Fifty-six experiments, each with 15 levels of P fertilizer in the presence of excess N and K fertilizer, were carried out on adjacent sites of the same field where the soil was maintained at the same low P status. Yields, in every experiment where there was a response, were related to level of P fertilizer by a diminishing-retums type curve, and fitted an inverse polynomial equation with a single parameter to define responsiveness. Responsiveness of many crops were similar but there were, nevertheless, considerable inter-crop differences.
Applications of P fertilizer increased the % P in the dry matter of lettuce and spinach as well as yields. They increased the % P in the Cruciferae and Chenopodiaceae without appreciably affecting yield. Conversely, theyhad little effect on the % P of leeks, onions, broad beans and French beans but increased yields.
When the optimum levels of P fertilizer were applied, % P (in the entire plant) of the different crops was negatively correlated with total dry weight per unit area and total uptake of P was related by a single curved relationship to total dry weight. In addition, the difference between the % P in the foliage and in the storage roots of the various root crops was asymptotically related to mean plant weight.
Percentage recovery of added P (100 kg/ha) by the different crops was largely determined by the total weight of dry matter. It varied from 1% when crop dry weight was 2 t/ha to 12% when it was 15 t/ha.
Applications of phosphate suppressed leaf scorch of spinach. On occasion they alleviated stem rot in summer cabbage and influenced the bolting of onions and the number of defective Brussels sprouts. Otherwise, the effects on quality were small.
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