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


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).


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.

pH: 1:5 SOIL:0.01M CaCL2 Suspension (4B2)

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 4B1 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 using calibrated electrodes positioned in the unstirred supernatant after settling of the suspension. Code 4B2 provides a similar measurement outcome but relies on the addition of 0.21M CaCl2 to a 1:5 soil/water suspension to achieve 0.01M CaCl2 prior to measurement of pH as for 4B1.

Codes 4B3 and 4B4 are identical to 4B1 and 4B2, respectively, except the soil/CaCl2 suspensions are stirred during measurement. Method 4B5 codes for an MIR surrogate measurement. There is merit in separate use of both water and calcium chloride to measure soil pH.


Total soil N – Dumas high-temperature combustion (7A5)

This method utilises automated and/or microprocessor controlled instrumentation, which mostly is able to measure at least total C, N and S in the same sample. Dumas-N dry oxidation includes all forms of soil N, without the need for lengthy pre-treatments, although results can occasionally differ from those expected in soils with high levels of fixed ammonium-N (lower results) and when soils are organically rich (high results, due to incomplete combustion resulting in the formation of methane rather than CO2). Typically, dry, finely-ground sample is subjected to high-temperature combustion (e.g. 950–1,250oC) in a stream of purified O2. An aliquot of the gases produced by combustion is carried by helium gas to a thermal conductivity cell for measurement of any N2 generated, a process typically taking 3–5 min. A heated copper catalyst reduces NOx to N2. The method specifies reporting results as %N 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