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Department of Agronomy

Soil Analysis

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Analysis for research soil samples include: pH, phosphorus (P), potassium (K), nitrate (NO3), organic matter, calcium (Ca), magnesium (Mg), sodium (Na), cation exchange capacity (CEC), iron (Fe), zinc (Zn), copper (Cu), manganese (Mn), ammonium (NH4), sulfate (SO4), chloride (Cl), aluminum (Al), texture, total nitrogen (N) and carbon (C) (dry combustion), total nitrogen (N) and phosphorus (P) soluble salts, and salt alkali.

Soil samples are transferred to sterile, labeled containers and dried in a forced air oven (unless analysis prohibits immediate oven drying). Once dry, they are ground with a pulverizing-type grinder and analyzed. When the data is complete and has been reviewed, sample data is emailed to the researcher. Samples may then be returned if requested.

Available Testing

Soil Preparation

Soil is prepared by drying overnight in a 50°C oven, then grinding to pass through a 2mm sieve. When iron is to be analyzed, samples are air-dried to prevent incorrectly high values. When nitrogen is to be analyzed, samples are dried as soon as possible to prevent bacterial conversion of nitrogen.

pH

pH is measured directly using a 1:1 slurry of  10 g of prepared soil with deionized water with an automated system.Buffer pH for lime requirement is measured with the SMP buffer technique. Lime recommendations are reported in lbs of effective CaCO3 per acre.

Phosphorus
Melich III Phosphorus

This P analysis uses a universal extractant that removes a wide range of elements. It is used by many laboratories for multiple-element analysis.It also requires 2 g of prepared soil.

Bray Phosphorus

The Bray P test is used for extractable (potentially plant available) phosphorus in soil because of its consistent correlation with yields from fertilizer recommendations generated from the test results. It utilizes an HCl-ammonium fluoride extractant and a colorimetric assay that requires 2 g of prepared soil.

Olsen Phosphorus

When the soil sample is calcareous, above pH 7.5, and the Bray P value is low, the Olsen P test is recommended. It makes use of a sodium bicarbonate extractant, a colorimetric assay, and 2 g of prepared soil.

Cations
Exchangable Cations

The four cations Ca 2+ , Mg 2+ , K + , Na + are extracted with 1 M ammonium acetate, pH 7.0. Analysis is by Flame Atomic Absorption or ICP Spectrometry.The test requires 2 g of prepared soil and only one extraction fee is charged for each sample.

Cation Exchange Capacity The displacement method with saturating ammonium acetate is used to measure the cation exchange capacity contained in a 2-g sample. After washing and elution, the NH 4 + released is determined by the colorimetric assay used for KCl extracts.

DTPA Extraction

The micronutrients Cu + , Fe 3+ , Mn 2+ , Zn + are extracted with the chelator DTPA and analyzed by Flame Atomic Absorption or ICP spectrometry.The test requires 10 g of prepared soil and only one extraction fee is charged for each sample.

Nitrogen

Both inorganic nitrogen forms, NH 4 + and NO 3 - , are extracted with 1 M KCl, using 2 g of prepared soil.Cadmium reduction is used for nitrate and colorimetric procedures are run in separate channels in a flow analyzer to measure these ions simultaneously.

Soluble Salts

The conductivity of a saturated paste water extract is determined with a digital conductivity meter.The value in mmhos/cm is an measure of the total soluble salts in the sample.The saturated paste requires 50 g of prepared soil.

Salt Alkali

This complete analysis of the saline and sodic properties of the soil sample includes the soluble salts measurement, soluble, extractable, and exchangeable sodium levels, pH, and classification of the soil for the sodium and sodium chloride risk. This test requires 50 g of prepared soil.

Texture

Using sodium hexametaphosphate as a dispersing agent, the sand, silt, and clay fractions of the sample are estimated with the hydrometer method. Fifty grams of prepared soil are needed.

Chloride

Soil chloride is extracted from a 5-g sample with calcium nitrate and analyzed with the Mercury Thiocyanate colorimetric method.

Sulfate

A monocalcium phosphate extraction of sulfate from 10 g of soil is analyzed on a flow analyzer by the turbidimetric mehod. Values are reported as elemental sulfur.

Aluminum

Extraction with 1 M KCl and analysis by ICP Spectrometry gives soil levels of Al 3 + . This test is recommended for samples with pH of 5.5 or below and requires 5 g of prepared soil.

Total Carbon & Nitrogen

A LECO CN 2000 combustion analyzer reports total levels (inorganic and organic) of C and N on a weight percent basis. A 0.5-g sample of prepared soil is normally used.

Total Nitrogen & Phosphorus

A modified Kjeldahl digestion is performed on 1 g of prepared soil. The diluted digest is analyzed for nitrogen and phosphorous in separate colorimetric reactions using a flow analyzer.

Organic Matter

The Walkley-Black procedure digests 1 g of prepared soil with sulfuric acid and dichromate, followed by a direct colorimetric measurement of the reduced Cr2O72- ion. The percent organic matter reported may also be estimated by calculation from the total carbon value obtained from combustion analysis.

Note: Many of the original methods used for the above tests may be found in the following reference: 1998. Recommended Chemical Soil Test Procedures for the North Central Region North Central Regional Publication No. 221(Revised). University of Missouri Agricultural Experiment Station, Columbia, MO.

Forms

Sample Collection

Scientist Grinding

Soil sample collection will vary depending on the experiment being conducted. Please label all samples and completely fill out the sample information sheets so lab analysis and processing can occur efficiently.

Contact Us

Soil Testing Laboratory
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K-State Research and Extension
2308 Throckmorton PSC
1712 Claflin Road
Manhattan, KS 66506-5503

Ph: +1-785-532-7897
Fx: +1-785-532-7412