| Water management of rice production not only concerns food security and water resources conservation,but also influences realization of carbon mitigation and sequestration.Currently,more attention has been paid on the research and application of technologies of watering-saving and high yield of rice production.However,less studies have been reported the effects on dynamics of soil organic carbon(SOC)and its stability by alteration of water management in paddy.Thus,to give an insight into greenhouse gases(GHGs)emission from paddy fields and SOC as affected by water-saving irrigation,and in turn to comprehensively evalvate the carbon mitigation and sequestration,water-saving and balance yield in rice production would be significant.The field experiments were conducted from 2012 to 2014 at an experimental base of modern agriculture demonstration center in the city of Wuxue,Hubei Province.The paddy rice-rapeseed rotation,as one of the major cropping systems in the middle reaches plain of the Yangtze River was selected in the present study.Different water management modes during rice growing season of rice-rapeseed rotation system are designed,including continuous flooding(CF),flooded and wet intermittent irrigation(FWI),flooded and dry intermittent irrigation(FDI),and rain-fed with limited irrigation(RFL).The soil physical and chemical properties,crop production,GHGs(CH4,N2 O and CO2)emission over the whole annual cycle of rice-rapeseed crop rotation,active soil organic carbon fractions(dissolved organic carbon,DOC and microbial biomass carbon,MBC),and different stability SOC pools(fPOM: unprotected free light particulate organic matter,iPOM: physico-chemically protected particulate organic matter in microaggregates,intra-SC: silt and clay protected in microaggregates,and free-SC: silt and clay non-occluded in microaggregates)would be studied as affected by different water managements during rice growing season of the rice-rapeseed rotation system.The results of this study are displayed as follows:(1)Compared with CF,FWI,FDI and RFL irrigation models saved 1%~78%,21%~82% and 54%~82% of irrigation water,respectively.In the drought year(2013),in comparison to CF treatment,the rice grain yields were decreased by 1%,10% and 18% under the FWI,FDI and RFL treatments,respectively.Therein rice grain yield in RFL plots decreased significant due to drought stress.While,there were no significant difference in rice grain yield among all irrigation treatments in the normal year(2012)and rainy year(2014).Moreover,the results indicated that rapeseed grain yield in RFL treatment increased significant in 2013;however,there was no difference in the rapeseed grain yield among water regimes in 2014.During the whole rice-rapeseed rotation system,in 2012-2013,there was no difference in the total crop grain yield among the four water regimes;while,compared to the RFL plots,the total grain yield of crop significantly increased by 16%,15%,and 7% for the CF,FWI and FDI treatments,respectively.(2)The GHG emissions from annual rice-rapeseed rotation systems depended significantly on the water regime practiced during the rice growing season.In contrast with the water regime of CF,during the rice seasons,FWI,FDI and RFL treatments significantly reduced CH4 emissions,while apparently increased N2 O and CO2 emissions.Water-saving irrigations practiced in rice season did not trigger significant CO2 emissions in the following rapeseed season.However,CH4 and N2 O emissions in the following rapeseed season were reduced by FWI,FDI and RFL treatments.Over the entire annual rotation cycle,in comparison with the plots preceded by the CF water regime,the annual cumulative CH4 emissions decreased by 62%,80% and 90% for the FWI,FDI and RFL water regimes on average,respectively;while,the annual cumulative CO2 emissions increased by 8%,28% and 29%,respectively.There was no significantly difference in annual N2 O emissions among four treatments.In terms of the combined global warming potential(GWP)of CH4,N2 O and CO2 as affected by water managements,in comparison to CF treatment,the averaged annual GWP over the whole rotation cycle were significantly decreased by 20%,17% and 21% under the FWI,FDI and RFL treatments,respectively.There was a trade-off between CH4 and N2 O emissions,as well as between CH4 and CO2 emissions,thus further cuts the irrigation water did not significantly reduced the GWP.The water regimes during rice-growing season had a significantly effect on the annual yield-scaled global warming potential(Yield-scaled GWP)of rapeseed-rice rotation system in 2012-2013,FWI treatment had the lowest Yield-scaled GWP,which was 25% lower compared with CF irrigation method,and there were no difference in the annual Yield-scaled GWP between FDI and RFL irrigation strategies.Although the CF increased the GWP compared with the water-saving irrigations,there was no difference in the Yield-scaled GWP for the annual rapeseed-rice rotation in four water regimes in 2013-2014 due to the increase in crop yield.Water-saving irrigation changed soil physical and chemical properties which lead to differences in GHGs emissions,among which the most outstanding contribution factors are soil water content(SWC)and soil DOC.(3)After 3-year water-saving irrigation during rice-growing season of rice-rapeseed rotation system,different stability SOC pools significantly varied across soil layers under different water regimes.The highest amount of SOC is stored in the iPOM fraction in the three water managements at all investigated soil depths,and this fraction contained 35 to 52% of total SOC stored in entire soil profiles(0-5,5-10,10-20 and 0-20 cm).Compared with CF,FWI had no influence on C concentration in iPOM,while significantly increased C stocks in iPOM at 5-10 cm of depth due to its higher percentage in bulk soil mass.RFL apparently decreased C concentration in iPOM and its proportion to bulk soil mass at 10-20 cm layer,further resulted in lower C stocks in iPOM.Water regimes had no effect on C stocks in fPOM and intra-SC.However,when scaled in the whole soil profile(0-20 cm),RFL significantly decreased total SOC stock,and there was no difference between CF and two intermittent irrigation modes(FWI and FDI),or RFL treatment.Hence,the shift of SOC toward iPOM fraction favors the long-term storage of SOC in the paddy field of FWI mode.In conclusion,3-year water-saving irrigations during rice growing seasons were capable of maintaining crop productivity of rice-rapeseed rotation system.In comparison to continuous flooding,the averaged annual global warming potential over the whole rapeseed-rice rotation cycle were significantly decreased under the water-saving irrigations modes;while there was a trade-off between CH4 and N2 O emissions,as well as between CH4 and CO2 emissions,thus further cuts the irrigation water of paddy field did not significantly reduced the global warming potential.In the rice drought season of 2013,the flooded and wet intermittent irrigation exhibited superiority in maintaining rice yields over the flooded and dry intermittent irrigation,thus the flooded and wet intermittent irrigation mode had the lowest Yield-scaled global warming potential in the rapeseed-rice rotation system of 2012-2013.Alternating wetting and drying irrigation by periodicity dry-wet cycles stimulated the formation of microaggregates,led to an increased mass and carbon concentration in the physico-chemically protected particulate organic matter in microaggregates across soil layers to some extent,which eventually led to enhancement of soil total soil organic carbon stability,and accumulation of soil organic carbon in the 0-20 cm soil depth.However,in the 0-20 cm soil layer,the flooded and wet intermittent irrigation had higher soil carbon stock and carbon sequestration potential than flooded and dry intermittent irrigation,meanwhile decreased methane emission during crop growing period.It is an ideal water-saving irrigation mode to realize of carbon mitigation and sequestration in rice-rapeseed rotation system and improve soil.Therefore,from a sustainable agricultural perspective,proper flooded and wet intermittent irrigation could be an effective and safe option for simultaneously ealizing the four goals of saving water,mitigating greenhouse gases,maintaining soil organic carbon stability,and maintaining sustainable rice-rapeseed production at lowlands in Middle reaches of the Yangtze River.Nonetheless,this proper water-saving irrigation needs further research and testing in the long-term experiment. |
PDF Full Text Request