Effects of Organic Matter on the Kinetics of P fixation in Different Type Soils

Effects of Organic Matter (OM) on the kinetics of P fixation were studied on four types of soil treated with different levels of cow manure and incubated for two months before being treated with K2HPO4 at the rate of 45 mg P/kg, and then incubated for a period of 100 days at 25○C. Samples were taken from the soils at within intervals of 0, 1, 5, 20, 50 and 100 days and then their Olsen-P determined. It was revealed that the rate of oxidation of OM and the amount of organic-P mineralized were negatively correlated with the clay fraction content of the soil. The rate of oxidation was also increased with increase in the amount of OM added to the soils. The P associated with the manure was of a higher availability than the P in the mineral fertilizer. Kinetics of P fixation in the presence of OM was influenced by the mineralization of P especially at shorter incubation times, and the net effects of adsorption, precipitation, immobilization and mineralization processes occurring during the incubation, determined the amount of Olsen-P at any time. Addition of OM to the soils caused an increase in the recovery of applied P, the effect being more pronounced at longer incubation times.