•54. ^ *,\1
IMAGE EVALUATION
TEST TARGET (MT-3)
^^
1.0
tea 128 ||2.5
moo
tii Ui 199
I.I
Hill 1 ft
1.25
l|i^
1.6
6"
vQ
v]
/
1/ "^^
Photographic
Sdences
Corporation
^
V
€^
k
<^
fv
^ ».
^
^
^\r ^ '%
23 WEST MAIN STREET
WEBSTER, N.Y. 14580
(716)872-4503
CIHM/ICMH
Microfiche
Series.
CiHM/ICMH
Collection de
microfiches.
Canadiair Institute for Historical Microreproductions / Institut Canadian de microreproductions historiquas
1
Technical and Bibliographiic Notes/Notes techniques et bibiiographiques
The Institute has attempted to obtain the best
original copy available for filming. Features of this
copy which may be bibliographically unique,
which may alter any of the images in the
reproduction, or which may significantly change
the usual method of filming, are checked below.
□ Coloured covers/
Couverture de couleur
I I Covers damaged/
D
D
D
D
D
D
Couverture endommagte
Covers restored and/or laminated/
Couverture restaur^ et/ou pelliculie
I I Cover title missing/
Le titre de couverture manque
I I Coloured maps/
Cartes giographiques en couleur
Coloured ink (i.e. other than blue or black)/
Encre de couleur (i.e. autre que bleue ou noire)
Coloured plates and/or illustrations/
Planches et/ou illustrations e.i couleur
.. Bound with other material/
^' ReliA r'vec d'autres documents
Tight binding may cause shadows or distortion
along interior margin/
La re liure serrie peut causer de I'ombre ou de la
distortion le long de la marge intirieure
Blank leaves added during restoration may
appear within the text. Whenever possible, these
have been omitted from filming/
II se peut que certaines pages blanches ajouttes
lors d'une restauration apparaissent dans le texte,
mais, lorsque ceia Atait possible, ces pages n'ont
pas iti filmies.
Additional comments:/
Commentaires suppi^mentaires:
L'Institut a microfilm^ le meilleur exemplaire
qu'il lui a M possible de se procurer. Les details
de cet exemplaire qui sont peut-Atre uniques du
point de vue bibliographique. qui peuvent modifier
une image reproduite, ou qui peuvent exiger une
modification dans la m6thode normale de filmage
sont indiquAs ci-dessous.
I I Coloured pages/
D
Pages de couleur
Pages damaged/
Pages endommagies
Pages restored and/oi
Pages restauries et/ou pellicul4e&
Pages discoloured, stained or foxet
Pages ddcolordes, tachetdes ou piqudes
Pages detached/
Pages ddtachdes
Showthrough/
Transparence
Quality of prir
Qualiti inigale de I'impression
Includes supplementary materit
Comprend du materiel supplimentaire
Only edition available/
Seule Edition disponible
I I Pages damaged/
I I Pages restored and/or laminated/
r^ Pages discoloured, stained or foxed/
I I Pages detached/
r^ Showthrough/
I I Quality of print varies/
r~1 Includes supplementary material/
I I Only edition available/
Pages wholly or partially obscured by errata
slips, tissues, etc., have been refilmed to
ensure the best possible image/
Les pages totalement ou partieilement
obscurcies par un feuillet d'errata. une pelure,
etc., ont 4t^ filmdes d nouveau de fapon d
obtenir la meilleure image possible.
4
This item is filmed at the reduction ratio checked below/
Ce document est filmi au taux de reduction indiquA ci-dessous.
10X
14X
18X
22X
26X
30X
y
12X
16X
20X
24X
28X
32X
Th« copy filmdd h«r« Hm b««n raprodue«cl thanks
to tho gonorosity of:
McLennan Library
McGill University
iMontreal
Tho ImagM appoaring hara ara tha bast quality
posaibia considarinf; tha condition and lagibility
of tha original copy and in kaaping with tha
filming contract spaciflcationa.
Original copiaa in printad papar eovars ara filmad
baginning with tha front cevw and anding on
tha laat paga with a printad or illustratad impras-
tion. or tht back covar whan appropriata. All
othar original copiaa ara filmad baginning on tha
first paga with a printad or illustratad impraa-
sion, and anding on tha laat paga with a printad
or illuatratad impraaaion.
L'axampinira film* f ut raproduit grica i la
g4n4rositi da:
IMcLennan Library
IMcGill University
IMontreal
Laa imt :aa suivantaa ont 4ti raproduitaa avac la
plua grand soin, compta tanu da la condition at
da ]a nattati da I'axampiaira film*, at an
conformiti avac laa conditions du contrat da
filmaga.
Laa axamplairaa originaux dont la couvartura mn
papiar aat imprimia sont fiimAs an comman9ant
par la pramiar plat at an tarminant soit par la
darnlAra paga qui comporta una amprainta
d'lmpraaaion ou u'illustration. soit par la sacond
plat, salon la caa. Toua laa autraa axamplairaa
originaux sont filmte an commandant par la
pramlAra paga qui comporta una amprainta
dimpraaaion ou dliiuatratlon at an tarminant par
la darnlAra paga qui comporta una taila
amprainta.
Tha last racordad frama on aach microficha
shall contain tha symbol —^(moaning "CON-
TINUED"), or tha symbol ▼ (moaning "END"),
whichavar appliaa.
Un daa symbolaa suhrants apparattra sur la
darniAra imaga da chaqua microficha, salon la
caa: la symbols — *• signlfia "A SUIVRE". la
symbols ▼ signlfia "FIN".
IMapa, plataa, charts, ate., may ba filmad at
diffarant raduction ratioa. Thoaa too larga to ba
antiraly included in ona axpoaura ara filmad
baginning in tha uppar laft hand comar, iaft to
right and top to bottom, aa many framaa aa
raquirad. Tha following diagrama illustrata tha
mathod:
Laa cartaa, planchaa, tablaaux, ate, pauvant Atra
filmia i daa taux da rMuction diff Grants.
Lorsqua la document aat trop grand pour Atra
raproduit an un saul clichA, il aat film* A partir
da i'angia supAriaur gaucha, da gaucha A droita,
at da haut an baa, an pranant la nombra
d'imsgaa nAcaaaaira. Laa diagrammas suivants
illuatrant la mAthoda.
1 2 3
1
2
3
4
5
6
T> " iqoU' Liuoi%
"W
■.HffW"fl^»*r»w»>«"***
DETERMINATIONS OF NITROGEN IN THE SOILS
OF SOME OP THE
EXPERIMENTAL FIELDS AT ROTHAMSTED,
AND THE
BEARING OF THE RESULTS ON THE QUESTION OF
THE SOURCES OF THE NITROGEN OF OUR CROPS.
BY
Sir JOHN BENNET LAWES, Bart., LL.D., F.R.S., F.C.S.,
AND
JOSEPH HENRY GILBERT, Ph.D., F.R.S., F.C.S., F.L.S.
Bead in the Chemical Section, at the Meeting of the American Association
for the Advancement of Science, held at Montreal, in Augrust, 1882.
{^Reprinted, with corrections, from an uncorrected copy issued hy the Government
Department of Agriculture, WashingtonJ]
LONDON:
HARRISON AND SONS, ST. MARTIN'S LANE,
JPrinte« in ©rbinHrg ia fa pajestg.
1883.
555!
<.t^
k'
^4
i
J
CONTENTS.
Introduction
Yield op Nitrogen in different Crops
Yield of nitrogen in wheat and barley
Yield of nitrogen in root-crops
Yield of nitrogen in leguminous crops
Yield of nitrogen by a rotation of crops
Yield of nitrogen in the mixed herbage of grass land
Yield of nitrogen in MeUlotus leucantha
Summary op yield of Nitrogen in Crops..
Sources op the Nitrogen in Crops . .
Combiiied nitrogen in rain, etc.
Other supposed sources of combined nitrogen
Do plants assimilate free nitrogen ? . .
Recapitulation
page
5
7
9
9
11
13
14
16
17
17
18
21
22
29
The Nitrogen op the Soil as a source op the Nitrogen of Crops £0
Nitrogen in the soils of the experimental wheat plots . . . . . . 32
Nitrogen in the soils of the experimental barley plots . . . . , . 39
Nitrogen in the soils of the experimental root-crop plots . . . . . . 40
Is THE Soil a source op the Nitrogen op the Lbguminos^ ? . . 41
Nitrogen in the soils of the experimental clover plots . . . . . 42
The soils of the MeUlotus leucantha and white clover plots . . . . 45
Nitrogen as nitric acid in the Melilotus and white clover soils . . . . 40
Nitrogen as nitric acid in other soilu and subsoils . . . . . . . . 48
Nitrogen in some of the soils of the experimental mixed herbago ])lo(8 . . 51
Source of the nitrogen of clover grown on rich garden soil . . 55
Q-ENERAL Conclusions .. ., .. .. .. - . 57
k 2
-*li..'
J ,-ff' Jff-JiFJg
!■■
DETERMINATIONS OF NITROGEN IN THE SOILS OP
SOME OP THE EXPERIMENTAL PIELDS AT ROTHAM-
STBD, AND THE BEARING OP THE RESULTS ON THE
QUESTION OP THE SOURCES OP THE NITROGEN OP
OUR CROPS.
By Sir John Bennet Lawes, Bart., LL.D., P.R.S., P.C.S., and Joseph
Henry Gilbert, Ph.D., P.R.S., P.C.S., P.L.S.
Introduction.
It is just about a century since the question of the sources of the
nitrogen of vegetation became a subject of experimental inquiry, and
also of conflicting opinion. It is nearly half a century since Bous-
singault was led by a study of the chemistry of agricultural produc-
tion to see the importance of determining the sources of the nitrogen
periodically available to vegetation over a given area of land. Some-
what later the Rothamsted experiments, now in their fortieth year,
were commenced, and in their progress many facts have been elicited
bearing upon the same subject. Still, almost from the date of Bous-
singault's first investigations, the question has been one of contro-
versy, and at the present time very conflicting views are entertained
respecting it.
Por ourselves, we have pointed out how entirely inadequate is the
amount of combined nitrogen coming down in the measureable
aqueous deposits from the atmosphere to supply the nitrogen of the
vegetation of a given area. Other possible supplies of combined
nitrogen from the atmosphere have also been considered, and pro-
nounced inadequate. Again, the question whether or not plants
assimilate the free or uncombined nitrogen of the atmosphere has
been the subject of laborious experimental inquiry, and also of critical
discussion, at Rothamsted. Finally, the question whether the stores
of the soil itself are an important source of the nitrogen of our crops
has frequently been considered.
It may at the outset be frankly admitted that so long as the facts
of production alone are studied, without knowledge of, or reference
to, the changes in the stock of the nitrogen in the soil, it would seem
essential to assume that a large proportion of the nitrogen of crops
B
growing without any direct supply of it by manure, must be derived,
in some way or other, from atmospheric sources.
The assumption which is most in favour with some prominent
writers is, that whilst some plants derive most or all of their nitrogen
from the stores of the soil itself, or from manure applied to it, others
derive a large proportion from the free nitrogen of the atmosphere.
We, on the other hand, whilst freely admitting that the facts of
production are not conclusively explained thereby, have maintained
that such collateral evidence as the determinations of nitrogen in our
soils afford, is in favour of the supposition that the soil may be the
source of the otherwise unexplained supply of nitrogen. This latter
conclusion we have frequently stated in general terms ; but we have
not hitherto published the numerical results upon which it is based.
Fairly enough, it has been objected that such an important conclusion
cannot be accepted without the numerical evidence to support it.
Further, erroneously interpreting our statements, calculations have
been made to show that it is quite beyond the reach of present
methods of determination of nitrogen in soils to afford results
justifying the conclusions we have drawn.
Since this subject of the sources of the nitrogen of our crops
has been much discussed in America, it has been thought that it
would not be inappropriate tO answer the challenge by bringing for-
ward some of the numerical evidence we have accumulated before
this meeting of the American Association for the Advancement of
Science, and to do this is the object of the present communication.
Before calling attention to the special results in question, it will
be necessary, in order to convey a clear idea of the problem to be
solved, to recapitulate some of the important facts which have been
established as to the amount of nitrogen yielded over a given area by
different crops.
In his original inquiries, Boussingault estimated the amounts of
nitrogen supplied by manure, and removed in the crops, in ordinary
agricultural practice. This mode of estimate is also the one generally
adopted by others, and we have ourselves not neglected it. But it is
obvious that the results of experiments in which different crops have
been grown for very many years in succession on the same land, both
separately and in an actual course of rotation, and both without nitro-
genous manure and with known quantities of such manure, must
afford very important data as to the amounts of nitrogen available to
vegetation, from soil and atmosphere, over a given area. The
Biothamsted field experiments are pre-eminently adapted to provide
such data. Thus, wheat has now been grown for thirty-nine years
in succession on the same land ; barley for thirty-one years ; wheat in
alternation with fallow thirty-one years ; beans for nearly thirty
years ; clover for many years ; turnips, sugar-beet, or mangels, nearly
forty years ; whilst experiments on the mixed herbage of grass land
have been continued for twenty-seven years, and on an actual course
of rotation for thirty-five years. "We have, from time to time, pub-
lished what we may call the nitrogen statistics of the crops so grown ;
and we have compared these facts of production with what is known
of the sources of nitrogen available to the crops.
Yield op Nitrogen in Different Crops.
The following table (I) shows the yield of nitrogen per acre per
annum, in wheat, barley, root-crops, beans, clover, and in ordinary
rotation, in each case without any nitrogenous manure. It will be
observed that only in the case of the root-crops is the record brought
down to a later date than 1875. Independently of the fact that the
requisite nitrogen determinations are not yet completed for the subse-
quent period, it has been decided that, owing to the number of very
exceptionally unfavourable seasons for corn crops which have occurred
since 1875, it would be fallacious to bring the result'' for those crops
in the later seasons as illustrating the falling off of yield due to soil
exhaustion.
n--
8
Table I.
Yield of Nitrogen per acre per anyiuin in various Crops grown at Bothani-
sted, without Nitrogenoiis Manure.
Crups, &c.
Wheat..
Barley .... -
L
Boot-crops •<
Beans . .
L
Clover
••••{
Barley .... "I
Clover . . . . /
Barley.
Botation . . <
7 courses. ■
Condition of Manuring, &c,
Unmanured
r
I
Complex mineral manure.
Unmanured
Complex mineral manure.
Complex mineral
Duration of Experi-
ment.
8 years, 1844-51
12 years, 1852 -'63
12 years, 1864-75
24 years, 1852-75
32 years, 1844-75
12 years, 1852-'63
12 years, 1864-75
24 years, 1852-75
12 years, 1852-'63
12 years, 1864-75
24 years, 1852-75
12 years, 1852-'63
12 years, 1864-75
24 years, 1852-75
'Turnips 8 years, 1845-'52
(Barley) 3 years, 1853-'55
Turnips 15 years, 1856-70*
manure "j Sugar beet ... 5 years, 1871-75
I Mangels 5 years, 1876-'80
(.Total 36 years, 1845-'80
Unmanured
Complex mineral manure ,
Unmanured
Complex mineral manui'e ,
Unmanured .
Unmanured .
Barley after
after barley .
{
f After barley . .
'" \ After clover . .
clover more than
}
1. Turnips '
2. Barley
3. Clover or beans
4. Wheat
Unmanured .
Superphos- "I
phate .. J
12 years, 1847-'58
12 years, 1859-70t
24 years, 1847-70
12 years, 1847 -'58
12 years, 1859-'70t
24 years, 1847-'70
22 years, 1849-'70t
22 years, 1849-'7o|
1 year, 1873
1 year, 1873
1 year, 1874
1 year, 1874
28 years, 1848-75
28 years, 1847-75
Average
Nitrogen per
Acre per
annum.
lbs.
25-2
22-6
159
19
20'
•3
•7
27
17
22
22-0
14-6
18-3
26-0
18-8
22-4
42-0
(24-3)
18-5
13 1
15-5
25-2
48-1
14-6
31-3
61-5
29 5
45-5
30-5
39-8
37 3
151-3
39-1
69-4
30-3
36-8
45-2
* Thirteen years' crop, two years failed.
t Nine years' beans, one year wheat, two years' fallow.
X Six years' clover, one year wheat, three years' barley, twelve years' fallow.
Yield of Nitrogen in Wheat and Barley.
The first series of results relates to the yield of nitrogen in wheat
grown thirty-two years in succession on the same land without
manure. It is seen that, over the first eight years, the yield was
25*2 pounds of nitrogen per acre per annum, over the next twelve
years 22'6 pounds, and over the last twelve of the thirty-two years
only 15-9. There has thus been a considerable reduction in the
annual yield of nitrogen over each succeeding period; and for the
third period of twelve years the average is less than two-thirds as
much as for the first period of eigh u years.
Excluding the first eight years of the growth of wheat, the
average annual yield of nitrogen over the next twenty-four years
was 19'3 pounds per acre per annum ; and the table shows that over
the same twenty-four years, barley without man ire yielded 18"3
pounds ; and whilst with the wheat the decline in yield was from
22'6 pounds over the first twelve of the twenty-four years to 15'9
over the second twelve, it was with the barley from 220 to 14'6
pounds, or almost in the same proportion
It might be objected that here the evidence is not conclusive that
the falling off is due to the gradual reduction in the amount of
nitrogen annually available from the soil. But the results with the
two crops, where there is a liberal supply of mineral constituents
every year, exclude the supposition that the decline is due to the
exhaustion of mineral constituents. Thus, over the same twenty-
four years, with a complex mineral manure, such as is very effective
in conjunction vrith artificial supply of nitrogen to the soil, the yield
of nitrogen in the wheat falls off from 270 pounds per acre per
annum over the first twelve years, to 17'2 pounds over the second
twelve yeara ; and in the barley, over the same two periods, it declines
from 26"0 to 18'8 pounds.
The similarity in the actual yield, and in the rate of decline
of yield, of nitrogen over the same periods in these two closely allied
crops, though growing in different fields, and with somewhat different
previous manurial history, is very striking. The slightly higher
yield in both cases with than without the mineral manure is doubtless
due to more complete utilisation of the previous accumulations
within the soil, and not to increased assimilation from atmospheric
sources.
Yield of Nitrogen in Boot-crops.
We now come to the yield of nitrogen by plants of other natural
families, and the first of such results relate to the so-called " root-
10
crops" — turnips of the natural order Cruciferce, and sugar-beet, and
mangel-wurzel of the order Chenopodiaceoe. The table records the
results for thirty-six years in succession, 1845-18S0 ; but it should be
stated that during three of those years barley was interposed without
any manure, in order, as far as possible, to equalise the condition of
the land before re-arranging the manurir.g; and during two other
years the turnips failed, and there was no crop. It should be further
explained that, without manure of any kind, root-crops, after a few
years, give scarcely any produce at all, and hence the results selected,
and recorded in the table, are those obtained by the use of mineral
manures, but without any supply of nitrogen.
During the first eight years (four years Norfolk whites and four
years Swedes), the turnips gave an average of 42 pounds of nitrogen
per acre per annum, or very much moi'e than either of the cereal
crops. During the next three years barley (without manure) yielded
243 pounds, or even somewhat less than the yield in wheat or barley
with mineral manures in the earlier years of their continuous growth.
During the next fifteen years (thirteen with Swedish turnips and two
without any crop), the yield was reduced to 18*5 pounds ; during the
next five years, with sugar-beet, to 13"1 pounds ; and during the last
five years, to 1880 inclusive (with mangel-wurzel), to 15'4 pounds.
Lastly, over the whole thirty-six years, the average annual yield of
nitrogen was 25"2 pounds.
Here, then, compared with wheat or barley, we have with the
root-crops, the growth of which extends much further into the
autumn months, a much higher annual yield of nitrogen in the earlier
y?ars, and with this a much more rapid rate of decline subsequently,
the annual yield over the last ten years being only about one-third as
much as over the first eight years ; whilst the yield in the later years
is actually less than in either wheat or barley with the same complex
mineral manure. Here, again, the marked decline in the yield of
nitrogen, with liberal mineral manuring, points to a deficiency in the
available supply of nitrogen itself as the cause of the deficient assimi-
lation of it by the crop.
It may here be observed, that those who maintain that the atmo-
sphere is an important source of the nitrogen of our crops assume
that the root-crops, if provided with a small quantity of nitro^Tenous
manure to favour the early development of the plant, will obtain the
remainder from the atmosphere. How far this is the case may be
illustrated by the following results, which are the average of five
years' successive growth of mangel-wurzel on the same plots, and in
each case with the same manure year after year.
d
le
11
Table II.
Averacje produce oj Mangel-wurzel Jive years, 1876 — 1880.
1. Superphosphate of lime, and sulphate potassium .
2. As 1, and 36^ lbs. ammonium salts (= 7"8 lbs. N)
3. As 1, and 400 lbs. ammonium salts (=86 lbs. N)
Boots.
Tons.
Cwt.
4
10
6
0
14
0
Leaves.
Tons. Cwt.
1 0
1 6
2 16
Thus, the annual application of about 7" 8 pounds of nitrogen, as
ammonium salts, has increased the crop of roots by only 30 cwts. per
acre per annum ; and the increased yield of nitrogen in the crop was
even somewhat less than the amount supplied in the manure. An
application of 86 pounds of nitrogen has, however, increased the crop by
160 cwts. more. It is obvious from these facts, that the small application
of nitrogen did not enable the plant to take up any from atmospheric
sources, and that it required further direct supply of nitrogen to
obtain further increase of crop. These results obviously aiford con-
firmation of the view that it was a reduction of the available supply
of nitrogen within the soil that was the cause of the decline in the
annual yield of the crop, and of the amount of nitrogen contained
in it.
JiJ
^
Yield of Nitrogen in Leguminous Crops.
We next come to the consideration of the yield of nitrogen in
crops of the leguminous family, when these are grown separately,
year after year, on the same land. Plants of this family are said to
rely almost exclusively on atmospheric sources for their nitrogen.
Table I shews that, without manure, beans gave over the first
twelve years an annual yield of 48-1 pounds of nitrogen, but over the
second twelve only 14-6 pounds. Over the first period, therefore, the
yield was about twice as much as in either wheat or barley, and more
even than with the roots. But with this greater yield in the earlier
years, the reduction is proportionally much greater over the second
period ; the yield then coming down to less than one-third, and to
much the same as in the later periods with the other crops. Over
the whole period of twenty-four years, however, there was an annual
yield of 31-8 pounds of nitrogen, or more than one and a half time as
much as in either wheat or barley, and more than in the roots.
It was seen that in the case of the cereal crops the mixed mineral
I
12
manure increased tlie yield of nitrogen but little. Not so in tLo case
of the leguminous crop, beans. During the first twelve years, the
complex mineral manure (containing a large amount of potash)
yielded 61'5 pounds of nitrogen per acre per annum, against 48'1
pounds without manure. During the next twelve years, the mineral
manure gave 29"5 pounds, against only 146 pounds without manure.
Daring the whole period of twenty-four years, the potash manure
yielded 45 "5 pounds of nitrogen per acre per annum, against
31"3 pounds without manure. Lastly, with the mixed mineral manure
beaui. have yielded over a period of twenty-four years more than
twice as much nitrogen per ncre as either whaat or barley.
But notwithstanding that the beans have for a long series of years
yielded so very much more nitrogen over a given area than either of
the gramineous crops, and much more also than the root-crops, the
significant fact cannot fail to be observed that this crop of the legu-
minous family, which is supposed to rely almost exclusively on the
atmosphere for its nitrogen, has declined in yield as strikingly as the
other crops, even when grown by a complex mineral manure, con-
taining a large amount of potash. Why should this be so if the
supply of nitrogen is from the atmosphere and not from the soil ?
The results next recorded relate to red clover, and the period of
experiment was twenty-two years. It is well known that on most
soils a good crop of clover cannot be relied upon oftener than once in
about eight years, and on mauy soils not so frequently. It will not
excite surprise, therefore, that in the course of the twenty-two years
of experiment, in only six was any crop of clover obtained, and in
some of those only poor ones. Indeed, the plant failed nine times out
of ten during the winter and spring succeeding the sowing of the
seed. In one year a crop of wheat, and in three years barley, was
taken instead ; whilst in the remaining twelve years the land was left
fallow after the failure of the clover. Still the annual yield of
nitrogen over the twenty-two years was 30'5 pounds without any
manure, and 39"8 pounds by a complex mineral manure containing
potash. Unfavourable as is this result in an aj^ricultural point of
view, it is still seen that the interpolation of this leguminous crop has
greatly increased the yield of nitrogen compared with that in either
wheat or barley grown continuously ; and here again, as with beans, a
potash manure has considerable increased the yield.
The next experiment afforus a still more striking illustration of the
large amount of nitrogen that may be taken up in a clover crop ; and
it further illustrates the fact, well known in agriculture, that the
removal of this highly nitrogenous leguminous crop is one of the best
13
possible preparations for the growth of a cereal crop, which charac-
teristically requires nitrogenous manuring. A field which had grown
six corn crops in succession, by artificial manures alone, was then
divided, and (in 1873) on one half barley, and on the other half
clover, vras grown. The barley yielded 37-3 pounds of nitrogen per
acre; but the three cuttings of clover yielded 151-3 pounds. In the
next year (1874) barley was grown on both portions of the field.
Where barley had previously been grown, and had yielded 37-3 pounds
of nitrogen per acre, it now yielded 391 pounds; but where the
clover had previously been grown, and had yielded 151-3 pounds of
nitrogen, the barley succeeding it gave 69-4 pounds, or 80-3 pounds
more nitrogen after the removal " 151-3 pounds in clover than after
the removal of only 37-3 pounds in barley. It will be seen further on
that this result was not in any way accidental.
Yield of Nitrogen hy a Rotation of Crops.
The last results recorded in the table relate to the yield of nitrogen
in an ordinary four-course rotation of — turnips, barley, clover or
beans, and wheat. The average yield per annum is given for seven
courses, or for a period of twenty-eight years ; in one case without any
manure during the whole of that time, and in the other with super-
phosphate of lime alone, applied once every four years, that is, for the
turnips commencing each course.
Here, with a turnip crop, and a leguminous crop, interpolated with
two cereal crops, we have, without manure of any kind, an average of
36-8 pounds of nitrogen per acre per annum, or very much more than
was obtained in either of the cereal crops grown consecutively. With
superphosphate of lime alone, which much increased the yield of
nitrogen in the turnips, reduced it in the succeeding barley, increased
it greatly in the leguminous crops, and slightly in the wheat suc-
ceeding them, the average annual yield of nitrogen is increased to
45-2 pounds, or to about double that obtained in either wheat or
barley grown consecutively by a complete mineral manure. On this
point it may be further remarked that in adjoining experiments, in
which, instead of a leguminous crop, the land was fallowed in the
third year of each course, the total yield of nitrogen in the rotation
was very much less. In other words, the removal of the most highly
nitrogenous crops of the rotation — clover or beans — was succeeded by
a growth of wheat, and an assimilation of nitrogen by it, almost as
great as when it succeeded a year of fallow ; that is, a period of some
accumulation by rain, &c., and of no removal by crops.
14
Yield of Nitrogen in the Mixed Herbage of Grass Land.
Another illustration of the amounts of nitrogen removed from a
given area of land by different descriptions of crop will be found in
Table III, which shows the results obtained when plants of the
gramineous, the leguminous, and other families, are grown together,
in the mixed herbage of grass land.
Table III.
Yield of Nitrogen on the Mixed Herbage of Permanent Grass Land
at Rothamsted.
Conditions
of
Manuring.
Average Produce per acre
per annum, 20 years,
1856-1875, according to
mean per cent., at six
Average Nitrogen
per Acre
per annum.
Plots.
periods, 1862, '67, '71,
'72, '74, '75.
Ten
years
1856-
1865.
Ten
years
1866-
1875.
Twenty
Grami-
netB.
Legumi-
nosse.
Other
Orders.
years
1856-
1875.
3
4-1
8
7
Unmanured
Superphosphate*. . . .
Comp ex Min. Man.f
Complex Min. Man. J
lbs.
1635
1671
2442
2579
lbs.
219
149
296
806
lbs.
529
673
639
573
lbs.
35 1
35-7
54-4
55-2
lbs.
30-9
31-5
38-1
56 0
lbs.
33-0
33-6
46 3
55-6
Before referring to the figures, attention should be called to the
fact that gramineous crops grown separately on arable land, such as
wheat, barley, or oats, contain a comparatively low percentage of
nitrogen, and assimilate a comparatively small amount of it over a
given area. Yet nitrogenous manures have generally a very striking
effect in increasing the growth of such crops. The highly nitro-
genous leguminous crops, on the other hand, such as beans and
clover, yield, as has been seen, very much more nitrogen over a
given area : yet they are by no means characteristically benefited by
nitrogenous manuring, but their growth is considerably increased,
and they yield considerably more nitrogen over a given area, under
the influence of purely mineral manures, and especially of potash
* Mean of four separations only, namely, 1862, 1867, 1872, and 1875.
t Including potash, six years, 1856-1861 ; without potash, 14 years, 1802-
1875.
X Including potash, 20 years, 1856-1875.
^./>
15
manures. Bearing these facts in mind, the results given in the table
will be seen to be quite consistent.
The first three columns in the table show, approximately, how
the mixed herbage was made up under the four different conditions
of manuring. It will be observed that, without manure, and with
superphosphate of lime alone, both the proportion and the amount of
the different descriptions of herbage are much the same. Plot 8,
with a complex mineral manure, including potash the first six years,
but excluding it the next fourteen years, gave a considerable increase
of both gramineous and leguminous herbage ; whilst plot 7, with a
complex mineral manure, including potash every year of the twenty,
there is a still further increase of gramineous herbage, but a very
much greater proportional increase of leguminous herbage.
It will be observed how much greater is the increase of gramineous
produce by the application of purely mineral manures to this mixed
herbage than in tie case of gramineous crops grown separately. It
is a question how far this is due to the mineral manures enabling
the grasses to form much more stem and seed, that is, the better
to mature, which in fact they do ; how far to their favouring more
active nitrification in the more highly nitrogenous permanent mixed
herbage soil ; or how far to an increased amount of combined nitrogen
in a condition available for the grasses in the upper layers of the
soil, as the result of the increased growth of the Leguminos89 in the
first instance, induced by the potash manure, as in the case of the
alternation of clover and barley, and as in the actual course of
rotation ?
To turn to the yield of nitrogen on the different plots of the
mixed herbage, it will be seen that the amounts are almost identical
without manure, and with superphosphate of lime alone, about
33 pounds per acre per annum. On plot 8, where a co/nplex mineral
manure, including potash six years, but excluding potash fourteen
years, was employed, the amount is raised to 46*3 pounds ; and on
plot 7, which received the mixed mineral manure, including potash
every year of the twenty, the yield is 55'6 pounds per acre per annum.
Further, without manure, and with superphosphate of lime alone,
there was a decline in the yield of nitrogen in the later, compared
with the earlier years. With the mineral manure, including potash
in the first six yea:'S only, there was a much more marked decline.
With the miners nanure, including potash every year, there was,
on the other hand, even a slight tendency to an increased yield of
nitrogen in the later years.
m
16
Yield of Nitrogen in Melilotus Lencantha.
One more striking illustration of high yield of nitrogen by a
plant of the leguminous family, this time on soil which had not
received any nitrogenous manure for nearly thirty years, must be
given. In 1878, the land upon which attempts had been made to
grow red clover in frequent succession since 1849, was devoted to
experiments with fourteen different descriptions of leguminous plants ;
so that the present season, 1882, is the fifth year of the experiments.
The object was to ascertain whether, among a selection of plants, all of
the leguminous family, but of different habits of growth, and especially
of different character and range of roots, some could be grown success-
fully for a longer time, and would yield more produce, containing
more nitrogen as well as other constituents, than others; all being
supplied with the same descriptions and quantities of manuring sub-
stances, applied to the surface soil. Further, whether the success in
some cases and the failure in others, would afford additional evidence
as to the source of the nitrogen of the Leguminosas generally, and as
to the causes of the failure of red clover in particular, when it is
grown too frequently on the same land. Fourteen different descrip-
tions of plants were jelected, and, after two or three immaterial
changes, the list at the present time includes eight species or varieties
of Trifoliurn, two of Medicago, Melilotus leucantha, Lotus corniculattis,
Vicia sativa, and Onohrychis sativa.
Of the numei'ous species or varieties of Trifoliwn, all gave but
meagre produce, excepting T. incarnatum. The Lotus corniculatus
also gave very small produce. The two species of Medicago, the black
Medick, and the purple MedicJc or Lucerne, and the OnohrycJiis, or
common Sainfoin, gave much more ; the Vicia sativa or common
vetch, more still. But of all, the Melilotus leucantha, or Bokhara
clover, has yielded the most. It is estimated that, taking the average
of four years, 1878-81, it yielded about 70 pounds of nitrogen per
acre per annum, on plots which have received no nitrogenous manure
for more than thirty years; whilst the produce of the fifth season,
1882, is heavier than in either of the preceding years ; and it is esti-
mated to contain about 150 pounds of nitrogen. In fact, in the
second, as well as in the fifth year, the melilotus yielded considerably
more than 100 pounds of nitrogen per acre ; and on the average of
the five years it has yielded between 80 and 90 pounds per acre on
this nitrogen-exhausted soil.
How long this very luxuriant growth,- and this very high yield of
nitrogen per acre, will continue, is a question of very great interest.
F
f
^ibi>
17
a
lot
be
to
to
its;
iits.
of
On tliis point it may be observed that, in parts of the continent of
Europe where some of the very free-growing and deep-rooted Legn-
minosaj are cultivated, it is usual to let them grow for several years,
after which they cannot be repeated for twenty years or more. We
shall recur to the result? above quoted further on.
Summary of Yield of Nitrogen in Crops.
The foregoing facts of production, showing the yield of nitrogen
in different crops grown without nitrogenous manure, generally for
very many years in succession on the same land, may be briefly
summed up as follows :
The average yield of nitrogen per acre per annum, was, with
wheat, thirty-two years without manure, 207 pounds, and twenty-four
years with a complex mineral manure, 22 "1 pounds ; with barley,
twenty-four years without manure, 18"3 pounds, and twenty-four years
with a complex mineral manure, 22"4 pounds ; with root-crops, thirty-
six years (including three of barley), with a complex mineral manure,
25*2 pounds; with beans, twenty-four years without manure, 31*3
pounds, and twenty-four years with a complex mineral manure, 45'5 ;
with clover, six crops in twenty- two years, with one crop of wheat, three
crops barley, and twelve years fallow, without manure, 30'5 pounds ;
with complex mineral manure, 39"8 pounds ; with clover, on land which
had not grown the crop for very many years, one year, 151*3 pounds ;
with a rotation of crops, seven courses, twenty-eight years, without
manure, 36'8 pounds, and with superphosphate of lime, 45'2 pounds ;
with the mixed herbage of grass land, twenty years without manure,
33 pounds, and with complex mineral manure, including potash, 55'6 ;
lastly, with Bokhara clover, five years, with mineral manure, between
80 and 90 pounds of nitrogen per acre per annum.
The root-crops yielded more nitrogen than the cereal crops, and
the leguminous crops very much more still.
In all the cases of the experiments on ordinary arable land —
whether with cereal crops, root-crops, leguminous crops, or a rota-
tion of crops (excepting as yet the Bokhara clover) — the decline in
the annual yield of nitrogen, none being supplied by manure, was very
great.
Sources of the Nitrogen of Crops.
We must next consider whence comes the nitrogen of the crops,
and especially whence comes the much larger amount taken up by
plants of the leguminous, and some other families, than by the
h
18
Gramineae. Lastly, what is the significance of the great decline in the
yield of nitrogen in all the crops grown on arable land when none is
supplied in the manure ?
Combined Nitrogen in Bain, 8fc.
It has been assumed by some that the amount of combined nitrogen
annually coming down in the measured aqueous deposits from the
atmosphere is sufficient for all the requirements of annual growth. In
Liebig's earlier writings he assumed the probability of a very much
larger quantity of ammonia coming down in rain than he did subse-
quently ; but even in his more recent work, " The Natural Laws of
Husbandry," published in 1863, he supposes that as much as 24
pounds of nitrogen per acre may be annually available to vegetation
from that source. Such an amount would, it is obvious, do much
towards meeting the requirements of many of the crops the nitrogen
statistics of which have been given.
The earliest considerable series of determinations of the amount of
ammonia coming down in rain in the open countiy were by Boussin-
gault, in Alsace. He gives the amount of ammonia per million of
rain-water in each fall for a period of between five and six months,
May-October, 1852 ; but he does not calculate the amount so coming-
down over a given area of land. His average amount per million
was, however, somewhat less than that found at Rothamsted in 1853
and 1854, and found by Mr. Way in Rothamsted rain-water collected
in 1855 and 1856 ; which, calculated according to the rain-fall of the
periods, give the following amounts of nitrogen so coming down per
acre. The amounts of nitrogen as nitric acid, as determined by
Mr. Way, and the amount of total combined nitrogen as ammonia
and nitric acid together, are also given.
Table IV.
Nitrogen, as Ammonia and Nitric Acid, in the Rainfall
Year's, at Rothamsted, in Pounds per Acre
of Three
Rainfall.
Nitrogen per Acre, as —
Years.
Ammonia.
Nitric
Acid.
Total
Nitrogen.
1853-54
Indies.
29-014
29 166
27-215
lbs.
5-20
E-82
7-28
lbs.
(0-74)
0-72
0-76
lbs.
5-04
1855
6 -.18
1856
8*00
Mean
28 -465
6-10
0-74
6-84
^
19
IS
It will be seen that, according to these results, an average of 6'84
pounds was contributed per acre per annum in the rain in the form
of ammonia and nitric acid. More recently, however. Dr. Frankland
has determined the amount of ammonia and nitric acid in numerous
samples of rain and snow water, dew, hoar-frost, &c., collected at
Rothamsted from April, 18G0, to ^lay, 1870, inclusive : and the average
amount of ammonia per million of water found by him is considerably
lower than the earlier determinations show. More recently .;till the
ammonia has been determined in the Rothamsted laboratory, in the
rain of each day separately (if any), for a period of six months, July-
December, 1881 ; also in the proportionally mixed rain for each
month, for a period o" thirteen months, June, 1881, to June, 1882.
The average proportion of ammonia in these most recent determina-
tions accords with the results of Dr. Frankland, and points to a
smaller amount of total combined nitrogen supplied per acre in the
average annual rainfall at Rothamsted than that recorded in the
table ; probably, indeed, to not more than four or five pounds of total
combined nitrogen per acre per annum.
Dr. R. Angus Smith, in his work entitled " Air and Rain, the
Beginnings of a Chemical Climatology," 1872, gives the results of
numerous analyses of rain-water collected both in country and
town districts in the United Kingdom. The amounts of ammonia
and nitric acid in the rain vary exceedingly, according to 1 xlity ;
b\it the amounts in the rain of country places accord generally with
those found in the Rothamsted rainfall.
The following table summarises the results of numerous determi-
nations made at various stations on the continent of Europe, in each
case extending over a whole year : —
B 2
20
Table V.
Nitrogen as Ammonia and Nitric Acid in the Rain of various
Localities in Europe.
[Quantities in Pounds per Aero per Annum.]
Localities.
Euschen
Kuschen
Insterburg
Tnsterburg
Dahme
Regenwalde
Regenwalde
Regenwalde
Ida - Marienhiitte ; mean
six years
Proskaw
Florence
riorence
Florence
Vallombrosa
Montsouris, Paris
Montsouris, Paris
Montsouris, Paris
Mean, 22 years
Years.
1864-'65
1865-'66
1864-'65
1865-'66
1865
1864r-'65
1865-'66
1866-'67
1865-'70
1864-'65
1870
1871
1872
1872
1877-'78
1878-'79
1879-80
Rainfall.
Inches.
11 85
17-70
27-55
23-79
17 09
23-48
19-31
25-37
22-65
17-81
36-55
42 -48
50-82
79-83
23-62
25-79
15-70
27-03
Nitrogen as —
Nitric
Ammonia.
Acid.
lbs.
lbs.
1-44
0-42
1-83
0-67
3-55
1-94
4-14
2-67
5-50
1-16
10-82
4-27
8-27
2-11
13-20
3-24
13-58
7-33
9-71
3-65
7-78
2 11
9-50
3 01
7-65
2-73
10-25
1-29
7 05
4-11
4 83
5-69
••
• •
Total.
lbs.
86
50
49
81
6-66
15 -09
10-38
16-44
9-92
20-91
13-36
9-89
12-51
10-38
11
11
54
16
10-52
10-23
It is seen that the numerous very widely varying determinations,
some made in the vicinity of towns and some in the open country, give
a mean of 10-23 pounds of combined nitrogen annually supplied per
acre by rain with a mean rainfall of 27-03 inches. Making all allow-
ance for far inland open country positions on the one hand, and for
proximity to towns on the other, the very small amounts of combined
nitrogen so supplied per acre in some of the cases, and the compara-
tively large quantities in others, seem difficult to explain, or to recon-
cile, either with one another or with the results of Boussingault and of
Rothamsted. When, however, the comparatively limited and uniform
total amounts recorded for Montsouris, within the walls of Paris, are
considered, 11*54 pounds, 11-16 pounds, and 10-52 pounds per acre per
annum, it will not excite surpi-ise that we should estimate the amount
of combined nitrogen coming down in the measured aqueous deposits
21
from the atmosphere at probably not more than, if as much as,
5 pounds per aero per annum in the open country at Rothamsted.
With records of the amounts of combined nitrogen contributed to
a given area in rain, we come to an end of all quantitative evidence
as to the amount of combined nitrogen available to the vegetation of
a given area from atmospheric sources. It will be seen how entirely
inadequate is the amount probably so available to supply the quanti-
ties yielded in different crops grown without nitrogenous manure, as
recorded in Tables I and III (pp. 8 and 14).
It is true that the minor aqueous deposits from the atmosphere are
much richer in combined nitrogen than rain, and there can be no
doubt that there would bo more deposited within the pores of a given
area of soil than on an equal area of the non-porous even surface of a
rain-gauge. How much, however, of this might be available beyond
that determined in the collected aqueous deposits, existing evidence
does not afford the means of estimating with certainty.
Other Supposed Sources of Combined Nitrogen.
Further, it has been argued that, in the last stages of the decom-
position of organic matter in the soil, hydrogen is evolved, and that
this nascent hydrogen combines with the free nitrogen of the atmo-
sphere, and so forms ammonia. Again, it has been suggested that
ozone may be evolved in the oxidation of organic matter in the
soil, and that, uniting with free nitrogen, nitric acid would be pro-
duced.
We have discussed these various possible supplies of combined
nitrogen to the soil from atmospheric sources on more than one occa-
sion ; and we have given our reasons for concluding that none of them
can be taken as accounting for the facts of growth. Incidentally, some
evidence will be given further on, confirming the conclusion that any
such supplies are limited and inadequate.
But, if the supplies from the atmosphere to the soil itself are
inadequate, how about the direct supplies from the atmosphere to the
plant ?
One view which has been advocated is, that broad-leaved plants
have the power of taking up combined nitrogen from the atmosphere,
in a manner, or in a degree, not possessed by the narrow-leaved
gramineous plants. The only experiments that we are aware of, made
to determine whether plants can take up nitrogen by their leaves
from ammonia supplied to them in the ambient atmosphere, are those
of Adolph Mayer in Germany, and of Schlosing in France. Both
22
found that very small qnantitics of nitrogen wcro so taken up ; but
both concluded that the action takes place in very immaterial degree
in natnral vegetation.
We have elsewhere shown that a consideration of the chemistry
and the physics of the subject would lead to the conclusion that the
plants which assimila'^e more nitrofjfen over a given area than others
do not do so by virtue of a greater power of absorbing already com-
bined nitrogen from the atmosphere by their leaves. But, apart from
such considerations, our statistics of nitrogen production seem to pre-
elude the idea tliat the broad-leaved root-crops, turnips and the like,
to which the function has with the most confidence been attributed,
take up any material proportion of their nitrogen by their leaves from
combined nitrogen in the atmosphere. We need only here recall atten-
tion to the fact that the yield of nitrogen in these crops, even with
the aid of a complex mineral manure, was in the later years reduced
to as low a point as in the cas^ of the narrow-leaved cereals.
:i
Do Plants Assimilate Free Nitrogen?
The question still remains to consider — whether plants assimilate
the free nitrogen of the atmo.sphero, and whether some descrijitions
do so in a much greatc ' degi'ee than others ? It is freely admitted
that if this were establisued many of our difficulties would vanish.
This question has been the subject of a great deal of experimental
inquiry, since the time that Boussingault entered upon it about the
year 1837 ; and more than twenty years ago it was elaborately investi-
gated at Rothamsted.
We will here give a snmmary of the very conflicting results which
have been published in reference to this subject, of the assimilation of
the free nitrogen of the atmosphere by plants, contining attention, for
want of space, to the three most comprehensive series of experiments
which have been undertaken relating to it.
Though not the first in point of date, we will first refer to the
experiments of M. G. Ville, the results of which led him to conclude
that plants do assimilate the free nitrogen of the air — a view of
which he has been the arch-apostle for many years, and upon which
ho may be said to have founded a system, in his work on " Artificial
Manures."
From 1849 to 1856, M. G. Ville made numerous experiments on
this subject. The following table (VI) gives a summary of his results,
and shows the special conditions of each separate series of experi-
ments:—
23
■bat
free
itrj
%
r
Table VI.
Eestilts o/M, G. Villk's Expentneiits, to determine whether Plants
assimilatii free Nitro'jen.
Plants
Nitrogen, grama.
In Seed,
and Ail' ;
and
Manuro,
if any.
Nitrogen
in
Products
tol
Supplied.
1849 : Car -.
•■>t of unwashed air aapphjing 0*001
gram N. as
Ammonia.*
Cress
0 -0260
0-0610
0 -0640
0 1470
0-0610
0 0470
0-1210
0 -0000
- 0 -0170
5-6
Large Lupins
Small Lupins
1-0
0-7
0 -1550
0 -2580
0 -1030
1-7
1850: Current of unwashed air supplying 0-0017 gram N. as Ammonia.
Colza (plants)
Wheat
Rye
Maize
0 -0260
0 -0160
0-0130
o-02yo
0 -OS.-)?
1 -0700
0-0310
0 0370
0-1280
1-2660
1 0440
0 -0150
0 -0240
0 -0990
1 -1803
41-1
1-9
2-8
4-4
14-8
1851 : Current of washed air.*
Sunflower
0 -0050
0 -00 10
0 -0040
0 -1570
0-1750
0-1620
0 -1520
0-1710
0 -1580
31-4
Tobacco
43-7
Tobacco
40-5
1852 : Current of washed air.*
Autumn Colza . ,
Spring Wheat . .
Sunflower ,
Summer Colza . ,
Summer Colza . ,
0 0480
0 -0290
0-0160
0 -1730
0 -1050 j
0 -2260
0 0650
0-4080
0 -5950
0 -7010
0-1780
0 -0360
0-3920
0-4220
0-5960
4-7
2-2
25-5
3-4
6-7
1854 : Current of washed air (under superintendence of a C
ommission) .
Cress
0 -0099
0-0038
0 -0039
0-0097
0 -0530
0 -0110
-0-0002
0 -0492
0-0071
10
Cress
13-9
Cress
2-8
* Recherches Experimentales sur la Vegetation, par M. Georges Villa, Paris,
1853.
u
Table VI. — continued.
Plants.
Nitrogen, grams.
In Seed,
and Air j
and
Manure,
if any.
In
Products.
Gain
or
Loss.
Nitrogen
in
Products
tol
Supplied.
1854: Current of washed air {closed, superintended by a Commission) *
Cress ,
0 -O063
0 -0350
0 -0287
5*6
1855 and 1856 : In pure air, icith 0*5 <jra7n Nitre = 0'ub9 Nitrogen.f
Colza
0-0700
0 -0700
0 -0700
0 -0700]:
0-0660+
0 -0680]:
0 -0000
-0-0040
-0-0020
1 -0
Colza
0-9
Colza
1 -0
1855 and 1856 : In free air, ivith 1 gram Nitre = 0-138 Nitrogen.f
Colza .
Colza .
Colza .
Colza .
0-1400
0-1400
0 -1400
0-1400
0 -19701
0 -3740f
0 -21601
0 -2500^
0 -0570
0 -2340
0 -0760
0 -1100
1-41
2-67
1-54
1-79
1856:
In free air, with 0'792 gram Nitre
= 0-110 Nitrogen.f
Wheat
0-1260
0-1260
0 -2180t
0 -22401
0 -0920
0 0980
1-7
Wheat
1-8
1855:
In free air, with 1'72 grams Nitre -
= 0-238 Nitrogen.f
Wheat
0 -2590
0 -30801
0 0490
1-2
1856:
In free ai"', witS 1-765 grams Nitre
= 0-244 Nitrogeyi.f
Wheat
0 -2650
0 -2650
0 -21701
0 -3500J
-00480
+ 0-0850
0-8
Wheat
1-3
These results, as well as those of others, we have fully discussed
elsewhere {Phil. Trans., 1859, aud Jour. Chem. Soc, vol. xvi, 1863), and
we can only very briefly refer to them in this place.
The column of actual gain or loss shows in one case, with colza,
a gain of more than 1 gram nitrogen ; and the amount in the products
is more than forty-one times as much as that supplied as combined
* Compt. rend., 1855.
t Recherches Experimcntales sur la Vegetation, 1857.
X In plants only.
1
mmmm
25
3d
id
a,
ts
jd
nitrogen in the seed and air. The results with wheat, rye, or maize,
showed very much less of both actual and proportional gain. Experi-
ments with sunflower showed in one case thirty-fold, and with tobacco
in two cases more than forty-fold, as much in the products as was
supplied. It will be observed, however, that upon the whole M. G.
Ville's later experiments showed considerably less both actual and
proportional gain than his earlier ones.
M. G. Ville in some cases attributed the gain to the large leaf
surface. In explanation of the assimilation of free nitrogen by plants,
he calls attention to the fact that nascent hydrogen is said to give
ammonia, and nascent oxygen nitric acid, with free nitrogen, and he
asks : Why should not the nitrogen in the juices of the plant combine
with the nascent carbon and oxygen in the leaves ? He refers to the
supposition of M. De Luca, that the nitrogen of the air combines with
the nascent oxygen given off by the leaves of plants, and to the fact
that the juice of some plants (mushrooms) has been observed to
ozonise the oxygen of the air, and he asks : Is it not probable, then,
that the nitrogen dissolved in the juices will submit to the action of
the ozonised oxygen with which it is mixed, when we bear in mind
that the juices contain alkalies, and penetrate tissues, the porosity of
which exceeds that of spongy platinum ?
The following table (VII) summarises the results of M. Boussin-
ganlt. His experiments on the subject commenced in 1837, and were
continued at intervals up to 1858. The conditions of each set of ex-
periments as to soil, air, or application of manurial substances, are
given in the table.
Table VII.
Results of M. Boussingault's Experiments to determine whether Plants
assimilate free Nitrogen.
Plants.
Nitrogen, grams.
In Seed,
or Plants ;
and
Manure,
if any.
In
Products.
Gain
or
Loss.
Nitrogen
in
Produets
to 1
Supplied.
1837 : Burnt soil, distilled water, free air, in closed summer-house.
Trefoil
Trefoil
Wheat
Wlieat
0-1100
0-1140
0 0130
0-0570
0-1200
0-1560
0 -0400
0 -0600
+ 0 0100
+ 0-0420
-0 0030
+ 0-0030
1-09
1-37
0-93
105
* Ann. Ch. Phys. [2], Ixvii. (1838).
26
Table Yl\.— continued.
Plants.
Nitrogen, grams.
In Seed,
or Plants ;
and
Miinure,
if anj.
In
Products.
Gain
or
Loss.
Nitrogen
in
Products
tol
Supplied.
1838 : Conditions as in 1837.*
Peas
0 -0 IfJO
0 -0330
0 -0590
0 -1010
0 -OoGO
0 -0530
+ 0 -OooO
+ 0 -0230
-0-0060
2-20
Trefoil (Plants)
Oats (Plants')
1-70
0-90
1851 and '52 : Washed and iijnited lonmice with ashes, distilled ivater,
limited air, under glass shade, tvith Carbonic Acid.f
Haricot, 1851
Oats, 1851.. .
Haricot, 1852
Haricot, 1852
Oats, 1852...
0-0319
0-0078
0-0210
0-0215
0 -0031
0 -0340
0-0067
0 -0189
0 -0226
0 -0030
-0-0009
■O-OOll
■0-0021
-0-0019
-0-0001
0-97
0-86
0-90
0-92
0-97
1803 : Prepared pumice, or burnt brick, tvith ashes, distilled water,
limited air, in glass globe, ivith Carbonic Acid.i
White Lupin
White Lupin
White Lupin
White Lupin
White Lupin
Dwarf Haricot
Dwarf Haricot
Garden Cress
White Lupin
04S0
1282
0319
0200
0399
0354
0298
0013
■1827
0 -04S3
0 1246
0 -0339
0 -0204
0 -0397
0 0360
0-0277
0 0013
0-1697
-H 0-0003
1-
-0-0036
0-
-0-00 10
0-
+ 0 -0004
1-
-0-0002
1-
+ 0 -0006
1-
- 0 -0021
0-
0 -OOOO
1-
-0-0130
0-
-01
1-97
•97
•02
-00
•02
• •93
•00
193
1854: Prepared pumice with ashes, distilled, water, current of washed
air, and Carbonic Acid, in glazed casc.'l
Lupin
Dwarf Harir-ot
Dwarf Haricot
Dwarf Haricot
Dwarf Haricot
Lupin
Lupin
Cress
0196
0322
0«35
0339
0676
0 -0180
0 •0175
0 -0O16
0-0187
-0-0009
0-95
0 -0325
+ 0 ^0003
1-01
0 0:541
-f- 0 ^0006
1-02
0 •0329
-0-0010
0-97
0 ^0666
-0-0010
0-99
1 0^0334
0 -0052
-0-0021
0-94
+ 0-0006
113
* Ann. Ch. Pliys. [2], Ixix. (1838).
t Ann. Cli. Phys. [3], xli. (1854).
I Ann. Ch. Phjs., Sor. [3], xliii. (1855).
27
Table VII. — continued.
Plants.
iV'itrogen, gram 3.
In Si!0(l,
or Plants ;
and
Manuro,
if any.
Tn
Products.
Gain
or
Loss.
Nitrogen
in
Product.s
to I
Supplied.
1851, '52, '53, a7id '54;: Prej^ctred soil, or pumice ivith ashes ; distilled
water, free air, under glazed case.*
Haricot (dwarf), 1851.
Haricot, 1852
Haricot, 1853
Haricot ( '
Lupin (w '
Lupin, I80 1
Lupin, 1851
Gars, 1852
VV'lieat, 1853
Garden Cress, 185 1.
), 185A. ...
1853 ....
0 -0.3 19
0 0213
0 0293
0 -0318
0 0214
0 0109
0 -OSfi?
0 0031
0 -OOfi l
0 -0259
0 -0380
0-0238
0-0270
0 -0350
0 0256
0 -0229
0 -0387
0-00 it
0 -0075
0 0272
+ 0-0031
+ 0 0025
-0-0023
+ 0-0032
+ 0-0042
+ 0 0030
+ 0-0020
+ 0-0010
+ 0-0011
+ 0.0013
•09
-12
•92
-10
-20
-15
•05
•32
•17
•05
1858 : Nitrate of Potassium as Ma^mre.f
Heliantlius
1
0^01 11 J
0 -025 j;
0 0130
0-0245
-0-0014
■ 0^0010
0^90
0 96
The last two columns of the table (VII) show the actual and pro-
portional gain or loss of nitrogen in M. Boussingault's experiments.
It will be seen that in his earlier experiments, those in free air in a
summer house, the leguminous plants, trefoil and peas, did indicate a
notable gain of nitrogen: but, in all his subsequent experiments, there
was generally either a slight loss, or, if a gain, it was represented in only
fractions, or low units, of milligrams. After 20 years of varied and
laborious investigation of the subject, M. Boussingault concluded that
plants have not the power of assimilating the free nitrogen of the atmo-
sphere. And in a letter received from him as recently as 1876, after
discussing several aspects of the question, he says : —
" If there is one fact perfectly demonstrated in physiology, it is
this of the non-assimilation of free nitrogen by plants ; and I may
add by plants of an inferior order, such as my^oderms and mush-
rooms."— (Translation.)
Our own experiments on this sub'oct were commenced in 1857,
and a young American chemist, the late Dr. Pugh, of the Pennsylvania
* Ann. Ch. Phys., S6r. [3], xliii. (1855).
t Compt. rend., xlvii. (1858).
X Nitrogen in Seed and Nitrate.
28
Table VIII.
Jlesalts of Experiments made at Bothamsted to determine whether Plants
assimilate free Nitrogen.
Nitrogen, grams.
In Seed,
and
Maniu-e,
if any.
In
Plants,
Pot, and
Soil.
Gain
or
Loss.
Nitrogen
in
Products
to 1
Supplied.
With NO combined Nitrogen supplied beyond that in the seed sown.
p 1857
f Wheat....
■< Barley ....
[ Barley ....
0-0080
0 -0056
0 -0056
0-0072
0 0072
0 0082
-0-0008
+ 0-0016
+ 0-0026
0-90
1-11
1-46
Gramineae . . . . ■
1858
["Wheat....
•< Barley ....
[Oats
0 -0078
0 -0057
0-0063
0-0081
0 -0058
0-0056
+ 0-0003
+ 0 0001
-0-0007
1-04
102
0-89
1858
r Wheat ....
X Oats
0 -0078
0-0064
0-0078
0-0063
0-0000
-0-0001
1-00
0-98
P 1857
Beans ....
0 -0796
0 -0791
-0-0005
0-99
Leguminosee . . ■
lt')8
f Beans ....
LPeas
0-0750
0-0188
0 -0757
0 -0167
+ 0-0007
-0-0021
I'Ol
0-89
Other Plants . .
1858
r Buck- l
L wheat . . J
0 '0200
0 -0182
-0-0018
0-91
With combined Nitrogen supplied beijond that in the seed sown.
Graminese
rWheat .
l_Barley .
f Wheat.
1858 < Barley .
[ Oats . . .
1858
A*
Leguminossc
I
1858
1858
r Wheal.
< Barley .
L Oats .
/ Peas. . .
\ Clover .
3ean8 .
Other Plants.. 1858 {^£; _ }
0-0329
0-0329
0 0326
0 -0268
0 -0548
0 -0496
0-0312
0 -0268
0 -0257
0 -0260
0 -0227
0 0712
0 0711
0 0308
0383
0331
0328
0337
0536
04G4
0216
0274
0242
0193
0211
0065
0 -0655
0-0292
+ 0-0054
+ 0-0002
+ 0 -0002
+ 0 -0069
-0 -0012
-0-0032
-0-0096
+ 0-0006
-0-0015
-0-0062
-0-0016
-0 0047
-0-0056
-0-0016
16
01
01
25
98
94
69
02
94.
76
93
93
0-92
0-95
* Those experiments were conducted in the apparatus of M. G. Villa.
29
State Agricultural College, devoted between two and three years to
the investigation at Rothamsted. The conditions of the experiments,
and the results obtained up to that date, are fully described in the
papers in the Fhilosopldcal Transactions for 1859, and in the Journal
of the Chemical Society in 1863, already referred to. Table VIII
(p. 28) summarises the results obtained.
The upper part of the table shows the results obtained in the experi-
ments in which no combined nitrogen was supplied beyond that con-
tained in the seed sown. The growth was in all cases extremely re-
stricted ; and the figures show that there was in no case, whether of
Graminese, Leguminosse, or buckwheat, % gain indicated by as much as
3 milligrams of nitrogen. There was in most cases much less gain, or
a slight loss.
The lower part of the table shows the results obtained when the
plants were supplied with known quantities of combined nitrogen, in
the form of a solution of ammonium sulphate applied to the soil. The
actual gains or losses rauge a little higher in these experiments, with
larger quantities of nitrogen involvtid ; but they are always represented
by units of milligrams only, and the losses are higher than the gains.
Further, the gains, such as they are, are all in the experiments with
the Gramineae, whilst there is in each case a loss with the Leguminosee
and the buckwheat.
It should be stated that the growth was far more healthy with the
Gramineae than with the Leguminosse, which are even in the open field
very susceptible to vicissitudes of heat and moisture, and were espe-
cially so when inclosed under glass sliades. It might be objected,
therefore, that the negative results with the Leguminosse are not so
conclusive as those with the Graminese. Nevertheless, we do not hesi-
tate to conclude from our own experiments, as Boussingault did from
his, that the evidence is strongly against the supposition that either
the Graminese or the Leguminosse assimilate the free nitrogen of the
atmosphere.
Recapitdlation.
In the foregoing re'smne of mostly previously recorded facts, we
have shown the amount of nitrogen assimilated by various crops over
a given area, wlien grown for many years in succession on the same
land without any nitrogenous manure ; that is, under conditions in
which the source of the nitrogen is as little as possible obscured by
the influence of indefinite amounts available from manure.
It has been shown that tlie determined amounts of combined nitrogen
annually coming down in the measured aqueous deposits from the
^.i
30
atmosphere in the open country are entirely insufficient to do more
than supply a small proportion of the nitrogen assimilated by crops so
grown.
With regar '^'^her possible supplies of already combined nitrogen
from the atmoH^ e to the soil, it has been pointed out that there is
no direct quantitative evidence at command, and that such evidence
as docs exist leads to the conclusion that such supplies are very limited
and inadequate.
The same may be said, even in a greater degree, of the supposed
combination of the free nitrogen of the air within the soil ; also of
the supposition that plants take up any material jjroportion of their
nitrogen from combined nitrogen in the atmosphere by their leaves.
Finally, it has been concluded that the balance of direct experi-
mental evidence is decidedly against the supposition that plants
assimilate the free nitrogen of the atmosphere. Indeed, the strongest
argument that we know of in favour of such a supposition is that, in
defect of other conclusive evidence, some such explanation of the
facts of production would seem to be needed.
W'i
The Nitrogen of the Soil as a Soukce of the Nitrogen of
Crops.
We now turn to that part of the subject which it is the special
object of this communication to bring furward, namely, the determi-
nations of nitrogen in the soils of some of the experimental fields at
Rothamsted, the yield of nitrogen in which has been given, and to
show the bearing of the results on the question of the sources of the
nitrogen of the crops.
We have no wish or intention to ignore the difficulties inherent in
the treatment of the subject from this point of vicAv. The difficulty
of the problem will at once be recognised when it is borne in mind
that a difference of 0"001 in the percentago of nitrogen in the dry soil
may represent a difference of from 20 to 25 pounds of nitrogen per
acre in a layer of 9 inches in depth. Again, it is farther to be borne
in mind that, in the case of the Rothamsted arable soils with which
we have to deal, the percentage of nitrogen in the first 9 inches of
depth is sometimes only about 0"1, and seldom exceeds 0'14 or 0'15 ;
that in the second 9 inches it ranges from under 0'07 to little over
0-08; in the third 9 inches from under 006 to about 0'07; and that
in the lower depths is rather lower still.
It will be seen, therefore, that if any quantitative estimates are to be
based on the percentage amounts of nitrogen determined in samples
31
I
of soil from different depths, the greatest care must be taken to insure
that the samples truly represent the exact depth supposed. The mode
usually adopted of taking samples of an indefinite area, perhaps not
to a definite depth, and ahncsfc certainly not of uniform breadth or
width to the depth taken, is obviously quite inapplicable for the
purposes of any such inquiry as tliat here supposed.
Another difficulty is that, in the case of subsoils, with a low actual
percentage of nitrogen, the variations in the amount in different
samples are often proportionally great, and obviously unconnected
with the special history of the plot.
Unfortunately, the few samples of soil that were collected in the
early years of the Rothamsted field experiments were not taken in
such a manner as to afford results applicable to our purpose. Com-
mencing in 1856, however, the mode adopted has been, after carefully
levelling the soil, to drive down a square frame, made of strong sheet-
iron, open at top and bottom, and of an exact area, and of an exact
depth, to the level of the surface. The inclosed soil is then carefully
taken out, and its weight determined. The soil around the frame is
then removed to the level of its lower edge, aiid it is again driven
down, and the inclosed soil removed ; and this process is repeated
until the desired depth of sampling is reached.
Of surface soils, samples are taken from three, four, or as many as
eight places on the same plot. A portion of each such sample is kept
separate, as a means of testing the range of variation, and, if need be,
of correction in case of any abnormal results due to accidental animal
droppings, or other causes. Another portion of each separate sample
of the surface soil is used to make a mixture of all. In the case of the
subsoils, the separate samples of corresponding depth from the same plot
are, as a rule, at once mixed. Surface soils are sometimes taken of an
area of 12 by 12 inches, but frequently of only 6 by G inches, and
subsoils almost invariably of the smaller area. The depth of each
sample is generally 9 inches ; but in some special cases it has been
only 3 inches, and in some 6 inchcF. It is perhaps to be regretted
that the depth originally fixed upon did not more nearly represent that
to which the soil is more directly affected by the mechanical operations,
and by the application of manure, say G inches. But having originally
adopted 9 inches, it has been necessary to adhere to this depth sub-
sequently, in order, as far as possible, to obtain comparable results at
different dates.
The soils when brought to the laboratory are first broken up, and
then partially dried in a stove-room at a temperature of about 130° F.,
to arrest nitrification, which would be liable to take place if the soils
Ill
I: I
32
were moist. Next, the stones are removed ; first those retained by a
sieve of 1-inch mesh, next by a sieve of one. half-inch mesh, and then
by a one-foarth-inch sieve. All that passes the ono-fourth-inch sieve
is termed the mould. Portions of this are very finely powdered and
sifted for analysis ; and the weights being recorded at each stage of
preparation, and the water lost on drying at 100° C. being determined
on the finely-powdered mould, all results of analysis are calculated
into percentage on the so-determined dry mould. From the same data
the amount of dry mould per acre is calculated, and upon this the
amount of nitrogen per acre. It will be seen further on, that not-
withstanding the means adopted to secure uniformity, the amounts of
dry mould per acre calculated for a given depth, from the samples
taken, vary considerably for the same field at diffc'rent times, accord-
ing to the dryness or wetness of the season, the condition of the land
as affected by the crop, the mechanical operations, and other circum-
stances. The amounts also vary very considerably for the soils of
adjoining fields.
Nitrogen in the Soils of the Experimental Wheat Plots.
The first series of determinations of nitrogen to which attention
will be called relates to those made in the soils of some of the plots of
Broadbalk field, which has now grown wheat for thirty-nine years in
succession, and the yield of nitrogen in which, on the plots receiving
no nitrogen in manure, has been given in Table I. It will be remem-
bered that, under those conditions, there was a very marked decline
in the annual yield of nitrogen in the crop, both without any manure,
and with a mixed mineral manure used alone.
The first wheat crop of the series was harvested in 1844, and
although isolated samples of the soil were taken in the early years, it
was not until 1856 that any were collected on the plan now followed.
At that date only four plots were sampled, and only to the depth of
the first 9 inches. Eight samples were, however, taken from each
plot, each 12 by 12 inches area, and the eight were mixed together.
In 1865, samples were taken from eleven plots, from eight places on
each plot, each sample 12 by 12 inches area, and this time to a depth
three times 9 inches, or to a total depth of 27 inches. Lastly, in 1881,
twenty plots were sampled ; six samples, each 6 by 6 inches area,
were taken from each plot, and in each case to three depths of 9 inches
each, or in all to 27 inches.
Thus, it is only in 1865 and 1881 that we have any considerable
series of samples, and the nitrogen determined in them ; that is, in
1865 after the twenty-second, and in 1881 after the thirty-eighth
M/'
83
a
m
re
id
of
ed
crop had been removed. It is obvious that, if tho results at these
two periods are to be compared, we must first determine whether the
samples taken represent layers of equal depth and weight in the two
cases. Confining attention on the present occasion to the results
relating to the first 9 inches of depth, the following figures show the
average weight of dry mould per acre ; that is, of soil excluding
stones and moisture, calculated from the weight of the samples taken,
and from the results of the mechanical separation, and of the deter-
mination of moisture in the soils. For 18G5, tho calculations are
based on the results afforded by 80 samples, eight from each of ten
of the eleven plots, the eleventh being the one annually receiving
farmyard manure ; and for 1881 they are based on the results relating
to 114 samples, that is, six samples each from 19 plots, again
excluding the one with farmyard manure.
Number of Samples.
1865, 10 plots, 8 samples from eacli
1881, 19 plots, 6 samples from each
Calculated
dry Mould
per Acre.
lbs.
2,299,038
2,552,202
ITU
s
Tho importance of taking samples of definite area and depth, and
of determining the weights, is here strikingly illustrated. Thus, it is
obvious that the samples analysed in 1881 represented, on the average,
almost exactly one-ninth more soil per acre than those analysed in
1865. In other words, if the samples of 1865 fairly represented
9 inches of depth in the average condition of consolidation of the soil,
those of 1881 represented 10 inches of soil in the same condition :
that is, they included 1 inch more of subsoil, with its much lower
percentage of nitrogen than the 9 inches above it. It may, of course,
be a question whether the condition of consolidation of the soil was
the more normal at the one period or at the other. It would, how-
ever, make scarcely any difFerence in the relation of the results to one
another at the two periods, whether the actually determined per-
centas-es of nitroeren in the 1865 samples were lowered, on the
assumption that they should have included 1 inch more of subsoil, or
whether the determined percentages in the 1881 samples are raised,
on the assumption that they contained 1 inch too much of subsoil.
We have concluded, from a consideration of all the facts afc command,
that the latter alternative is upon the whole the best. We adopt,
c
m/
34
therefore, the percentages of nitrogen as actually determined in the
166;') samples, and we assume the weight of dry mould (9 inches deep)
represented by the samples to be 2,300,000 pounds per acre. But, in
the case of the 1881 samples, we assume that one-tenth of the heavier
weight had the composition determined iu the second 9 inches (it
would be very slightly higher), and the percentage in the remaining
nine-tenths, representing 2,300,000 pounds of surface soil, is raised by
calculation accordingly.
The following table (IX, p. 35) gives for the surface soils (9 inches
deep), of the unmanured plot, and the nine artificially manured plots,
sampled in 1805, the actually determined percentages of nitrogen in
the dry mould ; and for the 1881 samples from the same plots, it gives
both the actually determined percentages, and the corrected percentages
calculated as above described. The table also shows the amount of
nitrogen per acre, reckoning 2,300,000 pounds of dry mould, calculated
for 1805 according to the actually determined percentages, and for
1881 according to the corrected percentages. The quantities per acre
more ( + ), or less ( — ), in 1881 than in 1805 are also given. Lastly,
for each period, there are given the quantities more or less on each of
the other plots than on plot 5a, which received the mineral manure
alone.
As already said, in 1865 the land had grown twenty-two crops of
wheat in succession, and in 1881 thirty-eight crops. Plot 3 had been
unmanured from the commencement. Plot lOci received mineral
manure in the first year, but the ammonium salts alone each year
since. The remaining plots were somewhat variously manured during
the first eight of the thirty-eight years ; but (excepting plot 16) each
has been manured every year for the last thirty of the thirty-eight
years, as described in the table.
It will be observed that, for every plot, the actual determinations
show a lower percentage of nitrogen in 1881 than in 1865, The cor-
rected percentages for 1881 are, of course, all rather higher than the
actual determinations ; and they, in some cases, show a higher, and in
others a lower, percentage than in 1865. Nevertheless, it cannot fail
to be noted that the relation of plot to plot is essentially accordant at
the two periods.
The significance of the results will, however, be rendered the more
appai'ent on an examination of the calculated quantities per acre. It
is obvious that absolute accuracy cannot be claimed for such figures,
but the general accordance of the indications at the two periods is
such as to leave no doubt of their import.
Keeping in view the special object of this communication, which
35
he
P)
in
ior
(it
ng
by
CO
l-(
O
02
M
Hi
03
O
8
S 00
S
r
22
o6
>>
1>
£
a^
c1
»*
K
s
o
a
O
PI
fc.
s^
kl
?*:
■e
c
O
.o
'4J
o
o
lO
^ I
5 I
M 05 -O
W 54 i-H
+ + +
05
CO CO
(N eo
+ +
00
CO
00
M I
00
X
^ CO
o
00
»0
U5 CO
i.O -*<
l« l-H
+ +
2?
eo
+
CO CO
+ +
10
T
+
05
+
O
+
^*;?
^ r-l -N
-11 +
O C5 t>.
CO 05
^ 00
+ I I
10
o
00
o 'T CO
« M (N
00
(N
CO iH
00 l>.
00 -^
(N 7i
'J
I-
o
lO
o
CO
00
IN
a 1.0 lo 00
Tfl 00
CO •+
O) lO
(N 74
CO
05
IN
00
00
. T3
■w lO 5<l Tf(
S -* rt to
goo iN
CO ^ ^
lO l^ o
C^ O F-t
<N
,i!oo
^1
oo
e8
u
00
3
u
^OO
O o
p^
O O
O o
^^
/^ >o
t '
p. 00
«-•
0) rt
!^
go o
+ I
«
•* (N
05 CO
!>. CO
l-H CO
ri o
't 10
CO
-ft r-
Oi lO
!■«• lO
IN (N
00 -"Jl CO
!>. l>. 10
i> 1^ t>.
!^ IN IN
lO >o
IN IN
IN
IN
'" C> rt t>. O -H p-( lO r-t CO CD
i-, © 00 O O CO IN lO 05 ID O
gOC5 IN INO rH iH r-t i-l O
.1— lO i-H I— lr-( r-l iH iH pH r-l
■S005 O INX pH 00 O 1> -^
C ClrH M coo t^ O O 05 O
SOrH IN e^i-< f-l IN IN l-H IN
.1-Hi-H i-H I— li-H l-H pH pH iH l-H
01
O
■-3
C
e3
^
d
3
eo
S3
"i*
r-
on
'"'
t-H
rt
r—^
0)
O
C
L.
3
c
S
«
rS
1".J
c
X
c
tJg
a
a
ID
3
3
o
T5
3
2"
3
3
F- sS
bD ,
o r3
O) J<
O Hi
3 f^
3
«
UQ
10 3
2 "
3 SC
o p
o .-S
m F-H
o II "
o
,3
<—
V
P.
3
ft-
&^
3
• CD
. o
:£-
■ ft^
. 3
i 91
3
: cs
3 • a
P 2
"S 2 c
m I
I CD
£ 3i; 3-0
. 3 „, 3
O, aJ O
t? o 5 o
3 i» .
3 js S i;
CO
00
CO
00
ci
to 3
lU
e. ^
"b 's
o
fl3 4) c
-73 cS
S O O
CO
00.2
a 5
S a ^<1
J ^
S 2
rfl 3
O 3
d 2
SOO g^#
II ^ II I
w r- 3
Q. to C « c-
-O rt-Sls 3
3 in 3 n 3
=^ d =5 d-^a
O c ^ G 51
-g 2^ g §
-3 3 ,3 3-3
Png Ag 3
O
eo lO t*
05
O r-<
IN
C3
CO
c 2
CO
.a
to
O)
3
S3
00
CO
I-H
♦
36
is to show tho bearing of what may bo called the nitrogen statistics of
the soils, on tho question of the sources of tho nitrogen in the crops, it
will be seen that, during tho sixteen years from 180-5 to 1881, both
the unraanured plot (;J),aiul tho mineral manured plot (5a), tho yield
of nitrogen in tho crops of which declined so sti-ikingly, show a groat
reduction in tho stock of nitrogen in the surface soil. The reduction
in these later years is considerably greater in tho surface soil of tho
mineral manured than in that of tho entirely unmanured plot, tho
previous accu.nulation in which had been many more years subject to
exhaustion. Taking tho results, however, for the first, second, and
third 9 inches, tlie calcnlatcd loss to the depth of 27 inches is approxi-
mately the same for tho two plots. The figures recorded for tho first
9 inches only are, however, sufficient to show that tho decline in tho
yield of nitrogen in the crop, where none has been supplied in manure,
is accompanied by a decline in the stock of nitrogen in the soil.
A further illustration on this point is afforded by tho results for
plot lOa. For tho thixteen years, 1852 — 1864, plot 16 received,
besides the mixed mineral manure, twice as much ammonium salts as
any of the other plots, tho results for which arc given in the table ;
and it gave on the average of those years 30| bushels of grain ^er
acre per annum. Since 18G4, however, the plot has been left un-
raanured, and during the seventeen years, 1865 — 1881, it has yielded an
average of only 14f bushels of grain; and in recent years the produce
has been very little more than witliout manure, or with purely
mineral manure. The table shows that in 1865, that is, after one
crop had been removed since the application of the excess of ammo-
nium salts, the surface soil still contained considerably more nitrogen
than any other plot in the series. In 1881, however, after sixteen
years more of cropping without manure, the stock of nitrogen on tho
plot was reduced by a greater amount than on any other plot, and to
a lower point than on any other of the ammonium plots, excepting
plot 10 with the ammonium salts alone.
Let us now refer to the last three columns in the table, which
show, for each of the plots receiving ammonium salts, the amount of
nitrogen per acre in the surface soil, more or less than in that of plot
5a, with mineral manure alone. All the plots, 7 to 14 inclusive,
received the same quantity of nitrogen, namely 86 pounds per
acre per annum. But it will be seen that the excess of nitrogen in
the surface soils compared with the mineral manured plot 5, varies
exceedingly. In fact, it is obvious that the amounts have no direct
relation to the amount of nitrogen supplied in the manure.
The following table (X) will afford some explanation of the diffei'-
M4^
of
37
ences. Tho plots under considoration, all of which received the same
amount of nitrogen in manure, are there given in tlie order of their
average annual increased yield of nitrogen in the crops over plot 5.
The first column shows the estimated average annual increased yield of
nitrogen per acre in the crops ; the second, the estimated annual loss
of nitrogen as nitric acid by drainage ; the tliird, the estimated pnnual
excess of nitrogen in the surt'ace soil over that on plot 5 with tho
mineral manure alone ; and the last column shows the relation which
that excess in tho soil bears to 100 increased yield of nitrogen in the
crops
Tahlk X.
.Estimated Nitrojen j)er Aero per Annum,
In
Excess
In
Loss by
Surface
in Sur-
PlotB.
Crops
Drainage
Soil
face Soil
over
over
9 inches
to 100
Plot 5.
Plot 5.
deep, over
increase
Plot 5.
in Crop.
lbs.
lbs.
lbs.
lbs.
10
Ammonia salts = 8G lbs. nitrogen
(1845 and since)
12-4
31-2
4-8
38-7
11
Ammonia salts = 8G lbs. nitrogen
and suporpliosphato
17-7
28-5
11 -G
G5-5
12
Ammonia salts = 80 lbs. nitrogen
superphosphate and soda
22-2
24 -5
14-0
G5-8
13
Ammonia salts = 80 lbs. nitrogen
siiporpliospliate and potash ....
23-4
25-0
17-8
76-1
14
Ammonia salts = 80 bs. nitrogen
superphosphate and magnesia . .
24-1
27-5
15-5
G4-3
7
Ammonia salts = 80 lbs. nitrogen
and mixed mineral manure ....
25-9
19 0
19-3
74-5
9
Nitrate soda = 80 lbs. nitrogen
and mixed mineral manure ....
26-5
23-7
18 -5
71-2
It is seen that tho increased yield of nitrogen in the crops also
varied exceedingly with the same amount supphed in manure, accord-
ing to the condition as to supply of mineral constituents. Plot 10,
with the ammonium salts alone, gives the smallest increased yield of
nitrogen in the crop ; and plots 7 and 9, with the most complete
mineral manure, each more than twice as much; the other plots
giving intermediate amounts.
The order of the estimated loss of nitrogen by drainage is almost
the converse of that of the increased yield in the crops. Plot 10,
which gives the least increased yield in the crop, shows the greatest
<c
38
loss by drainage ; and plots 7 and 9, which yield the greatest
increase in the crop, show the least loss by drainage.
The excess in the soils (over plot 6) is obviously much more in
the order of the increased yield in the crops. Plot 10, with the
least in the increase of crop and the most in the drainage, shows the
least excess in the soil ; whilst plots 7 and 9, with, the greatest
increased yield in the crop, and the least loss by drainage, show the
greatest excess in the soil.
It is clear, therefore, that whilst the excess in the soil has no
direct relation to the amount supplied in the manure, it has a very
obvious relation to the increased yield in the crop ; in other words, to
the amount of growth. The last column of the table brings this
out more clearly. Excepting in the case of plot 10, with the ammo-
nium salts alone, there is a general uniformity in the proportion
of the excess in the soil over plot 5 to the increased yield in the
crop over plot 5 ; and the variations, such as they are, have an
obvious connection with the conditions of growth. Thus, plots 11,
12, and 14, all with a deficient supply of potash, show approximately
equal proportions retained in the soil for 100 of increase in the crop.
Plots 13, 7, and 9, again, all with liberal supplies of potash, show
higher, but approximately equal, proportions retained in the surface
soil for 100 of increased yield in the crop.
Upon the whole, it is obvious that the relative excess of nitrogen
in the soils of the different plots is little, if at all, due to the direct
retention by the soil of the nitrogen of the manure, but is almost
exclusively dependent on the dift'erence in amount of the residue of
the crops — of the stubble and roots, and perhaps of weeds.
Recurring to the main point which it is our object to elucidate,
there can be no doubt that the determinations of nitrogen in the sur-
face soils of the plots of the experimental wheat field, at different
dates, establish the fact that the decline in the yield of nitrogen in
the crops, when none is supplied in manure, is accompanied by a
decline in the stock of nitrogen in the soil.
It will be well to consider, as far as the data at command will
allow, what relation the yield of the nitrogen in the crops bears to
the loss of nitrogen by the soil ?
On this point it may be stated that, taking the average of thirty
years, 1852 — 1881, it is estimated that the nnmanured plot yielded
18'6 pounds of nitrogen in the crops, and lost 10"3 pounds in the
drainage, or in all 289 pounds per acre per annum over that period.
In like manner, it is estimated that plot 6, which received nitro-
genous as well as mineral manure during the preceding eight yeais.
39
in
ho
he
est
ihe
bat mineral manure alone during the thirty years, yielded an average
of 20*3 pounds of nitrogen in the crops, and 12 pounds in the drain-
age, or in all 32 "3 pounds per acre per annum. It would thus
appear that, without nitrogenous manure, about 30 pounds of nitrogen
has been contributed per acre per annum, from some source, to crop
and drainage together. The determinations of nitrogen in the soils of
the two plots indicate that they have lost an average of about two-
thirds of this amount annually to the depth of 27 inches. There
would, therefore, according to this reckoning, i-emain about one-third
— say 10 pounds more or less — to be contributed by seed, by rain and
condensation from the atmosphere, and by all the other supplies of
combined nitrogen which have been supposed to be available, whether
by the combination of free nitrogen within the soil, or its assimilation
by the plant. Of this amount about 2 pounds will be due to seed,
and if we suppose, say, only 5 pounds to be annually supplied by rain
and the minor aqueous deposits from the atmosphere, there is but
little left to be provided by all the other sources assumed.
Nitrogen in the Soils of the Experimental Barley Plots.
Unfortunately we have not so complete a series of determinations
of nitrogen in the soils of the experimental barley plots as of those in
the experimental wheat field. In 1868 four of the barley plots were
sampled. Four samples, each 6 by 6 inches area, by 9 inches deep,
were taken from each plot, and the four mixed together. In March,
1882, 26 plots were sampled, four samples being taken from each plot,
each 6 by 6 inches area, and to the depth of three times 9, or 27
inches. Of the plots sampled in 1868 only one had received no nitro-
genous manure, but we are able to give the percentage of nitrogen in
the surface soil of this plot at the two dates.
Table XI. — Hoosfield Barley Land.
Nitrogen^ per cent, in the dry Mo^dd, first 9 inches.
[Barley, 31 years in succession, 1852-1882 inclusive.]
Description of Manure.
1868.
1882.
Per cent.
0 1202
Per cent.
0 1124
The calculated average weights of dry mould per acre, to the depth
of 9 inches, were not very different at the two dates. The 1882 samples
■ liv _
40
were, however, slightly the heavier, which vrould indicate that, for
comparison, the percentage of nitrogen given for the latter date is
perhaps somewhat too low. Still, it is obvious that, as in the case of
the "wheat land, so also in that of the barley land, there is, with the
decline in the yield of nitrogen in the crop at the same time a decline
in the stock of the nitrogen in the soil.
Nitrogen in the Soils of the Experimental Boot-crop Plots.
The next results relate to the land upon which root-crops — com-
mon turnips, swedes, sugar-beet, and mangel-wurzel (with the
exception of the interpolation of three years of barley without
manure) have been grown for forty years in succession, 1843-1882
inclusive. Samples of the soil have only been taken once, namely,
in April, 1870; that is, after the experiment had been continued
twenty-seven years. At that time 35 plots were sampled, and four
samples were taken from each plot, each 6 by 6 inches area, and to
a depth of 3 times 9, or 27 inches.
The following table shows the percentage of nitrogen in the surface
soil of the continuously unmanured plot, and of three plots with
mineral manure alone : —
Table XII, — Barnfield Root-crop Land.
Nitrogen, j)er cent, in dry Mould, first 9 inches.
[Root-crops (except barley three years) 40 years in succession, 1843-1882 inclusive.]
Description of Manure.
1870.
Plot 3. — Unmanured
Plot 4. — Mixed mineral manure. . . .
Plot 5. — Superphospliate alone ....
Plot 6. — Supcrph'isphate and potash
Mean of plots 4, 5, G. . . .
Per cent.
0 -0852
0 -0934
0 -0888
0 -0807
0 -0896
Having only taken samples once, we have, of course, no means of
comparing the condition of the land as to its percentage of nitrogen
at different periods. The point to b" observed in the results given in
the table is, that each of these four plots, which have received no nitro-
genous manure, shows, after twenty-seven years of experiment (twenty-
four years roots and three years barley), a lower percentage of nitrogen
41
or
is
of
,he
ine
in the surface soil tban lias been found in any of the other experi-
mental fields ; though determinations made in samples from other parts
of the same field, and also in an adjoining field, show considei'ably
higher results. The nearest approach to so low an amount in any
other field is where the land had been under alternate wheat and
fallow, without manure, for more than thirty years.
It will be remembered that the root-crops gave, with mineral
manure alone, a very much higher yield of nitrogen than the cereals
in the earlier years, and as low a yield in the later years. That they
did not give less still is probably owing to the fact that their growth
extends later in the season than that of the cereals, by virtue of
which they are probably enabled to arrest the nitric acid formed
within the soil during the early autumn months, which in the case of
the cereals would be more subject to loss by drainage.
Both the mechanical conditions of surface soil known to be favour-
able for the growth of th'^ root-crops, and the large amount of fibrous
root they throw out near the surface, are indications of an active
demand on the resources of the upper layers of the soil, and are per-
fectly consistent with the supposition that their growth has led to a
greater reduction in the stores of nitrogen of the superficial layers
than in the case of any of the other crops.
The evidence afforded, both by the facts of production, and by the
determinations of nitrogen in the soil, is indeed strongly in favour of
the view that the source of the nitrogen of the root-crops, as of the
cereals, is, when grown without nitrogenous manure, the soil itself,
and the small quantity of combined nitrogen annually contributed by
rain, and the minor aqueous deposits from the atmosphere. It is said,
however, that these crops require a certain amount of nitrogen to be
supplied by manure, and that they are able to take up the remainder
from atmospheric sources. The facts of production recorded at page 11
afford no countenance to such a view. We conclude, indeed, that the
dependence of these crops for their nitrogen, on the stores of the soil
itself, or on supplies by manure, is as clearly established as in the case
of the cereals.
Is THE Soil a Source of the Nitrogen of the Leguminos^ ?
We have now to consider the bearing of the evidence on the
question of the sources of the nitrogen of the Leguminosje ; and here
we approach not only the most important but the most difficult part
of our subject.
42
The first of the leguminous crops, the yield of nitrogen in which
is recorded in Table I, is beans. Without manure the yield of nitrogen
was in the earlier years very much higher than with the cereals ; but
the decline was very great, and in the later years it was as low as
with the cereals. With mixed mineral manure, including potash, the
yield throughout was much higher, but the decline was, as without
manure, very great. We have not a sufficiently comparative series of
determinations of nitrogen in the soils of the bean plots, but such
results as are at command lead to the conclusion that there has been
a gradual decline in the percentage of nitrogen in the surface soils ;
but, considering the little tendency of the plant to throw out feeding
root in the superficial layers, it may be a question how far the reduc-
tion is due to exhaustion by the direct action of growth, or how far
to nitrification and passage of the nitrates downwards.
Nitrogen in the Soils of the Experimental Glover Plots.
The most important of the leguminous crops to which reference
has been made is red clover. In Table I is recorded the yield of
nitrogen over twenty-two years, 1849-70, in only six of which, how-
ever, was any crop obtained. The experiment has ' een continued,
with some modifications ; and in 1877, that is after twenty-nine years,
in nine of the last ten trials the plant had died ofp during the winter
and spring succeeding the sowing of the seed. Several small crops
have since been obtained, and in March, 1881, samples of soil were
taken from five places where no nitrogenous manure has been applied
from the commencement, and at each place to thi'ee depths of 9 inches
each. Exactly corresponding samples were also taken from an imme-
diately adjoining plot, which had been thirty years under alternate
wheat and fallow, without manure of any kind. The nitrogen was
determined in each of the five separate samples, and also in the mix-
ture of the five. Table XIII summarises the results.
43
lich
ygen
but
as
the
lout
iS of
|mch
3een
loils ;
[ding
|duc-
far
I.
Table XIIL— Hoosfield Clover, and Wheat and Fallow, Land.
Nitrogen ;per cent, in dry Motdd, first 9 inches.
[Experiments more than 30 years.]
Mean.
Mean of determinations on five separate samples,
Mean on the mixture of the five samples
Mean ,
1881.
Clover Land.
Per cent.
0 -1007
0 -1055
0-1061
Fallow Land.
Per cent.
0 0925
0-0984
0 -0955
It is true that the tendency of the evidence on the point is to show
that red clover derives, at any rate much of its nitrogen, from the
lower layers of the soil ; but it is surely significant that, after the
growth of heavy crops in 1849, when the land was in ordinary condi-
tion as to manuring and cropping, and the constant failure since, there
is, coincidently with this, nearly as low a percentage of nitrogen in the
surface soil as with alternate wheat and fallow without manure. It is
obvious that any accumulation near the surface, due to residue from
the small crops, has been more than compensated by exhaustion. The
evidence afforded by the figures may be said to be of a somewhat
negative character ; but it is at any rate clear that failure of growth
of the clover has been associated with a declining, and a very low,
percentage of nitrogen in the surface soil.
The next results are of a very much more definite character. They
relate to the two portions of the field which had grown six corn crops
in succession by artificial manures alone, was then divided (in 1873),
and on one half clover (sown in the previous year), and on the other
half barley, was grown. Table I shows that in the clover crops
151 "3 pounds, and in the barley only 37"3 pounds of nitrogen were
removed. Yet, in the next year (1874), barley being grown over
both portions, the one which had yielded 151-3 pounds in clover
now yielded 69*4 pounds in barley ; and the other, which had yielded
only 37"3 in barley, now yielded only 39-1 pounds in barley.
In October, 1873, after the clover and barley had been removed,
and before the land was ploughed up, samples of the soil were taken
as follows : From each portion four separate samples, each 12 by 12
inches area and 9 inches deep, and the nitrogen was determined in
44
each separate sample, and also in an equal mixture of the four. Six
other samples, each 6 by G by 9 inches, were also taken from each of
the two portions, and the six samples representing each portion were
mixed, and the nitrogen determined in the mixture. At each place
corresponding separate samples were taken, and mixtures made, re-
presenting respectively the second and the third 9 inches of depth.
In all cases three and in many four determinations of nitrogen were
made on each sample. The following table gives the mean results on
each of the four separate samples, the mean of these, the mean on the
mixture of the four, the mean on the mixture of. the six, and the mean
of all : —
Table XIV.
Experimental Clover and Barley Land.
[Nitrogen per cent, in dry Mould, first 9 inches.]
Description of Samples.
•
1873.
Clover Land.
Barley Land.
Samnle No. 1 fl2 x 12 x 9 inches')
Per cent.
0-1574
0-1529
0-1484
0 1G31
Per cent.
0-14G8
Samole No. 2 (12 x 12 x 9 inches)
0-1341
Sample No. 3 (12 x 12 x 9 inches)
0 1431
Samnio No. 4 (12 x 12 x 9 inches)
0 • 1405
Mean on the four separate samples (12 x 12 x 9 inches)
Mean on a mixture of the four samples (12 x 12 x 9 ins.)
Mean on a mixture of six samples (G x G x 9 inches) ....
0 1554
0 15G6
0-1578
0-1411
0 -1387
0-1450
General means
0-15G6
0-141G
The determinations on the individual samples given in the upper
pr tion of the table (XIV), forcibly illustrate the inapplicability of
results obtained on single samples of soil. But the accordance of
the mean results of the three sets of determinations for the clover
land, and again of the three for the barley land, can leave no doubt
whatever that there was a considerably higher percentage of nitrogen
in the first 9 inches of the clover ground than to the same depth of
the barley ground.
The results must, indeed, be accepted as indicating a marked distinc-
tion, which, in direction, is entirely consistent with what is known of
the influence of a clover crop as a prepai'ation for a succeeding cereal
one, and entirely consistent with the results actually obtained with the
barley succeeding the clover. It is, however, difficult, to suppose
45
that the figures correctly r ^present, in degree, the average difference
in the composition of the first 9 inches of the two plots ; for, calcu-
lated per acre, the excess of nitrogen in the surface soil of the clover
plot would represent an accumulation equal to about twice as much
as was removed in the three cuttings of the clover, notwithstanding all
visible vegetable debris was removed before the soils were submitted
to analysis ;* nor have the subsequent crops benefited as much as might
have been expected from such an amount of accumulation. On the
othtir hand, samples taken in 1877 still show a higher percentage of
nitrogen in the surface soil of the clover than of the barley land.
It is, at any rate, obvious that the surface soil of the clover ground
has gained nitrogen, either from above or from below — from the
atmosphere or from the subsoil. And, so far as the determinations of
nitrogen in the subsoils go, the indication is that, if from below, it is
at least mainly from a lower depth than 27 inches.
It is freely admitted that, in the facts of this experiment as they
stand, there is no evidence as to the source of the large amount of
nitrogen of the clover crop, and of the increased amount of it
in the surface soil. In the absence of such evidence, it is natural
enough to assume that the atmosphere has been the source. But
whilst there is absolutely nothing in favour of this view excepting
the fact that an explanation is needed, and that if that source were
established the difficulty would be solved, there is, to say the least,
much more evidence in favour of the supposition that the subsoil has
been the source of at any rate much of the nitrogen.
The Soils of the Melilotus leucantha and White Clover Plots.
Reference has already been made to the enormous growth of
Melilotus leucantha, and the enormous amount of nitrogen it yielded,
for several years in succession, on the land where no nitrogen had
been applied for more than thirty years, and where red clover had so
frequently failed (p. 12). The crop of 1882, the fifth in succession,
was the highest, and the yield of nitrogen in it was not far short of
150 pounds per acre ; whilst, under exactly similar conditions, ordi-
nary red and white clover gave very small produce. Accordingly, as
soon as the crops were removed, samples of soil were taken from one
of the melilotus plots, and from the corresponding white clover plot.
Samples were taken from two places on each plot, and in each case to
* This was more completely done in the case of the four 12x12x9 inch samples,
than in that of the six 6 x 6 x 9 inch ones, and the latter are seen to give slightly
higher percentages of nitrogen.
46
the depth of six times 9 inches, or in all 54 inches. The examination
of these samples of soil is as yet very incomplete, but the following
interesting facts have been ascertained : —
Whilst the strong roots of the melilotus were found to penetrate
to the lowest depths of the sampling, there was very little develop-
ment of white clover roots beyond the surface soil. Whilst to the
eye, and to the hand, the subsoil where the melilokis had grown was
obviously pumped dry, and was somewhat disintegrated, to the full
depth sampled, that of the clover plot had no such characters. De-
terminations of moisture in the soils and subsoils show, at each of the
six depths, much less water in the melilotus than in the white clover
soils ; and the difference is by far the greater in the lower depths.
Calculated per acre, it would appear that, to the depth of 54 inches,
the melilotus soil had lost approximately 540 tons more water per
acre than the white clover soil ; and there can be no doubt that the
pumping action had extended deeper still.
There is here, then, clear evidence that the plant, whose habit of
gi'owth, and especially whose range, and feeding capacity, of root,
suited it to the conditions, was enabled to take up much more water,
and doubtless with it much more food, than, under exactly similar
conditions of soil, were at the command of the plant of the much
weaker and more restricted development.
Nitrogen as Nitric Acid in the Melilotus and White Clover Soils.
That the deep-rooting melilotus did derive more nitrogen from the
subsoil than the shallow-rooting white clover is obvious from the
following facts : — Watery exhausts were made of each soil, at
each depth, and the nitrogen as nitric acid determined in them, by
Schlosing's method, as nitric oxide, by its reaction with ferrous salts.
The f oUowir iable summarises the results : —
■»
ion
ate
47
Table XV.
Nitrogen as Nitric Acid.
Per million, dry Soil.
Per Acre.
Melilotus
Soil.
White
Clover Soil.
Melilotus
Soil.
White T^.„
Clover Sou. difference.
First 9 inches
Second 9 inches
Third 9 inches
Fourth 9 inches
Fifth 9 inches
Sixth 9 inches
1-28
0-36
0-21
0-33
0-28
0 55
3 24
1-10
0-66
1-03
146
1-77
lbs.
3 39
0-97
0-61
0-C9
0-84
1-65
lbs.
8 59
2-97
1-91
3 09
4-38
5-31
lbs.
5 20
2-00
1-30
210
3-54
3 66
Total
• •
••
8-45
26 25
17 -80
Thus the melilotus had not only exhausted the water, but the nitric
acid of the soil, at each depth very much more than the white clover
had done ; and the difference is very marked, and increases, at the
lower depths. It is seen that in the case of the white clover soil there
is a diminishing amount of nitric acid from the first to the third depth,
and then an increasing quantity to the sixth depth. There was, in
fact, about the same total amount found in the three lower as in the
three upper layers. It may fairly be supposed that there is greater
concentration lower still, and that the exhausting action of the melilotua
extended beyond the depth examined.
There is here direct evidence that the soil is the source of at
any rate some of the excess of nitrogen of the melilotus over that in
the white clover. The quantity, and the distribution, of nitric acid
in the soil at any one time are so dependent on temporary conditions,
that it would be fallacious to attempt to estimate from the figures as
they stand the exact amount which the melilotus has taken up more
than the white clover. Then it is obvious that the action extended
below the depth examined ; and it is a question whether, with the
greater disintegration, and greater aeration, nitrification would not be
favoured in the lower depths, and if so the supply would be in a sense
cumulative. Lastly, it may be that the deeply and widely distributed
m.elilotus roots have the capacity of taking up nitrogen from the soil
in other forms than as nitric acid.
\*..J^
48
i
Nitrogen as Nitric Acid in other Soils and Subsoils.
It will be some furtlicr aid in judging of tho possibility or pro-
bability that the nitric acid in the soil and subsoil may be an adequate
source of tho nitrogen of the LeguminoscB, if wo quote a few results
indicating the amount of nitric acid found in some other soils under
known conditions.
In the first place, three soil drain-gauges, one with 20, ono with 40,
and one with GO inches depth of soil, in its natural state of consolida-
tion, and each of one-thousandth of an acre area, have been under
experiment for between eleven and twelve years. No manure has been
applied to these soils, nor have they gi'own any crop, from the com-
mencement. The drainage has been regularly collected and measured ;
and for nearly the whole of the last five years the nitric acid has
been determined in monthly average samples of the drainage waters.
Taking the result of the three gauges, for four harvest-years (Sep-
tember 1, 1877, to August 31, 1881), these soils, which had been
about six years without any manure at the commencement of the
period under consideration, have lost by drainage an average of nearly
43 pounds of nitrogen as nitric acid per acre per annum, of which
perhaps not much more than 5 pounds would be duo to rain and con-
densation of combined nitrogen from the atmosphere. In fact, about
35 pounds, or perhaps more, would appear to have been annually due
to the nitrification of the nitrogenous matter of these unmanured soils.
It has to be borne in mind, however, that tho blocks of soil having
access of air from below as well as from above, the nitrification may
have been freer than it would be in soil in its ordinary condition.
Again, in some of the samples of soil taken from the plots in the
experimental wheat field, in October 18G5, and in many of those taken
in October 1881, that is in each case about two months after the
removal of the crop, the nitric acid has been determined.
In the case of one plot sampled in 18G5, which had received
annually mixed mineral manure and ammonium salts, determinations
made in 186G (by Br. Pugli's method), showed nearly 76 pounds of
nitrogen as nitric acid per acre to tho depth of 27 inches. As, how-
ever, these soils had been stored in a rather moist condition, it is
possible that nitrification may have taken place after the collection,
and that the results are so far somewhat too high.
The following table (XVl) gives an abstract of the results of the
determinations of nitrogen as nitric acid in the 1881 samples of the
experimental wheat field soils : —
\'WW^
49
Taiu-e XVT.
NUror/en as Nitric Acid.
Complex Mineral Manure
and
Ammonium
Salts.
and
Sodium
Nitrate.
Sodium
Kitrate
alone.
Unmanured
continuously.
Per Million Dry Soil.
Per Acre.
"Pirsf. P inrlifia
lbs.
22-8
11-3
5-8
lbs.
19-7
10-0
8-3
lbs.
16 3
20 1
18-0
lbs.
9-7
Second 9 inches
Third 9 inches
5-2
2-8
Total
39-9
38-0
54-4
17-7
Thus, in these 1881 samples, collected, like those in 18G5, about
two months after the removal of the crops, the amounts of nitric acid
found to the depth of 27 inches only, represented — in the soil of the
plot receiving mixed mineral manure and ammonium salts, 39"9
pounds of nitrogen per acre to that depth ; in that of the plot receiving
the same mineral manure and sodium nitmte, 38 pounds ; in that of
the plot to which nitrate of soda alone is annually applied, 54-4 pounds;
and in the soil of the continuously unmanured plot, 177 pounds.
As in the case of the white clover land, in all cases (except with the
nitrate alone), the amount decreased from the first to the third 9 inches
of depth from the surface ; and if, as in that case, it increased in the
lower depths, and in anything like the same degree, we have evidence
of a considerable store of nitric acid available for such plants as, by
virtue of their habit of growth, are able to gather up the residue
accumulated within the subsoil.
Determinations made in samples collected in the experimental rots,-
tion field, in September 1878, showed the following amounts of
nitrogen as nitric acid per acre to the depth of 18 inches -
iii#
50
With Super-
phosphate
only.*
With
Complex
Mineral and
Nitrogenous
Manure.*
After fallow
lbs.
30-3
10 -G
lbs.
48-8
After beana
20-5
Difference ■ . . >
25-7
28-3
Samples collected at the same date from the unmanured alternate
wheat and fallow plots showed to the same depth : —
lbs.
After fallow 33-7
After wheat 2 G
Diifercnce 31 '1
Lastly, two fields which had been manured and cropped in the
ordinary course of the farm, and had been fallowed since the previous
autumn, showed, according to determinations in samples collected in
October 1881, the following amounts of nitrogen as nitric acid per
acre to the depth of 27 inches : —
lbs.
Claycroft field 58-8
Foster's field 5G '5
Thus there was very much less nitrogen as nitric acid found in the
soils to the depths examined, after the growth of the leguminous crop
beans, as well '^er that of the gramineous crop wheat, than in the
correspond' .w soils; indicating, therefore, a like source of
some, r ' . jc;, of the nitrogen of both crops.
It oe seen, however, that even in the cases of the soils
receiving nitrogenous manure, the amuunt of nitric acid found to the
depths examined, is very far from sufficient to account for so large
an accumulation in the crop, and in the surface soil, as the figures
relating to the nitrogen in the produce of the clover, and in the clover
and barley soils, would indicate had been accumulated.
The amounts of nitric acid formed, or remaining, within a limited
depth from the surface, at any one time, is, it is true, as already
intimated, dependent on so many temporary circumstances, that it is
* The manures are applied every fourth year, for the root-crop commencing
each course of — roots, bp- ^ey, leguminous crop or fallow, and wheat.
51
IX
and
0U8
*
not to be expected that tlio amount found within such limits at any
given time would represent more than a fraction of that which would
be available, even within that range, during the long period of growth
of the clover crop. Then, the indications are that there is considerable
accumulation beyond the depth to which most of our examinations
apply. Still, it is difficult to suppose, with the evidence at command,
that the whole of ^he nitrogen which has to be accounted for, either
in the Melilotus, or in the clover and barley experiment, can be
attributed to that source. There remains the question whether the
roots of the plant do not take up nitrogen from the soil in other
states than as nitric acid.
Finally in regard to the experiments with clover and barley, it is
admitted that the various results of soil examinations which have
been adduced do not conclusively show the source of the whole of
the nitrogen to have been the soil. It will, we think, nevertheless
be granted, that they do clearly point to the fact that at any rate
much of it is derived from that source ; whilst there is no evidence
whatever of an atmospheric source of more than the small amount of
combined nitrogen coming down in rain, and the minor aqueous
deposits, and the probably still smaller amount absorbed from the
atmosphere by the porous soil.
Nitrogen in some of the Soils of the Ex;periviental Mixed Herbage Plots.
The results next to be referred to will afford additional evidence of
the soil-source of the nitrogen of the Logurainosaj.
In Table III it was shown that in the mixed herbage of permanent
grass land, without manure 33'0 pounds, and with a purely mineral
manure (including potash) 55-6 pounds of nitrogen were yielded per
acre per annum in the crop over a period of twenty years. Whence
comes the 22*6 pounds more nitrogen per acre per annum taken up
when the mineral manure was applied than without manure ?
After twenty years of continuous experiment, samples of soil
were taken from three places on each plot, and in each case to the
depth of six times 9 inches, or 54 inches. The mean results of the
determinations of nitrogen in the surface soils of the unmanured
plot, and of the plot receiving a complex mineral manure (including
potash), are given in Table XVII which follows :—
m-m
52
Table XVII. — Experiments on Permanent Meadow Land.
Nitrogen, per cent, in dry Mould, and per Acre.
1870.
187G.
1878.
Plot 3. — Unmanured -
Per cent.
0 2517
• •
• f
• •
• •
Per cent.
0 -2466
0'223G
Plot 7. — Mixed mineral
manure, including potash
0 -2246
Difference
0 0230
lbs.
506-0
25-3
Difference per acre
r Total 20 yeai^
\ Average per annum
• t
• •
Although we have not previously quoted the figures, we have on
several occasions stated in general terms that determinations of nitro-
gen show a lower amount in the mineral-manured soil, approximately
corresponding to the increased yield in the crop.
It is in reference to our statements on this point that M. Joulie has
called in question +he possibility of obtaining results of the kind appli-
cable to our argument. He takes the fact of the increased yield of
nitrogen under the influence of purely mineral manure as conclusive
proof of the atmospheric source of the increased amount of nitrogen
assimilated. He assumes that our calculations are based on determi-
nations of nitrogen in a sample of the mixed soil to the total depth of
54 inches. He calculates that in the mass of soil to that depth the
difference in the amount in the two cases would be far too small
to furnish a justitication for the important conclusion that the soil
was the source of the nitrogen. He objects that the roots of such
herbage would derive their nutriment chiefly in the superficial layers.
He further objects that if the diflerence we assume were a fact, it is
probably due to an accidental difference in the soil of the two plots,
such a difference having been admitted by us in the case of another
plot. Lastly, he suggests that if there really were the reduction we
suppose, it might be due to other causes — such as increased activity
of nitrification under the influence of the mineral manure and passage
of the nitrates downwards.
In the first place, in the case of the irregularity in the condition
of one of the plots referred to, the difference was readily seen in the
section of the soil, and there was no such difference in the instance
now under consideratior.
Then it is the determination of nitrogen in the first 9 inches of soil
M
53
alone, to which we have hitherto referred, and to which we confine
attention on the present occasion.
In the nex<- place, that the difference in the condition of the two
plots is not merely local is shown by the fact that the determinations
on a sample from the unmanured plot taken in 1870 entirely confirm
the relative composition shown Ly the samples of 1876. Again, the
lower percentage of nitrogen in the 1876 samples of the mineral
manured plot is entirely confirmed by the results obtained on samples
taken in 1878. Further, of the twenty experimental plots, there is
only one other showing so low a percentage as the mineral-manured
plot, and that is the one which had received the same mineral manure,
but for a shorter series of years.
We have in fact no doubt whatever that the differences indicated by
the figures are real, and dependent on the conditions of manuring and
of growth. The reduction is, moreover, very great, amounting to
nearly one-tenth of the total quantity of nitrogen, and far beyond
the limits of accidental difference in the sampling or the analysis.
Calculated per acre, the sui'face soil of the mineral-manured plot
contained, at the end of the twenty years, 50G pounds less nitrogen than
the soil oi the unmanured plot to the same depth, corresponding to an
annual reduction of 25"3 pounds of nitrogen per acre per annum. It
is, to say the least, a very remarkable coincidence that the in'^reased
yield of nitrogen in the crop on the mineral-manured plot which has
to be accounted for is 22'6 pounds per acre per annum.
We do not pretend to claim absolute accuracy for such results, but
we ourselves entertain no doubt whatever of their significance and
their importance.
It will be asked — How is it that in the case of the red clover, and
the melilotus, it was concluded that, so far as the plants had derived
their nitrogen from the soil, it was at any rate mainly from the lower
depths, and that here, in the case of the permanent mixed herbage
plots, we assume the increased yield of nitrogen to be derived from
the surface soil ?
Under the influence of the mineral manure, a larger proportion
and amount of leguminous herbage was developed than on any other
p,ot ; but the leguminous plant the most, indeed very prominently,
favoured was the Lathyrns p-atensis, which throws out an enormous
quantity of root near the surface ; and it is sufficiently established
that the potash of artificial manures remains almost exclusively in the
superficial layers. On the other hand, the perennial red clover, and
the Lotus corniculatus, which have a much more deeply-rooting ten-
dency, are comparatively little encouraged.
D 2 '
I!
54
The actual amount of leguminous herbage produced, however, is
not sufficient to account for nearly the whole of the increased yield
of nitrogen in the produce of the plot. The fact is that, besides a
porportionally very large increase in the growth of leguminous her-
bage, there has been a gradually increasing amount of gramineous
produce developed ; far beyond what would be anticipated from the
extremely limited effect of such manures on gramineous crops grown
separately on arable land. How far this result may be due to an
increased tendency of the grasses to form stem, and to ripen, under
such conditions ; — how far to more active nitriBcation induced under
the influence of the mineral manure in the much more highly nitro-
genous gi'ass-land than in the poorer arable soil, and so yielding a
direct supply to the Gi-amineoe of the mixed herbage ; — or how far to
an increased supply in a condition available for the grasses as the
result of a previously increased growth of the Legumiuosse, may be
a question. But it is of interest to note that the gramineous species
that are developed are among the most superficially rooting of the
grasses found on the experimental plots.
Before leaving the subject of these experiments on the mixed
herbage of grass land, it may be well to call attention to the fact that,
on the assumption that the whole of the nitrogen of the herbage,
beyond the small amount of already combined nitrogen coTjtributed by
rain and condensation from the atraosphe*"e, is derived from the soil,
we have to conclude that about 25 pounds per acre per annum have
been yielded by the soil of the unmanured plot, and nearly an addi-
tional 25 pounds, or in all about 50 pounds, from the mineral-
manured plot. It was estimated that, in the case of the continuous
wheat experiments, about 20 pounds of nitrogen had been annually
obtained in the crop, and a minimum of 12 pounds lost by drainage ;
in all 32 pounds. It cannot fail to be observed how closely this
amount corresponds with the annual yield of nitrogen (83 pounds) in
the unmanured mixed herbage. With the richer grass-land, tliough less
aerated than arable land, it might be expected there would be some
increased activity of nitrification, even in the unmanured soil ; and
there may be some loss by drainage. But, with a mixed herbage of
some 50 species, of very varying habit of growth, and with the
possession of the soil all the year round, it is only what would be
expected that there would be more of the available nitrogen taken up
by the crop, and less lost by drainage, than with the cereal grown sepa-
rately on arable land, and occupying the soil for only a very limited
period of the year.
We conclude, then, that the results relating to the two mixed
a
3r-
us
he
wn
an
er
er
fro-
a
I
55
herbage plots can leave little doubt that the increased yield of nitro-
gen in the more highly leguminous produce of the mineral-manured
plot had its source in the stores of the soil itself.
Source of the Nitrogen of Glover Grown on Rich Garden Soil.
We have one more illustration to bring forward having an import-
ant bearing on the question of the sources of the nitrogen of the
Leguminosee.
In view of the signal failure in the attempts to grow red clover on
a nitrogen exhausted arable soil, it is of much interest that large,
though declining, crops have been grown for twenty-nine years in
succession on a small plot of rich kitchen- garden soil.
The experiment was commenced in 1854, and the following table
shows the percentage of nitrogen in samples of the first 9 inches of
soil, taken in October 1857, and in IMay 1879 ; that is, with an
interval of twenty-one seasons of growth. In 1857 only one sample
was taken, and only to the depth of 9 inches ; but in 1879 three
samples were taken, in each case to the depth of twice 9, or 18 inches.
The results given in the table relate to the first 9 inches of depth
only : —
Table XVIII. — Clover Grown on Kitchen Garden Soil.
Nitrogen, per cent, in dry Mould, and per Acre.
1857.
1879.
Difference.
Per cent.
Per cent.
0-3C35
0 -3610
0 -3026
Per cent.
0-5095
0-3G3i
0 1461
"Ppi* nr»iv> tnfjil* ........••■'<••« ••
lbs.
9,528
lbs.
6,790
lbs.
2,732
130
The percentage of nitrogen given for the single sample collected in
October 1857, is the mean of determinations made in 1857, 1866, and
* In the original paper, too high an average weight of soil per acre was adopted,
and hence the amounts of nitrogen per acre were estimated to be higher than now
given ; but the difference was only 9 pounds more (139) than according to the
new calculation.
i;'W
If
1
^1
if
i >.:
56
1880, and is almost ideutical with the mean of those made at the latest
date.
The first point to observe is that the first 9 inches of the garden
ground contained more than half a per cent, of nitrogen, nearly four
times as much as the average of the arable soils, and nearly five times
as much as the exhausted clover land soil. It is of course true that
the soil would be correspondingly rich in all other constituents ; but
some portions of the arable soil where clover failed, had received
much more of mineral constituents by manure than had been removed
in the crops.
The means of the determinations made on the three separate
samples taken in 1879 are seen to agree very well, and the results can
leave no doubt that there has been a great reduction in the stock of
nitrogen in the surface soil. The reduction amounts to nearly 29 per
cent, of the total. Reckoned per acre, as shown at the foot of the
table, it corresponds to a loss of 2,732 pounds during the twenty-one
seasons of growth ; and although really good crops are still grown in
mo.st years, there has been, with this great reduction of the stock of
nitrogen in the soil, a very marked reduction in the clover-growing
capability of the soil. Thus, during the first fourteen of the twenty-
nine years of the experiment, seed was sown only three times ; whilst
during the last fifteen years it has been necessary to sow ten times. It
is obvious, therefore, that the plant stood very much longer during
the earlier than the later years. Then, again, the produce from the
three sowings during the first fourteen years was nearly twice as
much as has been obtained since.
The question obviously arises — what relation does the amount of
nitrogen lost by the soil bear to the amount taken off in the crops ?
We quite admit the uncertainty of calculations of produce per acre
from the results obtained on a few square yards. We are, however,
disposed to estimate the average yield of nitrogen over the twenty-one
years between the two periods of soil sampling at about 200 pounds
per acre per annum. The table shows that against this we have an
estimated loss of nitrogen by the first 9 inches of soil of 130 pounds
per acre per annum, corresponding approximately to two-thirds of
the amount estimated in the crop.
There is, however, evidence leading to the conclusion that, in the
case of arable soils to which excessive amounts of farm-yard manuro
are applied, there may be a loss by evolution as free li-^rogen ; and,
obviously, so far as this may have occurred in the garden soil, there
will be the less of the loss determined in the surface soil to be credited
to assimilation by the growing clover.
57
On the other hand, it is known that when growing on ordinary
arable soil, the clover plant throws out a large amount of roots in the
lower layers, and although in the case of so rich a surface soil, the
plant may derive a larger proportion of its nutriment from that
source, we must at the same time suppose that it has also availed
itself of the resources of the subsoil. Unfortunately, we did not
sample deeper than 9 inches in 1857, so that we can make no com-
parison of the condition of the subsoil at the two periods. It may,
however, be observed that, in 1879, the second 9 inches showed about
three times as high a percentage as the subsoils of the arable fields at
the same depth ; indeed, not far from twice as high a percentage as
several of the exhausted arable surface soils. It cannot be doubted,
therefore, that the subsoil of the garden plot has contributed to the
yield of nitrogen in the crop.
If, then, we have not here absolute proof that the source of the
whole of the nitrogen of the clover growing on the garden soil was
the soil itself, we have surely very strong grounds for concluding that
much, and perhaps the whole of it, has been so derived.
General Conclusions.
After this review of the evidence which the determinations of
nitrogen in the soils of our experimental plots afford, we end, as we
began, by saying that, although we admit the facts of production are
not yet conclusively explained, we maintain that there is, to say the
least, much more of direct experimental proof of the soil than of the
atmospheric source of the nitrogen. Moreover, we submit that this
rnay be said, not only c . the source of the nitrogen of the cereals, but
also of that of the root-crops, and of the Leguminosse.
If, on the other hand, the atmosphere is the main, if not the ex-
clusive, source of the nitrogen of the Leguminosoe, we would ask here,
as we have asked elsewhere — why those leguminous crops which take
up the most nitrogen can be less frequently grown on the same soil ?
Why we entirely failed to grow clover successively on ordinary arable
land, which was nevertheless in a condition to yield fairly good cereal
crops ? Why the only condition under which we have been able to
grow clover continuously was where the soil was very much richer in
nitrogen (and of course in other constituents also) than the arable
land ? And lastly, why its growth under such circumstances has been
accompanied by a rapid diminution in the amount of nitrogen in the
soil, and with this a marked decline in the produce ?
It will not for a moment be supposed that because in the foregoing
illustrations and arguments we have confined attention almost ex-
clusively to the nitrogen in the soils, we in any way ignore the
importance of a liberal available supply of the mineral constituents,
so essential for the effective action of the nitrogen. There is abundant
evidence, however, that the failures that have been cited have not
been due to a deficiency of mineral constituents.
If, then, the supply of mineral constituents not being defective,
the yield of our crops is in the main dependent on the amount of
nitrogen which is available to them within th„ period of their growth
from the soil itself, or from manure applied to it, surely the fertility of
a soil must be largely measured by the amount of nitrogen it contains,
and the degree in which it becomes available. And, if this be so, is
not the soil a *' mine," as well as a laboratory ?
In this connection, speaking here in America, it will not be in-
appropriate to conclude with a brief reference, such as the limited
data at our command will permit, to what we believe must be a cha-
racteristic difference between a large proportion of the comparatively
recently, or even not yet, broken up soils of this continent, and those
which have been long under arable culture on the other side of the
Atlantic.
A sample of Illinois Prairie soil, obtained some years ago by Mr.
(now Sir) James Caird, and submitted by him for analysis to Dr.
Voelcker, to whom we are indebted, not only for his own analytical
results, but also for a sample of the soil itself, shows, by almost
identical results in the two laboratories, very nearly 0*25 per cent, of
nitrogen. We have no special history of this soil, nor do we 1 low
the depth to which it was taken ; but Dr. Voelcker informs us that
the sample supplied to us was a mixture of both soil and subsoil as
supplied to him, and that in the separate surface soil he found 0"33
per cent, of nitrogen.
During the present year (1882), between forty and fifty samples of
soil from the North-west Territory, taken at intervals between Win-
nipeg and the Rocky Mountains, were sent over to the High Com-
missioner in London, and exhibited at the recent show of the Royal
Agricultural Society of England, at Reading. The soils were exhi-
bited in glass tubes four feet in length, and are stated to represent
the core of soil and subsoil to that depth. Three samples of the
surface soils have kindly been supplied to us for the determination
of the nitrogen in them : —
No. 1 is from Portage le Prairie, about 60 miles from Winnipeg,
and has probably been under cultivation for several years. The dry
mould contained 0"2471 per cent, of nitrogen.
^MEm'
59
No. 2 is from the Saskatchewan district, about 140 miles from
Winnipeg, and has probably been under cultivation a shorter time
than Wo. 1. The dry mould contained 0'3027 per cent, of nitrogen.
No. 3 is from a spot about 40 miles from Fort Ellis, and may be
considered a virgin soil. The dry mould contained 0'2500 per cent, of
nitrogen.
In general terms it may be said that these Illinois and North-west
Territory Prairie soils are about twice as rich in nitrogen as the average
of the Rothamsted arable surface soils ; and, so far as can be judged,
they are probably about twice as rich as the average of arable soils
in Great Britain. They indeed correspond in their amount of nitrogen
very closely with the surface soils of our permanent pasture land. As
their nitrogen has its source in the accumulation from ages of natural
vegetation, with little or no removal, it is to be supposed that, as a
rule, there will not be a relative deficiency of the necessary mineral
constituents.* Surely, then, these new soils are " mines " as well as
laboi-atories ? If not, what is the meaning of the term a fertile soil ?
Assuming these soils not to be deficient in the necessary mineral
supplies, and that they yield up annually in an available condition an
amount of nitrogen at all corresponding to their richness in that con-
stituent, it may be asked — whether they should not yield a higher
average produce of wheat per acre than they are reported to do ?
The exhausted experimental wheat field at Rothamsted, the sur-
face soil of which at the commencement of the experiments thirty-
nine years ago probably contained only about half as high a percentage
of nitrogen as the average of these four American soils, yielded over
the first eight years 17|; over the next fifteen years, 15| ; over the
last fifteen years (including several very bad seasons), only 11]|
bushels ; and over the whole thirty-eight years about 14 bushels per
acre per annum.
So far as we are informed, the comparatively low average yield
of the rich North-west soils is partly due to vicissitudes of climate,
partly to defective cultivation, but partly, also, to the luxuriant
growth of weeds, which neither the time at command for cultivation,
nor the amount of labour available, render it easy to keep down.
Then, again, in some cases, the straw of the grain crops is burnt, and
manure is not retu ned to the land. Still, if there be any truth in the
* Since the above was in type, we have seen Dr. Voelcker's report on the Illinois
Prairie soil above referred to, and find he caUed attention to its richness in potash
and other mineral constituents. He also called attention to the much higher per-
centage of nitrogen in it than in the soils of this country which he and others had
analysed.
60
views we have advocated, it would seem it should he an ohject of
consideration to lessen, as far as practicable, the waste of fertility of
these now rich soils. At the same time it is obvious that, with laud
cheap and labour dear, the desirable object of bringing these vast
areas under profitable cultivation cannot be attained without some
sacrifice of their fertility in the first instance, which can only be
lessened as population increases.
HAEBIBQir AND aONfl, PEINTEE8 IN OEDINABY TO HKB MAJE8TT, 8T. MAETIn'b IAKB.
Live Music Archive
Librivox Free Audio
Metropolitan Museum
Cleveland Museum of Art
Internet Arcade
Console Living Room
Books to Borrow
Open Library
TV News
Understanding 9/11