Reactive aluminum in the vermont soil test

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Abstract
Determination of reactive Al by extracting a soil sample with pH 4.8 NH4 OAc (1.25 N acetate) characterizes for northern acid soils the quantity of soil acidity that must be neutralized to meet lime need and also lower the P adsorbing capacity. Extracted Al is used in conjunction with pH in 10 mM CaCl2 to calculate the lime requirement directly. First, the amount of P fertilizer needed is approximated, based on the P intensity (available P) determined in the same NH4OAc extract. Then, the recommended amount is increased by a P-fixation factor obtained from the Reactive Al measured and decreased by a reserve P factor derived from fluoride extractable P. Unlike a buffer lime requirement method, which predicts lime needed to reach a target pH, the reactive Al test estimates the quantity of acidity that must be neutralized to prevent fixation of P fertilizer by soil Al and to release P from Al-bound sources. Attaining a particular target pH is not the primary goal. The reserve P test measures the amount of unavailable Al phosphates that becomes partially available when lime needs are met.

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