| Abstract
| - A mechanistic model is described for calculating the effects of starter fertilizer, granular fertilizer and 0.5 M NaHCO3pH 8.5 extractable soil phosphate on plant growth and plant P concentration during the entire period of growth up to commercial harvest. For each day, the model calculates the increment in root growth and partitions it into segments between the regions of soil enriched with starter fertilizer, those enriched with granular fertilizer and the remainder of the soil. It calculates the maximum possible amount of P that can diffuse through soil to each root segment in each region. Using this information and the P concentration in the plant, total P uptake is calculated. The increment in plant weight and root growth is calculated from the current plant weight, plant P concentration and air temperature. Subroutines calculate daily soil water content, the extractable and non-extractable soil P, and diffusion coefficients in the P-depleted zones around each root segment and in the remainder of the soil. Model simulations and sensitivity analyses indicate that extractable soil P and starter fertilizer P can lead to higher crop yields than are achieved when granular fertilizers are incorporated in soil, in the usual way, immediately before sowing. They also indicate that in the long-term, levels of extractable soil P will move towards a level characteristic of the soil. These findings are in agreement with results of long-term field experiments that have been reported in the literature. All inputs to the model that have a substantial impact on P-response of a single crop are easy to obtain. They include standard soil properties, the maximum potential yield, and daily rainfall, mean air temperature and evaporation from an open water surface. The model runs interactively at: www.qpais.co.uk/phosmod/phos.htm Copyright 2001 Annals of Botany Company
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