Mineralization of Organic P in an Ultisol

Abstract

One field experiment was conducted to measure residual effect of P in an Ultisol with corn as the indicator plant. Three greenhouse experiments with corn plants were also conducted to determine the relationship between plant P uptake and levels of soil organic P, soil inorganic P and available P, and to measure the effects of soil temperature, P and N applications and soil sterilization on the rates of organic P mineralization. Field data failed to reveal significant differences in respiration rates and soil pH. Soil P levels were higher in plots that received 1,120 kg/ha of P, with or with lime, than in those that received lesser amounts of P. In the greenhouse experiments, yields of corn tops were highly correlated with soil temperatures when no P was added. Plant P concentration and uptake were highly correlated with soil temperature when no fertilizer P was added. Soil sterilization with methyl bromide significantly increased N and decreased K concentrations irrespective of soil temperature. It is postulated that mineralization of organic P in Ultisols and perhaps in other highly weathered tropical soils may account for the lack of response to fertilizer P usually observed.