Phosphorus Loss into Ground Water in Paddy Soils as Influenced by Irrigation System and Rate of Added-P

A field experiment was carried out in delta Nile region of Egypt, to elucidate the impact of irrigation system and graded phosphorus fertilizer rates on P loss into ground water in paddy soils (heavy clay soil). Three irrigation system were used: submergence with continuous head of water (about 8 cm), irrigation with saturation percent and discontinous irrigation where soil was irrigated every 7 days. The rate of applied P were 45 and 90 Kg P2O5/acre as super phosphate. Values of dissolved reactive phosphorus (DRP) in ground water increased under saturation and discontinuous irrigation compared to it under submergence condition (e.g.,0.25,0.18 and 0.14 mg P/L, respectively) under 90 Kg P2O5 /ac. and after 15 days of added-P. Accumulation values of DRP in ground water after 105 days at 90 Kg P2O5 /ac. of added-P were 1.18,0.76 and 0.67 mg P/L under saturation, discontinuous and submergence irrigation methods, respectively. The rate of loss for DRP in ground water was the highest under saturation method at 90 Kg P2O5 /ac. ( 0.01 mg P/L/day). Results also showed that, accumulated total phosphorus (TP) at the end of ground water collection (105 days after transplanting) when 90 Kg P2O5 /ac. was added were 2.78,2.18 and 1.69 mg P/L under discontinuous, saturation and submergence irrigation system, respectively. Also, the rate of loss for TP was the highest under discontinuous irrigation condition (0.025 mg P/L). These results indicated that, increasing added phosphorus fertilizer let to increasing P loss into ground water by leaching through the soil profile.In addition, phosphorus loss into ground water was increased with decreasing added water for irrigation in paddy soils (increasing drought regime) and that was not expected