The status of inorganic and organic phosphorus in some soils in relation to plant availability

Pigeonpea, groundnut, and upland rice are able to take up sparingly soluble phosphorus (P) in low fertility soils, We examined the P forms present in the upland soils in order to study the P uptake mechanisms of these plants, The Chang and Jackson (CJ) fractionation method is commonly applied for determining the P status in soils, In Japan, the Sekiya method has been developed for Andosols, Three acid soils were fractionated according to the two methods, and the contents of both organic and inorganic P in the calcium-, aluminum-, and iron-fractions were determined. In this experiment, a shift of extracted P into the next fraction during the fractionation procedure occurred in both methods, Similar results were obtained with both the CJ and Sekiya methods in a non-allophanic Andosol and a Yellow soil, However, the CJ method overestimated the content of both organic and inorganic P in the calcium-bound fraction, compared to the Sekiya method in the case of an allophanic Andosol, The fractionation using the Sekiya method seemed to give better information than the CJ method about the P status in Japanese upland soils, especially Andosols, in terms of plant P availability.