Analytes Certified for in 2022 |
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Soil Testing |
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Air dry moisture content (2A1)
This method is required to adjust soil chemical results based on air-dry samples to an oven-dry (105oC)
basis. When the air-dry moisture content (M%) is known, the correction from air-dry
to oven-dry is as follows:
Oven-dry result = [Air-dry result x (100+ M%)]/100
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.
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.
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.pH CaCl2, stirred (4B3)
This pH test on milled air-dry sample is suitable for use on all soils, irrespective of whether acidic or alkaline. Values are usually unaffected by fertilisation prior to sampling, as changes to the soil’s ionic strength is masked by the calcium chloride. Code 4B3 indicates direct use of 0.01M CaCl2, at a soil/solution ratio of 1:5, with mechanical shaking for 1 h prior to pH measurement. The measurement is made using calibrated electrodes positioned in the stirred suspension.
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.Total soil nitrogen semi micro Kjeldahl,automated colour finish (7A2)
Method 7A2 is similar to Method 7A1, except that total N in the Kjeldahl digest is quantified by automated colorimetric procedures based on the Berthelot indophenol reaction. Method 7A2a relates to an automated colour, continuous segmented flow analytical finish, while Method 7A2b codes an automated colour finish by flow injection analysis. No significant difference is expected in results due to the choice of colorimetric finish. The test commence with finely-milled air-dry sample, while both methods specify reporting results as %N on an oven-dry (105oC) basis.
Total carbon - high frequency induction furnace (with prior physical removal of (6B3)
Following quantitative action / pre-treatment to account for or to physically remove (if present) charcoal and to chemically remove carbonate with excess 5% H2SO3 solution on a hot plate in a fume cabinet, the residual, re-dried soil sample is analysed for soil C by a suitable method, preferably Method 6B2b. The method involving carbonate removal and soil C analysis uses finely-milled air-dry sample, with weights varying with expected C concentrations. The method specifies reporting as %C on an oven-dry (105oC) basis.
Not Specified or mixed (NS)
The laboratory either did not specify the method used or uses a mix of methods when submitting to the certification body