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Standard operating procedure for soil available phosphorus - Olsen method









FAO. 2021. Standard operating procedure for soil available phosphorus - Olsen method. Rome.


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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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    Brochure, flyer, fact-sheet
    Standard operating procedure for soil available phosphorus - Mehlich I Method 2021
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    Mehlich I method is suitable for determining bioavailable P in acid soils with low cation exchange capacity; (CEC) less than 10 cmolc kg-1. The amount of P and K extracted with Mehlich-1 has been calibrated to quantify the amount of P and K fertilizer needed to maximize crop yields in various regions. This method has also been adapted for simultaneous determination of additional plant nutrients in the extract using ICP-OES.
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    Booklet
    Standard operating procedure for soil pH determination 2021
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    Soils are referred to as being acid, neutral, or alkaline, depending on their pH, with 7 being neutral, below 7 acidic and above 7 alkaline. The pH range normally found in soils varies from 3 to 9. As pH is measured in terms of hydrogen ion activity, pH is thus a measure of only the intensity of H+ activity and not the amount of acidity present. The desirable soil pH range for optimum plant growth varies among crops. Generally, a soil pH between 6.0-7.5 is acceptable for most plants, as most nutrients are available in this pH range. However, some plants have soil pH requirements above or below this range. An acidic pH may cause higher mobility of toxic elements potentially leaching into ground water or taken up and accumulated in plants. Additionally, inhibited plant growth may be observed in low pH soils due to aluminum toxicity. In higher pH soils, phosphorus and most micronutrients may become less available. As the pH value of many soils correlates with base saturation, it may also be used in the field for preliminary classification purposes.

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