Utilization And Evaluation Of Nitrogen In Food Chain In Quzhou, Hebei

Nitrogen?N?is an essential element for the growth of plants,and it circulates in the four earth spheres,including lithosphere,atmosphere,hydrosphere and biosphere.In recent years,the population growth has resulted in an increasing demand for animal and plant products,and a sharp increase in global N use.During the processes of food production and consumption,if the amount of N in a certain time or subsystem is abnormal,it will cause a disorder in the functional structure of system,and cause problems in N resources and environmental.Exploring N flow,N use efficiency?NUE?and N environmental losses,and clarifying the driving factors are of great significance for ensuring human food safety,promoting the use efficiency of N resources,and the healthy development of the ecological environment.Hebei Province is a large agricultural province,and Quzhou County is a typical intensive agricultural area.The environmental problems caused by the low NUE are becoming increasingly prominent.1986 is the beginning of the national?Seventh Five Year Plan?.Affected by the overheated economic development of the?Sixth Five Year Plan?,the industrial and agricultural economic development was rectified.In this study,Quzhou County was used as the research area.Based on the statistical data from 1986 to 2017 and the measured data,a N flow model in the processes of food production and consumption was constructed to quantitatively analysis the characteristics of N flux,NUE and environmental load of each step by multivariate statistics.Based on this,driving force D-pressure P-state S-impact I-response R?DPSIR?model evaluation method is used to construct evaluation index system,the N sustainable utilization of future level is forecasted with the grey prediction method,and a control strategy is proposed through scenario analysis.The main findings are as follows:?1?The N fluxes per unit area of the food production and consumption system in Quzhou County varies greatly.During 1986–2017,the flux of N input in the crop-productionsubsystem,livestock-breedingsubsystem,and household-consumption subsystem fluctuated within the range of 153.81–293.74 kg N·hm^-2,37.95–108.93 kg N·hm^-2 and 23.14–29.27 kg N·hm^-2.When the total N fertilizer application amount reached 475 kg N·hm^-2 in 2007,the N fertilizer application level gradually increased and close to the optimal plan for N demand in farmland.The N use efficiency of crop-production subsystem?NUEc?and livestock-breeding subsystem?NUEa?were 22.77%–38.61% and 36.45%–58.07%.NUEc decreased sharply with the increase of N fertilizer application,which was lower than China?39%?,the United States?56%?and the global scale?50%?.NUEa increased with the increase of feed N input,with an average value of 49.59%.?2?During 1986–2017,the N environmental losses during food production and consumption in Quzhou County was 72.75–160.07 kg N·hm^-2.During the processes of food production and consumption,the N losses were mainly gaseous?57.93%?,and the main component was ammonia.The N emissions from the crop-production subsystem,livestock-breeding subsystem,and household-consumption subsystem accounted for 55.75%of the total N input.And the contribution rate of each subsystem of environmental N losses followed the sequence:the crop-production>livestock-breeding>household-consumption.The average N cost of food consumption was 15.95 kg·kg^-1,still higher than the national and municipal standards,showing that the cost of N resources and environment was large.During the period,the waste N in Quzhou County increased from 47.77 kg N·hm^-2 to 100.63 kg N·hm^-2,mainly in the livestock manure N and straw N.If the waste N is not properly treated and used,the increasing N losses are expected to have a lager future impact on the environment.?3?The driving factors for N environmental losses in Quzhou County are mainly the N application level in agriculture and the manure return rate.During 1986–2017,the N environmental losses in Quzhou area showed an upward trend.From the perspective of the research medium,the results of sensitivity analysis showed that the N application level,meat percentage and human feces return rate affected the N load of various environmental media.In addition,the volatilization of chemical fertilizer NH₃ and the amount of defecation of livestock and poultry influenced the N load in the atmosphere.The chemical fertilizer leaching influenced the N load in the water bodies?sensitivity index I?0.20?.Analysis from a research system perspective,stepwise regression analysis showed that N application level,feed N input,crop planting structure and population density were closely related to N losses in Quzhou County?determination coefficient R²=0.99?.The results provide a reference for the effective management of N in Quzhou County.?4?The sustainable utilization of N resources in Quzhou County shows an upward trend.During 1986–2017,the evaluation values of N use driving force,state and influencing factors in Quzhou County showed an upward trend,which was opposite to the trend of pressure factor evaluation value,while the comprehensive evaluation index value of response factors decrease first and then increase.The N resource of Quzhou County generally developed from weak sustainable to basic sustainable development under the joint influence of multiple factors.In the evaluation of N utilization sustainability,seven indicators,such as N intensity per unit of GDP,waste N emission intensity,urbanization rate,GDP per capita,farmers'per capita net income,urban per capita disposable income,scale and method of livestock breeding were important.It is predicted that the sustainable use of N resources will be on the rise in2018-2030.?5?The agriculture in Quzhou County can continue to follow the development model of combining agriculture and animal husbandry.The results of principal component analysis showed that grain yield,fertilizer,and straw return to the field contributed greatly to the change of NUEc,and the level of NUEa was closely related to the planting structure and dietary structure.If the existing farming system is changed:the N fertilizer application can be reduced by 50%?Scenario 1?and the use efficiency of feed can be increased by 10%?Scenario 3?,which can increase the NUEc and NUEa by 51.76%and 18.29%.Combining the research results of the previous four parts,three strategies for N sustainable utilization are proposed:1)adjusting the farming system,the planting area of economic crops should be increased,and the combined application of livestock manure and chemical fertilizers can improve crop productivity;2)increasing the investment in treatment facilities to promote the recycling of waste N;3)adjusting the diet structure,the proportion of animal food consumption should be decreased to reduce the environmental N losses.