University of KentuckyCollege of Agriculture
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Soil: Tests: Methods

See: Basic Description | Detailed Description

Basic Description

Test  Material Tested  Method Used  Reported Units 

Routine Soil Test (pH, buffer pH; Mehlich III P, K, Ca, Mg, Zn)

Soil

Glass electrode in 1:1 soil:water for pH, use of Sikora buffer for Buffer pH, Mehlich III extraction for nutrients. Nutrients analyzed via ICP.

pH and Buffer pH are unitless, lbs/acre for Mehlich III nutrients

Heavy Metals, Mehlich III Extraction (Cd, Cr, Ni, Pb, Zn, Cu, Mo)

Soil

Mehlich III extraction and ICP analyses

mg metal / kg soil

Sand, Silt, Clay, and Textural Class

Soil

Micro-pipette method

% (w/w) of oven-dried soil for sand, silt, and clay

Cation Exchange Capacity, Bases, and Base Saturation

Soil

1 N, pH 7, ammonium acetate extraction and saturation, bases analyzed via ICP, NH4 analyzed via ion-selective electrode.

meq / 100 g soil for bases and CEC (equivalent to cmol(+)/kg), % of total CEC for base saturation

Triazine Residue (Atrazine and Simazine)

Soil

Gas chromatography

mg/kg soil

Hot water extract B

Soil

Hot water extraction and ICP analyses

lbs/acre

Organic Matter

Soil

LECO combustion

% organic matter (w/w) of oven-dried soil.  (%organic matter/1.72 = %carbon)

Soluble Salts

Soil

Electrical conductivity of a water extract

mmhos/cm (=dS/m)

Total Nitrogen

Soil

LECO combustion

lbs/acre

Water Holding Capacity

Soil

Pressure plate apparatus

% water (w/w) at field capacity

Mehlich III B, Cu, Mn, Na

Soil

Mehlich III extraction and ICP analyses

lbs/acre

Neutralization Potential

Soil or Mine Spoil

Weight loss after exposing soil with HCl

tons CaCO3 equivalence / 1000 tons material

Potential Acidity

Soil or Mine Spoil

Titration with NaOH after releasing acidity with hydrogen peroxide.

tons CaCO3 required for neutralization / 1000 tons material

pH of paste; P, K, Ca, Mg, NO3-N, and salts in saturation extract3-N, and salts in saturation extract

Greenhouse media

Saturated paste created.  Glass electrode placed in paste for pH.  Paste filtered via vacuum pressure.  P, K, Ca, and Mg in filtrate analyzed via ICP.  NO3-N analyzed via ion-selective electrode.

pH is unitless, ppm (=mg/L) in solution for others

pH, conductivity, alkalinity, NO3-N, P, K, Ca, Mg, Zn, Cu, Fe, Mn

Water

Glass electrode for pH, titration with HCl for alkalinity, NO3-N determined via an ion-selective electrode, others analyzed via ICP.

pH is unitless, mmhos/cm (=dS/m) for conductivity, ppm (=mg/L) for others

moisture (if solid), N, P2O5, K2O, Ca, Mg, Zn, Cu, Fe, Mn

Animal Waste

Solids are oven dried and ground.  Liquids treated as received.  Oven drying for moisture in solids, LECO combustion for N, others analyzed via ICP.

For solids, moisture as % and nutrients as lbs/ton.
For liquids, nutrients as lbs/1000 gal.
Values reported on an “as-received” basis.

Detailed Description

Routine Testing
Optional Testing

Routine Soil Test (pH, buffer pH, P, K, Ca, Mg, Zn)

Soil is oven-dried at 38oC and ground to pass a 2 mm screen. A soil-water paste is created by adding 10 ml of water to 10 cm3 of soil and stirring for with a glass rod and letting stand for at least 15 minutes but not more than 2 hours. A glass electrode is placed in the mixture to measure pH. After pH measurement, 10 ml of Sikora Buffer (a mixture of triethanoloamine, imidazole, MES, acetic acid, and KCl) is added to the soil-water paste and shaken for 10 minutes. A glass electrode is then placed in the mixture to measure Buffer pH within 2 hours after shaking. Soil pH and buffer pH are reported as unitless values.

Phosphorus, K, Ca, Mg, and Zn are determined in a Mehlich III extract which contains 0.2 N acetic acid, 0.25 N NH4NO3, 0.015 N NH4F, 0.013 N HNO3, and 0.001 N EDTA. Twenty ml of Mehlich III extract is added to 2 cm3 soil, shaken for 5 minutes, and immediately filtered through Whatman #2 filter paper. Filtration is terminated at the end of 10 minutes. In Lexington, the filtrate is analyzed via ICP (inductively coupled plasma spectroscopy). In Princeton, K, Ca, Mg, and Zn are analyzed in the filtrate via atomic absorption spectrophotometry and P is determined colorimetrically. The analytes are reported as lbs of nutrient / acre of land. The assumptions made with this reporting is that an acre of land contains 2 million pounds of soil and the density of air-dried ground soil is 1 g/cm3.

Soil and Plant Analysis Council. 2000. Chapter 3. Soil pH, and exchangeable acidity and aluminum. In: Soil analysis handbook of reference methods. Soil and Plant Analysis Council, Inc., CRC Press, Boca Raton, FL.
Soil and Plant Analysis Council. 2000. Chapter 6. Phosphorus. In: Soil analysis handbook of reference methods. Soil and Plant Analysis Council, Inc., CRC Press, Boca Raton, FL.

Soil and Plant Analysis Council. 2000. Chapter 7. Major cations (potassium, calcium, magnesium, and sodium). In: Soil analysis handbook of reference methods. Soil and Plant Analysis Council, Inc., CRC Press, Boca Raton, FL.

Soil and Plant Analysis Council. 2000. Chapter 8. Micronutrients (boron, copper, iron, manganese, and zinc). In: Soil analysis handbook of reference methods. Soil and Plant Analysis Council, Inc., CRC Press, Boca Raton, FL.

Sikora, F.J. 2005. Replacing SMP buffer with Sikora Buffer for Determining Lime Requirement of Soil (A Technical Review).

Sikora, F.J. 2006. A buffer that mimics the SMP buffer for determining lime requirement on soil. Soil Sci. Soc. Am. J. 70:474-486.

Potential Acidity in Mine Spoils

Soil is oven-dried at 38oC and ground to pass a 2 mm screen. The sample is further ground to pass an 80 mesh screen. To 0.2 to 5 g of soil, 120 ml of hydrogen peroxide are added at 10 ml increments. The mixture is kept at 50oC in a hot bath all day and through the night. The sample is then transferred to a hot plate set at 95oC until reaction ceases. After cooling, 150 ml of water is added to the sample. The potential acidity released during reaction with hydrogen peroxide is then titrated with 0.02 to 0.05 N NaOH to a pH of 7. Potential acidity is reported as tons of CaCO3 equivalents per 1000 lbs of mine spoil.

Thom, W.O. 1992. Strip-mine testing procedure for maximum potential acidity and alkalinity determination. In: S.J. Donohue (ed.) Reference soil and media diagnostic procedures for the southern region of the United States. Southern Cooperative Series Bulletin No. 374, Virginia Polytechnic Institute and State University.

Greenhouse Media

Greenhouse media is analyzed as-received. Approximately 200 cm3 of the media is addition to a beaker. Water is added slowly to the sample to create a saturated paste. After enough water is added to create a paste, the mixture is left to stand for 1 hour. The pH of the mixture is determined with a glass electrode. The paste is left to stand another hour. The paste is then filtered via vacuum pressure using a Buchner funnel. The leachate is collected and analyzed for nitrate-N using an Orion nitrate ion-selective electrode. Electrical conductivity of the solution is determined via a conductivity bridge and a conductivity cell. Phosphorus, K, Ca, and Mg are determined in the leachate by an ICP (Inductively Coupled Plasma Spectrophotometer). Phosphorus, K, Ca, and Mg are reported in units of ppm or mg/L in the leachate. Electrical conductivity is reported in units of mmhos/cm. The pH is unitless.

Kidder, G. 1992. Determination of pH, soluble salts, nitrate, phosphorus, potassium, calcium, magnesium, sodium, and chloride in potting media (non-soil mixes) by saturation extraction. In: S.J. Donohue (ed.) Reference soil and media diagnostic procedures for the southern region of the United States. Southern Cooperative Series Bulletin No. 374, Virginia Polytechnic Institute and State University.

Warncke, D. 1998. Greenhouse root media. p. 61-64. In: J.R. Brown (ed.) Recommended chemical soil test procedures for the north central region. North Central Regional Publication No. 221 (revised). North Central Agriculture Experiment Stations.

Water Test

Water testing is primarily designed to help growers using nutrient solutions to produce tobacco seedlings, vegetables, or flowers. Samples are taken as-received and refrigerated until analysis. The pH is determined via a glass electrode. Alkalinity is determined by titration with standardized HCl using a pH electrode to monitor an endpoint at pH 4.5. Conductivity is determined with a conductivity bridge and conductivity cell. Nitrate-N is determined using an Orion nitrate ion-specific electrode. Phosphorus, K, Ca, Mg, Zn, Cu, Fe, and Mn are determined by direct aspiration into an ICP (Inductively Coupled Plasma Spectrophotometer). The reported units for conductivity is mmho/cm. Nitrate-N, P, K, Ca, Mg, Zn, Cu, Fe, and Mn are reported as ppm in solution or mg/L. pH is unitless.

Greenberg, A.E., L.S. Clescerl, and A.D. Eaton. 1992. Standard methods for the examination of water and wastewater, 18th ed. American Public Health Association, Wash. D.C.

Animal Waste Test

Preliminary animal waste preparation depends on the type of waste received. Solid wastes, such as poulty litter, are dried in an oven at 75oC, ground to pass a 2 mm screen, and stored at room temperature prior to analysis. Liquid waste samples, such as from lagoons, are analyzed as received. Nitrogen is analyzed via a combustion instrument. Two grams of the ground solid waste or 2 ml of a well mixed liquid waste is analyzed. The animal waste is subjected to wet acid digestion for determination of other nutrients. Two g of material is digested with a combination of HCl and H2SO4 acids. The digestate is analyzed for P, K, Ca, Mg, Zn, Cu, Mn, and Fe using an ICP (Inductively Coupled Plasma Spectrometer). For solid wastes, moisture content is determined by weighing a sample before and after oven drying. Nitrogen, P2O5, and K2O are reported on an as received basis as lbs per ton of for solids or lbs per 1000 gallons of liquids. The other nutrients are reported in units of % or ppm depending on concentration levels. Concentrations are reported on an as-received basis. Publication AGR-146 and AGR-165 can be referred to for proper land application of animal waste.

Peters, J., S.M. Combs, B. Hoskins, J. Jarman, J.L. Kovar, M.E. Watson, A.M. Wolf, and N. Wolf. 2003. Recommended Methods of Manure Analysis (A3769). Univ. of Wisconsin-Extension, Madison, WI.

Organic Matter in Soil

Soil is oven-dried at 38oC and ground to pass a 2 mm screen. One-half gram of soil is weighed in porcelain boats and injected into a dry combustion instrument (LECO or Elementar). The instrument determines %C in the material. Organic matter is calculated as %C x 1.72 = % organic matter. Organic matter is reported as % by weight of air-dried soil.

Nelson, D.W. and L.E. Sommers. 1982. Total carbon, organic carbon, and organic matter. In: A.L. Page, R.H. Miller, D.R. Keeney (eds.) Methods of Soil Analysis, Part 2. Chemical and microbiological properties, 2nd ed. ASA-SSSA, Madison, WI.

Boron Test in Soil

Soil is oven-dried at 38oC and ground to pass a 2 mm screen. Ten g of soil is added to a 500 ml digestion flask. Twenty ml of dilute CaCl2 (0.01 M) is added to the soil. With the flask attached to a condensor, the solution is heated at boiling for 5 minutes. After cooling, the soil-solution mixture is filtered through Whatman #2 filter paper. The filtrate is analyzed for B via ICP (inductively coupled plasma spectroscopy). Boron is reported in units of lbs/acre with the assumption that an acre of land contains 2 million pounds of soil.

Cation Exchange Capacity, Bases, and Base Saturation

Cation exchange capacity (CEC) is determined via ammonium saturation of exchange site and analysis of saturated ammonium using an ammonium ion-selective electrode. Soil is oven-dried at 38oC and ground to pass a 2 mm screen. Ten g of soil is mixed with 25 ml of 1 N ammonium acetate solution in a 250 ml beaker and let stand overnight to ensure complete saturation of exchange sites with ammonium. The sample is then vacuum-filtered through Whatman 42 filter paper placed in a Buchner funnel. Approximately 75 ml of ammonium acetate solution is added to the soil on the Buchner funnel in 10 to 15 ml increments. The filtrate is transferred to a 100 ml volumetric flask and brought to volume. This solution is analyzed for Ca, Mg, K, and Na via ICP (Inductively Coupled Plasma Spectrophotometry) which provides quantification of bases on soil exchange sites. The bases are reported in units of meq/100 g (equivalent to cmol/kg).

To determine total cation exchange capacity, the ammonium saturated soil in the Buchner funnel is leached with 200 ml of 10% NaCl at pH 3 in 35 to 45 ml increments. The leachate is transfered to a 250 ml volumetric flask and brought to volume with 10% NaCl. The resultant solution is diluted ten fold with water and ammonium is measured with an ammonium ion-selective electrode. One ml of concentrated NaOH is added to the solution to convert ammonium to ammonia which is directly measured by the electrode. The equivalents of ammonium in solution is converted to cation exchange capacity of soil in units of meq/100 g (equivalent to cmol/kg). Base saturation is determined as total bases/CEC x 100 and reported in %.

Soil and Plant Analysis Council. 2000. Chapter 7. Major cations (potassium, calcium, magnesium, and sodium). In: Soil analysis handbook of reference methods. Soil and Plant Analysis Council, Inc., CRC Press, Boca Raton, FL.

Sand, Silt, Clay, and Textural Class

Micropipette method:
Soil is prepared by oven drying at 38oC and passing through a 2 mm screen. Four g of soil is treated with 10 ml H2O and 10 ml of dispersing agent (sodium hexametaphosphate, 5 g/L) in a 50 ml centrifuge tube. The mixture is shaken for 2 hours. After shaking, add 20 ml of H2O to each sample. Shake by hand to ensure all soil particles are in solution and place tubes in rack to allow settling. 5 ml of sample is taken in the middle of the tube at approximately 1 hour and 50 minutes (exact time depends on temperature) with a syringe. The sample is oven-dried and weighed to determine clay content. The whole tube contents in then poured through a #270 sieve. The particles remaining on the sieve are oven-dried and weighed to determine sand content. The silt content is determined as the difference between total weight and the weight of clay and sand. Sand, silt, and clay are reported as % of oven-dried soil. Textural class is also reported.

Miller, W.P. and D.M. Miller. 1987. A micropipette method for soil mechanical analysis. Commun. Soil Sci. Plant Anal. 18:1-15.

Burt, R., T.G. Reinsch, and W.P. Miller. 1993. A micro-pipette method for water dispersible clay. Commun. Soil Sci. Plant Anal. 24:2531-2544.

Soluble Salts in Soil

Soil is oven-dried at 38oC and ground to pass a 2 mm screen. Fifty ml of deionized water is added to 25 g of soil and shaken on a wrist action shaker for 30 minutes. The soil-solution mixture is completely filtered through Whatman no. 5 filter paper. Electrical conductivity in the filtrate is measured with a conductivity bridge and 1 cm conductivity cell. Soluble salts is reported as the conductivity in the solution in mmhos/cm (=dS/m).

Soil and Plant Analysis Council. 2000. Chapter 5. Conductance, soluble salts, and sodicity. In: Soil analysis handbook of reference methods. Soil and Plant Analysis Council, Inc., CRC Press, Boca Raton, FL.

Total Nitrogen in Soil

Soil is oven-dried at 38oC and ground to pass a 2 mm screen. One-half gram of soil is weighed in porcelain boats and injected into a LECO combustion instrument. The instrument determines %N in the material by measuring the N2 gas emitted upon combustion. Nitrogen is reported in units of lbs/acre assuming 2 million pounds of soil are in an acre (% x 20,000 = lbs/acre).

Triazine Residues in Soil

Soil is air dried and passed through a 2 mm screen. Ten g of soil is added to a 200 ml centrifuge bottle to which is added 1 ml of 1 ug/ml propazine in methylene chloride, 20 g anyhydrous sodium sulfate, 0.7 ml concentrated NH4OH, and 100 ml methylene chloride. The mixture is treated with Polytron in for 1 minute and centrifuged for 5 minutes. The centrifugate is filtered through Sharkskin filter paper to collect 80 ml of extract. Methylene chloride solvent is evaporated in a hood to reduce solution volume to 10 to 20 ml. Five ml of hexane is added to this solution and eluted through a Florisil Sep-Pak. The beaker is rinsed with an additional 5 ml of hexane and added to the Sep-Pak. The Sep-Pak is then eluted with 10 ml of a ether/petroleum ether mixture (1:1 v/v) into a 10 ml beaker. The eluted extract is evaporated until near dryness. A volume of 0.8 ml acetone is added to the residue. Five uL of the resulting solution is injected into a gas chromatograph. The ratio of atrazine and simazine peaks to propazine are determined and compared to ratios of standard atrazine and simazine solutions prepared in a similar format.

Neutralization Potential in Mine Spoil

The amount of neutralization bases, including carbonates, present in overburden material is found by treating a sample with HCl and determining the weight lost due to CO2 evolution. Soil is oven-dried at 38oC and ground to pass a 2 mm screen. 10 ml of 3 N HCl is added to a 50 ml Erlenmeyer flask. Ten g of sample is placed in the Erlenmeyer flask. The flask is left to stand with occasional stirring until the weight does not change more than 2 or 3 mg during a 30 minute period. Prior to weighing, carbon dioxide gas is displaced in the flask with air. The difference in weight before and after HCl reaction is assumed solely due to CO2 loss. The percent CaCO3 in the sample is calculated assuming CO2 was lost from CaCO3.

Heavy Metal Test in Soil (Cd, Cr, Ni, Pb, Zn, Cu, and Mo)

Soils are prepared and treated as described for analysis of P, K, Ca, Mg, and Zn (see Routine Soil Test). Mehlich III is used as the extractant and metals are determined in the soil extract via ICP (Inductively Coupled Plasma Spectrophotometry). Metals are reported in units of mg/kg (or ppm) in soil assuming the density of ground oven-dried soil is 1 g/cm3.

Mehlich III B, Cu, Mn, and Na in Soil

Soils are prepared and treated as described for analysis of P, K, Ca, Mg, and Zn (see Routine Soil Test). Mehlich III is used as the extractant and B, Cu, Mn, and Na are determined in the soil extract via ICP (Inductively Coupled Plasma Spectrophotometry). The measured constituents are reported in units of lbs/acre. The assumptions made with this reporting are that an acre of land contains 2 million pounds of soil and the density of air-dried ground soil is 1 g/cm3.

Soil and Plant Analysis Council. 2000. Chapter 8. Micronutrients (boron, copper, iron, manganese, and zinc). In: Soil analysis handbook of reference methods. Soil and Plant Analysis Council, Inc., CRC Press, Boca Raton, FL.

Water Holding Capacity of Soil

Soil is oven-dried at 38oC and ground to pass a 2 mm screen. Water holding capacity is determined by a pressure plate method. The amount of water held by soil under 0.33 atm of pressure (field capacity) minus the amount of water held at 15 atm (wilting point) is considered the water holding capacity and is reported as % water in soil on an oven-dried basis.

Topp, G.C., Y.T. Galganov, B.C. Ball, M.R. Carter. 1993. Chapter 53. Soil water desorption curves. In: M.R. Carter (ed.) Soil sampling and methods of analysis. Canadian Society of Soil Science. Lewis Publishers, Boca Raton, FL.