Impacts Of Rice-fish Coculture On The Concentrations And Ecological Stoichiometry Characteristics Of Nutrient Elements In The Water Of Aquaculture Pond

Pond culture plays an important role in the fish aquaculture in china.The intensive aquaculture pattern characterized by high density and feeding quantity is widly adopted by fish famers in order to improve the yield which leades to serious eutrophication pollution.Rice-fish coculture has a great potential in improving the nutrient use efficiency and in reducing aquaculture pollution.Rice-fish coculture in aquaculture pond is a new mode of rice-fish system.It is still unclear the impacts of this new system on the concentration and ecological stoichiometry of nutrient elements in the water of aquaculture pond.Therefore,we conducted a field experiment to investigate the impacts of this new rice-fish system on the concentration of carbon（C）,nitorgen（N）and phosphrous（P）and their ecological stoichiometry in the water of aquaculture pond.Furthermore,a pot experiment was conducted to study the response of C/N/P ratios to P addition.We hoped that the results of this study would provide a reference for the improvement of nutrient management of rice-fish coculture system.The primary results were as follows:（1）Rice-fish coculture in pond significantly improved the water quality.Rice-fish coculture significantly mitigated the contens of total N（TN）,ammonium N（NH₄⁺-N）,nitrite N（NO₂^--N）,total P（TP）by 49.9%,65.1%,38.4%and 61.0%as compared to fish monoculture,respectively.Rice-fish coculture also had a significantly effect on the basic properties of the water in pond.The contents of BOD,COD,TSS,turbity,DO and pH were significantly lower in rice-fish coculture pond than fish monoculture pond.（2）Rice-fish coculture significantly enhanced the C/N,C/P and N/P values in comparison with fish monoculture.The value of C/N was higher in the water of rice-fish coculture pond than fish monoculture pond during the whole culture season,indicating that rice-fish co-culrue reduced more N than C in the water.The C/P value was also higher in the water of rice-fish coculture pond than fish monoculture pond especially from August to September.The mean value of C/P in rice-fish coculture pond was increased by 124%.And the mean valued of N/P was also significantly enhanced（by 45%）in rice-fish coculture pond.（3）The addition of P tended to raise the mitigation effect of rice-fish coculture on the contents of C and N in the water.The effect of P addition was affected by its amount.Only the treatment of 50%P addition（RFP1/2）significantly reduced the content of TOC in the water.The treatments of 25%and100%P addition（RFP1/4 and RFP）did not show significant effects on the TOC content.P addition increased the TN content in the water during the early stage of coculture season,but reduced TN during the late stage,resulting in no significant impact on the mean contents of TN during the whole coculture season.However,P addition significantly reduced the nitrate in the water especially under the treatments of RFP1/4 and RFP1/2.The contents of TP and dissolved P did not show significant difference among three P addition treatments and no P addition treatment.（4）P addition significantly reduced the value of N/P in the water of rice-fish coculture pond,but did not affect the value of N/P in the rice and fish.The ratios of C/P and C/P were less in the water of three P addition treatments than no P addition treatment.However the reductions were not significant.The ratio of N/P was also reduced by P addition,especially under the treatment of RPF1/4.The N/P value of RFP1/4 was reduced by 37.4%than no P addition treatment.There was no significant difference in the N/P of rice and fish among three P addition treatments and no P addition treatment.（5）P addition enhanced the rice yield and the accumulation amounts of N and P;but did not significantly influence the fish yield.The biomass of rice stem and grain and the accumulation amounts of N and P were enhanced by three P treatments,especially under the RPF1/4 treatment.Rice-fish coculture significantly raised the total fish yiled and the mean biomass per one fish.However,P addition did not furtherly raise the fish yiled.There was no significant difference among the fish yields of three P addition treatments and no addition treatment.