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 (I_0.1) can be calculated as follows: I_0.1 = [0.0446*EC_1:5 – 0.000173], where I_0.1 has units of mM, and EC_1:5 has units of dS/m @ 25^oC.

Mehlich3 ICP (18F1)

Analysis of Mehlich 3 extract using inductively-coupled atomic emission spectroscopy (ICP-AES)

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)

DN-23

Microwave digestion - open system without HF, and final medium HNO₃/peroxide. ICP-AES finish.