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IC-NRLF



SB 75 3fiD



LABORATORY MANUAL



FOR



SOIL FERTILITY



CYRIL G. HOPKINS

AND

J. H. PETTIT






LIBRARY

COLLEGE OF

AGRICULTURE

Berkeley. Cai.



LABORATORY MANUAL

FOR

SOIL FERTILITY



BY
CYRIL G. HOPKINS

AND

J. H. PETTIT



\



NOTE. The student practices described in this laboratory manual are
the result of five years' experience by the authors in conducting classes in
a course of study in soil fertility. With some modifications the usual
chemical methods are employed, specific chemical directions being com-
monly based upon those adopted by the Association of Official Agricultural
Chemists. Otherwise these practices were originated in this University.

The increasing number of students in this institution, and the fact that
some other institutions also desire to use our manual, induced us to put
it in printed form.

Suggestions from other teachers of soil fertility regarding possible im-
provements in the manual will be gladly received.

THE AUTHORS.

College of Agriculture, University of Illinois,
Urbana, 111., July, 1905.



LIST OF STUDENT APPARATUS.



2 Bunsen burners with rubber hose.
2 Ring stands.
6 Rings (3 sizes).

1 Burette clamp.

2 Triangles, pipe-stem.

2 Erlenmeyer flasks, 200 cc.

2 Erlenmeyer flasks, 300 cc.

2 Beakers, 250 cc.

2 Beakers, 400 cc.

2 Beakers, 600 cc.

2 Kjeldahl flasks, 500 cc.

2 Copper flasks, 500 cc.

1 Bottle, 2500 cc.

2 Bottles, 1000 cc.
2 Bottles, 500 cc.

2 Bottles, 250 cc.
2 Crucibles, 25 cc.
2 Crucibles, 14 cc.
i Wash bottle, 1000 cc.

1 Funnel, 15 cm.

2 Funnels, 10 cm.
4 Funnels, 6 cm.

1 Pair crucible tongs.

2 Evaporating dishes, 8 cm.



2 Evaporating dishes, 10 cm.

I Graduated cylinder, 100 cc.

i Graduated cylinder, 25 cc.

i Burette, 50 cc.

i Pipette, 25 cc.

i Graduated pipette, 10 cc.

1 Desiccator.

2 Test tubes.

1 Double condenser with connect-

ing tubing.

2 Watch glasses.
2 Pinch cocks.

i Percolator, 500 cc.

i Measuring flask, 250 cc.

1 Bone spoon.

2 Safety distillation bulbs with rub-

ber stoppers.

1 Pair forceps.

2 Bottles, 400 cc., with corks,
i Thermometer, 100 C.

10 Glass battery jars, 5 liters, with
i cm. drainage hole in the side,
i cm. from the bottom.

2 pieces of iron gauze with asbestos
center.



3 C 5784



PRACTICE I.
PREPARATION OF A STANDARD HYDROCHLORIC ACID SOLUTION.*

By the use of a hydrometer and specific gravity tables prepare five
liters or more of approximately one-half normal hydrochloric acid, using
chemically pure concentrated acid and ammonia-free water.

Standardize by the silver nitrate method : Place exactly 25 cc. (note
temperature of stock solution when measured out) of the acid solution,
measured with a pipette, in a 300 cc. Erlenmeyer flask, dilute to 75 cc., add
at once from a burette sufficient $% silver nitrate solution to nearly, but
not quite, precipitate all the chlorin. Close the flask with a clean rubber
stopper and shake till the precipitate will settle nearly completely in a short
time. Then add the silver nitrate in i cc. portions, shaking after each
addition, until the precipitation is complete, avoiding more than I cc. ex-
cess of silver nitrate solution.

Shake until the silver chlorid settles well, wash three times by decanta-
tion (after shaking each time) using about 100 cc. of water containing I cc.
concentrated nitric acid per liter and decanting the liquid through a 9 cm.
filter. Transfer the precipitate to the filter, dry, transfer the bulk of the
precipitate to a watch-glass or crucible, and burn the paper in a weighed
crucible. Add 2 to 5 drops of concentrated nitric acid to dissolve reduced
silver and then 2 to 5 drops of concentrated hydrochloric acid. Evaporate
to dryness without spattering, add the main precipitate, dry to con-
stant weight at I20 9 to 130, cool in a desiccator, and weigh.

Record the weights of silver chlorid from duplicate 25 cc. portions of
the standard hydrochloric acid.



*To be done by the instructor.



6

PRACTICE 2.
PREPARATION OF A STANDARD AMMONIA SOLUTION.

Determine, by hydrometer, the specific gravity of concentrated am-
monia and calculate, by the use of a specific gravity table, the number of
cubic centimeters necessary to make two liters of approximately one-fifth
normal ammonia solution.

Sp. Gr ,

Grams NH 8 per cc

Grams NH 3 per liter in normal solution

Grains NH 3 in two liters of 1-5 normal solution

Cc. of cone. NH 3 equivalent to g. NH 3

Measure out the required amount of concentrated ammonia, add dis-
tilled water to make the total volume up to two liters, and mix thoroughly.
Standardize by titrating 10 cc. of the standard hydrochloric acid with the
ammonia solution, using lacmoid as an indicator. Make three titrations.

(1) 10 cc. HC1 is equivalent to cc. NH 3

(2) 10 cc. HC1 is equivalent to cc. NH 3

(3) 10 cc. HC1 is equivalent to cc. NH 3

Average c.c. NH 3

1 cc. NH 3 is equivalent to Mg N.

Give reactions in first and second practices, and explain the computa-
tions involved in ascertaining the weight of nitrogen in I cc. of the stand-
ard ammonia solution.



8

PRACTICE 3.
BLANK DETERMINATION OF NITROGEN IN REAGENTS USED IN DISTILLING.

Place 250 cc. of ammonia-free water in a copper flask, add 10 cc. of con-
centrated alkali solution (made by dissolving 1000 gm. sodium hydroxid
and 25 gm. potassium sulfid in 1000 cc. water), pouring carefully down the
side of the flask, connect with the condenser, shake the flask thoroughly,
heat up- slowly and distill into a 300 cc. Erlenmeyer flask containing 10 cc.
of the standard hydrochloric acid and about 15 cc. ammonia-free water.
The end of the delivery tube should dip into the acid solution. Distill to
a volume of 200 cc. Add lacmoid and titrate with standard NH.3.

Titration (1) cc. NH 3

Titration (2) cc. NH 8

Average cc. NH 3

State correction in cc. of standard NH 3 .

Explain all reactions involved, including the use of the indicator.



10

PRACTICE 4.
PREPARATION OF AN AMMONIUM SULFATE SOLUTION.

Weigh out exactly in a weighed crucible the number of grams of chemi-
cally pure ammonium sulfate (assuming the salt to be dry) equivalent to
500 cc. of the standard ammonia solution. Dry in the air bath at 115 to
120 for thirty minutes, cool in a desiccator, and weigh. Dissolve in am-
monia-free water in a 250 cc. measuring flask. Dilute to exactly 250 cc.
Mix well, and transfer to a dry 250 cc. bottle. Label and keep stoppered
when not in use.

500 cc. standard NH 3 contains gm. N

Percent N in (NH 4 ) 2 SO 4 by theory is

500 cc. NH 3 is equivalent to gm. (NH 4 ) 2 SO 4

Before After

ELeating Heating

Weight of crucible+(NH 4 ) 2 SO 4 =

Weight of crucible =

Weight of (NH 4 ) 2 80 4 =

Percent dry matter in salt is

How much of the ammonium sulfate will it be necessary to weigh out
in order to have exactly 5 gm. of the dry salt?



12

PRACTICE 5.
DETERMINATION OF NITROGEN IN AMMONIUM SULFATE.

Place 10 cc. of the ammonium sulfate solution in a 500 cc. copper flask,
add 240 cc. ammonia-free water and then add carefully, by pouring down
the side of the flask, 10 cc. of the concentrated alkali. Connect immedi-
ately with the condenser, shake the flask thoroughly, heat slowly, and dis-
till into a 300 cc. Erlenmeyer flask containing 10 cc. of the standard hydro-
chloric acid and about 15 cc. of ammonia-free water, to a volume of 200 cc.
Add lacmoid and titrate the excess acid with standard ammonia.



Titrations (1) ................................ cc.

(2) .................................. cc.NH 3

Average ..................................... cc. NH 3

Mgs. N in sample .....................................

Percent N in dry salt ...............................

The percentage purity of the dry salt is ................

Explain all reactions.

Does the percentage of nitrogen vary directly or inversely with the ti-
tration readings?



14

PRACTICE 6.
FIXATION OF BASES IN SOILS.

(a) Place a small bunch of glass wool in a percolator, cover with i cm.
of clean sand, and add 100 gm. of clayey soil. Upon this carefully pour
250 cc. of dilute ammonium sulfate solution (50 cc. of the solution pre-
pared in Practice 4, plus 200 cc. of ammonia-free water). When percola-
tion ceases, mix the percolate thoroughly and determine nitrogen in two
50 cc. portions.

Titrations (1) cc. NH 3

(2) cc.NH 3

Average , cc. NH 8

Mg. N per cc. in solution used

Mg. N per cc. in percolate

Percent N fixed by soil

(b) Repeat the experiment, using 200 gm. of the same soil.

Titrations (1) cc. NH 3

(2) cc.NH 3

Average cc. NH 3

Mg. N per cc. in solution used

Mg. N per cc. in percolate

Percent N fixed by soil

(c) Repeat the experiment, using 200 gm. of sandy soil.

Titrations (1) cc. NH 3

(2) cc. NH 3

Average cc. NH 3

Mg. N per cc. in solution used ...

Mg. N per cc. in precolate

Percent N fixed by soil

Give a general reaction for the fixation of bases by soils and explain
fully what chemical elements that are important in soil fertility may be
retained in soils by means of this reaction.



16

PRACTICE 7.

NITRIFICATION.

Dilute 20 cc. of the standard ammonium sulfate solution to 500 cc.,
add. 3 gm. of dipotassium phosphate, 5 gm. of calcium carbonate, and
about 2 gm. of fresh rich garden soil. Mix well, let settle, and draw off
two loo cc. portions.

Place 500 gm. of clean washed and dried white sand in a percolator.
Upon this pour 100 cc. of the above solution and immediately wash the
sand with about 500 cc. of ammonia-free water, collect the washings and
make up to exactly 500 cc. Place 250 cc. portions in copper flasks, add 10
cc. of alkali and determine the nitrogen in the usual way. Compare the
amount of nitrogen distilled as ammonia with that originally applied in
the ammonium sulfate.

Titrations (1) cc. NH 3

(2) cc. NH 3

Average cc. NH 3

Mg. N found

Add the other 100 cc. portion of ammonium sulfate solution to 500
grams of clean, washed and dried sand in a percolator and allow to stand
in a dark place at warm room temperature for four weeks. Then wash
out and determine the ammonia nitrogen as directed above.

Titrations (1) cc. NH 3

(2) cc. NH 3

Average cc. NH 8

Mg. N found

Percent N nitrified

What change has been brought about and how?
Explain fully.



18

PRACTICE 8.

DETERMINATION OF NITROGEN IN REAGENTS.

Measure out exactly 10 cc. of the concentrated alkali in a beaker and
dilute to 200 cc. with distilled water. Stir and add slowly (finally drop by
drop) concentrated sulfuric acid until the alkali is neutralized, as shown
by the change of color.

10 cc. alkali are equivalent to cc. H 2 SO 4

How many cc. of alkali are necessary to neutralize 20 cc. H 8 SO 4 ?

Place approximately 2 grams of pure sugar in a Kjeldahl flask, add by
measure approximately .650 gm. metallic mercury and 20 cc. sulfuric acid.
Digest in a ventilated hood over a low flame till colorless, add carefully,
while still boiling hot, powdered potassium permanganate until the solution
is green. Allow to cool. Transfer with 200 cc. of ammonia-free water to
a copper flask by means of a large funnel supported on an iron ring. Add
carefully sufficient concentrated alkali to neutralize 20 cc. of concentrated
sulfuric acid, connect with the condenser, shake until thoroughly mixed,
and distill as usual.

Titrations (1) cc. NH 3

(2) cc. NHa

Average cc. NH 8

Check up the standard ammonia solution by titrating against the stand-
ard hydrochloric acid solution.

Correction for nitrogen in reagents in terms of standard ammonia so-
lution cc.

Explain the use of the sugar. Give the reaction between the sugar and
the sulfuric acid. Why is the mercury used? the potassium permanganate?
the potassium sulfid?



20



PRACTICE 9.
DETERMINATION OF NITROGEN IN FARM PRODUCE.

Each group of students will work upon one of the following materials :

1. Wheat 5. Oats.

2. Corn. 6. Red Clover Hay.

3. Corn Stover. 7. Alfalfa.

4. Corn Cobs. 8. Oat Straw.

Weigh out exactly 2 gm. of the material numbered with your group
number and determine the nitrogen in it according to the method given
in the Eighth Practice.

Titrations cc. NH 3

cc. NH 3 Percent N

Average cc. NH 3

Calculate the results obtained and with these record the results ob-
tained by three members of each group as indicated upon the following
page, valuing nitrogen at 15 cents per pound. How many tons of red clover
must be plowed under in order to supply in this way the nitrogen for a
loo-bushel crop of corn and a 75-bushel crop of oats in a corn, oats and
clover rotation ?

Compute the pounds of nitrogen required to produce the crops given
in the table below. Compute the weight of sodium nitrate (95% pure),
which would supply the nitrogen found in these crops, and the cost of the
same.



KIND OF PRODUCE


Pounds
N in
Produce


Pounds
NaN0 3
equiv.


Cost
of

NaNO 3


(1) 85 bu. shelled corn








(2) 1 200 Ib. cobs








(3) stover, wt. equal to (1) -t~ (2)








(4) 75 bu. oats








(5) 4000 Ib. oat straw








(6) 3 tons clover hay








Total for three crops









PRACTICE 9 (Cont.)



NAME OF STUDENT


KIND OF PRODUCE


Percent N


N ii


i 1 ton








Ib.


Value
































AVERAGE








































AVERAGE








































AVERAGE








































AVERAGE








































AVERAGE








































AVERAGE








































AVERAGE








































AVERAGE











22

PRACTICE 10.
DETERMINATION OF NITROGEN IN ANIMAL EXCREMENTS : SOLID AND LIQUID.

Each group of students will work upon one of the following :

1. Horse excrements.

2. Steer excrements.

3. Cow excrements.

4. Sheep excrements.

5. Swine excrements.

6. Poultry excrement and fresh cow's milk.

7. Human excrements.

8. Wheat straw and manger refuse (for bedding).

Record age and condition of animals and food rations as nearly as
possible in all cases.

For solid excrements : Weigh out 10 grams of fresh substance on filter
paper, placed on a watch-glass, and transfer both paper and excrement to
a Kjeldahl flask.

For liquid excrement: Measure out 10 cc. and place in a Kjeldahl
flask. Compute weight from specific gravity .................... gm.

Solid Liquid.

Titrations (1) .............. cc. NH 3 Titrations (1) .............. cc. NH 8

(2) .............. cc.NH 3 (2) ............ cc.NH 3

Average ................... cc. NH 3 Average ............... . . cc. NH 3



Calculate the results obtained and with these record the results obtained
by three members of each group as indicated upon the following page.
Value N at 15 cents per pound.

10 tons alfalfa hay contain ......................... Ib. N

i ton fresh cow dung contains ...................... Ib. N

How many tons of fresh cow dung would be required to furnish nitro-
gen for 10 tons of alfalfa hay?



PRACTICE 10.-(Cont.)



NAME OF STUDENT


Kind of
Manure


Percent N


Lb. N per ton and value


Liquid


Solid


Liquid


Value


Solid


Value


















































Average






























































Average


























































i




Average






























































Average





























































Average






























































Average






























































Average






























































Average















24



PRACTICE ii.

DETERMINATION OF NITROGEN IN FERTILIZERS.

Weigh out Yz gram of each of the following materials and use 20 cc.
of standard hydrochloric acid in the receiver.

(a) Ammonium sulfate.

(b) Dried blood.

(c) Sodium nitrate. (Use the Kjeldahl method modified for nitrates.
Mix 2 gm. salicylic acid with the sodium nitrate in flask and add 30 cc.
sulfuric acid. Use i l / 2 times the usual amount of alkali in the distillation
to neutralize the larger amount of sulfuric acid.)



Titrations
cc. NH 3


Average
corrected


cc. NH 3
from sample


Percent N


Value per ton
(N 15c. perlb.)


<a) (1)










(2)










(b) (1)










(2)










(c) (1)










(2)











How would the reaction of the soil be affected by the residues left by
each of these materials when used to supply nitrogen for plant growth?



26

PRACTICE 12.
DETERMINATION OF NITROGEN IN SOILS.

Each group of students will work upon one of the following :

1. Surface of gray silt loam.

2. Subsoil of gray silt loam.

3. Surface of brown silt loam.

4. Subsoil of brown silt loam.

5. Surface of black clay loam.

6. Subsoil of black clay loam.

7. Sandy soil.

8. Peaty soil (use 5 gm. soil and 20 cc. standard HC in receiver.)
For all soils except peat weigh out 10 gm. air-dry soil and use 10 cc.

of standard hydrochloric acid in the receiver.

Titrations (1) cc. NH 3

(2) , cc.NH 3

Average cc. NH 8

Percent N

Calculate the results obtained and with these record the results ob-
tained by three members of each group as indicated upon the following
page.

Assuming there are 2,000,000 Ib. in an acre to the depth of seven
inches, how many pounds of nitrogen are there in this plowed soil? How
many loo-bushel crops of corn will this produce if the total crop is re-
moved ?



PRACTICE 12. (Cont.



NAME OF STUDENT


Kind of Soil


Percent

N


Pounds of N
Per Stratum


No. of 100-bu.
Crops of Corn
Equivalent
































AVERAGE




















-


















AVERAGE






































AVERAGE






































AVERAGE






































AVERAGE






































AVERAGE






































AVERAGE






































AVERAGE









28

PRACTICE 13.

Determine nitrogen in some soil or other material in which you are
interested, reporting to the instructor the material decided upon before
undertaking the work.

The results of the whole class shall be collected by each man and tabu-
lated as follows :



NAME OF STUDENT



Material



Source



Percent N



30

PRACTICE 14.

PREPARATION OF STANDARD SODIUM HYDROXID AND NORMAL POTASSIUM
NITRATE SOLUTIONS.*

These solutions are to be used in the determination of soil acidity.

(a) Weigh out enough sodium hydroxid (sticks, purified over alcohol,
about 75 <J NaOH) to make 3 liters of solution of such strength that I cc.
shall be equivalent to 4 mg. of calcium carbonate. Dissolve in ammonia-
free water, dilute to exactly 1000 cc., add 100 cc. of a saturated barium hy-
droxid solution, shake well, and allow to stand over night, or until clear.
Draw off 100 cc. of the clear solution, place in a 250 cc. bottle containing
100 cc. of the saturated solution of barium hydroxid. If a precipitate oc-
curs, add the 200 cc. to the main solution, shake and repeat the above op-
erations until no further precipitate occurs. (If no precipitate is formed
throw away the 200 cc.) Always keep an exact record of the amount of
liquid remaining in the stock bottle. When the solution is free from car-
bon dioxid, draw off 100 cc. and place in a 100 cc. bottle. Fill the burette
with this and titrate against 10 cc. portions of standard hydrochloric acid.
Add ammonia-free water so that I cc. of the standard sodium hydroxid
solution shall be exactly equivalent to 4 mg. of calcium carbonate.

(b) Prepare 5 liters of a normal potassium nitrate solution, assuming
the salt to be pure.

If 100 grams of an acid soil are placed in 250 cc. of normal potassium
nitrate solution and shaken for three hours a reaction takes place between
the potassium nitrate and the acid constituents of the soil, giving, as one
of the products, soluble acid salts and so making the acidity determinable.
An equilibrium is reached, however, before this reaction runs to an end
and if, after having drawn off 125 cc. to titrate, 125 cc. of fresh potassium
nitrate are added to the bottle and the bottle again shaken for three hours,
125 cc. drawn off will give a titration, which is more than one-half of the
first. By continuing this process until the last 125 cc. shows practically no
acidity, we have a series of titrations the sum of which represents the total
acidity of the 100 gm. of soil. It has been found by working with a num-
ber of different soils that as an average the sum of such a series is 2^2
times the first titration.

Consequently when the sodium hydroxid is made up so that i cc. is
equivalent to 4 mg. of calcium carbonate and 125 cc. (which represents
50 gm. of soil) are titrated, each o.i cc. required to neutralize corresponds
to i mg. of calcium carbonate required by the 100 gm. of soil, or to o.ooi
% of calcium carbonate required by the soil tested.



*To be done by the instructor.



32

PRACTICE 15.
DETERMINATION OF ACIDITY (OR LIME REQUIREMENT) OF SOILS.

Each group of students will work upon one of a group of soils selected
by the instructor using surface, sub-surface, and subsoil samples.

Place 100 gm. of soil in a 400 cc. (or 12 oz.) wide-mouthed bottle, add
250 cc. normal potassium nitrate solution, stopper, and shake continuously
for three hours in a shaking-machine, or every five minutes by hand. Let
stand over night. Draw off 125 cc. of the clear supernatant liquid, boil
10 minutes to expel carbon dioxid, cool, and titrate with the standard
sodium hydroxid, using phenolphthalein as indicator.

Surface. Subsurface. Subsoil.

Titrations (i) cc. NaOH

(2) cc. NaOH

Average cc. NaOH

Are carbonates present in the soil? Explain the test for carbonates.

Calculate the results obtained and with these record the results obtained
by three members of each group as indicated on the following page. Con-
sider 7 acre-inches to weigh 2,000,000 ft).

What kind of crops, and in what way, does ground limestone mainly
benefit?



PRACTICE 15 (Cont.)



NAME
OF
STUDENT


Kind
of
Soil


Percent CaCOj required


Pounds CaCOj Required per Acre


Surface


Subsurface


Subsoil


Surface


Subsurface


Subsoil


















































AVERAGE






























































AVERAGE






























































AVERAGE






























































AVERAGE






























































AVERAGE






























































AVERAGE






























































AVERAGE






























































AVERAGE















33



34

PRACTICE 16.
PREPARATION OF PLANT FOOD SOLUTIONS.*

Solution No. i. Nitrogen: Dissolve 80 gm. of ammonium nitrate in
2500 cc. of distilled water. Use 10 cc. per pot.

Solution No. 2. Phosphorus: Dissolve 25 gm. of monocalcium phos-
phate in 2500 cc. of ammonia-free water. Use 10 cc. per pot.

Solution No. 3. Potassium: Dissolve 50 gm. of potassium sulfate in
2500 cc. of ammonia-free water. Use 10 cc. per pot.

Solution No. 4. Magnesium : Dissolve 20 gm. of magnesium sulfate in
2500 cc. of ammonia-free water. Use 10 cc. per pot.

Solution No. 5. Iron: Dissolve o.i gm. ferric chlorid in 250 cc. of
ammonia-free water. Use I cc. per pot.

Prepare these solutions carefully, using chemically pure salts, and label
each bottle.



*To be done by the instructor.



36

PRACTICE 17.
PREPARATION OF POT CULTURES.

Use clean, white sifted sand in 5-liter heavy glass battery jars, having a
I cm. hole within I cm. of the bottom. Into the hole fit a drain tube made
of glass-tubing with a glass-wool filter at the inner end, so that it will
take liquid from the lowest place in the jar. Put up a series of ten of
these pots, eight to be used as indicated in the table below and two in an
experiment to be devised by the student. The previous treatment of the
sand in the latter two will depend upon the experiment to be made.

To extract the sand, fill the jar within I cm. of the top with dry sifted
sand and add to this dilute sulfuric acid (made by adding 100 cc. of con-
centrated chemically pure sulfuric acid to 900 cc. of ammonia-free water)
until the sand is saturated. Let stand two hours and then add ammonia-
free water, allowing the drainage to flow into a second jar until it is sat-
urated. Allow this jar to stand two hours and then wash both with


1

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