Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:6:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 6 (pt 1/3)
Character Range: 775090–778201

6                   Physicochemical analyses
6.1 Soil moisture content
    6.2 pH
    6.3 Electrical conductivity
    6.4 Cation exchange capacity
    6.5 Water soluble chloride
    6.6 Organic carbon

6.1              Soil moisture content

    6.1.1         Scope and application
This method (AS 1289.2.1.1-2005) measures the amount of water lost after drying a soil sample (field-moist or air-dried) in an oven (105110ºC) to constant mass. This allows a correction factor to be obtained to then express chemical concentrations on a dry weight basis.

This drying method will not remove all the water of crystallisation that may be associated with minerals.

The oven-dried moisture content is always determined on a separate representative sub-sample of the soil; the oven-dried sample should not be used for other chemical or physical tests as the drying step may affect results of other tests.

6.2              Soil pH

    6.2.1         Scope and application
This method (AS 1289.4.3.1-1997) measures the hydrogen-ion concentration in a soil-water or soil-aqueous calcium chloride suspension and is expressed in pH units.

It is recommended that soil pH be measured whenever other chemical constituents, particularly metals, are to be evaluated, as the pH may have a profound effect on the form and behaviour of chemicals in the soil.

The use of 0.01 M calcium chloride extract is recommended where the soil salt content may influence the pH value (Rayment & Higginson 1992, p. 17). Generally, the pH of the calcium chloride extract is about 0.5 to 1.0 pH units lower than the water extract and gives more accurate values.

The same 1:5 soilwater suspension for electrical conductivity determination may be used for measuring pH but to avoid contamination of the suspension from KCl in the pH probe, electrical conductivity should be analysed first.

When assessing acid sulfate soils, consult Analysis of acid sulfate soil—dried samples—methods of test— determination of pHKCl and titratable actual acidity (TAA) (AS 4969.2-2008) and Analysis of acid sulfate soil—dried samples—methods of test—determination of peroxide pH (pHOX), titratable peroxide acidity (TPA) and excess acid neutralising capacity (ANCE) (AS 4969.3-2008).

    6.2.2         Principle
Soil pH is measured electrometrically on a 1:5 soilwater suspension at approximately 25°C. A 1:5 soil  calcium chloride extract is also provided as an option. The analytical report should state which method was used.

6.3              Electrical conductivity

    6.3.1         Scope and application
This method measures the electrical conductivity (EC) of a 1:5 soilwater suspension. Electrical conductivity of the soil is sometimes used to estimate the soluble salt content of a sample (Rayment & Higginson 1992, p.17). A high soluble salt content may have physical detrimental effects on a soil, compromising its agronomic and structural attributes, for example, increasing potential for corrosion of below-ground structures.

The same 1:5 soilwater suspension for pH determination may be used for measuring the electrical conductivity