Phosphorus dynamics in trial floodplain soils of Bangladesh

Sound P fertilizer management and maximum efficiency, insists on adequate understanding of P-soil interactions. Max.P adsorption capacity ranged from 1250-1834 µg g-1. Energy of adsorption varied from 0.223-1.00 µg ml-1, P buffering capacity ranged from 139-243 and P saturation ranged from 0.27-1.59 µmol g-1. Acid although extracted the highest amount of both native and applied P, showed the poorest relationship with relative dry matter and P uptake by rice. The critical level for Olsen P was found 5 mg kg-1 for the coastal soils of Bangladesh. Tidal floodplain soils, on an average of 12 samples, contained 887 mg kg-1 of total P of which only 0.01% remained in solution form, 1.84% in NaHCO3 extractable, 4.24% in NaOH extracted Pi fraction, 46.65% in NaOH Po, 28.19% in acid pool and 18.97% in residual pool. Continuous rice cultivation without P application, decreased the conc. of labile P, moderately labile P and stable P but with the addition of P increased the labile and moderately labile P. The labile P and stable P estimated through plant based approach explained the variability of relative dry matter yield of rice and P uptake better than the soil test approach.