The Effect Of Reducing The Application Of Nitrogen Fertilizer On The Greenhouse Gas Emissions From Farmland Soil After Straw Returning To Field

Studies on the emissions of greenhouse gases and net global warming potential??GWP?in winter-wheat field under different modes of straw return with reduced N application is benefical to evoluate the effects of straw return and reduced N application on mitigating global warming,which is also helpful to establish measures to reduce GHG emissions.The field trial was carried out in one wheat growing season from September2015,which included a set of nine different treatments made from three modes of straw return?CK-no straw return,MS-mushroom-cultivated straw return and DS-direct straw return?and three N levels(210,255 and 300kg·hm^-2).CO₂,CH₄ and N₂ O fluxes in winter-wheat field under nine treatments were measured by using a static chamber-gas chromatograph technique,and total GHG season emissions were also estimated.Meanwhile,the amount of fuel consumed by farm machines,power consumed during irrigation,fertilizer application and straw burned were recorded and transformed to CO₂ equivalent by using a transformation coefficient.Crop yield and biomass were measured to calculate NPP.The net GWP under nine treatments were estimated based on the identified parameters of greenhouse effect.The results showed that winter-wheat field served as the source of CO₂ and N₂ O,and also the sink of CH₄.The emisson of CO₂ was significantlyincreased in DS and N3 treatments.The uptake of CH₄ was suppressed in MS treatments,and it was opposite in N₁ treatments?P>0.05??Direct straw return or less N application reduced the emissions of N₂ O.The grain yield was significantly increased by16.1% or 14.3% in MS or DS intreatments?P<0.01?.While there was no significant difference under different N application?P>0.05?.The indirect emissions of GHG caused by Farmland management measures accounted for one third of the direct emissions of GHG,which should not be ignored.The ?GWP in MS and DS treatments were were both negative(-14174 and-11565 kgCO₂·hm^-2,respectively),which indicated that farmland ecosystems under MS and DS intreatments served as GHG sink.Considering that less N application didn't reduce the grain yield,so mushroom-cultivated straw return or direct straw return with the N level of 210 kg·hm^-2 is suggested for winter-wheat farmland ecosystem,which is the best combination to mitigate global warming.