Effect Of Cover Cropping On Greenhouse Gas Emissions In A Winter Wheat Farmland Under Different Rainfall Patteren

Winter wheat monoculture is one of the main farming system of dry farming region of the Loess Plateau,introduction of cover crop on the effect of soil water content,soil nutrient and crop productivity have been studied systematically,but the effect of greenhouse gas emissions have not been involved.During fallow period?7-9?,which has high precipitation and high variation rate.A rainfall-manipulated winter wheat pot experiment was carried out to study effect of cover cropping on soil greenhouse gas emissions under different rainfall pattern.Two treatment factors as rainfall pattern?ambient and half reduced rainfall?and cover crop?ryegrass,changwu soybean,ryegrass mixed with changwu soybean?and fallow control without cropping?CK?were included in a random completed design.The fluxes of soil CO₂,N₂O and CH₄ were measured by using static chamber gas chromatograph method.The results showed that:?1?During summer fallow period.Soil CO₂ emissions were positively correlated with soil water content and cover crop biomass.Compared with ambient precipitation,half reduced precipitation significantly decreased daily average CO₂ emissions about 33%.Compared with CK,Changwu soybean,ryegrass and mixed daily average CO₂ emissions significantly increased by 140.8%,135.6%and 137.7%respectively,but there was no differencr among cover cropping treatments.Soil N₂O emissions were positively correlated with soil water content,Compared with ambient precipitation,half reduced precipitation significantly decreased daily average N₂O emissions about 17.9%.Compared with CK,Changwu soybean,ryegrass and mixed daily average N₂O emissions significantly decreased by 8%,21.8%and 27.4%respectively.The differences in N₂O emissions between ryegrass with other two cover cropping treatments were significant.Wheras precipitation patteren had no significant effect on CH₄ emissions.Compared with changwu soybean,CK,ryegrass and mixed significantly reduced 65.8%,63.7%and 68.9%soil CH₄ absorptions respectively.?2?During winter wheat period,incorporation of cover crop significantly increased CO₂and N₂O emissions and decreased CH₄ absorptions.Compared with ambient precipitation,half reduced precipitation significantly decreased daily average CO₂ emissions about 18%.Compared with changwu soybean,CK,ryegrass and mixed significantly increased 10%,7%and 9%respectively.In general,Compared with half reduced precipitation,ambient precipitation precipitation significantly decreased daily average N₂O emissions about 33%.divided into three stages,After just incoporation cover crops,the average daily N₂O emissions under ambient precipitation were significantly higher than half reduced precipitation.In the overwintering period,the N₂O emissions decreased and under half reduced precipitation were significantly higher than ambient precipitation.Reviving stage to mature stage,the N₂O emissions increased slightly under two precipitation patterns and had no significant difference.Changwu soybean daily average N₂O emissions were 13.6%,66.7%and 115%higher than CK,ryegrass and mixed respectively.As for CH₄ absorptions,compared with half reduced precipitation,ambient precipitation precipitation significantly increased 7%.Compared with CK,Changwu soybean,ryegrass and mixed decreased13.4%,7.3%and 9.6%respectively.?3?The tested soil was the source of CO₂ and N₂O,but it was the sink of CH₄ CH₄absorptions.Compared with half reduced precipitation,ambient precipitation CO₂cumulative emissions significantly increased 13%,CH₄ cumulative absorptions significantly decreased 13%.global warming potential increased 17%,winter wheat yield increased 18%.Wheras,there was no significant difference in N₂O cumulative emissions,greenhouse gas intensity and carbon balance.Cover cropping strengthened CO₂ emissions,weakened Compared with CK,Changwu soybean,ryegrass and mixed CO₂ cumulative emissions increased 14%,21.3%and16.7%respectively,CH₄ cumulative absorptions significantly decreased 18.9%,14.4%and 12.5%respectively,global warming potential increased 5.6%,10.7%and 6.4%respectively,greenhouse gas intensity increased 27.1%,39.2 and 62%respectively,wheras winter wheat yield reduced 17.4%,20.1%and 34%respectively.cover crop treatments reduced the winter wheat yield and increased the global warming potential.comprehensive assessment,CK can reduce the global warming potential while increasing the subsequent grain yield under ambient precipitation pattern.