Dynamics of phosphorus in soil under the influence of inorganic phosphorus supply

A field experiment was conducted in June 2006 in order to evaluate the adsorption and desorption behaviour of phosphorus in neutral normal soil. The experimental plot was located at Madurai District, Tamilnadu, India. The experimental soil has the pH of 7.2, EC 4 dSm-1 and the available phosphorus content is 8 kg ha-1. The experiment was conducted with different levels of P viz., 0 (T1), 75(T2), 100(T3), 125(T4), 150(T5), 175(T6) and 200 (T7) per cent recommended dose of phosphorus (RDP). The recommended dose of phosphorus is 62.5 kg/ha.The treatments were laid out in plots of size 5 x 4 m in Randomised Block Design with three replications. The test crop as maize was grown upto 105 days. During the crop growth, the soil samples were analyzed for the different fractions of phosphorus viz., Ca–P, Fe-P, Al-P, Saloid bound P, reductant soluble P and organic P at an interval of 15 days. Asper the analytical report, increasing levels of phosphorus increased the concentration of Ca-P and Fe-P, Al-P, Saloid bound P, reductant soluble P and organic P upto 200% RDP. Over a period of time, the concentration of Ca-P, Fe-P and organic P increased at all levels of P added from 15 to 105 days. The highest value was observed with the application of 200% RDP in all cases. But a decreasing trend was observed in the concentration of Al-P and saloid bound P with progress of time. The maximum release was observed with the application of 200% (T7) RDP. There was no definite pattern of change in the concentration of reductant soluble P with time at all the levels.