Agricultural Service Laboratory
April 28, 2000
TABLE OF CONTENTS
1. Arrange samples by date received, county and grower in sets of 100.
2. Assign a 7 digit lab number to each sample. The 2 left hand digits
3. Place samples into the set. Sample information on the boxes and record
4. Samples received in a damaged condition, missing samples, or
5. Within each set, place Check sample boxes at approximately positions
6. After a complete set is arranged, box tops should be removed with the
7. Place samples in drying racks and allow to dry.
8. After drying, crush and screen samples through a 10 mesh screen.
9. Following analysis, place samples into storage racks for 1 month from
the date of
10. Soil from Marion and Horry must be treated by heating at 121oC for 2 hr.
1. Collect papers and start stamping with beginning lab number.
2. Write beginning lab number on raw data sheet. Note position of checks
and blank on
3. Be careful to check for any special analyses. Note the special
analyses with a
4. Make labels for pH and extracted samples.
5. Turn papers in to data processing.
Sample order must be rechecked prior to any analyses.
1. Retrieve papers for individual sets from data processing with lab
2. Check through each sheet to make sure samples are in the proper order
3. Return sheets to data processing.
After samples are checked for proper order, labeled with Check and Blank
1. Using a 4 mL volumetric scoop (assume 5 g), measure an amount of soil
1) Dip scoop with sweeping motion and fill to overflowing
2) Hold scoop over box and firmly tap handle three times to settle
3) Strike off excess soil with leveling rod and transfer
2. Measure samples into extraction racks containing 10 polyethylene cups
3. Extract fifty samples at a time. Add twenty milliliters of Mehlich 1 extracting
4. Shake samples on a mechanical reciprocating shaker, adjusted to 180
5. Place prefolded, high quality filter paper, moistened with deionized
6. After shaking, immediately filter and save the collected extract for
7. All glassware and cups should be thoroughly rinsed between samples
Soil pH is determined on all samples using a 1:1 (weight:volume) soil to
pH 4.01 buffer standard - purchased at pH 4.0 (0.05M Potassium hydrogen
1. Transfer 12 mL scoop of soil (assume 15 g) to paper cups arranged in
2. Add 15.0 mL of deionized water by automatic pipette with enough force
3. An AS-3000 Dual pH Analyser is used to measure pH. Check the filling solution
4. Follow instrument procedures for calibrating
5. Set lab number parameters accordingly.
6. Allow the meter to stabilize at least 15 minutes.
7. Measure the pH of the check soils. The pH should be read to 1 decimal
8. After the set is completed, compare the additional recheck readings
9. Store electrodes in storage solution or buffer standard solution with
10. Clean electrodes weekly.
A routine buffer pH or lime requirement pH is made on all samples. The
Components of the Moore-Sikora Buffer
For every liter of solution, the following quantities of
chemicals are dissolved.
Quantitatively add each component above to a container that
will hold the appropriate
Calibrate a pH meter to pH buffers of 7.00 and 4.00. After
calibration, a pH 10.00 buffer
Fifteen mL deionized water is added to a 15 mL aliquot of
the solution and the pH of the
1. To each soil-water mixture from the pH determination (15 g soil + 15 mL H20) add
2. Stir thoroughly and allow to stand a minimum of 30 minutes.
3. Standardize pH meter with buffer 7.0 and 4.00. Read buffer blank (buffer blank =
4. Verify values of check samples before leaving analyser.
5. If the Check soil readings are not within tolerance, check
6. Save data to a text file and print.
7. Dump cups then autoclave samples from Marion and Horry.
8. Store electrodes in storage solution or buffer standard solution with
The same procedure for buffer pH on fish pond and shrimp pond samples is followed.
Extractable total sulfur is determined on request and on subsoil samples
1. Dissolve 38.5 g NH4OAC in deionized water in a 1 liter volumetric
2. To prepare 18 liters, add 600 mL of concentrated NH4OH to
approximately 10 liters
1. Samples are extracted using sulfate free glassware, with sulfate
2. After shaking, samples are filtered through number 42 Whatman filter
Samples should be logged in the log book.
1. Fill 600 mL plastic beakers with sample mix. Bring to field capacity
Note: At saturation, the sample will flow slightly when tipped and
can be easily stirred
2. Vacuum filter through # 4 filter paper and collect at least 110 mL of the extract.
3. Pour an aliquot into a test tube to determine extractable P, K, Ca,
4. Save 100 mL to use for the rest of the analyses.
5. Determine soluble salt content on the solubridge and convert to
(See Plant and Feed Manual for meter instructions.)
6. Determine soil pH by glass electrode in a separate subsample by
7. Determine NO3-N by FIAlab nitrate analyzer.
8. Saturated extract results are reported on the Special Analyses Report
Nitrate-Nitrogen (NO3-N) is determined routinely on saturated extracts
Nitrate Extracting Solution
Dissolve 173.2 g AL2(SO4)3.18H20, 12.8 g H3BO3, and 0.7222 g KNO3 in 8
Boric Acid Preservation Solution -
Dissolve 6.2 g boric acid in 100 mL hot distilled water.
Silver sulfate - Reagent grade Ag2SO4.
Outer filling solution - Dilute 2 mL ISA to 100 mL with distilled water
Inner filling solution - Orion cat. 900002
1. Measure 20 g soil (16 mL scoop) into a paper cup.
2. Add 40 mL NO3 extracting solution, mix thoroughly, and allow to
3. Filter through # 4 filter paper and collect filtrate in 50 mL beakers.
4. Working Standards (2, 10, 100 mg/l NO3-N)
To prepare 2, 10, and 100 ppm working standards from commercial 1000 ppm
5. Determine ppm NO3-N by specific ion electrode.
6. Instrument calibration and operation for soils:
a) Remove electrodes from storage solution and rinse thoroughly.
b) Place electrodes in 2 ppm standard. Press calibration then enter 3-yes
c) Rinse electrodes then place in 10 ppm standard. Wait for beep then
d) Rinse electrodes then place in 100 ppm standard. Wait for beep then
e) To read samples press measure. Red check sample should read 15-19.
7. Record as ppm NO3-N (no decimals) on lab result sheets for special
8. After analyses are completed, rinse electrodes, return to storage
Procedure (Saturated Extract):
1. Working Standards
a) To prepare 2, 10, and 100 ppm working standards, add 0.2, 1, and 10 mL
b) Prepare fresh standards every two weeks.
2. Add 1 mL preservation solution to each sample and standards.
3. Add 2 mL ISA to the standards and the samples.
4. Check levels of inner and outer filling solutions in reference
5. Instrument calibration for SE: (see NO3-N instrument calibration and
6. Rinse electrodes and place into sample. Record reading directly as
7. Recheck standards frequently.
8. When finished, place meter in Standby mode and submerge electrodes in Blank.
Nitrate-Nitrogen by Cadmium Reduction using Flow Injection FIALab 2500
Extraction reagent: 0.04 M (NH4)2SO4
To make 10 L: Add 6 L DI water to a 20 L carboy. Weigh 52.80 g
1. Use 4 mL
(approximate 5 g) mineral scoop and scoop soil into an extraction cup.
Reference: J. Benton
Jones, Jr., Laboratory Guide for Conducting Soil Tests and Plant
Loss on Ignition for Organic Matter.
1. Muffle Furnace
2. "High Form" Porcelain Crucibles
1. Number crucibles with wax pencil.
2. Weigh crucibles to 4 decimal places.
3. Scoop soil samples into crucibles using 5 g scoop.
4. Put crucibles plus samples on tray in left-hand furnace.
5. Set dial to 100. (This corresponds to a temperature of 105o +/- 5oC.)
6. Ash at this temperature for 2 h. (It takes 30 min for the furnace to
7. Remove samples from furnace with tongs, place in desiccator, and weigh
8. Replace crucibles plus samples in left furnace.
9. Turn dial up to 360. (This corresponds to a temperature of 360o +/- 5oC.)
10. Ash at this temperature for 2 h. (It takes 1 h for the furnace to
11. Turn furnace off and open door.
12. Place samples in desiccator with tongs and allow samples to cool.
13. Weigh samples to 4 decimal places.
14. Calculate OM % and record on data sheet with one decimal.
crucible wt = a
crucible wt + sample wt after 105oC heating = b
crucible wt + sample wt after 360oC heating = c
%OM = ((b-a) - (c-a))(100)/(b-a)
E. E. Schulte, Recommended Soil Organic Matter Tests.
Potassium Dichromate Solution (1.0N K2Cr2O7)
Place 49.04 g of potassium dichromate (K2Cr2O7) (dried at 105oC) in a
Ferrous Sulfate Solution (0.5N FeSO4.7H20)
Place 139.01 g of ferrous sulfate (hydrated) FeSO4.7H20 in a one liter
flask. Add about
Use 0.025 M O-phenanthroline ferrous sulfate (Ferroin) as an indicator
0.5946 g/100 mL phenanthroline = 0.01N
0.2780 g/100 mL FeSO4.7H20 = 0.01N
1. Place 1.0 g of soil in a 250-mL Erlenmeyer flask and prepare a Blank
by adding no
2. Add exactly 10 mL of 1.00N potassium dichromate and mix by gentle
3. Add 20 mL of concentrated sulfuric acid and mix for one minute by
4. Allow to stand for 30 minutes.
5. Add 150 mL demineralized water.
6. Add 10 mL of concentrated phosphoric acid and allow to cool to room temperature.
7. Add 4-5 drops of indicator. (If solution turns dark green weigh 1/2 g
8. Titrate immediately with 0.5N ferrous sulfate solution until end point
9. Determine % organic matter using given formula:
% O.M. = (1 - T/S) (6.8)
Where T = sample titration in mL of 0.5N ferrous sulfate
Where S = standard blank in mL of 0.5N ferrous sulfate
This formula is based on two important assumptions which may not be valid
(1) only 76% of the organic carbon present is oxidized to CO2, and (2)
10.Record on lab result sheets for special analyses as % O.M. (1 decimal place).
Soluble salts are run on samples as requested in mineral soils and on artificial mixes.
Samples should be logged in the log book.
1. Scoop 20 mL soil to a 250 Erlenmeyer flask.
2. Add 40 mL of distilled water with graduated cylinder, stir, and allow
3. Decant liquid (through screen filter) and collect in small wide mouth bottle.
4. Read mmhos/cm on conductivity meter. (See Plant and Feed Manual for
5. Record 2 decimal places, e.g., 0.200 = 0.20.
6. Report values on Report on lab sheet. Lab number should
Method of extraction is 1:2.
The large number of routine soil samples extracted and analyzed daily in
In a routine, daily soil-test run, two Check samples and one Blank are
placed in every
or Extension personnel may request that all or part of their analyses be rechecked for
accuracy. This allows for a monitoring of quality control as well as maintaining confidence
in the lab.
1. Isaac, R. A. (ed.). Reference Soil Test Methods for the Southern
Region of the
2. S. J. Donohue. Reference Soil and Media Diagnostic Procedures for the