Effects Of Rice-duck Farming On Rice Field Environment And Its Benefit Evaluation

Integrated rice-duck farming is one of important measures of ecological agriculture.The farming system utilizes the mutualism of duck and rice based on ecological priceples.Recently,much research reported effects of the farming on soil fertility,greenhouse gas?GHG?emissions,aquatic organism and rice growth,but few studies focused on economic and ecological benefits based on GHG emissions under the rice-duck farming system.Therefore,a field experiment was conducted in central China to assess effects of the rice-duck farming on N and P content of soil and floodwater,aquatic organism and GHG emissions,and also to evaluate the economic and ecological benifites.The results of this study provided scientific basis for realizing green and sustainable agriculture.The results were shown as below.?1?Integreted rice-duck farming significantly improved soil oxidizability,enhanced soil enzyme activity and increased soil inorganic N contents.Compared with conventional rice culture?R?,rice-duck culture?RD?significantly increased Eh by28.8⁴4.0 mV,urease activity by 28.3%⁴8.3%,dehydrogenase activity by27.2%³0.3%,catalase activity by 13.3%¹56.2%,and protease activity by19.9%²7.6%,and thus enhanced NH4⁺-N,NO₃^--N and microbial N contents by32.5%⁴2.7%,24.6%²6.2%and 12.6%¹6.7%,respectively.?2?Integreted rice-duck farming significantly improved dissolved O2?DO?content,and increased floodwater N and P concents.Compared with R,RD increased floodwater DO content by 20.0%²2.0%,total N content by 81.1%¹01.1%,NH4⁺-N content by45.4%⁸0.0%,NO3^–-N content by 11.8%¹8.3%,and total P content by 32.7%⁴1.2%during the period of rice-duck co-culture.?3?Integreted rice-duck farming significantly reduced algal and protozoa biomass,and decreased algal diversity.Compared with R,RD significantly decresed the species of Chlorophyta and Cyanophyta by 21.3%²6.7%and 29.9%³2.9%,the biomass of Bacillariophyta,Chlorophyta and Cyanophyta by 46.7%⁵2.9%,27.1%²9.0%and13.6%⁴7.1%,respectively,and thus reduced Simpson index by 11.6%²4.5%and Shannon index by 9.9%²1.3%.Moreover,the biomass of Protozoa,Rotifer,Cladocerans and Copepods under RD was markedly decreased 36.1%⁴8.2%and34.6%⁴1.0%relative to R,respectively.Correlation analysis indicated that the species and biomasses of Bacillariophyta,Chlorophyta,and Cyanophyta were significantly negatively related to several forms of N and P contents,and the species and biomasses of Euglenophyta were significantly positively correlated with several forms of N and P contents.?4?Integraed rice-duck farming significantly affected N2O and CH4 emissions,and GWP subsequently.RD significantly increased N2O emissions by 6.1¹5.5 fold,reduced CH4 emissions by 32.0%³2.7%,and thus GWP by 28.0%relative to R.Compared with R,RD increased rice gain yield by 2.7%³.6%,and thus decreased GHGI by41.3%⁴4.8%.Structural equation model anlysis indicated rice-duck system affected GHG emisisons by three paths.Firstly,the activities of ducks improve floodwater DO content and soil Eh due to controlled aquatic organism growth and improvement of exchange between the soil and the atmosphere.Secondly,the excretions of ducks enhance soil inorganic N content,which provides the substrates of nitrification.Thirdly,the activities of ducks eat the old and ill leaves of rice and control unproductive tillers,and promote rice growth.These three processes therefore affect N2O and CH4 emissions from the rice-duck system.?5?Economic and ecological benefits?EB?of different treatments showed that RD could increased economic benefits by 37.8%³9.2%,and net ecosystem economic benefits?NEEB?by 39.7%⁴0.8%.In summary,the integrated rice-duck farming can effectively increase available nutrient contents of soil and floodwater,improve soil oxidizability,and significantly mitigate CH4 emissions and GWPs.Moreover,the system can control weeds and aquatic organism growth,enhance rice grain yield,and thus increase economic and ecological benefits.Therefore,our results suggest that the farming is a key approach for realizing agricultural supply-side reform in China,and is also an important model of developing green agriculture and revitalizing rural areas.