Responses And Mechanism Of Greenhouse Gas Emissions From Semiarid Mulching Spring Maize Cropland To Nitrogen Fertilizer Management And Nitrification Inhibitor

High-yield,high-efficiency,and environment-friendly crop production are crucial factors for the sustainable agriculture development of China,which is fundamental requirement to the food quality and agricultural ecological security.To improve water use efficiency,the fully mulched ridge-furrow system on spring maize cultivation technology is widely used in the dry farming areas of the Loess Plateau.However,how to both achieve the goals of high yield and environmentally friendly under this cultivation system has become a new challenges for the development of local agricultural production.On the basis of the previous research on the nutrient demand of film-mulched farmland,we showed the key factor is further optimization of field nitrogen management to achieve high-yield,high-efficiency and sustainable production of rain-fed spring maize system on the Loess Plateau.However,there is still a knowledge gap about the influences of optimized fertilization ways on crop yield,environmental effects,the addition of nitrification inhibitors on N₂O emissions and its possible microbiological mechanisms in the film-mulched spring maize system in the Loess Plateau.To solve the above problems,we conducted a three-year field experiment at the Changwu Agricultural and Ecological Experimental Station of the Chinese Academy of Sciences,which considered five tratments including:excessive urea with a split application(HU),recommended urea with a split application(UR),one-time application of a mixture of controlled release and normal urea(CU),straw return with the combination of controlled release and normal urea(CS)and control(CK).Through the method of life cycle assessment(LCA),the environmental impact of the film-mulched spring maize system was comprehensively evaluated,and the nitrification inhibitor(DMPP)was also studied the further emission reduction potential and microbial mechanism of dryland film-mulched spring maize.This study provided a theoretical guidance for the sustainable development of fully mulched ridge-furrow system spring maize in the Loess Plateau.The main results of this study are as follows:(1)Compared to the traditional recommended topdressing practice,one-time application of a mixture of controlled release and solid granular urea further effectively reduced the soil apparent nitrogen loss(decreased by 16.4%)and maintained high maize yield and nitrogen uptake.Straw returning also effectively improved the content of mineral nitrogen in the soil,ensured the continuous high yield and high nitrogen absorption of maize,and also played a positive role in the radiation utilization of crops.(2)Compared with the traditional recommended topdressing practices,one-time application of a mixture of controlled release and solid granular urea reduced the risk of high greenhouse gas(GHG)emissions caused by high temperature rainfall in the middle and late stage of maize growth while its not caused a significant effect on soil GHG.emissions.Due to the addition of external organic matter,the straw returning significantly increased CO₂emissions by 34.5%and N₂O emissions by 51.2%.(3)Compared with the traditional recommended topdressing practices,one-time application of a mixture of controlled release and solid granular urea accelerated soil organic carbon sequestration rate,significantly reduced 21.6%net global warming potential,20.9%carbon footprint,and also had the potential benefits for farmers to increasing the net income of 5050 yuan ha^-1.Straw returning significantly increased soil organic matter content,reduced the net global warming potential of 61.2%and carbon footprint of 60.3%,thus greatly offsetting the environmental impact caused by high GHG emissions.(4)The addition of DMPP had a positive effect on crop yield and nitrogen uptake,effectively inhibited a large amount of soil N₂O emissions in a short term after fertilization by inhibiting the high nitrification rate after urea entered the soil,and significantly reduced the cumulative N₂O emissions of 48.9%-58.1%during the maize growth season.(5)Different field management measures affected the number and community composition of soil microorganisms by changing soil physical and chemical properties,and thus further affected soil N₂O emission.The p H has an important factor on soil N₂O emission by affecting the abundance and community structure of ammonia-oxidizing,and the content of soil MBC directly reflects the positive influence of soil microorganisms on N₂O emission.Although the abundance of Ammonia oxidizing Archaea(AOA)was higher than that of Ammonia oxidizing Bacteria(AOB),AOB played a major role in the process of soil Ammonia oxidation in dryland calcareous farmland,moreover,it significantly affected soil N₂O emission..Nitrosospira 3 clusters occupy an important position in upland soils in Northwest China,and in this study,Nitrosospira 3a.2 clusters were the most important driving factor of soil N₂O emission.In summary,the result showed that one-time application of a mixture of controlled release and normal urea could better realize the synergistic relationship between high crop yield and high nutrient efficiency,reduce soil GHG emissions in the middle and late stages of spring maize growth,and reduce unbenifit effect on the environment.Straw returning improved soil nutrients,promoted crop resource utilization,increased soil carbon sequestration,and decreased the net global warming and carbon footprint.DMPP significantly inhibited soil N₂O emission by inhibiting AOB,and the Nitrosospira cluster3a.2 played a major role in driving soil N₂O emission.In conclusion,the combination of DMPP,solid granular urea and controlled release urea with the straw return is an environment-friendly,high-yield,high-economic benefit and low-emission fertilization mode suitable for dry cropping and film-mulching spring maize production system in Northwest China.