Potassium movement and transformation in an acid soil as affected by phosphorus

When P and K fertilizer are applied to soil at the same time, the movement and transformation of K may be affected by P This study was conducted to quantify the effects of monocalcium phosphate (MCP) co-applied with KCI on the distance of K movement, the concentration of Kin different forms and soil pH change at different distances from the fertilizer application site in an incubation experiment with an acid red soil from Yingtan, Jianxi province in southern China. Fertilizers of 0.5 g KCI alone or in combination with 0.98 g MCP were added to the surface of soil cylinders with a height of 150 mm and packed in wax blocks. The fertilizers and soil were incubated at field capacity moisture content for 7 and 28 d. Extraction and analysis of each layer (first 25 layers of 2 mm thickness and then 20 layers of 5 mm) from the interface of soil and fertilizer showed that the movement distance of K was not affected by the addition of MCP. However, the concentration of water-extractable K decreased and the concentrations of exchangeable and nonexchangeable K increased significantly near the fertilizer site in the presence of P. The application of MCP also slowed down the decrease of KCI-induced soil pH close to fertilizer site. The results suggested that the transformation of Kin soil close to the fertilizer placement site was significantly affected by the addition of MCP, probably due to the reactions of MCP with AI and Fe in soil. The amounts of K in different forms in soil columns implied that the addition of MCP could reduce the bioavailability of K at the beginning of fertilizer application.