have often little effect in
such cases, so that free lime in the basic slag, by-
liberating potash, is evidently as important a factor in
the growth of the clover as the phosphoric acid. If the
basic slag is applied to a soil poor in potash it has
little effect, and again after two or three applications
to grass land it ceases to show its previous beneficial
action upon the clover, because the readily attackable
potash in the soil has all been brought into solution
and a direct application of potash salts becomes
necessary.

The fact that a solution of calcium bicarbonate will
react with the potash-containing double silicates in the
soil, so as to bring some of the potash into solution, is
only a particular case of a more general proposition,
which is applicable to any soluble salt brought into
contact with the zeolites. Whatever the salt may be,
if its base be one normally found in the zeolite, e.g.,
either sodium, potassium, calcium, or magnesium, it will

262 MATERIALS OF INDIRECT VALUE [chap.

effect an exchange with the bases in the zeoHte, to a
greater or less degree according to the relative mass
of salt and zeolite, becoming itself insoluble and bring-
ing the other bases into solution. Thus in practice the
application of any soluble salts of calcium, magnesium,
and sodium to the soil results in potash going into
solution and thus becoming available for the crop,
always supposing that the soil is provided with a
normal amount of clay containing zeolites derived
from potash felspar. This principle serves to explain
the fertilising value of all such bodies as gas lime,
gypsum, salt, and sulphate of magnesia, and also the
irregularity of their action, because they are only
effective when the soil contains potash and yet the
crop requires more than the soil can normally furnish.

This general action of soluble salts in increasing
the supply of available potash for the plant may be well
illustrated from the Rothamsted experiments. Taking
the wheat crop, there are five plots treated alike as
regards their supply of nitrogen and phosphoric acid,
but whereas one receives nothing further, one each of
the others also receives sulphate of sodium, potassium,
or magnesium respectively, and the fifth plot all three
of these salts, with the results set out in Table LXXXI.
for five successive ten-year periods.

It will be seen that in the first decade the lack of
any alkaline salt on Plot 1 1 caused a serious reduction
of crop, but on the other plots there was much the same
yield, the mixed sulphates giving somewhat the highest
and the sulphate of potash itself the lowest yield. From
this alone it might be concluded that it is a matter of
indifference to the plant which of the alkaline salts it
receives, but as time goes on it will be seen that Plot
13, receiving potash, remains but little behind Plot 7
receiving all the salts, but that Plots 12 and 14, receiving

IX.] ACTION OF SOLUBLE SALTS UPON SOIL 263

soda and magnesia without potash, fall further and
further behind, though they never reach the low level
of Plot II, with no alkaline salts at all. At first the
soda and magnesia can do the work of the potash
because they can render soluble enough potash in the
soil to satisfy the needs of the crop ; but as the treat-

Table LXXXI. — Effect of Alkaline Salts upon the
Wheat Crop (Rothamsted).

l-H

Alkaline Salt added to

ca

Plot.

Ammonium Salts and

*-*

•-;

r-l

r-t

Superphosphate in Manure :—

S

^

00

Oi

■^

r-l

■^

•^

GRAIN,

BUSHB

LS.

II

None ....

28-4

27-9

21-7

22-7

19-5

12

Sulphate of Soda

33-4

34-3

25-1

30-1

267

13

Sulphate of Potash .

32-9

34-8

26-8

32-5

29-6

14

Sulphate of Magnesia

33-5

34-4

26-4

3I-I

2S-0

7

Sulphates of Soda, Potash,

and Magnesia

34-7

35-9

26-9

35-0

31-8

STBAA

V, CWTS

.

II

None ....

28-2

24-5

21-3

20-8

i8-8

12

Sulphate of Soda

34-2

30-5

25-0

27-3

24-0

13

Sulphate of Potash . ,

34-4

33-4

27-6

31-9

28.6

14

Sulphate of Magnesia

35-0

30-7

26-3

28-6

23.4

7

Sulphates of Soda, Potash,

and Magnesia

36-4

34-3

28.7

34-1

3I-I

ment is continued the readily attackable potash in the
soil becomes depleted and the yield falls off despite
the great initial store of potash in the Kothamsted soil.
That the potash in the soil had been rendered soluble by
the soda and magnesia, is made still more clear by a con-
sideration of the composition of the ash of the plants
from these plots: and Table LXXXII. shows the
average composition of the straw ash for the 10 years

264

MATERIALS OF INDIRECT VALUE

[chap.

1882-91, the straw ash alone being given because there
is practically no variation in the composition of the ash
of the grain.

Table LXXXIL— Percentage Composition of the Ash of Wheat
Straw. Mixed Samples representing 10 years, 1882-1891
(Rothamsted).

Ammonium Salts and Superphosphate

with —

«

<D .

rt s

0.

^0

3 Oj

^j2

mS

m =s

Plot .

11

12

13

14

7

Ash (crude) in Dry Matter,

per cent.

5-84

5-69

5-93

5-52

5-89

Iron Peroxide, etc. ,

0-43

0-33

0-34

0-41

0-50

Lime ....

9-14

7-73

5-39

7-70

5-69

Magnesia . .

2.25

1-92

1-53

2-46

1.76

Potash ....

9-91

14-68

23-28

14-87

25-89

Soda . . • .

0-58

0-57

0.03

0-33

0-21

Phosphoric Acid .

4>26

3-65

3-39

3-87

3-82

Sulphuric Acid .

5-44

5-33

5-07

5-31

5-41

Chlorine ....

1-66

2-89

5-6r

2-81

6.60

Carbonic Acid . >

trace

none

none

trace

Sihca ....

65.19

61-93

54.26

6 1 -06

49-68

Sand ....

1-46

1-43

1-76

1-39

1-32

Charcoal . • • .

Total .

o-o6

0-19

0-60

0-42

0-61

100-38

100-65

101-26

100-63

101-49

Deduct 0 = QA.
Total .

0-38

0-65

1-26

0-63

1.49

1 00 -00

lOO-OO

loo-oo

1 00 -00

100-00

There is no great variation in the percentage of ash
in the dry matter, but while the percentage of potash in
the ash of the straw from Plot 13, receiving only potash,
is 23-28, it is raised to 25-89 when soda and magnesia

IX.] GAS LIME 265

are also added to the potash in the manure, but sinks
to 9-91 when all the alkaline salts are lacking. From
this low figure of 9-91 the addition of soda causes a
rise to 14-68, of magnesia to 14-87 ; the differences in
the yield of the plots are in fact reflected in the pro-
portions of potash in the ash, though the variations
are not so great. But though the addition of soda or
magnesia on Plots 12 and 14 causes an increase in the
proportion of potash in the ash, neither the magnesia
nor the soda in the ash are perceptibly raised. Hence,
we may conclude that the whole effect of either sulphate
of soda or sulphate of magnesia upon the crop is
indirect and due to their attack upon the potash
reserves in the soil.

These results with wheat at Rothamsted are con-
firmed by the parallel experiments upon mangolds and
grass ; in each case sodium and magnesium salts add to
the effect of a potash dressing, and in the absence of
potash partially do its work, more in the earlier than in
later years of the experiment when the easily attacked
soil potash is becoming exhausted.

Gas lime is a greenish yellow, evil smelling sub-
stance obtained during the purification of coal-gas by
its passage over trays of freshly slaked lime, which
absorbs sulphuretted hydrogen and other sulphur com-
pounds from the crude gas. Various sulphides and
partially oxidised sulphur compounds of calcium are
formed, as may be seen from the analyses set out below,
and these are to some extent attacked by the carbon
dioxide of the air with the liberation of the original
gaseous sulphur compounds. The main action, however,
on exposure to the air is one of oxidation, so that
eventually the material becomes little more than a
mixture of gypsum and calcium carbonate from the
uncombined lime. It is in this oxidised form only

266

MATERIALS OF INDIRECT VALUE

[chap.

that gas lime should be appHed to the land unless the
ground is badly infested with some insect pest which
the raw sulphur compounds may check or destroy, and
even then on light soils the fertility of the land may be
impaired for some time. It is on heavy land that gas
lime is of most value ; the flocculating effect of the
calcium salts improves the texture, and the soil also
contains a great reserve of dormant potash compounds
to be rendered soluble. The crude material from the
gas works should be laid up in heaps, mixed with a
little earth for a year or more, spread on the stubbles in
the early autumn, and then ploughed in.

Table LXXXIII. — Analyses of Gas Lime.

London,
fresh.

London,

a little

Oxidised.

Oxidised.

Water

19-2

32-3

30-1

Calcium Hydrate (Slaked Lime)

I5-I

17-7

32-6

„ Carbonate

24-2

44-5

17-5

„ Sulphide

6.9

trace

„ Thio-sulphate

11-8

12-3

„ Oxy-sulphide

3-2

„ Sulphite

1-5

14-57

\ 20-2

„ Sulphate

0-25

2-80

Sulphur

4-3

5-14

Silica, etc

3-55

0-71

...

Gypsum. — That gypsum, crystallised sulphate of
lime, or land plaster, CaSO^, 2H2O, had a beneficial
effect upon certain crops and soils has been known for
a very long time ; it was probably familiar to the
Romans, and the knowledge survived to a certain
degree among the southern nations, especially in con-
nection with vines. In Britain it appears to have been
less commonly used and no very general agreement as
to its value had become traditional ; in fact it was only
among the hop growers of Kent and especially of Sussex,

IX.] GYPSUM 267

that any regular use was made of gypsum. In this
latter case it is not easy to make out to what extent its
employment was the result of experience, or of a quasi-
scientific opinion which traced a connection between the
action of sulphur upon the mildew of the hop, a
supposed lack of sulphates in a mildewed leaf, and
the sulphates in the gypsum. In the latter part of
the eighteenth century the value of gypsum for legu-
minous crops like clover and lucerne became widely
recognised ; Benjamin Franklin, in America, is said to
have sown gypsum so as to form the word "plaster" on
clover crops by the wayside, in order that passers by
should learn by the eye what had so stimulated the
growth. It is, in fact, on leguminous and such other
crops as are specially dependent upon potash, that
gypsum has an effect. This is intelligible on the
principle set out above, that the solution of calcium
sulphate which arises from the gypsum will attack the
zeolites containing potash and will so bring some
potassium sulphate into solution in the soil water.
In confirmation of this view, Boussingault has shown
that when clover is manured with gypsum and improved
thereby, the ash of the crop contains a greater pro-
portion of potash but shows no increase in either the
lime or the sulphuric acid.

The figures obtained by Boussingault are set out in
Table LXXXIV.

Thus, while the variations in lime and sulphuric
acid — the constituents of the gypsum, are small, the
proportion of potash has been greatly increased by the
use of gypsum.

Similarly, it has been found, in testing the action of
gypsum upon hops, that it has a beneficial effect only
upon the soils where hops also respond to dressings of
potash salts, and that the result of applications of

268

MATERIALS OF INDIRECT VALUE

[chap.

gypsum is similar to that of potash salts, though to a
less degree. Some crops, like Swede turnips and
cabbage, may take up more sulphur compounds than
the soil can normally supply and so be benefited by the
sulphur in the gypsum, but in the main its value is as a
liberator of potash in the soil.

Table LXXXIV.— Composition of Clover Ash.

Potash

Soda .....

Magnesia .....
Lime .....

Oxides of Iron and Manganese .
Chlorine . . . . .
Phosphoric Acid
Sulphuric Acid ....
Silica . . , . .

Without
Gypsum.

23-6
I -2
7-6

28-5

1-2

4-1
9-7

3-9

20'0

With
Gypsum.

35-4
0-9

6-7
39-4
i-o
3-8
9-0

3-4
iO'4

Salt. — The use of salt, alone or as an adjunct to
other fertilisers, is a common farming practice ; for
example, in growing mangolds it is customary to give
them 2 or 3 cwt. per acre of salt as a top dressing with
or without nitrate of soda. On the fen land of Lincoln-
shire potatoes are generally grown with farmyard
manure, superphosphate, and a liberal dressing of salt,
and in barley growing, salt alone is sometimes used
where roots have been folded off, with an idea of
stiffening the straw. Though, in the first case, the value
of salt is often ascribed to the fact that the mangold
has been derived from a maritime plant, it is really
due to the dependence of mangolds upon an abundant
supply of potash (see p. i68), because the soluble
sodium chloride will bring into solution the reserves of
insoluble potash in the soil and the manure. Potatoes
again are much in need of potash, and the straw

IX.] SALT 269

stiffening effect is similarly explicable by the extra
potash made available for the barley plant. Even the
ill effects of salt upon the malting quality of the barley
that are sometimes experienced, can be paralleled by
the observed effects of potash in prolonging the growth
of barley and deepening the colour of the grain. Salt
is also credited at times with injuring the tilth of heavy
soils and rendering them sticky and wet ; this effect
again is paralleled by the action of potash salts (p. 176) ;
an interaction takes place between the salt and the
carbonate of lime in the soil, and a little free alkaline
carbonate is formed, which deflocculates the clay.

We may therefore conclude that the action of salt
is entirely indirect, rendering available the potash in the
soil instead of itself feeding the crop. None the less it
forms a valuable adjunct to other manures for all crops
requiring large supplies of potash, such as mangolds and
other root crops, and may greatly economise if not
entirely replace the use of potash salts themselves. In
some districts a waste product termed " gunpowder
salt " is obtainable ; this is the bye-product in the
manufacture of saltpetre by the interaction of nitrate of
soda and potassium chloride, and is identical with
common salt except that it also contains a little nitrate
and some potash. These technical impurities render it
more valuable for agricultural purposes, so that it forms
a very excellent top dressing for mangolds.

Sulphate of Magnesia. — The action of this salt has
already been explained (p. 262) ; it is never required to
supply the plant with magnesia, sufficient quantities of
which are to be found in all ordinary soils for the needs
of the crop, and while it would render available some
potash in the soil, common salt will do the same thing
more cheaply. Carbonate of magnesia has from time
to time been suggested, and even put upon the market,

270 MATERIALS OF INDIRECT VALUE [chap.

as a manure, but there is no evidence to show that its
action is in any way different from that of calcium
carbonate, i.e.^ it behaves as a base but is not of any
further value as supplying magnesia to the plant.

Sulphate of Iron. — It is well known that iron is one
of the essential constituents of all green plants ; for
example, in water cultures it is easy to show that
seedling plants become blanched, chlorophyll does not
form in the leaf, and the plants soon die, unless a
small quantity of some soluble iron compound is
added to the culture liquid. Such an addition is
followed by a rapid return of the green colour to the
leaf and by the renewed growth of the plant. A
very widespread opinion has been based upon such
experiments and is specially current in horticultural
literature, that high colour in fruit and flowers
is to be associated with an abundance of iron com-
pounds in the soil, and that in consequence sulphate of
iron is valuable as an adjunct to manures. One argu-
ment advanced in favour of this opinion is the bright
colouring of apples, roses, etc., grown on the red sand-
stones and loams of Herefordshire and Worcestershire,
the red hue of which is admittedly due to oxides of iron.
When the facts are more closely examined, they afford,
however, little support to such a theory. In the first
place, the plant requires very little iron indeed : as a
rule, not more than i per cent, of the ash of a plant
consists of oxide of iron, 2 per cent, might be taken as
an outside limit, so that the amount of oxide of iron
taken from the soil by a heavy crop of mangolds (the
leaf of which is specially rich in iron) only amounts to
about 10 lbs. per acre. Now it is very rare to meet
with a soil that does not contain 2 per cent, (or 20 tons
per acre in the top 9 inches) of oxide of iron soluble in
hydrochloric acid, and of this a considerable proportion

IX.] FUNCTION OF IRON SALTS 271

is soluble in the weakest acids and must be regarded as
available for the plant. Moreover, the red sands and
loams mentioned above show rather less than the normal
amount of iron on analysis ; the bright red colour is
due to some variation in the mode of deposition of the
oxides of iron and not to any excess in their amount.
These facts alone render the theory improbable, but the
chief point is that no direct evidence has been adduced
for the beneficial effect of an application of iron salts,
either on colour or yield. From time to time experi-
ments with iron sulphate have been quoted, but they have
never been conducted in a manner to raise the supposed
increase due to the iron beyond the range of experi-
mental error. Even had the results been positive they
would have required futher examination, because the
application of sulphate of iron to the soil would result
in a variety of secondary effects, due to the precipitation
of the iron and the solution of a corresponding amount
of other bases present. As far as colour goes, no
evidence has ever been adduced to show that iron plays
a part ; experiments made by the author upon apples
gave purely negative results ; and though some effects
upon the colour of carnations were seen, no positive
conclusions could be drawn. In practice the employ-
ment of sulphate of iron for either farm or garden
crops may be dismissed.

Manganese appears also to be a constituent of all
plants, and recently experiments have been put forward
to show that small quantities of manganese salts have
a stimulating effect upon the growth of crops. The
experiments are, however, by no means conclusive, and
pending further investigations, the use of manganese
salts cannot be recommended in practice.

Silicates, — Silica is so large a constituent of the ash
of many plants, particularly of the straw of cereals, that

272 MATERIALS OF INDIRECT VALUE [chap.

it was inevitably regarded as a necessary constituent of
the food of such plants, and was naturally enough
supposed to contribute to the stiffness of the straw.
In his manures Liebig supplied the alkalies combined
with silica, and when Way discovered that certain
strata of the Upper Greensand, near Farnham, con-
tained considerable quantities of silicates readily dis-
solved by acids, the rock was for a time extracted
and ground up as a manure for cereals. But Sachs
showed that these plants, however rich in silica
their ash was when they had grown on ordinary soil,
could yet be grown with complete success in a water
culture devoid of any silica, and Jodin succeeded even
in raising four generations of maize in water cultures
with no more silica than was contained in the original
seed. It was also shown that the stiffness of the straw
depended upon such physiological factors as light and
exposure, rapidity of growth, etc., and was independent
of the amount of silica present, so that the use of
silicates for manurial purposes ceased, except at the
instance of one or two unscrupulous firms puffing
worthless materials. However, it must not be supposed
that so large a constituent of a plant's ash is entirely
without physiological function, and from the Rothamsted
barley experiments (which include plots receiving
sodium silicate) it may be seen that soluble silica does
play some part, at present not properly understood,
which enables the plant to make better use of the
dormant phosphoric acid in the soil. The silicates,
however, possess no practical use as fertilisers, the
increase thus produced would not repay the expense
of applying the silicate of soda.

Green manuring. — Green manuring consists in the
ploughing under of some rapidly growing crop — mustard
or tares in this country, lupins on sandy soils on the

IX.] GREEN MANURES 273

Continent, and covvpeas in America being among the
plants most commonly employed. The practice has
three objects : —

(i) The improvement of the texture of the land by
increasing the store of humus ; this is particularly
valuable on heavy clays and on the light sandy soils
at the other end of the scale.

(2) The saving of the store of nitrates, which on
light warm soils form with great rapidity after harvest,
and which may then easily be washed away. If some
catch crop like mustard is sown immediately the stubbles
are clear, it will grow with great rapidity after the first
rain and will gather up these nitrates, converting them
into proteins, which become more slowly available on
the decay of the plant material.

(3) For cleaning purposes ; when the land is in very
foul condition a good many weeds can be got rid of by
growing a smothering crop.

On many soils green manuring may be extremely
valuable, especially where there is any shortage of
farmyard manure ; a green crop of mustard turned in,
especially if it had been previously manured with some
mixture of artificials, will have all the lasting beneficial
effects of a coat of dung. Of course the " seeds " crop
in the rotation has much the same effect, because of the
roots and stubble left behind, but it does not always
come round often enough in the rotation to keep the
land in condition.

When vetches, lupins, or other leguminous crops are
grown, the land is also enriched by the nitrogen gathered
from the atmosphere by the bacteria living in the root
nodules, and large areas of land in Pomerania and East
Prussia have been brought under cultivation from the
state of barren sandy heath, by ploughing in lupins

S

274 MATERIALS OF INDIRECT VALUE [chap.

manured with basic slag and potash salts, until a soil
had been built up.

Curiously enough, on the sandy soil at Woburn,
Voelcker has always obtained better crops after mustard
than after vetches, despite the fact that the vetches had
contributed a greater weight both of dry matter and
nitrogen to the land. The vetch compounds may decay
the more slowly, but Voelcker further showed that the
land was left drier by the vetch crop ; that this was
the cause of the superiority of the mustard as a
green manure is rendered more probable by the fact
that the result was reversed on the strong Rothamsted
soil, where the vetches are the better preparation for a
succeeding wheat crop. The real difficulty experi-
enced in utilising green manuring and catch crops
generally on many soils in this country, to which they
are otherwise most admirably suited, is the way they
deplete the water-supply for the succeeding crop. For
example, a crop of vetches or crimson clover may be
sown on the stubble in August or September and
harvested in May, in plenty of time to prepare the land
for turnips, but in many cases the soil and subsoil will
be left so dry that the turnip crop will fail or be greatly
reduced, unless the incidence of rain be unusually
favourable. The difficulty of starting the catch crop
after the drying effect of the harvested corn, and the
dryness of the land which again ensues after the
catch crop in spring, form the great objection to catch-
cropping, which indeed only flourishes where the annual
rainfall is well over 30 inches. In this respect mustard
is the least objectionable crop, since it will grow in
six or eight weeks under good conditions in autumn,
and can then be turned in, leaving the ground broken
to catch the late winter rainfall. On the light soils
it is more general to fold sheep on the catch crops

IX.] CATCH CROPS 275

than to plough them in, and though the greater part of
the humus is thus lost to the land, there is still a con-
siderable gain, while the essential manurial substances —
nitrogen, phosphoric acid, and potash — are almost
wholly returned to the soil. Where the land is light
enough to be improved by the treading of sheep and
the rainfall admits of catch-cropping, there is no better
way of building up a fertile soil than by folding ; the
actual enrichment of the soil can be effected either by
manuring for the catch crops with inorganic fertilisers
like superphosphate and nitrate of soda or by consuming
cake and corn with them. The losses inherent in making
dung are thus obviated, for when the urine falls directly
on the land, no evaporation of ammonia is allowed to
take place ; no labour is required ; the tilth of the land
is improved by the humus and the trampling of the
sheep ; no more effective nor cheaper system of growing
corn can be devised than to alternate it with green crops
consumed on the land, as is practised with so much
success on the brick earths of West Sussex and the
chalky loams of Wiltshire.

CHAPTER X

THEORIES OF FERTILISER ACTION

Liebig's Ash Theory — Part played by the Soil in the Nutrition of
the Crop — Villa's Theory of Dominants — Liebig's Law of the
Minimum — Law of diminishing Returns — Limiting Factors
in Plant Growth — Is the Composition of the Soil Water
unaffected by Fertilisers ? — Attack of the Plant's Roots upon
Insoluble Fertilisers — The Part played by Carbon Dioxide in
the Soil — Excretion of Toxic Substances from Plant Roots —
Rotations as a Substitute for Fertilisers — Unexplained Factors
in the Nutrition Problem.

It is to Liebi'g that we owe the first general theory of
the nutrition of the plant and the function of fertilisers :
although Liebig himself did not add anything to the
knowledge of the process of carbon assimilation which
had been acquired by Priestley, Senebier, and others,
nor to the study of the nitrogen and ash constituents
which had been begun by de Saussure, he yet drew up
from these facts a coherent theory of the course of
nutrition, and put it before the world with such vivid-
ness that it forthwith took its place in the general body
of accepted scientific opinion. Liebig argued that since
the ash constituents alone are drawn from the soil, it
is only necessary that there shall be no deficiency in
such inorganic materials as are left behind when the
plant is burnt, in order to ensure the complete nutrition
of the plant. According to Liebig, the function of the

2T6

CHAP. X.] LIEBIG'S THEOR Y OF PLANT NUTRITION 277

fertiliser is to supply to the soil the materials removed
therefrom by the crop, and the fertiliser required can
be ascertained beforehand by the analysis of a similar
crop, so that the soil can be supplied with the exact
amounts of potash, soda, magnesia, lime, phosphoric
acid, etc., which would be removed by a normal yield
of that particular crop. Neglecting Liebig's miscon-
ception of the source of the plant's nitrogen and the
long controversy which arose as to the necessity of its
artificial supply, we can restate the theory as assuming
that the proper fertiliser for any particular crop must
contain the amounts of nitrogen, phosphoric acid, potash,
and other constituents which are withdrawn from the
soil by a typical good yield of the plant in question.

In this form the opinion that the composition of the
crop affords the necessary guide to its manuring pre-
vailed for some time and still survives in horticultural
publications, but the course of field experiments,
particularly those at Rothamsted, and the accumula-
tion of farming experience soon demonstrated that it
was a very imperfect approximation to the truth.
Liebig's theory fails because it takes no account of the
soil and of the enormous accumulation of plant food
therein contained. Water culture experiments demon-
strated that certain elements, e.g., sodium and silica,
though universally present in the plant's ash, are
unessential to its nutrition. Field experiments also
showed that other elements — magnesium, calcium,
chlorine, sulphur, iron — though essential, are always
supplied in sufficient quantities by all normal soils.
Thus the elements to be supplied by the fertiliser
became reduced to three — nitrogen, phosphorus, and
potassium — and even the amounts required of each of
these are not indicated by the composition of the crop.
To take an example — normal crops of barley and wheat

278

THEORIES OF FERTILISER ACTION [chap.

would withdraw from the soil approximately the follow
ing fertilising materials.

Table LXXXV.— Fertilising Constituents contained
IN Wheat and Barley Crops.

Yield
of Grain,

Bushels.

Lb. per acre Removed.

Nitrogen.

Phosphoric
Acid.

Potash.

Wheat
Barley ,

36
48

50
49

21
21

29
36

Now the results of field -experiments, which are
abundantly confirmed by ordinary farming experience,
go to show that the yield of wheat is chiefly determined
by the supply of nitrogen ; phosphoric acid is of second-
ary importance, and only on exceptional soils will there
be any return for the application of potash. With
barley, though its composition is very similar to that
of wheat, the results are very different : nitrogen is still
the most important element in nutrition, but phosphoric
acid has equally marked effects, whilst in ordinary soils
potash counts for little or nothing.

This may be illustrated from the Rothamsted experi-
ments, and the part played by the reserves in the soil
will be made evident by comparing the results obtained
in the first and the fifth series of ten years.

The analysis of the barley plant would indicate that
it requires nitrogen in the largest amounts, then potash,
and, least of all, phosphoric acid ; but if the results for
the first ten years of the experiment are considered, it
will be seen that the omission of either nitrogen or
phosphoric acid from the fertiliser causes a big decline
in yield in comparison with that of the completely
fertilised plot. The omission of potash, however, is of
little or no moment, since it only causes the yield to fall

X.]

FERTILISERS REQUIRED BY BARLEY

279

from 46-1 to 45-6 bushels per acre. Evidently the soil
was able to supply all the requirements of the plant for
potash, despite the large amounts which the crop
removes. In the latter years of the experiment this
stock of available potash in the soil had become some-
what depleted, so that the omission of potash from the
fertiliser reduced the yield from 36-3 to 28-0 bushels per
acre. The exhausted soil in these latter years causes the

Table LXXXVI. — Average Yield of Barley Grain (Hoos
Field, Rothamsted).

Plot.

Manuring.

Average Yield of Grain,
Bushels.

First

Fifth

10 years
(1852-1861).

10 years
(1892-1001).

46-1

36-3

35-0

22-1

45-6
33-6

28-0

i6-6

30-5

12-8

22-4

lo-o

4A

3A

2A

lA
4O

lO

Complete Fertiliser — Nitrogen, Phosphoric

Acid, Potash

Phosphoric Acid omitted — Nitrogen and

Potash

Potash omitted — Nitrogen and Phosphoric

Acid

Nitrogen only ......

Nitrogen omitted — Phosphoric Acid and

Potash

Unmanured ......

crop to respond to the constituents of the fertiliser only
when they are all present together ; taken singly, they
increase the yield but little, and the omission of any one
of them reduces the crop almost to the minimum pro-
duced on the unmanured plot. The soil has thus become
but a small factor in the nutrition of the crop, whereas,
as regards potash, it was a very large one at the begin-
ning of the experiment, and the defect of Liebig's theory
was to neglect it entirely.

These differences in the manurial requirements of
wheat and barley, differences which would not be

28o THEORIES OF FERTILISER ACTION [chap.

apprehended from their respective compositions, may
be correlated with the habits of growth of the two
plants : wheat is sown in the autumn after but a slight
preparation of the ground, nitrification is thus restricted,
especially as the chief development of the plant takes
place in the winter and early spring before the soil has
warmed up ; as a consequence, the crop is particularly
responsive to an external supply of some active form of
nitrogen. On the other hand, the wheat plant possesses
a very extensive root system and a long period of
growth, hence it is specially well fitted to obtain
whatever mineral constituents may be available in the
soil. In ordinary farming the only fertiliser used for
the wheat crop will be a spring top-dressing of i cwt.
per acre or so of nitrate of soda, or an equivalent
amount of sulphate of ammonia or soot.

Barley is a spring-sown crop, for which the soil
generally receives a more thorough cultivation ; in
consequence the nitrates produced with the rising
temperature will be sufficient for the needs of the
crop ; often more than enough when the barley follows
a root crop that has been liberally manured and perhaps
consumed on the ground by sheep. But being shallow-
rooted, and having only a short growing season, the
barley plant experiences a difficulty in satisfying its
requirements for phosphoric acid, hence the necessary
fertiliser consists, in the main, of this constituent. Only
on sandy and gravelly soils, exceptionally deficient in
potash and subject to drought, is any benefit derived
from a supply of potash to the barley crop.

A still more noteworthy example is provided by the
Swede turnip crop ; an analysis of a representative
yield would show it to withdraw from the soil about
150 lb. per acre of nitrogen, 30 lb. of phosphoric acid,
and 120 lb. of potash. Yet the ordinary fertiliser for

X.] DOMINANT MANURES 281

the Swede crop will consist in the main of phosphatic
material, with but a small quantity of nitrogen and
rarely or never any potash. For example, 4 cwts. of
superphosphate or 5 cwts. of basic slag, according to
the soil {i.e., 50 to 100 lb. of phosphoric acid), together
with 12 to 15 lb. of nitrogen as contained in half a
hundredweight of sulphate of ammonia, will form a
very satisfactory mixture. Swedes are sown late in
the season after a very thorough preparation of the soil,
so that the nitrification alone of the nitrogenous residues
in the soil is capable of furnishing almost all the large
amount of nitrogen they require ; they are very shallow-
rooted, and must be supplied with an abundance of
phosphoric acid. It was considerations of this kind
which led Ville to suggest that for each crop there is a
" dominant " fertilising constituent, e.g., nitrogen for
wheat, phosphoric acid for Swedes, and that the parti-
cular dominant is the constituent which the plant finds
the most difficulty in appropriating from the soil, and
which is, therefore, more often indicated by a compara-
tive deficiency than by an abundance in the ash of the
plant. Such a theory is, however, not borne out by more
general experiments ; many plants do not exhibit such
idiosyncrasies as are shown by wheat and Swedes, but
require a general fertiliser, the composition of which is
determined more by the soil than the plant. Indeed, no
theory of manuring can be based upon the plant alone
but must also take the soil into account, so that a
fertiliser may be regarded as rectifying the deficiencies
of the soil as far as regards the requirements of the crop
in question. What those special requirements are can
only be decided by experiment, just as the soil con-
ditions are ascertainable by trial rather than from a
priori considerations of analysis. If an analysis be
made of any soil in cultivation it will be found to

282 THEVRIES OF FERTILISER ACTION [chap.

contain sufficient plant food for the nutriment of a
hundred or more full crops : the soil of the unmanured
plot on the Rothamsted wheatfield contained in 1893,
after fifty-four years' cropping without fertiliser, 2570 lb.
per acre of nitrogen, 2950 lb. of phosphoric acid, and
5700 lb. of potash. Of course much of this material is
in a highly insoluble condition, but though attempts
have been made by the use of weak acid solvents to
discriminate between the total plant food in the soil and
that portion of it which may be regarded as available for
the plant, no proper dividing line can be thus drawn.
The availability of a given constituent, say of phosphoric
acid, will depend upon the nature of the crop. A given
soil may contain sufficient easily soluble phosphoric
acid for the needs of the wheat plant and yet fail
to supply Swede turnips with what they require.
Again, the mechanical texture of the soil may be
such as to limit the root range of the plant, so that a
richer soil is necessary to produce as good results as are
obtained in a poorer soil of more open structure ; the
state of the micro-flora of the soil may also have much
to do with the amount of a given nutrient that can
reach the plant.

Perhaps the best general point of view of the action
of fertilisers is obtained by extending the " law of the
minimum " originally enunciated by Liebig, according
to which the yield of a given crop will be limited by the
amount of the one particular constituent which may
happen to be deficient ; if the soil, for example, is
lacking in nitrogen, the yield will be proportional to the
supply of nitrogen in the fertiliser, and no excess of
other constituents will make up for the shortage of
nitrogen. To take an example from the Rothamsted
experiments. Table LXXXVII. shows the yield of
wheat grain and straw from the unmanured plot,

X.] WHEAT YIELD WITH INCREASED NITROGEN 2^^

and from a series of plots, all of which receive an
excess of phosphoric acid, potash, etc., but varying
amounts of nitrogen, ranging from 43 lb. to 172 lb.
per acre. That the nitrogen was deficient is shown by
the almost negligible increase produced by the mineral
constituents without nitrogen ; from this point the
increase of yield is roughly proportional to the supply

Table LXXXVI I.— Experiments on Wheat (Broadbalk Field,
Rothamsted). Averages over 13 years (1852-1864).

Plot.

Manures per acre.

Dressed Grain.

Straw.

Produce

Increase
for each
additional

Produce

Increase

for each

additional

per acre.

43 lb. N.
in Manure.

per acre.

43 lb. N.
in Manure.

Bushels.

Bushels.

Cwts.

Cwts.

3

Unmanured

15-6

14-6

.».

5

Minerals alone

18.3

16.6

...

6

Minerals and 43 lb. N.

as Ammonium Salts.

28-6

IO-3

27-1

IO-5

7

Minerals and 86 lb. N.

as Ammonium Salts .

37-r

8-5

38-1

II -o

8

Minerals and 129 lb. N.

as Ammonium Salts.

39-0

1-9

42-7

4-6

16

Minerals and 172 lb. N.

as Ammonium Salts.

39-5

0-5

46-6

3-9

of nitrogen, until it reaches an excessive amount. The
table also illustrates the generalisation which is familiar
to economists under the name of the " law of diminish-
ing returns " — that the first expenditure of fertiliser or
other factor of improvement is the most effective, each
succeeding application producing smaller and smaller
returns, until a further addition causes no increase in
the yield. If the cost of the fertiliser, added to a
prime outlay of 80s. per acre for the cultivation,
and the value of the returns in cash, are expressed
in the form of a diagram, the law is clearly expressed

284 THEORIES OF FERTILISER ACTION [chap.

by the series of curves in Fig. 5 ; where the cost of
production forms a straight line that is always inter-
sected by the curves expressing the value of the returns,
which begin by rising more rapidly than the cost of
production, but tend to become horizontal. The point
of intersection, when profit ceases, is nearer the origin
the lower the range of prices obtainable for the crop,
as shown by the two curves representing the returns at
low and high prices respectively ; this demonstrates that
the expenditure on fertilisers or anything else required
by the crop must be reduced when prices of produce
are low, or, as expressed by Lawes, high farming is no
remedy for low prices,

Liebig's law of the minimum must, however, be
extended to all the factors affecting the yield as well as
to the supply of plant food, e.g., to such matters as the
supply of water, the temperature, the texture of the soil.
Any one of these may be the determining factor which
limits the yield, or two or more of them may act
successively at different periods of the plant's growth.
On poor soils the water-supply is very often the limiting
factor — on very open soils because the water actually
drains away, on extra close soils because the root range
is so restricted that the plant has but little water at
hand and the movements of soil water to renew the
supply are very slow ; in either case for comparatively
long periods the plant will be sure to have as much
nutriment as is required for the small growth permitted
by the water present. It is only when the water-supply
is sufficient that the resources of the soil, as regards all
or any of the constituents of a fertiliser, are tested and
may become in their turn the limiting factors in the
growth of the crop. Hence it follows that fertilisers
may often be wasted on poor land, where growth is
limited by the texture of the soil, by the water-supply, or

Yield,
ushels or Cwt.

Returns & Cost.
Shillings .

^\e\^

(

40

,0'^

400

/

^l^-— ^^

of Grain.

//

/

//

30

//

30O

//

/^

<

//

//

/

Returns _at

Vvl^h prices..

20

/ /

*

200

/ '°

> '

^^^^'

/

_^ -^

CO

s^-^--*"^

^

^-'

^'''

'**^

\.>^

J>*'''^eturns

at Tow "prices.

Vlineral Manures +200 lb. +400 lb. +600 lb. +800 lb. Amm. Salts.

Fig. 5.— Relation between Cost of Production and Returns avith
varying (juantities of manure.

[To face page 284.

X.] SOLUBILITY OF FERTILISERS IN SOIL WATER 285

by some other factor hardly controllable by the farmer :
it is a truism that poor land cannot be converted into
good by manuring and that fertilisers give the best
returns when applied to a good soil.

One fundamental difficulty still remains in consider-
ing the action of fertilisers ; it has already been pointed
out that a soil by no means notably fertile may contain
enormous quantities of plant food, which is however
combined in so insoluble a form as to reach the plant
in quantities insufficient for the requirements of the
crop. For example, a soil may contain o-i per cent,
or 2500 lb. per acre, of phosphoric acid, and yet yield a
very indifferent Swede crop unless it be supplied with
an additional dressing of 50 lb, per acre of soluble
phosphoric acid. It is usually assumed that the effect
of this phosphoric acid manuring is due to the soluble
nature of the fertiliser, because of which the additional
plant food is directly available for the crop. But a little
consideration of the reactions set up in the soil will
show how insufficient such a theory must be ; the
phosphoric acid is very rapidly precipitated within the
soil, as is shown by the fact that on many soils it
remains close to the surface for many years, and is
never washed out into the drains. Bearing in mind
this precipitation of the phosphoric acid in an in-
soluble condition, Whitney and Cameron argue that
previous to the addition of the fertiliser a certain
amount of phosphoric acid exists in solution in the soil
water, this amount being in equilibrium with the various
phosphates of calcium, iron, aluminium, etc., making up
the great store of phosphates in the soil. This particular
state of equilibrium would be but little disturbed by the
addition of the soluble fertiliser in quantities which are
small compared with the great mass of undissolved
phosphates in contact with the soil water ; the added

286 THEORIES OF FERTILISER ACTION [chap.

phosphoric acid would only displace an almost equivalent
amount of the phosphoric acid already in solution, and
the concentration of the new solution would only differ
from the old in the same degree as the ratio of the
phosphoric acid in the soil plus fertiliser (2500+50 lb.
of phosphoric acid), bears to the phosphoric acid
originally in the soil (z>., 2500 lb. phosphoric acid). In
other words, before the fertiliser was added, the soil
water was as fully saturated with phosphoric acid as
the amount of calcium, iron, aluminium, and other bases
would permit, and as these bases are present in enormous
excess, the soil water must remain at the same satura-
tion point after the fertiliser has been added, just as
water will only hold 35 per cent, of common salt in
solution with however large a quantity of salt it may
be in contact. In the same way the soil contains
certain double silicates of which potassium is a con-
stituent, and these hydrolise to a slight extent in contact
with the soil water to yield a solution containing
potassium ions. The addition of a soluble potassium
salt, as in a fertiliser, will diminish the dissociation and
therefore the solubility of the double silicate, the
potassium of which is thrown out of solution ; until, as
Whitney and Cameron argue, no more potassium ions
remain in solution than were present before the addition
of the fertiliser. According to this point of view, the
concentration of the soil water for a given plant food,
such as phosphoric acid, must be approximately constant
for all soils of the same type, however much or little
phosphatic fertiliser may have been applied, and since
water culture experiments show that this low limit of
concentration attained by the soil water is more than
sufficient for the needs of the plant, no soil can be
regarded as deficient in this or any other element of
plant food. It therefore follows that the action, if any,

X.] FERTILISING CONSTITUENTS IN SOIL WATER 287

of a fertiliser must be due to some other cause than the
direct supply of plant food, with which the soil water
must always be saturated to a degree which is quite
unaffected by the supply of fertiliser.

This view of the interactions between the sparingly
soluble phosphates of the soil, the soil water, and the
added soluble fertiliser can hardly be regarded as valid
in theory, even if the conditions under which the
reagents exist in the soil were the same as those
which prevail in the laboratory when such states of
equilibrium between sparingly soluble solids and water
are worked out. It has no bearing whatever on the
amount of nitrates in the soil water, since they come
into a dissolved state as fast as the nitrifying bacteria
produce them and are not in equilibrium with any store
of undissolved nitrates in the background. As regards
phosphoric acid, the theory assumes such an excess of
bases that all soils behave alike in immediately pre-
cipitating the phosphoric acid in the same form ;
while as regards potash, the argument seems to
forget that though the addition of a soluble potassium
salt may throw some of the other sparingly soluble
potassium compounds out of solution, the total amount
of potassium remaining in solution will still be greatly
increased. The function of the carbonic acid in the soil
water is ignored, as also is the fact that the processes
of solution in the soil must be in a constant state of
change, so that it is the rate at which the constituents
go into solution rather than the actual amount dissolved
at any given moment which is of importance. The soil
is too complex a mixture to permit as yet of attaching
great weight to theoretical deductions as to the actions
taking place in it, and that the state of affairs postulated
by Whitney and Cameron does hold in the soil, has
not however been verified by experiment ; the analyses,

288 THEORIES OF FERTILISER ACTION [chap.

given by the authors of the theory, of the cold water
extracts from a number of soils show great variations in
their concentration in nitrates, phosphoric acid, and
potash; nor is any evidence forthcoming that such
concentrations are not immediately raised by the
addition of fertilisers. Indeed, when the Rothamsted
soils, with their long-continued differences in fertiliser
treatment, are extracted with water charged with
carbon dioxide — the nearest laboratory equivalent to
the actual soil water — the amount of phosphoric acid
going into solution is closely proportional to the
previous fertiliser supply, and this proportionality is
maintained if the extraction is repeated with fresh
solvent, as must be the case in the soil. In the field it
is not merely the initial concentration of the soil water
in plant food which determines the supply of nutriment
to the crop ; it is also the capacity of the soil to keep
renewing the solution as the plant withdraws from it
the essential elements.

In one essential respect again the conditions pre-
vailing in the soil are very different from those of the
laboratory. In the soil all reactions are extremely
localised, since they take place in the thin film of water
normally surrounding the soil particles, in which
movement of the dissolved matter takes place very
slowly, mainly by diffusion. Of the extreme slow-
ness of the diffusion of soluble salts in the soil the
Rothamsted experiments afford some good examples.
For instance, on the grass plots only an imaginary line
divides the plots receiving different fertilisers ; the
manure is sown right up to the edge of the plot, a
screen being placed along the edge to prevent any
being thrown across the boundary, then immediately
on the other side of the boundary the different treat-
ment begins. In two cases plots receiving very large

X.] SLOW DIFFUSION OF FERTILISERS IN SOIL 289

amounts of soluble fertiliser, e.g., 550 lb. per acre of
nitrate of soda, or 600 lb. per acre of ammonium salts,
march with plots receiving either no fertiliser or a
characteristically different one, yet in neither case is
there any sign in the herbage that the soluble fertiliser
has diffused over the boundary. Although the treat-
ment has been repeated now for fifty-two years,
the dividing line between the two plots remains per-
fectly sharp, and the rank herbage produced by the
excess of nitrogenous fertiliser on one side does not stray
6 inches over the boundary. Again, on the Rotham-
sted wheatfield the plots were 24-7 feet in breadth,
and were separated by unfertilised strips only about a
foot in breadth; in 1893, each plot was sampled down
to a depth of 7-5 feet, and the amount of nitrates was
determined in each successive sample of 9 inches in
depth. The amount of nitrates found was in each case
characteristic of the supply of nitrogen to the surface of
the plot, and right down to the lowest depth there were
no signs of the proportions approximating to a common
level, as they would have done had any considerable
amount of lateral diffusion been taking place. Con-
sidering that the plots are only separated by a foot or
so of soil, and each had been receiving its particular
amount of nitrogen for forty and in some cases for fifty
years, the sharp differentiation of plot from plot in the
amount of nitrates at a depth of 7 feet is sufficiently
remarkable, and is evidence that the movements of the
soluble salts in the soil are almost wholly confined to
up and down motions due to percolation and capillary
uplift, lateral diffusion taking place only to an insignifi-
cant extent.

From these considerations we may conclude that
when a fertiliser is mixed with the soil, each particle
will establish round itself a zone of a comparatively

T

290 THEORIES OF FERTILISER ACTION [chap.

concentrated solution, to which the plant's roots will be
drawn by the ordinary chemiotactic actions, and that
these zones will extend but a little way into the
generally much less dilute mass of the soil water,
because of the slowness of the diffusion process.

That some such state of things prevails in the soil
may be surmised from the common farming experience
of the benefits derived from sowing the fertiliser close
to the seed, as when superphosphate is sown with turnip
seed, because in that case the fertiliser is not injurious
to germination and the young plant is specially dependent
on being rapidly pushed into growth in the early stages.
Again, the intimate way in which the feeding fibrous
roots of a plant will surround and cling to a fragment of
fertiliser in the soil, such as a bone or a piece of shoddy,
shows that some other actions are at work in the soil
than the feeding of the plant upon the nutrients con-
tained in the general soil solution.

Whitney and Cameron's theory also supposes that
the plant itself exerts no solvent action, whereas it has
often been supposed that the roots excrete substances
of an acid nature which exert a solvent action upon the
soil particles. In this direction an experiment of Sachs'
has become classical. He took a slab of polished marble
and set it vertically in a pot of soil in which beans or
some kindred plant were grown. After the plants had
been growing for some time the contents of the pot
were turned out and the slab of marble washed, where-
upon the polished surface was found to be etched
wherever the roots had been growing in contact with
it. A polished slab of gypsum similarly treated shows
a raised pattern wherever the roots have protected the
surface from the solvent action of the general mass of
water in the soil. Although Sachs himself attributed
the etching to the action of the carbon dioxide which is

X.] EXCRETIONS FROM PLANT ROOTS 291

alwaj's being given off by the roots, it has also been set
down to fixed acids excreted by the root hairs, and
determinations have been made of the acidity of the
sap of the roots with the idea of differentiating between
the solvent power of various plants. The roots of
germinating seedlings are also found on occasion to
redden blue litmus paper, and undoubtedly may excrete
substances of an acid character, but the behaviour of
seedlings, which are building up their fresh tissue out
of the broken-down reserve materials contained in the
seed, is essentially different from that of plants leading
an independent existence, so that nothing is thereby
proved as to the source of the etching in Sachs'
experiments.

Czapek instituted a fresh series of experiments with
smooth slabs prepared by floating on to glass plates
mixtures of plaster of Paris and various phosphates
of calcium, iron, and aluminium ; since the iron and
aluminium phosphates were attacked, most of the possible
acids were excluded, and the etching action of the plant's
roots could only be due to carbon dioxide or acetic acid.
The latter was again excluded by a further experiment in
which the slab was coloured with Congo red, and as this
was not affected the sole remaining solvent body the
plant could have excreted was carbon dioxide. Again,
it has already been shown that water cultures containing
nitrates, where the plant is growing in such solutions as
exist under normal soil conditions, tend to become
alkaline instead of acid, so that the balance of evidence
is against the idea that plant roots excrete any fixed
acids exerting a solvent action upon the soil particles.
The carbon dioxide, however, probably exerts a con-
siderable action, especially in the immediate vicinity of
the root from which it is given off, for as it passes
through the cell wall it must momentarily form a

292 THEORIES OF FERTILISER ACTION [chap,

solution of considerable concentration' possessing a
proportionally increased solvent power, and it is to this
supersaturated solution that may be attributed the
highly localised attack of the roots upon the soil
particles. An experiment by Kossowitsch illustrates
the part played by the roots in attacking the insoluble
materials in the soil : two pots of sand were prepared,
each mixed with the same quantity of calcium
phosphate in the form of ground rock phosphate, a third
pot contained sand only. In this latter and in one of
the pots containing the calcium phosphate, seeds of
mustard, peas, and flax were sown. The growing plants
were then furnished with a slow continuous supply of
water containing appropriate amounts of nitrates,
potash, and other nutrient salts except phosphates.
Before, however, this nutrient solution reached the pot
containing the sand only, it was made to percolate
through the second pot containing sand and calcium
phosphate, but it was applied directly to the pot con-
taining calcium phosphate. In the pot containing
calcium phosphate, the growth was much greater than
in the other pot, where the nutrient solution only con-
tained what phosphoric acid it could dissolve in its
passage over the calcium phosphate in the pot in which
nothing was growing, although this solution was
continually renewed. The only factor determining the
supply of phosphoric acid and the consequent difference
in growth was the solvent action of the roots when
they were actually in contact with the calcium
phosphate, and this solvent action, as has already been
shown, may most probably be attributed to the carbon
dioxide they excreted.

Following up their conclusions that the soil water
possesses an approximately constant composition under
all circumstances and always contains more of the

X.] EXCRETION OF TOXIC SUBSTANCES 293

constituents of plant food than would be required for
the nutrition of the plant, Whitney and his colleagues
have suggested another theory of fertiliser action.
According to this point of view, a soil falls off in fertility
and ceases to yield normal crops, not because of any
lack of plant food brought about by the continuous
withdrawal of the original stock in the soil, but because
of the accumulation of injurious substances excreted
from the plant itself These toxins are specific to each
plant but are gradually removed from the soil by
processes of decay, so that if a proper rotation of crops
be practised, to ensure that the same plant only recurs
after an interval long enough to permit of the destruc-
tion of its particular self-formed toxin, its yield will be
maintained without the intervention of fertilisers. The
function of fertilisers is to precipitate or to put out of
action these toxins, and various bodies such as lime,
green manure, and ferric hydrate are also effective in
this direction ; the same result of destruction of the
toxins excreted by the plant may even be brought about
by minute quantities of certain bodies like pyrogallol.
According to this theory the function of fertilisers is to
remove toxins rather than to feed the plant : they are
only required when the same crop is grown continuously,
and the need for them may be obviated by a judicious
rotation which permits of the destruction of the toxins
by natural causes. Careful consideration will show
that this theory can be made to fit a good many of the
phenomena of plant nutrition, it would also explain the
difficulties experienced in growing certain crops con-
tinuously on the same ground ; it is in fact an elaborated
revival of one of the earliest explanations of the value
of rotations, originally suggested by de Candolle.
Furthermore, Whitney's colleagues have succeeded in
extracting certain substances from the soil — di-hydroxy-

294 THEORIES OF FERTILISER ACTION [chap.

stearic acid, picoline-carboxylic acid, etc., which when
introduced into water cultures are toxic to seedling
plants. The compounds isolated are, however, all of
them products of the oxidation and decay of proteins,
fats, and other compounds contained in plant residues ;
there is no evidence to show that they are specific
excretions from particular plants or that they are more
abundant in soil impoverished by the continuous
growth of a crop than in soil which would be usually
termed rich. Again, it has not been demonstrated that
such substances, although harmful to young plants in
water culture, are toxic under soil conditions ; it is well
known how exceedingly sensitive are plants in water
culture, where growth, for example, is inhibited by
traces of copper not to be detected by ordinary methods
of analysis. A body like ammonia, itself a product of
protein decay and present in the soil, is exceedingly
toxic to water cultures, yet when applied to the soil it
increases the growth of the plant. Turning to the
fertiliser side of the theory, evidence is yet lacking to
show that fertilisers in such dilute solutions as they
form in the soil water can exert any precipitating or
destructive action on such toxic substances as have
been extracted from the soil ; particularly the specific
action of fertilisers is difficult to explain. Why should
substances so dissimilar as nitrate of soda and
sulphate of ammonia exert the same sort of action on
the same toxin ? Why should phosphates cause all
classes of plants to develop in one direction, or why
should they be appropriate to the toxins of all plants
on one particular type of soil, whereas potash answers
on another soil type?

Lastly, there is a lack of evidence for the funda-
mental thesis that the rotation will take the place
pf fertilisers and that the yield only falls off when a

X.] CAN ROTA TIONS REP LA CE PER TILISERS ? 29 \

particular crop is grown continuously on the same land.
On the rotation field at Rothamsted the yield of
wheat on the unfertilised plot has been remarkably
maintained ; for the last five courses (loth to 14th of
the whole series) it has averaged 26-2 bushels per acre,
but it is below the yield of the fertilised plots on the
Broadbalk field, which averaged 35-7, 32, and 39-7
bushels for the same years, and also below the fertilised
plot on the same rotation field, which averaged for the
same period 37-1 bushels per acre, although the fertiliser
is only applied once in four years to the Swedes, which
are followed by barley and either clover or a bare fallow
before the turn of the wheat comes round. But with
other crops than wheat no such maintenance of yield is
to be seen on the unfertilised plot of the rotation field —
the barley yield has been reduced to 15-8 bushels
against 27-7 on the fertilised plot, the clover yield to
94 cwts. against 37-8 on the fertilised plot, and the
turnips to as little as 16 cwts. against 400 on the
fertilised plot. Here we see that with the barley, clover,
and particularly with the turnip crop, a rotation is quite
unable to do the work of the fertiliser ; the yield of
turnips is reduced to a minimum on the impoverished
soil, even though the crop only comes round once in
four years and then grows so poorly that it can do little
specific excretion to harm the succeeding crop. Many
instances could be given of the incapacity of certain
plants to grow in soil the fertility of which had been
exhausted by other crops ; for example, at Rothamsted
in 1903, Swede turnips were sown on Little Hoos field,
which was known not to have been cropped with Swedes
or any kindred crop for more than forty years, and the
average yield from thirty-two unmanured plots was only
9-3 tons per acre, although an exceptionally good start
was made by the plant. In the following season barley

296 THEORIES OF FERTILISER ACTION [chap.

was grown and the unmanured plots averaged 24-2
bushels per acre, a relatively much higher yield than
the Swedes had shown — yet barley had been repeatedly
grown on the field in the years immediately before it
was brought under experiment.

As it stands at present Whitney's theory must be
regarded as lacking the necessary experimental founda-
tion ; no convincing evidence has been produced of the
fundamental fact of the excretion of toxic substances
from plants past the autotrophic seedling stage, nor is
there direct proof of the initial supposition that all soils
give rise to soil solutions sufficiently rich in the elements
of plant food to nourish a full crop, did not some other
factor come into play. If, however, we give the theory
a wider form, and instead of excretions from the plant
understand debris of any kind left behind by the plant
and the results of bacterial action upon it, we may
thereby obtain a clue to certain phenomena at present
imperfectly understood. The value of a rotation of
crops is undoubted and in the main is explicable by the
opportunity it affords of cleaning the ground, the
freedom from any accumulation of weeds, insect, or
fungoid pests associated with a particular crop, and to
the successive tillage of different layers of the soil, but
for many crops there remains a certain beneficial effect
from a rotation beyond the factors enumerated.

The Rothamsted experiments have shown that
wheat can be grown continuously upon the same land
for more than fifty years, and that the yield when
proper fertilisers are applied remains as large in the
later as in the earlier years of the series ; any decline
that is taking place is hardly outside the limits of
seasonal variation and can easily be accounted for by
the difficulties of tillage and the increase of one or two
troublesome weeds. Mangolds, again, in the Rothamsted

X.] VALUE OF ROTATION OF CROPS 297

experiments show no falling off in yield, though they
have now been grown upon the same land for thirty-
two years ; but with the barley crop, despite the applica-
tion of fertilisers, there is a distinct secular decline in
the yield. Again, it was found impossible to obtain
satisfactory crops of Swede turnips upon the same land
for more than ten or twelve years in succession, and
clover is well known to render the land " sick " for its
own renewed growth for a period of from four to eight
years on British soil. In this last case the persistence
of the resting stages of the sderotinia disease in the
land may be the determining factor, but there are other
crops, e.g., flax, hemp, and strawberries, which are con-
sidered by the practical cultivator to render the land
more or less " sick," so that their growth cannot profit-
ably be renewed until an interval of some years has
elapsed.

Again, it is well known that when a plant is sown
upon land which has not carried that particular crop for
many years beforehand, it starts into growth with a
vigour it rarely displays upon land where it forms an
item in the regular rotation, even though the new land
is so impoverished that the final yield is indifferent
In the instance quoted above, where Swedes were
sown on the Little Hoos field after a very long
interval, although the yield was poor on the unmanured
plots yet the seeds germinated and made their early
growth in a very remarkable fashion, incomparably
better than did the same seed sown upon adjoining
land in a high state of fertility, but which had been
cropped with Swedes from time to time previously.
There is thus some positive evidence that most plants
— some to a very slight degree, like wheat and mangolds,
others markedly, like clover, turnips, and flax — effect
some change in the soil which unfits it for the renewed

298 THEORIES OF FERTILISER ACTION [chap.

growth of the crop. The injurious action may even
arise from the growth of a different crop, as in the well-
known experiments at the Woburn Fruit Farm, where
Pickering has shown that the roots of grasses exert a
positively injurious effect, distinct from competition for
food, water, or air, upon fruit trees growing in the same
soil.

Assuming that the persistence in the soil of obscure
diseases appropriate to the particular plant can be
neglected as the cause of these phenomena, there still
remains some unexplained factor arising from a plant's
growth which is injurious to a succeeding crop, and this
may either be the excreted toxins of Whitney's theory
or may be some secondary effects due to the competi-
tion or injurious products of the bacteria and other
micro-flora accumulated in the particular soil layer in
which the roots of the crop chiefly reside. Experi-
mental evidence is as yet wanting as to these highly
complex interactions between the higher plants and
the micro-flora of the soil, but Russell and other
observers have shown how greatly a disturbance of the
normal equilibrium of the flora of the soil may affect its
fertility, as measured by the yield of a higher plant
Partial sterilisation, such as is brought about by heating
the soil to 98° for ten hours, will double the yield of the
succeeding crop and will show a perceptible beneficial
effect up to the fourth crop after the heating; and
exposure to the vapours of volatile antiseptics like
toluene or carbon bisulphide, which are afterwards
entirely removed by exposure, will increase the yield in
a similar but smaller degree ; even drying the soil
appears to have an influence upon its fertility.

It is in this direction perhaps that the clue may be
found to the unexplained benefits of the rotation of
crops, and to some of the other facts difficult of ex-

X.] VALUE OF ROTATION OF CROPS 1C)C)

planation upon the ordinary theories of plant nutrition
which have been advanced by Whitney and his co-
workers. The soil however is such a complex medium
— the seat of so many and diverse interactions, chemical,
physical, and biological — and is so unsusceptible of
synthetic reproduction from known materials, that
experimental work of a crucial character becomes
extremely difficult and above all requires to be inter-
Dieted with extreme caution and conservatism

CHAPTER XI

SYSTEMS OF MANURING CROPS

High and Low Farming — Fertilising Constituents removed in
Meal and Corn — Losses of Nitrogen increased when Land is
in High Condition — Manures for Wheat — Barley : Importance
of Quality — Oats — Root Crops : Swedes, Mangolds, Potatoes
— Importance of Farmyard Manure for Root Crops —
Leguminous Crops : Beans, Clover, Lucerne, Sainfoin —
Value of Potassic Fertilisers — Grass Land — Effect of Manures
in changing the Botanical Character of the Herbage — Land
laid up for Hay — Manures for Poor Pastures — Hops — Fruit —
Garden Manures — Manures for Tropical and Semi-Tropical
Crops : Sugar Cane, Tobacco, Cotton, Tea.

In dealing with the specific properties of the various
fertilisers, a number of illustrations have been given
from the results of field experiments on particular crops
from which conclusions might be drawn as to the
fertilisers most appropriate to those crops, but in the
main these experiments have been selected to illustrate
the action of the fertiliser rather than the requirements
of the plant. It remains to reconsider the information
derived from experiments under its practical aspect, so
as to obtain a guide to the methods of manuring which
the farmer should adopt for the crops he is setting out
to grow. It is never possible to do this absolutely ; the
proper manure for any particular crop must always be
conditioned by a number of local circumstances special
to the farm in question ; from which it follows that the

900

CHAP. XI.] SYSTEMS Of FARMING 301

mixtures sold as " Turnip Manures," " Potato Manures,"
and so forth, must be in the majority of cases more or
less wasteful if they are to be effective everywhere.
Instead of applying a kind of average manure, the farmer
ought to have such an appreciation of manurial principles
that he can adapt his fertilisers as economically as
possible to his own soil and conditions of farming.

In discussing the application of fertilisers to crops,
even when the special features presented by the soil are
neglected, we can draw no conclusions as to the proper
methods of manuring unless we take into account the
place the crop occupies in the rotation adopted by the
farmer, and also the character of his land and style of
farming. For example, we have not to consider the
wheat crop as standing by itself in the manner we see
it in the Rothamsted experiments, but as it is generally
grown in practice — after a clover crop, or perhaps after
mangolds which have been manured with dung.
Furthermore, one man may be in possession of good
land in high condition, and may be farming "high" for
big crops ; he will be justified in a greater outlay upon
fertilisers than would be advisable for an equally good
farmer on poorer land, where it may be more economical
to be content with smaller crops and to keep down the
expenditure. The manuring to be adopted on a given
farm must be looked at as a whole, as a system to be
shaped as much by various wider considerations of
farming policy as by the particular crops that are being
grown. It is easy, for example, to indicate the com-
position a manure for Swedes should possess, but
whether a farmer should spend 15s. or 40s. an acre on
fertilisers for his Swede land depends entirely upon the
general character and style of his farm. It is for
this reason that many field experiments, however
ostensibly designed on a cash basis to show the returns

302 SYSTEMS OF MANURING CROPS [chap.

for a given outlay in manure, are really unpractical ; so
variable is the basis — the condition of the land — upon
which the return depends, and so much does the power
of realising products like roots change from farm to
farm. The style of farming, and with it the amount of
fertilisers that can be profitably employed, will always
be dictated by such local conditions as the markets
available, the supply of labour, and the rent of the land.
On the one hand we have the systems prevailing in the
middle west of America and other more newly settled
countries where the farmer is living upon the capital
originally stored up in the virgin soil. He grows, for
example, maize and wheat alternately, using no fertiliser
and restoring nothing to the soil, often burning the
straw and not even taking the trouble to cart out
the manure accumulated beneath any cattle he may
feed. Year after year 50 to 100 lb. of nitrogen per acre
are being removed and the soil is getting steadily
poorer, yet it has proved to be more profitable to move
to fresh land than to spend money in restoring the lost
fertility. On the other hand, in many parts of Great
Britain we may see a strictly conservative system at
work. The land possesses a certain condition and will
yield fair average crops, only part of which are sold —
the wheat and barley — the rest are converted into meat
and dung, by which means the greater part of the plant
food drawn from the soil is returned. There is, however,
a certain removal in the corn and meat and a certain
amount of waste in dung-making, but this is repaired
by the growth of clover, etc., and by the purchase of a
comparatively limited amount of fertilisers or feeding
stuffs, so that the condition of the land is maintained
but not at a very high level. Again, at the other end
of the scale we have the intensive farmer who uses
his land as a sort of manufacturing medium to convert

xr.] PLANT FOOD REMOVED FROM A FARM 303

fertilisers into crops, and steadily increases the fertility
of his soil by putting on more plant food every year
than he removes in his crops.

We can begin by considering what is necessary to
maintain the condition of the land under a conservative
system of farming, and we may take the case of a farm
under a four-course rotation, where nothing but corn
and meat are sold and all the dung goes back to
the land. Under such conditions, as we have already
learnt, the feeding animals only retain about 10 per
cent, of the fertilising constituents of the food they
consume ; the other 90 per cent, comes back in the
manure and wholly or in part reaches the land again.

Table LXXXVIII. — Fertilising Constituents removed from
Farm in Corn and Meat Sold.

Nitrogen.

P2O5.

K2O.

Swede Turnips, 20 tons fed
Barley, 6 quarters sold ....
h ton Straw fed, the rest made into Dun;;- ,
Clover, 2 tons Hay fed ....
Wheat, 4 quarters sold ....
Straw made into Dung.

Total for 4 acres . <>

Per acre per annum .

Lb.

lO-O

40-0

1-2

4-1
35-2

Lb.

5-8

180

07

2-8

15-3

Lb.

0-7

12-0
O-I

0-4
10-3

90-5

42-6

23-5

22-6

IO-6

5-9

In this way the land loses 226 lb. of nitrogen per
acre per annum ; but this estimate fails to take into
account the very considerable losses that occur during
the making of the farmyard manure, which may be
estimated at 50 lb. in the four years, and those due to
drainage and bacterial action. On the other hand, the
nitrogen contained in the clover crop has been obtained

304 SYSTEMS OF MANURING CROPS [CHAP.

from the atmosphere ; indeed, the Rothamsted experi-
ments would show that the land is left richer in nitrogen
after a big clover crop has been grown and taken away.
A further consideration of the rotation field at
Rothamsted shows that the clover crop alone would be
able to maintain the fertility of the land at about the
condition which would produce such yields as are shown
in the table. For instance, the Agdell field in the 47th
to the 50th years gave the following crops on the portion
which had received no nitrogen throughout the whole
period, though phosphates and potash are supplied to
the Swede crop.

Table LXXXIX.— Produce of Agdell Field under Rotation.
No Nitrogen supplied in Manure. (Rothamsted.)

1894

1895
1896
1897

Clover Hay
Wheat
Swedes
Barley

Carted away ,
Carted away
Consumed on the land
Carted away

64-7 cwts.

r39-6 bushels, and 25-3 cwts.

\^ Straw.

I2-0 tons.

{37'7 bushels, and 24-9 cwts.
Straw.

If, then, in this case the Swede turnips had also
received whatever manure would have been made from
the clover hay and the wheat and barley straw, it is
evident that the production would have been little short
of the average indicated in Table LXXXVIIL, and
that the nitrogen necessary to maintain the fertility of
the land at such a level would be supplied indefinitely
by the recurring clover crop. In the Agdell example
phosphatic and potassic fertilisers were however freely
employed, and it is obvious that the soil possesses no
power of increasing its stock of these constituents in the
same way as it can obtain nitrogen from the atmosphere.
Three hundred and fifty pounds of superphosphate per
acre during the four-year period of rotation would,

XI.] FERTILISERS IN ORDINARY FARMING 305

however, repair the losses, and as regards potash the
losses are so small that on a loamy or clay soil they
would be made up by the continual slow weathering into
an available form of the insoluble potash compounds in
the soil.

It is, however, a low level of production that is
attained in this example of an almost self-supporting
piece of land, and if the average yield is to be raised,
say to 5 qrs. of wheat and 6 qrs. of barley per acre, an
external supply of nitrogen must be obtained, either in
the form of fertilisers or feeding stuffs. Moreover, this
additional nitrogen must be considerably more than
would be contained in the extra quarter of wheat and
other larger crops that are grown ; there must be enough
to compensate for the greatly increased waste by drain-
age, denitrification, etc., which will accompany the higher
fertility of the soil. Several examples have already been
given to show that the greater the amount of fertiliser
added to the soil the smaller is the proportion returned
in the crop ; these are only particular cases of the
general rule that the wastage of nitrogen is greater
the higher the fertility of the soil. Fertilisers go
less to feed the crop directly than to maintain the
level of fertility of the land, and as this rises all the
actions which result in loss of nitrogen are increased
at a rapid rate. Thus the intensive farmer often
becomes wasteful because, after his land is in good
heart, he continues to add fertilisers at the same rate as
he did when he was building up its condition.

It therefore follows that an account of what is
removed from the soil year by year by the crops or
animals raised upon the farm provides very little
guidance towards determining the amount of fertiliser
which must be brought in ; at a low level of production,
good land will practically recuperate itself without any

U

3o6 SYSTEMS OF MANURING CROPS [chap.

extraneous manure, while really high farming for big
crops involves a considerable wastage of nitrogen
applied to the land and never recovered in the crop. It
is only by experience, by the knowledge of his own land
and the market conditions which prevail, that the
individual farmer can tell how high it is profitable for
him to farm, and therefore to what degree he can
utilise the information as to feeding his crops which is
provided by field experiments.

The discussion that follows of the manures appropri-
ate to each of the staple crops is therefore intended to
supply the farmer, not with a series of recipes or patent
mixtures that are universally applicable, but with
principles out of which he can construct a rational
system appropriate to his own farm. In the practice of
farming many things may at once be set down as
" wrong," but there can be nothing absolutely " right " ;
the proper course of action is never anything more than
a judicious compromise adapted to all the various con-
ditions of climate, soil, and markets. We can now
consider the ordinary farm crops separately.

Wheat in the typical four-course rotation follows
the ploughed-up clover ley, and generally derives all
the nitrogen it requires from the residues left by the
clover in the soil. In many cases, however, oats are
now substituted for wheat after the ley, because more
time is thus obtained to graze the aftermath and
break up the land before seeding; oats also after the
ploughed land has been exposed for the winter suffer
less than wheat from the wireworm which is apt to be
prevalent in the old clover land. Should wheat follow a
good crop of clover further manuring is not required ;
though if the second growth of the clover has been
allowed to ripen seed, which removes a large proportion
of the stored up nitrogen, or if much rye grass has been

.-ii.] MANURES FOR WHEAT 307

present in the seeds mixture and the clover has failed
somewhat, it may be desirable to enrich the ground still
further. This may be done either by spreading a coat-
ing of dung ( i o tons per acre) on the clover before plough-
ing, or by a spring top-dressing of i to li cwts. per acre
of nitrate of soda or sulphate of ammonia, preferably
the former for wheat. When wheat follows mangolds,
as is not unfrequently the case, no manure is likely to
be required, because the mangolds will have received
dung and will have been frequently cultivated. Speak-
ing generally on soils in good heart wheat will rarely
require manuring ; at any rate, it will be wise to wait
until the early spring, if the plant then appears to be
growing badly or losing ground a top dressing of nitrate
of soda (i to 1 1 cwts. per acre), sulphate of ammonia
(i cwt. per acre), or soot (20 bushels per acre) will do
all that is needful. Soot has for some centuries been
employed as a spring top-dressing for wheat ; besides
the nitrogen it supplies, it also tends to preserve the
plant from the attacks of the small slugs and snails
which are so active at that time of year.

Of course, when wheat and other cereals are grown
continuously on the same land, as on Mr Prout's farm
at Sawbridgeworth, it is necessary to employ a more
complete fertiliser — 2 cwts. per acre of nitrate of soda or
sulphate of ammonia will be required as a spring top-
dressing, and 3 cwts. of superphosphate or 2 cwts. of basic
slag, according to the amount of calcium carbonate in
the soil, should be sown before the seed. Potash would
only be necessary on the lighter soils, on which wheat
is not likely to be grown continuously, but in such a
case 3 cwts. or so per acre of kainit would be desirable.
Fertilisers for wheat may be crude salts, like nitrate of
soda or superphosphate ; the establishment of a plant
is little affected by the amount of humus in the soil and

3o8 SYSTEMS OF MANURING CROPS [chap.

the extra price of organic manures like the guanos will
rarely be repaid by any increased yield.

Barley is grown under two very different conditions
of tilth. In the first place, it may follow wheat and
form the second or even the third white straw crop after
roots or a clover ley; in the Isle of Thanet three, four,
or even five barley crops may be taken in succession
after an old lucerne or sainfoin ley has been broken up.
In such cases the high condition will have been taken
out of the soil by the first crop of wheat, there will no
longer be any excess of readily available nitrogen, and
as there is a good opportunity of getting the soil early
into tilth, barley of high quality may be expected.
Good malting barley contains a low percentage of
nitrogen, hence the soil on which it grows must not be
too rich, nor must any large quantity of nitrogenous
manure be employed. On the other hand, however, it
is a mistake to suppose that impoverished soil alone
will yield good barley ; unless a reasonable amount of
nitrogen be available not only will the yield be small
but the size of the berry will fall away. This may be
illustrated from the Rothamsted experiments on the
Agdell field, where the barley follows Swede turnips in
the rotation. On this field the plots are manured for
the root crop but not for the barley which follows, and
on three of the plots the following average results were
obtained (Table XC).

The soil of the first plot was in a very impoverished
condition because a crop of roots had been grown
without nitrogenous manure and had been wholly
removed from the soil ; the grain in consequence was
poorly developed for want of nitrogen, as is shown by
its low weight per bushel and per looo grains ; its value
was, in consequence, low in spite of the small percentage
of nitrogen it contained. The second plot, on which a

XL]

MANURES FOR BARLE V

309

small crop of roots had been fed, gave the best results ;
the third plot, on which a large crop of roots had been
fed, evidently received too much nitrogen, as shown
by the high percentage in the grain ; as a result the
value fell off. The figures are the means of several
years' valuations.

Table XC— Relation of Quality of Barley to the Nitrogen
SUPPLIED IN Manure (Rothamsted).

Manuring
for Roots.

Treatment
of Roots.

Yield of
Barley,
per acre.

(B.Q

0.

o.S ™-
•£0 w>

9 '5

ID U

i

^.2

Grain.

Straw.

Minerals, no

Bush.

Cwts.

Nitrogen .
Minerals, no

Carted off .

13-6

9.2

54-0

397

1-484

28/7

Nitrogen .
Minerals and

Fed on Land

28-9

17-5

55-3

44-3

1-576

29/11

Nitrogen .

Fed on Land

34-1

23-4

55-3

46-2

1-693

29/6

In preparing for a crop of barley of high quality it
is therefore necessary not to allow the land to become
really poor, but it is desirable that the nitrogen should
come more from condition in the land than from very
active manures. If the land is in really high condition
before the first straw crop of wheat or oats is taken,
barley may follow without any fertiliser, especially
if the ground can be got into good tilth and the
barley sown really early. But for a second barley
crop or for the first on land in poorer heart some
nitrogenous manure must be used, and sulphate of
ammonia and rape cake are found to give better
quality than nitrate of soda, though in neither case
must a large quantity be used. Furthermore, it has
been shown earlier (p. 140) that phosphoric acid is a very
essential constituent of any fertiliser for barley, and

3IO SYSTEMS OF MANURING CROPS [chap.

whatever the tilth it seems desirable to give this crop
about 3 cwts. per acre of superphosphate, or its equivalent
in steamed bone flour or phosphatic guano on light soils
poor in carbonate of lime. The question of potash is
more doubtful ; while potash manures have been found
to stiffen the straw and increase the size of the berry-
by promoting starch-formation, they also prolong the
maturity of the barley and darken its colour slightly.
Hence, potash manures must be used carefully and are
only likely to be valuable on light sandy or gravelly
soils. We thus arrive at the following mixture for a
barley manure, when barley follows one or more white
straw crops and the land is no longer in high condi-
tion : —

Sulphate of ammonia ^ to i| cwts., or rape dust 4 to
6 cwts. per acre.

Superphosphate 3 cwts. per acre, or steamed bone
flour 2 cwts.

Sulphate of potash \ cwt. per acre, on light soils
only.

The superphosphate and sulphate of ammonia or
rape dust should be mixed and sown broadcast before
the seed is drilled ; it is impossible to distribute small
quantities like a | to i cwt. as a top dressing evenly
unless they are mixed with a much larger bulk of
ashes.

A mixture of this kind would also serve for the rare
case of barley following roots which have been grown
without farmyard manure and then carted off the land.

When barley follows roots which have been highly
manured with farmyard manure, still more so when the
roots have been folded off by sheep, the land is already
too rich in readily available nitrogen to grow barley of
the highest quality, the more so as the roots are often
left so late on the ground that a good seed-bed cannot

XI.] MANURES FOR OATS 31 1

be obtained early in the year. Early sowing is essential
for barley of high quality, and except on the very
lightest soils if the root land cannot be broken up before
the New Year, so that the frosts may have time to break
down the clods which have been formed by the sheep
treading the wet land, it is better to sow either oats or
a barley like Archer's, which will yield well for feeding
purposes though the quality may not reach a malting
standard. When the roots have been fed on the land
3 cwts. per acre of superphosphate sown with the seed is
found to improve the quality of the grain and help to
correct the excess of nitrogen ; but neither potash
fertilisers nor salt, which is sometimes recommended
and which acts as a liberator of potash in the soil, are
of value except on the very lightest of soils. When the
roots have been grown with farmyard manure and then
carted off the land will be in about the right condition
for barley, and will want no help except a little super-
phosphate, should none have been used for the root crop.
Oats. — The general principles of manuring for barley
hold also for oats, except that, being grown for feeding
purposes only, they can be given much larger quantities
of nitrogen without any fear of injuring their quality.
When grown on a ploughed-up ley, which in many cases
is also lightly dunged before ploughing, oats are not
likely to require any fertiliser; at the most a little
nitrate of soda if they are found to be starting away too
slowly. As an all-round fertiliser for oats when the
land is in poor condition i to 2 cwts. of nitrate of soda
or sulphate of ammonia, and 2 cwts. of superphosphate
or basic slag, according to the class of soil, will answer
all the requirements of the oat crop ; potash fertilisers
would be wasted, as also would the more expensive
organic forms of nitrogen with a crop which occupies
the land for so short a period. Of course, in a wet

312 SYSTEMS OF MANURING CROPS [chap.

season as much as 2 cwts. per acre of nitrogenous manure
might easily result in the crop going down.

Rye, which is grown in the south of England for
early spring keep is rarely manured ; but maize, which is
also grown to some extent as fodder, requires the land
to be brought into fairly high condition. A preliminary
dressing of 12 to 15 loads of dung per acre should be
given, with 2 to 3 cwts. per acre of superphosphate at
the time of sowing, then i cwt. per acre of nitrate of
soda may be used as a top dressing round the plants
when they are set out and side hoed.

Root-crops. — In British farming the bulk of the
manure that is made upon the farm or purchased is
applied to the root-crops — Swedes or mangolds ; though
in the east and south-east of England it is more general
to apply the farmyard manure to the seeds before
ploughing up for wheat. In these warm soils much
nitrogenous manure is apt to cause Swedes to run to
top and to be more susceptible to mildew. Big crops
of roots mean more food for the stock, and so in turn
more farmyard manure. Moreover, the roots are grateful,
and continue to respond to liberal treatment without
lodging or growing an excess of straw, as cereal crops
will do. It is questionable, however, whether the very
common practice in the north of putting on all the
available manure, farmyard and artificial, for the root-
crop and making that serve for the whole of the rotation,
is wise ; better results will be obtained by a careful
adaptation of the fertiliser to the particular crops form-
ing the rotation. As regards Swedes, the earliest work
that was done at Rothamsted consisted in showing the
dependence of this crop upon an ample supply of
phosphatic manure of an available character, and it was
the response of this crop to soluble phosphates which
built up the superphosphate and other artificial fertiliser

XI.] MANURES FOR SWEDES 313

industries. The point may be illustrated from the
Rothamsted experiments on the Agdell field, where
crops are grown in rotation with the following average
results : —

Unmanured 16 cwts.

Mineral only — Superphosphate and
Sulphate of Potash . . , . 208 „

Complete Manure — Nitrogen, Super-
phosphate, and Sulphate of Potash . 400 „

Without manure the yield is trifling, but with the
mineral manures (and the phosphoric acid is the
effective factor) the yield rises to 208 cwts. per acre,
although the land had been continually cropped without
any nitrogen supply ; lastly, when nitrogen also is
added, the yield becomes that of a high average crop
for the south of England. In practice, however, it is
found that where the land has been kept in good con-
dition and there has been adequate preparation of the
seed-bed, little or no manurial nitrogen will be required
to supplement the nitrates produced from the soil
reserves, and that consequently the great increase due
to the nitrogen in the experiments quoted will not be
reproduced under ordinary conditions of farming.

In a large co-operative series of trials undertaken
by the Highland and Agricultural Society over the
whole of Scotland it was found that 84 lb. per acre of
sulphate of ammonia, or its equivalent in i cwt of nitrate
of soda, was as much nitrogenous manure as could be
profitably employed. About 5 cwts. per acre of super-
phosphate, or 4 cwts. of basic slag, or 2 cwts. of steamed
bone flour, according to the soil, were indispensable ; the
superphosphate being best on loams and calcareous
soils, the basic slag on clays and peaty land, and the
steamed bone flour on sands and gravels.

314

SYSTEMS OF MANURING CROPS [chap.

An abstract from these experiments shows the
following average results obtained from io8 plots
during the years 1892-94: —

Table XCI. — Yield of Turnips with different Fertilisers.

Roots
per acre.

Unmanured .....,..«■

Tons.
II-3
17-9
i8-9
I9-I
i8-4
17-0
19-2
19-4

Superphosphate and Basic Slag (7^ cwts. only) .
Superphosphate (6 cwts.), Sulphate of Ammonia (|) .
Superphosphate (6 cwts.), Nitrate of Soda (i cwt.)
Basic Slag (9 cwts.), Nitrate of Soda (i cwt.)
Bone Meal (4 cwts.). Nitrate of Soda (J cwt.)
Superphosphate, Basic Slag, Nitrate of Soda (i cwt.)
Superphosphate, Basic Slag, Nitrate of Soda (2 cwts.)

It will be seen that in these experiments the
phosphatic manures are the most effective in producing
an increased yield ; phosphate alone put up the crop
from 11-3 to 17-9 tons per acre: i cwt. of nitrate of
soda or sulphate of ammonia only add about another
ton to the crop, while a second hundredweight produced
no perceptible increase at all.

The question of the most appropriate manurial
treatment for Swedes depends upon how much farmyard
manure is available ; while the ordinary four-course
rotation is being practised, most of the dung made will
come back to the land for the Swede crop, about 10 tons
to the acre being available. Of course, with such
quantities of farmyard manure the Swedes will require
no further nitrogenous dressing; phosphates are, however,
still indispensable. In such cases it is generally the
custom to finish off the seed-bed preparation with a
ridging plough, and to apply the dung to the furrows
just before sowing. The ridges are then split back over
the dung, the new ridges thus formed are rolled, and

XI.] MANURES FOR SWEDES 315

the seed and superphosphate are sown from the same
drill on the top of the ridge. This plan answers
excellently in the cooler and moister parts of the
country, where the Swede flourishes and grows big
crops, but in the south and east of England such a
method exposes the crop too much to risk of damage
from drought, both through evaporation from the sides
of the ridge and because the fresh manure as it rots
leaves the land too open. On warm dry soils it is better
to plough in the farmyard manure in the autumn, and
to sow the Swedes on the flat with their appropriate
artificial manure. It is in the south again that farm-
yard manure is often lacking for the Swede crop, because
it has been wanted for wheat or hops or potatoes, or
sometimes for the grass land ; many sheep farmers,
again, who fold on the Swede land have a strong
objection to Swedes grown with farmyard manure. A
suitable mixture in this case, when no farmyard manure
is available, will consist of 4 cwts, of superphosphate
(or its equivalent in basic slag or steamed bone flour
as before), 2 cwts. of fish or meat guano, and \ cwt. of
a mixture of nitrate of soda and sulphate of ammonia
as a top dressing when the plants are singled. If the
land is in really good heart, the fish guano can be
omitted or reduced. It will be seen that various com-
pounds of nitrogen are used in order to ensure a steady
and continuous supply of nitrates as long as the plant
is growing ; the mixture of sulphate of ammonia and
nitrate of soda ensures a neutral reaction in the soil.
Though superphosphate and sulphate of ammonia are, on
the whole, the best fertilisers in their respective classes
for Swedes, they must be employed with care where
there is little lime in the soil, and not at all if the land
is known to be subject to " finger-and-toe." Both are
acid manures, and the organism causing finger-and-toe

3i6 SYSTEMS OF MANURING CROPS [chap.

only flourishes in an acid medium. Potash salts are
rarely used for the Swede crop, though, like other root-
crops storing up a good deal of carbohydrate, the Swede
will respond to liberal allowances of potash. On the
lighter soils, when farmyard manure is only scantily
used, it is undoubtedly wise to apply about 3 cwts. of
kainit while the land is being prepared for the seed-
bed.

Of the other crops allied to Swedes, white turnips
require much the same treatment, except that the fish
guano may be omitted because they possess a shorter
period of growth, while the potash is more necessary.
Kohl rabi may have just the same treatment as Swedes,
as may thousand-headed kale and cabbage, with the
addition of more nitrogen. Cabbages in particular will
respond to enormous quantities of nitrogen ; in addition
to the farmyard manure or fish guano recommended
for the Swedes, up to 3 cwts. per acre of the mixture of
nitrate of soda and sulphate of ammonia may be used
in two or three top dressings. In market garden work
such active nitrogenous manure brings the cabbages
earlier to cutting and renders them tenderer, though
they are reputed in consequence not to travel so well to
distant markets. Stock feeders do not like cabbages or
any other root crop grown with an excessive amount of
nitrogen, especially of nitrate of soda ; the plant
material that has been forced in this fashion becomes
a poor or even a harmful food, but whether this is due
to the increased amount of nitrates in the plant or to
other compounds of nitrogen is as yet uncertain.

Mangolds are often described as heavy feeders, by
which we may understand that the yield will go on
responding to very large additions of manure rather
than that the crop removes a specially large amount of
manurial constituents from the soil ; a fact which would

XL]

MANURES FOR MANGOLDS

317

not be apparent in the succeeding crops but could only
be ascertained by analysis. The mangold differs entirely
from the Swede in its requirements. In the first place,
it will give returns for very large quantities of nitrogen ;
secondly, it needs much potash and but little phosphoric
acid in the fertiliser. The Rothamsted experiments show
that mangolds can be grown successfully for very many
years in succession upon the same land if suitable
fertilisers are provided. The only difBculty experienced
lies in the getting of a plant on the plots where the
tilth of the soil has been injured by long-continued
treatment in one particular direction.

The results given by some of the Rothamsted plots
are set out in Table XCII.

Table XCII.— Average Yield of Mangolds (Rothamsted).
32 Years, i 876-1 907.

Superphosphate.

Dung.

No
Potash.

Potash,
etc.

Alone.

With
Phosphate
and Potash.

Rape Cake ==98 lb. N.
Nitrate of Soda = 86 lb. N.
Ammonium Salts = 86 lb. N .

II-I

iS-3
7-5

22-0

l8-o

15-2

24-5
25-9
22.5

25.7
26-4
24.0

These results illustrate the following points in the
manuring of mangolds : —

(i) The value of dung and of organic manures like
rape cake, which, by maintaining a good texture in the
soil, ensure a plant and a vigorous start.

(2) The value of an addition of active nitrogenous
manures, particularly nitrate of soda, even when dung
is also used.

(3) The importance of potash salts even when

3i8 SYSTEMS OF MANURING CROPS [chap.

farmyard manure rich in potash is also used. The
beneficial effect of potash salts is, however, less apparent
when nitrate of soda is employed as a source of nitrogen,
because the soda attacks and renders soluble some of
the reserves of potash in the soil. Potash thus becomes
more necessary when ammonium salts or rape cake
form the source of nitrogen ; but in any case it is
desirable to use some sodium salt, such as common salt
itself, as an economiser of the more valuable potash.

(4) That with proper manuring mangolds can be
grown year after year on the same land without any
falling-off in yield or any accumulation of disease. It
is sometimes convenient to keep a little piece of land near
the homestead always in mangolds, this can be done
for a long time in perfect safety if organic manures are
employed to maintain the texture of the soil.

Coming now to the requirements of the crop in
practice, not much variation will be required because of
its position in the rotation, since mangolds are practically
always grown on a stubble with the land in compara-
tively poor condition. The basis of a manure for man-
golds should be dung ; probably there is no crop in the
rotation to which farmyard manure can be better applied
than to mangolds. When, therefore, the mangolds are
grown on a portion of the root breadth, the dung should
be concentrated on this part of the field. On light
soils and in dry climates it is better to plough in the
dung in the autumn and grow the mangolds on the
flat, lest the fresh manure should leave the soil too open
and let in the drought, but on heavier land and where
the rainfall is greater the land will generally be laid up
in ridges. The dung should be spread in the furrows ;
the artificial manure, other than nitrate of soda or other
active nitrogenous manure, should be sown on the
dung and the ridges then split back on to the dung.

XI.) MANURES FOR POTATOES 31^

Supposing 20 loads of dung per acre to be available for
the crop, the supplementary manure should consist of
3 to 5 cwts. per acre of kainit (the larger quantity on
light soils), and 2 cwts. of fish guano or kindred fertiliser
if the land is in poor heart and a large yield wanted.
Phosphates in many cases, as at Rothamsted, are not
required when dung is used, but on soils where
phosphates are specially necessary, as on many of the
clay soils so suited to the mangold crop, it will be well
to add 2 cwts. of superphosphate to the mixture when-
ever the fish guano is omitted. The after-treatment
will consist in giving top dressings of a mixture of
equal weights of nitrate of soda and salt ; about 3 cwts.
of the mixture at singling time, and perhaps an equal
amount a few weeks later, should a specially heavy
yield be aimed at.

Potatoes. — It is more than usually difficult to lay down
general rules for the manuring of the potato crop, so
varied are the tilths upon which it is grown and so
different are the yields that are aimed at. Potato
growing is largely carried out in the neighbourhood of
great cities where dung can be cheaply obtained ; in
such cases the farmer will often crop suitable land every
other year with potatoes, taking a cereal or a green
crop in the intervening years. On the other hand the
farmer who does not make a speciality of potatoes will
simply plant them on a portion of his mangold or
Swede land, while in good potato-growing districts
they will form one item in a five- or six-year rotation.
In the Lothians, for example, a common rotation is : —

Turnips "

/ Turnips.

Barley
Clover
Oats

- or -

Barley.

Potatoes.

Oats.

Potatoes

Clover.

Wheat ,

. Potatoes.

320 SYSTEMS OF MANURING CROPS [chap.

In both these cases about 30 loads of farmyard
manure are put on the stubble and ploughed in the
autumn before the potatoes are grown, artificial
fertilisers to the value of 20s. or 30s. are also added in
the spring.

Another rotation in the Dunbar country, so famous
for the high quality of its potatoes, avoids the use of
any farmyard manure : —

Swedes, in part fed on the land.

Barley.

Clover, cut for hay.

Clover, grazed with cake and corn.

Potatoes, no farmyard manure.

Oats.

On the Lincolnshire fen soils a common rotation is
as follows : —

Swedes ^, Potatoes J, with farmyard manure.

Wheat.

Seeds.

Wheat.

Oats.

On the black soils of Lancashire a common rotation
is : —

Oats.
Potatoes.
Oats.

Seeds, farmyard manure being used in
large quantities.

In view of all these variations in practice it will be
best to discuss a few general principles : —

(i) Potatoes do not want an excess of nitrogenous
manure, because it renders them waxy and gives them
a tendency to boil a bad colour ; it also makes them
susceptible to disease. As quality is so important, the

XI.] MANURES FOR POTATOES 321

nitrogen they require should be derived more from
mellow soil in high condition than from recent manure.

(2) A good supply of phosphatic manure has been
shown to be important.

(3) Potash is essential, since the potato is a starch-
making plant.

(4) Manures setting up an alkaline reaction should
be avoided, since they facilitate the attack of Oospora
scabies, the fungus causing potato scab. Hence sulphate
of ammonia should be preferred to nitrate of soda for a
top dressing and superphosphate to basic slag; lime
also should not be used.

As regards the use of dung it has been repeatedly
shown that a better return is obtained by using
farmyard manure in moderate quantities of 20
loads per acre or so and supplemented with artificial
manures, than by spending all the money available for
manuring upon dung alone. On any but the heaviest
soils it is better to plough in the farmyard manure in
the autumn and so get the land into good heart, but on
the close badly working soils it is an advantage to the
potato plant to have the ground left a little hollow by the
decay of the farmyard manure ; on such soils, therefore,
the dung should be applied in the drills just before
planting. The mixture of artificials should either be
sown broadcast before the land is ridged up or sown
upon the farmyard manure in the drills before the
ridges are split. For ordinary cropping a mixture of
4 cwts. per acre of superphosphate, i cwt. of sulphate of
potash and i cwt. of sulphate of ammonia will be ample ;
when extra heavy crops are aimed at, 2 cwts. or so of a
good guano may be added to the mixture already
specified, and a further hundredweight of sulphate of
ammonia may be applied as a top dressing when the
haulm is beginning to appear.

X

322 SYSTEMS OF MANURING CROPS [chap.

The Leguminous Crops. — It has already been
explained that the leguminous plants are able to obtain
nitrogen from the atmosphere by the agency of the
bacteria in their nodules and can in this way satisfy
their requirements for nitrogen : it should, however,
not be forgotten that they also feed upon combined
nitrogen like all other plants, and as a rule derive their
nitrogen both from the air and from the soil. To
obtain the biggest crops rich soil and certain nitro-
genous manures are necessary, but to secure the greatest
profit out of a leguminous crop, it should be left as
far as possible to derive its nitrogen from the atmo-
sphere. All leguminous plants are particularly sensitive
to any trace of acidity in the soil, so alkaline fertilisers
like basic slag or nitrate of soda should be selected.
Lime is also desirable, both for its basic properties and
as a liberator of insoluble potash in the soil, because all
leguminous crops are specially dependent upon an
abundant supply of potash.

Beans. — Beans no longer play the important part in
British agriculture that they once possessed ; essentially
a heavy land crop, the cultivation has declined since so
much of the strong clay land has been laid down to
grass. In the rotation beans generally come between
two white straw crops. They will follow oats or barley,
for example, and precede wheat, and as a rule they do
not receive any manure. A little farmyard manure
may be spread on the stubble before it is ploughed,
but other nitrogenous manures have little beneficial
effect upon the crop. The Rothamsted experiments
show that beans, like other leguminous plants, respond
chiefly to phosphates and potash, to the latter especially,
and are able to derive most of the nitrogen they require
from the atmosphere. For example, the average results
for eight years at Rothamsted were —

XI.] BEANS AND CLOVER

Table XCIII. — Yield of Beans at Rothamsted,
1847-1854.

323

Unmanured.

Minerals
only.

Minerals
and Nitrogen.

Corn

1205 lb.

1676 lb.

1763 lb.

More recent experiments made by the Highland and
Agricultural Society, and others in Essex, upon beans
under ordinary farming conditions confirm these results,
showing that nitrogenous manures are non-effective but
that the crop responds to phosphates and potash. Thus
in practice, when beans are being grown on strong land,
we may reduce the manuring to 3 or 4 cwts. per acre of
basic slag, any other expenditure on fertiliser is not
likely to be repaid by the increase in the crop.

Clover. — Red Clover forms perhaps the most
important crop cultivated by the farmer ; not only does
the hay furnish a particularly valuable fodder, the
nitrogen in which is largely derived from the atmo-
sphere and is therefore clear gain to the farm, but the
nitrogen left behind in the roots and stubble also
enriches the land for future crops.

Since the time of the Romans it has been known that
the wheat is most luxuriant where the clover had grown
best in the preceding year ; the Rothamsted experi-
ments afford some interesting examples from which the
gain of nitrogen can be estimated. One example of
the great benefit which the succeeding crops in a
rotation derive from a good crop of clover, although
it is removed from the land as hay, has already been
quoted (Table VIII., p. 33).

Again, in 1873 a piece of land in Little Hoos field
was cropped, part with barley and part with clover, in
1874 barley was taken over the whole, and the amount

324

SYSTEAIS OF MANURING CROPS

[chap.

of nitrogen removed in the crop from each piece of
land was estimated as follows : —

Table XCIV.— Gain of Nitrogen by Clover Crop,
rothamsted.

Lb. of Nitrogen removed per acre
in the Crop.

1873 .

1874 . .

Nitrogen per cent.

in Soil, end of 1873.

Barley, 37-3
Barley, 39-1

Clover, 1 51 -3
Barley, 69-4

0-1416

0-1566

Thus, although 151 lb. per acre of nitrogen was
removed in 1873 from the clover portion of the field, as
compared with 37 lb. from the barley portion, the former
in the following year yielded an extra 20 bushels of
barley.

As to the manurial treatment of clover, it is difficult
to quote very extensive experiments, because of the
failure of the plant which takes place through clover
" sickness." On the best clover soils in this country it
cannot be grown more frequently than once in four
years, and more often once in seven or eight years only
is safe. The Rothamsted experiments all go to show
that manuring alone will not keep off clover sickness,
though it was found possible to maintain a long succes-
sion of clover crops on a small patch of rich garden soil.
Lime and potash salts are helpful but cannot be trusted
to maintain the plant in health. The Rothamsted
experiments, however, served to show that nitrogenous
manures have little effect (indeed, sulphate of ammonia
may be harmful), but that mineral manures, and potash
in particular, are of great value. Nitrate of soda has
sometimes been found beneficial to st-'mu'ate a weakly

XL] BEANS AND CLOVER 325

plant in the sprinc;, and doubtless the soda had a share
in this result, but clover so forced has a bad effect upon
stock. In practice clover is rarely manured ; it is nearly
always sown in the barley crop, and is then left to the
mineral residues from the preceding root crop and the
nitrogen it can gain from the atmosphere ; at the most,
a little farmyard manure may be spread during the
winter and is valuable as affording shelter to the young
plants. If plenty of phosphates have been used for the
Swede and barley crops, nothing more in this direction
is likely to be required, but on many soils, especially of
the lighter kind, an application of potash during the
late autumn or winter after the clover has been sown
will have a marked effect upon the yield of clover, and
the cost of about 4 cwts. of kainit per acre will be amply
repaid.

It is rarely wise to attempt to manure standing clover
for a second year's crop ; nitrogenous fertilisers are not
required, and the potash and phosphates hardly have
time to get well down to the plants' roots in the time
the crop still occupies the ground. A thin coating of
dung in the winter is valuable for its shelter, and if the
crop must be forced along, then in the winter 3 cwts. of
basic slag and 3 cwts. of kainit may be sown broadcast ;
even if they do not produce much immediate return
they will not be washed away.

Lucerne and Sainfoin. — The principles which have
been laid down for the treatment of clover apply equally
to lucerne and sainfoin {i.e., that mineral manures should
be used, and that only the young plant will respond to
fertilisers), but since these crops are generally sown to
stand five years or more, it is wise to make a good
preparation of the soil before sowing. As a rule, they
are sown in barley or oats and about 5 cwts. per acre of
basic slag should be worked into the soil before sowing

326 SYSTEMS OF MANURING CROPS [chap.

the corn crop. The potash salts (4 cwts. per acre of
kainit), being soluble, can be kept until the autumn or
winter. Beyond this it is not wise to use fertilisers on
these crops ; a little nitrate of soda may serve to give
the young plant a start in its first spring, and a coat of
dung is often valuable, but the proper way to regard
lucerne or sainfoin is as a cheap means of enriching the
land with a minimum of expenditure.

Vetches, Trefoil, Crimson Clover, and similar rapidly
growing leguminous crops are usually grown as catch
crops on land that is already in good heart and do not
require any fertiliser. Lupins are sometimes grown on
poor sandy land in order to be ploughed in as green
manure ; in such a case the preparation of the land
(supposing it to be poor heathy land undergoing
reclamation) should include the application of 4 to 5
cwts. per acre of basic slag and 3 to 4 cwts. of kainit to
supply the lupins with the necessary mineral food, for
without it they could neither gather nitrogen nor
accumulate humus for the amelioration of the soil.

Grass Land. — In considering the effect of manures
upon the grass crop, we have to take into account not
only the weight of the produce but the character and
botanical composition of the herbage that ensues.
Every meadow possesses a characteristic vegetation
made up of various species of grasses, a few leguminous
plants like white and red clover, bird's foot trefoil, the
yellow vetchling, etc., and sundry miscellaneous species
which are, in the main, of little value to stock and may
be classed as weeds. The proportion which each of
these species contributes to the herbage represents the
degree to which it is suited by the various conditions of
food, water, soil, texture, etc., which prevail in that field.
A strenuous competition is going on between the
different species, each of which is endeavouring to

XI.] MANURES FOR GRASS LAND 327

crowd out its neighbours, so that the characteristic
vegetation of the field represents the state of equili-
brium which has been attained by the various plants
under the prevailing conditions of soil and climate.
The physical texture of the soil has much to do with
the nature of the grasses which will establish themselves
under the stress of competition : on the deep, kindly
alluvial pastures rye grass becomes prominent ; on the
thin chalky soils of the Downs sheep's fescue thrives
best ; on heavy clays where aeration is deficient the
creeping rooted bent grass will cover the surface, while
sandy droughty soils often become covered with tufts
of cock's foot or brome grass. Just in the same way
manuring, by altering the food conditions in the soil,
can effect a great change in the character of the herbage
of a given field, and the direction which these changes
will take must be kept in mind in any discussion of the
application of fertilisers to grass land, since in Great
Britain we are never dealing with a crop of a pure
unmixed grass, like the crops of timothy or blue-grass in
America. The best example of the effect of long-
continued manuring on the composition of the herbage
is afforded by the Rothamsted experiments, where
certain plots of old grass land receive the same treat-
ment every year and are mown for hay.

Table XCV. shows the average yield for fifty-three
years, and also the character of the resulting herbage,
as shown by its separation into grasses, clovers, and
weeds in 1902, the forty-seventh year of the experi-
ment.

From this table certain facts become apparent. If
grass is constantly mown without any return in manure,
the resulting impoverishment is shown not only in the
small yield but in the preponderance of weeds in the
herbage. One - sided manures, which contain only

328

SYSTEMS OF MANURING CROPS

[chap.

nitrogen or only phosphoric acid, however successful
at first, eventually result in increased impoverishment
of the land. Nitrogenous fertilisers promote the growth
of the grasses at the expense of the clovers. Mineral
manures, and particularly potash, promote the growth
of leguminous plants and enable them to make headway
against the grasses.

Table XCV.— Yield and Composition of Hay at Rothamsted.

Botanical Composition,

Yield

per cent

Plot.

Manure.

of

ffi

8

Hay.

c

o

a

<s> u

a

g

+^t3

2

3
1

°o

Cwts.

3

Unmanured

21-5

34-3

7-5

58-2

I

Nitrogen only as Ammonium Salts

34-7

77-6

1-4

2I-0

17

Nitrogen only as Nitrate of Soda .

35-5

43-8

3-4

52-9

7

Mineral Manures, no Nitrogen

40-9

20-3

55-3

24-4

4-2

Phosphoric Acid and Nitrogen, no

Potash .....

35-8

91-5

8-5

9

Complete Manure, Nitrogen as

Ammonium Salts

54-8

91-2

1-3

7-5

H

Complete Manure, Nitrogen as

Nitrate of Soda

6o.8

88-8

3-7

7-5

ii-i

Complete Manure, excess of Nitro-

gen

66-8

99-2

...

0-8

Another consequence follows from these experi-
ments ; since any special combination of fertilisers or
any method of treatment encourages particular species,
the best results in any given field will always be
attained by persisting in the treatment selected. For
instance, when a field is laid up for hay certain strong-
growing grasses get an advantage ; when the field is
grazed other grasses of a dwarfer-spreading habit are
more suited by the conditions. It is therefore desirable
to keep one field for hay every year and another for

XI.] MANURES FOR GRASS LAND 329

grazing, rather than alternately to graze and hay the
same field, in which case particular grasses are first of
all encouraged and then repressed.

Again, we may conclude that manure will be wasted
upon a field unless there is a proper herbage to take
advantage of it ; in dealing with poor grass land it is
uneconomical to spend much on manure until by
degrees the character of the vegetation has been
reformed. With these general principles in mind, we
may proceed to the consideration of a few typical
cases, which, however, cannot be made to cover all the
variations of soil and management to be met with in
practice.

Land laid up for hay every year must receive a
regular manuring, unless it happens to be rich river
meadow or alluvial flat which derives its fertility from
the percolating water or the mud deposited during flood
time. But if it is ordinary medium grass land, about
3 cwts. per acre of kainit and 2 cwts. of superphosphate
should be applied in the early spring, in January or
February, followed by i to i| cwts. of nitrate of soda as
soon as the grass begins to move. On heavy soils,
especially on old grass land, basic slag may be
advantageously substituted for the superphosphate.
At intervals of five years or so the mixture of artificial
manures should be replaced by a winter dressing of
15 tons or so of farmyard manure. Occasionally, once
in five or six years, a light dressing of lime should be
given, a ton to the acre put on in the form of ground
quicklime is best. Land that has been but recently laid
down to grass should be dunged more frequently. If
much cake and corn is fed on the aftermath the nitrate
of soda can be reduced or even omitted.

Pasture that is of any value to begin with will rarely
require any general manuring, so much cake and corn

330 SYSTEMS OF MANURING CROPS [chap.

will usually be fed to the stock fattening upon it in the
summer that as regards nitrogen the soil is likely to
become richer every year. Lime and phosphates may,
however, often be deficient on these rich old pastures,
and for lack of these constituents the great residues of
manure left on the land every year are not adequately
realised. For this reason occasional dressings of ground
lime (i ton per acre) and of basic slag (5 cwts. per acre)
are of great value on these rich lands where cake and
corn are fed. The result of the application may not be
visible in an increased growth of grass, but the cattle
will be found to prefer the manured portions of the field
and to thrive there better. The prevalence of weeds,
especially buttercups and to a less degree daisies, is
an indication of this over-richness produced by heavy
cake feeding, unconnected by an adequate supply of
minerals.

Poor pasture cannot repay any large expenditure ;
indeed, any liberal application of manures at first will
only encourage the strongly growing weeds. The poor
grass land in Great Britain may be divided into three
classes: (i) poor clay land covered with creeping-rooted
bent grass ; (2) thin sandy soils covered with sheep's
fescue, fiorin, sweet vernal, and soft brome grasses ;
(3) thin soils near the chalk with an extremely
variegated herbage.

As regards the first class of land, the experiments
initiated by Somerville at Cockle Park, and extended
later to many other clay soils all over the country,
show that dung and other nitrogenous manures are
worse than useless on such soils. The sound way of
improvement is to give them a dressing of 10 cwts. or
so per acre of basic slag, whereupon the white clover,
which before existed as tiny plants under the bents, is
favoured and becomes prominent in the herbage. The

XI.] MANURES FOR GRASS LAND 331

grazing is at once improved, and as the nitrogen con-
sumed mostly comes back to the grass, a permanent
improvement sets in. Should white clover not appear
the season after the basic slag has been sown, it is
possible that the land was without the small plants
mentioned above, and a few pounds of white clover
seed should be sown and harrowed in. After this first
dressing of basic slag, the land will steadily improve for
five or six years, after which time a fresh application of
fertiliser is called for. By this time the soil will have
gained nitrogen through the growth of the white clover,
but it will not be wise to trust to basic slag alone for
the second dressing, since the land will have lost some
of the potash liberated by the original treatment with
basic slag. The second and later dressings should
therefore be accompanied by about 3 cwts. per acre of
kainit to keep the clover vigorous ; and if the land is
ever laid up for hay, it will be necessary to use
nitrogenous fertilisers pretty freely. As long as a
pasture containing a good proportion of white clover
is only grazed, it is probable that the nitrogen content
of the land does not fall off, but we cannot trust to
white clover to make good the large removal of nitrogen
in a hay crop.

The thin sandy soils are more difficult to improve
than the clays ; basic slag exerts but little effect, partly
because the soil is too dry to allow it to act very freely,
but more because there is but little potash in the soil
to be liberated by the action of the lime in the basic
slaer. Bone meal has often been recommended for these
soils, remembering the improvement which bones have
effected upon the Cheshire pastures. Bone meal is,
however, too slow in its action to be profitable, and a
phosphate like steamed bone flour or phosphatic guano
will be better. About 2 to 3 cwts. of such a phosphate

332 SYSTEMS OF MANURING CROPS [chap.

and an equal amount of kainit forms the only mixture
which will improve the herbage on these very light soils,
but even then the change will be slow and never so
pronounced as on clay land, because the tufted deep-
rooting grasses which prevail are better able to resist
the competition of the leguminous plants. Nitrogenous
manures, and particularly dung, are harmful and only
encourage the coarse herbage.

On the thin chalky soils nitrogenous manures are
valuable, and a pasture may be permanently improved
as well as enabled to carry more stock in the current
season by the application of 3 or 4 cwts. per acre of a
mixed fertiliser, containing 3 of superphosphate, 3 of
kainit, and i of sulphate of ammonia. But for the
creation of a good pasture on the thin chalk soils, dung
is the most essential manure ; as much farmyard manure
as possible should be spared for the grass land and a
hay crop taken the season after the application ; then it
should be grazed and, if necessary, helped during the
grazing by the artificial mixture specified above.

But it must always be remembered that on the thin
dry soils, whether chalk or sand, only a very limited
expenditure on fertilisers is likely to be repaid ; large
applications of manure will be certainly wasted, but it
is possible gradually to build up better pastures by
repeated small applications of the nature described.

Seeds hay should not require any manuring ; if the
land has been properly treated before the seeds were
sown there should be enough residue from previous
manuring to grow a good crop of mixed seeds. Any
active nitrogenous manure will stimulate the rye grass,
etc., at the expense of the more valuable clovers. A
fertiliser is sometimes used in the spring when the land
has lost plant severely through the winter, but this is
generally a wasteful proceeding, because fertilisers

XI.] MANURES FOR HOPS 333

should only be used when there is a crop or the prospect
of a crop to utih'se them.

When land has been newly laid down to grass, there
often comes a very critical period from its fourth to its
seventh year, especially on stiff soils and when the first
two or three crops of grass have been fed off by store stock
only. At that period the leguminous plants have begun
to die away, and the grasses have lost vigour because
the plant food that had been rendered available by the
tillage has become exhausted. The mechanical con-
dition of the soil has also deteriorated because as yet
little humus has been accumulated. Applications of
basic slag have less effect than usual on such young
grass land, there are no residues of past growth to be
set in action by the lime of the basic slag. What is
wanted is either farmyard manure or applications of a
complete fertiliser such as has been described above.
Better still, the land should be carefully pastured, the
sheep should not be allowed to eat too closely, and
should be fed with cake or corn to enrich the land.

Hops. — No other crop is so liberally manured as
hops ; potato land may perhaps receive as much in any
one year, but on hops the expenditure for fertilisers will
average ^8 or ;^io per acre year after year. The hop
plant shows no special requirements, so that it is the
needs of the soil rather than the crop which should
determine variations in the character of the manure.
The manurial treatment of hops should begin with a
liberal use of dung, and most hop growers either buy
it in quantities from London or other large towns, or
fatten cattle or pigs in order to make enough for their
requirements. As much as 40 tons per acre are some-
times employed and that year after year, but one such
application every third year will be sufficient to maintain
the requisite soil texture, and in the intervening years

334 'SYSTEMS OF MANURING CROPS [chap.

the necessary plant food can be more cheaply obtained
in other forms. The subsidiary manures for hops are
of the most varied nature, but shoddy in some form or
other is a highly favoured substance, and should be
applied at the rate of from i to 2 tons per acre, accord-
ing to its richness in nitrogen, in the autumns when
dung is not being used. When the ground is first
worked in the spring the more active fertilisers should
be applied, 6 cwts. per acre of fish or meat guano or of
rape dust, with about 4 cwts. per acre of superphosphate,
or 3 cwts, of steamed bone flour or phosphatic guano,
will then carry the crop through. Many growers are
in the habit of using a further dressing of rich guano
or active nitrogenous manure when the hops are coming
into burr, but this is probably unwise, as it induces late
sappy growth, very susceptible to attacks of blight. A
good coat of dung at this time is, however, of great
value, especially on young hops, but its immediate action
is more as a mulch than a fertiliser. Potash manures
are only required on the light sandy or chalky lands ; in
such cases they should be applied in the winter or early
spring. Phosphates are, however, most essential ; on
the strong soils as much as 10 cwts. per acre of basic
slag may be applied in the winter in place of the super-
phosphate specified above.

Fruit plmiiations under tillage should receive much
the same kind of manuring as hops do, though in smaller
quantities. Dung is not so desirable, and the necessary
nitrogen can be well supplied by digging in i ton per
acre of shoddy in the winter, or a spring manuring of
meat or fish guano or rape dust may take its place.
Phosphates are very important, and potash is also
indispensable, especially on the lighter soils and for all
stone fruit. Four cwts. of kainit per acre may be given
in the winter. Fruit trees in grass land should not

XI.] MANURES FOR TROPICAL CROPS 335

receive any fertiliser, but should be manured by keep-
ing the land closely grazed with sheep receiving hay
roots, cake, and corn, etc.

Tropical and sub-tropical crops. — It is very difficult to
lay down any general rules for the manuring of tropical
and sub-tropical crops, because the conditions of soil
and climate are subject to such extreme variations that
entirely different methods of treatment have to be
pursued in different countries. Certain general prin-
ciples may, however, be indicated, to be taken into
account whenever any scheme of manuring has to be
tentatively adopted in practice. All the processes by
which the insoluble constituents of plant food in the soil
are rendered available for the plant are greatly acceler-
ated in tropical soils, always provided they contain a
sufficiency of water. The decay of organic matter takes
place with extreme rapidity, so that the humus content
of cultivated soils will be quickly reduced unless means
are found of repairing the losses ; for the same reason
all organic manures containing nitrogen are both more
quickly and more completely utilised by the plant than
they are in temperate soils. The higher temperature of
the soil water, the greater production of carbon dioxide
in the soil, also result in a more rapid weathering of the
mineral constituents of the soil, so that the reserves of
phosphoric acid and nitrogen present in the soil are
more available in tropical countries.

It also follows that smaller amounts of manure in
proportion to the plant food withdrawn by the crop are
effective under tropical conditions ; whereas, in England,
one cannot hope to recover more than one-half of the
nitrogen applied as farmyard manure, in a hot soil with
an abundant rainfall nearly the whole will be available,
and a correspondingly smaller application will be
required. It is always the crops of short duration on

336 SYSTEMS OF MANURING CROPS [chap.

the land — tobacco, cotton, and to a less extent sugar
cane — which most require manuring ; really perennial
crops like tea and coffee require much less manure and
that of a more slowly acting kind. It is only the short-
period crops which will respond properly to active
sources of nitrogen like nitrate of soda or sulphate of
ammonia.

The incidence of rainfall must be closely studied.
No manure can be effective when the soil is either dry
or waterlogged ; and as the nitrogenous manures cannot
be expected to persist very long in the soil, their applica-
tion should be timed so as to be followed by a period of
growth with neither excessive rain nor a dry soil.

Sugar cane. — A large number of experiments have
been conducted with sugar cane, and, though the results
naturally vary in the different countries, certain general
conclusions can be drawn. Before planting, a compara-
tively slow acting nitrogenous fertiliser should be used,
either the equivalent of farmyard manure or some seed
residue like castor pomace, to supply about lOO lb. of
nitrogen per acre. For the rattoon growths more active
forms of nitrogen are desirable — either sulphate of
ammonia or nitrate of soda supplying 50 lb. of nitrogen
per acre ; which of the two will prove the more suitable
depends upon the soil. Excess of nitrogen must be
avoided, as it induces late cane and an impure juice.
On many soils applications of potash salts (sulphate
of potash is generally the most economical form) are
very effective. Phosphates are less needed, though
superphosphate is often valuable on black alluvial soils.

Cotton. — Cotton responds freely to fertilisers, and
there is evidence that the fertiliser should be a mixed
one but mainly phosphatic. About 4 cwts. per acre
of superphosphate and 2 cwts. per acre of cotton
seed meal or some equivalent organic source of

XI.] MANURES FOR TOBACCO AND TEA 337

nitrogen, should be ploughed in before sowing, and this
may be followed up by a ^ cwt. per acre of a more
active nitrogenous fertiliser like sulphate of ammonia or
nitrate of soda when the crop has begun to grow.
Potash manures are only required on certain soils of a
light type.

Tobacco. — Tobacco is a crop requiring comparatively
rich land, and the fertilisers should chiefly supply
nitrogen and potash, phosphates being less required.
Too great an amount of nitrogenous fertiliser should not
be used, or the quality of the leaf falls off, up to 50 lb.
per acre is safe ; and ammoniacal manures should be
avoided, as they result in a leaf burning badly. Before
planting out the tobacco 200 to 300 lb. of an organic
nitrogen compound — cotton seed meal or castor pomace
— 200 lb. of superphosphate and 100 lb. of sulphate of
potash should be applied, followed by 100 lb. of nitrate
of soda when the plant is growing. Potash appears to
be very essential, and may be given as nitrate, carbonate,
or sulphate.

Tea. — Being perennial the tea plant requires neither
heavy nor active manuring ; it is also very important to
maintain both the proper habit of growth of the plant
and the quality of the leaf. If any large amount of
nitrogen is employed an excessive development of weak
vegetative shoots takes place on the bush, and the plant
suffers in ensuing seasons. The fertility of a tea garden
as regards nitrogen can be maintained by carefully
burying the lighter prunings and weeds, and by digging
in from time to time leguminous plants which have been
grown between the rows, cut down, and allowed to
wither and rot somewhat. By also supplying basic slag
at the rate of about 2 cwts. per acre the residues thus
utilised are balanced by the phosphates, and the lime of
the basic slag is beneficial in keeping the soil healthy

Y

338 SYSTEMS OF MANURING CROPS [chap.

and in assisting the decay of the organic matter. When
manures are necessary it is best to employ slow acting
substances like bone meal and castor pomace.

Garden manures. — In an ordinary way gardens
require little artificial fertiliser, since they receive a
superabundance of stable manure until the soil often
becomes over-rich in nitrogenous residues. Under such
conditions the only fertiliser wanted will be some form
of phosphatic manure, and this is very desirable to
induce a properly balanced growth in the crops. Super-
phosphate may be used on the loams, basic slag on the
strong soils, steamed bone flour or phosphatic guano
when the soil is sand or gravel, and about \ lb. per
square yard of one of these fertilisers should be dug
in with the farmyard manure on those portions of
the ground which come to be dunged in the usual
rotation. Nitrate of soda is often valuable to push
on early lettuce, cabbage, peas, etc., in a backward
spring; it may also be applied with advantage to
asparagus and celery. The compound garden man-
ures sold under fancy prices should be avoided :
though good fertilisers enough, their cost is exces-
sive, even considering the small parcels in which
they are sold. Where stable manure is not available
and a mixed fertiliser is required, nothing is better
than a good Peruvian guano with 6 or 7 per cent.
of nitrogen. In such circumstances the humus of the
soil should be maintained by digging in as much organic
matter — weeds, grass clippings, vegetable refuse, etc. —
as possible, and by growing mustard on any land that is
not wanted for a short time, and digging the green crop in.
It should not be forgotten that lawns which are con-
stantly cut must become greatly impoverished if they
are not manured, for which purpose Peruvian guano at
the rate of 2 oz. per square yard every other year forms

XI.] MANURES FOR TOBACCO AND TEA 339

a suitable dressing. When Peruvian guano or any
similar concentrated fertiliser is used to enrich potting
soil, the mixture should be allowed to stand a week
before potting, because guano and all kindred manures,
when in a raw condition, are very destructive of young
plant roots.

CHAPTER XII

THE VALUATION AND PURCHASE OF
FERTILISERS

Valuation on the Unit System — The current Market Price of the
Unit of Nitrogen, Phosphate of Lime and Potash — Variations
in Unit Values due to Market Fluctuations — Valuation of
Fertilisers before Purchase — The Fertilisers and Feeding
Stuffs Act ; Obligations of the Vendor — Sampling Consign-
ments of Fertilisers — Mixed v. Unmixed Fertilisers — Incom-
patibles — Residues of Fertilisers after the Growth of one or
more Crops — Valuation of unexhausted Residues derived
from the Consumption of purchased Feeding Stuffs.

In buying fertilisers the farmer will generally have a
considerable choice between materials of different origin
and composition, but which will so far serve the same
purpose that their relative price becomes the most
important factor in determining the purchase of one or
the other. For example, should an active nitrogenous
manure be needed, for many soils and crops it is a
matter of indifference whether nitrate of soda or
sulphate of ammonia is used ; among phosphatic
manures the choice may be between superphosphate,
basic slag, and a neutral manure like steamed bone
flour ; or, to take a case where even fewer secondary
considerations enter, practically nothing but relative
cheapness need determine a decision between such
materials as fish and meat guanos or rape cake. But

810

CHAP. XII.] VALUATION OF FERTILISERS 341

since all these materials possess different compositions,
a method of valuation must be found which will reduce
them to a common basis of the cost of the actual
fertilising ingredients alone — i.e.^ of the nitrogen, the
phosphoric acid, and the potash respectively. It is
possible, for example, to calculate the price per pound
of each of these fundamental substances, but the more
convenient method is to ascertain the cost of a unit
consisting of one-hundredth of a ton ; such unit cost
being obtained by dividing the price per ton of the
fertiliser by the percentage of the constituent in
question.

It is the custom of merchants to set out the
analysis of the various fertilisers in terms of both
nitrogen and ammonia, and to express the phosphatic
constituents sometimes as phosphoric acid but more
commonly as tri-calcium phosphate, and again to give
the potassium in terms of potash, whatever may happen
to be the form in which the element is actually com-
bined. For example, nitrate of soda contains no
ammonia, and the statement that a given sample of
nitrate of soda contains 19 per cent, of ammonia is only
meant to signify that the 15-5 per cent, of nitrogen
present is equivalent to 19 per cent, of ammonia. In
superphosphate the phosphoric acid is chiefly combined
as di-hydrogen calcium phosphate, CaH^PgOg, hence
an analysis setting out the presence of 26 per cent, of
soluble phosphate or of tri-calcium phosphate rendered
soluble, must be read as meaning that it contains 11-9
per cent, of phosphoric acid soluble in water, which
amount of phosphoric acid would be also contained in
26 per cent, of tri-calcium phosphate. Similarly, muriate
of potash, which is potassium chloride — KCl — might be
described as containing 50 per cent, of potash — K2O —
though no true potash or potassium oxide is present ;

342

VALUATION AND PURCHASE

[chap.

the statement merely signifies that the essential
element, potassium, is present in such a quantity that
if it were combined with oxygen as potash the latter
would amount to 50 per cent, of the fertiliser. It is
therefore necessary to remember that 14 of nitrogen
are equivalent to 17 of ammonia, and that 142 of
phosphoric acid are contained in 310 of tri-calcium
phosphate (see p. 377), but that necessity of making
such calculations is obviated by the fact that in the
United Kingdom dealers in fertilisers are now obliged
to give the analysis of their wares in terms of nitrogen,
tri-calcium phosphate, and potash, on which basis the
calculations which follow will be made.

The prices given are the wholesale prices ruling in
London in October 1908; naturally they do not hold for
other times and places, and they do not include
carriage, but they are comparable among themselves
and with due additions for the locality show the range
of prices which may be expected at the present time.

In order to find the price of nitrogen, we can take
nitrate of soda and sulphate of ammonia, which contain
nitrogen only, and calculate the unit value as follows : —

Table XCVI. — Price of Unit of Nitrogen.

Price per ton.

Nitrogen,
per cent.

Unit- value
of Nitrogen.

Sulphate of Ammonia .
Nitrate of Soda .

/ll, 15s.
£10

19-75 to 20-0
I5-0 „ 15-5

I2S.

13s.

In making this calculation the farmer must be
careful to base it upon the price per ton delivered
at his local station, since freight charges fall more
heavily on the less concentrated manures, to such an
extent indeed that at distant points the relative cost

XII.]

UNIT VALUES

343

of different fertilisers may be entirely altered by the
carriage charges. In the instances quoted above the
two fertilisers contain nitrogen only and the calculation
is consequently of the simplest ; as a rule, however, more
than one constituent is present The unit values of
the two have to be obtained by a little adjustment and
do not possess quite the arithmetical certainty which
characterises the single constituent fertilisers. Among
phosphatic fertilisers there are practically only three
which contain no other constituent, and in these the
unit value of tri-calcium phosphate may be calculated as
follows : —

Table XCVII.— Price of Unit of Phosphate of Lime.

Tri-calcium

Phosphate,

per cent.

Price
per ton.

Unit-value

of Tri-calcium

Phosphate.

Superphosphate, high grade
Superphosphate, low grade

Basic Slagjg] ; ; ;

Basic Superphosphate

35

26
38

35
25

66s.
50s.
48s.

45s.
52s.

IS. lid.
IS. lid.
IS. 3d.
IS. 3d.
2S. Id.

The unit is dearer in the superphosphates because
acid has been employed to render them soluble in water.

Supposing it is now desired to find the value of the
phosphate unit in certain other fertilisers which also
contain a little nitrogen, it is necessary to make a
deduction from the price of the fertiliser for the
nitrogen present, assuming this latter to have approxi-
mately the value calculated from such purely nitrogenous
fertilisers as the nitrate of soda already quoted. For
example, steamed bone flour containing 1-25 per cent,
nitrogen and 59 per cent, tri-calcium phosphate is quoted
at £\, 7s. 6d. per ton; taking nitrogen at 13s. per unit
the 1-25 per cent, would be worth i6s. 3d., which

344

VALUATION AND PURCHASE

[chap.

deducted from ;^4, 7s. 6d. leaves ;^3, lis. 3d. for the
phosphate. Dividing this figure by 59 (the percentage
of phosphate), we get is. 2|d. as the price of the unit of
phosphate of lime.

Calculating in this way, the following figures are
obtained for phosphatic manures containing some
nitrogen : —

Table XCVIIL-

-Price of Unit

OF Phosphate of

Lime.

Price.

Nitrogen,
per cent.

Value at

13s.
per unit.

Phosphate,
per cent.

Valuation
per unit.

Steamed Bone Flour.
Bone Meal
Phosphatic Guano .

87s. 6d.
105s.

IIOS.

1.25
4.0

2-5

1 6s. 3d.

52s.
32s. 6d.

59
44
58

IS. 2 Id.

Is. 2 id.
IS. 4d.

We have thus obtained a valuation for tri-calcium
phosphate ranging from 2s. per unit for its water
soluble form in superphosphate, down to is, 3d. or less
per unit in bones or phosphatic guanos.

Potassic fertilisers do not show a large variation, the
more concentrated and purified forms being naturally
somewhat the more costly, as follows : —

Table XCIX.— Price of Unit of Potash.

Potash,
per cent.

Price.

Unit Value.

Sulphate of Potash .

Muriate of Potash

Kainit ....

48 to 50
50 „ 52
12 „ 13

2003.
1 80s.

47s.

4s. id.
3s. 7d.
3s. gd.

In dealing with mixed fertilisers the nitrogen is
generally the more important element to consider, as
being the most valuable and the most subject to

XII.]

UNIT VALUES

545

variations in price ; its unit value is, therefore, the
one to be determined after deductions have been made
for the phosphates and potash at the rates quoted
above. For example, in the fish, meat, and oil cake
residues the phosphates are all of much the same order
of solubility and may be valued at the same rates, the
small amount of potash present also may be neglected,
so that the following range of values is obtained for the
nitrogen : —

Table C— Unit Values in Mixed Fertilisers.

Price.

Phosphates.

Nitrogen.

Per cent.

Value at
Is. 3d.

per unit.

Per cent.

Cost
per unit.

Fish Guano, I
Fish Guano, 2
Meat Guano, I
Meat Guano, 2
Dried Blood .
Bone Meal .
Rape Meal .

1 40s.
120s.
130s.

II OS.

I90S.
105s.

1 1 OS.

I5-0
"•5

9-0
27-0

5-0
44.0

5-0

1 8s. 9d.
14s. 4d.
IIS. 3d.
33s. 9d.

6s. 3d.
S5S. od.

6s. 3d.

8-0
6-0

8-5
6-0
12.5
4-0
4-5

15s. 2d.
17s. 7d.
14s. od.
I2S. 8d.
14s. 8d.
I2s. 6d.
23s. id.

The variation in the price of nitrogen in these very
closely related manures is therefore enormous, and the
important thing to realise is that these variations do
not represent intrinsic differences in value — i.e., greater
or less effectiveness in producing crops — but are market
variations due to temporary or local fluctuations of
supply and demand. As far as anyone knows the
nitrogen and phosphoric acid in fish guano are exactly
of the same value to the crop as in meat guano, and
only a few years ago they were to be obtained much
more cheaply in fish guano, the present high price of
which is due to a recent falling off in the supply, coupled
with a large new demand from Japan. Just in the same

346 VALUATION AND PURCHASE [chap.

way, rape dust was formerly almost as cheap a source of
nitrogen as nitrate of soda and established itself in the
favour of hop growers and other farmers, who have
continued to demand it in the face of a falling supply
until the price per unit of nitrogen has been forced up
to nearly double its former level.

In Peruvian guano the potash must also be taken
into account, and some of the phosphoric acid is water
soluble, so that a higher allowance must be made on
that account.

When all these allowances have been made, it will
be found that the unit value of either nitrogen or
phosphoric acid shows considerable variation in passing
from one fertiliser to another, and that the relative
position fluctuates from time to time. Even in
fertilisers so similar in their use as nitrate of soda
and sulphate of ammonia the unit of nitrogen rarely
possesses the same price ; sometimes one and some-
times the other is the cheaper, the changes being
determined by factors of supply and demand outside
the fertiliser market, or by the operations of the com-
binations controlling the production and sale of each
commodity. Furthermore, in comparing the price of
the unit of nitrogen generally, it is not as might be
expected at its highest in the most active fertilisers
such as nitrate of soda, in which form experiments have
shown it to be most available to the crop. On the
contrary the experience of the market shows that
farmers are willing to pay more per unit for nitrogen
in organic than in inorganic combinations, thus in-
directly bringing into the account the value of the
organic matter in maintaining the texture of the soil.
The prepossession arising from an old experience of
the well-balanced nature of the manure and its safety
under almost any conditions also counts in the farmer's

XII.] CHOICE OF FERTILISERS 347

estimation of a fertiliser ; for example, the Peruvian
guanos have been favourably known for so long
that they always command the highest unit value.
Unmixed fertilisers, which require combining by the
farmer and so demand more knowledge in their use,
are generally the cheaper ; and as a rule, little attention
is paid to the imperfect availability of the slow-acting
forms of nitrogen, only the shoddies show any such
lowering of the unit value as would compensate for
their low availability.

It is impossible, in fact, to reduce all fertilisers to a
common basis and choose among them simply accord-
ing to the unit value ; the wheat grower who wants a
nitrogenous top dressing must choose between nitrate
of soda, sulphate of ammonia, and soot, to which
nitrate of lime and cyanamide may nowadays be added ;
the hop grower requiring an all-round spring fertiliser
would not get the quality of growth from a mixture
of superphosphate and sulphate of ammonia that
is equivalent in nitrogen and phosphoric acid to
the guano he usually employs, though a fertiliser
made up from the former substances might be per-
fectly satisfactory to the grower of barley or Swede
turnips. The advantages of the unit system of valua-
tion really come in the means of comparison it affords
between fertilisers of closely related origin but different
composition, as, for example, between the fish and
meat guanos in Table C. ; it rarely happens but that a
careful enquiry will not reveal on the market some one
fertiliser of the desired kind which is considerably
cheaper than the rest.

To this end it is generally more convenient to make
a slight change in the form of valuation just described ;
instead of calculating out for each manure the unit value
of the constituents, we m.ay take a standard series of

348

VALUATION AND PURCHASE

[chap.

such values and compare the actual price with the
estimates formed on that basis. In such comparisons it
is not necessary to know the exact current unit value of
each constituent, as long as a due proportion between
them is preserved, and it will be sufficiently accurate
to use what are approximately the rates prevailing in
1908, viz.: — 14s. per unit for nitrogen, is. 3d. per unit
of insoluble and 2s. per unit of soluble phosphate, and
4s. per unit of potash.

For example, fish and meat guanos were offered as
follows : —

Table CI. — Estimated Value of Fertilisers.

Fish Guano, 1.

Fish Guano, 2.

Meat Meal, 3.

Meat Meal, 4.

Nitrogen, at

14s. .
Phosphates,

at IS. 3d. .

Estimated
value per ton

Sale price .

cent. Value.
7i = io5s. od.

13 = i6s. 3d.

cent. Value.
10^ = 1473. od.

15 — i8s. gd.

c?nt. Value.
7 = 98s. od.

30 = 37s. 6d.

l!L value.
6 = 84s. od.

20 = 25s. od.

121S. 3d.

165s. gd.

135s. 6d.

109s. od.

146s. 3d.

19OS. od.

127s. 6d.

115s. od.

Clearly, among these manures No. 3 is much the
cheapest fertiliser, while No. i is exceptionally dear;
unless there was something wrong with the mechanical
condition of No. 3 there is nothing in the relative
nature of the fertilisers to prevent the farmer taking
advantage of its lower cost.

The example just quoted, which was derived from
actual experience, shows the importance to the farmer
of a careful consideration of the analysis of fertilisers on
sale ; too much stress cannot be laid on the necessity of
conducting all transactions regarding fertilisers on such

XII.] SALE OF FERTILISERS 349

a basis of exact knowledge, especially as the farmer has
no difficulty in obtaining the analyses beforehand or in
checking the results on delivery. The trade in fertilisers
is regulated by the Fertilisers and Feeding Stuffs Act
of 1906, according to which " Every person who sells for
use as a fertiliser of the soil any article which has been
subjected to any artificial process in the United
Kingdom, or which has been imported from abroad, is
required to give to the purchaser an invoice stating the
name of the article and what are the respective per-
centages (if any) of nitrogen, soluble phosphates, and
potash contained in the article, and the invoice is to
have effect as a warranty by the seller that the actual
percentages do not differ from those stated in the
invoice beyond the prescribed limits of error."

Certain limits of error are laid down for each fertiliser
in the regulations accompanying the Act ; for instance,
one grade of superphosphate is guaranteed to contain
26 per cent, of phosphates made soluble ; the warranty
implied is that the fertiliser contains 27 to 25 per cent,
and that the purchaser can sustain a claim against a
vendor if the percentage has fallen below 25 per cent.
Vendors of manures are no longer allowed to give
nominal guarantees such as i per cent, of nitrogen ;
any statements of composition, made either verbally or
in a circular about the fertiliser, have all the effect of a
warranty.

Every county council and county borough is bound
by the Act to appoint an agricultural analyst, who for
a fee (generally small) must analyse and report on
samples sent to him, provided these samples have been
taken within ten days of the receipt of the fertiliser or
of the invoice. The purchaser must supply a copy of
the invoice to the analyst, but may omit therefrom the
name of the vendor. The samples for analysis must, of

3SO VALUATION AND PURCHASE [chap.

course, be taken with great care; an official sampler
can be called in, and this will be the wisest course to
follow when the purchaser has any reason to suspect
fraud. When the farmer samples himself he must
select a certain number of- bags, two for the first ton in
the consignment and one more for each other ton up to
ten bags, empty the contents of each on to a clean dry
floor, work it up and set aside a spadeful from each,
either separately or one after the other. These
spadefuls must then be thoroughly mixed, all lumps
broken down, and 4 to 6 lb. taken out for the sample
for analysis. It is never right merely to open the bags
and take out a spadeful from the mouth of each ; most
fertilisers, especially heavy powders like basic slag, will
show considerable differences between top and bottom
of a bag which has been in transit for some time. The
sample as soon as taken should be put in a clean dry
bottle or jar, and either corked or fastened up with a
bladder or other waterproof packing ; it must never be
allowed to lie about in a package or tin to gain or lose
moisture.

Now that every farmer in the country can so readily
and cheaply obtain an analysis of any fertiliser he
purchases, for besides the county agricultural analyst
most of the large agricultural societies have retained an
analyst for the assistance of their members and the
agricultural colleges also undertake analyses for the
farmers resident within the area they serve, he ought
to get analyses made of every purchase of certain
classes of fertiliser, if he has any regard to the
economical conduct of his business. While it is true
that with very {q^n exceptions the manufacturers and
vendors of fertilisers are strictly honest and only wish
to supply the farmer with the material they have
undertaken to sell, still a great number of fertilisers

XII.] IMPORTANCE OF ANALYSIS 351

are, from their mode of origin, subject to variations of
composition which may escape the notice of the vendor
himself. As regards the pure unmixed fertilisers,
standard articles made on an enormous scale, such
as nitrate of soda, sulphate of ammonia, superphos-
phate, kainit, and sulphate of potash, any farmer
dealing with a reputable firm may count on getting
what he pays for, because these materials do not vary
in composition except they have been deliberately
falsified after they have left the wholesale hands.
But with basic slag, guanos, fish, meat, and bone
compounds, so many different samples exist of varying
composition, and so easily may even a single cargo
show differences in passing from one part to another,
that the farmer will be always wise to check his
purchases by an analysis, not of course of the sample
that may be submitted to him before purchase, but of
the consignment on arrival.

The farmer should buy his fertiliser on the strength
of the analysis or guarantee which he must get from the
vendor before he gives his order, and on which he
should work out a valuation by the method described
earlier in the chapter ; he must then be careful to see
that the invoice agrees with the guarantee on which he
bought, and check the invoice by getting an analysis
made of a sample drawn from the bulk delivered. But
in both his own interests and those of the vendor the
farmer must take some trouble over the sampling; a
good many of the disputes that arise between the two
parties are due to careless sampling or to the storage
of the sample afterwards where it can lose or gain
moisture.

In order to exercise to the full his power of buying
in the cheapest market prevailing, it is clearly necessary
for the farmer to know with some exactitude the kind

352 VALUATION AND PURCHASE [chap.

of fertiliser he wants for the crop in question, so that he
can compound the available materials in the right propor-
tions and not be dependent upon the much more limited
range of fertilisers already mixed by the manufacturer.
For example, every merchant's catalogue will show
examples of turnip manures, barley manures, mangold
or grass manures, containing such mixtures of nitrogen,
phosphoric acid, and potash as experience has shown to
be generally suitable to the crops in question. In such
cases the farmer gets the advantage of the knowlege of
the merchant and also obtains a carefully mixed
fertiliser of even composition throughout, which can
be distributed without further trouble. Such mixtures,
however, can only represent a certain average adapta-
bility to the crop and cannot take into account either
the particular kind of land or the condition it has been
left in by previous cropping. The farmer who has
really made himself acquainted with the theory of
manuring and with the special conditions of his own
land can always manure both more cheaply and
more effectively by purchasing unmixed fertilisers.
These he must either sow separately, or by paying
a little extra to the merchant he may get made
up whatever mixture he desires before delivery.
It should not, indeed, be a matter of any difficulty to
make up a sufficiently accurate mixture on the farm
itself, all that is necessary being a suitable weighing
machine and a floor with a space cemented or paved, on
which lumps can be crushed. The heaps of separate
manures should be weighed out and thrown into a
common heap by alternate shovelfuls ; the mixture should
be then passed through a half-inch screen and the lumps
broken down with a wooden rammer or the back of a
shovel, the resulting heap being cast down and remade
two or three times until it is uniform in appearance.

XII.] INCOMPATIBLE MANURES 353

It must be remembered that certain fertilisers
cannot be mixed together without setting up reactions
which are either wasteful or render the mixture difficult
to work. Basic slag and basic superphosphate cannot
be mixed with sulphate of ammonia or guano or any
other fertiliser containing ammonium salts, because the
caustic lime reacts with the ammonium salts and sets
free ammonia, which escapes as a gas. Superphosphates
cannot long remain mixed with nitrate of soda without
setting free a certain amount of nitric acid, which is
both wasteful and injurious to anyone handling the
mixture. It is, however, safe enough to make up the
mixture and sow it straight away ; the nitric acid only
begins to be in evidence when the mixture is left in a
heap or in bags overnight, or when it is sown from a
machine which has some moving part working in the
manure. Most mixtures containing superphosphate
will turn into a paste round machine parts working in
the material. Kainit and superphosphate will also
begin to set free hydrochloric acid if they are left long
together.

Superphosphate, either mineral or bone, can be
safely mixed with sulphate of ammonia or guano or
any of the fish or meat compounds, but the only
nitrogenous fertiliser that can properly go with basic
slag is nitrate of soda. In any case, however, these
latter are better sown separately because they differ so
much in density and fineness that the mixture would
separate very much in sowing ; very rarely, indeed,
would anyone want to sow them at the same time. Of
course lime, like basic slag, should never be mixed with
sulphate of ammonia or any of the guanos or organic
nitrogen fertilisers.

Under ordinary conditions of farming, however, very
little mixing will be required, partly because the

z

354 ' VALUATION AND PURCHASE [chap.

manures are adjusted to the various crops in the
rotation, and partly because it is generally advisable to
apply the nitrogenous fertilisers as top dressings at a
later period than the phosphatic or potassic manures.

One other question of valuation and price comes
into play in connection with fertilisers, and that is the
value of the residues left behind in the soil after one or
more crops have been grown. The provisions of the
Agricultural Holdings Act of 1900 award the tenant
compensation for any unexhausted fertility he has
brought to and leaves behind on the holding. A
tenant, for example, who has given his grass land a
dressing of 10 cwts, per acre of basic slag and then
leaves his farm within the following two years will by
no means have reaped the full benefit the land has
derived from its treatment. On the other hand, a
tenant who has used nitrate of soda to grow his last
crop of oats or wheat, and then sells the grain pro-
duced, will have obtained all that the manure can
return ; no nitrogen will be left behind in the soil for
the benefit of the succeeding tenant.

It is thus necessary to consider each fertiliser
separately and attach some value to the residue left
behind after one or two crops have been grown since
its application. It cannot, however, be said that proper
data exist for the compilation of such a scale of com-
pensation ; it is not sufficient to estimate what propor-
tion of the fertilising materials that have been applied
the crop may be expected to remove, and then assume
that the remainder is available for future crops.
Experiments already quoted will have served to
show that residues of slow-acting fertilisers, such as
farmyard manures and shoddy, are very far from being
wholly recovered even after such long intervals of time
as would render any compensation quite out of the

XII.] UNEXHAUSTED MANURES-COMPENSATION 355

question. To a certain extent, again, the value of the
residue left by a particular fertiliser will be determined
by the nature of the land and the crop to which it has
been applied ; kainit applied to heavy clay land would
not add to the value of the land, but on the other hand
the benefit derived from the application of fertilisers to
grazing land is largely cumulative, depending upon the
change it effects in the botanical composition and
quality of the herbage, so that the benefit may be
greater at the end of the third or fourth year after
application than earlier. Certainly no a priori rules for
compensation based upon purely theoretical considera-
tions can be laid down ; any scale of compensation must be
based upon experiments only and must always be con-
sidered as approximate and subject to revision according
to the particular conditions of soil and cropping.

Experiments instituted at Rothamsted to provide
data for drawing up such a scale have not progressed
far enough to eliminate the experimental error that
occurs in dealing with such small quantities as are
involved in the residual effects of most fertilisers after
one or two crops have been grown. The crude practice
adopted by many valuers of allowing to the outgoing
tenant half the cost of the purchased fertilisers he has
applied during the last year of his tenancy, can find
little or no justification, and in the case of such sub-
stances as nitrate of soda and sulphate of ammonia is
obviously unjust to the incoming tenant, unless the
manure has been applied to root crops which have been
consumed on the farm. The whole subject is very
complex, and data do not as yet exist for constructing
any table that would serve as a basis for valuation, for
the compensation to be awarded will always have to be
decided on the merits of each case after due considera-
tion of the soil and other local circumstances.

356 VALUATION AND PURCHASE [chap.

In the somewhat analogous case of the compensa-
tion to be paid to the outgoing tenant for the fertiUty
he leaves on the farm from foodstuffs purchased and
consumed during the last years of his tenancy, it is
possible to draw up a fairly satisfactory scale. The
custom in many parts of the country was, and still is, to
allow the outgoing tenant one-half of the cost of the food-
stuffs he had brought on to the farm during the last
year of his tenancy, but such a system has obviously no
scientific basis. The price of a given feeding stuff is
determined by its value as food, not as manure ; oil or
fat, for example, is one of the most costly constituents
of a feeding stuff and yet leaves no fertilising residue
behind. Many foods, e.g. maize and rice, consist mainly
of carbohydrates and contain an unusually small pro-
portion of nitrogen and ash which would wholly or in
part add to the fertility of the farm. The proper basis
is to begin by ascertaining the nitrogen, phosphoric
acid, and potash contained in each class of feeding
stuff; an estimate can then be formed of how much of
each of these is likely to reach the manure, and a
valuation made of these latter quantities at the current
rates. The difficulty lies in estimating the proportion
in which the fertilising constituents will reach the
manure ; for example, it has already been shown
(p. 199) that of the nitrogen fed to an animal anything
up to 15 per cent, will be retained by the animal, and
of the rest that is excreted as much as one-half may be
lost in making the dung. Taking a general average
from the experiments quoted, it will be seen that about
one-half of the nitrogen in the food is likely to find its
way to the land in the dung produced under ordinary
conditions of farming. If the manure is carelessly
managed the losses will be greater ; on the other
hand, if the food is consumed directly on the land

XII.] MANURE VALUE OF FOOD RESIDUES 357

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358 VALUATION AND PURCHASE [chap. xii.

the only loss will be the amount retained by the animal.
Similarly, milch cows will retain more than fatting
bullocks, young growing stock than work horses ; and
again, these variations will be set off by the fact that
both milch cows and young stock are largely fed on the
land.

Taking these and other considerations into account
J. A. Voelcker and the author have constructed a
scale of compensation for purchased foods, which has
been largely adopted by valuers in practice, on the
following basis — one-half the nitrogen, three-quarters
of the phosphoric acid, and the whole of the potash
in the food consumed during the last year of the
tenancy will be found in the dung, while of the food
consumed in the previous year only one-half of these
latter values will remain on the farm. Thus the figures
given in Table CI I. are obtained for i ton of purchased
foods.

A more complete set of figures for the foods in
general use may be found in /. Roy. Ag. Soc, 1902,
p. Ill, or in a report published by the Central Chamber
of Agriculture.

Of course, no such table can hope to be more than
an approximation to the truth ; as has been indicated
above, the style of farming must introduce variations
special to each case, nor can the table take into account
any bad management of land or manure on the part of
the farmer. The table assumes ordinary mixed farming
and reasonably good management of the dung heap.

CHAPTER XIII

THE CONDUCT OF EXPERIMENTS WITH FERTILISERS

Magnitude of Experimental Error involved in Field Experiments
— Choice of Land for Field Experiments — Size and Shape of
Plots — Machines for sowing Fertilisers — 'Should Farmers con-
duct Experiments upon their own Land ?

The value of any fertiliser, new or old, on any par-
ticular soil can only be settled by experiment; for
though it is now possible to a large extent to recognise
types of soil by their analysis and predict their
behaviour, because the main outlines of the principles of
the manuring are understood, yet unknown factors will
often intervene and upset expectations. The proper
conduct of field experiments is therefore a matter of
considerable moment, and it is of particular importance
that the degree of accuracy which may be expected
from a series of such trials should be realised before any
scheme of experimentation is embarked upon. One
often sees experiments so designed that the differences
between the plots are likely to be less than the
experimental error ; still more often one sees conclu-
sions drawn from differences between the yields of the
plots that are smaller than the experimental error. Nor
must it be supposed that by any amount of care the
experimental error can be got rid of; there are various
ways by which it may be diminished, but in some form

36o EXPERIMENTS WITH FERTILISERS [chap.

or other it must exist in all work involving measure-
ments, and the only scientific method of dealing with it
is to estimate its magnitude and to draw no conclu-
sions from results which are not well outside that
magnitude. For example, the experimental error of a
field plot on average soil and under ordinary farming
conditions in this country may be taken as about lo
per cent. ; this means that if the yield of the standard
Plot A be taken as lOO, and another Plot B yields 109,
while a third C yields 91, the conclusion cannot be
drawn that B is better than A, and A better than C,
because the same variations in the results might have
been seen had the three plots been treated exactly
alike. Furthermore, unless the real difference brought
about by two different methods of treatment is greater
than 10 per cent, it is hopeless to expect to reveal
the difference at all by a single pair of experimental
plots.

These points may be illustrated by actual examples
drawn from the Rothamsted experiments, where the
soil conditions are fairly uniform, though by no means
exceptionally so, and the control and management is
about as good as they can be under ordinary farming
conditions.

On the grass fields are two unmanured plots almost
at the two extremities of the field, and taking a fifty
years' average, one of these plots (No. 12) is 10 per
cent, better than the other (No. 3), owing to some
fundamental superiority of soil or situation. Table
cm. (pp. 361-2) shows the actual results given by these
plots year by year, reduced to a common standard by
taking the yield of Plot 3 in each year as 100.

It will be seen that though on the average of the
whole period Plot 12 is represented by no when Plot
3 is 100, yet there are twelve occasions when Plot 12

xni.]

ACTUAL AND RELATIVE YIELD

361

Table CIII.— Actual and Relative Yield on Two Unmanured
Grass Plots. Rothamsted.

Yield of Hay.

Relative

Yield
of Plot 12.
Plot 3 = 100.

Mean
of Plot 12.

5-year periods.

Plot 3.

Plot 12.

Lb.

Lb.

1856

2515

2351

93

'

1857

2856

2592

91

1858

2472

3360

136

105

1859

2540

2576

lOI

i860

2760

2884

104

.

I86I

2844

3304

116

^

1862

3052

3424

112

1863

2284

2844

125

121

1864

2688

2808

104

1865

1296

1932

149

.

1866

2660

3012

113

A

1867

3332

3048

91

1868

i960

2676

137

128

1869

4256

4352

102

1870

644

1260

196

-

I87I

2844

2960

104

1872

1644

2252

137

1873

1372

1804

131

121

1874

1412

1642

116

1875

3620

4232

117

1876

1384

1599

116

1877

2364

2165

92

1878

1848

1832

99

108

1879

3028

3157

104

1880

848

108 1

127

I88I

1480

1393

94

1882

2524

2340

93

I8S3

2266

2322

102

102

1884

1804

1996

III

1885

2I0I

2339

III

1886

2547

2672

105

1887

I47I

1330

90

1888

2296

2298

100

96

1889

2638

2383

90

X890

1648

1565

95

362 EXPERIMENTS WITH FERTILISERS [cpiap.

Table CI 1 1. — Continued.

Yield of Hay.

Relative

Yield
of Plot 12.
Plot 3 = 100.

Mean

of Plot 12.

5-year periods.

Plot 3.

Plot 12.

I89I
1892

1893
1894
1895

1896

1897
1898
1899
1900

1 901
1902

1903
1904
1905

Lb.
2060
1627

391
2685
1402

1 144
1742
1922
1342
1379

455
1004

1509
2949
1936

Lb.
2422
2130

487
2538
1399

1272

2048
2256
1788
1859

765
1200

1571
2872
2297

118
131
125

95
100

III
118
117
133
135

168
119
104

97
119

114
123
121

Average

2057

2254

no

yielded less than Plot 3, while in a single year Plot 12
has risen as high as 196 per cent or fallen as low as 90
per cent, of Plot 3.

Applying what is known as the method of least
squares to the results, we can calculate that the mean
error of a single result is ± 10 per cent, and that the
probable error of the fifty years' mean is ± 1-9
per cent. In other words. Plot 12 is probably better
than Plot 3 by more than 8-i, and less than 11-9 per
cent ; but this superiority could never be assured from a
single year's experiment, because it is smaller than the
mean error, which is equal to a lo per cent difference
between the two plots. The probable error is always
reduced by the number of trials ; if the fifty years are

XIII.] CALCULATION OF EXPERIMENTAL ERROR 363

collected into ten groups of five years each, we should
get the following figures for Plot 12 — 105, 121, 128, 121,
108, 102, 96, 114, 123, 121. In all cases except one the
five years' average of Plot 12 is higher than that of Plot
3, and as we can calculate as before that the mean error
attached to each figure is ± 10-5, we could hardly have
concluded with confidence from any five years' series that
Plot 12 was superior to Plot 3, and the extent of the
superiority would have remained unknown.

To take another example, Table CIV. represents the
results of five years' experiments with different crops on
five similarly treated plots in Little Hoos field, reduced
each year to a common standard by taking the mean of
the five as 100.

Table CIV.

Plot.

1904.

1905.

1906.

1907.

1908.

Mean of 5 years.

A

98-1

88-8

95-8

86.3

92-8

92-3 ± 1-4

B

95-8

92-4

90-6

95.1

94.9

93-7 i 0-7

C

lOl-O

98.9

99-2

102-4

100-2

IOO-3 ± 0-6

D

1017

II4-I

105-0

109-1

114-9

109-0 ± 1-7

E

103-4

105-8

109-2

io7'0

97-3

104-5 ± 1-4

Again, it will be seen that the variations from the
mean of the single plots in any given year are consider-
able, the mean error being ± 7-5, on the assumption that
all the plots should be exactly alike. But from the five-
year means there would seem to be some constant
difference in the plots, which improve from A to D,
though the superiority indicated is still of much the
same magnitude as the experimental error, and that can
only be reduced by continuing the trials over a longer
series of years.

It will not be necessary to go into further detail, but
the above numbers illustrate the general principle that

364 EXPERIMENTS WITH FERTILISERS [chap.

as an error of 10 per cent, or so must be expected in
the returns from a single plot, this error must be taken
into account in the design of any scheme of field
experiments.

For example, if trial plots are being laid out and are
only expected to continue a single year, it would be
useless to include among them a comparison of sulphate
of ammonia and nitrate of soda containing equal
amounts of nitrogen. There is abundant evidence that
the superiority of the nitrate of soda is somewhere
about 10 per cent. ; but as this is no more than the
expected experimental error a single experiment must
be inconclusive. If it is important to settle for the
particular soil the relative value of nitrate of soda and
sulphate of ammonia more plots must be given up to
this one question ; at least five would be needed, and
even then there would remain a possibly considerable
error due to the season.

This suggests that the prime consideration in
designing a set of field experiments should be to limit
the scheme strictly to certain definite questions which
can be answered in the time and space available.
There should be no haphazard laying-out of plots with
all sorts of variations of manuring ; the problems to be
solved should be clearly thought out beforehand ; it
will generally be found that only a very small number
of problems can be attacked at one time and every
plot should be arranged to contribute to the result
without the Introduction of any secondary or disturbing
factors.

As to the choice of land for experimental plots little
can be done beyond exercising ordinary discretion in
selecting a field which promises to be uniform. The
geological drift map should be consulted, and places
marked by thin patches of drift or on the boundaries of

XIII.] CHOICE OF LAND FOR FIELD PILOTS 365

one or more outcrops should be avoided ; trial holes
should be sunk to see that the depths of soil and subsoil
are fairly uniform ; thin soils on the chalk or limestone
should be avoided, because of the very irregular surface
of the underlying rock. Naturally, sharp slopes should be
avoided ; if there is any gradient, the plots should be laid
out to run parallel to one another up and down the slope,
so that each plot shares both the higher and the lower
levels. Other points will suggest themselves ; speaking
generally, the opinion of an intelligent farmer well
acquainted with the land is the most valuable guide.
It has been suggested to weigh up a number of areas
when the field is in ordinary crop, but, as indicated above,
the normal variations are so great that several years of
such trials would be required to arrive at any exact
conclusion. The condition of the land is equally im-
portant , land in high condition should be avoided, since
for some years at least the effect of the manures would
be swamped and all the plots would give very similar
results. On the other hand, bad land is not desirable, if
the object is to illustrate the action of fertilisers and not
to work out a method of dealing with that particular
class of land ; good land in poor condition after two or
more white straw crops is the best. Care should also
be taken to ascertain that the field has not been cropped
or manured irregularly for the five or six years previous
to the trials ; it is astonishing how long the disturbing
effect of farmyard manure or a leguminous crop, or
folding sheep on a portion only of a field, will
persist and become manifest under experimental con-
ditions.

The size of experimental plots is a matter on which
there are considerable differences of opinion ; on the
one hand, large plots smooth out the small irregularities
due to minor differences of soil and drainage, insect

366 EXPERIMENTS WITH FERTILISERS [chap.

attacks, and preparation of the land; errors of weighing
and measuring are also proportionally reduced by being
spread over the larger quantities involved. On the
other hand, the larger plots mean greater risks of
meeting with irregular patches of soil, and much greater
difficulty is experienced in getting the cultivation of all
the plots carried out under uniform conditions. It is of
the first importance that the whole of the experimental
land should be worked on the same day ; autumn
ploughings perhaps matter least, but spring ploughings
and cultivations, and above all seeding, should be
carried through in a single day. Otherwise, if part of
the land is worked and left and then the weather
changes, a considerable interval may elapse before the
operation can be completed, and a new factor, often of
considerable magnitude, is thus introduced into the
results. Sometimes large plots are necessary to
obtain sufficient material for further investigation ;
account, too, should be taken of the facilities for
weighing up the crop ; if no weighbridge large enough
to take a cart is available on the farm it is difficult
to deal with large areas. Speaking generally, it may
be said that with due care a plot one-twentieth of an
acre can be made to answer all ordinary purposes.
But whether large or small the most important point is
to repeat the plots on some regular system about the
ground, and to have four or five similar plots of one-
twentieth of an acre for each treatment rather than one
of a fifth or a quarter of an acre. In the Danish
experiments conducted by Dr Sonne upon the relative
value of different varieties and management of barley,
which may be taken as the most carefully elaborated
series of field trials for practical purposes which have
ever been carried out, the plots are about ^V acre each,
and at any one station there are always four plots

Xiii.J ARRANGEMENT OF EXPERIMENTAL PLOTS s^;

receiving the same treatment, arranged about the field
as follows : —

A

F

E

G

B

G

D

F

C

A

C

E

D

B

B

D

E

C

A

C

F

D

G

B

G

E

F

A

In this way the experimental errors due to inequalities
of soil and other accidentals are greatly reduced. With
several stations repeating the same experiment in
different districts the effects of soil may also be largely
eliminated, and in the course of a single season a result
can be obtained which is only subject to the error
due to variations of season. The shape of the plots
should be long and narrow rather than square, as this
tends to equalise, the soil conditions, and their breadth
should be chosen to give each exactly the same number
of rows of roots or corn, as the case may be, a point
which must be closely watched in seeding. When the
plots are continued for more than one season, some
method must be adopted to mark their position per-
manently, but posts at the corners interfere with
cultivation and are often in consequence taken up by
the labourers. At Rothamsted the method adopted is
to set out the plots initially in the field, keeping the
boundaries well away from the hedges and trees (the
soil on the headlands of a field is generally irregular,
and trees have a very wide-reaching effect), and then
mark the outside lines of the experimental area by
means of stout posts painted white and set in the
hedges round the field. These being out of the way

368 EXPERIMENTS WITH FERTILISERS [cHAP.

are subject to no disturbance until they need renewing
through decay, and they afford sighting lines along
which lie the corners of the actual plots. Each of these
corners is marked by a stake or post of creosoted oak,
I foot long X 2\ inches square, sunk a foot below
the surface, so as to be out of the way of the plough or
any other cultivating tools. When the time comes for
setting out the plots before sowing the manures, the
operator measures off along the sighting line the known
distance to the corner of the first plot and then probes
the ground with a pointed steel rod until he finds the
buried post, above which he sets up a temporary but
sufficiently conspicuous stake. Proceeding in the same
way he marks the corners of all the plots, after which the
manures can be sown and the temporary stakes removed
before the manures are ploughed or harrowed in. As a
rule it is desirable to set out the plots with paths or
dividing strips between ; division strips are particularly
necessary on arable land to prevent the plough carrying
manured soil from one plot across on to the next. Paths
result in a stimulus, " the fallow effect," to the outside row
whether of corn or of roots ; consequently each plot
must be bordered by the same extent of path ; in some
respects it would be better to dispense with them, but
the necessity of studying the plots during growth, and
often of showing them to large numbers of people,
renders them indispensable. Whatever divisions are
adopted, it is better to sow the whole field and strike
out the paths afterwards by a hoe, care, of course, being
taken to start the drills each time at the same distance
from the edge of each plot.

If the plots are continued year after year, it is
necessary to watch the method of ploughing; if a
turnwrest plough be used, the mould-board should be
set to throw the furrows opposite ways in alternate

XIII.] CONDUCT OF EXPERIMENTAL PLOTS 369

ploughings, otherwise the manured soil will gradually
be displaced sideways ; if the plots are ploughed in
lands the furrows should be alternately gathered to and
cast away from the middle of the plot, or the manured
soil will be accumulated towards the middle.

It is best to sow the manures (except the nitrates
and ammonium salts) a week or so before the seed and
plough them in. For sowing the manures, one of the
machines to be described later is best ; hand-sowing
produces considerable irregularities which can only be
obviated by mixing the manure with sufficient ashes or
burnt earth to make up a bulk of 10 or 12 cwts. per
acre and sowing the mixture in three successive opera-
tions. Calm weather must be chosen for sowing the
manures ; many fertilisers blow considerably if there is
the least wind stirring ; generally a few still hours may
be secured in the early morning.

It will often be necessary, indeed always when the
manures are sown broadcast by hand, to have a screen on
the edge of the plot when sowing the strip which comes
up to this edge. At Rothamsted a canvas-covered
screen 16 feet long x 4 feet 3 inches high is carried
along the edge parallel with the machine or man sow-
ing. After sowing, the usual operations of cultivation
are carried out, but rather more care than usual should
be given to the singling of root crops, so as to obtain a
uniformly set out plant Gaps and misses can, on some
soils, be repaired by transplanting at this stage, but it
is not always desirable to do so, because one of the
properties of the manure under examination may be to
increase or diminish the tendency to lose plant In all
experiments with root crops the actual number of
plants on the plot should be counted before harvest
and recorded, as the figures often afford a means of
criticising the weight results, and of estimating the effect

2 A

370 EXPERIMENTS WITH FERTILISERS [chap.

of the manures upon the constitution of the plant. At
harvest-time cereal plots can either be cut by scythe or
a small reaping-machine ; if the plots are large and the
paths wide, an ordinary binder can be employed, as is
done on the Broadbalk vvheatfield at Rothamsted. As
the sheaves are tied they must all be gathered on to
the plot from which they were cut, and a distinguishing
label may also be tied to each, especially if the plots are
small. In some cases threshing is done in the field, but
generally in the United Kingdom it will be necessary
to carry the unthreshed sheaves to a rick or preferably
a barn. To keep the produce of each plot separate
until threshing time, a number of squares of thin
canvas should be prepared, of a fabric sufficiently open
to allow of the freest ventilation but not the passage of
any shed corn. The bottom of the stack should begin
with some non-experimental corn over which one of the
canvas squares is thrown, followed by the produce of one
plot together with two wooden tallies by which it can
be identified. Another cloth is then spread before the
produce of the next plot is stacked, and so on with the
other plots. Threshing may be done with a special
machine, but the ordinary travelling steam-thresher, if
of modern construction, will do all that is required ; at
the end of each run the screens must be removed and
a little of the straw again put through the machine,
so as to work out all the grain, the last pint or so of
which must be extracted by hand from the hopper.
The grain should be measured out bushel by bushel, and
every bushel weighed and recorded ; the tail corn should
be weighed as a whole ; the straw and cavings should
also be weighed. Hay is best weighed ar» it leaves
the field on the way to the stack, and a^ different
manures are liable to lead to different rates of drying,
it is well to take a weighed sample from each plot of

Sq

c H

X

►J

o

i-i

H

Oii

U

n

W

cyj

Q

Id

<;

1

S

oi

S

Ci

<

H

«

D

I To face paoi' 37S.

XIII.] THE SOWING OF FERTILISERS 371

the hay as carted, and preserve it for a dry-matter
determination in the laboratory.

In dealing with root crops it is found convenient to
cut the tops off and weigh them in large baskets in the
field ; the roots themselves are carted off to the weigh-
bridge. Whatever the crop, the whole produce of the
plot should be weighed ; to cut out and weigh a small
area introduces a fatal source of error — the selection
of the area. There are a number of other precautions
to take which cannot be here enumerated, but speaking
generally, the original records should be as full of detail
as possible ; forms for the entries should be drawn up
beforehand in such a fashion that there is a place for
every figure obtained in the work without any additions
or subtractions, and all this original material should be
preserved untouched.

In the use of fertilisers, whether for experimental
purposes or in practical farming, it is very important to
get them distributed evenly on the land ; nothing is
more common in a hay or cereal crop where nitrate of
soda has been used as a top dressing than to see regular
waves of a darker green and stronger growth than the
bulk of the crop, representing the places where the
fertiliser fell from the sweep of the sower's arm. With
other manures the irregularity is not so evident, partly
because they are often sown before the final working of
the ground, and partly because they have not the
striking effect upon the colour and vegetative develop-
ment of the crop that nitrate of soda has. But if
artificial manures are to be sown evenly by hand, it is
necessary to mix them with a much greater bulk of
burnt earth or ashes and to go over the land more than
once ; better and quicker work will always be done by
a machine if there is enough work of the kind on the
farm to justify its purchase. Some fertilisers, basic slag

372 EXPERIMENTS WITH FERTILISERS [chap.

and ground lime in particular, are unpleasant and even
dangerous to sow by hand. There are a number of
different types of machine on the market, and all will
do good work with unmixed dry fertilisers, though some
fail to do so with mixed manures. With a mixture
containing superphosphate, or still more so dissolved
bones, any machine which possesses moving parts
working in the manure will be sure to cause the forma-
tion of a paste which eventually clogs up the machine
and puts it out of action. Whenever a farmer expects
to sow mixtures, he must be careful to get a machine
of which no part in contact with the manure is actively
moving.

At the Rothamsted experiment station a machine
made by Coultas, of Grantham, has been in regular use
for some time, and answers admirably. The principle
upon which the machine works will be gathered from
the diagrams. Fig. 6, which show a section through
the box 0 n,Z ft. or lo ft. 6 ins. long, which contains the
manure. The manure is thrown over the lip of n by
the revolving spindle m, running the whole length of
the box, and furnished with a series of radial arms
which dip in the manure and toss it over the lip. As
the machine travels the bottom and side o of the
manure box lift, being driven by the rack and pinion
k and /, which are geared to the wheels of the machine *.
the side n of the box, however, remains stationary.
The spindle is also geared to the wheels of the machine, ■
and the rate at which it revolves, and therefore the rate
at which manure is delivered, can be varied by changing
the gear wheels. After it is tipped over the lip of «,
the manure falls through a closed channel and can be
delivered only a few inches from the ground, so as to
avoid blowing. It will thus be seen that this machine
fulfils the great desideratum of havmg no parts working

XIII.] MACHINES FOR SOWING FERTILISERS 373

in the manure, its delivery can be stopped and started
sharply, the rate of sowing can be accurately gauged,
and by filling part of the manure box with ashes only it
can be made to sow a narrow strip at the edge, should
the width of the plot not form a round number of widths
of the machine ; thus it forms a very suitable tool for
experimental work. On a very similar principle is a
machine made by Messrs J. Wallace & Sons, of Glasgow,
shown in diagrammatic section in Fig. 7. Here the
bottom of the hopper box A, containing the manure, is
formed by a revolving drum B, which carries out the
manure through the aperture regulated by the adjust-
able slide-plate N on to the tray C, from which it is
thrown so as to fall on the ground by the revolving
spindle with radial arms, as in the previous machine.
The rate of sowing is regulated by the size of the
aperture controlled by N.

Several other makers construct machines akin in
principle to the two described, in that a revolving
spindle with arms corresponding to the cups of a seed
drill takes up the manure and delivers it ; they only
differ in the way in which the manure is presented to
delivery arms.

Entirely different are the machines constructed by
several makers on the principle illustrated in the section
Fig. 8, derived from a tool manufactured by B. Reid
& Co,, of Aberdeen. Here the manure is again con-
tained in a long hopper, across the bottom of which a
number of endless chains move, actuated by a series of
pitch chain wheels geared to the wheels of the machine.
The chains come out of the box through a narrow slit
and drag with them some of the manure, which then
falls to the ground ; the rate of sowing being regulated
by the gear wheels which actuate the spindle carrying
all the pitch chain wheels. A more slowly moving

374 EXPERIMENTS WITH FERTILISERS [chap,

stirrer within the hopper box keeps the manure moving
down to the delivery chains.

Again, on a different principle are the well-known
broadcast distributors, of which an example made by
Messrs J. & R. Wallace, of Castle-Douglas, is shown
in Fig. 9. Here the manure is carried in a
circular hopper from which it simply falls through
two apertures the size of which can be regulated, the
manure being kept in motion by stirrers within the
hopper. The manure is, however, not allowed to fall
direct to the ground, but is intercepted by two
horizontal discs with radial ribs, which are kept in
rapid revolution by gearing connected with the wheels
of the machine. As it reaches these discs the manure
is flung rapidly in all directions, and so falls on the
ground over a much wider strip than the track of the
machine. Machines of this type are cheap, light to
drive, and handy, and are very convenient for sowing
large acreages of grass land with lime or basic slag.
The distribution is, however, not very uniform ; if the
manure is a mixture, the heavy particles are thrown
further than the light, while the very lightest powders
are so beaten up into a dust that they float for a con-
siderable distance, especially in a wind ; they are thus
unsuited for experimental purposes or any very exact
work.

The question is often raised of how far very small
plots, a few yards square, cultivated with all the care
and attention given by a good gardener to his plants,
or even pots, can be made to serve for experimental
work on fertilisers, in place of the ordinary field plots of
•^ acre or more. For demonstration purposes they do
well enough, but for investigation and local enquiry the
very care with which the cultivation is carried out prevent
the variations induced by the manures in the constitution

Pitch Chain
Wheel

Rollep

Roller

Fig. 8.

Diagrammatic Section of Manure Distributor — Endless Chain
Feed Type.

Fig. 9. — BRo.A.nLAST Mani re Sower with Revolving Discs

FOR DiSTRlliUTION.

XIII.] EXPERIMENTAL WORK B V FARMERS 375

of the plants as regards disease, insect attacks, etc., and
in the texture of the soil, from having due weight. In
pot work the artificiality of the conditions is increased ;
pot experiments are only of value to the investigator in
clearing up the earlier stages of an enquiry before the
applications to practice begin to be considered.
Deductions from pot experiments with regard to field
work must be drawn with great caution and always
regarded with suspicion.

It will follow from what has been said about the care
with which field experiments are to be conducted and
the large margin of error inherent in their results even
under favourable conditions, that they are hardly to be
lightly entered upon by the ordinary busy farmer, and
that the advice so often given to him to work out by
experiment the manures best suited to his own farm
would really involve a disproportionate amount of work.
Single-handed it will take too long and cost too much
to arrive at accurate results ; the farmer's experimenting
should be done as part of a large co-operative local trial
designed to establish the characteristics of the soil on
which he is working, in regard to its customary cropping.
Even the usual habit of testing a fertiliser by leaving
one breadth of the field unmanured may often deceive ;
concentrated nitrogenous manures easily show up under
such conditions, because they affect the colour and vege-
tative appearances of the crop so markedly ; basic slag,
again, effects an extraordinary change in the appearance
of some pastures ; but, speaking generally, the effects of
the mineral and some mixed manures are only to be
seen in the yield. Experience shows that it is difficult
to detect by eye the difference between two adjoin-
ing plots when the yield of one is 20 per cent, above
the other; differences like 10 per cent, will always go
unperceived. In estimating the yield of root crops the

376 EXPERIMENTS WITH FERTILISERS [chap. xiii.

difficulty is increased by the way the leaf takes the eye,
so that a lighter but more leafy crop, due to a com-
parative excess of nitrogen, will generally be set down
as the heavier.

In field experiments, as in all other applications of
science to agriculture, the problems involved are so
complex, the factors which intervene are so various and
unexpected, that the greatest rigour and technical
skill are called for in the conduct of the investigation,
to be followed by an even greater measure of scientific
caution in interpreting the results.

TABLES FOR THE CONVERSION OF NITROGEN INTO
AMMONIA AND PHOSPHORIC ACID INTO TRI-
CALCIUM PHOSPHATE.

Ammonia.

Nitrogen.

Nitrogen.

Ammonia.

I

-

•8235

I

=

1. 214

2

=

1-647

2

=

2.429

3

—

2.471

3

=

3-643

4

=

3-294

4

=

4-857

5

=

4-II8

5

=

6-071

6

=

4.941

6

=.-

7.286

7

=

5-765

7

=

8.500

8

=

6.588

8

=

9.714

9

=

7-412

9

=:

10-93

Tri-calcium

Pliosphoric

Phosphoric

Tri-calcium

Phosphate.

Acid.

Acid.

Phosphate.

I

=

•4576

I

=

2.185

2

=

.9152

2

=

4-370

3

=

1-373

3

=

6-556

4

=

1-831

4

=

8-741

5

r-

2-288

5

=

10-926

6

=

2-746

6

=

i3-iir

7

—

3-203

7

=

15-297

8

=

3 -66 1

8

=

17-482

9

=

4-119

9

=

19-667

Exampk-

-Reduce 6-43 per

cent. Ammonia and

35-21

per cent.

cium Phosphate to

Nitrogen and Phosphoric Acid :

Tri-calcium

Phosphoric

Phosphate.

Acid.

6 Ammonia

= 4-941 Nitrogen

30

=

13-73

•4

,,

= -329

5

=

2-288

•03

II

= -025

•2

=

091

5-295

01 =

•005

16.114

INDEX

Absorptive power of litter, 182
Acetylene evolved from cyanamide,

Acidity of soil, 62, 258, 315
Adulteration of manures, 235
Agricultural Holdings Act, 354
Air a ccespitosa^ 256
Algerian phosphates, 1 18
Alkaline, reaction in soil, 55, 321 ;

salts required by plant, 170, 262
Ammonia, absorbed by peat-moss

litter, 183 ; conversion into

nitrogen, tables for, 377 ; fixers

of, 200 ; lost in dung-making,

189
Ammonium carbonate from urea,

184
Ammonium citrate as a solvent, 126,

132, 143
Ammonium salts, 12 ; action on

soil, 62 ; duration of, in soil, 96 ;

in rain, 29 ; nitrification of, 60 ;

versus nitrate of soda, 94
Ammonium sulphate, composition

of, 58 ; in drainage water, 60 ;

production of, 58 ; retention of,

by soil, 61
Analysis of fertilisers, 349
Anhydrite, 160

Antiseptics in dung-making, 202
Apatite, 104, 117, 121
Artificial manures, 24
Australia, value of superphosphate

in, 140
Assimilation, 6, 14, 165
Availability, of manures, 91, 97, 145,

156, 215 ; of plant food, 23, 282
Azotobacter chroococcum, 35, 257

Bacteria, competing for nitro-
genous manures, 66 ; denitrif}'-
ing, 185 ; humus-forming, 186 ;
in soil, 257; nitrogen - fixing,
II, 32, 34, 273; putrefactive,
185

378

Bacterial changes in dung-making,
190

Barley, Danish experiments on,
366 ; effect of phosphatic
manures, 137 ; effect of potassic
manures, 168 ; quality, effect of
salt on, 269 ; quality with nitro-
genous manures, 66, 81, 308

Basic slag, 13, 106, 127, 143, 150;
composition of, 129 ; effect on
poor pastures, 329

Basic superphosphate, 133, 152

Bat guano, 236

Beans, manures for, 322

Beijerinck, 35

Berkeland - Eyde, process for
nitrogen fixation, 43

Bessemer process, 127

Blithe, W., on manures, 11, 72, 107

Blood, dried, 11, 239, 248

Bone flour, 145

Bone meal, 109, 145, 153 ; effect on
pastures, 331

Bones, ii, 103, 106, 145 ; dissolved,

"3, 155
Bonnet, oxygen evolved by leaves, 6
Boussingault, action of gypsum,

267 ; theory of plant nutrition, 7
Bracken fern, as indicator of lack of

lime, 254 ; as litter, 182
Bradley and Lovejoy, electrical

fixation of nitrogen, 42
Rrown on assimilation, 14

Cabbages, manures for, 316
Cake-fed dung, 203 ; cost of, 227
Calcium carbide, 38
Calcium carbonate, 250; removed

from soil, 56, 62
Calcium cyanamide, 38
Calcium phosphates, 104, 142
Caliche, 46
Candolle, 293
Carbide, combination of nitrogen

with calcium, 38

INDEX

Z79

Carbohydrates, denilrification
favoured by, 185 ; potash required
for production of, 166 ; required by
nitrogen-fixing organisms, 35, 1 71

Carbon bisulphide, 202, 241

Carbonic acid, assimilation of, 6,
14 ; excretion of, by roots, 290 ;
in soil water, 143, 149, 156, 287

Carnallile, 160

Cartilage, 108, 154

Castor cake, 242, 248

Catch crops, 274

Chalk, 252

Cellulose, fermentation of, 187

Cercosporium melonis, 88

Cheshire, use of bones in, ill

Chinchas guano, 231

Chlorophyll, 14, 173

Christmas Island, 1 16

Cinereals, 24

Citric acid solution as solvent, 126,
132, 143, 149, 165

Cleveland iron ore, 127

Clover, effect of potash on, 171 ;
manures for, 325 ; value of lime
to, 261 ; value of, in rotation, 33,

295, 323

Clover sickness, 34, 297, 324

Club root, 259

Coal, nitrogen in, 58

Colour, relation to iron salts, 270

Compensation for unexhausted
fertilisers, 354

Composition affected by manuring
and season, 83, 86

Composition of, ash of wheat, 264 ;
average crops, 22 ; basic slag,
129; bone manures, iii ; clover
ash, 268 ; excreta, 181 ; farmyard
manure, 202 ; gas lime, 266 ;
gases in dunghill, 188 ; guanos,
248 ; lime, 255 ; litter, 182 ;
London dung, 207 ; Peruvian
guano, 230, 233; plant, 13;
sewage sludges, 247 ; Stassfurt
salts, 161

Condition in soil, lOI, 2I0

Continuous growth of crops on same
land, 296

Conservative systems of farming, 302

Coprolites, discovery of, 13, 1 14,
121, 153

Corn marigold, 254

Cotton, manures for, 336

CoUon cake, damaged, composition

of, 248
Cow, composition of excreta of, 181
Crookes, Sir W., on fixation of

nitrogen, 42
Crust guanos, 1 16
Cyanamide, 38
Czapek, 2gi

Damaraland guano, 235, 248
Danish barley experiments, 366
Daubeny, 114

Davy, nutrition of plants, 6, 104
Defiocculation due to, nitrate of
soda, 54 ; potash salts, 176 ; salt,
269
Defoe, use of the word manure, i
Deh^rain, 187
Denitrification, 185, 305
Diffusion of soluble salts in soil, 288
Digby, Sir Kenelm, on nitre, 12
Digestion, process of, 179, 191
Diminishing returns, law of, 283
Diseases, fungoid, 86, 174, 216
Dissolved bones, 109, 113, 155
Dissolved Peruvian guano, 235
Dominant fertilisers, 89, 280
Dormant plant food, 23, 282
Drainage, affected by farmyard man-
ure, 220 ; water, composition of,
61, 165
Dried blood, 239

Dry and wet seasons, effect of farm-
yard manure in, 220 ; value of
potash salts in, 175 ; with nitro-
genous manures, 67 ; with phos-
phatic manures, 137
Dundonald, 103
Dung, cake-fed, 203 ; definition of,

178 ; value for mangolds, 316
Dyer, 148, 165, 206

Earth closet system, 244
Egypt, nitrate of soda deposits in, 47
Ellis, W., on manures, 12, 159, 241
Epichloe typhina, 87
Error of experiment, 359
Estremadura, phosphates in, 114,

117, 123
Evelyn, J., on bones, 107 ; on

manures, 11 ; on nitre, 12
Excreta, composition of, 181, 243

38o

INDEX

Experimenls, with fertilisers, 359 ;
pot, 375

FAECES, nature of, 179, 243

Farmyard manure, changes during
making, 189 ; composition of, 202,
205 ; cost of mailing, 224 ; defini-
tion, 178 ; fire-fanged, 191 ; last-
ing action of, 212; loss of nitrogen
in making, 192 ; management of,
207; physical effects of, 216;
slow availability of, 215 ; utilisa-
tion of, 222, 315, 318, 321 ; value
of, 209, 216

Feathers, 11, 71

Felspar, 163

Fermentation, of cellulose, 187 ; of
urea, 184

Fertilisers, compensation for residues
of, 354 ; experiments with, 359 ;
machines for sowing, 372 ; mixed,
352 ; required in ordinary farm-
ing, , 305 ; sampling of, 350 ;
significance of term, 2, 23 ; valua-
tion of, 340

Fertilisers and Feeding Stuffs Act,

235> 349
Fertility, of soil, 305 ; unexhausted,

354

Finger-and-toe, 151, 216, 259, 315

Fire-fanged manure, 191

Fish guano, 236, 248, 345

Fish waste, 12, 75, 236

Five fingers, 75

Fixation of nitrogen, by bacteria,
32 ; by calcium carbide, 38 ; by
electricity, 42 .

Flocculation of soils by lime, 255

Flock dust, 71

Florida phosphates, 1 16

Folding of sheep, 274

Foods, fate of nitrogen in, 180;
manure value of, 225, 356

Foxglove, 254

Frank and Caro, cyanamide, 38

Franklin, Benjamin, 267

Fray Bentos guano, 238

Fruit, manures for, 334

Function of, iron salts, 270 ; nitro-
genous manures, 77 ; phosj^hatic
manures, 136; potassic manures,
165 ; silica in plant nutrition, 271

Fungi in dung, 191

Fungoid diseases, and lime, 259 ;
and nitrogenous manures, 86 ;
and potash manures, 174; carried
by farmyard manure, 216

Garden manures, 338

Gases contained in dunghill, 187

Gas lime, 254, 262, 265

(Gilbert, Rothamsted experiments, 9

Grasses, appearance of potash -

starved, 173 ; developed by nitro-
genous manures, 65
Grass land, effect of lime on, 259 ;

effect of potash on, 173 ; manures

for, 326 ; value of dung on, 221
Greaves, 74, 239, 248
Green manuring, 272
Grinding of bones, 107; of fertilisers,

value of fine, 150, 154
Ground lime, 253
Guano, 12, 145, 346 ; bat, 236 ;

Damaraland, 235 ; fish, 236 ;

Ichaboe, 235 ; meat, 236, 238 ;

native, 246; phosphatic, 115,

145, 152, 229
Gunpowder salt, 269
Gypsum, 106, 113, 124, 160, 262,

266 ; as an ammonia fixer, 201 ;

phosphatic, 134

Hair, ii, 71

Hay, manures for, 329

Hellriegel, experiments upon barley,

166 ; growth and nitrogen supply,

28; nitrogen-fixing bacteria, 11
Henslow, discovery of coprolites, 13,

121
High farming, 301
Highland and Agricultural Society's

experiments, 153, 313
History of manuring, 2, 11, 103, 158,

249
Holdings Act, Agricultural, 354
Hoofs, II, 71

Hop bine, composition of, 181
Hops, manures for, 333 ; spent, 74
Horn, II

Horse, composition of excreta of, 181
Hughes, F., analysis of Egyptian

nitrate of soda, 47
Hughes, J., basic superphosphate,

133
Humboldt, A. von, 231

INDEX

381

Humus, formation in dunghill, 186 ;

in soil, value of, 216, 273
Hydrogen evolved from dunghill,

187

ICHABOE guano, 235, 248

Incompatibles, 353

Ingenhousz, light essential to
assimilation, 6

Inoculation of soil, 36

Iron in soil, function of, 270 ; sul-
phate of, 270

JODlN, 272

Kainit, 160, 164, 201

Kalk-stickstoff, 38

Kellner, 191

Kelp, 158, 163

Kiln dust, 74

Kirwan, 104

Knop, water cultures, 10

Kohl rabi, manures for, 316

Kossowitsch, 292

Lahn phosphates, 116

Law of, diminishing returns, 283 ;
the minimum, 282

Lawes, manufacture of superphos-
phate, 13. 120 ; on turnip culture,
138 ; origin of Rothamsted ex-
periments, 9 ; use of ammonium
salts, 12

Lawns, manures for, 338

Leather, 71

Leaves, assimilation b}-, 6, 14, 168 ;
stimulated by nitrogen, 85

Leguminous crops, manures for,
322 ; plants and nitroijen, 10, 32 ;
effect of potash on, 171

Leuchstadt, experiments at, 192, 202

Leucite, 163

Liebig, on bones, 104, 107 ; on
superphosphate, I19 ; silicate
manures, 272 ; £Ource of plants'
nitrogen, 9, 1 1 ; theory of plant
nutrition, 7, 276 ; use of am-
monium salts, 12

Lime, action of, on soil, 63, 249,
257 ; ashes, 251 ; ground, 253 ;
in basic slag, 128, 151

Limestone, 250

Limiting factors for growth, 284

Liquid manure, 205

Litter, composition of, 181 ; effect

of, on losses of nitrogen, 195
Lobos phosphatic guano, 115
Lodging, due to excessive nitrogen,

Lcihnis, decomposition of cyanamide,

39
London dung, 206
Lucerne, manures for, 325
Lupins as green manure, 272

Machines for sowing fertilisers, 372
Maercker and Schneidewind, 192
Magnesium salts in manures, 163,

262, 269
Magnesian limestone, 251
Maize, manures for, 312
Malt dust, 12, 74
Manganese salts, action of, 271
Mangolds, with increasing nitrogen,
29 ; effect of sodium salts on, 52 ;
late growth with nitrate of soda,
66 ; effect of manuring on com-
position, 86 ; effect of manuring
upon number, 102 ; effect of
potassic manures, 168 ; value of
salt for, 268 ; manures for, 316
Manure, significance of term, i, 24
Manure value of foods, 225, 356
Manures, compounded, 301
Manures for barley, 308 ; beans,
322 ; cabbages, 316 ; clover, 324 ;
cotton, 336 ; fruit, 334 ; garden,
338 ; grass land, 326 ; hops, 333 ;
lucerne, 325 ; maize, 312 ; man-
golds, 316; oats, 311; pasture,
329; potatoes, 319; rye, 312;
sainfoin, 325 ; sugar, 336 ;
Swedes, 312 ; tea, 337 ; tobacco,
337 ; tropical crops, 335 ; vetches,
326 ; wheat, 306
Marl, 249
Marsh gas evolved from dunghill,

187
Maturity, accelerated by phosphoric
acid, 136 ; deferred by excess of
nitrogen, 78 ; effect of potash on,

174
Meat guano, 236, 238, 248, 345
Micrococcus iirccc, 184
Mineral manures, 24 ; duration of,

in soil, 96

382

INDEX

Minimum, law of, 282
Mixed fertilisers, 352
Miinlz and Girard, 195
Murray, Sir James, 123
Mussels, 75

Mustard, as green manure, 272
Mustard seed in rape cake, 240
Mulch, farmyard manure as a, 221

Native guano, 246

Night soil, 244

Nilson, 134

Nitrate of lime, 44

Nitrate of soda, 12, 307 \ action on
soil, 51, 54 ; compared with
ammonium sulphate, 64, 94 ;
composition, 49 ; for cabbages,
316 ; in Egypt, 47 ; source of,
45 ; value of soda, 53, 170

Nitrates, saving of soil, 273 ; soil,
289

Nitric acid in rain, 29

Nitrification, in spring, 90 ; in wet
seasons, 67

Nitrogen, and fungoid diseases, 86 ;
compounds of, in dung, 206 ;
contained in rain, 29 ; conver-
sion into ammonln, tables for,
377 ; electrical fixation of, 42 ;
fixation by calcium carbide, 38 ;
fixed by Leguminosas, 1 1 ; growth
proportional to supply of, 28 ; in
food, fate of, 180 ; in wheat grain
and flour, 84 ; losses by denitri-
fication, 185, 305 ; lost in dung-
making, 192 ; origin of combined,
30; recovered in crop, 99, 210;
removed in four-course rotation,
303 ; source of plants', 9, 26 ;
value of unit, 342 ; vegetative
growth promoted by, 77

Nitrolim, 38

Nodule organisms, 273

Nucleo-proteins, 140

Nutrition, theories of, 5-6, 13

Oats, manures for, 31 1
Oilcake, 12, 240, 242, 345
Oil in manures, 72, 237
Oospora scabies^ 321
Organic manures, value of, 94, lOO
Organic matter, value of, in soils,
73

Palissy, B., observationson manures,

4

Pasture, manures for, 329

Peat moss, as litter, 181, 195 ;
manure, 183

Peruvian guano, 12, 115, 229, 248,
338, 346 ; dissolved, 235

Phosphate rock, 115, 156

Phosphatic guano, 115, 152

Phosphate, conversion into phos-
phoric acid, tables for, 377 ; of
iron, 125; of lime, 104, 142;
value of unit, 343

Phosphates, action of lime on soil,
260 ; required by barley, 309 ;
required by turnips, 313

Phosphatic gypsum, 134

Phosphoric acid, 103, 136 ; and
nitrogen in plant, 140 ; conver-
sion into phosphate of lime, tables
for, 377 ; value of unit, 343

Phosphorus in iron, 127

Photo-synthesis, 15, 169

Pickering, 298

Pigs, composition of excreta of, 181

Plant food, dormant and available,
23 ; in soil and crop, 21

Plasmolysis, 18, 50

Plasmodiophora brassiccp, 259

Pliny, 250

Plots for field experiments, size of,
365

Poly halite, 160

Polzenius, stickstoff-kalk, 41

Pot experiments, 375

Potash salts, 13

Potash, 158 ; value of unit, 344

Potassium carbonate, 163 ; function
of, in nutrition of plant, 166 ;
salts, retention by soil, 164

Potatoes, manures for, 319

Precipitated phosphate, 134, 152

Preservatives in dung-making, 200

Priestley, discovery of assimilation,
6, 276

Pugh, source of plant nitrogen, 9

Quality in produce, 66, 72, 81,

269, 270, 308, 320
Quicklime, 250

Rabbit hair, 71
Rags, II, 72

INDEX

383

Rain, nitrogen contained in, 29

Rape dust, 94, 240, 248, 345

Recovery of nitrogen in crop, 99,
210

Residues from manufactories, 67 ;
compensation for manuriai, 354 ;
duration of manuriai, 71, 96, 98,
212

Retention of fertilisers by soil, 148,
164

Reverted phosphate, 106, 126

Ripening caused by phosphatic
manures, 136

Rochdale manure, 245

Rock salt, 159

Roman agriculture, 2, 250

Roots, development of, with nitro-
genous manures, 65 ; effect of
phosphatic manures on, 139;
ratio of, to leaf, 85 ; solvent action
of, 290

Root system, importance of, 280

Rotations, 32, 293, 301, 319

Rothamsted, analysis of soil, 20 ;
experiments, 9, 13, 26, 277, 360;
grasB plots at, 65

Russell, dung-making experiments,
199 ; on heated soil, 298 ; com-
position of seaweed, 75

Rye, manures for, 312

Sachs, 272, 290

Sainfoin, manures for, 325

Sale of fertilisers, 349

Salt, 262, 268, 319; gunpowder,

269 ; nitrate of, 51
Sampling of fertilisers, 349
Saussure, nutrition of the plant, 6,

17, 276 ; on ammonia, I2 ; on

phosphate of lime, 104
Scabby potatoes, 321
Schubler, theory of manures, 7
Schneidewind, 192, 202
Sclerotinia disease, 34, 297
Season, effect of, on yield and

quality, 67, 83
Seaweed, 75
Secular decline in yield of crops

grown continuously, 296
Selective action of plant, 19
Senebier, assimilation, 6, 276
Sewage, 245 ; sludge, 246
Sheep, composition of excreta of, 181

Shoddy, 71, 334

Short manure, 190, 205

Sickness of land, 297

Silica, action of, on plants, 271

Skin, 12, 71

Slaked lime, 251

Slaughter-house refuse, 13, 70

Sodium perchlorate, 51 j salts,
action of, 53, 170

Solubility of phosphatic manures,
143 ; soil phosphates, 285

Soil, acidity, 62 ; analysis of Rotham-
sted, 20; condition in, 210; ino-
culation of, 36 ; phosphates in,
144 ; temperature, 69 ; texture
affected by manures, lOl, 163,
176, 216, 269, 273; requiring
potash manures, 177

Somme phosphates, 116

Sonne, Danish barley experiments,
366

Sorrel, 254

Soot, II, 68, 307

Sprengel, theory of manures, 7

Spurrey, 254

Stassfurt deposits, 13, 159

Steamed bone flour, 109, 145, 1 52

Stickstoff-kalk, 42

Stohmann, water cultures, lO

Straw, composition of, 182

Stimulus due to manganese salts, 271

Sugar cane, manures for, 336

Sulphuric acid, as an ammonia-
fixer, 202 ; in manures, 74

Superphosphate, 106, 1 19; as an
ammonia-fixer, 202 ; retention by
soil, 148; use of, 150; value in
Australia, 140

Swede turnips and nitrogenous
manures, 90, 280, 312

Surface tension of dung solutions,
221

Sylvinit, 161

Systems of manuring, 300

Tafla, 47

Tankage, 238

Tares as green manure, 272

Tea, manures for, 337

Temperature of soil raised by soot,

69
Tetra-basic phosphate of lime, 106,

131, 143

3^4

INDEX

Texture of soil affected by manures,

loi, 163, 176, 216, 269, 273
Thaer, theory of plant nutrition, 5,

7
Theories of, plant nutrition, 5-6, 13 ;

fertiliser action, 276
Thomas and Gilchrist, 127
Thomas phosphate, 129
Tillering promoted by phosphoric

acid, 139
Tobacco, manures for, 337
Top-dressings, 58, 307
Toxic substances excreted by plants,

293
Transpiration, 18
Trefoil, manures for, 326
Tropical crops, manures for, 335
Toll, theory of plant nutrition, 5
Tunis phosphates, 118
Turnips, manures for, 313

Unexhausted residues, compensa-
tion for, 354
Unit system of valuing manures,

341, 348 . .

Urea, decomposition of, 184; in

guano, 230, 233
Urine, nature of, 179
Uromyces betm, 87, 174

Valuation, of farmyard manure,
223 ; of manures, 73, lOO, 155,

340
Van Helmont, theory of plant

nutrition, 5
Vetches, as green manure, 272 ;

manures for, 326
Ville, 89, 281
Virgin soils, 31, 35, 302
Vitriolised bones, 109
Voelcker, 195, 274, 358

Wagner, comparison of nitrogen-
ous manures, 97

Walter de Henley's Husbandries 3

Warrantry of fertilisers, 349

Waste products as manures, 67

Water, effect of dung on surface
tension of, 221 ; retained by
humus in soil, 219

Water cultures, 10, 16, 55, 277

Way, analysis of superphosphate,
124 ; retention of manures by
soil, 164 ; soluble silicates as
manures, 272

Wet seasons, effect of farmyard
manure in, 220 ; with nitrogenous
manures, 67 ; with phosphatic
manures, 137 ; with potash
manures, 175

Wheat, development of grain, 142 ;
effect of phosphatic manures on,
139; habit of growth, 89; manures
for, 306 ; nitrogen in grain and
flour, 84 ; yield with increasing
nitrogen, 80

Whitney and Cameron, 285

Wiborg phosphate, 134

Wilfarth, nitrogen - fixing bacteria,
II

Woburn, acidity of soil at, 62 ; ex-
periments at, 95, 274 ; experi-
ments on dung-making, 195 ;
fruit farm, 298

Wolff and Lehmann, 243

Wolter phosphate, 135

Wood, dung-making experiments,
198

Wood ashes, 11, 159, 163

Wool, ir, 72

Worlidge, 107

Wrightson and Munro, 128

Young, A., on woollen rags, 72 ;
on bones, 107

Zeolites in soil, 51, 260, 267

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