Influence of Phosphorus and Zinc Application on the Availability of Zinc, Copper, Iron, Manganese, and Phosphorus in Waterlogged Rice Soils

Laboratory incubation experiments were conducted with three clay loam, lowland rice soils (Haplustalf) to study the effect of applying three different levels of phosphorus (0, 50, and 100 ppm) and zinc (0, 5, and 10 ppm), in all possible combinations, on the changes in DTPA-extractable zinc, copper, iron, and manganese wand Bray's 2 extractable phosphorus in soil. We sought to understand whether the effect of such interaction is responsible, at least partly, for the decreased uptake of some of the nutrient elements in rice on phosphorus and zinc fertilization, as reported by others. The results showed that applying phosphorus decreased the content of DTPA-extractable Zn, Cu, Fe, and Mn in soils, the rate of decrease gradually declining with the progress of the incubation period. The depressive effect of P on extractable Zn content was found to be more prominent in respect of soil native Zn than of the applied one. Application of Zn also depressed the content of extractable Cu, Fe, and P, but increased that of extractable Mn. The decrease in the uptake of Zn or P, Cu, and Fe by rice, resulting from the application of P or Zn as reported by others, was attributed at least partly to the decrease in the availability of these elements in soil.