Response Of Greenhouse Gas Emissions In Winter Wheat Field To Water Regulation Under The Ridge-furrow Mulching System With Supplementary Irrigation

High emissions of greenhouse gases?CO₂,CH₄,and N₂O?are the main cause of global warming and various associated environmental problems.The fourth IPCC assessment report indicated that agriculture is the second largest source of greenhouse gases,where it accounts for about 13.5%of global man-made emissions and the levels are increasing.In recent years,the ridge-furrow mulching?RF?system and supplementary irrigation have been used widely in arid and semiarid areas where water resources are scarce as a new water-saving and high-efficiency irrigation technology because it significantly increases the soil temperature and moisture content.However,mulching with plastic film can improve the crop yield by increasing the soil water and temperature but it may also exacerbate greenhouse gas emissions.In this study,in order to explore the the effects of soil respiration and N₂O emission characteristics and their influencing mechanisms,greenhouse gas emissions and global warming potential?GWP?in winter wheat fields under the ridge-furrow mulching system?RF?with supplementary irrigation,three rainfall conditions?heavy rainfall=275 mm,normal rainfall=200 mm,and light rainfall=125 mm?and four irrigation treatments?150,75,37.5,and 0 mm?were simulated during the growth period.Traditional flat planting?TF?was used as the control and we determined the emissions of N₂O,CO₂,and CH₄ and their influencing factors,as well as the GWP and greenhouse gas emission intensity?GHGI?.The main findings are as follows:?1?The soil respiration rate did not differ significantly between the ridge-furrow mulching system and traditional flat planting under rainfall at 275 mm during the winter wheat growth period.Under rainfall at 200 and 125 mm,the soil respiration rates with different irrigation amounts were 12.59%-27.69%and 2.16%-22.20%higher with the furrow-ridge system than traditional flat planting,respectively.Path analysis showed that the effect of the soil temperature on soil respiration was greater than that of the soil moisture content.Under rainfall at 275,200,and 125 mm,the coefficients of determination for the effects of the water temperature and water content on the soil respiration were lower with the ridge-furrow mulching system than traditional flat planting.The coefficients of determination also tended to increase as the amounts of rainfall and supplementary irrigation decreased.?2?The RF system with supplementary irrigation can increase soil microbial respiration in the 0-20 and 20-40 cm soil layers of winter wheat fields.Under the condition of 275 mm rainfall in winter wheat growth period,compared with TF,the average soil microbial respiration intensity of RF increased by 2.47%-21.67%and3.28%-7.10%in 0-20 and 20-40 cm soil layers under the same supplementary irrigation amount,respectively.Only the treatment without supplementary irrigation reached significant difference in the surface layer.Under the rainfall conditions of 200 and 125mm,in 0-40 cm soil layer,when the supplementary irrigation amount?75 mm,the soil microbial respiration of RF increased by 2.29%-14.29%?the treatment of 150 mm supplementary irrigation?and 3.25%-16.67%?the treatment of 75 mm supplementary irrigation?than that of TF,respectively.However,there was no significant difference between the treatments.When the supplementary irrigation were 37.5 and 0 mm,the soil microbial respiration of RF increased 4.08%-34.62%and 7.90-36.00%than that of TF,respectively,which reached a significant difference in the later stage of winter wheat growth.?3?At 275 mm rainfall during winter wheat growth,compared with those of TF,the N₂O emission flux of RF treatment decreased 21.62%-30.72%?P<0.001?,soil water content increased by 6.26%-8.82%?P>0.05?,available nitrogen content decreased by1.71%-16.24%?P>0.05?,and the content of denitrification enzyme increased by 0.2%-24.16%under rainfall at 275 mm during the winter wheat growth period,respectively.Under the condition of 200 and 125 mm rainfall,compared with the TF,the N₂O emission flux increased 3.66%-12.46%and 6.08%-15.57%respectively?P>0.05?,soil water content increased by 6.13%-11.49%and 8.05%-13.88%,soil available nitrogen content decreased by 11.0%-21.42%and 19.93%-34.44%,and the content of denitrification enzyme increased by 0.01%-24.08%and 0.03%-20.79%under RF,respectively.The results of principal component analysis?PCA?showed that the main factors affecting N₂O emissions in the RF are soil moisture content and soil available nitrogen content,both of which can explain the N₂O emission flux 94.37%.However,the main factors affecting the N₂O emissions in TF were soil moisture content and content of nitroglutase.They can explain 85.81%of N₂O emission flux.?4?At 275 mm rainfall during winter wheat growth,when the amount of irrigation was the same,the CO₂ emission flux under RF increased by 5.93%–6.45%,the N₂O emission flux and GHGI decreased by 3.30%–23.78%and 5.01%–23.72%,respectively,compared with those under TF.At 200 and 125 mm rainfall during winter wheat growth,compared with those under TF,the N₂O emission flux under RF increased by 4.18%-10.8%?5.05%-13.53%,the CO₂emission flux increased by 7.83%-13.72%?17.49%-32.46%under the same level of supplementary irrigation,respectively.The GHGI significantly decreased by 25.57%–35.35%and 6.22%–30.20%,respectively.Under the three rainfall conditions,the absorption of CH₄ in the winter wheat field increased as the supplementary irrigation decreased.In a comprehensive consideration,under heavy rainfall conditions during the winter wheat growth period,RF and irrigation at 75 mm reduced the amount of water used and increased the yield compared with TF and irrigation at 150 mm,as well as reducing GHGI by 5.39%significantly.Under normal rainfall conditions,compared with TF of irrigation 150 mm,RF with supplemental irrigation at 150 mm did not significantly increase GHGI and it obtained a higher yield,supplemental irrigation at 75 mm can reduce GHGI while ensuring that yield does not decrease and save water.Under conditions with less rainfall,applying supplemental irrigation at 150 mm and RF can ensure that a good crop yield is obtained,while also increasing GHGI.The results are of great significance for predicting the emission trends of CO₂ and N₂O under the conditions of future climate change and formulating corresponding emission reduction measures for farmland water management.At the same time,under the premise of saving water,it can provide a theoretical basis for farmland greenhouse gas emission reduction and the establishment of a high-yield crop system.