Rice field for the treatment of pond aquaculture effluents
We conducted an experiment to evaluate the efficiency of rice fields in treating pond aquaculture effluent and its responses to different fertilizer treatments. Four treatments was considered in the experiment: no rice planted as the control (CT); rice planted and no fertilizer input (RE); rice planted and a rate of approximately 1.0 g m-1 d-1 potassium chloride application (RK) and rice planted and mineral fertilizer (N: P2O5: K2O = 0.6: 0.5: 0.8) applied before the experiment (RF). Inflow and effluent water from the treatments were monitored weekly. The water quality parameters monitored in this study included: total phosphorus (TP), dissolved phosphorus (PO43--P), total nitrogen (TN), ammonia-nitrogen (NH4+-N), nitrate-nitrogen (NO3--N), nitrite-nitrogen (NO2--N) and chemical oxygen demand (COD). Rice plant height and yield were evaluated at the end of the experiment. Under different fertilizer treatments, high average removal rates of TN, TP and COD were obtained (over 56, 68 and 53%, respectively). They showed no significant differences (p > 0.05), indicating that the rice field could remove the pollutants effectively and the different fertilizer treatments had no impact on the removal efficiencies. However, the different fertilizer treatments showed significant differences in rice yield (p < 0.05). The RF treatment resulted in the highest production of 649.53 ± 94.2 g m-2, followed by RK at 523.83 ± 71.5 g m-2; the fertilizers increased yield by 42.93 and 15.27%, respectively over the RE trial. Rice fields can purify pond effluents efficiently without reducing production when appropriate mineral fertilizers are applied.
Key words: Rice field, pond effluent, nutrient removal.