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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

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Nitrate Nitrogen (7C2)

Initially, milled air-dry soil is extracted for 1 h with 2M KCl at a 1:10 soil/solution ratio. For 7C1a to 7C1h methods, mineral-N components are quantified by steam distillations and subsequent titrations. For 7C2 methods, mineral-N fractions in the clarified soil extract are determined by automated colorimetric procedures. Ammonium ions (NH4+) are measured by a modified Berthelot indophenol reaction, while the Griess-Ilosvay reaction is used for NO3-N (and NO2-N). The methods specify reporting results for NH4-N and NO3-N [plus NO2-N if present], respectively, as mg N/kg on an oven-dry (105oC) basis. Specifically, method 7C2a relates to an automated colour, continuous segmented flow analytical finish, while Method 7C2b codes an automated colour finish by flow injection analysis. Little difference is expected in results due to choice of colorimetric finish.

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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 Chloride (15A1)

Method for measuring exchangeable bases (Ca2+, Mg2+, Na+, K+) - 1M ammonium chloride at pH 7.0

 

Suited for use on all soils, irrespective of whether acidic or alkaline, but preferred on acidic to weakly alkaline soils not dominated by solid-phase carbonates. Method 15A1 has no pre-treatment to remove soluble salts, with alternatives to remove them chemically (15A2) or to adjust for the presence of soluble sodium (15A3).

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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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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.

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Total organic carbon - Heanes wet oxidation (6B1)

The chemical basis of this procedure is similar to that of method 6A1, except that external heating on a hot-plate digestor is included. Expensive apparatus is not required, while interference from carbonate is negligible. Correction for positive Cl‑ interference in saline soils (>0.5% Cl) is recommended. The method 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.

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Soil organic matter by loss-on-ignition (6G1)

This simple test involves the ignition of finely-milled air-dry sample initially to 105oC and then to 550oC. One hundred times the difference in sample weight in grams between these two temperatures, i.e, [100(Weight105C – Weight550C)] = Loss on ignition550C (LOI550C), which is assumed to approximate % Organic Matter.
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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