Effect of high phosphate fertilization rate on pond phosphate concentrations, chlorophyll a, and fish growth in carp polyculture

The effect of different application rates of triple superphosphate (22.4, 44.8, and 67.2 kg P2O5 ha(-1)) was observed on total and available phosphorus concentrations in pond soil, total and filterable orthophosphate concentrations in pond water, chlorophyll a, and fish growth in a carp polyculture system during summer (22-32A degrees C) months to determine the economical dose of P2O5. pH, hardness, calcium and alkalinity of soil and water did not differ significantly among treatments (P > 0.05) and were within the desired ranges. Average total phosphorus concentrations in pond soil were not significantly different between treatments but available phosphorus (P > 0.05) in pond soil, total phosphorus (P > 0.001), and filterable orthophosphate (P > 0.0001) concentrations in pond water, chlorophyll a (P > 0.0001), and net fish production (P > 0.01) were significantly higher in fertilized ponds than in controls. Overall, fish yield did not significantly differ among treatments, suggesting that a very high dose of P2O5 may not be necessary for high yields. Reducing the dose of P2O5 could reduce cost without reducing fish production.