The effect of particle size of superphosphate on the availability of its phosphorus and sulphur to pasture plants

In glasshouse experiments, the responses of plants to the phosphorus and sulphur in top-dressed superphosphate were affected by its particle size. On four soils, yields of subterranean clover differed by 12–25% owing to differences in particle size of applied superphosphate. Both rate of solution and spatial distribution of the fertilizer affected plant response. Under non-leaching conditions, the sulphur in large particles of superphosphate was always less available than that in fine. The phosphorus in large particles was slightly less available when superphosphate was applied to soils of low, or moderate, capacities to sorb phosphate but more available when applied to a soil of high capacity to sorb phosphate.Pastures would probably respond better to granulated superphosphate than to normal on sulphur-deficient soils subject to strong leaching, or on soils of high capacity to sorb phosphate. On many soils, however, no difference would be expected, and on some sulphur-deficient soils the granulated product may even be inferior in some seasons.