Effects Of Combined Nitrogen Reduction And Enhanced Efficiency N Fertilizers Application On Yield,n Use Efficiency And N₂O Emissions Of Open-field Pepper In Southwest China

Southwest China is one of the advantageous producing areas of vegetable planting in China,and is important strategic significance for vegetable security and agricultural green production in China.However,the excessive application of nitrogen fertilizer in intensive vegetable production in southwest China,coupled with the climate characteristics of regional high temperature and rainy,and the soil properties of shallow soil layer,light texture and weak fertility preservation ability,lead to low nitrogen use efficiency,serious loss of active nitrogen and high environmental costs in the process of vegetable production,especially the emission of N₂O,which seriously restricts the green and sustainable development of vegetables in southwest China.In view of the above problems,it is urgent to explore the nitrogen management strategy to achieve high crop yield,efficient utilization of resources and low N₂O emission.In this study,the open field pepper in Southwest China was taken as the research object,and different nitrogen management measures were set,including no nitrogen fertilizer(CK:0 kg N ha^-1),farmer’traditional treatment(FP:400 kg N ha^-1),optimized nitrogen fertilizer treatment(OPT:250 kg N ha^-1),nitrogen reduction combined with nitrification inhibitor(NI:250 kg N ha^-1),and nitrogen reduction combined with controlled release nitrogen fertilizer(CRF:250kg N ha^-1).Field experiments were conducted in Hechuan Experimental Farm of Southwest University from 2019 to 2020.The comprehensive effects of different nitrogen management strategies on pepper yield,nitrogen uptake,nitrogen use efficiency and N₂O emission in vegetable fields were systematically elucidated.The main research results are as follows:（1）The results of two-year field experiments showed that in the FP treatment traditionally managed by local farmers,the nitrogen input of pepper during the whole growth period was 400 kg N ha^-1 and the crop absorbed 138 kg N ha^-1,resulting in the yield of 37.4 t ha^-1.Compared with the FP treatment,the OPT treatment based on root zone nitrogen regulation technology,on the premise of reducing the application rate of nitrogen fertilizer by 37.5%,rationally allocated the proportion and time of nitrogen fertilizer application,reduced the redundant growth of plants,optimized the biomass and nitrogen distribution to fruit,thereby maintaining the high yield of pepper and improving the nitrogen recovery efficiency by 55.9%.Under the same optimized nitrogen application rate,NI treatment with nitrification inhibitor and CRF treatment with controlled-release nitrogen fertilizer could improve the biomass accumulation and nitrogen absorption of pepper after flowering and fruiting compared with OPT treatment with traditional urea,and then increased the total vegetable yield by 9.54%and 10.5%,and the nitrogen recovery efficiency by 27.6%and 28.8%,respectively.In addition,there was no significant difference in dry matter accumulation,nitrogen uptake,yield and nitrogen use efficiency between NI treatment and CRF treatment.（2）The results of two-year field experiments showed that the total N₂O emissions and emission factors during the whole season of pepper planting under the traditional management of local farmers（FP treatment）were 3.88 kg N₂O-N ha^-1 and 0.92%,respectively.Compared with FP treatment,OPT treatment based on root zone nitrogen regulation technology could effectively reduce N₂O emission by 117%and N₂O emission factor by 46.4%.Under the same optimized nitrogen dosage,NI treatment and CRF treatment could further reduce the total N₂O emissions by 77.7%and 37.2%,and N₂O emission factors by 98.4%and 42.0%,respectively,compared with OPT treatment with traditional urea.The N₂O mitigation effect of the NI treatment was significantly better than that of the CRF treatment.In addition,among soil factors,WFPS,NO₃^--N and NH₄⁺-N were the main factors affecting N₂O emission.In conclusion,it is clear that N fertilizers are used excessively in the current open-field pepper cultivation in southwest China,and that optimizing N fertilizer rate based on the root nitrogen regulation technology combined with the application of enhanced efficiency N fertilizers（nitrification inhibitors and controlled-release N fertilizers）instead of traditional urea can significantly improve pepper yields,increase plant N uptake,improve nitrogen use efficiency and reduce N₂O emissions on the basis of lower N fertilizer dosage,which has important reference significance for the sustainable development of vegetable production in southwest China.