Effect of phosphate topdressing on a Soil from andesitic Volcanic Ash

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Abstract
As an introduction to a method for fractionation of phosphorus in acid soils, the nature of soil phosphorus is discussed. Phosphorus in acid soils has been divided into three major categories, (a) organic phosphorus, (b) apatite phosphorus and (c) Fe- and Al-bound phosphorus. Organic phosphorus may be determined by an alkaline extraction procedure or by an ignition method, the latter being the more rapid and simpler but more liable to error due to changes in the solubility of the inorganic phosphorus during ignition. Apatite phosporus is assumed to be the phosphorus not extracted by boiling 0.1 N NaOH after the exchangeable calcium has been removed. Fe- and Al-bound phosphorus is the difference between the total inorganic phosphorus and the apatite phosphorus. The experimental procedures are described and discussed.