Acid-extractable Phosphorus (9G2)
This test is often referred to as BSES-P. Soil extracts are obtained by shaking milled air-dry soil at a ratio of 1:200 (w/v) with 0.005M sulfuric acid for 16 h. Method 9G1 codes the manual analytical finish of Truog and Meyer, with absorbance at 660 nm. Method 9G2 codes automated analytical finishes (continuous segmented flow and flow injection analysis) based on molybdenum-blue and a preferred absorbance of 882 nm. The methods specify reporting results as mg P/kg on an air-dry basis.Bicarbonate Extractable Phosphorus - Colwell (9B1)
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.
Exchangeable Acidity (15G1)
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.
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).
DTPA Trace Elements (12A1)
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.
Colwell extractable K (18A1)
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.
KCl-ext.S (10D1)
Empirical extraction at 40oC in 0.25M KCl, for 3 hours. Total S in the extract is measured by ICP-AES.
Mehlich3 ICP (18F1)
Analysis of Mehlich 3 extract using inductively-coupled atomic emission spectroscopy (ICP-AES)
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.Extractable Phosphorus - Olsen (9C1)
This extractable P test on milled air-dry sample uses freshly prepared 0.5M sodium bicarbonate @ pH 8.5 as the extractant. The soil/extractant ratio of 1:20 and a relatively short extraction time of 30 min favours readily available forms of soil P, while suppressing the solubility of basic calcium phosphates often found in neutral and alkaline soils. Method 9C1 involves a manual, molybdenum-blue colorimetric finish with a preferred absorbance at 882 nm. Method 9C2a defines an equivalent automated molybdenum-blue continuous segmented flow analytical finish, while Method 9C2b codes an automated colour finish by flow injection analysis. No significant difference is expected in results due to the analytical finishes described. The methods specify reporting results as mg P/kg on an air-dry basis.Organic carbon - W & B (6A1)
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 Cl‑ 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.
(9I4C)
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
Ext Chloride - IC (5A3)
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.
DE-23
Microwave Digestion - closed system without HF, and final medium HNO3 and/or HCl. ICP-AES finish.
DE-24
Microwave Digestion - closed system without HF, and final medium HNO3 and/or HCl. ICP-MS finish.