Frocedures used
for soil and plant
analysis by the
Auburn University
Soil Testing
Laboratory
January 1986
Department of Agronomy and Soils Departmental 
Series No. 106
Alabama Agricultural Experiment Station 
Auburn University
David H. Teem, Acting Director 
Auburn University, Alabama
I I I Is I _

PROCEDURES USED BY THE AUBURN UNIVERSITY
SOIL TESTING LABORATORY
January 1986
TABLE OF CONTENTS
Page
I. Introduction ....... .............. ....... 1
II. Soil Sample Preparation ...... ............... 1
III. Instrumentation Setup in the Laboratory . . . .... . 2
IV. Soil Sample Extraction ... ........... ........ 6
V. Routine Elemental Analysis ..... 7............. 7
1. Phosphorus Determination ..... ............. 7
2. Potassium Determination ...... ............. 8
3. Calcium and Magnesium Determinations ..... . . . 8
VI. Soil pH and Lime Requirement Determinations . . . .. 9
VII. Data Summary and Quality Control .......... . . . 15
VIII. Special Analyses ....... ................... 17
1. Micro-nutrients and Toxic Elements .......... . 17
2. Organic Matter Determination ............. .. 19
3. Nitrate Determination ..... ............... 20
4. Sulfate Determination ................... ... 21
5. Soluble Salts. ..................... .. 22
6. Particle Size Analysis ................... .. 25
IX. Plant Analysis ...................... 
27
1. Dry Ashing of Plant Samples ... ............ .27
2. Wet Ashing of Plant Samples . . . .... ....... 27
3. Total N Determination .............. ... 28
4. Total S Determination .... ............ . .. 30
References ........ ...................... 31
LIST OF TABLES
Table
1. The Amount of Agricultural Lime Needed to
Raise the pH of Acid Soils to 6.5 based on
the Soil pH and the "Adams-Evans" Buffer 
pH
2. The Amount of Agricultural 
Lime Needed to
Raise the pH of Acid Soils to 6.0 Based 
on
the Soil pH and the "Adams-Evans" Buffer 
pH
3. The Amount of Agricultural 
Lime Needed to
Raise the pH of Acid Soils to 5.5 Based on
the Soil pH and the "Adams-Evans" 
Buffer pH
4. The Amount of Agricultural Lime Needed 
to
Raise the pH of Acid Soils to 7.0 Based 
on
the Soil pH and the "Adams-Evans" Buffer 
pH
5. Soil Test Data Summary .......... . .
6. Interpretation of Soluble Salts 
Measurement
7. Range of Salt Tolerance of Crops 
. ...
Page
11
12
.da S i r
13
14
16
23
24
LIST OF FIGURES
Fioure
1. Block Diagram of the Computer System 
of the
Auburn University Soil Testing 
Laboratory .......
2. Operator-and-instrument Interface 
. . . . . . . . .
3. Block Diagram of an ICAP ........... 
. . ..
4. Guide For Textural Classification 
...........
3
4
18
26
Information contained herein is available to all persons 
regardless
of race. color, sex or national origin
. . . . . .0
PROCEDURES USED BY THE AUBURN UNIVERSITY
SOIL TESTING LABORATORY
N. V. Hue and C. E. Evans
I. Introduction
The soil testing program at Auburn University is a joint
project of the Alabama Agricultural 
Experiment Station and the
Alabama Cooperative Extension Service. The Alabama Agricultural
Experiment Station conducts soil-test calibration research and
operates the soil testing laboratory. The Alabama Cooperative
Extension Service has primary responsibility for education on soil
testing and distribution of supplies.
Soil samples are routinely tested for pH, lime requirement,
and extractable P, K, Mg, and Ca. Extractable Ca is only reported
on samples where peanuts, tomatoes, peppers, or peaches are to be
grown. When requested or a need is indicated, soil organic matter,
soluble salts, and micronutrients such as Zn, Mn, Fe, Cu, and B may
be determined for additional charges. Fertilizer recommendations
are made from the soil test results. In addition to routine soil
tests, a limited plant analysis service is offered.
II. Soil Sample Preparation
1. Checking samples. Soil samples are received daily and
immediately checked for farmers' name, address, number of
samples, crops to be grown, and payments ($3 per sample for
routine analysis, and an additional $2 per sample when organic
matter determination is requested). The checking operation is
carried out by comparing the information listed on each
soil-sample box with that written on the "information sheet."
If the two sources of information do not match, an attempt is
made to reconcile the differences, and if needed, a comment
will be made on the report returned to the farmer.
2. Numbering samples. After checking, soil samples are placed on
shelves and numbered consecutively, beginning with No. 1 on the
first of July each year.
1
Former Research Associate and Professor of Agronomy & Soils Department,
respectively. Senior author is currently Assistant Professor of Soil
Chemistry, Univ. of Hawaii at Manoa, Honolulu, HI. 96822.
3. Identifying Black Belt soil samples. Soils from the Black Belt
area of Alabama, which are often calcareous and high in clay
content, are extracted with a different solution. Therefore,
an effort is made to separate them from other soils before
chemical analysis is performed. The separation is carried out
by visually inspecting, hand-feeling the soil texture in
conjuction with the county (location) where the soil was
sampled, and by the HC1 effervescent test.
4. Drying samples. Soils are placed in metal trays 
in sequence
beginning on the left front row of the tray. Each tray
consists of 36 (6 x 6) samples. They are then dried in a large
forced-air oven at 55
0
C (130'F) for at least 24 hours or until
samples are dry.
5. Screening samples. Dry samples are ground in a mechanical
grinder and screened through a 10-mesh sieve to obtain
homogeneity of the soil. Soil samples are then ready for
chemical analyses.
III. Instrumentation Setup in the Laborator
Since 1978, the Auburn University Soil Testing Laboratory has
been equipped with a mini-computer (MODCOMP II/25). Various
analytical instruments, including an electronic balance (Mettler,
PE 200), an atomic absorption spectrometer (Perkin-Elmer 373), two
digital pH meters with BCD output (Sargent-Welch, PAX), and a
visible spectrophotometer (Bausch & Lomb, SPECTRONIC 100) are
interfaced to the computer either directly or via a custom-built
interface box. A block diagram of the instrumentation setup is
shown in figure 1. Laboratory data, such as soil-water pH, buffer
pH, and P, K, Mg, and Ca concentrations in soil extract, are
acquired automatically by the computer. With this setup, a
technician does not have to write down readings or punch-in
numbers. The computerized process for soil-test data acquisition
and its applications have been discussed elsewhere (10, 9).
Computer Interface
The interface serves three functions: (1) provides
communication from the computer to the technician, (2) allows the
technician to input test parameters and identification, and (3)
provides translation and input of digital data signals from the
instrument to the computer.
A pictorial diagram of an interface is presented in figure 2.
The interface has 4-digit LED display by which the computer relays
messages to the technician. The display shows either position
number, or instrument reading, or error messages. For analysis,
each batch of samples is placed in laboratory trays in which
positions are numbered. These begin at "1" and are numbered in
increasing order. Position numbers represent laboratory numbers
INPUT/OUTPUT BUS
Fig. 1. Block diagram of the computer system of the
Auburn University Soil Testing Laboratory
MO DCOMP 
COMPUTER
(128 K- byte
MEMORY)
KAYPRO U
MICROCOMPUTER
AUBURN UNIV.
COMPUTER 
CENTER
IBM 3033
Operator nutter
Interface number
Element 
nurber
Rua nuiber
-Position nuiber
-ig. . Operator-and-Instrument Interface,
4
for the samples in a "run". The upcoming 
position number is displayed
for the technician before each analysis. 
After each analysis, the
computer momentarily shows the reading back to the 
technician on the LED
display, indicating that it has 
been recorded, and then it advances 
to
the next position number. Error codes are shown when there is a
hardware or software problem or if 
the technician is attempting to
perform an unacceptable task. The LED 
display is surrounded by three
lights, which are cues to the technician. 
A yellow light indicates that
the computer is ready to accept data, 
a green light indicates that the
computer has acquired valid data and 
is doing the bookkeeping to accept
the next data, and a red light indicates 
an error or an invalid
operation.
The interface has five sets of thumbwheel switches 
located on the
right side of the upper-front panel. These 
digits are set by the
technician at the beginning of each run 
so that data can be correctly
collected by the computer. Beginning 
on the left, the first two digits
identify the operator, the third and fourth 
identify the interface, and
the fifth identifies the element being 
analyzed. Digits 6-8 identify
the run number. A run contains from 1 to 499 samples, 
and the run
number is advanced consecutively with groups 
of samples analyzed each
year. Digits 9-12 set the beginning position 
number for startup of
analyses on the instrument. By using run 
numbers to identify groups of
samples, the position numbers can be repeated 
for each group of samples
to represent different laboratory numbers.
The interface has five pushbuttons (Figure 
2): Initialize, Test,
Mea/Adv, Rev/Dis, and Adv/Dis located on the 
lower-front panel. Upon
pressing one of these buttons, the associated 
software program will be
activated, and certain operations will be carried 
out:
Function Operation description
TEST Allows the operator 
to check for proper
computer communication and for proper
hardware operation of the interface.
INITIALIZE Commands the computer 
to obtain
information from the thumbwheel switches,
check for the validity of the
information, and set up the necessary
data files on disc for the data
acquisition process.
MEA/ADV Initiates the transfer 
of an analytical
measurement to the computer. The
computer then performs the necessary
bookkeeping chores, stores the data on
disc, and advances its internal position by
one.
REV/DIS Allows the operator to decrement the
position by one with respect to the
current position and shows on the
LED display the measurement that has been
stored. If the operator does not like
the reading, the MEA/ADV switch can be
pressed to take a new reading.
ADV/DIS Allows the operator to advance the
position by one with respect to the
current position and displays the
reading that had been taken, if any.
IV. Soil Sample Extraction
Two extracting solutions are being used by the laboratory to
handle the diversity of soils throughout the State. The Mehlich 1
(12) solution, also known as the Double-Acid (0.05 N HCl + 0.025 N
H SO ) solution, is used for soils other than Blfck Belt. The
l1ttar soil group is extracted with the Mississippi solution
(11).
1. Reagents (extracting solutions)
a. 0.05 N HCI + 0.025 N HOSO, solution (12). Pour
approximately 30 L deionized'H
2
0 into 40 L bottle. Add
28 mL concentrated. H SO
4 
and 166 mL concentrated HC1.
Dilute to 40 L with de~onized H
2
0. Mix thoroughly.
b. Mississippi solution (11) . Add 900 mL glacial acetic
acid, 65 g of malonic acid (Eastman practical or
equivalent), CH(COH), 120 g of malic acid (Eastman
practical), CHCHOHCO1I2) , and 13.8 g of NH
4
F, to 7500
mL of deionized H20 abd x well to dissolve reagents.
Add 30 g of AICl .6H 0, mix well, and adjust pH to 4.0
with NH OH. Dildte 
2
to 10 L with deionized H
2
0. Mix
thoroughly.
2. Procedure
a. Scoop 4 cubic cm of soil into a weighing pan so that soil
weight can be recorded automatically by the computer (the
weight is approximately 5 g, depending on the soil
texture, i.e., sandy soils are heavier and clayey soils
are lighter). Pour it into a 50-mL Erlenmeyer flask (12
flasks are fitted into a special wooden rack which is
numbered at both ends).
b. Deliver a 20-mL aliquot of extracting solution
simultaneously to each of the 12 flasks with an automatic
pipette assembly.
c. Place a set of racks (a maximum of 6) on a mechanical
shaker (180 oscillations/minute, 3.8-cm
displacement/stroke). Cover them with a thin
polyethylene sheet. Shake for 5 minutes for the
Double-Acid, and 10 minutes for the Mississippi.
d. Filter the samples immediately through a 9-cm Whatman
No. 1 filter paper into 1-oz plastic cups. The cups are
fitted into racks congruent to the extractant racks.
e. Pour the filtrate into a 10-mL plastic vial. The
samples are now ready for P, K, Mg, and Ca
determinations.
V. Routine Elemental Analyses
1. Phosphorus Determination (14, 13).
Principle. Phosphate reacts with sulfomolybdic acid in the
presence of a reducing reagent (ascorbic acid) to yield a blue
compound (phosphomolybdic). The intensity of the color is linearly
proportional to'the concentration of solution phosphate.
Phosphorus Reagents (14)
a. Reagent A. Dissolve 100 g of ammonium molybdate,
(NH )6
Mo O 
.
4 H 
0, in approximately 500 mL deionized H0 in
2 U vouf trig flask. Dissolve 2.425 g of antqmony
potassium tartrate, K(SbO)C H 0
4 
.H 0, in molybdate
solution. Add 1,400 mL conce4nratio H
2
SO
4
, cool, and
make to volume with distilled H
2
0. Store in polyethylene
or pyrex glass bottle in a dark, cool compartment.
b. Reagent B. Dissolve 88 g of ascorbic acid in deionized
H 0. Dilute to 1 L. Store in dark glass in cool
cgmpartment.
c. Reagent C (color developer). Dilute needed quantity of
Reagents A and B, using the following ratio: 2 mL A + 1 mL
B + 97 mL extracting solution for a total volume of 100 mL.
Prepare fresh solution daily, and allow the solution to
stand a minimum of 1 hour before use (the solution is good
for @ 48 hours).
Procedure
a. Add one part (0.85 mL) of the soil extract to 9 parts (7.65
mL) of phosphorus reagent C (color developer), using a
diluter/dispenser (MANOSTAT, DILUTOR II) set for 1:9. This
solution is transferred into a glass vial for P
determination. Allow 30 minutes for color to develop.
b. Aliquot duplicate sets of P standards: 0, 
0.5, 1.0, 2.5,
5.0 and 10.0 ppm P (as KH PO
4 
solutions), and mix them with
color developer as des ibed in [a]. These standards
correspond to soil-test P of 0, 4, 8, 20, 40, and 80 pounds
per acre, respectively.
c. Turn on the B & L SPECTRONIC 100, and allow it to warm-up
for 15 minutes. Set the wavelength at 740 nm. Read
absorbance of the standards and samples.
2. Potassium Determination
Potassium is determined by atomic absorption spectroscopy on
the undiluted soil extract.
Principle. At elevated temperatures (@ 2,000
0
C with C
2
H /air
flame), K salt in soil extract is converted into atomic 2and
simple K compounds. Potassium atoms in the ground state will
absorb certain energy (provided by a K hollow cathode lamp). The
energy difference between the unabsorbed reference light beam and
the absorbed sample beam is proportional to K concentration in the
liquid extract.
Procedure
a. AA (Perkin-Elmer 373) operating parameters. Wavelength =
766.5 nm, slit width = 2, burner angle = 300 from the light
path.
b. Standards. 20 and 50 ppm K in the Double-Acid solution.
The standards, however, are entered as 160 and 400 (pounds
per acre of K in soil). The instrument absorbance is first
zeroed with the Double-Acid solution.
3. Calcium and Mg Determinations
Calcium is determined by using a CH
2
/air flame in La solution.
The La addition is to help redu e interferences from other
elements, especially P, on Ca determination.
Magnesium is also determined on the La diluted solution for
convenience. This matrix, however, is not required for Mg
determination.
Reagent (lanthanum solution)
5% Lanthanum Solution. Wet 58.65 g of La 0 with H 0. Add
250 mL of concentration HCl very slowly u~t l the m terial is
dissolved. Dilute to I L with deionized H
2
0.
Working solution. Dilute La solution to 0.5% La as needed
(100 mL of 5% La solution to 1 L with the Double-Acid
solution).
8
Procedure
a. Using a diluter/dispenser, take a 1.5-mL aliquot of soil
extract and mix with 6 mL of 0.5% La solution.
b. AA operating parameters.
Parameter Ca Mg
Wavelength, nm 422.7 285.2
Slit width 0.7 0.7
Burner angle (degree) 30 30
Low standard, ppm 30 3
Hi standard, ppm 60 6
Note: Ca and Mg standards should be prepared
in La matrix.
VI. Soil pH and Lime Requirement Determinations
Apace of soil extraction, soil pH and lime requirement (for
acid soils) are determined.
Reagent [Adams-Evans 
(1) buffer for 
lime requirement]
1. Dissolve 360 g of p-Nitrophenol (practical grade) in
approximately 4 L of hot tap H
2
0. Use low heat to
dissolve.
2. Dissolve 270 g of boric acid in 3 L of hot tap H
2
0. Use
low heat if necessary.
3. Dissolve 189 g of potassium hydroxide (KOH) in
approximately 200 mL tap H
2
0.
4. Place 1,332 g of potassium chloride (KCI) in 18-L bottle.
To this add about 6 L tap H
2
0. Mix thoroughly.
5. To the KC1 solution, add the previously mixed solutions in
same order as listed. Make to 18 L with 
tap H
2
0. Adjust
the pH to 8.00 with KOH or HC1 if necessary.
Procedure
1. Transfer one scoop of soil (20 mL) to a 3-oz waxed paper
cup, and add 20 mL of deionized H
2
0 by means of an
automatic pipette assembly.
2. Place a tray of 48 samples on a mechanical stirrer which is
equipped to stir all samples simultaneously. Stirring rods
should be rinsed between trays. After 30-seconds stirring,
samples are allowed to stand for at least 30 minutes.
3. Stir each sample immediately before pH determination. The
pH meter should be calibrated before use and regularly
throughout the day's run. Buffer solutions of pH 4,00 and
7.00 should be used for calibration.
4. After soil-water pH has been taken, add 20 mL of
Adams-Evans (1) buffer solution with a similar automatic
pipette assembly.
5. Stir samples for 4 minutes on the same mechanical stirrer.
6. Standardize pH meter. Set the Adams-Evans buffer at pH 8.00
from a "blank" of the buffer solution (1:1 by volume of the
buffer-water mixture).
7. Read buffer pH while stirring (changes in reading during
this measurement indicate incomplete mixing of soil and
buffer).
8. Take soil-water pH measurements with one decimal, buffer pH
with 2 decimals.
9. Lime requirement is calculated from soil pH and buffer pH
for an acid soil (tables 1 to 4).
10
Table 1. The Amount of Agricultural Lime Needed to Raise the pH of Acid Soils to 6.5 Based
on Soil pH and the "Adams-Evans" Buffer pH
Hundreds of pounds ag. lime at different pH
1
5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 Tons/
acre
7.90 - 6 6 7 8 8 9 9 9 10 10 10 11 11 11 12 13
1.0
7.85 - 9 10 11 11 12 13 13 14 15 15 16 16 17 17 18 19
7.80 - 12 13 14 15 16 17 18 19 20 20 21 22 22 23 24 25
1.5
7.75 - 15 16 18 19 20 21 22 23 24 25 26 27 28 29 30 31
7.70 - 17 19 21 23 24 26 27 28 29 30 31 32 33 34 36 38
1_-2.0
7.65 - 20 23 25 27 28 30 31 33 34 35 37 38 39 40 42 44
7.60 - 23 26 28 30 32 34 36 37 39 40 42 43 45 46 48 50 2.5
7.55 - 26 29 32 34 36 38 40 42 44 46 47 49 50 52 53 56
. . .I 3 .0
7.50 - 29 32 35 38 40 431 45 47 49 51 52 54 56 57 59 63
7.45 - 32 36 39 42 441 47 49 52 54 56 58 59 61 63 65 69 3.5
7.40 - 35 39 42 46 48 51 54 56 59 61 63 65 67 69 71 75
. 4.0
7.35 - 38 42 46 49 53 56 58 61 63 66 68 70 72 75 77 81
7.30 - 41 45 49 53 57 60 63 66 68 71 73 76 78 80 83 88
7.25 - 44 . 48 53 57 61 64 67 70 73 76 78 81 84 86 89 94
-J
7.15 - 49 55 60 64 69 73 76 80 83 86 89 92 95 98 101 106
7.10 - 52 58 63 68 73 77 81 84 88 91 94 97 100 103 107 113
7.05 - 55 61 67 72 77 81 85 89 93 96 99 103 106 109 113 119
7.00 - 58 65 71 76 811 85 90 94 98 101 105 108 111 115 119 125
Pure CaCO
3
x 1.5; for tillage 
depth of 8 inches.
11
Table 2. The Amount of Agricultural Lime Needed to Raise the pH of Acid Soils to 6.0 Based on
the Soil pH and the "Adams-Evans" Buffer pH
Hundreds of pounds ag. lime at different pH
5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 Tons/
acre
7.90 - 1 2 3 4 4 5 6 6 7 7 8 8 9 9 10 11
1.0
7.85 - 2 3 4 5 7 8 9 9 10 11 12 13 13 14 15 16
7.80 - 2 4 6 7 9 10 11 13 14 15 16 17 18 19 20 22
7.75 - 3 5 7 9- 11 13 14 16 17 18 20 21 22 23 25 27
7.70 - 3 6 9 11 13 15 17 19 20 22 24 25 27 28 30 33
7.65 - 4 7 10 13 15 18 20 22 24 26 28 29 31 33 35 38
7.60 - 4 8 11 15 17 20 23 25 27 29 31 33 35 38 40 43
7.55 - 5 9 13 16 20 23 26 28 31 33 35 38 40 42 45 49
5 , 2.5
7.50- 5 10 14 18 22 25 28 31 34 37 39 42 44 47 50 54
7.45 - 6 11 16 20 24 28 31 34 38 40 43 '46 49 52 55 60 3.0
7.40- 6 12 17 22 26 30 34 38 41 44 47 50 53 56 60 65
3.5
7.35 - 7 13 19 24 28 33 37 41 44 48 51 54 58 61 65 71
7.30 - 7 14 20 25 35 31 40 44 48 51 55 59 62 66 70 76
7.25 - 8 15 21 27 33 38 43 47 51 55 59 63 67 70 75 81
7.20 - 8 16 23 29 35 40.45 50 55 59 63 67 71 75 80 87
7.15 - 9 17 24 31 37 43 48 53 58 62 67 71 75 80 85 92
7.10 - 9 18 26 33 39 45 51 56 61 66 71 75 80 84 90 98
7.05 - 10 19 27 35 41 48 54 59 65 70 75 79 84 89 94 103
7.00 - 10 20 28 36 44 501 57 63 68 74 79 84 89 94 99 109
Pure CaCO x 1.5; for tillage depth of 8 inches.
3
12
Table 3. The Amount of Agricultural Lime Needed to Raise the pH of Acid Soils to 5.5 Based on
the Soil pH and the "Adams-Evans" Buffer pH
Hundreds of pounds ag. lime at different pH
5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 Tons/
acre
7.90 - 0 0 0 0 0 1 2 3 3 4 5 6 6 7 8 9
7.85 - 0 0 0 0 0 1 3 4 5 6 7 8 9 10 12 13
1.0
7.80 - 0 0 0 0 0 2 4 5 7 8 10 11 12 14 15 18
7.75 - 0 0 0 0 0 2 4 7 8 10 12 14 15 17 19 22
7.70 - 0 0 0 0 0 3 5 8 10 12 14 17 19 21 23 27
S 1.5
7.65 - 0 0 0 0 0 3 6 9 12 14 17 19 22 24 27 31
7.60 - 0 0 0 0 0 4 7 10 14 16 19 22 25 28 31 36
2.0
7.55 - 0 0 0 0 0 4 8 12 15 18 22 25 28 31 35 
40
7.50 - 0 0 0 0 0 5 9 13 17 21 24 28 31 34 38 45
7.45 - 0 0 0 0 0 5 10 14 19 23 26 30 34 38 42 
49 2.5
7.40 - 0 0 0 0 0 6 11 16 20 25 29 33 37 41 
46 54
7.35 - 0 0 0 0 0 6 12 17 22 27 31 36 40 45 50 58
3.0
7.30 - 0 0 0 0 0 6 13 18 24 29 34 39 43 48 54 63
7.25- 0 0 0 0 0 7 13 20 25 31 36 41 46 
52 58 67
- 3.5
7.20 - 0 0 0 0 0 7 14 21 27 33 39 44 50 55 61 71
7.15- 0 0 0 0 0 8 15 22 29 35 41 47 53 59 65 76
7.10 - 0 0 0 0 0 8 16 23 30 37 43 50 56 62 69 80
4.0
7.05 - 0 0 0 0 0 9 17 25 32 39 46 52 59 66 73 85
7.00 - 0 0 0 0 0 9 18 26 34 41 48 55 62 69 77 89
Pure CaCO
3
x 1.5; for tillage depth 
of 8 inches.
13
Table 4. The Amount of Agricultural Lime Needed to Raise the pH of Acid 
Soils to 7.0 Based on
the Soil pH and the "Adams-Evans" Buffer pH
Hundreds of pounds ag. lime at different pH
5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 
Tons/
acre
7.95 - 3 4 4 4 5 5 5 5 5 6 6 6 6 
6 6 6
1.0
7.90 - 7 7 8 9 9 10 10 10 11 11 
11 12 12 12 12 13
7.85 - 10 11 12 13 14 14 15 16 16 17 17 17 18 18 
19 19
7,80 - 13 15 16 17 18 19 20 21 22 22 23 
23 24 24 25 25
1.5
7.75 - 17 19 20 22 23 24 25 26 27 28 29 29 30 30 31 
31
7.70 - 20 22 24 26 28 29 30 31 32 33 34 35 
36 36 37 38
2.0
7.65 - 23 26 28 30 32 34 35 37 38 39 40 41 
42 42 43 44
7.60 - 27 30 32 35 37 39 40 42 43 44 46 47 
48 49 49 50 2.5
7.55 - 30 33 36 39 41 43 45 47 49 50 51 52 54 
55 56 57
3.0
7.50 - 33 37 40 43 46 48 50 52 54 55 57 58 59 
61 62 63
7.45 - 37 41 45 48 51 53 55 57 59 61 63 64 65 
67 68 69 3.5
7.40 - 40 45 49 52 55 58 60 63 65 67 68 70 
71 73 74 175
4.0
7.35 - 43 48 53 56 60 63 65 68 70 72 
74 76 77 79 80 82
7.30 - 47 52 57 61 64 68 70 73 75 
78 80 82 83 85 86 88
4.5
7.25 50 56 61 65 69 72 75 78 81 83 85 
87 89 91 93 94
7.20 - 53 59 65 69 74 77 80 83 86 89 91 93 
95 97 99 101
7.15 - 57 63 69 74 78 821 86 89 92 94 97 99 101 
103 105 107
7.10 - 60 67 73 78 83 87 91 94 97 100 102 105 107 109 
111 113
Pure CaCO
3
x 1.5; for tillage depth of 8 inches.
14
VII. Data Summary and quality Control
Since laboratory results are collected automatically as an
integral part of a computer-assisted data acquisition system, a
unique opportunity is presented for using the computer to control
the quality of analytical work.
In addition to the use of blank and check samples, which are
randomly but regularly (every 20 to 40 samples) inserted into a
run, table 5, to detect such problems as contamination, error in
instrument calibration, and/or misplacement of soil samples, the
CEC of each soil sample is calculated by two independent methods.
One is based on the sum of extractable cations and buffer pH CEC+,
Table 5; the other on soil-water pH and buffer pH CEC, Table 5 (9).
For most Alabama soils, where Mehlich 1 is used as the extracting
solution and the buffer pH is determined by the Adams-Evans method,
the two estimated CECs should be practically identical. On the
other hand, a discrepancy between them would mean one of these
possibilities:
(1) The inappropriateness of the testing procedures, e.g., the use
of Mehlich 1 and buffer solutions in calcareous soils, and/or
(2) The dissolution of unreacted lime giving high Ca readings,
and/or
(3) Errors in analytical measurements, especially soil pH,
buffer pH, and extractable Ca.
The computer is programmed to pinpoint the discrepancy, when it
exceeds a set tolerance limit (50%), and to print a warning such as
an asterisk. Actions can be promptly taken to recheck, identify,
and correct errors or to identify the reason for the discrepancy.
Upon completion of a "run" and all quality-control measures are
satisfied, soil-test data and associated information (e.g., farmer
number, run number) are sent through a MODEM' (2400 baud) to an IBM
mainframe computer for execution of the fertilizer recommendations
program and print-out of recommendations to be returned to the
farmer (7).
15
Table 5. Soil-test Data Summary
A.U. SOIL TEST LABORATORY DATA SUMMARY FOR RUN 104 PAGE 1 ** 12:19:27 ** 2/19/85 **
POSNO MPOSNO FARMER LABNO
1 6983 34162
2 6983 34163
3 6983 34164
4 6983 34165
5 6984 34166
6 6984 34167
7 6984 34168
8 6984 34169
9 6985 34170
10 6985 34171
11 6986 34172
12 6987 34173
13 6987 34174
14 6988 34175
15 6989 34176
16 6990 34177
17 6990 34178
18 6990 34179
19 6991 34180
20 6992 34181
21 6993 34182
22 6994 34183
23 6995 34184
24 6995 34185
25 6996 34186
26 6996 34187
27 6996 34188
28 6997 34189
29 . 6997 34190
30 6997 34191
31 6997 34192
32 6998 34193
33 6998 34194
34 6998 34195
35 6999 34196
36 6999 34197
37 6999 34198
38 6999 34199
39 7000 34200
40 7000 34201
NR PH LIME P K Mg Ca NOTE
-------- Lb/A-------
1 5.59 7.59 1 123 146 780
1 5.68 7.65 5 138 186 920
1 5.19 7.61 1 62 123 400
1 5.63 7.67 3 104 124 730
1 4.24 7.61 30 31 31 180
1 4.96 7.70 62 115 64 400
1 5.18 7.80 43 60 69 430
1 5.30 7.71 171 158 47 430
2 5.40 7.68 126 165 112 570
1 6.39 7.76 88 414 1101 4450 *
1 6.10 7.75 270 116 266 1530
2 5.28 7.74 18 100 69 400
2 5.72 7.78 26 65 47 360
1 5.41 7.64 5 74 149 470
3 5.70 7.78 19 114 77 380
1 6.70 7.81 102 156 467 1430
1 6.95 7.83 104 196 443 1360
1 5.13 7.56 45 226 72 440
1 6.98 7.83 178 341 222 5290
1 5.25 7.63 121 116 51 460
1 5.77 7.77 61 164 84 870
1 5.40 7.59 54 112 46 880
1 5.52 7.57 71 239 262 1310
1 7.40 7.78 280 276 3460 6660 *
1 6.44 7.85 91 80 31 980
1 6.42 7.74 61 50 17 1010
1 6.67 7.85 120 97 35 1090
1 5.97 7.86 92 76 64 340
1 5.82 7.80 50 47 141 660
1 5.70 7.81 31 91 54 310
1 5.36 7.76 96 35 32 280
1 5.48 7.64 297 108 65 950
1 6.14 7.99 0 1 6 30 BL* 1I
1 5.65 7.75 69 109 94 440 CK 51
1 5.76 7.79 26 66 54 290
1 5.78 7.77 28 76 73 320
2 6.14 7.78 49 49 70 320
2 6.57 7.74 17 81 169 520 *
1 4.59 7.44 152 165 83 560
1 6.46 7.63 77 66 290 5990
CEC CEC+ K-RATIO
MEQ/100g %
6.59 5.93
5.95 6.04
4.94 4.70
5.44 5.08
5.44 3.67
3.31 3.80
2.52 2.95
3.92 3.71
4.59 4.63
6.72 18.13
5.61 7.04
3.47 3.48
3.83 2.93
5.19 4.69
3.78 3.12
7.06 7.16
8.39 6.85
5.38 5.20
8.72 15.91
4.85 4.41
4.14 4.50
5.88 5.81
6.62 8.03
24.30 5.82
4.38 3.82
7.47 4.71
5.41 4.16
2.87 2.27
3.71 3.84
3.27 2.55
3.36 2.79
5.41 5.58
0.23 0.10
4.17 3.62
3.75 2.68
4.16 3.03
5.08 2.91
8.52 4.18
4.81 6.43
10.99 19.14
6.30
7.23
3.62
5.81
1.86
7.82
4.65
10.37
9.85
15.06
5.91
6.88
4.53
4.27
7.87
7.50
9.10
12.60
12.46
6.91
10.12
5.94
11.32
9.12
5.07
2.60
5.69
6.08
3.10
6.84
2.56
5.91
0.32
7.08
4.72
5.14
3.14
4.12
8.92
2.18
*Indicates discrepancy in CEC calculations.
16
VIII. Special Analyses
Upon request, several non-routine analyses can be performed.
These determinations are classified as "special" because additional
cost will be charged for their services and results are not kept by
the computer.
1. Micro-nutrients (Cu, Fe, Mn, Zn, B, Mo) and toxic elements (Al,
Ni, Cr, Pb).
These elements are determined with an Inductively-coupled argon
Plasma Spectrometer (Jarrell-Ash, ICAP 9000).
Principles of Operation
Inductively-coupled argon plasma spectroscopy is a "finely
tuned" version of emission spectroscopy. In this technique,
radio frequency (RF) radiation is used to heat a flow of argon
gas into a plasma by means of an induction coil, figure 3.
When a sample is introduced into this extremely hot (5,000 to
10,000?K) argon plasma, the sample is broken down into
individual atoms, which are then further excited by the plasma.
These excited atoms subsequently re-emit the excitation energy
as electromagnetic radiation (light) which is characteristic of
their respective chemical elements.
The emitted light is then passed into the spectrometer,
which disperses the light across its focal curve, separating
the various emission lines present in the radiation. At
appropriate locations on the focal curve are positioned
photomultiplier tubes, one for each analytical line desired on
the system (total 16 in our ICAP). Light energy is converted
into electrical current, which is integrated over a period of
time (a few seconds), and then digitized so that data may be
fed into a computer (Apple lie) for calculations and storage.
Analytical results can then be printed out on the computer
terminal or displayed on a video screen.
The computer, besides collecting data and calculating
results, also controls the overall functioning of the
spectrometer, making the system reasonably "automatic" and
fail-safe.
ICAP Operating Parameters
Incident RF power 1.1 KW
Reflected RF power minimum ( 20W)
Nebulizer type cross flow
Nebulizer pressure 30 p.s.i.
Argon flow rates
cool ant 18 L/minute
sample 0.4 L/minute
plasma (not required) 0.5 L/minute
Sample aspiration rate 1.5 mL/minute
Observation height 18 mm above load coil
Profiling element Cu (channel #13 at center
of the focal curve)
17
Fig;s 3. Block diagram of an ICAP.
18
2. Organic Matter Determination
Organic carbon is determined by a dry combustion method
with- a LECO WR-12 carbon analyzer. Then,, organic matter is
calculated by multiplying organic carbon by 1.90 (6).
Prnilge Oerton
Soil sample is mixed with an electrically conductive material
and burned under pure 0 atmosphere in an inductive furnace.
Carbon dioxide produced i;s measured with a thermal conductivity
cell, which consists of a Wheatstone bridge that responds to the
heat difference carried by 02 and CO
2 
gas.
0 2 pressure 35 pIs~i.
0 flow rate 1.2 to 1.5 L/minute
barn time 70 seconds
detector temperature 50
0
C
Procedure
a. Weigh 0.25 g of carbonate-free soil into a' ceramic crucible.
b. Add 1 scoop (@ 2 g) of iron chip (to make sample
electrically conductive.
c. Add 1 scoop of granular copper.
d. Load the crucible into the inductive furnace.
e. Press ANALYZE button on the C ANALYZER.
NOTE:
a. Digital readout on the display is based on 1 g sample.
Therefore, if soil weight is 0.25 g, multiply the reading by
4 to get percent C in soil.
b. If sample contains carbonates, a pre-treatment is required,
as follows: slowly add 1 mL of 4 N H 
2 
s0
4 
to 0.25 g of soil.
The mixture is allowed to stand for 1 hour, then is placed in a
forced.-air oven at 80'C until completely dried. Organic
carbon can then be determined on the treated sample.
19
3. Nitrate Determination
The phenoldisulfonic acid method 
is used for NO3-N
determination (5,2).
Soil Extraction
a. Place 5 g of soil in a 50-mL 
Erlenmeyer flask
b. Add 20 mL of deionized H
2
0
c. Shake for 15 minutes, then filter.
Preparation of reagents
a. Sodium hydroxide 1N. Dissolve 4 
g of Na0H granules in 100
ml of deionized H
2 
.
b. Phenoldifulfonic acid. Dissolve 25 g of pure, 
white phenol
in 150 mL of concentrated H SO in a 
500-mL Erlenmeyer
flask. Then, add 75 mL of finin H SO (13 percent 
SO).
Mix the solution. Place the flask lotsely stoppered) 
in
hot water (90
0
C) for 2 to 4 hours.
c. 1:1 NH40H. Mix equal parts of concentrated 
NH40H and H
2
0.
d. NO -N standards. Dissolve 7.216 g 
of oven-dried KNO in
de onized H 0 and dilute to 1 L in a 
volumetric fask.
This solutign contains 1000 ppm NO -N 
Prepare working
standards of 0 to 10 ppm NO -N 
ith proper dilution.
Standard solutions can be kept for about 
2 weeks. Low
concentration NO
3
-N standards ( 5 p.p.m.) go bad easily.
Procedure
a. Aliquot 1 mL of soil extract into 
a 50-ml Pyrex beaker, add
1 drop of 1 N NaOH, evaporate to dryness on a 
hot plate.
Cool beaker to room temperature.
b. Add 1 mL of phenoldisulfonic acid, rotate 
the beaker to
dissolve the residue. Allow the mixture to 
stand for 10
minutes for the reaction to complete.
c. Add 5 mL of deionized H 0 Let it cool (@ 5 minutes), add
6 mL of 1:1 NH
4
0H solut on. Cool to room temperature.
d. Read absorbance on a B & L spectrometer at 420 nm.
e. Standards of 0, 1, 2, 5, and 10 p.p.m. NO
3
-N should always
be run along with samples.
20
4. Sulfate Determination
An indirect2method is used for SO 2- determination (8); in
this method SO is precipitated completely with an excess but
known amount oi BaC1 The unreacted Ba will then be measured
with an AA spectromeier, using a C
2
H
2
/N
2
0 flame.
Soil Extraction
Calcium monophosphate is used to extract soil 
SO
4
2
(3).
a. Place 5 g of soil in a 50-mL Erlenmeyer flask
b. Add 20 mL of 0.01 M Ca(H
2
P0
4
)
2
c. Shake for 30 minutes. Then, allow to stand overnight.
d. Filter
Preparation of Reagents
a. Ca(H2PO 
)  
- 0.01 M. Pour slowly 1 g of CaCO
3 
into 40 mL
of 0.5 PO (concentrated H
3
PO
4 
= 14.7 M). Dilute to 1
L with H 0
b. Stock 1,000 p.p.m. Ba solution. Dissolve 1.7786 g
BaC1
2
.2H
2
0 in deionized water and dilute to 1 L.
c. Working Ba solutions. Dilute 10 and 25 mL of the stock Ba
solution to 100 mL with deionized water to give 100 and 250
p.p.m. Ba solutions.
d. Stock 1,000 p.p.m. SO
4 
solution. Dissolve 1.814 g of K2SO
in deionized water and dilute to 1 L. Prepare worKin
solutions of 1.0 to 40.0 p.p.m. SO
4 
by dilution of the
stock 
solution.
e. C1CH COOH-KOH solution. Dissolve 47.25 g CICHCOOH
(mongchloroacetic acid) in deionized water; add 3.40 
KOH
and dilute to 250 mL.
f. BaSO seeding suspension. Mix 0.1 g BaSO powder with 100
mL o% deionized water. Shake well before se.
Procedure
a. Aliquot 5 mL of soil extract into a 50-mL Erlenmeyer flask.
b. Add 1.5 mL of 100 p.p.m. Ba (as BaCl
2
)
c. Add 1 mL of monochloroacetic acid-KOH mixture
21
d. Add 0.1 mL of BaSO
4 
seeding solution
e. Add 7.5 mL of 95% Ethanol
f. Stopper and shake for 15 minutes
g. Transfer about half of the solution into 10-mL centrifuge
tube and centrifuge samples (maximum 24 samples per batch)
at 10,000 g for 30 minutes.
h. Decant the supernatant and save it.
i. Measure Ba in the supernatant with an AA
j. Sulfate standards: 0 to 15 p.p.m. S0
4
-S should always
accompany 
samples
5. Soluble Salts
Specific conductance (indicator of soluble salts) is
determined in the supernatant of 1:2 soil:water 
slurry (13).
Procedure
Measure 40 cm
3 
of 2-mm sieved soil into a beaker, add 80 mL of
water, stir thoroughly and allow suspension to settle for at
least 30 minutes or long enough for the solids to settle.
Draw supernatant into the conductivity pipette to slightly
above the constricted part of pipette. Avoid drawing liquid
into rubber bulb. If this occurs, rinse bulb before continuing
with the next sample.
Calculations
.Specific conductance (SC) of the soil extract is calculated as
fol 1 ows:
1,4118 x Cext
SC, mmhos per cm at 25
0
C =
Cstd
where the value of 1.4118 is the specific conductance of the
standard 0.01 N KC solution in mmho per cm at 25
0
C and Cstd
and Cext refer to conductance in mhos of the standard (0.01 N
KCl) solution and extract, respectively.
See tables 6 and 7 for interpretation of the results.
22
Table 6. Soluble Salt Reading in mmho/cm and Corresponding Approximate
ppm of Salt in 1:2 Air-dried Soil (Volume to Volume) Water
Extract and Salinity Effects
Reading Salt Salinity
mmho/cm* p.p.m. effects
0.40 512 Salinity effects mostly negligible
0.40-0.80
0.81-1.60
1.61-2.40
2.41-3.20
512-1024
1025-2048
2049-3072
3073-4096
Very slightly saline. Yield of crops of
low salt tolerance may be reduced by 50%
all classes of crops (see table 2).
Slightly saline. Yields of fruit and
vegetable crops of medium salt tolerance
may be reduced by 50%. Similar yield
reductions may occur in the more sensitive
forage and field crops of medium salt
tolerance. Lower half (0.81-1.20) of range
satisfactory for well-drained mineral green-
house soils. Upper half (1.21-1.60) of
range higher than desirable for greenhouse
soils except for peat and lightweight mixes.
Moderately saline. Yields of virtually all
fruit crops significantly reduced. Yield
reductions of 50% may occur in the more
sensitive forage and field crops of high
salt tolerance. Similar yield reductions
occur in the more highly salt-tolerant 
veg-
etable crops. For greenhouse crops ( 2.0)
leach soil with enough water so that 2-4
quarts pass through each square foot of
bench area of 1 pint of water per 6-inch
pot; repeat after about 1 hour. Repeat
again if readings are still in the high
range.
Strongly saline. Only highly salt-tolerant
forage and field crops will yield satisfac-
torily.
4096 Very strongly saline.
salt-tolerant grasses,
and certain shrubs and
Only a few highly
herbaceous plants
trees will grow.
*mmho/cm x 1000 = mg salt/d
3
*mmho/cm 100 mg salt/dM
23
3.20
Table 7. Range of Salt Tolerance of Crops
SC,
mmho/cm Rating Salt tolerance
Forage Crops
0.5-0.8 Low* Ladino clover, burnet, red clover, alsike
clover, meadow foxtail, white dutch clover
0.81-2.6 Medium Milkvetch, sourclover, tall meadow oatgrass,
smooth brome, big trefoil, reed canary,
meadow fescue, blue grama, orchardgrass, oats
(hay), wheat (hay), rye (hay), alfalfa, hubam
clover, sudan grass, dallis grass, strawberry
clover, mountain brome, beardless wildrye,
birdsfoot trefoil, perennial ryegrass, yellow
sweetclover, white sweetclover
2.61-3.6 High Hardinggrass, barley (hay), tall fescue,
crested wheatgrass, canada wildrye, tall
wheatgrass, rescue grass, rhodes grass, ber-
muda grass, nutall alkaligrass, saltgrass,
alkali sacaton
Field Crops
0.5-0.8 Low Field peas, soybeans, field beans
Medium
High
Low
Medium
High
Castorbeans, sunflower, flax, broadbean
lima, pinto, etc., corn (field), rice, sesba-
nia, soybean, sorghum (grain), oats (grain),
wheat (grain), rye (grain), safflower
Cotton, rape, sugarbeet, barley
Vegetable Crops
Beans, celery, radish
Cucumber, squash, pea, onion, carrot, let-
tuce, cauliflower, bell pepper, potato, sweet
potato, sweet corn, cabbage, broccoli,
tomato
Spinach, asparagus, kale, beets
*No crop injury at low end of range to as much as 50% yield reduction at
high end of range.
24
0.81-2.6
2.61-3.6
0.5-0.8
0.81-1.6
1.61-2.4
6. Particle Size Analysis
Purpose. A particle size analysis is made for determining the
texture of a soil. It consists of obtaining the percentages of
sand, silt, and clay in the soil.
Principle. When the mineral fragments of soil are suspended in
water, they tend to sink. The rate at which they settle
depends on the relative size of the particles. The largest
particles settle first and the smallest particles settle last.
Two steps are necessary to obtaining satisfactory particle size
analysis:
1. Thorough shaking of the sample in water with a chemical
dispersing agent so that each particle is functioning as
nearly separately as possible.
2. Placing the suspension of the sample in a suitable amount
of water in preparation for unequal settling.
There are several methods for making particle size analysis of
the soil. One of the most rapid is the Bouyoucos Hydrometer
method (4). This method consists of placing a hydrometer,
which is calibrated to read grams per liter, in the soil
suspension in a special sedimentation cylinder at the desired
time. Theoretically, the hydrometer measures the density of a
suspension at a given depth.
Procedure
a. Place 40 g of soil in a special baffled metal cup. Fill
the cup to within 4 cm of the rim with water. Add 50 mL of
Calgon dispersing agent (a solution of 100 g Calgon per
liter) to break up the soil aggregates.
b. Stir with electric motor for 10 minutes. Then pour the
soil and water suspension into a special settling cylinder,
wash the coarse fraction from the cup with a stream of
water.
c. Bring the final volume to 1000 mL. Stopper the cylinder,
and shake while in a horizontal position. Place upright on
the bench and note the time immediately.
d. Place the hydrometer in the suspension, and take a reading
at 40 seconds from the time placed on bench.
This reading is:"__________
e. A second reading is taken at the settling time of 6.0
hours.
This reading is:"________
25
Explanation:
The first hydrometer reading represents the concentration of
silt and clay (all sand having settled in 40 seconds), and the
second reading the concentration of clay (silt having settled
in 6 hours).
Calculations:
% (silt + clay) = (100/40)*(40-sec reading)
% (clay) = (100/40)*(6-h reading)
% (silt) = % (silt + clay) - % (clay)
% (sand) = 100 - % (silt + clay)
Textural Class Name:
See figure 4 for textural class name.
Clay
100% 0
80 20
70 30
60 Clay 40
0silty
Sandy 
clay
Clay loam 
Silty clay
30 Sandy clay loam 70
loam
10 Sandy 
lom -
Siltoamo
Sand 
100%
% 90 so80 70 60o 50 40 30 20 10 0Silt
-*- Per Cent Sand
Fig. 4. Guide for textural classification.
26
Sand
IX. Plant Analysis
The Soil Testing Laboratory offers a pecan leaf analysis
service, which includes a routine soil test, and a leaf analysis
for N, S, P, K, Ca, Mg, and Zn. The package costs $11. Samples
received for a pecan leaf analysis are numbered consecutively
beginning with number 1 for the first sample of the calendar year
(e.g., 85-1, 85-2, 85-3, etc.). Soil and leaf samples from the
same orchard receive the same number.
"Trouble shooting" samples including several plant species and
plant parts, which are often brought in by Extension specialists,
are also analyzed by the laboratory similarly to pecan leaves plus
Fe, Mn, Cu, and B.
1. Dry Ashing of Plant Samples
a. Weigh 0.5 g of dry plant material into 50 mL pyrex beaker.
Plant material should be ground to pass a 40-mesh (0.60 mm)
stainless steel sieve.
b. Cover with watch glass and place in muffle furnace. Heat
to 450
0
C and hold at that temperature until all carbon is
burned off (@ 4 hours). The ash should be greyish white.
c. Add 10 mL of 1.N HNO , and evaporate to dryness slowly on a
hot plate. Take jusi to dryness and do not bake.
d. Add 10 mL 1 N HC1 to dissolve the residue.
e. Warm nearly to boiling then transfer to a 100-mL volumetric
flask. Wash beaker 3 times with small amounts of water.
f. Bring to 100 mL, and filter. Do not wash filter paper or
add more water in this step.
NOTE: 1 N HC1 = 83 mL concentrated HC1 per liter.
1 N HNO
3 
= 64 mL concentrated HNO per liter.
g. Use the ICAP to determine P, K, Ca, Mg, Mn, 
Cu, Fe, and Zn.
h. If B is determined, Pyrex beaker must be replaced with a
special ceramic crucible and step [c] is omitted.
2. Wet Ashing of Plant Samples
Reagents
Acid mix: 70 percent concentrated HNO
3 
+ 30 percent HCIO
4
(60-72 percent)
1 N HCl
Whatman #40 filter paper
Deionized H 0
2
27
Apparatus
250-mL digestion tubes and rack
100-mL volumetric flasks
Steam bath in hood
Block digestor in hood
Balance (to 0.01 g)
Procedure
a. Weigh 0.5 g of plant material into a 250-mL digestion
tube.
b. Add 10 mL of the Acid Mix and heat for 1 hour on the steam
bath or let stand overnight.
c. Transfer the tubes to the block digestor and heat at 190
0
C
until the material is digested (@ 2 hours). Add more Acid
Mix as needed to keep the tubes from going dry.
d. Remove the tubes from the block, cool down.
e. Add 10 mL of 1 N HCl and bring to 100 mL with deionized H
2
0.
f. Filter a portion of the solution through a Whatman No. 40
filter paper.
g. Carry a blank through the procedure.
h. Store the solutions in glass bottles.
i. Use the ICAP to determine P, K, Ca, Mg, Mn, Cu, Fe, and Zn.
Note: Wet ashing procedure is not suitable for B determination
because a portion of B would be lost as H
3
BO
3
.
3. Total N Determination.
A Leco CHN-600 is being used for total N determination.
This instrument has an advantage over the "conventional"
Kjeldahl method because the digestion of the sample is not
required. The time it takes to obtain total N content of a
solid sample is @ 5 minutes.
The determination of N is made by burning a weighed
quantity of sample (solid or liquid) in pure 0p at @ 950?C;
COH 0 vapor, oxides of nitrogen, N
2
, and Oxli'des of sulfur
ar' po'ssible products of combustion. Oxides of sulfur are
removed with CaO in the secondary combustion zone so that water
vapor cannot combine to form H fS04. The remaining gases of
combustion are collected in a ballast and are allowed to mix
28
thoroughly. Then, 10-mL aliquot is taken for N determination.
The aliquot is carried by He into a reagent train consisting of
hot Cu for the removal of 02 and the reduction of NO to N ,
NaOH for the removal of CO , and Mg(ClO ) for the removal2of
H 0. The remaining elemenial N is meaL ed by the thermal
cnductivity cell. This detectgr cell has the ability to
detect the difference in the thermal conductivity of gases.
The cell consists of two pairs of matched filaments used in
four legs of a Wheatstone bridge. The "reference" filaments
are maintained in a constant gas (pure He), pressure, flow, and
temperature environment, while the "measure" filament is
maintained in a constant pressure, flow, and temperature
environment, but the gas type is allowed to vary (a mixture of
He and N
2
).
Operating Parameters
02 profile 3, 4, 1
O gas back pressure 6 - 10 psi
Cgmbustion pressure 3 - 8 psi
He pressure 12 psi
N
2 
Blank <0.2 percent (ultra pure 02 gas -
99.99)
Procedure
a. Press the GAS ON key on the computer keyboard to turn on
the He gas.
b. Weigh out a known quantity of plant tissue (0.07 to 0.15 g)
into a tin capsule.
c. Crimp end of the capsule to keep sample from falling out.
d. Enter sample weight either automatically or manually by the
keyboard.
e. Place sample on the automatic sampling disc.
f. Press ANALYZE to start.
Note:
a. Halt the operation immediately if WARNING light comes on.
b. Try to determine the possible cause; if the problem is
found and solved, press RESET key to resume the operation.
c. Press GAS ON key again to shut He off.
29
4. Total S Determination.
A LECO IR-32 sulfur analyzer is used to determine total S
in plants and soils.
Principle of Operation
Solid sample is mixed with an electrically conductive material
(Fe powder) and with catalysts (W and V
9
0
5
). Then, the mixture is
burned under pure 02 atmosphere in an ihductive furnace to produce
SO
2
, CO
2
, and H 0. Water vapor is then 
eliminated with Mg(ClO
4
),
SO in the re aining gaseous mixture is detected with an R
deiector. Because CO
2 
gas absorbs at some of the same infrared
wavelengths as SO , a CO filter is needed. This CO filter is a
sealed chamber co tainin CO gas, which completely absorbs energy
at the CO wavelengths. Between the CO filter and the shutter
mechanism ;re two chambers, one is called the reference cell, the
other is called the measure cell. During calibration, both cells
are filled with pure 0 However, when SO from the sample enters
the measure cell, the R radiation in that ortion of the system is
partially absorbed by the sample SO gas. The difference in IR
energy between two cells is then onverted electronically into
percent S in the sample.
Operating Parameters
0 pressure 20 p.s.i.
Ihtegration time 60 seconds
Standard cotton leaf containing 0.60 percent S
Procedure
a. Weigh 0.100 g of plant material or 0.250 g of soil into a
ceramic crucible.
b. Add 1 scoop (2 g) of iron powder, 1 scoop of tungsten fine
granules, and 1 disk of vanadium pentoxide (V
2
0
5
),in this
order.
c. Place a lid on the crucible, and then place the crucible
into the inductive furnace.
d. Press ANALYZE button on the S analyzer.
Note:
a. Always standardize the machine with comparable standards
before running samples.
b. The reading is displayed as percent of sample on a 1-g
basis. Therefore, if only 0.1-g sample is used, the result
(percent) is 10 times the reading.
30
References
(1) Adams, Fred and C.E. Evans. 1962. A Rapid Method for Measuring
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(2) American Public Health Association. 1975. Standard Methods for
the Examination of Water and Wastewater. 14th ed. American Public
Health Association, Inc., New York.
(3) Barrow, N.J. 1967. Studies on Extraction and on Availability to
Plants of Adsorbed Plus Soluble Sulfate. Soil Sci. 104:242-249.
(4) Bouyoucos, G.J. 1962. Hydrometer Method Improved for Making
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(5) Bremner, J.M. 1965. Inorganic Forms of Nitrogen. In C.A. Black
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(6) Broadbent, F.E. 1965. Organic Matter. In C.A. Black (ed.)
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(7) Cope, J.T., C.E. Evans, and H.C. Williams. 1981. Soil-test
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(8) Hue, N.V. and F. Adams. 1979. Indirect Determination of
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(9) and C.E. Evans. 1983. A Computer-assisted Method for
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(10) , R,M. Patterson, A.C. Bailey, R.L.
Schafer, and J.T. Cope. 1983. A Computerized Process for
Soil-test Data Acquisition. Agron. J. 75:144-145.
(11) Lancaster, J.D. 1970. Determination of Phosphorus and Potassium
in Soils. Miss. Agr. Exp. Sta. Mimeo.
(12) Mehlich, A. 1953. Determinations of P, Ca, Mg, K, Na, and NH by
North Carolina Soil Testing Laboratories. N.C. State Univ. Minieo.
(13) Southern Cooperative Series. 1983. Reference Soil Test Methods
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(14) Watanabe, F.S. and S.R. Olsen. 1965. Test of an Ascorbic Acid
Method for Determining Phosphorus in Water and NaHCO
3 
Extracts
from Soil. Soil Sci. Soc. Am. Proc. 29:677-678.
31