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Acid-extractable Phosphorus (9G1)

This test is often referred to as BSES-P. Soil extracts are obtained by shaking milled air-dry soil at a ratio of 1:200 (w/v) with 0.005M sulfuric acid for 16 h. Method 9G1 codes the manual analytical finish of Truog and Meyer, with absorbance at 660 nm. Method 9G2 codes automated analytical finishes (continuous segmented flow and flow injection analysis) based on molybdenum-blue and a preferred absorbance of 882 nm. The methods specify reporting results as mg P/kg on an air-dry basis.
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Bicarbonate Extractable Phosphorus - Colwell (9B1)

This popular Australian P test on milled air-dry sample is suitable for acidic, neutral and alkaline soils. The extractant is freshly prepared 0.5M sodium bicarbonate @ pH 8.5. The wide soil/extractant ratio of 1:100 and an extended shaking time of 16 h favours readily available and more slowly available forms of soil P, while suppressing the solubility of basic calcium phosphates often found in neutral and alkaline soils. Method 9B1 describes a manual, molybdenum-blue colorimetric procedure with a preferred absorbance at 882 nm, whereas Method 9B2 refers to the same initial soil extraction, followed by an equivalent automated molybdenum-blue colorimetric finish (continuous segmented flow or flow injection analysis). The methods specify reporting results as mg P/kg on an air-dry basis.

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Electrical conductivity (EC) of 1:5 soil/water extract (3A1)

This test on milled air-dry sample at a soil/water ratio of 1:5 for 1 h is suitable for use on all soils, irrespective of whether acidic or alkaline. It usually underestimates the soluble salt status of soils containing natural or added gypsum, particularly if ³ 1% of gypsum is present. Such soils would have an EC of about 2 dS/m. Soil EC x 0.336 (Method 3B1) approximates percent total soluble salts, while approximate soil ionic strength (Method 3C1) at 0.1 bar (I0.1) can be calculated as follows: I0.1 = [0.0446*EC1:5 – 0.000173], where I0.1 has units of mM, and EC1:5 has units of dS/m @ 25oC.

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Exchangeable Bases - Ammonium Acetate (15D3)

 

Exchangeable bases - 1M ammonium acetate at pH 7.0.

 

This rapid method for exchangeable cations in non-saline acidic through to slightly alkaline soils has no pre-treatment for soluble salts. It should yield similar data to those of method 15A1, except it can overestimate exchangeable Ca in soils containing calcium carbonate.

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DTPA Trace Elements (12A1)

Soils are extracted with 0.005M DTPA, at a 1:2 soil:solution ratio, and shaken for 2 hr at 25oC.  Analytical finish is either ICP-AES or Flame AAS.

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Ca(H2PO4)2 extractable S (10B3)

Sulfate sulphur is extracted in the absence of activated charcoal from air-dry soil <2 mm particle size, by 0.01M Ca (H2PO4)2 at pH 4.0 using a soil/solution ratio of 1:5 and an extraction time of 17 h at 25 degrees C. This extracted sulphur is then determined in an aliquot of particle-free soil extract by ICP-AES.

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Phosphorus buffer index, with Colwell P (PBI+ColP) pooled analytical finishes (9I2A)

This index of soil P sorption embraces adsorption as well as precipitation reactions. In addition, it utilises the Colwell-P test on the same soil sample as a measure of current soil P fertility (PBI+ColP). Equilibrium soil extracts are obtained by shaking milled air-dry soil continuously for 17 h at a ratio of 1:10 (w/v) with a P equilibrating solution initially containing the equivalent of 1000 mg P/kg in 0.01M CaCl2. In method 9I2a, orthophosphate-P in final particulate-free supernatant solutions is analysed by a molybdenum-blue analytical finish, at a preferred absorbance of 882 nm. Methods 9I2b and 9I2c code for analytical finishes based on ICPAES and a vanadate-P colour finish, respectively. PBI+ColP is calculated as {[Ps (mg P/kg) + Colwell-P (mg/kg)] / c (mg P/L)0.41}, where Ps = freshly sorbed P and c = final solution P concentration. The methods specify reporting results on an air-dry basis.
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PBI - Unadjusted (9I4A)

This index of soil P sorption embraces adsorption as well as precipitation reactions. Equilibrated soil extracts are obtained by shaking milled air-dry soil continuously for 17 h at a ratio of 1:10 (w/v) with a P equilibrating solution initially containing the equivalent of 1000 mg P/kg in 0.01M CaCl2. The residual P in the extract is determined using the Murphy and Riley colorimetric finish.  In other related methods (9I2a, 9I3a) the PBI value is modified to allow for the soil fertility level.  In this method, there is nosuch adjustment. The methods specify reporting results on an air-dry basis.

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pH of 1:5 soil/water suspension (4A1)

This test on milled air-dry sample involves mechanical shaking with deionised water in a closed system for 1 h at a soil/water ratio of 1:5 prior to pH measurement using calibrated electrodes, while stirring the soil/water suspension. The method is suitable for use on all soils, irrespective of whether acidic or alkaline. Values may be lower than expected on recently fertilised soils due to a temporary increase in soil solution ionic strength.
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Chloride - 1:5 soil/water extract (5A1)

Tests for water-soluble chloride (Cl) on milled air-dry sample are suitable for use on all soils. For method 5A1, Cl‑ in clarified 1:5 soil/water extracts is determined by potentiometric titration with AgNO3 in conjunction with an Ag/AgNO3 electrode array. For method 5A2a, Cl‑ in clarified 1:5 soil/water extracts is determined by an automated, continuous flow colorimetric procedure based on the formation — in the presence of ferric ions and free thiocyanate ions — of highly coloured ferric thiocyanate in proportion to the Cl‑ concentration. Method 5A2b is similar, except it pertains to the use of flow injection analysis (FIA). For 5A1 and 5A2 methods, it is assumed there are no chemical interferences of significance. Moreover, Method 5A2a has proven more precise than method 5A1, particularly at soil concentrations <50 mg Cl/kg. Other analytical finish options involve chemically-suppressed ion chromatography (5A3a), single-column electronically suppressed ion chromatography (5A3b), and direct measurement by ICPAES (Method 5A4). The methodology specifies reporting results on an air-dry basis.

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GJ-23

Wet digestion - open system without HF - diacid (HNO3/HClO4).  ICP-AES finish.

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GJ-13

Wet digestion - open system without HF - diacid (HNO3/HClO4).  AAS-Flame with pulsed hollow cathode lamp background correction, using air-acetylene.