SOLUTION-PHOSPHATE CONCENTRATION AND MAINTENANCE-P APPLICATIONS IN A HILL SOIL

Abstract

Capital and maintenance dressings of phosphate to hill pastures are considered as part of an overall curvilinear response to phosphate under conditions of phosphate accretion with the degree of response in the maintenance period dependant on the level of prior phosphate input. The response to phosphate in plant growth rate is governed by the concentration of phosphate in solution in the soil. The concentration of phosphate in solutions in equilibrium with hill soils of different histories of phosphate application has been measured and the results expressed in termsof a hyperbolic convergence derived from the concept of capital and maintenance dressings. A reduced response, in solution phosphate concentration, to phosphate application was observed in soils which had received lower prior applications and in soils from which current phosphate inputs had been withheld. It follows, that any reduction in phosphate input will cause, not only a lowered solution phosphate concentration, but also a lowering of the increase in phosphate concentration per incremental phosphate addition. This points to a possible lowering of the efficiency in the utilisation of applied phosphate when the input of phosphate to hill pastures is reduced. Keywords: solution phosphate, phosphate fertility, capital inputs, maintenance inputs, hill soils