Assessment Of Fertilizer Application,Environmental Cost And Mitigation Potential For Vegetable Production In Chongqing City,China

Chongqing is one of the important regions for vegetable production in the southwest China.The application of fertilizers is generally excessive,and the risk of environmental cost is high.However,the resource input and environmental cost of vegetable production in this region,as well as the mitigation potential of fertilizer saving and environmental cost reduction,are still unclear.Therefore,on the one hand,based on the analysis of farmer survey data and statistical data,combined with the life cycle assessment method,the nutrient input and environmental costs（active nitrogen loss and GHG emissions）of the main open-field vegetable production in Chongqing were systematically quantified.Additionally,the differences of fertilizer application and environmental costs among various vegetable crops and regions were compared.On the other hand,based on the cost of the agricultural response to application rates from large number on-farm experiments and data mining method,the optimal fertilization rate of nitrogen,phosphorus and potassium for the main open-field vegetable species in Chongqing were clarified.This work makes the mitigation potential of the main open-field vegetable system clear and provides a theoretical basis to achieve sustainable production of vegetables for Chongqing province.The main research results are as follows:（1）The research results show that the fertilizer input and environmental cost of the open-field vegetable production system in Chongqing were high.The average application rates of N,phosphorus（P₂O₅）,and potassium（K₂O）were 366,231 and 245 kg·ha^-1,respectively.The active nitrogen loss and GHG emissions were 106 kg N·ha^-1and 4981 kg CO₂-eq·ha^-1,respectively.The total consumption of vegetable nitrogen,phosphorus and potassium fertilizers in Chongqing was302·10³t,184·10³t and 200·10³t,respectively.As far as different vegetable growing regions were concerned,the fertilizer input and environmental costs（active nitrogen loss and greenhouse gas emissions）in western Chongqing were the highest,which were 25%-44%and 29%-35%higher than other regions,respectively,followed bythe middle,the southeast and the northeast of Chongqing province.As far as different vegetable types were concerned,melons have the highest fertilizer input and environmental costs,which were 29%-44%and 23%-45%higher than other vegetable types,followed by cabbages,solanaceous fruits,leafy greens,mustard vegetables,root vegetables.The amount of nitrogen,phosphorus and potassium fertilizers and active nitrogen loss,GHG emissions of the melons accounted for 34.4%,22.5%,22.2%,39.5%,and 39.3%of the total fertilizer input and environmental cost of open-field vegetables in Chongqing,respectively.（2）Based on the cost of the agricultural response to application rates from large number on-farm experiments and data integration analysis,the optimizing the fertilizer rate of the main open-field vegetables in Chongqing was systematically clarified,and based on this,the fertilizer saving and environmental costs reduction potential of the open-field vegetable production system in Chongqing was revealed.The fertilizer saving and environmental costs reduction potential of different types of vegetables and different region are great.The fertilizer saving potential of nitrogen,phosphorus and potassium fertilizers per unit area of open-field vegetable production in Chongqing were 41.5%,66.7%and 41.6%,respectively,and the total amount of fertilizer saving were103.0·10³t,99.1·10³t and 71.4·10³t,respectively.Active nitrogen loss and GHG emission reduction potential were 41.1%and 41.8%per unit area,respectively,and the total cumulative emission reduction was 25.6·10³t and 1196·10³t,respectively.In terms of different vegetable planting regions,western Chongqing has the greatest fertilizer saving and environmental costs reduction,followed by the middle,the southeast and the northeastern of Chongqing respectively.The saving amount of nitrogen,phosphate,potash,and reduction potential of reactive nitrogen loss and GHG emission accounted for 47.7%,42.6%,54.9%,55.9%and 52.3%of open-field vegetables in western Chongqing respectively;in terms of different vegetable types,Leafy greens have the greatest potential for fertilizer saving and emission reduction per unit area,followed by cabbages,melons,solanaceous fruits,mustard vegetables and root vegetables.Cabbages had the greatest potential of total amount fertilizer saving and emission reduction,The saving amount of nitrogen,phosphate,potash,active nitrogen loss and GHG emission accounted for 34.4%,22.5%,22.2%,39.5%,and39.3%of the total fertilizer saving and emission reduction of open-field vegetables in Chongqing,respectively.