Everglades Stat'iohnlMimeo Report EES65-18 February 1965
SP S PLING IAND METHODS USED FOR ANALYSIS OF SOILS IN THE
SOI UTt (liABORATORY OF THE EVERGLADES EXPERIMENT STATION
F. H. Thomas
The soil testing laboratory was established at the Everglades Experiment
Station during the period 1943 to 1948. It has operated as a free service to
farmers, ranchers, and homeowners of the area since 1948. Its purpose has
been to guide the grower toward the most economical and effective fertiliza-
tion practices based on findings by the Experiment Station Staff.
Soil tests are of little value unless correlated with plant responses to
fertilization. Most of the correlation studies and methods used in this labora-
tory were established by W. T. Forsee, Jr. 2/; however, the staff of the Ever-
glades Experiment Station is continuously making correlations between fertili-
zation, soil test values and plant response. Continued correlation work is
made necessary by continuous changes of emphasis between major crops, and
varieties and strains within crops.
This Mimeo Report is a revision of Everglades Experiment Station Mimeo
Report 55-6. The purpose is to include soil sampling procedures established
by the Everglades Station Staff and to publish the laboratory procedures in
current use in the Everglades Soil Testing Laboratory.
FART I: SAMPLING THE SOIL
Reliable information from a soil test begins with proper taking of the
soil sample. Research conducted at the Everglades Experiment Station indicates
that pastures which have had cattle on them should be sampled differently than
areas being established to pasture or row crops. Also, stubble sugarcane
should be sampled differently than either of the above.
Sampling Soils to be Planted to Crops
The field to be sampled should be disked and ready for fertilization
before sampling. One should avoid sampling near the marl roads and obvious
ditch spoil areas. If these spoil areas comprise significant acreage then a
separate sample should be taken from that area. Start near one end of a
field and walk in a zigzag fashion taking a core to a 6-inch depth, periodi-
cally, so as to have a minimum of 20 cores making a sample from a 40-acre
block. These 20 cores should be composite and thoroughly mixed and a pint
sample taken from this composite, placed in a clean container and properly
labeled for grower identification.
l/ Assistant Chemist, Everglades Experiment Station, Belle Glade, Florida.
2/ Chemist in Charge, Everglades Experiment Station, Belle Glade, Florida.
If necessary for diagnostic purposes, a sample can be taken in growing
row crops when fertilizer has been broadcast before planting. However, after
side-dress applications have been made, soil test results are not reliable.
Sampling Soils Established in Pastures
Each pasture should be sampled to a depth of 5 to 6 inches in at least
three locations. Each sample collected from a location is placed in a separate,
clean container. The containers are.given a pasture designation identifiable
by the.rancher followed by the letters A, B, or C, respectively, for each sam-
ple from that pasture. Potassium is determined on each of the three samples
but equal volumes from each sample are composite for pH and phosphorus deter-
The locations from within the pasture should be selected as average areas
judging by topography and grass growth. Be sure to avoid all detectable urine
and manure spots.
Sampling Soils in Stubble Sugarcane
Each field or block of stubble cane should be sampled to a depth of 10
to 12 inches taking a minimum of 20 cores per 40 acre block. The cores
should be composite and thoroughly mixed and a pint sample taken from this
composite, placed in a clean container and properly labeled for grower 'identi-
Submitting the Samples to the Laboratory
Bring or mail organic soil samples to the Everglades Experiment Station,
or submit them through the County Agricultural Agent. Except for sugarcane,
sandy soil samples must be submitted through the County Agricultural Agent.
Also, the following information should be submitted with each sample: Grower's
name and correct mailing address, who took the samples and who brought or sent
them to the laboratory, location of samples (general area), past years' crop-
ping and fertilization history as well as any comment on definite problems
(remarks), and crop you expect to plant (recommendation desired). Information
sheets are available in the soil testing laboratory and through your County
PART II: METHODS OF ANALYSIS
Most of the methods described on the following pages are adaptations of
methods found in the literature that have been modified to suit local conditions.
The methods for determination of the bases which involve acid extraction are not
suitable for soils containing more than traces of alkaline salts. The water ex-
traction procedure described for phosphorus is not the most desirable to use on
soils with high pH values. Under such conditions a carbonic acid extraction
should perhaps be used.
All these procedures have evolved during a number of years of use in
these laboratories for analyses. associated with-research op fertilizer re-
quirements of crops and plant nutrition studies, and in the operation of a
limited soil testing program on a service basis for growers in the south
S' Procedures" give in this section for moisture equivalent, percent ash,
and nitrate nitrogen are not normally included:on service samples submitted
to this laboratory. However, after discussing a particular problem with
the grower these analyses may be made if the-staff member thinks it may help
solve the particular problem.
Preparation of Samples for Analysis
Soil samples to -be" tested- should be placed' on clean trays in the soil
preparation room and air dried. As soon as the samples are sufficiently dry
they should be put through a 2 mm. sieve. For mucks especially, it'-isbest
to sieve the samples before they are completely air dry because the lumps of
plastic material will breakup much easier when handled at a moisture level
between field moist and air dry. Peat samples should not be stored more than
4 to 6 weeks after drying before analysis because of the shrinkage and change
in volume which takes place. Peat or muck samples to be analyzed for nitrogen
should not be air dried. Such samples should be brought to the laboratory and
analyzedimmediately after they are taken. They..may be run through the ,2 mm.
sieve, if they are sufficiently dry in their field.moist condition.
.Testing the Soil for pH
.Measure out into a 4 to 6 ounce, waxed paper cup 30 cc. of sieved, air
dry soil. Add 60 ml. of distilled .water (30 ml. to; sandy soil) and allow to
stand about 2 hours with intermittent stirring. Measure the pH by means.of
aglass electrode stirring each sample just prior to immersing the electrode.
Testing the Soil for Moisture-Equivalent '
Fit squares of filter paper into the.bottoms of the centrifuge boxes.
Measure out in duplicate approximately 30 ml. of homogenized soil which has
passed a 2 mm. sieve and place in the centrifuge boxes. Level the surface
of the soil by light tapping, place the cover on the boxes and place in a
tray containing almost enough water to submerge the soil. After the samples
have remained for,20 to 24 hours in this saturated condition, take them out
of the water and allow to'drain for 30 minutes before centrifuging. Then
place the boxes in the centrifuge with duplicate samples diametrically oppo-
site each other and gradually increase speed until a force 1000 times gravity
is reached (2440 rpm on moisture equivalent centrifuge). Centrifuge at this
speed for 40 minutes, then allow centrifuge to "coast" to a smooth stop.
Transfer the soil only to aluminum cans or weighing bottles with close fitting
lids. Weigh to nearest 0.01 gram the can or bottle containing the soil and
place in an oven.set at 1050C. After 24 hours take out, desiccate, and re-
weigh. The moisture equivalent is calculated on the oven-dry basis.
M. loss in wt. x 100
dry wt. sample
Duplicates should check within 0.4%.
Determining the Percent Ash in Peat and Muck Soils
Weigh out to the nearest mg. approximately 25 gms. duplicate samples
of oven dry soil into porcelain evaporating dishes. Place in cool muffle
furnace and increase temperature to approximately 2000C. for about 2 hours,
leaving the muffle furnace door cracked. Then close the furnace door and
increase the temperature to about 4000C. for an hour and then increase
temperature to 560o. for 3-4 hours. Cool furnace down, remove samples,
desiccate and reweigh. Calculate ash on oven dry soil basis.
SAsh Wt. of ash x 100
Wt. of oven dry soil
Testing the Soil for Potassium, Sodium, Calcium, and Magnesium
Prepare a 0.5 N acetic acid solution by diluting 540 ml. glacial
acetic to 19,000 ml.
Measure out 10 cc. (2-1/2 teaspoons) of air dry sieved soil into a
25x200 mm. screw cap culture tube. Add 25 ml. of the 0.5 N extracting
solution, mix and allow to stand over-night. This allows thorough wetting
of the soil. Place the rack with the tubes containing the soil and ex-
tracting solution on an end-over-end shaking machine and shake for 60 minutes.
Allow to settle and decant supernatant liquid into a S & S No. 576 filter
paper. Pour back the first few ml. that come through in order to obtain a
clear filtrate. Use this filtrate for the determination of the bases using
a flame photometer.
Preparation of Standard Solutions
A. Standard Potassium Solution
Weigh out 1.1219 gms. oven dried, reagent grade KC1 and dilute to
1,000 ml. with 0.5 N acetic acid. This solution contains 588.4 ppm K
(equivalent to 2000-1bs. K/A.).
Make a series of standards containing 0 to 400 pounds K per acre
and determine the calibration curve using a flame photometer at 768 milli-
microns wave length.
B. Standard Sodium Solution
Weigh out 1.4958 gms. oven dried, reagent grade NaC1 and dilute to
1000 ml. with 0.5 N acetic acid. This solution contains 588.4 ppm Na
(equivalent to 2000 Ibs. Na/A.).
Make a series of standards containing 0 to 400 pounds Na per acre
and determine the calibration curve using a flame photometer at 588
millimicrons wave length.. Standard calibration curves may be made using
lesser quantities as maximum if Na is low.
C. Standard Calcium Solution
Weigh out 3.6740 gms. of oven dried, reagent grade CaC03 and dilute
to 1,000 ml. with 0.5 N acetic acid. This solution contains 1471 ppm Ca
(equivalent to 5,000 ls. Ca/A.)
Make appropriate dilutions with 0.5 N acetic acid from this solution
to give a series of standards for the calibration curve containing 0 to
5,000 pounds Ca per acre. 'Determine calibration curve on flame photometer
at 422 millimicrons wave length.
D. Standard Magnesium Solution
Weigh out 1.9511 gms. oven dry reagent grade MgO and dilute to 1,000
ml. with 0.5 N acetic acid. This solution contains 1176.8 ppm Mg (equi-
valent to 4,000 lbs. Mg/A.).
Make appropriate dilutions using 0.5 N acetic acid to give a series
of standards of 0 to 1,000 lbs. Mg/A. Determine calibration curve on
flame photometer using a wave length of 378 millimicrons.
Ten cc. of dry soil is 1/61,672,248 of an acre six inches deep.
(28,316 cc./ft3 x 21,780 ft3/acre six inches = 616,722,480 cc./acre six
10 cc. soil extracted with 25 ml. soln. = 2.5 dilution factor
If we find 1 ppm K in the extract then 2.5 x 1 = 2.5 ppm K.
Since 1 ppm =l~,g/mi. then 10 cc. soil contains 25 p&g. K.
Then 25 /.g. K/10 cc. soil x 61,672,21L8 = 1,541,806,200 Ag. K/A.'
To convert to lbs./A: 1,541,806,200 4- 453.592,428 /g/lb. = 3.3991
Ibs. K/A. . .! .....
Therefore under the conditions this Procedure:
1 ppm K = 3-3991 lbs. K/A. or 1 Ib. K/A. = 0.2942 ppm K.
Testing the Soil for Phosphorus
Extracting Solution Distilled Water
Extraction Procedure ..
Measure out 4 cc. (1 teaspoon) of air-dry, sieved soil into a 25 x 200 mm.
screw cap culture tube. Add 50 ml. of: distilled water, mix and allow to stand
over-night. This allows thorough wetting of the soil. Place rack containing
the tubes on an end-over-end shaking machine and shake for 60 minutes. Remove
from shaker, and filter through Whatman No. 32 filter paper. Collect filtrate
until exactly 20 ml. has been obtained. Add 4 ml. of 0.3 N HC1 and about 1/8
teaspoon decolorizing charcoal 3/ (phosphate free) from tip of spatula. Shake
by hand.vigorously about 2 seconds and filter after 3 to 5 minutes. Pour back
the first few ml. of filtrate so a clear filtrate is obtained. Use this fil-
trate for subsequent determinations of phosphorus.
3/ Darco G-60 is satisfactory after washing with N HC1 and thoroughly rinsing
with distilled water.
Preparation of Solutions
Standard Phosphorus Solution
Weigh out 1.1932 gms. oven dry, reagent grade KH2PO4 and dilute to 1,000
ml. with 5.0 N HC1. This solution contains 271.56 ppm P. Dilute 10 ml. of
this solution to 1,000 ml. with distilled water. The latter solution contains
2.7156 ppm P. When 10 ml. of this solution is carried through the colorime-
tric procedure described below it is equivalent to 40 lbs. P/A. Determinations
equivalent to 2 to 40 pounds phosphorus per acre may be made by diluting to 12
ml. with 0.05 N HC1 aliquots of 0.5 to 10.0 ml. and carrying through the pro-
cedure for phosphorus determination.
Dissolve 12 gms. ammonium molybdate in 260 ml. water. Add a mixture of
225 ml. concentrated hydrochloric acid and 50 ml. water store in an amber
glass bottle. Make fresh every two months.
Stannous Chloride Stock Solution
Dissolve the contents of a 1 ounce bottle of stannous chloride (SnCl2.2H20)
in 67.5 ml. concentrated hydrochloric acid. Store in a small tightly stoppered
amber glass bottle.
Stannous Chloride Reagent
Add 1 ml. of stannous chloride stock solution and dilute to 250 ml. with
distilled water. Make up fresh daily.
Procedure for P Determination
Pipet 12 ml. of soil extract into an 18 x 150 mm. tube. For soils whose
phosphorus level is above the range of the test, use a smaller aliquot and
add sufficient 0.05 N HC1 to bring the volume to 12 ml. Add 2 ml. of molybdate
reagent, mix thoroughly, and 1 ml. of stannous chloride reagent and mix immedi-
ately. Read the resulting blue color after 7 to 10 minutes in a colorimeter
set at 660 millimicron wave length (red filter). The color is usually stable
for at least 20 minutes after adding stannous chloride provided nitrate nitro-
gen in the sample is not excessively high. here difficulty of fading is
encountered make the readings within 5 to 10 minutes after adding the stannous
chloride. The P content of the soil in pounds per acre may be read from the
standard calibration curve.
Four cc. of air dry soil is 1/154,180,620 of an acre, six inches deep.
4 cc. soil extracted with 50 ml. water = 12.5 ml. dilution factor.
Then 20 ml. extract diluted to 24 ml. volume with .3 N HC1 = 1.2 dilution
factor. Total dilution factor is 12.5 x 1.2 =13
If we find 1 ppm in the diluted extract, then 13 x 1 = 13 ppm P in the,
4 cc. soil.
Since 1 ppm = 1 /g P/ml. then 13 ppm P x 4 cc. soil = 52 A/g P in 4 cc. soil.
Then 52 /Ag. P x 154,180,620 = 8,017,392,240 /ig P/A.
To convert to Ibs./A. 8,017,392,240 i 453,592,428 /tg/lb. = 17,6752 lb. P/A.
Therefore: 1 ppm = 17.6752 lbs. P/A. or 1 lb. P/A. = 0.056576 ppm P.
Testing the Soil for Nitrate Nitrogen
Nitrate Nitrogen Reagent
Dissolve 0.05 gm. diphenylamine in 25 ml. concentrated H2SO at room temper-
ature. Store in a glass stoppered amber glass bottle. This solution should
be made fresh every two weeks.
Procedure for Test
Carefully measure 4 cc. (1 teaspoon) of freshly sampled field moist soil
into an 18 x 150 mm. test tube. Add 10 ml. of the 0.5 N acetic acid extracting
solution and shake vigorously for 2 minutes. Filter through S & S No. 576
filter paper. Carefully transfer 1 drop of soil extract to a white porcelain
spot plate. Add 5 drops of nitrate nitrogen reagent and stir with a thin glass
rod. A blue color indicates the presence of nitrate nitrogen. No perceptible
blue color after 2 minutes indicates less than 2 pounds nitrate nitrogen per
acre. A pale blue color indicates a very low nitrate nitrogen level. A strong
blue color indicates ample nitrogen for most crops. A heavy blue color indi-
cates very high nitrate nitrogen.
This test is only an indication of the presence of low, medium or high
amounts of nitrate nitrogen. Such a test is usually sufficient for checking on
the advisability or necessity for nitrogen fertilization, especially on peat
and muck soils. Vhen a more exact estimate is desired a quantative method
should be used.
Testing the Soil for Total Soluble Salts
Weigh out 50 gms. of air dry soil into 250 ml. Erlynmeyer flask. Add 50
ml. of distilled water, mix thoroughly, let stand for 30 minutes. Stopper
flask and place on an and-over-end shaker for 30 minutes. Remove and filter
through a rapid qualitative filter paper discarding the first few ml. of
filtrate. Determine "K" factor on a "solu-bridge" instrument. Compare this
with a calibration curve made with NaCl concentrations of 0 to 5000 ppm. If
a 1:1 ratio of soil:water does not yield sufficient filtrate for the test,
use a 1:1.5 or 1:2 ratio.
If a 1:1 soil:water ratio is used, the total soluble salts are read direct-
ly from the calibration curve. If a different ratio is used, appropriate cor-
rections must be made. Example: if 1:2 ratio is used, multiply ppm from
calibration curve by 2.