Research On Nitrogen Utilization And Sustainability Of Food Chain In Suzhou City

Active nitrogen(Nr),one of the vital resources for food production,is closely related to food security of human.In recent years,severe challenges have focused on low Nr utilization rate,vast Nr loss,environmental pollution and so on.Therefore,Nr utilization in the system of food production-consumption has aroused general concern all around the word.In this dissertation,Suzhou city was selected as the study area.To investigate the Nr resource utilization and environmental conservation,a Nr cascade model of the food production-consumption system was built.From the aspect of resource utilization efficiency,food Nr balance between supply and demand,and Nr environmental load were discussed.Hence,the sustainability level of Nr resource utilization was evaluated.Results are as follows:(1)The annual average Nr use efficiency of crop production and livestock breeding subsystem were 27.69%and 24.30%,respectively,from 2000 to 2014 in Suzhou city.Those were higher than other domestic districts but lower than some developed countries.The annual average Nr loss rates in crop production,livestock breeding and household consumption subsystem were 61.54%,36.57%and 62.09%,respectively.Among them,the contribution of household consumption subsystem was highest.The annual average Nr recycling rates of crop production,livestock breeding and household consumption subsystem were 51.04%,54.40%and 36.76%,respectively.It could be deduced that reuse of waste Nr should be enhanced urgently for further Nr management in Suzhou city.(2)From 2000 to 2014,1.99±0.32 million tons/a of plant-derived food Nr and 0.52±0.06 million tons/a of animal-derived food Nr were produced in Suzhou city.The outputs of plant-derived and animal-derived food Nr showed a decreasing trend due to the narrowing scale of agricultural production.1.96±0.14 million tons/a of plant-derived food Nr and 0.86±0.31 million tons/a of animal-derived food Nr were consumed.The consumption quantity of plant-derived food Nr showed a smaller inter-annual variation,while the consumption quantity of animal-derived food Nr increased yearly with livestock and poultry meat being eating more.The plant-derived food Nr had 0.03±0.04 million tons/a of surpluses,while the animal-derived food Nr had-0.34±0.36 million tons/a of deficiencies.Both food Nr data reflected imbalance between supply and demand.The imbalance of plant-derived food Nr was mainly affected by the total output of crops,demand of plant-derived food Nr and rural resident disposable income.The impact factors of imbalance of animal-derived food Nr were demand of animal-derived food Nr,production of livestock and poultry products Nr,and rural population.The self-sufficiency rate of plant-derived food Nr was 101.85%,which reflected a higher self-supply ability and weaker external dependence.The self-sufficiency rate of animal-derived food Nr was 71.67%,indicating that the self-supply ability was lower and the import relying degree was stronger.(3)The Nr load of water body was 2.36±0.19 million tons/a in Suzhou City from 2000 to 2014.The fluctuating increased trend was found.The Nr concentrations in the water varied from 5.76 mg/L to 12.66 mg/L.Therefore,reducing Nr load in the water was necessary for water quality improvement.The annually average Nr load of soil environment were 1.90±0.94 million tons.The decreased trend revealed that the Nr pressure from the soil environment weakened continuously.The farmland load warning value of excrement Nr was low,ranging from 0.14 to 0.28.The soil environment faced relatively less pollution risk.Additionally,the Nr load in atmospheric environment was 1.90±0.94 million tons/a.The load decreased year by year by the continuous reduction of proportion of the primary industry.(4)Assessment results of Nr resource utilization in the food production-consumption chain in Suzhou city during 2000-2014 show different variations.The index of food security sub-goal declined yearly.The index of resource utilization sub-goal dropped firstly and then rose.The index of environmental protection sub-goal increased with fluctuations.Therefore,the above three aspects didn’t realize coordinated development very well.The comprehensive evaluation index of Nr resource utilization sustainability show a fluctuating downward trend,reflecting that the sustainable utilization level of Nr resource should be further improved.