Impact Of Straw Return With Different N Rates On Carbon Sequestration And Emissions Reduction In A Spring Maize System And Model Simulation

In response to the problems of excessive application of nitrogen fertilizer and unreasonable application of chemical fertilizer with straw to spring corn in northeast China,which led to increased greenhouse gas emissions and decreased soil organic carbon content.To study the effects of straw return combined with chemical N（N）fertilization on spring maize yield and N use efficiency（NUE）as well as the potential of reducing chemical N input and carbon sequestration and greenhouse gas（GHG）emission reduction under long-term straw return,aiming to provide a theoretical basis for high use efficiency of nutrient resources and low-carbon agricultural production in Northeast China.A field experiment was established under straw return and straw removal with different N fertilizer application rates（0,70,140,210,280 and 350 kg/hm²）,respectively,in Gongzhuling City,Jilin Province from 2017 to 2022.The effects of different N management treatments on spring maize yield,NUE,soil inorganic N,soil organic carbon（SOC）and nitrous oxide（N₂O）emissions were analyzed.The impacts of long-term straw return for 30 years（1991～2020）on the yield,NUE and the potential for reducing N fertilizer input under climate change scenarios were simulated using the verified denitrification-decomposition（DNDC）model based on the field observations.The main results are as follows:（1）Both chemical N fertilization and straw return significantly increased the yield and N uptake of spring maize,increased the contents of soil inorganic N and SOC.Straw returning treatment reached the maximum yield at 210 kg/hm² N application rate,and straw removal treatment reached the maximum yield at 280 kg/hm² N application rate.Under the same n application rate,maize yield,nitrogen absorption,soil organic carbon and soil inorganic nitrogen under straw returning treatment increased by 14.2%,17.1%,11.9%and 17.8%,respectively,compared with straw removal treatment.Compared with straw removal treatment,returning straw to field increased N₂O emission by 5.7%～18.0%.（2）After calibration,the DNDC model can well simulate the spring maize yield,biomass,N uptake,and soil inorganic N content under straw return and straw removal with different N rates.The normalized average relative errors（n ARE）between the simulated and measured values were-8.7%～17.5%,and normalized root mean square errors（n RMSE）were 3.2%～23.4%.The DNDC model can well simulate the N₂O emission flux,the normalized average relative errors（n ARE）between the simulated and measured values were-16.9%～11.3%,the fitting index（d）were 0.88～0.93,indicating that the model can reflect the actual pattern of crop growth under different fertilization treatments.（3）Long-term simulation showed that when the maximum yield at the optimal N application rate was reached,the maize yield,N recovery efficiency,agronomic efficiency,and partial productivity of N under straw return increased by an average of 5.6%,5.6%,0.5 kg/kg,and 8.0kg/kg,respectively,relative to straw removal,while the average N surplus rate decreased by an average of 45.4%.When obtaining the same maximum yield with the straw removal treatment,the average reduction in chemical N fertilizer input under straw return would reach 36.5 kg/hm²and the average substitution rate of straw return would reach 18.6%.The reduction in chemical N input first increased and then decreased with the increasing duration of straw return and then reached a plateau level.The highest average substitution rate of chemical N fertilizer was 25.1%under 6-15 years of straw return.Additionally,the highest average substitution rate of chemical N fertilizer under straw return was 22.7%in the wet year,17.3%in the normal year and the lowest（15.4%）in the dry year.In summary,straw return in spring maize mono-cropping system in Northeast China improved spring maize yield and soil nutrient content,promoted SOC sequestration,and reduced Net GHG emissions.The DNDC model is suitable to simulate spring maize growth and soil nutrient dynamics in Northeast China.According to the simulation of DNDC,compared to the treatments without straw return,the yield and NUE of spring maize under long-term straw return are significantly higher,while the N fertilizer input and N surplus rates are significantly lower.The N fertilizer application rate under straw return could be reduced by 10%～20%,which can maintain the yield of spring maize and improve the nutrient utilization efficiency.The results of this study can provide practical reference and technical support for the optimal application of N fertilizer combined with straw return in the spring maize fields in Northeast China.