A semi-descriptive model for predicting residual-P from fertilizer P applications

Abstract

The increasing pressure on world food supplies and the recent increase in the cost of energy and fertilizers point to the need for efficient use of applied nutrients. A semi-descriptive model was developed to predict the change in extractable P with time, assuming that P added through fertilizer and amounts removed in harvested plant products were the main fluxes affecting available P status. The relationship between extractable P and the rate of P fertilization was quadratic. ‘Availability’ coefficients were evaluated from the data of a long term fertilizer experiment at Ludhiana centre. It was assumed that fixation of applied P was accommodated in these, and that practically there was no leaching and run-off of applied P in these soils. Good agreement (r = 0.99^**) was found between the predicted and observed soil test P of alluvial soils of Barrackpore and New Delhi, medium black soils of Coimbatore and Jabalpur and sub-montane soil of Palampur centre. The model, however, failed to predict available P of Pantnagar and Hyderabad soils.