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Standard operating procedure for soil available phosphorus - Mehlich I Method









FAO. 2021. Standard operating Procedure for soil available phosphorus - Mehlich I method. Rome. 


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    Standard operating procedure for soil available phosphorus - Olsen method 2021
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    This procedure is suitable for calcareous, alkaline, neutral, and slightly acidic soils containing CaPO4, since the calcium concentration in the solution is suppressed by the precipitation of CaCO3, increasing PO4 concentration in solution. Neutral and slightly acid soils (pH 6.0 to 7.0) may contain both Ca- and Al-phosphates. The NaHCO3 extractant can remove Ca-phosphates and phosphate adsorbed on the surface of calcium and magnesium carbonates along with Al-phosphates and is considered the most suitable extractant for these soils.
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    Booklet
    Standard operating procedure for soil available phosphorus - Bray I and Bray II method 2021
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    P-Bray 1 and P-Bray 2 methods are normally limited to acid soils with water pH values less than 6.8. The P-Bray 1 Method removes a fraction of the “adsorbed” phosphorus (Al-P, Fe-P, Mn-P and Ca-P but less efficient) while the P-Bray 2 Method is best suited to acid soils where rock phosphate has been the primary P fertilizer source and/or the major portion of P exists in the soil in various forms of calcium phosphate. Bray extractants should not be used on alkaline soils because the acid tends to be neutralized and/or excessive calcium phosphates may be extracted, giving a false high test for available P.
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    Standard operating procedure for soil available micronutrients (Cu, Fe, Mn, Zn) and heavy metals (Ni, Pb, Cd), DTPA extraction method 2022
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    The method provides a potential indicator of the plant available copper, iron, manganese and zinc, which are essential soil micronutrients for plant growth and living organisms. It can be used to extract heavy metals such as nickel, lead and cadmium assisting with conclusions as to their potential bioavailability. This method must be used in combination with suitable determination methods, for example, flame atomic absorption spectrometry, electrothermal atomic absorption spectrometry or inductively coupled plasma – optical emission spectrometry.

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