| Abstract: | Transformation and availability of rock phosphate (Hyperphos) compared with other fertilizer phosphates under controlled temperature and moisture conditions . In order to characterize the efficient portion of a fertilizer after transformation in soil, in samples of typical soils of Schleswig-Holstein the easily mobilizable and the mobile P-content were investigated with specific extractants. The transformation under controlled varied temperature and moisture conditions results first (besides in mobile phosphates) in easily mobilizable Ca-phosphate. In acid soils this changes gradually into Al- and Fe-phosphate the content of which decreases due to ageing (transformation into hardly mobilizable forms). The pH is the most important factor influencing the kind of transformation whereas high temperature and moisture content mainly increase speed and extent (high temperature accelerating especially the ageing process). The water soluble phosphate is less influenced by temperatur and moisture. The best efficiency of rock phosphates results from rapid transformation (promoted by low pH) into easily mobilizable soil phosphate followed by an ageing-retarding constellation of factors such as low temperature and moisture. |
