Effects Of Different Mulching Applications On Greenhouse Gas Emissions And Responds On Future Climate

Constant increasing of global anthropogenic greenhouse gas?CO₂,CH₄ and N₂O?emissions,“very likely”could be the main reason for more than half of the global warming.Fragile ecological environment and arid climate in the Chinese Loess Plateau,have made agricultural production in this area seriously affected by global climate change.Thus,to meet the growing food demand,mulching applications like straw and plastic film mulching have been widely used in the Loess Plateau,China.But few studies have focused on straw and plastic film mulching effects on soil gaseous emissions,especially on their long-term effects.Therefore,it is crucial to investigate a mulching practice which could sustain the crop production,mitigate greenhouse gas emissions and sequestrate carbon,with the background of global climate change in the future.In this study,a field experiment with different mulching applications was conducted during 2013-2016,in Yangling,Shaanxi province from the southern Loess Plateau,China,to explore effects of different mulching applications on soil temperature and moisture conditions,winter-wheat and summer-maize yields and soil greenhouse gas emissions.Future climate change data of different scenarios was used on calibrated and validated DNDC model to predict long-term change trends of crop yield and soil N₂O emission and to explore the optimum mulching application which could maintain crop production of the winter-wheat and summer-maize cultivation system,mitigate greenhouse gas emissions while sequestrate carbon as well.The main results of this study are as follows:?1?Straw mulching application could decrease annual mean soil temperature and increase annual mean soil moisture,and significantly increase crop yields during 2013-2014 and 2014-2015.Plastic film mulching could increase annual mean soil temperature and moisture,and significantly increase crop yield during 2014-2015.Both straw and plastic film mulching increased annual soil CO₂ emissions,and soil CO₂ emissions under all treatments significantly and positively correlated to soil temperature?5 cm?.Both straw and plastic film mulching increased annual soil CH₄ absorption,but there was no clear seasonal or annual patterns of soil CH₄ absorption,and no significant correlation between soil CH₄ absorption and soil temperature or moisture.Straw and plastic film mulching significantly decreased annual soil N₂O emissions of 2013-2014,but significantly increased annual soil N₂O emissions of 2014-2015.Meanwhile,there was significant and positive correlation between soil N₂O emissions under plastic film mulching and soil volumetric water content?0-10 cm?.Both straw and plastic film mulching applications possibly significantly increased the global warming potential?GWP?of CH₄ and N₂O,however,they both significantly decreased the greenhouse gas intensity?GHGI?of CH₄ and N₂O eventually.Therefore,promoting crop production is an efficient way to decrease GHGI.?2?Field data during 2013-2015 and 2015-2016 was used to calibrate and validate DNDC model,respectively.Normalized root mean squared error?nRMSE?and determination coefficient?R²?were used to test the applicability of DNDC model in the study area.Results showed that measured and modeled results of crop yields,soil temperature and moisture,and N₂O emissions were in agreement with each other,and indicated that DNDC model could simulate change trends of crop yield and soil N₂O emission under both straw and plastic film mulching practices in Yangling,Shaanxi Province,China.Sensitivity tests were conducted by the validated DNDC via varying each of six factors,i.e.,temperature,precipitation,soil texture,soil organic carbon?SOC?content,nitrogen application amount,and straw amount under straw mulching,in its range commonly observed in the study region while keeping other input factors constant.Results indicated that crop yields of all treatments were mainly related to precipitation;and soil N₂O emissions of no-mulching and straw mulching treaments were largely depended on SOC content,while those of plastic film mulching treatments were mostly decided by nitrogen application amount.?3?Historical climate date during 1961-2005 was used to calibrate and validate down-scaling model SDSM in Yangling,Shaanxi Province,China.Daily climate data under RCP2.6,RCP4.5 and RCP8.5 scenarios during 2006-2100 based on CanESM2 was simulated by calibrated and validated SDSM model.Results showed that it might be warmer and wetter under different climate change scenarios in the study area,and the increases of air temperature and precipitation under RCP8.5 scenario might be significant.?4?Based on RCP2.6,RCP4.5 and RCP8.5 scenarios of CanESM2,DNDC model was used to predict crop yields and soil N₂O emissions of the winter-wheat and summer-maize cultivation system under different mulching applications during 2017-2100,and yield-scaled N₂O emissions were calculated.Results showed that crop yields under different mulching practices would decrease at different levels owing to climate change in the future,and straw mulching had the least decrease and could maintain the current crop production under RCP4.5and RCP8.5 scenarios.While soil N₂O emissions would greatly increase under different mulching treatments,and the highest emisions and increasing rate were both found in straw mulching practices under all three scenatios.Based on yield-scaled N₂O emissions and SOC content?0-10 cm?,straw mulching application would be the optimum mulching application to sustain the crop production,mitigate greenhouse gas emissions and sequestrate carbon of the winter-wheat and summer-maize cultivation system,with the background of global climate change in the future,in Yangling,Shaanxi Province,China.