Effects Of Different Rotation Systems And Cultivation Modes On Greenhouse Gas Emissions And Nitrogen Balance In Rice Field

Rice is one of the most important food crop in the world.With the increase of global population and the improvement of dietary structure,global demand for agricultural crops is increasing.To cope with this pressure,chemical fertilizers have been increasingly used in rice fields.However,the excessive use of nitrogen(N)and the waterlogging condition of rice fields leads to increased N loss to the ambient environment and enhanced greenhouse gas(GHG)emissions,which threat to security of the ecological environment.Nowadays,reducing GHG emissions and N losses from rice fields without decreases crop production has become the focus of people's attention and the problem of agricultural production.Therefore,an understanding of the trade-offs between crop productivity,GHG emissions and N losses is an essential requirement for the development of sustainable strategies that aim to improve crop yields to meet food demand and to mitigate GHG emissions and N losses to protect the environment.This experiment was conducted with two rice cultivation modes(CM)of integrated rice-duck farming(IRDF)and conventional farming(CF)under four rotation systems(RS):rice-wheat rotation with annual straw incorporation(RWS),rice-wheat rotation with annual biogas residues incorporation(RWB),rice-green manure rotation(RGM)and rice-fallow rotation(RF).A 2-year split-plot field experiment was performed to evaluate the effects of different RS and CM on surface water and soil characteristics,rice yield and root traits,methane(CH4)and nitrous oxide(N2O)emissions and N balance in rice season.The main results were shown as following:1.The surface water and soil characteristics were obviously affected by different RS and CM.Compared to traditional RWS system,RWB,RGM and RF systems increases the dissolved oxygen(DO)content in surface water and soil redox potential(Eh).Among different RS,the highest total N and ammonium N content in surface water of paddy were found in RF system,and then was RWS,RWB and RGM system.And the highest total soil organic carbon content and active organic carbon content of rice field were found in RWS system.Compared to CF,IRDF increased the DO and soil Eh,and decreased the total amount of reductive matter.Moreover,IRDF enhanced the N content in surface water,soil ammonium N content,active organic carbon content and soil urease activity.2.Across the two rice season,the RWB system showed the highest rice yield(9.94 kg·ha-1),and significantly higher than the RWS and RF systems.The order of rice yield among different RS is RWB>RGM>RWS>RF.Compared to CF,IRDF increased the rice yield by 0.76%?2.43%,and obviously improved the harvest index,indicating that IRDF enhances translocation of photosynthate to grains.For root traits,RWB and RGM systems increased the root activity in each period,and RWB improved the roots radial oxygen loss(ROL)at effective tiller critical leaf stage,when compared to RWS and RF systems.Among two rice cultivation modes,compared with CF,IRDF significantly increased the deep root ratio(DRR)and ROL in each period,and root activity after elongation stage.3.The RWS system showed the highest total CH4 emissions(261.59 kg·ha-1)in rice season,and then was RGM,RWB and RF system,and the difference was significant among the four RS.On the contrary,the lowest total N2O emissions were found in RWS system,and the order of total N2O emissions among different RS is RGM>RWB>RF>RWS.Compared to CF,IRDF reduced the total CH4 emissions by 8.80%?16.68%,while increased total N2O emissions by 4.23%?15.20%.In addition,both RWB,RGM or RF systems and IRDF mode contribute to mitigates the global warming potential(GWP)and yield-scaled GWP.The correlation analysis showed that DRR,ROL,DO,soil Eh and soil organic carbon were important factors for CH4 emission,while N2O emission were closely related with root bleeding rate,ROL,easily and dissolved organic carbon content.4.In this study,rice plant uptake,ammonia volatilization and soil residual is the main fertilizer-N fate,while the loss by leaching and run off is relatively low.Results showed that the nitrogen use efficiency(NUE)was 33.09%?40.90%,and the fertilizer-N loss by ammonia volatilization,leaching and run off were 13.23%-21.14%,1.28%?1.85%and 1.57%?2.75%,respectively,while the soil residual rate was 19.01%?23.95%.Compared to traditional RWS system,RWB and RGM systems improved the NUE and soil residual rate,and reduced the amount of N loss.Moreover,IRDF enhanced the NUE while obviously decreased the rate of fertilizer-N volatilization,when compared to CF.