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
AR Dig. elelements (17C1)
Aqua Regia block digested. ICP-AES/ICP-MS/GF-AAS finishes. Produces 'Pseudo-totals'.
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.
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).
pH: 1:5 SOIL:0.01M CaCL2 Suspension (4B1)
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.
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, steam distillation. (7A1)
Method 7A1 provides a good estimate of total soil N in soils with little NO3: otherwise slightly lower apparent total soil N concentrations are likely. The method initially involves semi-micro Kjeldahl digestion. Subsequently, NaOH solution is added to release NH3 by steam distillation. The NH3 released is quantitatively absorbed in dilute boric acid, with total soil N determined by titration with standard acid. The method uses finely-milled air-dry sample and specifies reporting results as %N on an oven-dry (105oC) basis.
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.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
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.