Effects Of Combined Application Of Biochar And Chemical Fertilizer On Greenhouse Gas Emissions And Crop Nitrogen Use In Wheat-maize Multi-cropping Field

Emission reduction and efficiency enhancement are important goals of current green agricultural production in China.As a soil amendment,biochar can improve soil physical and chemical properties,enhance crop nitrogen utilization efficiency,increase crop yield,and is important for mitigating greenhouse effect and preserving and maintaining sustainable development of farmland.However,the effects of biochar with chemical fertilizer on greenhouse gas emissions and crop nitrogen utilization are not clear.In this study,a two-factor interaction experiment between biochar and chemical fertilizer application was conducted from 2020 to 2021 in Guanzhong area wheat-maize multi-cropping farmland,in which two levels of biochar:B(4 t ha^-1 biochar application)and NB（no biochar application）;four levels of chemical fertilizer ratios:no fertilizer application（CK）,nitrogen fertilizer（N）,nitrogen phosphorus fertilizer（NP）,application of nitrogen phosphorus potassium fertilizer（NPK）.The effects of the interaction between biochar and NPK fertilizer on soil physicochemical properties,greenhouse gas emissions and crop nitrogen utilization efficiency were investigated,to provide a theoretical basis and technical support for the efficient and sustainable utilization of biochar resources in the region.The main research results are as follows:（1）Compared with the NB treatment,the B treatment reduced soil p H at the early stage of crop fertility,and soil p H gradually recovered with the extension of biochar application,with no significant effect on soil water content.The interaction between biochar and chemical fertilizer had a significant effect on soil total N.The combination of biochar and N was more beneficial to increase soil total N content,and the combination of biochar and NP was the second most beneficial.Compared with the NB treatment,the B treatment increased the nitrate-nitrogen content of soil in the cultivated layer（0-40 cm）,decreased the nitrate-nitrogen content of soil in the deep layer（40-100 cm）,and reduced the soil ammonium-nitrogen content in different soil layers.（2）The application of biochar can increase the content of soil organic carbon components.Compared with NB treatment,the soil SOC content of B treatment increased by 3.88 g kg^-1,and the difference reached a very significant level.Compared with NB treatment,soil POC content and soil MOC content increased by 2.24 g kg^-1 and 2.54 g kg^-1,respectively.The interaction between biochar and chemical fertilizer was not significant,and the combination application of biochar and N was more beneficial to increase SOC.（3）The biochar effect had a significant effect on soil N₂O emissions and CH₄ uptake.Compared with the NB treatment,the cumulative soil N₂O emissions increased by 234.73 g ha^-1 yr^-1 and soil CH₄ uptake decreased by 0.32 g ha^-1 yr^-1 in the B treatment,with no significant effect on soil CO₂ emissions.The fertilizer effect had a significant effect on cumulative soil N₂O emissions and no significant effect on CH₄ uptake and CO₂ emissions,with cumulative soil N₂O emissions increasing by 433.05,222.19 and 408.95 g ha^-1 yr^-1 for the N,NP and NPK treatments,respectively,compared to the CK treatment.The interaction effect of biochar and fertilizer had no significant effect on N₂O,CH₄ and CO₂.（4）Biochar had a significant effect on the total nitrogen content of the crop seeds,which was significantly increased by 1.55 g kg^-1 in treatment B compared to treatment NB.Biochar had a significant effect on the nitrogen uptake and nitrogen uptake efficiency of the crop,which was significantly increased by 29.20 kg ha^-1and 6.84%in treatment B compared to treatment NB,the nitrogen agronomic efficiency and nitrogen bias productivity were increased by 3.33 kg kg^-1 and 2.99 kg kg^-1,respectively.Fertilizer had a significant effect on N uptake in wheat,which increased by 40.50,44.30 and 32.79 kg ha^-1 in N,NP and NPK treatments,respectively,compared with the CK treatment.Biochar and fertilizer interaction conditions,biochar with N was more favorable to increase nitrogen uptake and improve nitrogen uptake utilization of the crop.Biochar with NPK was more favorable to increasing crop bias productivity and nitrogen fertilizer agronomic utilization rate.（5）Biochar application can increase crop yield in two seasons,and the yield increase has a long-term effect.NPK treatment had better yield increase than other chemical fertilizer treatments.The combined application of biochar and NPK is more beneficial to increase crop yield,and the yield increase effect is significant.Compared with NB treatment,the crop yield of B treatment increased by 324.65 kg ha^-1.Compared with CK treatment,crop yield of N,NP and NPK treatments increased by 922.48,978.04 and 1493.02 kg ha^-1,respectively.In summary,the benefits of biochar for soil and crops were significant,and biochar facilitated the improvement of soil nitrogen content,increased soil organic carbon fraction content,and improved crop nitrogen use efficiency and crop yield.It is noteworthy that biochar application increased soil N₂O emissions.The application of biochar with N fertilizer was more beneficial to improve soil fertility and nitrogen utilization efficiency,and the yield increase benefits of biochar with NPK fertilizers were significant,and the soil and yield benefits of biochar with NP fertilizers were the second most beneficial.