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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

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(9.00E+01)

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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.

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Exchangeable Bases - Ammonium Acetate (15D3)

 

Exchangeable bases - 1M ammonium acetate at pH 7.0.

 

This rapid method for exchangeable cations in non-saline acidic through to slightly alkaline soils has no pre-treatment for soluble salts. It should yield similar data to those of method 15A1, except it can overestimate exchangeable Ca in soils containing calcium carbonate.

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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.

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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.

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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.
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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.