Changes In Crop Productivity And Greenhouse Gas Intensity With Straw Return Conditions Under Maize Wheat Rotation System From Central China

Recently,the concentration of greenhouse gas has increased at atmosphere,which already become a focus worldwide.Climate change mitigation,promotion of green-agricultural and low-carbon have become the mainstream all over the world.As an important source of greenhouse gas emissions,the farmland ecosystem has been increasingly taken seriously for agricultural carbon sequestration and greenhouse reduction.Produced from agricultural waste such as crop straw and woods,biochar is a rich carbon product.Its agricultural use has been already recognized by researchers at home and abroad.However,few studies were about the integrated warming effects under straw biochar treatment with the reduction of N application.In this study,therefore,one typical dryland(cinnamon soil)in North China Plain was selected.Two field trials were conducted.Trail 1St,the comparison between different biochars of straw sources,was including treatment of none fertilizer(CK),wheat straw biochar with N(WCN1)or without N(WCNO)and maize straw biochar with N(MCN1)or without N(MCNO).Trail 2nd,comparison of straw return and biochar return,was including treatment of straw return with total nitrogen(SN100),reduction of 10%nitrogen(SN90),reduction of 20%nitrogen(SN80);biochar return with total nitrogen(BN100),reduction of 10%nitrogen(BN90),reduction of 20%nitrogen(BN80).Effects of straw return and biochar return with different levels of nitrogen fertilizer as well as the different biochars on soil properties,crop yield and greenhouse gas emissions in wheat-maize rotation.The main results are as follows:(1)Soli properties:Compared to CK,content of SOC,TN,NO3--N,available P and available K significantly increased for Biochar of wheat straw(BCW)and biochar of maize straw(BCM),but soil bulk density significantly decreased.Except a significant increase by 16.01%of available K,no significant effect on other physical and chemical properties.Soil microbial biomass,associated with growing stage,increased from seeding stage to elongation stage,and descended to maturing stage.Except the heading stage in the following maize season,soil microbial biomass of BCW significantly increased 24.68%compared to that of BCM,while the others showed no significant differences.(2)Crop yield and AEN:BCW and BCM,with and without N fertilizer,had a higher crop yield than CK.Without N fertilizer,there were no significant differences between BCW and BCM in the maize yield,while BCM had a significant increase by 12.34%than BCW in the yield of wheat.With N fertilizer,the following maize yield of MCN1 was 9.18%larger than that of WCN1,the others had no significance.Response of BCW and BCM to yield and AEN was different.Nonetheless,AEN of MCN1 was higher in maize season while AEN of WCN1 was on the contrary.(3)Greenhouse gas emissions and comprehensive greenhouse influence:with or without N fertilizer,N2O and CH4 emissions had no significant difference between BCW and BCM.Emissions of CO2 increased by 24.72%under MCNO than WCNO in the following maize season,while no difference was between BCW and BCM in other conditions.Without N fertilizer,the GWP and GHGI in the first maize season of WCNO significantly decreased by 23.16%and 13.70%respectively compared to MCNO.While with N fertilizer,no significance was between WCN1 and MCN1 in the GWP and GHGI.(4)There was significant difference in the effects of straw return and biochar return with reduction of N fertilizer on soil properties and crop yield.Compared with the conventional straw return directly,biochar return could improve content of soil organic carbon(SOC)significantly with 13.37%～16.79%.Compared with conventional soil total nitrogen(TN),in the reduction of 10%N fertilizer,no significant difference existed between two ways;in the reduction of 20%N fertilizer,straw return on TN decreased significantly,while biochar return showed no difference.Moreover,with the reduction of 10%and 20%N fertilizer,biochar return could get the same level of maize and wheat yield,however,straw return could also get the same maize yield,with the reduction of 20%N fertilizer,and its wheat yield significantly decreased by 6.42%.(5)Effects of straw return and biochar return with reduction of N fertilizer on soil greenhouse gas emissions and comprehensive greenhouse effect:N2O,CO2 and CH4 emissions dynamics in dryland varies according to gas species.Both returns decreased emissions of N2O with the reduction of N fertilizer season.Compared to the total N fertilizer treatment(SN100),except the SN90 in the first maize season with no significance,N2O emissions of straw return,with a reduction of 10%and 20%N fertilizer in the maize and wheat season,could be reduced by 32.14%～36.90%.While N2O emission of all biochar returns with the reduction of 10%and 20%N fertilizer could be significantly reduced by 36.90%～54.25%.The CH4 emission dynamics had no significance between two returns with the reduction of N fertilizer in three crop season,and mainly showed weak absorptions.With reductions of N fertilizer,CO2 emission of straw return increased,while CO2 emission of biochar return decreased.The decline of GHGI of crop production could be caused by reduction of N fertilizer.Compared to the GWP and GHGI of SN100,for straw return during the three crop season,no significance with SN90,but a significant decrease was in the wheat seasons by 38.79%and 36.40%for SN80,respectively.However,reduction of N fertilizer for biochar return,both GWP(52.06%～54.63%)and GHGI(52.19%～53.51%)in the maize season and GWP(40.87%～52.08%)and GHGI(40.48%～42.86%)in the wheat season could decreased greatly.Compared to corresponding straw return treatment,N2O emission,GWP and GHGI of biochar return all decreased with the reduction of 10%and 20%N fertilizer..Therefore,in the wheat-maize rotation,for BCW and BCM,not only MCNO could increase wheat yield compared with WCNO without N fertilizer,but also MCN1 could increase maize yield compared with WCN1 with N fertilizer.AEN of them varied with crop types.With the reduction of N fertilizer and the insurable crop yield,biochar returns could still get the reduction of 20%N fertilizer,while straw return could achieve just 10%.Moreover,biochar returns could reduce emission of greenhouse gas and the comprehensive warming effect.