INFLUENCE OF SALTS IN ASSOCIATION WITH MONOCALCIUM AND DIAMMONIUM PHOSPHATES ON THE CHEMICAL CHARACTERISTICS AND MOVEMENT OF SOIL SOLUTION

Abstract

Various salts thoroughly mixed with monocalcium phosphate monohydrate (MCP) and diammonium phosphate (DP) were made to react with moist Lima silt loam soil arranged in 5-mm layers and separated by filter papers. After a reaction period of 3 weeks, soil moisture, pH, hot nitric acid-soluble phosphorus, and sodium bicarbonate-soluble phosphorus were determined in the different layers. As compared with MCP, the more soluble salts in association with MCP enhanced soil solution movement away from the fertilizer layer, and there was considerably greater movement of soil solution from the fertilizer layer with DP compared with MCP. The movement of soil solution with DP was attendant with greater movement of phosphorus into soil layers than for MCP, with the result that phosphorus was distributed into a greater volume of soil. When calcium sulphate was associated with DP, movement of soil solution and the diffusion of phosphorus into soil layers was markedly restricted because of massive precipitation reactions. At the soil layer closest to the MCP–fertilizer layer, a pH of 2.8 units developed. These very acid conditions were in every case ameliorated when MCP was associated with different soils. No changes in the natural soil pH were occasioned by the use of DP.By sampling soil solutions with filter papers at increasing distances from a fertilizer layer containing MCP, considerable amounts of Al, Fe, Mn, and Ca were detected. When various salts were associated with MCP, the amounts of soluble constituents moved to greater distances than with pure MCP, thereby effecting a greater diffusion of potentially toxic elements into a greater volume of soil. Chloride salts were particularly effective in causing the diffusion of manganese away from the fertilizer layer. No measurable amounts of Al, Fe, or Mn were found in soil solutions when DP reacted in soil.