ANR Analytical Lab
Soil Analysis O

SOIL SALINITY

200 SATURATED PASTE AND SATURATION PERCENTAGE

Saturated Paste Extract: SP

The saturation of soil with water and subsequent vacuum extraction of the liquid phase for the determination of dissolved salts.

Summary: This method involves saturating the soil with water and subsequent extraction under partial vacuum of the liquid phase for the determination of dissolved salts. Soil moisture at the point of complete saturation is the maximum amount of water held when all the soil pore space is occupied by water and when no free water has collected on the surface of the paste. Over a wide soil textural range, the saturation percentage (SP) is approximately twice the Field Capacity (FC) or -33kPa soil water potential and is four times the Permanent Wilting Point (PWP) or -1500 kPa soil water potential for soils of loam, to clay loam texture. The soil pH may be determined directly on the paste. From the saturated paste extract, estimates of ECe, and solution concentrations of Ca2+, Mg2+, K+, Na+, Cl-, B, HCO3-, CO32-, SO4 estimate (actual measurement is total S in extracts), SAR and ESP can be made. The method is generally reproducible within 8%.

Rhoades, J. D. 1982. Soluble salts. p. 167-179. In: A. L. Page et al. (ed.) Methods of soil analysis: Part 2: Chemical and microbiological properties. Monograph Number 9 (Second Edition). ASA, Madison, WI.

205 SOIL pH

Saturated Paste Extract: pH
Semi-quantifies soil pH using the saturated paste and pH meter.

Summary: This method determines the pH of soil, using a saturated paste prepared from the soil and a pH meter. It is most applicable to soils with a pH ranging from 4.0 to 9.0. It is not possible to determine the total acidity or alkalinity of the soil from pH because of the nature of the colloidal system and junction potential. This method does however provide information on the disassociated H-ions affecting the sensing electrode. The method is generally reproducible within 0.2 pH units.

U.S. Salinity Laboratory Staff. 1954. pH reading of saturated soil paste. p. 102. In: L. A. Richards (ed.) Diagnosis and improvement of saline and alkali soils. USDA Agricultural Handbook 60. U.S. Government Printing Office, Washington, D.C.

210 pH OF A 1 + 10 SOIL SUSPENSION

By Special Request
Semi-quantifies soil pH using an extract of a 1 to 10 dilution of soil with water.

Summary: This method determines the pH of soil, using an extract of a 1 to 10 dilution of soil with water and a pH meter. The pH of a soil sample increases with the degree of saturation (dilution effect). This rise in pH from pHs to pH 1+10 is usually 0.2 to 0.5 pH units but may be one or more units in certain alkaline soils where there is an increase in dissociation due to dilution of soluble salts.

Rible, J. M., and Quick, J. 1960. Method S-3.1. In: Water soil plant tissue tentative methods of analysis for diagnostic purposes. Davis, University of California Agricultural Experiment Service. Mimeographed Report.

215 ESTIMATED SOLUBLE SALTS (ECe)

Saturated Paste Extract : EC
Semi-quantifies the amount of soluble salts in the saturation paste extract using conductivity meter.

Summary: This method semi-quantifies the amounts of soluble salts in the liquid phase extracted from the saturated paste of soils and is based on the measurement of the electrical conductivity (ECe) of a saturated paste extract. The higher the concentration of salt in a solution, the higher will be the electrical conductance (the reciprocal of resistance). Electrical conductivity is a function of quantity and specific types of cations and anions in the extract. Plant tolerance can be related to the ECe value of the saturated paste. The method has a detection limit of approximately 0.01 dS m-1(mmhos cm-1) and is generally reproducible within 7%.

Rhoades, J. D. 1982. Soluble salts. p. 167-179. In: A. L. Page et al. (ed.) Methods of soil analysis: Part 2: Chemical and microbiological properties. Monograph Number 9 (Second Edition). ASA, Madison, WI.

 220 BICARBONATE AND CARBONATE IN SATURATED PASTE EXTRACT

Saturated Paste Extract: HCO3, CO3
Quantification of the bicarbonate (HCO3-) and carbonate (CO32-) in the saturated paste extract by titration with acid.

Summary: This method quantifies bicarbonate (HCO3-) and carbonate (CO32-) levels in a soil water extract, such as from saturated paste extract. Quantitation is by titration with 0.025 N H2SO4. The measurement should be made immediately due to the potential of the extract being super saturated relative to calcium carbonate (CaCO3). The method has a detection limit of approximately 0.1 meq L-1 and is generally reproducible within 7%.

U.S. Salinity Laboratory Staff. 1954. Carbonate and bicarbonate by titration with acid. p. 98. In: L. A. Richards (ed.) Diagnosis and improvement of saline and alkali soils. USDA Agricultural Handbook 60. U.S. Government Printing Office, Washington, D.C.

227 CHLORIDE IN SATURATED PASTE EXTRACT - FLOW INJECTION ANALYZER METHOD

Saturated Paste Extract: Cl
Amount of chloride by Flow Injection Analyzer method.

Summary: This method quantifies the amount of Cl- in a soil water extract, such as from the saturated paste extract. Thiocyanate ion is liberated from mercuric thiocyanate by the formation of soluble mercuric chloride. In the presence of ferric ion, free thiocyanate ion forms the highly colored ferric thiocyanate, of which the absorbance is proportional to the chloride concentration. The absorbance of the ferric thiocyanate is read at 480 nm. Plant tolerance to chloride can be related to the concentration of chloride in the saturated paste extract. The method has a detection limit of 0.1 meq/L of Cl- and is generally reproducible within 5%.

Diamond, D. 2001. Determination of Chloride by Flow Injection Analysis Colorimetry. QuikChem Method 10-117-07-1-H. Lachat Instruments, Milwaukee, WI.

Rhoades, J. D. 1982. Soluble salts. p. 167-179. In: A. L. Page et al. (ed.) Methods of soil analysis: Part 2: Chemical and microbiological properties. Monograph Number 9 (Second Edition). ASA, Madison, WI.

230 BORON IN SATURATED PASTE EXTRACT

Saturated Paste Extract: B
ICP-AES determination of amount of boron in saturated paste extract.

Summary: This method quantitatively measures the concentration of boron in the extract of the saturated paste. It is based on the determination of boron in the extract using an Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES). Plant tolerance to soil boron can be related to the boron concentration in the saturated paste extract. The method has a detection limit of approximately 0.1 mg/L.

Horneck, D. A., Hart, J. M., Topper, K. and Koespell, B. 1989. Methods of soil analysis used in the soil testing laboratory at Oregon State University. Agric Exp Stn SM 89:4.

 

235 POTASSIUM, SODIUM, CALCIUM, AND MAGNESIUM IN SATURATED PASTE EXTRACT

Saturated Paste Extract: K, Na, Ca, Mg
Amounts of soluble calcium and magnesium in the saturated paste extract by ICP-AES. Amounts of soluble potassium and sodium in the saturated paste extract by emission spectrometry.

Summary: This method quantitatively determines the concentration (meq L-1) of dissolved K, Na, Ca, and Mg in the saturated paste extract using inductively coupled plasma emission spectrometry (ICP) for Ca and Mg and emission spectrophotometry (AA) for K and Na. These four ions generally are the dominant cations in the saturated paste extract of soils. Concentration of soluble Na, Ca, and Mg is used to determine the sodium absorption ratio (SAR) of soils. Extract solutions containing greater than 10,000 mg L-1 (1.0% w/v, estimated from ECe) will require dilution since solutions this concentrated with salt may impair instrument operation. The detection limits for these cations are approximately 0.1 meq L-1 on a solution basis.

Knudsen, D., Peterson, G. A. and Pratt, P. F. 1982. Lithium, sodium and potassium. p. 225-246. In: A. L. Page et al. (ed.) Methods of soil analysis: Part 2. Chemical and microbiological properties. ASA Monograph Number 9.

Soltanpour, P. N., Benton Jones, Jr.,  J. and Workman, S. M. 1982. Optical emission spectrometry. p. 29-65. In: A. L. Page et al. (ed.) Methods of soil analysis: Part 2. Chemical and microbiological properties. Monograph Number 9 (Second Edition). ASA, Madison, WI.

 

240 SAR (SODIUM ADSORPTION RATIO) AND ESP(EXCHANGEABLE SODIUM PERCENTAGE)

Saturated Paste Extract: SAR, ESP
Sodium Adsorption Ratio estimated calculation from calcium, magnesium and sodium on saturated paste extract. Exchangeable Sodium Percentage calculated from SAR values.

Summary: The exchangeable sodium percentage (ESP) and the sodium adsorption ratio (SAR) are calculated after determining Ca, Mg and Na concentrations in a saturation extract (SOP# 235).

U.S. Salinity Laboratory Staff. 1954. Choice of determinations and interpretation of data. p. 26. In: L. A. Richards (ed.) Diagnosis and improvement of saline and alkali soils. USDA Agric. Handb. 60. U.S. Government Printing Office, Washington, D.C.

 

245 SULFATE-SULFUR IN SATURATED PASTE EXTRACT

Saturated Paste Extract: SO4S
Concentration of sulfate-sulfur in the saturated paste extract, by ICP-AES.

Summary: This method quantitatively measures the concentration of sulfate in the extract of the saturated paste. It is based on the determination of sulfate sulfur in the extract using an Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES). Sulfate uptake by plants can be related to the sulfate concentration in the saturated paste extract. The method has a detection limit of approximately 0.1 mg L-1 and is reproducible within 8%.

Rhoades, J. D. 1982. Soluble salts. p. 167-179. In: A. L. Page et al. (ed.) Methods of soil analysis: Part 2: Chemical and microbiological properties. Monograph Number 9 (Second Edition). ASA, Madison, WI.

 


SOIL FERTILITY

312 SOIL NITRATE AND EXTRACTABLE AMMONIUM BY FLOW INJECTION ANALYZER METHOD

Fertility: NO3-N, NH4-N
Equilibrium extraction of soil for nitrate and ammonium with potassium chloride and subsequent determination by flow-injection analyzer.

Summary: This method involves the quantitative extraction of nitrate (NO3-N) from soils using an equilibrium extraction with 2.0 N KCl solution. Nitrate is determined by reduction to nitrite via a copperized cadmium column. The nitrite is then determined by diazotizing with sulfanilamide followed by coupling with N-(1-naphthyl)ethlyenediaminie dihydrochloride. The absorbance of the product is measured at 520 nm. This method is also semi-quantitative for ammonium (NH4-N) in soils. Ammonia is heated with salicylate and hypochlorite in an alkaline phosphate buffer. The presence of EDTA prevents precipitation of calcium and magnesium and sodium nitroprusside is added to enhance sensitivity. The absorbance of the reaction product is measured at 660 nm and is directly proportional to the original ammonia concentration. Extracts can be stored for up to three weeks at low temperature (<4°C). For long term storage, toluene or thymol may be added to the sample to prevent microbial growth. The method has detection limit of approximately 0.1 mg/kg (on a soil basis) and is generally reproducible within 7%.

Hofer, S. 2003. Determination of Ammonia (Salicylate) in 2M KCl soil extracts by Flow Injection Analysis. QuikChem Method 12-107-06-2-A. Lachat Instruments, Loveland, CO.o:p>

Knepel, K. 2003. Determination of Nitrate in 2M KCl soil extracts by Flow Injection Analysis. QuikChem Method 12-107-04-1-B. Lachat Instruments, Loveland, CO.

315 TOTAL KJELDAHL NITROGEN (TKN)

Fertility: TKN
Total reduced nitrogen by the wet oxidation of soil organic matter and botanical materials using a micro Kjeldahl procedure with sulfuric acid and digestion catalyst.

Summary: The Total Kjeldahl Nitrogen (TKN) method is based on the wet oxidation of soil organic matter and botanical materials using sulfuric acid and digestion catalyst and conversion of organic nitrogen to the ammonium form. Ammonium is determined using the diffusion-conductivity technique. The procedure does not quantitatively digest nitrogen from heterocyclic compounds (bound in a carbon ring), oxidized forms such as nitrate and nitrite, or ammonium from within mineral lattice structures. The method has a detection limit of approximately 0.001% N and is generally reproducible within 8%.

Note: This is the same method as SOP# 515.

Bremner, J. M. and Mulvaney, C. S. 1982. Nitrogen-total. p. 595-624. In: A. L. Page, et al. (ed.) Methods of soil analysis: Part 2. Chemical and microbiological properties. ASA Monograph Number 9.

Isaac, R. A. and Johnson, W. C. 1976. Determination of total nitrogen in plant tissue, using a block digestor. J. Assoc. Off. Anal. Chem. 59:98-100.

 

320 TOTAL NITROGEN AND CARBON - COMBUSTION METHOD

Fertility: N, C
Combustion gas analyzer method for total nitrogen and total carbon.

Summary: This analytical method quantitatively determines the total amount of nitrogen and carbon in all forms in soil, botanical, and miscellaneous materials using a dynamic flash combustion system coupled with a gas chromatographic (GC) separation system and a thermal conductivity detection (TCD) system. The analytical method is based on the complete and instantaneous oxidation of the sample by "flash combustion" which converts all organic and inorganic substances into combustion gases (N2, NOx, CO2, and H20). The method has a detection limit of 0.01% for carbon and 0.04% for nitrogen and is generally reproducible within 5% (relative).

Method 972.43. Official Methods of Analysis of AOAC International, 16th Edition (1997), AOAC International, Arlington, VA.

 

330 SULFATE - SULFUR

Fertility: SO4-S
Estimate of the concentration of sulfate-sulfur in soil by extraction with monocalcium phosphate.

Summary: This method estimates the quantitative concentration of sulfate sulfur (SO4-S) in the soil by extraction with monocalcium phosphate. This method for extractable sulfur as SO4-S follows the procedure originally outlined by Schulte and Eik (1988) with the following exception: (1) elimination of activated carbon and (2) determination of S by ICP-AES. The ICP-AES determines all sulfur, both organic and inorganic. This method is inappropriate for soil containing greater than 4% organic matter. The method is quantitative only for the time of sampling since sulfur is constantly being mineralized in the soil. The method has a detection limit of approximately 0.5 mg/kg sulfur as sulfate and is generally reproducible within 8%.

Schulte, E. E. and Eik, K. 1988. Recommended sulfate-sulfur test. p. 17-19. In: Recommended chemical soil test procedures for north central region. North Dakota Agric Exp Sta Bull No. 499 (revised).

 

340 EXTRACTABLE PHOSPHORUS - OLSEN METHOD

Fertility: Olsen-P
Extractable phosphate based on alkaline extraction by 0.5 Normal NaHC03. Plant available phosphate for soils with pH greater than 6.5 by ascorbic acid reduction of phosphomolybdate complex and measurement by flow injection analysis.

Summary: This method estimates the relative bioavailability of inorganic ortho-phosphate (PO4-P) in soils with neutral to alkaline pH. It is not appropriate for soils which are mild to strongly acidic (pH <6.5). The method is based on the extraction of phosphate from the soil by 0.5 N sodium bicarbonate solution adjusted to pH 8.5. In the process of extraction, hydroxide and bicarbonate competitively desorb phosphate from soil particles and secondary absorption is minimized because of high pH. The orthophosphate ion reacts with ammonium molybdate and antimony potassium tartrate under acidic conditions to form a complex. This complex is reduced with abscorbic acid to form a blue complex which absorbs light at 880 nm. The absorbance is proportional to the concentration of orthophosphate in the sample. The method has shown to be well correlated to crop response to phosphorus fertilization on neutral to alkaline soils. The method has a detection limit of 1.0 mg/kg (soil basis) and is generally reproducible within 8%.

Olsen, S. R. and Sommers, L. E. 1982. Phosphorus. p. 403-430. In: A. L. Page, et al. (eds.) Methods of soil analysis: Part 2. Chemical and microbiological properties. Agron. Mongr. 9. 2nd ed. ASA and SSSA, Madison, WI.

Prokopy, W. R. 1995. Phosphorus in 0.5 M sodium bicarbonate soil extracts. QuikChem Method 12-115-01-1-B. Lachat Instruments, Milwaukee, WI.

 

355 EXTRACTABLE PHOSPHORUS - BRAY METHOD

Fertility: Bray-P
Extractable phosphate for acid soils (pH less than 7.0) using a dilute acid-fluoride extractant.

Summary: This method estimates the relative bioavailability of inorganic ortho-phosphate (PO4-P) in soils with acid to neutral pH, using a dilute acid solution of hydrochloric acid containing ammonium fluoride. The orthophosphate ion reacts with ammonium molybdate and antimony potassium tartrate under acidic conditions to form a complex. This complex is reduced with abscorbic acid to form a blue complex which absorbs light at 880 nm. The method is shown to be well correlated to crop response on neutral to acid soils. The absorbance is proportional to the concentration of orthophosphate in the sample. The method has a detection limit of approximately 0.5 mg kg-1 (soils basis) and is generally reproducible within 8%.

Diamond, D. 1995. Phosphorus in soil extracts. QuikChem Method 10-115-01-1-A. Lachat Instruments, Milwaukee, WI.

Olsen, S. R. and Sommers, L. E. 1982. Phosphorus. p. 403-430. In: A. L. Page, et al. (eds.) Methods of soil analysis: Part 2. Chemical and microbiological properties. Agron. Mongr. 9. 2nd ed. ASA and SSSA, Madison, WI.

360 EXCHANGEABLE POTASSIUM, CALCIUM, MAGNESIUM, AND SODIUM

Fertility: X-K, X-Ca, X-Mg, X-Na,
Equilibrium extraction of soil for plant available exchangeable potassium, sodium, calcium and magnesium using 1 Normal ammonium acetate (pH 7.0) and subsequent determination by atomic absorption/emission spectrometry.

Summary: This method is semi-quantitative and determines the amount of soil exchangeable K, Ca, Mg, and Na residing on the soil colloid exchange sites by displacement with ammonium acetate solution buffered to pH 7.0. Generally, these cations are associated with the exchange capacity of the soil. The method does not correct for calcium and magnesium extracted as free carbonates or gypsum. The method has a detection limit approximately of 1 mg/kg or 0.01 meq/100g and is generally reproducible within 7%.

Thomas, G. W. 1982. Exchangeable cations. p 159-165. In: A.L. Page et al. (ed.) Methods of soil analysis: Part 2. Chemical and microbiological properties. ASA Monograph Number 9.

 

370 POTASSIUM -SULFURIC ACID EXTRACTION

By Special Request
Extraction of K with sulfuric acid.

Summary: As the exchangeable K of soils is removed by cropping or leaching, some K from the mineral reserve becomes exchangeable K. Soils with low exchangeable K content need not be deficient, as the mineral reserve may be able to supply K for plant growth. Extraction of K with H2SO4 removes an amount of K that seems to be correlated with the removal by extensive cropping. The method has a detection limit of 1 mg kg-1 (on a soil basis) and is generally reproducible within 10%.

Brown, A. L., Quick, J. and deBoer, G. J. 1973. Potassium deficiency by soil analysis. p. 13-14. Cal. Agr. June.

 

380 EXTRACTABLE MICRONUTRIENTS USING DTPA EXTRACTION - ZINC, MANGANESE, COPPER, AND IRON

Fertility: Zn, Mn, Cu, Fe
Equilibrium extraction of soil using DTPA and subsequent determination by atomic absorption spectrometry.

Summary: The DTPA (diethylenetriaminepentaacetic acid) micronutrient extraction method is a non-equilibrium extraction for estimating the potential soil availability of Zn, Cu, Mn, and Fe. It has been used for cadmium, nickel and lead in soils. The method has shown to be well correlated to crop response to fertilizer for zinc and copper. The amount of micronutrients and trace metals extracted are affected by solution pH, temperature, soil extraction ratio, shaking time, extraction time, and extractant concentration. Extracts are analyzed by ICP-AES or Flame AA. The method has a detection limit of approximately 0.1 mg/kg for Zn, Cu, Mn, and Fe and is generally reproducible within 10% for Cu and Zn and 15% for Fe and Mn. The method is not well characterized for other elements.

Lindsay, W. L. and Norvell, W. A. 1978. Development of a DTPA soil test for zinc, iron, manganese, and copper. Soil Sci. Soc. Amer. J. 42:421-428.

 

390 TOTAL ELEMENTS (INCLUDES PHOSPHORUS, ZINC, MANGANESE, IRON, COPPER, MOLYBDENUM, CADMIUM, CHROMIUM, LEAD AND NICKEL)

Soil Totals: Zn, Mn, Fe, Cu, Cd, Cr, Pb, Ni, P, Mo

Microwave acid digestion/dissolution of sample and quantitative determination by AAS and ICP-AES.

Summary: This method determines the concentration of Zn, Mn, Fe, Cu, Cd, Cr, Pb, Ni, P, Mo and additional elements as requested utilizing a nitric acid/hydrogen peroxide closed vessel microwave digestion. Analysis is by Atomic Absorption Spectrometry (AAS) for Zn, Mn, Fe, Cu and Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) for other elements. The approximate method detection limit is 1mg/kg for all elements except phosphorus (0.001%).

Sah, R. N. and Miller, R. O. 1992. Spontaneous reaction for acid dissolution of biological tissues in closed vessels. Anal. Chem. 64:230-233.

392 KCL EXTRACTABLE ALUMINUM

Fertility: AL-KCL
Aluminum concentration determined in the extract by ICP-AES.

Summary: This method is semi-quantitative and determines the amount of 1N KCl extractable aluminum in soil. Aluminum concentration is determined in the extract by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The method has a detection limit of approximately 1.0 mg/kg.

Gavlak, R., Horneck, D., Miller, R. O., Kotuby-Amacher, J. 2003. Soil, Plant and Water Reference Methods for the Western Region. p.134-135.

 394 SELENIUM

Totals: (Complete Digestion) Se
Total selenium, nitric/perchloric acid digestion/dissolution of sample and determination by vapor generation by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

Summary: This method is quantitative for selenium and is based on the wet oxidation of selenium bearing organic carbon and inorganic selenium compounds utilizing nitric, perchloric and sulfuric acids, reduction of selenate to selenite (IV), and determination by Vapor Generation Inductively-Coupled Plasma Emission Spectrometer (VG-ICP). The method has a detection limit of 0.10 ppm. It is generally reproducible within 10%.

Tracy, M. L. and Moeller, G. 1990. Continuous flow vapor generation for inductively coupled argon plasma spectrometric analysis. Part 1: Selenium. J. Assoc. Off. Anal. Chem. 73:404-410.

 396 ARSENIC

Totals: (Complete Digestion) As
Total arsenic, nitric/perchloric acid digestion/dissolution of sample and determination by vapor generation by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

Summary: This method is quantitative for arsenic utilizing nitric, perchloric and sulfuric acids, reduction of arsenate to arsenite, and determination by Vapor Generation Inductively-Coupled Plasma Emission Spectrometer (VG-ICP). The method has a detection limit of approximately 0.10 ppm. It is generally reproducible within 10%.

Tracy, M. L. and Moeller, G. 1990. Continuous flow vapor generation for inductively coupled argon plasma spectrometric analysis. Part 2: Arsenic. J. Assoc. Off. Anal. Chem. 74:516-521.



SOIL PHYSIO-CHEMICAL

410 ORGANIC MATTER - WALKLEY-BLACK METHOD

Physio Chem: OM, Org C
Organic Matter by potassium dichromate reduction of organic carbon and subsequent spectrophotometric measurement (modified Walkley-Black).

Summary: This method quantifies the amount of oxidizable organic matter in which OM is oxidized with a known amount of chromate in the presence of sulfuric acid. The remaining chromate is determined spectrophotometrically at 600nm wavelength. The calculation of organic matter is based on organic matter containing 58% carbon. The method has a detection limit of approximately 0.10% and, on homogeneous sample material, is generally reproducible within 8%.

The method requires 2 g sample, but 10 g is requested to allow for quality control.  Samples with concentrations greater than 80% OM are best tested by the Loss-on-Ignition (OM-LOI) method.

Nelson, D. W. and Sommers, L. E. 1982. Total carbon, organic carbon and organic matter. pp. 539-579. In: A. L. Page et al. (ed.) Methods of soil analysis: Part 2. Chemical and microbiological properties. ASA Monograph Number 9.

 

415 SOIL ORGANIC MATTER - LOSS ON IGNITION METHOD

By Special Request
Organic Matter by measurement of the amount of organic matter lost on sample ignition.

Summary: This method quantifies the amount of organic matter that is lost when sample is ignited at 550oC in a controlled muffle furnace overnight. This method is used on samples such as soil, compost and manure samples with organic matter content greater than approximately 17%. The method has a detection limit of 0.1 % and is generally reproducible within 10%.

Nelson, D. W., and Sommers, L. E. 1996. Chapter 34. p 1001-1006. Total Carbon, Organic Carbon, and Organic Matter. In: J. M. Bigham et al. (ed.) Soil Science Society of America and American Society of Agronomy. Methods of Soil Analysis. Part 3. Chemical Methods-SSSA Book Series no. 5. Madison, WI.

420 GYPSUM CONTENT

By Special Request
Estimated value of the amount of gypsum present in soils.

Summary: The procedure is based on the measurement of the loss of crystal water associated with the hydrated form of gypsum. The precise determination of gypsum is difficult because of sources of Ca and SO4 other than from gypsum. The method has a detection limit of approximately 0.1meq 100 gm-1 and is reproducible within 20%.

Klute, A. 1986. Water retention: laboratory methods. p. 635-662. In: A. Klute (ed.) Methods of soil analysis: Part 1. Physical and mineralogical methods. ASA Monograph Number 9.

 

430 CATION EXCHANGE CAPACITY

Physio Chem: CEC
Cation Exchange Capacity by barium acetate saturation and calcium replacement.

Summary: The method determines the cation exchange capacity (CEC) of soil. The soil is quantitatively displaced of all exchangeable cations with barium, followed by four deionized water rinses to remove excess barium. A known quantity of calcium is then exchanged for barium and excess solution calcium is measured. CEC is determined by the difference in the quantity of the calcium added and the amount found in the resulting solution. The method has a detection limit of approximately 2.0 meq/100g.

Rible, J. M. and Quick, J. 1960. Method S-19.0. In: Water soil plant tissue. Tentative methods of analysis for diagnostic purposes. Davis, University of California Agricultural Experiment Service. Mimeographed Report.

440 CALCIUM CARBONATE EQUIVALENT

Physio Chem: CaCO3
Gravimetric determination by reaction with hydrochloric acid.

Summary: This method is based on the gravimetric loss of carbonates as carbon dioxide in the presence of excess hydrochloric acid. Major sources of error are: evaporation of water and failure to adequately degas CO2 from the sample. Soil carbonates are measured to determine soil buffering capacity with relation to soil fertility, chemical and pedogenic processes. This procedure is an estimate of free calcium carbonate in the sample. This procedure does not adjust for magnesium, potassium, or sodium carbonates or organic matter which may be present. The method detection limit is approximately 0.2% CaCO3 equivalent (on a dry soil basis) and is generally reproducible within 10% (relative).

U.S. Salinity Laboratory Staff. 1954. Alkaline-earth carbonates by gravimetric loss of carbon dioxide. p. 105. In: L. A. Richards (ed.) Diagnosis and improvement of saline and alkali soils. USDA Agric. Handb. 60. U.S. Government Printing Office, Washington, D.C.

 

450 LIME REQUIREMENT

Physio Chem: LiR
The amount of lime required to raise the soil pH to its desired value, usually 6.5 - 7.0.

Summary: Buffer pH is the measure of a soil's active and reserve acidity (i.e., buffer capacity) and is used to estimate lime recommendations. The method is based on the reaction of soil buffered acidity with a chemical buffer resulting in a change in the pH of the buffer. This method is used for estimating exchange acidity including that associated with exchangeable aluminum. Standard calibration curves exist for liming based on a SMP value to a desired pH for soil groups in a geographic area. The lime requirement reported for this test is based on a desired pH of 7.0. The result is reported in T/A/8in (tons per acre of 100% CaCO3 required based on an 8 inch furrow slice weighing 2.4 million pounds). The table used is taken from Soil, Plant and Water Reference Methods for the Western Region.

Shoemaker, H. E., McLean, E. O. and Pratt, P. F. 1961. Buffer methods for determining lime requirement of soils with appreciable amounts of extractable aluminum. Soil Sci. Soc. Am. Proc. 25:274-277.

 

460 MOISTURE RETENTION

Physio Chem: Moisture Retention
Moisture retention determination using the pressure plate system.

Summary: The method determines the soil moisture content under constant preset pressure potential (ranging from -10 to -1500 kPa (0.1 atm to 15 atm)). Soil is brought to near saturation and then is allowed to equilibrate under a set atmospheric pressure potential. The method is used to determine the available water capacity of soils and/or moisture release curve. The method detection limit is 0.5%.

Klute, A. 1986. Water retention: laboratory methods. p. 635-662. In: A. Klute (ed.) Methods of soil analysis: Part 1. Physical and mineralogical methods. ASA Monograph Number 9.

 

470 PARTICLE SIZE ANALYSIS

Particle Size Analysis (Sand/Silt/Clay)
Particle Size Analysis of sand, silt and clay in soil suspension by hydrometer.

Summary: This method quantitatively determines the physical proportions of three sizes of primary soil particles as determined by their settling rates in an aqueous solution using a hydrometer. The hydrometer method of estimating particle size analysis (sand, silt and clay content) is based on the dispersion of soil aggregates using a sodium hexametaphosphate solution and subsequent measurement based on changes in suspension density. The use of the ASTM 152 H-Type hydrometer is based on a standard temperature of 20°C and a particle density of 2.65 g cm-3. Corrections for temperature and for solution viscosity are made by taking a hydrometer reading of a blank solution. The method has a detection limit of 2% sand, silt and clay (dry soil basis) and is generally reproducible within 8% (relative).

Sheldrick, B. H. and Wang, C. 1993. Particle-size Distribution. pp. 499-511. In: Carter, M. R. (ed), Soil Sampling and Methods of Analysis, Canadian Society of Soil Science, Lewis Publishers, Ann Arbor, MI.

 

480 BULK DENSITY

Physio Chem: BD
Determination of bulk density by measurement of volume and mass.

Summary: Soil bulk density is the ratio of the mass of dry solids to the bulk volume of the soil. The bulk volume includes the volume of the solids and of the pore space. The determination of bulk density consists of drying (105°C) and weighing a soil sample, the volume of which is known (core method) or must be determined.

Blake, G. R. and Hartge, K. H.  1986. Bulk density. p. 363-375. In: A. Klute et al. (ed.) Methods of soil analysis: Part 1: Physical and Mineralogical Methods. Monograph Number 9 (Second Edition). ASA, Madison, WI.

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