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Full text of "Chemical soil diagnosis by the universal soil testing system /"

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Bulletin 450 October, 1941 



Chemical Soil Diagnosis 
By the Universal Soil Testing System 

(A Revision of Bulletin 392) 



M. P. Morgan 




(fi,axmtrtimt 
2fotu Wurtm 



Bulletin 450 October, 1941 

Chemical Soil Diagnosis 
By the Universal Soil Testing System 

(A Revision of Bulletin 392) 
M. F. Morgan 




(ftanneritcut 

Agricultural ^Experiment JStatinn 

Nfm Hauert 



CONTENTS 



Soil Extracting Solutions for Rapid Chemical Tests 579 

The Universal Soil Extracting Solution 583 

The Soil Sample 584 

Soil Reaction (pH) Tests 586 

Soil Examination for Physical Characteristics 589 

Details of Universal Soil Testing Method 591 

General plan 591 

Equipment 591 

Preparation of reagents and solutions 592 

The soil extraction 595 

Routine tests 596 

Special chemical tests 599 

Plant tissue testing 604 

Quantitative calibration of tests 605 

Testing saline and alkali soils 608 

The Interpretation of Soil Tests 610 

Estimating Fertilizer Needs 620 

Summary 624 

Bibliography 626 



CHEMICAL SOIL DIAGNOSIS 
BY THE UNIVERSAL SOIL TESTING SYSTEM 

(A Revision of Bulletin 392) 
M. F. Morgan 

DURING the past ten years numerous methods have been devised 
or improved for the purpose of evaluating the chemical status 
of the soil with respect to the nutrition of plants by means of rapid, 
simple soil tests. This Station has issued several publications in this 
field. The earliest of these, Bulletin 333, "Microchemical Soil Tests", 
issued in January, 1932, (35) was the first to propose tests for nitrate 
and ammonia nitrogen, calcium and aluminum, in addition to the phos- 
phorus test, in order to obtain some measure of the interdependence 
of various chemical factors involved in soil fertility. These methods 
were revised and amplified so as to provide for the simultaneous 
testing for various constituents from a single soil extract. The "Uni- 
versal soil extracting solution" employed in these tests was first in- 
troduced as a mimeographed supplement to Bulletin 333, issued in 
February, 1933 (36). The methods in substantially their present 
forms were described in detail in Bulletin 372, "The Universal Soil 
Testing System", issued in 1935, (37) and in Bulletin 392, under the 
same title, issued in 1937 (38). Circular 127, "Soil Testing Methods 
— The Universal Soil Testing System", issued in 1939, (39) is an 
abbreviated description of the methods, without the useful charts in- 
cluded in the earlier publications, now no longer available for dis- 
tribution. 

During the past five years the soil testing methods developed at 
this Station have become extensively used for practical chemical soil 
diagnosis, not only in Connecticut, through its service testing by the 
Extension Service of the University of Connecticut, and by this Sta- 
tion at New Haven and Windsor (Tobacco and Vegetable Field Sta- 
tion), but in many other states and in numerous foreign countries. 

Agricultural services in Great Britain have been employing 
these methods extensively in their campaign for growing more food. 
The war efforts of our own country now demand increased crop 
production for ourselves and our allies with less available farm labor. 
The supply of many fertilizer materials will be curtailed. Ships, 
trains, and trucks moving fertilizers toward the farm are needed for 
the transportation of vital war supplies. The competent employment 
of soil testing will do much to promote greater efficiency in the 
farmer's part in winning this war. 

SOIL EXTRACTING SOLUTIONS FOR RAPID CHEMICAL TESTS 

THE earlier methods of chemical soil study for fertility evaluation 
were based on analyses of solutions resulting from the treatment of 
the soil with strong solvents, such as concentrated mineral acids. 
Practically inert sand and silt particles and humus residues were more 



580 Connecticut Experiment Station Bulletin 450 

or less completely broken down. The results of such analyses were 
of great value in revealing the fundamental constitution of the soil 
as affected by soil-forming processes. However, they failed to show 
any consistent differences between soils that were known to vary 
widely with respect to the responses of crops to various chemical 
treatments, such as fertilizers, manures and lime. 

Extractions of the soil with solutions of less drastic solvent power, 
such as the 1 percent citric acid employed by Dyer (13) and the fifth 
normal nitric acid of Fraps (22), have been used by numerous soil 
chemists for many years in detailed laboratory procedures. On some 
soils each gave good correlation with crop results, while on others 
the results were not satisfactory. Citric acid tended to attack the 
iron and aluminum of acid soils to too great a degree, while the dilute 
nitric acid was diminished in solvent power by neutralization due to 
dissolved bases in soils containing carbonates. The methods were 
too expensive in laboratory time and equipment to be suitable for 
general application in soil diagnosis, even when the results were con- 
sidered to be of practical benefit. 

At first thought, the natural solvent to which soils are subjected 
in nature would seem to be pure water. However, the liquid that 
bathes the soil particles in a moist soil in the field is more or less 
charged with carbonic acid, as well as small but significant amounts 
of various mineral and organic acids, more or less buffered with salts 
resulting from interaction with the soluble constituents of the soil. 
The contact of the rootlets and root hairs with the colloidal particles 
of the soil provides a mechanism for the absorption of chemical 
elements by plants that can now be explained to a degree as a result 
of recent expansion of knowledge concerning colloidal interface 
phenomena. No one artificial solvent, acting upon the soil for a few 
minutes to a few hours of time, can hope fully to duplicate all the 
conditions involved in the ability of the soil to provide properly for 
the chemical nutrition of the crop. 

Thus it must be emphasized at the outset that any chemical 
method of soil extraction is quite empirical in character, and the re- 
sults at best can give only approximate quantitative expression to 
beneficial or harmful concentrations of various chemical constituents 
that are most likely to be prevalent in the active soil-plant system. 

Most laboratory methods of chemical soil analysis are based on 
the washing from the soil of practically all of the constituents capable 
of being removed by the action of a given solution. Quick chemical 
tests must necessarily rely upon the results of an incomplete extraction 
wherein the interaction between the extracting solution and the soil 
is permitted to continue for but a few minutes, and only a portion of 
the extract is removed from contact with the soil. This might be 
considered a serious limitation. However, it is a condition somewhat 
analogous to the crop itself as a soil extractant. This may be a factor 
in the apparently greater practical value of "quick test" results as 
compared with those from the more detailed soil analyses. 



Extracting Solutions for Rapid Tests 581 

The various quick test methods that have been developed during 
the past few years may be classed in four general types with reference 
to the soil extractant. 

The first of these involves solvent action of the same order of 
magnitude as pure water. The very dilute acetic acid (.025 N) of 
Spurway (45) in his general procedure falls in this category. Fully 
soluble soil constituents, such as nitrates and chlorides, are readily 
measured. Soils of very high chemical fertility, such as intensively 
fertilized greenhouse or garden soils, may also contain quite measur- 
able amounts of strictly water-soluble phosphorus, potassium or other 
constituents usually not extractable from field soils in amounts that 
can be distinguished by simple testing reagents. 

A second type of extractant consists of a neutral salt of fairly 
strong concentration (usually greater than half-normal). The 25 per- 
cent sodium perchlorate solution proposed by Bray (7), and the nor- 
mal ammonium acetate solution used by Peech (41) in micro methods, 
are of this character. Such an extractant removes bases from the 
soil through the mechanism of base exchange, in addition to the water- 
soluble constituents. However, a neutral salt extraction fails to lib- 
erate measurable amounts of phosphorus, aluminum, and iron that are 
capable of dissolving under the slightly acid conditions that exist in 
most natural soil solutions. 

A third type of extractant is employed in quick test methods most 
commonly used in the Middle West. A strong mineral acid, such 
as hydrochloric, nitric or sulfuric acid, is employed. This is neces- 
sarily in dilute concentrations, usually less than half normal, in order 
to prevent the dissolving of mineral particles or humus substances that 
are only slightly attacked under natural soil conditions. The acid 
solution is frequently buffered at a given pH, such as 2.0 or 3.0, by 
the addition of a neutral salt. The total acid concentration is weak, 
in the sense that it may be readily exhausted by the neutralizing action 
of amounts of lime or other basic materials frequently existing in soils. 
On the other hand, the hydrogen-ion concentration existing at a pH 
of 2.0 or 3.0 exerts a strong solvent effect upon difficultly soluble min- 
erals, particularly upon apatite or phosphate rock particles. Such sol- 
vents dissolve some potash and other bases in addition to the water- 
soluble and absorbed forms. However, it is difficult to confirm this 
on non-calcareous soils under quick test conditions, since only a par- 
tial extraction is effected. Carbonates are actively decomposed by 
the strongly ionized acid; hence calcium and magnesium tests on cal- 
careous soils include quantities of these bases that may be considered 
part of the insoluble base reserve, rather than actively affecting the 
soil-plant system. 

Methods employing such soil extractants are as follows: 

Truog (51) original phosphorus procedure, using .002 normal 
sulfuric acid, buffered at 3 pH with ammonium sulfate. 

"Truog-Hellige" commercial set (25), using dilute hydrochloric 
acid, buffered with a salt. 



582 Connecticut Experiment Station Bulletin 450 

Bray (5), Thornton (49) and Emerson (15) phosphorus tests; 
also the "Hi-lo-fos" and "Sudbury" phosphorus tests, using hydro- 
chloric acid (0.7 to 0.8 Normal) and ammonium molybdate. 

Bray (6) potash test, using nitric acid and sodium acetate. 

Spurway (46) outlines tests for "reserve" phosphorus and potash, 
using 0.135 Normal hydrochloric acid. 

Baver and Bruner (2) soil testing methods, using 0.3 Normal 
hydrochloric acid. 

Miles (31) tentative procedure, using a buffered perchloric acid 
extractant. 

A fourth type of extractant employs a weakly ionized organic acid 
buffered with its sodium salt. A mixed solution of acetic acid and so- 
dium acetate is now most extensively used as the soil extractant for 
quick chemical tests. As introduced by the writer (37), under the des- 
ignation of the "Universal soil extracting solution", it is approximately 
0.5 Normal in total acetic acid concentration and is buffered at approxi- 
mately 4.8 pH with sodium acetate. Hester (26) adopted a solution 
modified from that used in a laboratory phosphorus test independently 
proposed by Dahlberg and Brown (11) appearing later in the same year 
(1933) as the writer's original use of this type of extractant. Hester's 
solution is more dilute, with a total acetic acid concentration of ap- 
proximately 0.2 Normal, buffered at from 4.8 to 5.0 pH. Merkle (32) 
gives soil testing procedures based on the original Dahlberg and 
Brown extractant, of approximately twice the strength of that of 
Hester. Fink (20) reports using the Universal soil extracting solu- 
tion modified by the addition of a sufficient amount of hydrochloric 
acid to bring it to 3.0 pH. Such an extractant is probably inter- 
mediate in solvent power between the third and fourth types of ex- 
tractants described herein. 

The Egner (14) lactic acid-calcium lactate extracting solution, 
now frequently used in laboratory procedures abroad, is similar in 
principle to the acetic acid-sodium acetate extractants. The chemi- 
cals do not lend themselves so readily to employment in quick test 
methods. 

Other extractants proposed for use in quick test methods include 
the 0.1 Normal acetic acid of Harper (24) and the 1 percent potas- 
sium carbonate of Hockensmith, Gardner and Goodwin (28), both 
employed for phosphorus tests. 

Some investigators have proposed the idea of measuring the ab- 
sorption of phosphorus or potash, or both, by a given amount of 
soil from solutions containing known concentrations of these constitu- 
ents. Emerson (15) proposed such an absorption method for potas- 
sium. This has been applied in the Sudbury commercial soil testing 
set. Purvis and Blume (42, 43) have developed a method for both 
phosphorus and potassium based on this principle. Such procedures 
may give valuable information when used in correlation with direct 
methods. 



The Universal Soil Extracting Solution 583 

THE UNIVERSAL SOIL EXTRACTING SOLUTION 

THIS solution, of the fourth type previously discussed, was 
selected by the writer on the basis of the following characteristics: 

1. It is buffered at a hydrogen-ion concentration closely approximated 
by that of aqueous solutions saturated with carbon-dioxide in con- 
centrations normally existing in soil air, or of weak plant root acid 
secretions. This degree of acidity is readily attained by most soils 
in humid regions. 

2. Its solvent action is practically unchanged by contact with the soil. 
Its total acidity and buffer capacity are sufficient to prevent a change 
of more than 0.2 pH on prolonged contact with a soil containing 
the equivalent of 2.5 percent of calcium carbonate, using the propor- 
tion of soil to extracting solution here employed. 

3. The resultant soil extract permits the development of the color and 
turbidity reactions for the various tests with a minimum of manipu- 
lation. 

4. The ions present in the extracting solution do not interfere with the 
tests for the constituents to be determined. 

5. The resultant soil extract contains concentrations within the range 
of sensitivity of the various tests, for all normal agricultural soils. 

6. Turbidity or discoloration of the extract thus obtained is not suffi- 
cient to interfere with the tests, except in extreme cases. 

7. Tests of soil extracts made with this solution are in harmony with 
known crop performance over a wide range of soils. 

8. The solution does not become contaminated by biological decompo- 
sition. 

During the past eight years, the writer has carefully studied tests 
of soil extracts obtained by this solution on many soils, not only from 
Connecticut, but from many states, and from areas in the American 
tropics. Concepts involved in the interpretation of the tests must 
necessarily vary under different soil and climate conditions and for 
different types of crops. Although the methods herein described were 
first developed for conditions existing in southern New England, it 
is now confidently believed that they serve to give useful information 
concerning almost any soil that may be thus examined. 

As chairman of the Sub-committee on Soil Testing of the General 
Fertilizer Committee, American. Society of Agronomy, during the past 
five years, the writer has studied the independent results of numerous 
collaborators on a series of 31 check soils from 15 states east of the 
Great Plains area, assembled by the sub-committee. In its recent re- 
port (40) there has appeared to be a consistent difference in relative 
results on a few soils between methods using the Universal and other 
acetic acid-sodium acetate extractants from those using dilute solutions 
of the stronger acids. Certain silt and clay loams of the Corn Belt give 
lower phosphorus and potassium tests by the former type of extractant, 
while the higher results by Thornton, Truog and similar methods 
appear more in line with the "case history" of the soils in question. 
On the other hand, the latter methods have given inconsistently low 
tests for phosphorus on a highly calcareous soil and somewhat higher 
phosphorus and potassium tests on a few other soils than are indicated 
by field responses to treatment. Of most significance is the general 



584 Connecticut Experiment Station Bulletin 450 

agreement in relative results, for a given constituent, irrespective of 
the type of extractant used in the various quick test procedures, when 
the data are obtained by a skilled operator. 

Certain modifications in procedure for adapting the tests to spe- 
cial soil conditions will be indicated in the presentation of the details 
of the methods. 

THE SOIL SAMPLE 

THE interpretation of soil tests must be based on an assumption 
that the sample actually tested is truly representative of the conditions 
existing in the particular layer of soil and position with respect to 
the plant roots or fertilizer placement existing in the given area of 
ground in question. A large field, planted to one crop, that has been 
of uniform past production and soil treatment and that is apparently 
a single soil type, may possibly be represented by a single test sample, 
comprising a careful mixture of numerous borings or soil slices of uni- 
form thickness through the depth of the plowed zone (usually 6 to 
7 inches) well distributed over the field. However, in many cases, 
several separate composite samples from differing portions of the field 
must be examined. Samples from portions of a field that show defi- 
nitely poorer or better results than the average, not readily explainable 
on the basis of obvious physical soil differences, should be compared 
with the samples from areas of normal production. Permanent grass 
turf, such as pasture sod, should be sampled to the depth of only 2 
inches if any treatment that might be used must be applied as a top- 
dressing. Separate samples from two or more soil depths may reveal 
significant information. No simple rule for soil sampling will apply to 
all cases. Common sense is the best guide, bearing in mind that in 
the final mixed portion actually subjected to test is only a spoonful 
from an area of land usually representing thousands of tons of soil. 

Instructions for those who collect and submit their own soil 
samples for testing in Connecticut, as issued in Circular 131, "Soil 
Testing in Connecticut", are as follows: 

The soil sample should be a thorough mixture of equal amounts 
of soil collected at 20 or more points well distributed over the field 
or area in question. Vertically cut shovel or trowel slices of uniform 
thickness, or borings, should be taken. For cultivated soils, sample 
to the depth of 6 inches. Permanent sod, as in pastures and lawns, 
should be sampled from the upper 2 inches. If desired, separate 
samples of soil from lower depths may be made. Mix the soil thor- 
oughly, and remove stones, coarse roots or hard clods. Each sample 
should be packed in a clean carton, box or bag not previously used 
for drugs, chemicals or other contaminating substances. An unused 
half-pint ice cream carton is quite desirable. The County Farm 
Bureaus supply suitable mailing tubes. Each sample should be 
marked by number, name of field, or other identifying legend. 

If there are distinct types of soil in the field, or important differ- 
ences in past treatment or crop growth, separate samples should be 
submitted. 



The Soil Sample 585 

Soils are received for testing at the following laboratories: 
Agronomy Department, University of Connecticut, Storrs 
Tobacco Substation, Windsor 

Soils Department, Connecticut Agricultural Experiment Station, 
New Haven 

Record sheets, letters or notes accompanying samples must indi- 
cate the crop or crops involved, and as much as possible of the fol- 
lowing information: 

1. Land surface (whether hilly, rolling or level). 

2. Drainage, either natural, or as improved by tile or ditches. 

3. Underlying formation, whether "hardpan", sand, gravel or rock. 

4. Special soil features such as mellowness or hardness, tendency to 
erode, unusual shallowness of soil, stoniness, etc. 

5. Crops grown in past few years, and description of any abnormal 
results not caused by other factors. 

6. Soil treatment with respect to lime, manure, fertilizer, etc., in recent 
years. 

7. Approximate area represented by the sample. 

8. Amount and kind of manure available for soil improvement. 

9. Description of all unusual conditions. 

When the samples are brought to the laboratory, most of this 
information may be given orally. 

Time of sampling: The soil is a dynamic body, teeming with 
micro-organisms whose activities vary from day to day and from 
season to season with changes in temperature, moisture and food sup- 
ply. Nitrate and ammonia nitrogen contents of the soil are especially 
variable, as will be discussed in the section on test interpretations. A 
rapidly growing crop depletes some of the active constituents of the 
soil. For this reason, at the end of the growing season, soils show 
high tests for nitrates and potassium only when the amounts of these 
constituents added in the fertilizer, or becoming available in the soil, 
are in excess of crop demands. There are also seasonal fluctuations 
in soil acidity, which influence the availability of plant nutrients to 
some extent. Acidity is normally at a minimum in early spring, and 
at a maximum in midsummer. 

All of the above factors must be taken into consideration in the 
interpretation of the tests. For general soil diagnosis, tests on 
samples taken in early spring are most reliable. However, soils 
studied during the growing season give tests most closely related to 
the performance of the crop, and are particularly valuable in deter- 
mining immediate need for supplemental fertilization. Tests in the 
autumn, after the crop is harvested, best indicate whether or not the 
fertilizer has been in excess of crop needs. Thus the choice of time 
when the sample is to be taken depends upon the purpose for which 
the test is made. 

Preparing the soil sample for testing: The field-collected sample, 
upon receipt for testing, is usually more or less moist. If too sticky 
to be screened, it should be dried to a mellow-moist condition. After 



586 Connecticut Experiment Station Bulletin 450 

mixing the entire sample, a portion of suitable size (usually about 100 
cc.) should be screened with a 2 mm. or 10-mesh sieve to remove 
stones, gravel or coarse roots. The screened sample, further mixed, 
should be tested as quickly as possible, preferably before loss of all 
of its field moisture. Samples reserved for future testing should be 
promptly air-dried, and stored in containers with tight covers, in a 
place that is free from strong laboratory fumes, particularly am- 
monia or acid vapors. 



SOIL REACTION ( P H) TESTS 

SOIL reaction, in terms of the pH scale, is now generally accepted 
as one of the most important single factors involved in the chemical 
fertility of soils. Knowledge of the degree of acidity or alkalinity is 
almost essential in the proper interpretation of the results of the other 
chemical tests, especially those for phosphorus, calcium, magnesium, 
aluminum and manganese. The pH test is necessarily a separate 
measurement from the tests that are applied to the soil extract in the 
Universal soil testing system. Most laboratories or testing centers 
that conduct several hundreds or thousands of tests each year find it 
desirable to make the pH tests by electrical apparatus. Several re- 
liable commercial pH meter sets using the principle of the glass elec- 
trode are now on the market. These instruments enable a skilled 
operator to make accurate pH measurements on hundreds of soils in 
a few hours. The quinhydrone electrode type of instrument is still 
fxequently used with good results, but is subject to considerable error 
on certain soils, particularly those containing oxidizing materials, such 
as manganese dioxide. 

When soil testing is not conducted on a sufficient scale to justify 
the purchase of electrical equipment, the measurement of pH may be 
done colorimetrically by the use of indicator dyes. A procedure that 
has been successfully used by many persons during the past 15 years 
is the one developed by the author (33) and described in Bulletin 333 
of this Station. Since this publication is now out of print, the details 
of the method are outlined here. 

The Morgan pH testing set: The technique employed involves 
the use of a special porcelain block, as illustrated in Figure 1. This 
facilitates the operation of extracting the soil without the resultant 
color due to turbidity from the soil itself. The soil is placed in com- 
partment "B", on the lower side of the perforated partition. The 
surface is pressed gently with a clean knife, or spatula, to prevent 
the possibility of open channels through the soil mass, and leveled off 
with the sloping face of the block. The narrow channel "C" and 
test cup "B" should be wiped clean of soil particles. If desired, a 
small dam of clean, coarse quartz sand of high purity may be poured 
in at the upper end of channel "C" at the lower edge of the soil 
mass. This is especially useful on silty soils that tend to flow down 
the channel upon saturation with liquid. 



Soil Reaction (pH) Tests 



587 



An extracting solution, prepared by dissolving 3 grams of sodium 
chloride, of analytical reagent purity, in 1 liter of distilled water, may 
be employed. It is also feasible to use the indicator solution itself 
as the soil extractant, except on soils that absorb the color from the 
dye, or that tend to give a turbid extract. The extracting solution, 
or indicator solution, is added to compartment "A", above the per- 
forated partition, drop by drop, until the soil mass becomes saturated 
and liquid begins to trickle down the channel into the test cup "D". 
Uniform flow along the channel may be guided by the tip of a clean 
tinned paper clip or glass rod. 




Figure 1. Morgan Soil Test Block used in colorimetric pH test tech- 
nique. Compartment "A" for addition of liquid extractant, separated 
from soil in compartment "B" by a perforated partition; channel 
"C" for flow of extract into test cup "D". 



If the extracting solution is used, the indicator solution should 
be added to the test cup before the extract flows into it. A half-drop 
quantity, obtained by touching the tip of the indicator transfer pipette 
or eye-dropper to the bottom of the cup and squeezing out a bead 
about three-eighths inch in diameter, should be used. When the 
liquid of a uniform color fills the test cup, it is compared with the 
color chart for the particular indicator 1 used in that section of the 
block. 



J The color charts, test blocks and indicator solutions may be obtained from the LaMotte 
Chemical Products Company, Baltimore, or the Fischer Scientific Company, New York, 



588 



Connecticut Experiment Station Bulletin 450 



The test block supplies three testing sections, for simultaneous 
extraction and use of the three indicators, as follows: 



INDICATOR 
Bromthymol blue (0.04%) 

Chlorphenol red (0.04%) 

Bromcresol green (0.04%) 



RANGE 

6.0-7.6 P H (slightly 

acid to slightly alkaline) 

5.0-6.6 pH (moderately 
to slightly acid) 

3.8-5.4 pH (strongly to 
moderately acid) 



One of the above three indicators is almost certain to cover the 
proper range for any soil in the humid section of the country. In 
arid regions, where alkali soils occur, or for extremely acid peaty 
soils, other indicators may be selected, such as the following: 



INDICATOR 

Cresol red (0.04%) 

Thymol blue (0.04%) 
Bromphenol blue (0.04%) 



RANGE 

7.2-8.8 pH (slightly to 
moderately alkaline) 

8.0-9.6 pH (moderately 
to strongly alkaline) 

3.0-4.6 pH (extremely to 
strongly acid) 



These indicators are conveniently used from one-ounce bottles 
with screw cap dropping pipette caps. 

The indicators should be of a color approximating the mid-color 
of their range. In bottles, indicators may gradually become more al- 
kaline through contact with the glass. Thus the bromthymol blue 
may become deep blue, or chlorphenol red may become violet red. 
In such case, dilute hydrochloric acid (1 to 20) may be added to the 
bottle, drop by drop until the proper color is restored. 

In case charts are not available, the approximate colors developed 
by the most commonly used indicators; in relation to pH, are as fol- 
lows: 

pH and Color 



red 



INDICATOR 


3.8 


4.2 


4.6 


5.0 


5.4 


Bromcresol 

green 
Chlorphenol 

red 


yellow 


greenish 
yellow 


green 

orange 
red 


blue- 
green 
orange 


blue 
salmo: 


Bromthymol 
blue 












Bromcresol 


6.2 


6.6 


7.0 


7.4 




green 
Chlorphenol 
red 


violet 
red 













Bromthymol 
blue 


greenish 
yellow 


green 


blue- 
green 


blue 





yellow 



Other colorimetric pH methods: A technique that has come into 
frequent use in recent years involves the use of barium chloride as 
a clarifying agent. The test is conducted in test tubes or glass vials. 



Examination for Physical Characteristics 589 

A suggested procedure is as follows: Place a teaspoonful of soil, 
one-fourth teaspoonful of powdered barium sulfate ("X-ray purity" 
reagent) and 10 ml. of distilled water in a one-half ounce glass vial. 
Stopper with a clean cork and shake thoroughly. Let the vial stand 
until the upper third of the contents has settled clear. Add 1 drop 
of the indicator solution and stir the supernatant liquid gently, taking 
care not to roil the settled portion. The resultant color should be 
compared as indicated for the previously described procedure. 

The above method is especially useful on heavy soils that tend 
to yield turbid extracts or that are too impervious for the application 
of the Morgan test block procedure. 

A number of inexpensive simple field pH kits are also on the 
market. These give the approximate pH of the soil, usually to within 
0.4 pH of the results obtained by the best laboratory methods, which 
is often sufficiently close for practical purposes. 

The pH test is not a direct measure of the amount of lime that 
is desirable to apply in the correction of an acid condition. However, 
when the texture and humus content of a soil are taken into considera- 
tion, the pH serves as a practical guide to lime use. This is discussed 
in a later section on "Interpreting Soil Tests". 



SOIL EXAMINATION FOR PHYSICAL CHARACTERISTICS 

Soil Texture 

SOIL texture, involving the relative proportion of sand, silt and 
clay in the soil, is an important consideration in the proper interpreta- 
tion of quick chemical tests. A definite measure of soil texture is ob- 
tained by mechanical analysis. A useful method, giving satisfactory 
practical results on most soils, is the hydrometer technique devised by 
Bouyoucos (4). However, it is usually impractical to make such 
measurements on the large numbers usually involved in quick test 
operations. As a rule, the texture of the soil can be fairly assessed 
by a skilled observer, chiefly on the basis of the feel of a moderately 
moist soil when rubbed gently between thumb and forefinger. A few 
simple rules are helpful in this connection, for characterizing soils of 
the more common textural classes. 

Loamy sand: harsh, gritty feel; very slight tendency of the 
moist soil to stick together when pressed. 

Sandy loam: definitely gritty; may be pressed into a soft mass, 
if moist. 

Fine sandy loam: mellow and only moderately gritty feel; may 
be pressed into a firm mass, if moist. 

Loam: mellow, moderately smooth feel; moist soil may be 
rolled into firm rods; not perceptibly sticky. 

Silt loam: Smooth and "floury" feel; moist soil only slightly- 
sticky; readily rolled into firm, slender rods. 



590 



Connecticut Experiment Station Bulletin 450 



Clay loam: Very smooth, "slippery" feel; definitely sticky when 
moist; easily modeled into any shape. 

A more detailed description of soil textures has been published 
in Bulletin 423 of this Station, pages 8 to 11. 



Organic Matter 

Some evaluation of the organic matter content of a soil is also 
essential to the proper interpretation of soil tests. A number of soil 
testing laboratories make some measurements of organic matter as 
a supplement to the quick test procedure. A reliable, reasonably 
rapid technique is the Turin (50) modification of the Schollenberger 
(44) dichromate method, also outlined recently by Merkle (32). 
Thomas and Williams (47) employ an abbreviated adaptation of the 
Schollenberger method, involving only partial decomposition of all of 
the organic matter. 

Some soil testing laboratories estimate organic matter content 
from the loss effected by igniting the previously oven-dried soil at 
full red heat to constant weight. Loss-on-igr|ition is a useful soil 
measurement. However, it gives values of much higher magnitude 
than can be ascribed to the organic matter content, particularly on 
loamy or clay soils relatively low in humus, due to the volatilization 
of chemically combined water and certain inorganic elements. Such 
a procedure is most satisfactory when soils of similar textural type are 
being compared. 

Persons who are familiar with the color of the soil at various 
organic levels can usually make a fair estimate of organic matter by 
observation. It must be borne in mind that the dark color imparted 
to the soil by humus is deepened by moisture; also, that a sandy soil 
is much darker at the same organic content than a heavier soil. Un- 
der Connecticut conditions, approximate colors of moderately dry 
soils, at varying organic levels, are approximately as follows: 

Color Range and Organic Content 



Soil texture 


Brownish yellow, 
reddish yellow, 
or light gray 


Light yellow 

brown, 

light reddish 

brown or 

light gray brown 


Medium 
brown 
or medium 
grayish 
brown 


Dark 
brown 
or dark 
grayish 
brown 


Very dark 

brown 

or 

gray 

black 




% 


% 


% 


% 


% 


loamy sand 


minus 0.5 


0.5-1.0 


1.0-2.5 


2.5 - 4.0 


4.0 plus 


sandy loam 


minus 0.7 


0.7-1.5 


1.5-3.0 


3.0-5.0 


5.0 plus 


fine sandy loam 


minus 1.0 


1.0-2.0 


2.0 - 4.0 


4.0-6.0 


6.0 plus 


loam or silt loam 


minus 1.2 


1.2-2.5 


2.5-5.0 


5.0 - 7.0 


7.0 plus 


clay loam 


minus 1.5 


1.5-3.0 


3.0-6.0 


6.0 - 8.0 


8.0 plus 



In prairie regions, soils are usually darker at the same organic 
matter content than indicated in the above scheme. 



Details of Universal Soil Testing Methods 591 

DETAILED DESCRIPTION OF THE UNIVERSAL SOIL TESTING METHOD 

General Plan 

THE filtered extract obtained from soil treatment with the Uni- 
versal soil extracting solution or other extractant is tested for various 
constituents by transferring small quantities, usually from 1 to 10 
drops, to either a porcelain or glass spot plate, with depressions hold- 
ing approximately 20 drops, or to small glass vials of uniform size 
(50 mm. by 10 mm.), followed by the addition of appropriate reagents 
for the development of color or turbidity tests. The general plan of 
such micro-chemical tests follows the general technique for micro- 
chemical tests most extensively developed by Feigl (18, 19). Ap- 
plication of such procedure in quick chemical soil testing was first re- 
ported by the author in connection with the nitrate test (34). 

Chemical tests of such a nature must be conducted with reagents 
that are sensitive to approximately the same concentrations of the 
constituent in question, irrespective of the presence of other elements 
or ions that are likely to be present ni the soil extract. When some 
other constituent interferes by giving a similar test or by increasing 
or decreasing the sensitivity of the test, the extract must be purified 
by some chemical technique designed to remove or inactivate the dis- 
turbing substance. This may be accomplished in a refined laboratory 
method, but is not ordinarily practicable in quick test procedures. 

Equipment 

The following list itemizes the equipment normally required for 
conducting the usual routine tests. Specifications are those that have 
been found most generally desirable, and the tests are calibrated on 
the basis of their use. A sufficient quantity of glassware, etc., is pro- 
vided for testing six soil samples at the same time. 1 For larger op- 
erations, the numbers may be increased. 

1 Supply bottle, 1 liter or larger capacity, for soil extracting solution. 

1 Cylinder, or burette, graduated, 10 ml. 

1 Spoon, measuring, teaspoon size. 

1 Block, wooden, with 6 holes of % i ncn diameter, for supporting filtering 
tubes. 

1 Block, wooden, with 12 holes of Yi inch diameter, for supporting test 
vials. 

1 Filter paper, box of 100 sheets of 9 cm. diameter, C. S. and S. 597 
(American manufacture), Munktell No. or similar grade. 

6 Tubes, soil filtering, 15 mm. inside diameter, with funnel mouth 35 mm. 
diameter and air vent (or separate tubes and funnels of similar dimen- 
sions). 

6 Pipettes, eyedropper type, with unflattened straight tip of 2 mm. diameter, 
or transfer pipettes graduated to 0.05 ml. 

6 Rods, glass, 100 mm. by 4 mm. 

12 Vials, glass, 50 mm. deep, 10 mm. inside diameter. 



Arrangements have been made with the LaMotte Chemical Products Company, Baltimore, 
Maryland, for supplying assembled sets of the above equipment and commercially prepared 
extracting solutions and reagents to those who desire this service. 



592 Connecticut Experiment Station Bulletin 450 

2 Spot plates, white porcelain, sets of 12 depressions of 20 mm. diameter 
and 7.5 mm. depth. 

9 Bottles, 1 oz., with dropper pipette in screw cap, for test reagents. 

3 Bottles, 2 oz., with dropper pipette in screw cap. 

1 Bottle, glass dropping stopper, 1 oz. (for nitrate reagent). 

Preparation of Solutions and Reagents for Routine Testing 

(All chemicals should be of reliable C. P. 
or A. R. grade, or of special type as noted) 

Universal soil extracting solution: Add 100 gms. of sodium 
acetate (NaC 2 H 3 2 .3H 2 0) to 500 ml. of distilled water. After this 
is dissolved, add 30 ml. of glacial acetic acid and make up to 1 liter. 

Nitrate nitrogen reagent: Dissolve 0.05 gm. of diphenylamine in 
25 ml. of concentrated sulfuric acid, at a temperature not to exceed 
24° C. The resulting solution should have no trace of bluish color, 
and should give a colorless "spot" when 4 drops are added to 1 drop 
of distilled water. This test should be made frequently since con- 
tinued exposure to light and accidental contamination may require 
the preparation of a fresh reagent. The solution is very corrosive, 
and should not be allowed to come into contact with rubber. Care 
should also be taken to prevent injury to hands or clothing. 

Ammonia nitrogen reagent: ("Nesslers reagent"): Dissolve 5 
gms. of potassium iodide in 15 ml. of distilled water. Add a saturated 
solution of mercuric chloride until a slight precipitation occurs. Add 
40 ml. of a 50 percent solution of potassium hydroxide. Dilute 
to 100 ml., allow to settle for one week, decant and keep in a brown 
glass bottle. Two drops of this reagent, added to 4 drops of the 
"Universal" leaching solution, should give a practically colorless spot. 
Nesslers reagent prepared according to other reliable laboratory 
formulae may also be employed. 

Phosphorus reagent "A": Dissolve 12.5 gms. of sodium molyb- 
date, by gentle heating, in 100 ml. of distilled water. Mix 50 ml. of 
acetic acid and 350 ml. of distilled water in a 600-ml. beaker. Add 
the above solution of sodium molybdate slowly with constant stirring. 
Store in a brown glass bottle. 

Reagent "A" should not show more than a trace of sediment in the 
bottle in which it is stored. If the molybdate has a definite tendency 
to precipitate, the reagent is unreliable. This reagent, when carefully 
prepared, should be stable for six months or more; but unless the di- 
rections are carefully followed, it may deteriorate in a much shorter 
time. 

Phosphorus reagent "B": This should be freshly prepared on 
the day of use as follows: Place 25 ml. of "Universal" extracting 
solution in a one-ounce dropper bottle. Add .005 to .01 gm. of stan- 
nous oxalate (an amount about the size of a match head, conveniently 
transferred by means of the flattened tip of a thin glass rod) and 
shake thoroughly. 



Details of Universal Soil Testing Methods 593 

Potassium reagent "A": Dissolve 5 gms. of Co(NO. ; ), and 30 gms. 
of NaN0 2 in 50 ml. of distilled water acidfied with 2.5 ml. of glacial 
acetic acid. Make up to 100 ml. with distilled water. Let stand 24 
hours and filter. 

Potassium reagent "B": Iso-propyl alcohol, 90 ml., mixed with 
formaldehyde, neutral, 10 ml. (Store in a bottle with a tightly fitting 
screw cap). 

Calcium reagent: Mix 10 gms. of sodium oxalate with 100 ml. of 
distilled water. Let stand for 24 hours, and decant clear supernatant 
solution to the reagent bottle for use as required. 

Magnesium reagent "A~l": Dissolve .01 gm. of para-nitroben- 
zene-azo-resorcinol (Eastman Kodak Company) in 2 ml. of 1 percent 
NaOH. Dilute to 200 ml. 

Magnesium reagent "A-2": Dissolve 0.10 gm. of Titan yellow 
(Eastman Kodak Company) in a mixture of 50 ml. of methyl alcohol 
and 50 ml. of distilled water. This should be freshly prepared every 
three or four months. 

Magnesium reagent "B": Dissolve 15 gms. of sodium hydroxide 
in 100 ml. of distilled water. This is also used as Manganese reagent 

Aluminum reagent: Place 0.05 gm. of hematein (Eastman Kodak 
Company) in a 30-ml. beaker. Add 5 ml. of ethyl alcohol (95 per- 
cent.) Triturate with a rubber tipped stirring rod and decant clear 
solution to the storage bottle. Triturate with successive 5 ml. por- 
tions of alcohol and decant, until all of hematein is dissolved. Make 
up to a volume of 100 ml., with the ethyl alcohol. (This should be 
freshly prepared every two months, under ordinary conditions of 
storage). 

Aluminum stain remover: Mix 25 ml. of concentrated hydro- 
chloric acid and 25 ml. of distilled water. (Same as Iron reagent 
"A"). 

Manganese reagent "A": Dissolve 0.1 gm. of benzidine in 20 ml. 
of glacial acetic acid. Dilute to 200 ml. and filter. 

Manganese reagent "B": See Magnesium reagent "B". 

Preparation of Reagents and Extracting Solutions for Special Tests 

Iron reagent "A": Dilute hydrochloric acid of ordinary C. P. 
concentration (approximately 38 percent HC1) with an equal volume 
of distilled water. 

Iron (ferric and ferrous) reagent "B": Dissolve 10 gms. of po- 
tassium ferrocyanide and 0.1 gm. of potassium ferricyanide in 100 
ml. of distilled water. 

Ferric iron reagent "B": Dissolve 15 gms. of potassium sulpho- 
cyanate in 100 ml. of distilled water. 



594 Connecticut Experiment Station Bulletin 450 

Ferrous iron reagent "B": Dissolve 0.2 gm. of potassium fer- 
ricyanide in 100 ml. of distilled water. 

Sulfate sulfur reagent: Dissolve 5 gms. of barium chloride in 
100 ml. of distilled water. 

Nitrite nitrogen reagent: Dissolve 1 gm. of sulphanilic acid, by 
gentle heating, in 100 ml. of a saturated solution of ammonium 
chloride. Add 1.5 gms. of phenol and mix thoroughly. 

Special sodium extracting solution: Add 2 ml. of copper sulfate 
solution (10 percent) to 100 ml. of distilled water. 

Sodium reagent: Make up two separate lots as follows: (A) 
Uranyl acetate, 10 gms.; acetic acid (30 percent), 6 ml.; distilled 
water to 65 ml. Dissolve by heating. (B) Zinc acetate, 30 gms.; 
acetate acid (30 percent), 3 ml.; water to 65 ml. Dissolve by heating. 
Add (A) to (B) and continue heating until clear. Let stand several 
days and filter out the sediment. 

Chloride reagent: Dissolve 2 gms. of silver nitrate in 100 ml. 
of distilled water. Store in an amber, glass-stoppered bottle. 

Boron reagent "A": Dissolve 0.5 gm. turmeric powder in 100 
ml. of ethyl alcohol (95 percent). Filter through a "double acid- 
washed" paper. 

Boron reagent "B": Mix 70 ml. of orthophosphoric acid (85 
percent) and 30 ml. of concentrated sulfuric acid. Let stand for a 
few days, and decant the clear liquid. 

Zinc reagent "A": Dissolve .0807 g. of cobalt chloride in 100 
ml. of 0.5 N hydrochloric acid solution. 

Zinc reagent "B": Dissolve 8 gms. of mercuric chloride and 9 
gms. of ammonium thiocynate in 100 ml. of distilled water. Let stand 
for three or four days and decant the clear solution. 

Zinc reagent "C": Ethyl ether. 

Copper reagent: Dissolve 5 gms. of alphabenzoinoxime in 100 
ml. of ethyl alcohol (95 percent). 

Manganese reagent for supplemental test: A saturated solution 
of tetra-base (Eastman Kodak Company) in ethyl alcohol (95 per- 
cent.). 

Mercury reagent: Dissolve 0.1 gm. of s-diphenylcarbazide in 
100 ml. of ethyl alcohol (95 percent). 

Lead reagent: Dissolve 0.05 gm. of dithizone in 100 ml. of car- 
bon tetra-chloride. This should be freshly prepared, since most 
glass containers contaminate the reagent after a few days of contact. 

Arsenic, material required for the test: Concentrated sulfuric 
acid, granular zinc AR (low arsenic content), silver nitrate solution 
(see Chloride reagent). 



Details of Universal Soil Testing Methods 595 

The Soil Extraction 

The procedure that has been most extensively used with success on 
the sandy and loam soils of Connecticut involves direct extraction 
of the soil by percolation of the soil mass as placed in the folded 
filter paper cone. This technique works best on soils that are readilv 
moistened throughout upon the addition of the first two or three ml. 
of the extracting solution, so that the remainder of the liquid perco- 
lates readily through the entire soil mass. Other investigators using 
the Universal soil extracting solution or similar types of extractants 
have adopted other procedures of extraction. While less simple and 
rapid than the author's original technique, they may be used to ad- 
vantage' on soils that are less readily saturated with the extractant, or 
that are of more impervious texture. Hence, alternate procedures of 
extraction are included. 

Simple percolation extraction; Fit a folded filter paper of 9 cm. 
diameter (of American-made C.S. and S, 597, Munktell No. or similar 
grade) into the funnel of the soil filtering tube or the funnel in posi- 
tion above the tube or flask to be used in the collection of the extract. 
Place a level teaspoonful of the soil sample inside the filter cone, 
and press down gently with the back of the spoon. Measure out a 
10 ml. portion of the Universal soil extracting sloution, and pour 
slowly over the soil mass in the filter. If the soil does not readily 
absorb the liquid, the extraction should be repeated with the soil mois- 
tened slightly with distilled water before being measured into the 
funnel. Permit the filtration to proceed to completion, or until there 
is no liquid on the soil surface. In removing the filter cone of soil, 
squeeze it gently to extract any remaining liquid which may have col- 
lected at its tip. Remove the funnel and insert a clean eyedropper 
pipette into the filtrate vessel. Pump the liquid up and down the 
pipette two or three times to insure thorough mixing of the soil extract. 
Each lot of extract should be supplied with an individual pipette for 
transferring portions for the various tests. 

Alternate extraction I: Place a teaspoonful of soil, gently 
packed and leveled, into a 50-ml. beaker. Add 10 ml. of the Uni- 
versal soil extracting solution. Stir vigorously for one minute and 
filter through a paper of quality indicated above into a 20 by 75-mm. 
glass vial or other suitable container. Remove the funnel, and insert a 
clean eyedropper pipette into the filtrate vessel. Proceed as directed 
above. 

Goss and Owens (23) recommend placing the soil and extracting 
solution in a 50-ml. Erlenmeyer flask and shaking with an automatic 
shaking machine for 15 minutes before filtration. Results by such 
a procedure are somewhat higher, for some constituents, than by the 
shorter time of extraction. However, data on check soils by various 
methods do not show any consistent improvement in correlation for 
(he more exhaustive extraction. 

Alternate extraction II: Place a rubber policeman over the end 
of the stem of a 50-mm. filter funnel provided with an 18-mm. disc 
of fritted glass ( porosity- 1 ). Add 10 ml. of the extracting solution and 



596 Connecticut Experiment Station Bulletin 450 

a level teaspoonful of the soil sample. After 15 minutes, remove the 
policeman, permitting the extract to drain into the collecting flask or 
tube. This general procedure is used by Thomas and Williams (47) 
and by Miles (31). Results have not been studied in detail in com- 
parison with the simple percolation extraction, but are believed to be 
similar to those obtained by the Goss and Owens modification. 

It is likely that no one method of extraction will be uniformly 
applicable to all types of soil. It is suggested that each of the pro- 
cedures be studied on numerous soils representative of the locality in- 
volved, before selecting the one that appears to be most desirable. 

Lighting Conditions in Conducting the Tests 

It is possible to make reasonably close comparisons of color and 
turbidity reactions developed in the various quick tests under good 
natural light. A north or northeast window is preferable, since the 
reflections obtained in direct sunlight make matchings difficult. Very 
dark cloudy days and late afternoons in the winter season are an ob- 
jectionable feature of natural lighting; hence, if possible, artificial il- 
lumination by a good lamp of the "daylight" type, preferably the re- 
cently devised fluorescent tube, with suitable screen to throw the light 
down and behind the table upon which the testing operations are in 
progress, is desirable. The value of attention to lighting and other 
details in soil testing techniques has been discussed by Constable and 
Miles (10). 

Tests Most Commonly Used in Routine Testing 

Nitrate nitrogen test 1 : Transfer 1 drop of soil extract to the 
spot plate. Add 4 drops of the reagent; let stand for two minutes; 
stir with a glass rod and compare the intensity of the resultant blue 
color with the color chart. The true color is slightly more blue than 
shown. 

Stirring immediately after adding the reagent is not recommended, 
since the blue color develops most rapidly in the film of contact 
between the reagent and the extract. Somewhat deeper colors result 
from the prolonged standing in excess of two minutes, but for con- 
venience of operation, the charts are standardized on the basis of this 
time. 

If a very deep blue color is obtained, corresponding to the top 
value of the chart, the test should be repeated on 1 drop of diluted 
extract, prepared in the ratio of 1 drop of extract to 4 drops of water 
or the extracting solution. Heavily fertilized soils often contain sev- 
eral times as much nitrate nitrogen as indicated by the chart, on the 
basis of the undiluted soil extract. 

If the first drop of the reagent produces an immediate blue 
color, the presence of nitrogen as the nitrite is suggested, and a test 
for nitrite is desirable. 



1 This is adapted from the method originally proposed by the author (34). 



Details of Universal Soil Testing Methods 597 

Ammonia nitrogen test 1 : Transfer 4 drops of the soil extract to 
the spot plate. Add 2 drops of the reagent. Let stand one minute; 
stir with glass rod and compare the resultant yellow to orange color 
with the color chart. 

Phosphorus test 2 : Transfer 10 drops of the soil extract to the 
spot plate. Add 1 drop of reagent "A" and 2 drops of reagent "B" 
(the latter freshly prepared on the day of use). Stir, let stand for one 
minute and compare the intensity of blue color with the color chart. 

If more than 1 drop of reagent "A" is added, the test is abnor- 
mally high. If more than 2 drops of reagent "B" are used, or if that 
reagent contains more than the designated amount of stannous oxalate, 
a "dirty" blue or greenish blue color results. 

The test should be read in one minute since, with a longer period 
of standing, the soil extracting solution, when tested as a blank, de- 
velops a definite blue color. Also, the blue color tends to develop 
a hue not readily matched with the chart, upon standing for a longer 
time. 

Occasional golf greens soils and other soils that have been treated 
with mercury compounds have been encountered that yield a grayish 
to black precipitate upon the addition of reagent "B". This is due to 
reduction to metallic mercury by the stannous compound in this rea- 
gent. In such a case, the phosphorus cannot be reliably measured. 

Soils that have been treated with heavy amounts of arsenic com- 
pounds for insect grub or earthworm control may give abnormally 
high posphorus tests. However, moderate treatments and arsenical 
spray residues rarely affect the test, by the procedure described above. 

Potassium test 3 : Transfer 10 drops of the soil extract to the test 
vial (10 mm. inside diameter). Add 1 drop of reagent "A" and 10 
drops of reagent "B". Let stand one minute; shake the vial gently 
and let stand two minutes longer. Estimate the resulting amount of 
yellow precipitate by the following use of the "line" chart: 

Hold the vial vertically, directly over the lines on the chart, 
with the bottom of the vial 1 inch above them. Look down 
through the vial at the different groups of lines, until the set is 
found which can be barely perceived. The test is read which cor- 
responds to this set of lines. 

The printed "line" chart does not permit precise differentiation at 
the lowest tests. If but the faintest perceptible turbidity is to be ob- 
served, the estimate should be "very low", with a Relative Test Index 
of 1. If the liquid remains clear and limpid, the estimate should be 
"extra low", with a Relative Test Index of 0.5. 



If the test is beyond the visibility of the deepest lines on the chart 
preliminary dilution of the extract with the extracting solution may be 
lade. It is necessary to mix fully the diluted liquid before testing. 

J This is adapted from the procedure originally proposed by the author (35). 
2 This is adapted from the color reaction test of Deniges (12). 
3 This is adapted from the method originally proposed by Bray (6). 



598 Connecticut Experiment Station Bulletin 450 

Calcium test 1 : Transfer 10 drops of the soil extract to the test 
vial. Add 1 drop of the reagent, shake vigorously and let stand for 
five minutes. Compare the resultant white turbidity with the chart, 
using the following procedure: 

Hold the vial vertically over the black background to the 
left of the gray discs, with the bottom of the vial one inch above 
the chart. Look down through the vial, comparing it with the 
various discs on the chart. 

Magnesium test 2 : Transfer 10 drops of the soil extract to the 
spot plate. Add 1 drop of reagent "A-2" and 3 drops of reagent "B". 
Stir, let stand one minute and compare the resultant light salmon to 
deep red color with the chart. 

If a "high" or "very high" reading is found, it is desirable to re- 
peat the test, using reagent "A-l", which is especially sensitive in this 
range, in place of reagent "A-2". The procedure is otherwise the 
same. A deep blue test is read as "very high", while with decreasing 
amounts of magnesium, lavender and pink colors are obtained. No 
separate chart is included for reagent "A-l". In the lower ranges 
of magnesium concentration, reagent "A-2" gives more readable tests. 

The magnesium test is somewhat affected by aluminum in amounts 
sufficient to give high or very high tests. Under such conditions, the 
magnesium test is somewhat lower than should be represented by the 
amount actually extracted from the soil. Due allowance should be 
made for this factor in interpreting the tests. 

Soils of high active calcium content give extracts that tend to 
coagulate the magnesium color, making test readings difficult and un- 
reliable. This may be overcome in most cases by adding 4 drops of 
a 50 percent glycerin solution prior to adding Reagent "A". The 
liquid in the test cup should be stirred thoroughly with a glass rod 
before adding Reagent "B". 

Aluminum test 3 : Transfer 2 drops of the soil extract to the spot 
plate. Add 2 drops of the Universal soil extracting solution and 1 
drop of the reagent. Let stand one minute, and compare the resultant 
yellow, brownish yellow to lavender color with the chart. The true 
top color is slightly more blue than shown. 

If a "dirty" blue-gray color results from this test, it is indicative 
of abnormal concentrations of active ion; hence a test for this constit- 
uent is desirable. 

After completing the reading, add 1 drop of the aluminum stain 
remover (1:1 HC1) and shake the block gently before washing it. 
This prevents the formation of a stain on the porcelain which inter- 
feres with subsequent tests. 



'This is adapted from the procedure proposed by the author (35). 

2 This is adapted from the spot plate test of Feigl (18) in the employment of the "A-l" 
reagent, and from the method of Spurway (45) in the use of the "A-2" reagent. 

3 This is adapted from the use of logwood extract in the testing for aluminum by Colwell 
and Parker (9). 



Details of Universal Soil Testing Methods 599 

Manganese tests 1 : Transfer 10 drops of the soil extract to the 
spot plate. Add 2 drops of reagent "A", stir and add 1 drop of rea- 
gent "B". Stir and compare the resultant blue color with the chart 
as quickly as possible, since the intensity of color fades rapidly after a 
few seconds. 

If more than 1 drop of reagent "B" is added, or if the tip of the 
pipette used in transferring that reagent is abnormally large, the test 
may fail, since too much alkalinity interferes with the test. 

If the soil contains abnormal concentrations of nitrite nitrogen, 
a brownish yellow discoloration is to be noted in the routine manga- 
nese test. 

If no perceptible blue color is detected, add 2 drops of reagent 
"C". Stir at once with a glass rod and let stand for two minutes. 
If not more than a faint blue color appears, the test is recorded as 
"negative", and the soil contains less than 2 pounds of manganese per 
acre. If there is a strong blue color, without a trace of green or yel- 
low, a "'trace" amount is read, representing approximately 2 pounds 
per acre. If the color is green, gradually changing to yellow, this 
is recognized as "trace plus", or approximately 3 pounds per acre. 
If any blue color was apparent in the previous stage of testing, a deep 
yellow to orange-yellow color develops almost at once. 

The above additional procedure is especially useful in differenti- 
ating soils suspected of being manganese-deficient. 

The following alternate procedure may also be used to advantage 
when little or no reaction is obtained from the above method: Trans- 
fer 10 drops of the soil extract to the spot plate. Add 1 drop of rea- 
gent "C" and 1 drop of the special supplemental reagent (Tetrabase 
solution). A deep blue color develops almost at once in soils usually 
rated as "very low" or better by the regular method. When the re- 
sultant color is only faintly blue, the test may be considered as "nega- 
tive". With experience, an operator can readily distinguish differ- 
ences between tests even with the traces of extractable manganese 
that usually typify manganese-deficient soils. A similar method has 
been used by Thomas. (48) It should also be noted that traces of 
the violet permanganate color can be observed upon the addition of 
reagent "C", alone, after two or three minutes, when the extract con- 
tains a considerable amount of manganese. 

Special Chemical Tests 

One or more of the following tests may be of definite diagnostic 
value, under conditions that seem to warrant them, or when the ab- 
normal conditions of the soil are not evidently correlated with the 
routine tests. 

Iron test (both ferric and ferrous) 1 : Transfer 10 drops of the 
extract to the spot plate. Add 3 drops of reagent "A" and 1 drop 

^his is adapted from the spot plate test of Feigl (16). 
2 This was introduced by the author (37) as a soil test. 



600 Connecticut Experiment Station Bulletin 450 

of reagent "B". Stir, let stand two minutes. The resultant colors 
indicate amounts approximately as follows: 



Color 


Test 


Relative 
Test Index 


Blue 

Blue green 
Apple green 
Pale green 
Greenish yellow 
Lemon yellow 


Very high 
High 

Medium high 

Medium 

Low 

Very low 


10 
8 
6 
4 
2 
1 



In this and subsequent iron tests, care should be taken to prevent 
the soil extracting solution or soil extract from coming in contact with 
any implement or piece of apparatus containing metallic iron. 

Ferric iron test: Transfer 10 drops of the soil extract to the 
spot plate. Add 3 drops of reagent "A" and 1 drop of reagent "B". 
Stir and let stand two minutes. The resultant colors represent 
amounts approximately as follows: 

Relative 
Color Test Test Index 

Deep brownish red Very high 10 

Medium brownish red High 8 

Pale brownish red Medium high 6 

Very pale brownish red Medium 4 

Slight reddish tint Low 2 

Very faint reddish tint Very low 1 

Ferrous iron test: Transfer 10 drops of the soil extract to the 
spot plate. Add 2 drops of reagent "A" and 1 drop of reagent "B". 
Stir and let stand two minutes. The resultant colors and correspond- 
ing tests are the same as indicated for the above general iron test 
(ferric and ferrous). 

A suggested alternate test for ferrous iron employs a reagent 
prepared as follows: A 1 percent aqueous solution of alpha-alpha- 
dipyridyl, aciduated with 1 ml. of concentrated hydrochloric acid per 
100 ml. Ten drops of the soil extract, treated with 2 drops of this 
reagent, give a deep red color when considerable ferrous iron is 
present, grading to no color when no ferrous iron is present. This 
is a somewhat more sensitive test than that described above. 

Sulfate sulfur test: Transfer 10 drops of the soil extract to the 
test vial. Add 1 drop of the reagent. Shake vigorously and let stand 
for five minutes. The calcium chart is used in reading the results. 

Since this test is not sensitive over the range of concentrations 
existing in most soils of humid regions, except as a result of heavy ap- 
plications of sulfate materials, it is not conducted as a routine pro- 
cedure. 

Nitrite 1 nitrogen test: Transfer 10 drops of the soil extract to 
the spot plate. Add 1 drop of the nitrite reagent, 1 drop of hydro- 
chloric acid (1:1) and 4 drops of magnesium reagent "B" (15 percent 
NaOH). Stir and let stand one minute. The resultant colors may 
be rated from the following: 

'This is adapted from the test as employed by Spurway (45). 



Details of Universal Soil Testing Methods 601 

Relative 
Color Test Test Index 

Yellowish orange Very high 10 

Orange yellow High 7 

Lemon yellow Medium 4 

Pale yellow Low 2 

Trace of yellowish tint Very low 1 

Soils very rarely show readable nitrite tests under normal field 
conditions. 

Sodium test 1 : Since the Universal soil extracting solution con- 
tains sodium, the soil must be extracted with special sodium extracting 
solution. The procedure of extraction is not otherwise different. 

Transfer 5 drops of the extract, thus obtained, to a test vial. 
Add 20 drops (1 ml.) of the reagent. Shake vigorously at one minute 
intervals for 10 minutes and compare, using the potassium chart. 

Soils in humid regions, except those receiving overflow water 
from oceanic tides, rarely show readable tests by this procedure. 
This test is especially applicable to alkaline conditions existing in arid 
soils. 

Chloride test 2 : Since the Universal soil extracting solution gives 
a precipitate of silver acetate when tested with the chloride reagent, 
the soil must be extracted with the special chloride extracting solution, 
or by distilled water, if clear extracts can be obtained thus. The 
procedure of extraction is the same in other respects. 

Transfer 10 drops of the soil extract, so obtained, to the test 
vial. Add 1 drop of the reagent. Shake vigorously, and compare, 
using the calcium chart. 

This test is valuable on saline soils, or when contamination from 
sea water or sea spray is suspected. Normal soils of humid regions 
rarely give readable tests, except when recently receiving liberal 
amounts of fertilizers containing chlorides. 

Carbonate test: A soil containing carbonates in appreciable 
amounts is readily identified by the development of effervescence on 
the soil surface when the Universal soil extracting solution is filtered 
through it. This usually results in the development of a convex soil 
surface at the end of the extraction. No quantitative measurement is 
attempted. 

Soils high in carbonates also give extracts which show white 
precipitates on the addition of an alkaline reagent (Ammonia reagent 
or magnesium reagent "B"). Normally this precepitate does not in- 
terfere with the color reactions and is due to the formation of calcium 
hydroxide in excess of its solubility. 

Boron test 3 : Place 1 level tablespoonful of soil in a 30 ml. beaker 
Add the Universal soil extracting solution slowly, a few drops at a 

iThis is adapted from the test as employed by Spurway (45). 
2 This is adapted from the test as employed by Spurway (45). 

3 This is adapted from the test proposed by the author (38). Helpful suggestions have been 
provided by T. R. Swanback of this Station. 



602 Connecticut Experiment Station Bulletin 450 

time, stirring the soil mass with a glass rod, until the soil is thoroughly 
wetted. Add an additional 5 ml. quantity of the soil extracting so- 
lution. Stir for one minute. Filter. Transfer 5 drops of the extract 
to a spot plate depression. Add 2 drops of pure glycerin (AR). Add 

1 drop of reagent "A" and 6 drops of reagent "B". Stir thoroughly 
and let stand for 15 minutes. A clear lemon yellow is negative, re- 
presenting an amount of boron below the limits of sensitivity of the 
test. Boron is indicated by increasing depths of a reddish color. A 
golden yellow, very slightly tinged with red, appears at approximately 

2 p. p.m. in the extract. At 4 p.p.m., a pale peach color appears. At 
10 p.p.m., a deep peach color develops. At 20 p.p.m., a salmon red is 
in evidence. At 50 p.p.m., or higher concentrations, a full red color 
is obtained. The color deepens quite materially during the first few 
minutes. 

Boron tests should be conducted at the same time as "blank" tests 
on the Universal soil extracting solution itself. The number of drops 
of reagent "B" may need to be adjusted. It should be 1 drop less 
than the amount required to produce a barely perceptible reddish 
tinge to the blank test. (A red color can be developed in the ab- 
sence of boron, by adding an excess of the acid reagent "B". 

Boron tests should be calibrated carefully on the basis of stan- 
dards prepared from boric acid dissolved in the Universal soil ex- 
tracting solution. 

It has been noted that with soils giving high iron or aluminum 
tests the boron test color may be erroneously in evidence, while high 
amounts of nitrates tend to diminish the sensitivity of the test. 
Hence, if possible, the boron test should be confirmed by em- 
ploying a laboratory procedure, such as the hot water extract method 
of Berger and Truog (3). It is doubtful if the limits of boron de- 
ficiency for most crops can be estimated by the quick test procedure. 

Zinc test 1 : Prepare the soil extract in the same manner as for the 
boron test. Transfer 10 drops of the extract to a test vial. Add 4 
drops of reagent "A" and 10 drops of reagent "B". Shake thorough- 
ly and let stand for two minutes. Add 20 drops of reagent "C". 
Shake gently and let stand for 10 minutes. The appearance of a blue 
color at the film of contact between the ether and the aqueous solu- 
tion is evidence of zinc. A barely perceptible film of blue indicates 
approximately 10 parts per million in the extract. Above about 25 
p.p.m., a blue precipitate begins to accumulate in the bottom of the 
vial. The test should be compared with those obtained from stan- 
dard amounts of zinc as zinc acetate, dissolved in the Universal soil 
extracting solution. It has not yet been possible to calibrate the 
above amounts in the extract in terms of that which is active in the 
soil. However, the presence of considerable zinc, thus shown, is evi- 
dence of the accumulation of harmful concentrations, as occassionally 
found in the vicinity of industrial plants processing zinc ore or metal. 



J This is adapted from the method of Krumbholz and Sauchez (30). 



Details of Universal Soil Testing Methods 603 

Copper test 1 : Prepare the soil extract as for the boron test. 
Transfer 10 drops of the extract to the spot plate.. Add 2 drops of 
the reagent. Stir and let stand for five minutes. A barely percepti- 
ble trace of greenish yellow color is observed when approximately 
2 p. p.m., of copper are present in the extract. The color deepens 
in greenish hue, with higher amounts, being quite definite at 5 p. p.m.. 
at 10 p. p.m., a good apple green color is developed. Readings 
of the test should be calibrated against standard amounts of copper, 
as copper sulfate, dissolved in the Universal soil extracting solution. 

The copper test is especially useful in examining soils with con- 
siderable accumulations of spray residues. 

Mercury test 2 : Prepare the soil extract as for the boron test. 
Transfer 10 drops of the extract to the spot plate. Add 2 drops of 
the reagent. Add 3 drops of sodium hydroxide solution (same as 
Magnesium reagent "B"). Stir and let stand for one minute. A pale 
salmon red, from the indicator itself, is a negative test. A deep sal- 
mon red is observed when approximately 5 p. p.m. are present in the 
extract. The color is a deep red at 10 p. p.m., violet red at 20 p. p.m.. 
violet at 50 p. p.m., purple at 100 p. p.m. Readings of the test should 
be calibrated against standard amounts of mercuric chloride, dissolved 
in the Universal soil extracting solution. 

The mercury test is occasionally useful in revealing mercury ac- 
cumulations from fungicides containing this element. It confirms the 
indication of mercury in the phosphorus test, and is considerably 
more sensitive. 

Lead test 3 : Prepare the soil extract as for the boron test. 
Transfer 5 drops of the extract to the test vial. Squeeze out 1 drop 
of the reagent upon the center of the liquid surface. The green col- 
ored spot thus formed should remain undisturbed. Observe during 
a two-minute period. If the color of the spot remains green, no 
measurable amount of lead is present in the extract. At approximate- 
ly 10 p. p.m. (in the extract), an olive green hue develops in two min- 
utes; at 20 p. p.m., the resultant color is olive brown; at 40 p.p.m., — • 
reddish brown; at 60 p.p.m. — brick red within one minute; at 100 
p.p.m. — brick red in one half minute. 

The lead test is useful in identifying soils treated with lead com- 
pounds in insect control, or soils contaminated with lead compounds 
as residues from sprayed crops. It should be noted that mercury 
compounds give a golden yellow color, and zinc salts give a cherry 
red color, with the reagent used in the lead test. 

Arsenic test 4 : Prepare the soil extract as for the boron test. 
Place a few grains of granular zinc in the bottom of a test vial. Add 
5 drops of concentrated sulfuric acid. Add 10 drops of the soil ex- 
tract. Place a disc of filter paper, approximately 15 mm. in diameter. 



iThis is adapted from the method proposed by Hosking (29). 

2 This is adapted from the method of Feigl and Neuber ( 17 ) . 

3 This is adapted from the method of Fischer (21). 

4 This is adapted from the Feigl (19) modification of the original Gutzeit test. 



604 Connecticut Experiment Station Bulletin 450 

over the top of the test vial. Moisten the filter paper with 1 drop 
of silver nitrate solution (Chloride reagent). Shake the vial gently 
several times, until gas bubbles are freely liberated. Let stand for 
two minutes. Examine the bottom side of the test paper disc. A 
faint yellowish or silvery sheen, with no perceptible darkening, is a 
negative test, the slight coloration resulting from other constituents 
that may be present. With increasing amounts of arsenic, the test 
paper shows darker spots. The test is sensitive to approximately 10 
parts per million in the extract. 

The arsenic test is useful in studying arsenic accumulations and 
residues from insect control treatments, sprays and dusts. 

Special Precautions 

All glassware, spot plates, stirring rods, etc., should be washed 
with clean tap water and rinsed with distilled water immediately after 
being used. The spot plates require occasional cleaning with a sul- 
furic acid-dichromate cleaning solution, to remove stains. 

The eyedropper pipettes may be flushed by vigorously pumping 
water from a beaker in and out of them by intermittent pressure on 
their bulbs. Any adhering precipitates should be carefully brushed 
loose from the bottoms of the test vials before final rinsing. 

Reagent bottles should be kept clean, and encrustations should 
not be permitted to accumulate around their caps. 

Any reagent that fails to give a satisfactory blank test with the 
soil extracting solution, or that fails to give high tests on "check" 
soils consistently giving high results on previous trials for a given 
constituent, should be rejected and replaced. 

Transfer pipettes calibrated in .05 ml. subdivisions give greater ac- 
curacy of measurement. One drop is assumed to represent .05 ml., 
but there is a considerable discrepancy between many of the com- 
mercial eyedropper pipettes. 

The Adaptation of the Tests to Plant Tissue Testing 

During the past few years, numerous investigators have found 
it desirable to supplement quick tests of soils with similar tests con- 
ducted on fresh plant tissue or plant tissue extracts. It has been fre- 
quently possible thus to verify a case of suspected crop deficiency or 
other nutrient abnormality. The visible symptoms produced by ser- 
ious deficiency or excess of a given constituent are frequently recog- 
nized by the trained observer. Such symptoms are well illustrated 
in a recent joint publication of the American Society of Agronomy 
and the National Fertilizer Association ( 1 ) . However, in the field, 
the plant may suffer from combinations of various symptoms that are 
not readily identifiable. Under such conditions chemical plant tissue 
tests are often of much value. 

Methods for such testing have been outlined by Thornton (49), 
Carolus (8) and Hester (27). A suggested adaptation, employing the 



Details of Universal Soil Testing Methods 605 

Universal soil extracting solution and the various tests previously 
described, is as follows: 

Obtain fresh plant material from the growing crop, both from 
normal and questionable plants. Select small lots of the leaf petioles 
or succulent portions of the stem in the part of the plant most affected 
by any observable abnormal symptoms. Using a clean sharp safety 
razor blade, cut the material into fine bits not more than 2 mm. in 
length or thickness. Place 0.5 gm. of the material in a 50 ml. Erlen- 
meyer flask and add 10 ml. of the Universal soil extracting solution 
and a pinch of decolorizing charcoal. Shake vigorously for five min- 
utes, and filter. The extract may be tested for various constituents 
by the procedures described for the soil tests. 1 The extract may re- 
quire dilution with the extracting solution in order to bring the tests 
to a distinguished scale. Such dilutions should be in definite ratios 
(e.g.: 2 drops diluted to 10 drops, or 1 drop diluted to 4 drops). 

The charts may be used in a comparative sense. However, no 
definite ratings can be used for general application, since the magni- 
tude of the tests obtained on different species and under different 
growing conditions may vary significantly. Interpretations should be 
based on comparisons between plants of the same species and age and 
grown under the same general environment. 

Hester (27) has proposed the use of the Waring blender or sim- 
ilar equipment for the comminution of the plant tissue material. In 
this procedure, 5 gms. of the tissue and 100 ml. of the extracting so- 
lution, together with one-quarter teaspoonful of clarifying charcoal 
(Darco or similar grade), are placed in the machine for a period of 
three to five minutes, until thoroughly comminuted. After filtration, 
the tissue extract is tested as usual. The amounts of decolorizing 
charcoal required to give a colorless extract varies with the different 
types of plant material. 



Quantitative Calibration of Test Charts 

The charts and scales of reading given in the back section of this 
bulletin were initially based on an assumption that a given constituent 
is extracted by the percolation of the 10 ml. portion through the soil 
mass in a fairly definite relation to the total amount that would become 
active, or extractable, by a series of successive extractions repeated 
until all that can be thus removed is recovered. On this basis, the 
first approximates the following percentages of the total thus extract- 
able: 

Nitrate nitrogen — 80 percent; ammonia nitrogen — 50 percent; 
phosphorus — 4' percent; potassium — 50 percent; calcium — 50 per- 
cent; magnesium — 50 percent; aluminum— 10 percent; manganese 
— 20 percent; iron — 20 percent; sulfur — 80 percent; nitrite ni- 
trogen — 80 percent; Sodium — 60 percent; chlorides — 80 percent. 



*In the manganese test on plant tissue extract, use four drops of reagent "A". 



606 Connecticut Experiment Station Bulletin 450 

In the above connection, it is of interest to note that practically 
all of the nitrate and similar water-soluble constituents are removed 
by four successive extractions. The exchangeable bases, such as po- 
tassium, calcium and magnesium, are obtained in six or seven portions. 
On the other hand, the phosphorus concentrations of the second ex- 
tract is usually slightly higher than the first. Successive extractions 
diminish only slightly in phosphorus content, even up to the twentieth 
portion. Aluminum and iron diminish slowly in concentration for six 
or seven extractions, and thereafter remain practically constant, with 
definite amounts of these constituents proportional to the amount in 
the first extract. 

In previous publications on the Universal soil testing system 
(Bulletins 372 and 392) these relationships have been used to calcu- 
late the number of pounds per acre to plow depth that would be repre- 
sented by the test. Such an expression of results provides a helpful 
concept in evaluating the magnitude of the test, but has been fre- 
quently misused, or applied too literally, in the interpretation of re- 
sults by some soil testing laboratories using these methods. Hence 
it has been decided to substitute the use of a Relative Test Index 
scale developed in the course of the correlation of results of the A.S.A. 
soil testing study referred to on a preceding page. This rating in- 
dex scales up to 10 for the normal range of tests ordinarily en- 
countered. The Index Number provides a helpful basis for comparing 
the quantitative magnitude of the test, and simplifies comparisons be- 
tween tests. 

Composite solution standards for the calibration o£ the charts: 

The color and turbidity charts given in this bulletin are the results 
of the best efforts of the engraver and printer. However, it is very 
difficult to obtain reproductions by the photo-engraving process. It 
is desirable to check them with solutions containing various concen- 
trations representing the ranges of sensitivity of the tests. The fol- 
lowing scheme employs a series of single stock solutions for each 
of the constituents in the routine tests. These are combined in a 
series of three mixed stock solutions that may be kept ready for ref- 
erence at any time. The mixed stock solutions are combined and 
diluted in varying proportions in order to furnish convenient quanti- 
ties for immediate comparisons. (Calculations from the exact con- 
centrations employed, through the successive mixtures and dilutions, 
should not be used in an exact quantitative sense when such mixed 
standard is employed.) 

1. Prepare separate solutions for each constituent, dissolving 
quantities of the C.P. chemical shown in the following table in 100 
ml. of the Universal soil extracting solution: 



Details of Universal Soil Testing Methods 



607 



Constituent 
Nitrate Nitrogen 
Ammonia Nitrogen 
Phosphorus 
Potassium 
Calcium 
Magnesium 
Aluminum 
Manganese 



Chemical 

NaN0 3 

(NH«)*SO* 

NaH 2 PO,.H 2 

KC1 

Ca(GH 3 2 ) 2 .H 2 

Mg(GH 3 2 ) 2 .4H 2 

A1C1 3 .6H 2 

MnS0 4 .4H 2 



Gms. 
per 100 ml. 


Concentration 

of 

Constituent 

p.p.m. 


.182 


300 


.473 


1,000 


.036 


80 


.191 


1,000 


8.800 


15,000 


.442 


500 


.335 


500 


.162 


400 



2. Prepare three mixed stock solutions from the above separate 
solutions. 

Mixed Stock Solution "A" 

10 ml. of N0 3 N ( 300 p.p.m.) 

10 " " NH 4 N (1000 " ) 

10 " " P ( 80 " 

10 " " Mg (500 " ) 

10 " " Universal soil extracting solution 

Mixed Stock Solution "B" 

10 ml. of K ( 1,000 p.p.m.) 

io " ;; Ca (15,000 " ) 

30 " Universal soil extracting solution 

Mixed Stock Solution "C" 

10 ml. of Al (1,000 p.p.m.) 
10 " " Mn ( 400 " ) 
30 " Universal Soil extracting solution 

The above may conveniently be kept available for ready use in 
2-ounce dropper bottles. 

3. For chart calibration, set up a series of 6 one-half ounce glass 
vials, numbered to correspond to Rating Index Number. A 10 ml. 
mark should be provided on each vial. 

The amounts of the three mixed stock solutions to be added to 
each vial are as follows, in drops: 



Relative Test Index: 




l 


2 


4 


6 


8 


10 


Mixed Stock Solution 


"A" 


1 


3 


6 


12 


18 


30 


" " " 


"B" 


8 


14 


20 


24 


28 


32 


" " " 


"C" 


1 


3 


6 


12 


18 


30 



Make up the contents of each vial to the 10 ml. mark with Uni- 
versal soil extracting solution. Mix thoroughly. Test for each con- 
stituent as usual, except for Al, when U drops, undiluted, should be 
tested. These standards are not suitable for the Mg-A-1 reagent pro- 
cedure. When this reagent is used, omit mixed stock solution "C" 
in preparing the standards. This reagent is unreliable in the presence 
of significant concentrations of Al, and to some extent, in the 
presence of Mn. 



608 Connecticut Experiment Station Bulletin 450 

The special tests may be calibrated with appropriate solution 
standards prepared from pure salts dissolved in the extracting solu- 
tion and diluted to their proper range of sensitivity. 

Application of Tests to Drainage Water from Soils, Irrigation Waters, Etc. 

It is frequently desirable to obtain a rough picture of the relative 
amounts of various soluble chemical constituents in the drainage water 
from soils, water used for irrigation purposes, or from springs, wells 
and streams. The tests used for soil extracts can be applied for this 
purpose, although a few adjustments are required to compensate for 
the poor buffer action of such dilute solutions. The modifications are 
indicated below for the various routine and special tests that are thus 
affected: 

Ammonia nitrogen: Use only 1 drop of the test reagent. 

Phosphorus: Use only 5 drops of the water, adding 5 drops of the Uni- 
versal soil extracting solution. Use only 1 drop of reagent "B". 

Calcium: Add 2 drops of the Universal soil extracting solution to 10 
drops of the water and mix before adding the test reagent. 

Magnesium: Add 5 drops of the Universal soil extracting solution to 10 

drops of the water and mix before adding the test reagents. Use 

only 2 drops of Reagent "B" (15 percent NaOH) in developing the 
test. 

Aluminum: Use 4 drops of the water, add 1 drop of the Universal soil 
extracting solution and mix before adding the test reagent. 

Manganese: Add 1 drop of 1:3 acetic (one part glacial acetic acid to 3 
parts of distilled water) to 10 drops of the water and mix before adding 
the reagents. , 

Copper: Add 2 drops of the Universal soil testing solution to 10 drops of 
the water and mix before adding the reagent. 

Carbonates: Place 2 ml. of the water in a test vial that has been very thor- 
oughly rinsed with distilled water. Add 1 drop of phenolphthalein indica- 
tor (prepared by dissolving 0.5 gm. of phenolphthalein powder in 50 ml. 
of ethyl alcohol and diluting to 100 ml.). A pink to red color indicates 
the presence of carbonates. Add standard KHS0 4 solution (.034 gms. 
of potassium acid sulfate dissolved in 100 ml. of distilled water) drop 
by drop, until the pink color entirely disappears, after shaking. Each 
drop thus required is equivalent to 50 parts of carbonate (C0 3 ) per 
million, in the water tested. 

In case it is desired also to estimate bicarbonates (HC0 3 ), add 
1 drop of methyl orange indicator (0.1 gm. methyl orange in 50 ml. 
ethyl alcohol, diluted, to 100 ml. with distilled water), and continue 
the addition of KHS0 4 solution, drop by drop, until the yellow orange 
color changes to reddish orange. Each drop of KHS0 4 solution re- 
quired, not including the amount required to decolorize the phenolph- 
thalein, is equivalent to approximately 75 parts of bicarbonate (HC0 3 ) 
per million, in the water tested. 

The other tests are conducted exactly as previously described in 
the section on soil extract testing. 

Quantitative estimations in water tests: It is possible to make a 
fair estimate of the concentration of the various soluble constituents 
in water thus tested, within the range of sentivity of the test. Re- 



Details of Universal Soil Testing Methods 



609 



suits are suitably expressed in terms of parts per million. The fol- 
lowing table indicates the approximate amounts thus indicated, based 
on the use of the charts or described colors. 



Table 1. Approximate Quantitative Indications in Water Tests 

Concentrations, in parts per million, at Relative Test Index 
shown on chart, or described 





l 


2 




4 


6 


8 


10 


Nitrate nitrogen 


0.3 


0.9 




1.5 


3 


6 


12 


Ammonia Nitrogen 


1 


3 




5 


10 


20 


40 


Phosphorus 


0.2 


0.5 




0.8 


1.5 


3 


6 


Potassium 


10 


15 




20 


30 


40 


50 


Calcium 


100 


150 




200 


300 


400 


500 


Magnesium using A 2 reagent) 


0.5 


1 




2 


5 


10 


20 


Aluminum 


0.5 


1 




2 


5 


10 


20 


Manganese (A and B 
















reagents only) 


0.5 


1 




2 


4 


8 


16 


Iron 


1.5 


3 




5 


10 


25 


50 


Sulfate sulfur 


50 


100 




200 


300 


400 


600 


Nitrite nitrogen 


0.5 


1 




2 


4 


6 


10 


Sodium 


120 


180 




240 


360 


480 


600 


Chlorine 


25 


50 




100 


200 


400 


800 


Boron — 


Sensitivity 


range: 


2 


to 50 


parts per 


million 




Zinc — 


" 




5 


to 50 








Copper — 






2 


to 25 








Mercury — 






5 


to 100 








Lead — 


" 


" 


10 to 100 


" " 


" 




Arsenic — 




" 


10 


to 100 









Adaptation of Quick Tests to Saline or Alkali Soils 

The method of soil extraction with an acetic acid-sodium acetate 
buffer solution, such as employed in the Universal soil testing system, 
is primarily adapted to soils of humid regions, containing relatively 
low amounts of water-soluble salts, and either acid or only slightly 
alkaline (below 8.2 pH) in reaction. 

Saline or white alkali soils contain large amounts of water-soluble 
salts, such as the chlorides and sulfates of sodium, magnesium and 
calcium. When the salt concentration is fairly high (3,000 parts or 
more per million), a mixture of the soil with distilled water, for in- 
stance, 1 level teaspoonful per 10 ml. of distilled water, is sufficiently 
flocculated by the presence of the salts to yield a clear water extract 
upon filtration. However, if the salt concentration is low, or if the 
soil is deflocculated by the presence of alkali carbonate, a clear water 
extract is not thus obtained. 

A suitable procedure for obtaining clear, colorless extracts of soils 
that may be reliably tested for the common alkali or saline constitu- 
ents is as follows: 

Place 1 teaspoonful of the soil in a 30 ml. beaker. Add 10 ml. 
of distilled water to which from 1 to 5 drops of a neutral 1 percent 
copper acetate solution have been added. (Heavy soils low in salts 
require more copper acetate to effect clarification. Use no more than 



610 Connecticut Experiment Station Bulletin 450 

is actually necessary to give a clear filtrate). Stir thoroughly for one 
minute, and filter through a paper of the quality used in the usual 
procedure. 

The extract may be subjected to various tests following the 
techniques recommended for drainage waters, etc. The copper test, 
of course, cannot be included. The most useful tests are those for 
chlorides, sulfates, nitrates, sodium, calcium, magnesium and potas- 
sium. "Black alkali" soils yield extracts showing the presence of sol- 
uble carbonates by the phenolphthalein indicator. However, a pH 
test of the soil should be employed to confirm the presence of alkali. 
(Black alkali soils are indicated by pH tests above 8.5). 



THE INTERPRETATION OF SOIL TESTS 

SOIL test data should be considered with reference to the limit- 
ing effects on crop growth that may be expected from other factors, 
such as the following: poor aeration or restricted root system caused 
by undesirable soil structure or soil tilth, deficient drainage, unfavor- 
able seasonal conditions, plant pests, plant diseases. Irrespective of 
the chemical fertility of the soil, the crop expectation is less than nor- 
mal when one or more of these factors is in operation. It is impractic- 
able to seek to attain the most desirable tests on soils otherwise re- 
stricted in productive capacity. 

The economic productive level of the crop under consideration 
determines to a marked degree the extent to which one can afford to 
build up the fertility level of the soil. Fertilizers can be profitably 
applied in much larger amounts for crops capable of giving high net 
returns, per acre. This is conspicuously true of intensive vegetable 
crops, tobacco or potatoes, as contrasted with hay or pasture crops. 

Soil test should be compared in the light of past practices with 
respect to fertilizers, manures and lime. Many obvious correlations 
may be observed. On the other hand, when the soil treatment has 
been so favorable as to justify an expectation of relatively high 
ratings for phosphorus, potassium and calcium, and a low test for alu- 
minum, the explanation for less desirable tests should be sought, 
giving consideration to the fixing power of the soil and the degree of 
exhaustion of available constituents that could be accomplished by 
crop withdrawal. 

Some tests, notably those for nitrate and ammonia nitrogen, de- 
pend upon temporary conditions, such as the activities of soil micro- 
organisms, seasonal effects and amounts of leaching that have been 
in recent operation. A test may be given much weight, or entirely 
disregarded, depending upon whether or not the conditions have been 
such as to favor the accumulation of such conditions in the soil. 

The interrelation of various quick tests and the pH test should 
be especially considered. Chemical soil fertility is best estimated from 
a study of the composite pattern thus presented. 



Interpretation of Soil Tests 611 

No definite limits for favorable or unfavorable soil tests can be 
set for a given constituent, even for a particular crop, that will apply 
under all conditions. Sound judgment, thorough agronomic training 
and much experience in the applying of the results of soil tests on soils 
of known performance are all essential to the diagnostic interpretation 
of soil tests in terms of soil management practices. A laboratory tech- 
nician who can follow simple chemical routines can be quickly trained 
to make tests described in this bulletin. The practical value of the 
tests is limited chiefly by the qualifications of the person who is re- 
sponsible for translating the data into amounts and kinds of fertilizers, 
manures, lime and other soil amendments that are most likely to be 
effective in promoting profitable crop production. 

The following details pertaining to soil test interpretation are 
based chiefly upon the author's experience in applying soil test re- 
sults to many thousands of cases, chiefly on Connecticut soils, during 
the past 10 years, and to nearly 200 soils that have been exhaustively 
studied both by laboratory analyses and by crop responses to various 
treatments in greenhouse pot cultures. However, they may need to 
be considerably modified in interpreting soil test results on soils of 
other sections of the country, or for crops other than those commonly 
grown in this locality. 

The interpretation of pH tests: As previously stated, pH tests 
do not directly indicate lime needs. The amount of lime required to 
change a soil from a given pH to a higher, less acid-indicating one, 
depends not only upon the change in pH to be effected, but also 
upon the base exchange capacity of the soil, chiefly as related to the 
organic matter and clay content of the soil within a given region. 
The soils of Connecticut may be roughly classified into four groups, 
as shown in Table 2. 

Table 2. Soil Groups in Terms of Lime absorption as Related 
to pH Adjustment 









Organic 










Mater 




Lime Absorption 


Textural 




Content 




Group 


Class 




Approximate 
Percent 


Base Exchange 
Capacity* 


I 


Loamy sand 




2-4 ) 






Sandy loam 




1-3 ) 


4-6 


II 


Loamy sand 




5-7 ) 






Sandy loam 




4-6 ) 


7-10 




Fine sandy 1 


oam 


2-4 ) 




III 


Sandy loam 




7-10) 






Fine sandy 


loam 


5-7 ) 


11-15 




Loam 




3-5 ) 




IV 


Fine sandy 


loam 


8-10) 






Loam 




6-8 ) 


16-20 




Clay loam 




3-6 ) 





*ln terms of milligram equivalents per 100 gms. of soil 

The degree of pH adjustment in the positive direction that is 
desirable depends upon the minimum pH at which the crop will give 
normal production on an otherwise favorable soil. Crops vary con- 



612 



Connecticut Experiment Station Bulletin 450 



siderably in their range of adjustment to varying pH levels. How- 
ever, for all practical purposes, four soil reaction preference groups 
are now reasonably well established. Crops representing these 
groups are shown in Table 3. 

Table 3. Soil Reaction Preference Groups 



A 


B 


C 


D 


Alfalfa 


Bluegrass 


Beans 


Arbutusf 


Asparagus 


Broccoli 


Carrots 


Azalea 


Barley 


Brussels Sprouts 


Clover, alsike 


Bent grass 


Beets 


Cabbage 


Clover, white 


Blueberries^ 


Celery 


Cauliflower 


Corn 


Buckwheat 


Lettuce 


Clover, ladino 


Eggplant* 


Fescues 


Onions 


Clover, red 


Fescue, red 


Laurelf 


Radishes 


Cucumbers 


Parsnips 


Oats 


Spinach 


Muskmelons 


Peppers 


Potatoes 


Sweet Clover 


Peas 


Pumpkins 


Red top 




Rape 


Soybeans 


Rhododendronf 




Rhubarb 


Strawberries 


Rye 






Squash 


Sweet potatoes 






Timothy 


Vetch, hairy 






Tobacco* 


Watermelons 






Tomatoes 








Turnips 








Wheat 





Group "A" crops are preferably grown on soils ranging from 
6.2 to 7.6 pH. However, if the soils give negative manganese tests, 
and are above 6.4 pH, there are possibilities of manganese deficiency. 
With high calcium and low aluminum tests, most of these crops may 
be successfully grown at reactions as low as 5.8 pH. 

Group "B" crops usually do well at reactions as low as 5.6 pH, 
unless the calcium test is low, or the aluminum test is high. They are 
not usually adversely affected by pH values up to 7.2, but it is pre- 
ferable to maintain a slight degree of acidity (6.0 to 6.6 pH). 

Group "C" crops do reasonably well down to as low as 5.0 pH, 
unless the calcium test is very low or the aluminum test is very high. 
The crops marked with an asterisk (*) need degrees of acidity rang- 
ing from 5.0 to 5.6 pH, because of disease trouble favored by higher 
reactions. 

Group "D" crops are favored by a considerable degree of acidity, 
and may be grown successfully at reactions as low as 4.6 pH, if other 
factors are properly adjusted. Potatoes require reactions below 5.2 
pH in order to protect them from scab. The plants marked with a 
dagger (t) are usually adversely affected by reactions above 5.4 pH. 

Soils with high calcium tests, when the aluminum test is not 
high, should be interpolated on the basis of recommendations for the 
next lower crop group. 

(Illustration: pH 5.6; very high calcium test; very low aluminum 
test. For crops in group II, lime as for crops in group HI.) 

Soils with high aluminum tests should be limed on the basis of 
the next lower pH interval, for the first two crop groups. 



Interpretation of Soil Tests 



613 



(Illustration: 5.6 pH; high aluminum test; low calcium test, 
on basis of recommendations for 5.2 pH.) 



Lime 



Soils with low to extra low magnesium tests (relative test in- 
dex below 3) should be limed with dolomitic (magnesian) lime if 
the pH test indicates that lime is needed. If the pH is sufficiently 
high so as not to require lime, magnesium should be used as mag- 
nesium sulfate or 'double manure salts". 

If the calcium is very low, and the magnesium test is very high, 
the liming should be in the form of a "high-calcic" material, preferably. 

The following table (Table 4) is based on pH measurements 
made in spring or late fall. If tests are made in midsummer, it is 
desirable to add the following pH corrections, based on differences 
in soil, for the various groups, before applying the table of lime re- 
quirements at various pH levels: 

Soil Group I — 0.5 pH 

Soil Group II — 0.4 pH 

Soil Group III — 0.3 pH 

Soil Group IV — 0.2 pH 

Table 4. Liming Recommendations for Various Crop Groups 
In Relation To Soil and pH 

Amounts in tons of agricultural limestone, per acre 
(Use three-fourths these amounts of hydrated lime) 





Crop 


Group A 








Soil 


Group 








I 


II 


III 


IV 


6.8 














6.4 


X 


X 


X 


X 


6.0 


.5 


.9 


1.2 


1.7 


5.6 


1.0 


1.7 


2.4 


3.3 


5.2 


1.4 


2.5 


3.5 


4.7 


4.8 


1.8 


3.1 


4.4 


5.8 


4.4 


2.1 
Crop 


3.5 

Group C 


5.0 


6.5 




Soil Group 








I 


II 


III 


IV 


6.4 


* 


* 


* 


* 


6.0 














5.6 














5.2 


.5 


.9 


1.2 


1.7 


4.8 


1.0 


1.7 


2.4 


3.3 


4.4 


1.4 


2.5 


3.5 


4.7 



4.0 



1.8 



3.1 



4.4 





Crop 


Group B 






Soil Group 




I 


II 


III 


IV 


























X 


X 


X 


X 


.5 


.9 


1.2 


1.7 


1.0 


1.7 


2.4 


3.3 


1.4 


2.5 


3.5 


4.7 


1.8 


3.1 


4.4 


5.8 




Crop 


Group D 






Soil 


Group 




I 


II 


III 


IV 


Z 


Z 


Z 


Z 


Z 


z 


Z 


z 


* 


* 


* 


* 














.5 


.9 


1.2 


1.7 


1.0 


1.7 


2.4 


3.3 


1.4 


2.5 


3.5 


4.7 



Z For crops of this group, a more acid soil is desirable. 

* Fertilizers with an acid residual effect should he used. 

Neutral fertilizers preferable. 

X Fertilizers with an alkaline residual effect should be used, or very light liming is optional. 

The amounts shown in the previous tables are based on lime ap- 
plications made to cultivated land, thoroughly worked into the soil in 
the preparation of the ground for cropping. When the lime is ap- 
plied as a top-dressing, as on permanent sod, from one-half to one- 
third as much is all that should be used, since the soil can only be af- 
fected for two or three inches when lime is thus used. 



614 Connecticut Experiment Station Bulletin 450 

Conditions Indicated by Various Quick Tests 
Nitrogen tests (ammonia, nitrite and nitrate): Nitrogen exists in 
the soil largely in the form of partially decomposed organic residues 
containing proteins. Micro-organisms (bacteria and fungi) gradually 
transform this nitrogen into ammonia compounds. Organic nitro- 
genous fertilizer materials and leguminous crop residues are more 
readily attacked due to their high protein content. Urea and cyanamid 
are fertilizer materials that are rapidly hydrolyzed to produce am- 
monium compounds, while nitrogen in this form is directly supplied 
in fertilizer containing sulfate of ammonia, ammophos or ammoniated 
phosphates. 

Nitrogen in ammonium compounds may be utilized as such by 
many plants, especially during their early growth, thus consuming the 
visible supply as indicated by the test. However, the chief reason 
for the failure of the ammonia test to reveal more than small amounts 
on normal field conditions is due to the rapid change to nitrites and 
nitrates by further bacterial activity. The pace of the change to ni- 
trates is usually so rapid in proportion to that of the earlier stages 
of nitrogen transformation that only a few weeks after fertilizer ap- 
plications supplying much ammonia, little or no ammonia nitrogen and 
no nitrite can be identified by tests. Except during a short period 
after such fertilizer treatment, a substantial ammonia test is an indi- 
cation of unfavorable conditions for nitrification, such as high acidity, 
excessive or deficient moisture supply, or other abnormal factor. 

Nitrite tests are rarely obtained, except as a temporary condition 
occasionally resulting from a very heavy nitrogenous fertilizer treat- 
ment that has not been well mixed into the soil, especially under poor 
aeration resulting from excess water. Nitrite tests in more than trace 
amounts should be considered as harmful. Instances of severe injury 
to plant growth have been noted on soils showing medium to high 
readings. 

Irrespective of the diagnostic value of the ammonia tests, it is 
desirable to make it in order to identify inaccurately high apparent 
potassium tests on soils that contain unusual amounts of ammonia ni- 
trogen. 

Nitrate nitrogen, whether formed in the soil from nitrification of 
ammonia derived from organic residues and fertilizer materials, or 
directly supplied in the fertilizer (as, for example, nitrate of soda), 
is rapidly assimilated by the roots of living plants, and is readily lost 
from the soil by the percolating action of heavy rains. Hence high tests 
for nitrate nitrogen in field soils are to be expected only when the 
root system of the crop is not yet fully developed. 

High tests indicate a large reserve of readily available nitrogen 
for the use of the crop as it begins to draw heavily upon the soil. 
Rapidly growing annual crops require a larger reserve during the 
early part of their life in the soil, since the gradual processes of ni- 
trogen liberation are rarely sufficiently rapid to meet their require- 
ments during the period of most active growth. Crops with perennial 



Interpretation of Soil Tests 615 

root systems, such as sod grasses, shrubs and trees, take up nitrogen 
through a much longer period of the year, and low nitrate tests do 
not necessarily indicate a lack of available nitrogen. 

Low tests are to be expected at the end of the cropping period, 
during winter and early spring, and after a period of heavy rainfall. 
Under such conditions, when all other factors are favorable, the ab- 
sence of nitrates may not indicate poor availability of soil nitrogen, 
but the crop is apt to respond to the addition of a readily available 
nitrogenous fertilizer. 

Abnormally high nitrate nitrogen tests are occasionally encoun- 
tered in greenhouse and other intensively fertilized soils, and are an 
indication of possible injury to the crop due to excessive concentration 
of the nitrate salts. Such a condition may be corrected by leaching 
the soils with large amounts of water. 

Thus the nitrogen tests may either be given much significance or 
practically disregarded, depending upon whether or not conditions are 
favorable to the development of accumulations of these mobile con- 
stituents. 

In order to give a reliable indication of the amount of readily 
available nitrogen in the soil, tests may be made on samples which 
have kept in "mellow-moist" condition, in a loosely covered vessel 
at a temperature of 60° F. or above, for several weeks. Low nitrate 
tests on such samples indicate real nitrogen deficiency in the soil. 
However, it is rarely practicable to do this on account of the delay 
thus involved. 

Since other factors than the soil test are usually most important 
in assessing the amount of available nitrogen that is likely to be sup- 
plied by the soil during the active growing period of the crop, it is 
convenient to recognize one or more of the soil characteristics that 
are usually involved in rating a given soil with respect to the fol- 
lowing Nitrogen Availability Classes: 

I — High: Liberal manure applications (such as 15-25 tons of 
stable manure) within a few months preceding the crop; unusually 
favorable amount of soil organic matter, as indicated by dark color, 
provided that the soil is well drained and not strongly acid; high to 
very high nitrogen tests. 

II — Medium: Light manure applications (8-14 tons of stable 
manure) within a few months preceding the crop; a large green 
manure or a heavy clover or alfalfa sod plowed under; medium to 
medium high organic matter, as indicated by medium dark color, 
under favorable drainage conditions; medium to medium high ni- 
trogen test ratings. 

Ill — Low : Average cultivated cropping conditions, or with 
grass sod plowed under; loamv soil texture, with fair organic matter 
content; low to very low nitrogen tests. 

IV— Very Low : Cultivated crops on sandy soils of relatively 
low organic content; very low nitrogen tests. 



616 Connecticut Experiment Station Bulletin 450 

The phosphorus test: Phosphorus occurs in unfertilized soils in 
slowly soluble mineral and organic combinations. It is a component 
of all mixed fertilizers, and is frequently applied alone as superphos- 
phate or bone meal. 

Under high levels of fertilization, in excess of 500 pounds per acre 
per year of fertilizers containing as much as 8 percent of "phosphoric 
acid", crops remove less phosphorus than is applied to the soil. This 
element is not leached downward. In soils of only moderate degrees 
of acidity, applied phosphates remain for long periods in fairly avail- 
able form. On highly acid soils, containing much active aluminum 
and iron, difficultly soluble phosphate compounds are formed with 
these elements. At low rates of fertilization, the phosphorus supplied 
by the fertilizer results in little or no accumulation, and there may be 
a net loss when little manure or fertilizer is used. When such a soil 
receives little or no lime, low phosphorus availability is the most com- 
mon condition. 

The phosphorus test indicates the level of more readily available 
phosphorus in the soil, either native or as a residue from previous ap- 
plications. There are marked differences in the abilities of various 
crops to thrive at the different degrees of phosphorus availibility 
shown by this test. Most market garden crops, potatoes, tobacco, 
and most legumes require applications of phosphatic fertilizers unless 
high tests are obtained. Many soils showing only medium tests grow 
good grass hay, corn, oats, and alsike clover with very little phosphorus 
fertilization, when otherwise in a fertile state. Low or very low tests 
indicate the necessity for proportionally high amounts of "phosphoric 
acid" in the fertilizer, depending upon the crop grown. 

The active phosphorus content of the soil is a fairly stable prop- 
erty, except as affected by recent fertilizer application. Soils which 
have received applications of arsenical materials may give high tests, 
regardless of their phosphorus content. Hence results in such cases 
are subject to question. 

At a given level of phosphorus availability, higher pH values 
(5.6 or above) tend to increase the test actually obtained. On the 
other hand, at greater degrees of acidity (below 5.0 pH), considerable 
amounts of slowly available aluminum and iron phosphates may be 
present in soils giving low tests. Reasonable allowance should be 
made for this factor, especially on soils known to have received con- 
siderable amounts of phosphorus in fertilizer applications during pre- 
vious years. 

The following conditions are usually to be considered in asso- 
ciation with one another in determining the Phosphorus Availability 
Classes: 

I — High: Liberal applications of complete fertilizers for sev- 
eral years, especially on a sandy soil; a slight degree of acidity; 
a low aluminum test; a high to very high phosphorus test. 

II — Medium: Moderate applications of complete fertilizers 
for several years: light loam or sandy loam texture; moderate to 



Interpretation of Soil Tests 617 

slight acidity; a medium aluminum test; a medium or medium high 
phosphorus test. 

Ill — Low: Light, infrequent fertilizer applications; a strong 
degree of acidity; a medium to high aluminum test; a low or medium 
low phosphorus test. 

IV — Very Low : No fertilizers on previous crops; a loam, 
silt loam or clay loam soil; a very strong degree of acidity; a high 
or very high aluminum test; a very low phosphorus test. 

The potassium test: Potassium occurs in soils in large amounts 
in the form of difficultly soluble rock minerals. Their gradual de- 
composition liberates small quantities of potassium which are loosely 
combined with colloidal material (clay and humus) capable of being 
displaced into the soil solution by base exchange reactions. Potas- 
sium is also added to the soil in fertilizers containing potash, or as 
manures or crop residues, and largely goes over into the exchangeable 
form. Some potassium is removed from the soil by leaching, especial- 
ly when under cultivation and liberally fertilized. 

The active potassium of the soil, best capable of nourishing the 
crop, is that which exists in exchangeable form, or in true solution. 
Quick tests indicate such supplies of this constituent. 

Active potassium may be removed from the soil more rapidly 
than replenished by natural process. Thus tests may be lower at 
the end of the growing season of a crop with high potash require- 
ments, than after the soil has been fallow or supporting little vege- 
tation for several months. Hence most reliable tests are obtained 
in the spring, prior to fertilization. 

Soils treated with liberal amounts of potassium fertilizers in re- 
cent years may contain some residues of moderately available potas- 
sium that are not recoverable by the methods of extraction des- 
cribed in this bulletin. This is due to the fixation of applied potassium 
in the non-exchangeable forms, from which the element may be more 
easily taken up by the crop than from the potassium existing in native 
soil minerals. Reasonable allowance for this factor should be made 
under such conditions. 

The following conditions are usually to be considered in associa- 
tion with one another in determining the Potassium Availability 
Classes: 

I — High : Heavy applications of complete fertilizers, supplying 
from 120 to 200 pounds of potash per acre, annually, or heavy 
treatment with manure of good quality; a loamy soil texture; cal- 
cium or magnesium tests not unusually high in relation to the po- 
tassium test; a high to very high potassium test. 

II — Medium: Moderate applications of complete fertilizers, 
supplying from 40 to 100 pounds of potash per acre during recent 
years; fair applications of manure of good quality; intensive crop- 
ping; a medium heavy soil texture; a medium to medium high po- 
tassium test. 

Ill — Lotv : Under intensive cropping, irrespective of past fer- 
tilizer treatment; under average cropping, with little or no fertilizer 



618 Connecticut Experiment Station Bulletin 450 

or manure, or with manure of poor quality (badly leached); a 
fairly low potassium test. 

IV — Very Low : No fertilizer or manure; very sandy soil tex- 
ture; a very low or extra low potassium test. 

The calcium test: Calcium in soils occurs in the form of un- 
decomposed carbonates (in calcareous soils), rock minerals, as ex- 
changeable calcium (absorbed by the soil colloids) and as soluble cal- 
cium salts. Acid soils contain no carbonates and are depleted in ex- 
changeable calcium. However, many soils which show a considerable 
degree of acidity by pH tests may have a fair amount of exchangeable 
calcium. This is especially true of soils high in organic matter or 
active mineral colloids. In many cases the calcium test is a better 
indication of lime needs than is the pH test. 

Soils with high and very high calcium tests contain adequate 
amounts of calcium for all crops. Usually they do not respond to 
liming, unless a high active aluminum concentration is indicated. 
Medium calcium tests on soils near the neutral point may be expected 
on light sandy soils, but on acid soils a need for lime is revealed for 
growing alfalfa, sweet clover and lime-loving vegetable crops. A low 
calcium test on soils with a high aluminum test is a certain indication 
of lime requirement for all except the most acid-tolerant plants, such 
as blueberries, strawberries, or ericaceous shrubs. When a very low 
test results, lime should be used in liberal amounts for most crops, 
unless only moderate applications may be made with safety on ac- 
count of disease factors. 

Certain disease-producing soil organisms seem to be closely re- 
lated to the available calcium in the soil, in relation to the other bases, 
especially potassium and magnesium. Thus club root is made less 
severe by increasing the calcium supply. Physiological root distur- 
bances, such as the brown root rot of tobacco, are frequently engen- 
dered by calcium deficiency. On the other hand, the black root rot of 
tobacco and the scab organism on potatoes become more troublesome 
on soils with higher relative amounts of calcium. 

It must be borne in mind that, unless all other tests are satisfac- 
tory, heavy liming may produce an abnormal soil balance. Thus 
liming has frequently proven injurious on many sandy soils of the 
southern United States which are deficient in other elements, such as 
magnesium, manganese, potassium or iron. A deficiency of boron in 
the soil is also accentuated by liming treatment. 

The magnesium test: Magnesium occurs in soils in the follow- 
ing forms: Dolomitic carbonates; unweathered minerals; exchange- 
able magnesium, absorbed by the soil colloids; soluble magnesium 
salts. 

High and very high tests for magnesium are developed from cal- 
careous soils derived from dolomitic limestones, and from moderately 
acid soils resulting from the weathering of rocks high in ferro-magne- 
sian minerals. Medium tests are more common on soils of moderate 
acidity, on calcareous soils from high calcic limestones, or on soils 



Interpretation of Soil Tests 619 

which have been moderately limed with material of dolomitic origin. 
Low tests are common on acid soils. Some strongly acid soils give very 
low or negative tests. This is particularly true of sandy soils. In such 
cases magnesium should be applied. The cheapest form is in dolomitic 
lime or limestones. On soils giving high calcium and very low mag- 
nesium tests, or pH values as high as desired for the crop, magnesium 
sulfate or other magnesium compounds commercially reclaimed from 
sea water may be used in order to supply magnesium without sweeten- 
ing the soil. Commercial fertilizers which are thus formulated are 
now on the market. 

The aluminum test: Aluminum occurs in large amounts in all 
soils, in the form of undecomposed minerals and in the inorganic col- 
loidal material. In neutral, slightly acid or slightly alkaline soils, the 
element is in inert combinations that have no direct effect upon plant 
growth. At greater degrees of acidity, aluminum becomes active, 
capable of combining as soluble salts and thus exerting a toxic effect 
upon the growth of many plants, especially those which are benefited 
by liming when grown on acid soils. A high or very high test is a 
certain index of an undesirably acid soil, upon which acid-sensitive 
crops are almost certain to fail. A medium test is not serious, especially 
with grasses, corn, oats, potatoes, and tobacco. A low or negative 
test is desirable, except for distinctly acid-tolerant plants. 

The manganese test: Manganese occurs in small amounts in all 
soils, chiefly in relatively insoluble combinations. In some calcareous 
soils and acid soils that have been heavily limed, practically no man- 
ganese is present in active forms, and some crops are unable to ob- 
tain even the small amounts necessary to meet their requirements. 
Poor growth and a yellow, chlorotic condition result. 

On the other hand, strongly acid soils may contain injurious con- 
centrations of active manganese compounds. Under such conditions 
liming is a corrective measure. 

Manganese is changed by oxidation to less active forms, or may 
be leached from the soil. Hence tests are of most significance when 
made just prior to planting or during crop growth. A negative test 
at such time indicates the desirability of applying manganese. Twenty- 
five pounds of commercial manganese sulfate per acre are usually 
adequate to correct any possible deficiency. It is doubtful if man- 
ganese is needed if any positive test whatsoever is developed. 
Medium or moderately low tests are of little significance, except as 
indicating no manganese deficiency. High or very high tests are un- 
desirable on all acid soils, and indicate a need for lime. The signifi- 
cance of high tests on soils which are neutral or alkaline has not yet 
been thoroughly studied. However, it is not likely that the crop will 
develop manganese toxicity except at the more acid soil reactions, 
even though the test is high. 

The iron test: Iron is an abundant constituent of all soils, ex- 
isting in the form of iron oxides and many complex mineral combina- 
tions. Normally only very small amounts of iron are in active form 



620 Connecticut Experiment Station Bulletin 450 

in the ferric state of oxidation. Under conditions of high acidity, 
larger amounts are to be found, and under poor drainage conditions, 
especially in the presence of organic matter, active ferrous iron com- 
pounds are developed. Soluble ferrous salts are harmful to plant 
growth, and contribute to the infertility of poorly aerated soils. 

The presence of very- low, yet definite amounts of active iron, 
as revealed by the test, is desirable for all crops. Higher amounts, 
on well drained soils, may not be injurious to crops capable of grow- 
ing under strongly acid conditions. Abnormally high iron tests on 
poorly drained soils indicate an unfavorable condition of soil aeration. 

Negative iron tests may occasionally result on heavily limed 
soils of excessive sandiness. In such cases, a chlorotic condition of 
the leaves may develop, which is controlled by spraying the plants 
with iron salts. No case of this sort has been encountered in this 
State. 

Indication of other tests: Occasionally soils which give poor 
crops contain unusual or harmful concentrations of other chemical con- 
stituents. The presence of sea water or white alkali salts is indicated 
by chloride, sodium and sulfate tests. Soluble carbonates and high 
sodium tests indicate black alkali accumulations. Zinc, lead, copper, 
mercury and arsenic tests suggest the development of injurious 
amounts of these elements as a result of soil contamination by indus- 
trial plants, or as residues from soil treatments to control plant 
diseases or insects. The boron test may be applied when crops are 
suspected of boron deficiency, and if a positive test is not obtained, 
a more accurate laboratory test for boron should be applied. 



ESTIMATING FERTILIZER NEEDS FROM NUTRIENT 
AVAILABILITY RATINGS 

IN preceding pages, it has been suggested that soils be rated, 
with respect to nitrogen, phosphorus and potassium availability, in 
four classes: "high", "medium", "low", and "very low". It has also 
been emphasized that numerous other factors besides the chemical test 
should be taken into consideration in such a rating. 

It is also necessary to recognize the different fertility levels with 
respect to the common fertilizer constituents that meet the require- 
ments of the various crops. Crops differ in their abilities to give sat- 
isfactory results at a given degree of chemical fertility. This is due 
in part to actual differences in the amounts utilized by the crops, in 
part to the indirect effects of the relative concentrations of the various 
constituents of the active soil system upon the normal functioning of 
the plant. Economic factors also make it impractical to provide a 
crop of low acre value with the liberal amounts of "plant food" that 
may be desirable for maximum yields. 

The various common field and vegetable crop plants, for Con- 
necticut conditions, have been arranged in four groups with respect 



Estimating Fertilizer Needs 621 

to the practicable minimum fertility levels for the three principal fer- 
tilizer constituents. These groupings are shown in Table 5. 

Table 5. Common Crops of Connecticut, Classified According 
To Relative Requirements for Various Fertilizer Constituents 

Requirement Group: A — very high (A+ — extra high), B — high, C — medium, D — low 
(D* — nitrogen supply from legume organisms) 





Nitrogen 


Phosphorus 


Potassium 




Requirement 


Requirement 


Requirement 




Group 


Group 


Group 


Special Crops 








Potatoes, early 


A 


A 


A 


late 


B 


A 


A 


sweet 


D 


C 


B 


Tobacco 


A+ 


C 


A 


Vegetable Crops 








Asparagus * 


A 


B 


A 


Beans, lima or string 


D 


C 


C 


Beets, early 


A 


A 


A 


late 


B 


A 


B 


Broccoli 


B 


B 


B 


Brussels sprouts 


B 


B 


B 


Cabbage, early 


A 


A 


A 


late 


B 


B 


B 


Carrots, early 


B 


B 


B 


late 


C 


C 


C 


Cauliflower, early 


A 


A 


A 


, late 


B 


B 


A 


Celery, early 


A 


A 


A 


r, " * late 


B 


B 


A 


Corn, sweet, early 


B 


B 


B 


" , " late 


C 


C 


C. 


Cucumbers 


B 


B 


B 


Egg Plant 


B 


B 


B 


Lettuce, head 


A 


A 


A 


, leaf 


B 


A 


A 


Muskmellons 


B 


B 


B 


Onions 


B 


B 


B 


Parsnips 


C 


C 


C 


Peas, early 


C 


B 


B 


Pumpkins 


C 


C 


C 


Radishes 


B 


A 


A 


Rhubarb 


B 


B 


B 


Rutabagas 


C 


B 


C 


Spinach 


A 


A 


A 


Squash, early 


B 


B 


B 


" , late 


C 


C 


C 


Tomatoes, early 


C 


B 


B 


, late 


B 


B 


B 


Turnips 


D 


B 


C 


Watermellons 


C 


C 


C 


Feed, Hay and 








Pasture Crops 








Alfalfa 


D* 


B 


B 


Barley 


C 


B 


C 


Bent grass 


C 


D 


D 


Blue grass, Kentucky 


C 


C 


D 


Clover, alike 


D* 


C 


C 


, ladino 


D* 


C 


C 


, red 


D* 


B 


B 


, wild white 


D* 


C 


C 



622 



Connecticut Experiment Station Bulletin 450 





Nitrogen 


Phosphorus 


Potassium 




Requirement 


Requirement 


Requirement 




Group 


Group 


Group 


Corn, field 


c 


c 


c 


Grasses, mixed 


c 


D 


D 


Oats 


B 


C 


C 


Orchard grass 


C 


c 


C 


Rye 


C 


D 


D 


Rye grass 


C 


D 


D 


Timothy 


c 


D 


C 


Green Manure Crops 








Buckwheat 


c 


D 


D 


Millet 


c 


D 


C 


Peas, field Canada 


D* 


C 


C 


Rye 


C 


D 


D 


Soybeans 


D* 


C 


C 


Vetch, hairy 


D* 


C 


C 


Fruit Crops 








Apples 


C 


D 


D 


Blackberries 


D 


D 


D 


Blueberries 


D 


D 


D 


Grapes 


C 


C 


C 


Peaches 


c 


D 


C 


Pears 


c 


D 


D 


Raspberries 


D 


D 


D 


Strawberries 


C 


C 


D 


Nursery Plantings 








Deciduous 


C 


D 


D 


Evergreen 


D 


D 


D 


Flowers, Annuals 


B 


B 


B 


, Perennials and Bulbs 


C 


C 


C 


Shrubs, Ornamental 








Deciduous 


C 


C 


D 


Evergreen 


D 


D 


D 


Shade Trees 








Deciduous 


C 


D 


D 


Evergreen 


D 


D 


D 


Turf 








Lawns, parks and fairways 


C 


C 


D 


Playing fields 


C 


C 


D 


Putting greens and bowling greens B 


D 


D 



The amounts of the three principal fertilizer constituents, in terms 
of pounds of nitrogen (N), "phosphoric acid" (P 2 5 ) and "potash" 
(K 2 0) per acre, that "would be likely to prove effective on soils of 
varying nutrient availability classes, for the above crop requirement 
groups, are shown in Table 6. 

Table 6. Amounts of Fertilizer Constituents (N, P 2 5 or K 2 0), in Lbs. 
Per Acre, in Relation to Soil Fertility Levels and Crop Requirements 



Nutrient 

Availability 

Class 


IV 

III 
II 


very low 

low 

medium 


I 


high 



A 
very high 

160-180 

120-140 

80-100 

50- 70 



Crop Requirement Group 
B C 

high medium 



120-140 
80-100 
50- 70 
30- 40 



80-100 
50- 70 
30- 40 
10- 20 



D 
loiv 

50-70 

30-40 

10-20 





The above amounts are on the basis of broadcast applications. When applied 
in bands along the rows, according to approved methods of placement, the quantities 
may be approximately 60 percent of those shown in the Table. 



Estimating Fertilizer Needs 623 

The following examples illustrate the above scheme of estimating 
desirable fertilizer applications, utilizing both soil tests and other per- 
tinent information. 

Case 1. Farmer Jones has a field of well-drained, me- 
dium brown, loam soil, in grass sod for several years, occa- 
sionally top-dressed with manure. It is to be planted to 
field corn, without additional manure. Fertilizer is to be 
applied in bands along the row, with a planter of recent 
model. Soil tests in April are as follows: 

pH — 5.2 





Relative Rating Index 


Test Designation 


Nitrate nitrogen 


1.5 


very low 


Ammonia nitrogen 


2.0 


low 


Phosphorus 


1.2 


very low 


Potassium 


4.0 


medium 


Calcium 


2.5 


low 


Magnesium 


1.5 


very low 


Aluminum 


6.0 


medium high 


Manganese 


2.0 


low 



Lime absorption group: III. See Table 2. 

Soil reaction preference group, for Corn: C. See Table 3. 

Liming recommendation at 5.2 pH for III C : 1.2 tons of 
agricultural limestone, per A (should be dolomitic be- 
cause of "very low" magnesium test). See Table U- 

Nitrogen availability class: II. See page — 

Nitrogen requirement group, for Corn: C. See Table 5. 

Nitrogen recommendation for II C : 30 to 40 lbs. X 0.6 = 
18 to 24 lbs. of N per A. See Table 6. 

Phosphorus availability class: IV. See page — 

Phosphorus requirement group, for Corn: C. See Table 5. 

Phosphorus recommendation for IV C: 80 to 100 lbs. X 0.6 
= 48 to 60 lbs. of P 2 5 per A. See Table 6. 

Potassium availability class: II. See page — 

Potassium requirement group, for Corn: C. See Table 5. 

Potassium recommendation for II C : 30 to 40 lbs. X 0.6 
= 18 to 24 lbs. of K 2 per A. 

Final recommendations: 1.5 tons agricultural limestone, 
dolomitic broadcast; 500 lbs. of a U-l-U fertilizer per 
acre, drilled in bands. 

Case 2. Farmer Smith has a field of medium dark 
brown, well-drained sandy loam soil, in potatoes and other 
cultivated crops for several years, liberally fertilized. A 
winter cover crop of rye has been plowed under. The field 
is to be planted to potatoes (Green Mountain variety). 
The fertilizer is to be drilled in bands. Soil tests last 
October were as follows: 

Relative Rating Index Test Designation 
pH — 5.0 
Nitrate Nitrogen 
Ammonia Nitrogen 
Phosphorus 
Potassium 
Calcium 
Magnesium 
Aluminum 
Manganese 



2.0 


low 


1.0 


very low 


6.0 


medium high 


4.0 


medium 


2.0 


low 


3.0 


medium low 


4.0 


medium 


3.0 


medium low 



624 Connecticut Experiment Station Bulletin 450 

Lime absorption group : II. See Table 2. 

Soil reaction preference group, for Potatoes: D. See 

Table 3. 
Liming recommendation at 5.0 pH for II D : 0.5 tons of 

limestone per A. (interpolated). See Table U- 
Nitrogen availability class: IV. See page — 
Nitrogen requirement group, for Potatoes: B. See Table 5. 
Nitrogen recommendation for I V B : 120 to 140 lbs. X 0.6 

= 72 to 84 lbs. of N per A. See Table 6. 
Phosphorus availability class: II. See page — 
Phosphorus requirement group, for Potatoes: A. See 

Table 5. 
Phosphorus recommendation for II A: 80 to 100 lbs. X 0.6 

= 48 to 60 lbs. of P 2 O s per A. 
Potassium availability class: III. See page — 
Potassium requirement group for Potatoes: A. See 

Table 5. 
Potassium recommendation for III A : 120 to 140 lbs. X 0.6 

= 72 to 84 lbs. of K 2 per A. See Table 6. 
Final recommendations: 1000 Z6s. of agricultural lime- 
stone, broadcast; 1200 lbs. of 7-7-7 fertilizer, per A., 

drilled in bands. 

The mechanics of such a scheme for using soil tests and other 
information as a guide to recommend treatments is obviously some- 
what cumbersome. However, it is to be used chiefly as a means of 
systematizing one's reasoning in applying soil tests to practical prob- 
lems. After a number of cases have thus been worked out in de- 
tail, the soil diagnostician will arrive at the final recommendations 
by subconscious recognition of all the various stages that must be 
"thought through'' in order to arrive at a reasonably sound result. 

SUMMARY 

THE soil testing methods developed at this Station during the past 
10 years have been built around the employment of a half-normal 
acetic acid solution, buffered at 4.8 pH with sodium acetate, for the 
soil extraction. This has been designated, for convenience, as the 
"Universal'' soil extracting solution. This scheme of testing, identi- 
fied as the "Universal Soil Testing System", has been found to be 
of great value in chemical soil diagnosis, not only in this State, but 
in many sections of the United States as well as numerous other 
countries. 

The revised methods used in these tests are presented in detail. 
Routine tests, of general application, are as follows: nitrate and am- 
monia nitrogen, phosphorus, potassium, calcium, magnesium, alumin- 
um, and manganese. Special tests provide indications relative to the 
following constituents: Iron (both ferric and ferrous), sulfates, ni- 
trites, sodium, chlorides, carbonates, boron, zinc, copper, mercury, 
lead, and arsenic. 

The adoptions of the tests to plant tissue testing, the examination 
of drainage and irrigation waters and other dilute aqueos solutions, 
and the testing of saline and alkali soils are also presented. 



Summary 625 

Considerations involved in the practical interpretation of the 
tests, under various conditions, are discussed at length. A systematic 
scheme for applying these interpretations in estimating fertilizer needs 
is proposed. 

Details of simple pH testing are also included. The significance 
of soil reaction with respect to lime requirement, and the interpreta- 
tion of quick chemical tests is given due attention. 

The modifying effects of physical soil properties and other fac- 
tors limiting crop growth are also stressed. 

Methods such as these described in this bulletin are capable of 
yielding valuable information concerning the chemical characteristics 
of the soil and are extremely helpful when interpreted by a person who 
is otherwise competent to offer sound advice in soil management prac- 
tices. 



626 Connecticut Experiment Station Bulletin 450 

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Bibliography 627 

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PLATE I. 



NITRATE NITROGEN COLOR CHART 

Universal Soil Testing System 



Rating 



Relative Test 
Index 



Very High 
High 

Medium High 
Medium 
Low 



10 




■ :■■:■ 



Very Low 



PLATE II. 



AMMONIA NITROGEN COLOR CHART 

Universal Soil Testing System 



Rating 



Relative Test 
Index 



Very High 
High 

Medium High 
Medium 



10 



Low 



Very Low 



PLATE III. 



PHOSPHORUS COLOR CHART 

Universal Soil Testing System 



Relative Test 
Index 



Very High 
High 

Medium High 
Medium 
Low 



10 




Very Low 



PLATE IV. 



POTASSIUM READING CHART 

Universal Soil Testing System 



Rating 

Very High 
High 

Medium High 
Medium 



Relative Test 
Index 



10 




Low 



Very Low 



PLATE V. 



CALCIUM READING CHART 

Universal Soil Testing System 



Rating 



Very High 

High 

Medium High 

Medium 

Low 

Very Low 



Relative Test 
Index 



10 




PLATE VI. 



MAGNESIUM COLOR CHART 

Universal Soil Testing System 

(using Reagent A-2 (Titan Yellow) 

Relative Test 
Index 



Very High 
High 

Medium High 
Medium 



10 



Low 



Very Low 



PLATE VII. 



ALUMINUM COLOR CHART 

Universal Soil Testing System 



Rating 



Relative Test 
Index 



Very High 
High 

Medium High 
Medium 
Low 



10 




Very Low 



PLATE VIII 



MANGANESE COLOR CHART 

Universal Soil Testing System 



Relative Test 
Index 



Very High 
High 
Medium High 



10 



Medium 



Low 



Very Low