Response of ley plants to rock phosphate and superphosphate

The results of two field trials in which the efficiency of superphosphate phosphorus and rock phosphate (Hyperphosphate Reno) phosphorus were compared on a fine sand soil and a humus soil, did not show any differences in the dry matter yields produced by the two fertilizers within the experimental period including the nurse crop and three years of ley. The analyses of the hay yields harvested from the third year red clover-timothy ley, fairly poor in red clover, proved that the phosphorus content of the hay from the hyperphosphate plots was markedly lower than that of the hay from the superphosphate plots. The respective figures were 0.17 and 0.21 per cent P of dry matter, while the phosphorus content of the hay from the untreated plots was 0.15—0.16 per cent. Red clover seemed to be able to synthesize plant material equally rich in phosphorus both when feeding on superphosphate and when feeding on hyperphosphate. On the other hand, the grasses, in these cases mainly timothy, took up far less phosphorus from hyperphosphate than from superphosphate. The differences in the phosphorus content of the respective plant groups were almost exclusively due to differences in their content of inorganic phosphorus, or phosphorus determined as inorganic forms by the simple fractionation procedure employed. No effect of the different phosphate treatments on the content of ash, calcium, potassium, or nitrogen in the ley plants could be detected. The results of the present study corroborate the earlier observation that on a ley, poor in clover, rock phosphate may produce crops too low in phosphorus for the needs of domestic animals. The results also emphasize that it is important not to judge the response to phosphate fertilizers only on the basis of the dry matter yields.