Analytes Certified for in 2019
This popular Australian P test on milled air-dry sample is suitable for acidic, neutral and alkaline soils. The extractant is freshly prepared 0.5M sodium bicarbonate @ pH 8.5. The wide soil/extractant ratio of 1:100 and an extended shaking time of 16 h favours readily available and more slowly available forms of soil P, while suppressing the solubility of basic calcium phosphates often found in neutral and alkaline soils. Method 9B1 describes a manual, molybdenum-blue colorimetric procedure with a preferred absorbance at 882 nm, whereas Method 9B2 refers to the same initial soil extraction, followed by an equivalent automated molybdenum-blue colorimetric finish (continuous segmented flow or flow injection analysis). The methods specify reporting results as mg P/kg on an air-dry basis.
Exchange acidity (hydrogen and aluminium) by 1M potassium chloride
This is a preferred method for estimating the acidic cation status of acidic sub-tropical and tropical soils.
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).
Soils are extracted with 0.005M DTPA, at a 1:2 soil:solution ratio, and shaken for 2 hr at 25oC. Analytical finish is either ICP-AES or Flame AAS.
The Colwell extraction was developed for measuring available P, but can also be used for determining available K. The extractant is freshly prepared 0.5M sodium bicarbonate @ pH 8.5, with a soil:extractant ratio of 1:100 and a shaking time of 16 hr. The sodium cation is considered the primary extractor, displacing the similar potassium cation from exchange sites.
Empirical extraction at 40oC in 0.25M KCl, for 3 hours. Total S in the extract is measured by ICP-AES.
Analysis of Mehlich 3 extract using inductively-coupled atomic emission spectroscopy (ICP-AES)
This measure of soil organic carbon (OCW&B; expressed as %C) usually yields a lower figure than the true total organic carbon value. The method uses finely-milled air-dry sample. It involves wet oxidation by a dichromate-sulphuric acid mixture and relies only on heat of reaction. Soil weight should take account of the expected concentration of OC, and it is expected that allowance will be made for positive soluble Clâ€‘ interference in soils containing >0.5% Cl. The method specifies reporting on an oven-dry (105oC) basis. Nowadays this method is less preferred than 6B methods.
The laboratory either did not specify the method used or uses a mix of methods when submitting to the certification body
Tests for water-soluble chloride (Cl) on milled air-dry sample are suitable for use on all soils. Chloride in clarified 1:5 soil/water extract is determined by ion chromatography. The methodology specifies reporting results on an air-dry basis.
Microwave Digestion - closed system without HF, and final medium HNO3 and/or HCl. ICP-AES finish.
Microwave Digestion - closed system without HF, and final medium HNO3 and/or HCl. ICP-MS finish.
Extraction with water. Spectrophotometric (automated) finish.