Field trials on the store dressing with rock phosphate

The possibility of improving the soil phosphorus status by a store dressing with rock phosphate has been studied in two field trials of five years standing. Hyperphosphate Reno was applied to the nurse crop of a red clover-timothy ley in amounts of 0, 1000 kg/ha, or 2000 kg/ha, respectively. The split-plot technique was used to study the response of the ley to an additional annual application of 200 kg/ha of superphosphate. The soil analyses distinctly proved that, in spite of a careful working in of the hyperphosphate with a spade harrow, the fertilizer had not penetrated deeper than to the layer from 1 to 3 inches, with a large part of it remaining in the top inch. The treatment with hyperphosphate had mostly increased the fraction of the calcium-bound phosphorus, and, to a very low degree, the aluminium-bound phosphorus. The effect of superphosphate could be detected only in the fractions of aluminium- and iron-bound phosphorus of the surface inch. Although the store dressing did not produce marked responses in the yields of either trial, the statistically significant negative interaction between the effect of it and of superphosphate may be taken to indicate that hyperphosphate was able to improve the phosphorus status of these soils to some degree. The analyses of the hay samples from one of the trials in the fifth experimental year showed that the store dressing, particularly with the higher amount of hyperphosphate was able to increase the phosphorus content of hay to a satisfactory level which was equal to that produced by the annual superphosphate dressing only. Their combined effect resulted in the production of hay dry matter containing more than 0.24 % of P. In one of the experiments the residual effect of the treatments on rye was studied. The response to superphosphate was highly significant, probably owing to the high demands of phosphorus by rye, connected with the overwintering conditions, and also to the fact that ploughing in of the ley had brought superphosphate phosphorus within the reach of the plant roots