United States Department of Agriculture^

BUREAU OF CHEMISTRY.

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\ 1'LAX FOK COOPERATING IN TIIK STUDY OF AYAILAISLK
PLANT FOOD.

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At the San Francisco meeting of the American Association of
Agricultural Colleges and Experiment Stations in isw), a committee
on cooperative work between stations and the Department was
appointed.

The report of this committee was most favorable, especially with
reference to the desire for cooperation on the part of station workers.
Among the suggestions from the committee is the following :

"A fourth type of cooperation is seen in those investigations which
require the combined work of many stations, for example, an attempt
to obtain definite information on the changes produced in plants by
environment, and the value of this factor in the study of the vary-
ing effects of soil and climate in some single crop. Such experiments
call for the work of many stations at the same time. It is manifest
that the uniformity and efficiency of the work would require that
such cooperation be arranged and supervised by some central organi-
zation; and it is equally manifest that the Department is best pre-
pared to undertake the task."

In accordance with this suggestion, the Bureau of Chemistry
two years ago arranged for cooperative experiments as to the effect
of environment on the chemical composition of plants, and it now
desires to arrange a cooperative study of the methods for determin-
ing available plant food in soils, not only between the stations and
tin- Department of Agriculture, but between the stations themselves
and farmers who will be interested in the work.

The intention is to arrange a systematic plot study, in which the
sr.MJing of the plots, sampling of the soil, harvesting of the crop, and
tin- chemical study of the soil will be the same in every detail, and
will be carried out by each of the stations taking part in the work,
there being a distribution of the material and results obtained from
rarli station among all stations taking part. From the analysis of
the crop will be determined the ability of the soil to supply plant
food, while upon the soil sample, taken previous to planting, efforts
will be made to secure chemically, as near as possible, the result
obtained by the crops.

As a basis for analytical work, a method for the estimation of avail-
able P3O5 and K>O is proposed by this Bureau. Detailed instruction

as to the use of this method is given, and every station is asked to
follow it minutely. In addition to this, it is asked that other methods
be suggested by the stations, which will be submitted to all taking
part, and, upon the general approval of any one method, it will be
used by each according to the detailed instructions as arranged by
the author, it being understood that no one will offer a method for
trial until he has worked it out to his own satisfaction. After the
work above indicated has been completed, individual study on the
soils can be taken up, and where the study gives promise of success
and the method has been reduced to its simplest form, it can be sent
to the other stations cooperating, with the expectation that it shall
be used according to explicit directions.

If all proposed methods have been carefully worked over by their
authors, it will require but little time for the stations to apply the
methods and send in the results, which results will be distributed.
In instances where the stations are too busy on other lines to make a
specialty of the work, it will be sufficient for them to do only the
proposed work, leaving it for such as are especially interested in this
line to formulate and experiment on methods.

In this it may be seen that there is much room for individual
effort upon collective material, while those who supply the collective
material will have access to all data and proposed methods, with the
privilege of suggesting and amending.

It is arranged to make a study of one soil with four kinds of crops,
this Bureau undertaking to supply the seed and all apparatus as far
as possible, analyze the crops, receive the soil samples and prepare
and distribute the subsamples for analysis, in addition to running a
control-pot of each plot.

The work in detail is as follows :

Select a plot 60 feet square on even, homogeneous soil — if possible,
one which has never had any fertilizer, especially P2O5 nor K2O. It
is immaterial whether old or new ground is used, it being hoped that
all kinds will appear in the collection of results. On this plot run
lines from the centers of the opposite sides, as illustrated in the dia-
gram (fig. 1).

This makes four plots of about 1-50 acre each. In the center, at
the intersection of the lines, the soil sample is to be taken. In tak-
ing this sample, use the measure which will be sent for laying off
the surface. This measure consists of a tape attached to three
pegs, so as to form an equilateral triangle of 3 feet on the sides.
After putting one peg in the ground, draw tight one side of the tape
and drive in the second peg; then draw tight the two remaining
sides of the tape and drive in the third peg. With a spade dig out
the enclosed area to a depth of 9 inches, having the sides of the
hole vertical. Place all of this soil in the sacks which will be sent,

being careful to have the pit cleaned down to an even depth of 9
inches. The sack should be labeled: "First nine inches," with the
name of the station. Then obtain the second 9 inches in a similar
manner, being careful to label accordingly. These sacks should be
forwarded to the Department, where each sample will be weighed,
thoroughly mixed, put through a 2-mm. sieve, subsampled, and dis-
tributed, about forty pounds being retained for the control-pot
experiment. The moisture and basicity of all the samples will be
determined and the figures supplied, so that the results will be on
the same moisture-free basis, with the same correction for basic
matter. These figures will be sent out with the samples.

Oak.

Sprint]
Barley.

, foil Sample

Spring
Bye.

Spring

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FIG. l.- Experiment plot, 60 feet square, 1-50 acre in each small square.

In the seeding of the plots the soil is to be prepared by ordinary
plowing and smooth harrowing. Packages containing the four
kinds of seed will be supplied, and the entire contents of each pack-
are to be sown broadcast as uniformly as possible and covered
with a harrow. This will give a uniform rate of seeding with a uni-
form variety of seed. The plots will require no further attention
until harvest time. During the interval, work on the soil samples
can be progressing. When the crops are ready for harvesting use
tli" triangular cord measure, which will be supplied, and lay off a
definite area in the center of each of the four plots. This measure
will be a cord with three pegs attached, so that when all sides are
drawn tight it forms an equilateral triangle of 0.3 feet on each side,

equaling nearly 1-2500 of an acre. The method of procedure is the
same as that prescribed for the soil sample, namely : Drive in one peg ;
stretch one side of the tape and drive in the second peg; then stretch
the two remaining sides and drive in the third ; cut the inclosed crop
even with the ground, taking care to lose no grain by shattering.
Place the total crop in the bag which is supplied, label carefully and
forward to the Department, where it will be dried, weighed, ashed,
and analyzed, and the material and analyses distributed, the whole
being calculated to pounds per acre of the different parts of the crop
removed.

One method for the determination of available P2O5 and K2O,

FIG. 2.— Shaking machine for soil extraction at constant temperature.

which this Bureau proposes, has been worked out in connection with
a very elaborate research. It has been printed as a contribution
from this Bureau in the Journal of the American Chemical Society,
Vol. 24, page 79, and a reprint has been prepared for distribution.

A very simple and inexpensive form of shaking machine (fig. 2)
has been designed for this work, which, with the accompanying
flasks, will be supplied. By the use of this apparatus it is possible to
have a uniform agitation and temperature throughout the work.
The machine may be run by any motive power at hand at the speed
of about 40 revolutions per minute. The temperature is kept at
40° C. by means of a flame under the air chamber, and owing to the

stirring of the air inside, and especially by use of a thermostat, the
temperature can be kept within one-half degree of that specified.

The method of digestion in detail is as follows :

Weigh and place in one of the digestion flasks the quantity which
will be specified in a supplementary table, this weight being based on
tin- moisture found to be in the sample and equivalent of 186 grains
of dry soil. Measure out the number of cubic centimeters of N-10
HC1, which will be given in the supplementary table, and dilute to
1 liter. This table is based upon the basicity of each soil sample.
Half fill the flask containing the soil ; shake with the diluted HC1
thoroughly, so as to displace the air held in the soil, and then fill up
to the neck with the dilute acid. The contents of the flask will be
the equivalent of 200 grams of soil in one litre of N-200 HC1. The
ilasks are stopped with rubber stoppers, which must be tied in.
Fasten the flasks in the shaking machine and digest for five hours
at 40° C., the apparatus making about 40 revolutions per minute.
This has the effect of keeping the soil constantly suspended in the
liquid, insuring a maximum and constant effect of the solvent.

At the close of the digestion the flask with its contents is shaken
well and emptied into a 32 cm. fluted filter. Unless the sediment is
poured on with the liquid the filter will become clogged. The first
part of the filtrate is generally cloudy and is poured back as soon as
the liquid has begun to run clear. A small filter first placed in the
funnel will prevent the breaking of the larger paper when it is
1< >aded. These filtrates generally drain through in less than an hour,
and the volume is found to be so near 800 c. c. that it is not neces-
sary to measure. To the filtrate is added 2 or 3 c. c. of HNO3 and
about 10 c. c. of HC1, and it is evaporated to dryness in a porcelain
dish G or 8 inches in diameter on the steam or water bath. The HNO:l
roys organic matter in solution and drives off any ammonium
chloride which may have resulted from the liberation of ammonia in
tin process of digestion, and which, if present, would subsequently
interfere with the determination of potash. To the residue in the
dish is now added strong HC1, at first slowly, to prevent loss by
spurting. It is then evaporated until the nitrates have become com-
pletely converted into chlorides, which can be told by the absence of
i eenish tinge and fumes upon the addition of HC1 to the dry
residue.

It sometimes requires from 50 to 100 c. c. of HC1 before the con-
ion is completed. When complete, the solution is evaporated to
dryness and cooled; then a few drops of HC1 are added and about
r 30 c. c. of water, and the whole is warmed on the bath until
solution is secured.

Filter to remove silica and wash until clean. To the filtrate, which
corresponds to IfiO grams of soil, in a :j or 4-inch porcelain dish, add

about 1 c. c. of the ordinary platinic chloride solution and evaporate
on the steam or water bath according to the usual method for
determination of K2O, being careful to trail the liquid around the
side of the dish as it becomes concentrated and to remove just before
dryness, so as to have the evaporation completed during the cooling
of the dish. This procedure insures a very perfect formation of
crystals of the double salt. To the dish is now added about 20 or
30 c. c of acidulated alcohol. The preparation of this reagent will
be described later. The dish is allowed to stand 3 or 4 minutes
with an occasional stirring, then decanted into a 7 cm. filter. The
salt is now washed into the filter with 90 per cent alcohol, as usual,
until free of platinic chloride. Now wash with the ordinary Lindo
solution of ammonium chloride (200 grams per liter of water), using
about 20 c. c., and allow these washings to mix with the previous
filtrate. The filtrate is stirred and set aside overnight to allow the
ammonium platinum chloride to settle. The salt in the filter is then
washed with 90 per cent alcohol until free of ammonium chloride.
The filter is then dried and the contents washed through with
boiling water into a previously weighed small platinum dish, which,
after evaporation and drying in a bath for thirty minutes at 100° C.,
is weighed. The calculated weight of the K2O is to be divided by
160 grams. This is to be expressed in parts per million, a part per
million being the equivalent of the fourth .decimal place in percentage.

The acidulated alcohol is prepared by conducting HC1 gas into cool
90 per cent alcohol until 1 c. c. of the alcohol neutralizes about
2^ c. c. of normal alkali, using phenolphthalein as an indicator.

The method of acidifying is as follows :

Put 200 or 300 c. c. of strong HC1 into a rather large flask, con-
nect by means of a glass tube with a flask holding about one-half
liter of 90 per cent alcohol, this flask being kept cool by surrounding
with ice or running cold water. The tube containing the gas extends
to the bottom of the alcohol. A trap is interposed between the flasks
to prevent the alcohol running back into the acid in case the pressure
is varied. The flask containing the acid is heated moderately until
water begins to pass over, when the process is discontinued, to be
renewed with a fresh portion of acid if the alcohol is found to be not
sufficiently acidulated. The apparatus as used in this laboratory is
illustrated in fig. 3.

After the filtrate from the potash determination above referred
to has stood over night, nearly all of the liquid can be decanted
into a porcelain dish of 5 or G inches diameter. Then with ordinary
alcohol wash directly into a filter, washing two or three times, and
adding the washings to the decanted liquid in the dish. Any sedi-
ment that may have gone over in the decantation can do no harm.
The evaporation should be carried on very slowly on a steam < >r

water bath, else the alcohol will boil over. When the alcohol has
evaporated there will be left a large amount of ammonium chloride
in the residue. Care must be taken that all the alcohol is volatilized,
after which the residue is dissolved in about 30 or 40 c. c. of water.
T<> the solution add 2 or 3 c. c. of HNO;{; cover and heat on the bath
very gradually (else there will be a violent ebullition due to the liber-
al i«>n of nitrous oxide). When ebullition has subsided, remove the
cover and evaporate to dryness; then to the dish when cooled add
two or three drops of HNOa, 10 or 15 c. c. of water, and warm until
solution is effected. Wash from the dish with a minimum quantity
of water into a beaker of suitable size for the determination of P-( ).-,,
volumetrically.

To this solution add about a teaspoonf ul of dry ammonium nitrate ;
let stand in a water bath at a temperature of about 50° C. ; add 10 or

FIG. 3.— Apparatus for preparing acidulated alcohol.

1 .') c. c. of the ordinary molybdate solution, and let stand about thirty
minutes, \vith an occasional shaking. Decant through a 9 cm. filter;
wash the precipitate into the filter, and continue the washing until
live of acid, by test with phenolthalein or litmus. It generally
iv.juires about 200 c. c. of water for this washing. The filter and
its contents are returned to the beaker, and by the use of a stirring
md and a little water the paper is beaten into a pulp. The titration
is made in the usual way, with KOH and HC1, using phenolthalein
in indicator. In this laboratory the alkali used is one-half the
otHeial strength; that is, 100 c. c. neutralizes 16.19 c. c. of normal
acid. This makes 1 c. c.=.0005 gram P8OS. The weight of P < >
here found is to be divided by 1GO grams, and the result expressed in
parts per million, as was that for K2O.

As will be seen, in this method the total weight of soil is used in
each determination instead of dividing the solution, as is generally

done. The large amount used adds greatly to the accuracy of th<>
results. Having found the parts per million of these ingredients in
the soil, and having the dry weight of the original sample, which
was taken over a definite area, it is a very simple matter to calcu-
late to pounds per acre for the depth to which the sample was taken.

It is believed that this method will give the amount of plant food
which is in condition to be taken up by the oat plant, provided there
is a suitable balance in such plant food. It is the result of experience
in a large number of analyses. The calculation in pounds per acre
in this work is on the assumption that plant food does not exist to a
greater depth than 18 inches.

It is desired that those who wish to cooperate in the work will
notify this Bureau as soon as possible, as arrangements should be
made without delay.

C. C. MOORE,

In Charge of Soil Analysis Laboratory.
Approved :

JAMES WILSON,

Secretary.

WASHINGTON, D. C., January 3, W02.

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