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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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CaCl2 extractable B - ICP (12C2)

The soil is extracted with boiling 0.01M Cacl2 solution at a 1:2 soil:solution ratio for 10 mins.  It is then quickly filtered to avoid any re-fixation of the solubilised B.  The extract is then analysed by ICP-AES.

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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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Water soluble nitrate - automated colour (7B1)

This method uses the same 1:5 soil/water suspension described for method 3A1. The filtered or centrifuged aliquot is subjected to automated colorimetric analysis based on the Griess-Ilosvay reaction, either by continuous segmented flow analysis (sub-method 7B1a) or by flow injection analysis (sub-method 7B1b) The methods specify reporting nitrate-N (mg N/kg) on an air-dry basis. Note that in some highly weathered soils with a measurable anion exchange capacity, water may not extract all of the adsorbed nitrate-N.
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Organic carbon - W & B (6A1)

This measure of soil organic carbon (OCW&B; expressed as %C) usually yields a lower figure than the true total organic carbon value. The method uses finely-milled air-dry sample. It involves wet oxidation by a dichromate-sulphuric acid mixture and relies only on heat of reaction. Soil weight should take account of the expected concentration of OC, and it is expected that allowance will be made for positive soluble Cl‑ interference in soils containing >0.5% Cl. The method specifies reporting on an oven-dry (105oC) basis. Nowadays this method is less preferred than 6B methods.

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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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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.