Study On Rice Field For The Treatment Of Pond Effluents

Aquaculture effluents can contribute to several serious problems to environment. Rice field appears to be a good alternative for the disposal of pond effluents.In order to investigate the removal efficiency and its response on different fertilizer treatments concerning the rice field for pond effluent treatment,an experiment with four treatments was conducted in a series of cement tanks(4.1m×6.7m×1.0m):without rice planted as the control(CT);rice planted and no fertilizer input(RE);rice planted and about a rate of 1.0 g m^-1 d^-1 potassium chloride application(RK);rice planted and mineral fertilizer(N:P₂O₅: K₂O=0.6:0.5:0.8) applied before the experiment(RF).Twenty days after transplanting, about 15.0cm pond effluents were pumped into tanks draw off antecedently at 8:00-9:00 AM every day.Inflow and effluent water from the treatments were monitored weekly. The evaluated water quality parameters were:total phosphorus(TP),dissolved phosphorus(PO₄^3--P),total nitrogen(TN),ammonia-nitrogen(NH₄⁺-N),nitrate-nitrogen (NO₃^--N),nitrite-nitrogen(NO₂^--N) and chemical oxygen demand(COD).Evaluations for plant height,panicles per plant,spikelets per panicle,thousand-grain weight,filled-grain percentage,yield and dry matter were performed at the end of the experiment,both effluent-treating fields and the control field(no fertilizer application,no water exchanged and its water level maintain 15.0cm throughout the experiment) and the traditional field (fields cultivated by local farmer in traditional manner).The main conclusions drawn from this study conducted in 2007 and 2008 were as follow:(1) Pond effluents were polluted seriously,and it was necessary to be purified before discharged or re-used.(2) Rice field could remove the nutrients from pond effluents effectively;RE(TP: 68.69%,PO₄^3--P:42.64%,TN:36.43%,NH₄⁺-N:59.01%,NO₃^--N:24.85%,NO₂^--N: 70.38%,COD:53.78%),RK(TP:69.25%,PO₄^3--P:55.66%,TN:42.49%,NH₄⁺-N: 65.78%,NO₃^--N:24.77%,NO₂^--N:66.67%,COD:54.81%),RF(TP:65.95%,PO₄^3--P: 26.67%,TN:41.40%,NH₄⁺-N:57.59%,NO₃^--N:28.01%,NO₂^--N:71.04%,COD: 53.27%).There were no statistical differences in removal efficiency along different fertilizer treatments(p＞0.05),indicating that fertilizer treatments had little impact on nutrient removal.(3) The temporal courses of nutrient removal efficiencies were bound up with the nutrient loadings evidently,and the relation to rice growth period was inconspicuous.(4) Nitrogen and phosphorus nutrients provided by pond effluents solely can not meet the demand of rice crop fully.Though potassium application during the experiment cannot increase the yield constitutes(p＞0.05),it could improve the yield and dry matter significantly(p＜0.05).Basic mineral fertilizer application before the experiment could increase plant height,panicles per plant,spikelets per panicle,yield and dry matter significantly(p＜0.05).(5) Pilot experiments showed that the rice field dealing with pond effluents had a certain decline in grain yield(16.1%),while the Economic benefit of pond increased by 22.2%as a result of the survival rate and growth rate improved for the good status of water quality,on the whole,the rice field-pond had significant economic and ecological benefits.