Phosphorus changes during the leaching and decomposition of hayed-off pasture plants

Ground samples of hayed-off pasture plants were decomposed in the laboratory under continuously moist, and intermittently moist and dry, conditions. During the course of decomposition they were leached at different frequencies and the resulting changes in inorganic and organic phosphorus measured. The dissolution of superphosphate and its conversion to organic phosphorus were also studied under some of these conditions.Inorganic phosphate was readily leached from the samples when microbes were inhibited. Microbial activity, on the other hand, largely prevented the loss of inorganic phosphate by leaching from a phalaris sample over a period of 3 months. Intermittent drying increased the amount of phosphate leached from decomposing plants but the leaching frequencies examined had little effect. The percentage of the phosphorus leached from plants varied with the type of material. In all cases less than half was recovered as inorganic phosphate, even after decomposition and leaching for 6 months. When superphosphate granules were leached in the presence of decomposing plants the conversion of fertilizer phosphate to organic phosphorus was small, but the dissolution of phosphate was sometimes retarded. The recycling of phosphate in hayed-off pastures is discussed in the light of these results.