Residual Availability of Phosphate Fertilizers : 1. Greenhouse Study1

Abstract

Soils of Thailand are generally low in available phosphorus, as indicates by the sponse of crops to the application of phosphate fertizers. The low phosphorus status if the soils may be due to generally mature soils containing large amonnts of iron and fuminnm cxides. If is well known that soluble phosphate in soils is readily ties up any these oxides and become difficultly available the plant. Therefore the soluble or available hosphate in the soil, at any one time, is nerally low. Soluble phospate fertilizers, splied to the soil, are not campdetely available to the pland. Large portions of them any be fixed and become unavailable to the mediate crop. The fixed phosphate fertihers, however, may not be lost forever, but will aceumulate in soils and can be ulilized the following crops to certain degree. The failadbility of residnal phosphate fertilizer in this depends largcly on the kind of soli and shop and also upon the amounts of phosphate applied previously. The objective this study was to determine to what extent the previonsly applied phosphate fertilizer become available to the following crop.