Resource And Environmental Evaluation And Green Development Strategies Of Grain And Oil Crop Production System In Yangtze River Basin

The crop production system is the basic source of food and energy supply for mankind.The"Green Revolution"in the 1960s promoted the shift of traditional crop production to an intensive mode of production characterized by high input and high yield.Hence,the increase of crop production system not only meets the growth demand of global population,but also becomes a hotpots of resource consumption and environmental emissions.The Yangtze River basin（YRB）is an important intensive agricultural production area and plays an irreplaceable role in ensuring China’s grain and oil security.It feeds more than 40%of the total population with 33%of the cultivated land in China,contributing 65%and 84%of domenstic rice and rapeseed production.The agricultural production in the YRB is a typical subtropical mountain sterepscopic agricultural model.Due to the special climatic and topographic conditions,the nutrient resource loss in agricultural production activities is common,which not only limits the enhancement of crop yield,but also produces a series of negative effects on the loss of nutrients to the environment.However,current studies on nutrient management and environmental potential of crop production systems in this region are mostly confined to a single plot or a small scale,and lack the results of spatio-temporal changes.Also,the coefficient of nutrient flows in evaluation models is the global default parameter that does not distinguish crop type and planting region.Besides,urbanization and red lines for ecological protection have limited the area for crop production in YRB,and the continuous increase of the proportion of cash crops（fruit,vegetable and tea）within the crop planting system further intensifies the pressure for meeting grain and vegetable oil demand under the future population growth.Hence,how to produce more crop yield with limited land resources and minimize resource consumption and environmental impact is an urgent scientific problem in this region.A systematic and comprehensive analysis on the spatio-temproal changes of nutrient management and the environmental potential of crop system in the YRB,as well as the analysis on emission sources,influencing factors,and optimization potential and methods,is helpful to clarify the direction and strategy of green development of planting industry in YRB,so as to promote the realization of regional and even national agricultural green development.In this study,the evaluation model of material flow and environmental effects of grain and oil crop production system in YRB was established,by embedding the NUFER-crop model into the life Cycle assessment（LCA）framework.Aiming at reducing the environmental footprints of rice and rapeseed production systems,this paper analyzed the changes of nutrient management and environmental effects of rice and rapeseed systems in YRB and its sub-regions during the past 20 years,and proposed an optimization approach and quantified the potential of increasing production and reducing emissions.Based on a rice-winter fallow field experiment conducted for three consecutive years in the upper reaches of YRB,this study evaluate the effects of optimal nutrient management（OP）compared with farmers’practice（FP）on annual yield,nitrogen efficiency,environmental impact,human health damage and economic benefits of a typical rice-winter fallow production system in the region.In order to satisfy the future self-sufficiency of grain and vegetable oil in YRB,the differences of resource efficiency（land and nutrients）and environmental effects（reactive nitrogen loss and greenhouse gas emissions）for per ton grain and vegetable oil production in YRB,southern and northern regions were analyzed,and green production strategies were put forward that takes into account self-sufficiency,resource consumption and environmental emissions in the future.The main research results are as follows:（1）The rice yield in YRB increased significantly by 12.0%in the past 20 years,reaching to 7.54 t/ha on average during 2016-2020,with the highest rate in the lower sub-region（7.80 t/ha）.The results of nutrient balance analysis showed that there was no significant change in total fertilizer application and nitrogen（N）input（315 kg/ha and 198kg N/ha on average during the past 20 years）,but phosphorus（P）and potassium（K）input increased significantly by 10.0%and 8.00%,respectively,which was 70.8 kg P₂O₅/ha and70.6 kg K₂O/ha in 2016-2020,respectively.The highest nutrient application rate was found in lower sub-region,which was 387 kg/ha.The N and P surplus was all positive in2001 to 2015,but the formor decreased and the latter incresed,and the K surplus was negative and decreased.The average N,P,and K surplus in recent 5 years was 57.1 kg N/ha,22.0 kg P₂O₅/ha and-49.9 kg K₂O/ha.In the past 20 years,the area-scaled active nitrogen（Nr）loss,eutrophication potential（EP）and acidification potential（AP）of the rice system in YRB had no significant changes,while the greenhouse gas emissions（GHG）increased significantly.However,the yield-scaled environmental potential showed significant downward trend,decreasing by 4.32%-8.26%.The methane emission is the main source of GHG emission（66.2%）of rice production system,and fertilizer production,transportation,and field application contribute more than 90%of the Nr loss,EP,and AP.The N surplus was positively correlated with each environmental potential.Compared with other rice producing areas globally,the yield-scaled environmental potential of the rice system in YRB is higher,especially in the lower reaches.The results of the optimization scenario showed that regional specific integrated management strategies（including fertilizer application optimization,controlled release fertilizer application,rice variety change,inter-mittent flooding management）could reduce the yield-scaled environmental potential by 38.1%-44.3%while increasing rice yield.（2）The experiment of optimal nutrient management was carried out in the typical rice-winter fallow rotation system in the upper reaches of YRB for three consecutive years.It was found that compared with the FP treatment,the OP treatment reduced the input of N fertilizers by 31.8%,but increasing the grain yield of rice by 11.2%on average in three years,and also enhancing N use efficiency（NUE）from 33.1%to 48.1%.In addition,compared with FP treatment,the yield-scaled GHG emission,EP and AP of rice production under OP treatment were reduced by 35.1%,18.5%and 39.4%,respectively.Furthermore,human health risk of OP treatment decreased from 2.10 E-03 DALY/t treated by FP to 1.60 E-03 DALY/t.Methane was the most important emission source,followed by nitrogen fertilizer input,of which the sum contributed more than 90.0%to human health damage.Due to the increase of grain yield and the decrease of fertilizer input under OP treatment,the farmers’direct economic income increased from 17612yuan/ha to 20795 yuan/ha,with an increase of 18.1%.Further considering the reduction of environmental damage and health damage costs by OP treatment,the net ecosystem economic benefit（NEEB）of the system under FP treatment was increased by 28.2%.（3）From 2001 to 2020,the productivity,efficiency of resource and environmental of the grain system in YRB improved significantly.Total prduction and grain supply per capita increased by 24.2%and 15.9%,respectively;land consumption and N consumption per unit grain decreased significantly by 11.4%and 9.43%;and yield-scaled Nr loss and GHG emission decreased significantly by 7.22%and 8.25%,respectively.In the past five years,the average annual grain supply in the YRB was 354 kg/capita/year,with a supply structure of 64.0%rice,17.6%wheat and 18.4%corn.Grain production per ton consumes0.16 ha of land resources and 57.0 kg of nutrient resources,resulting in 8.29 kg N-eq and1073 kg CO₂-eq of Nr loss and GHG emissions,respectively.Although the grain planting structure has changed and the efficiency of nitrogen fertilizer has improved in the past 20years,the average annual GHG emissions from the grain system in YRB have increased by 13.4%due to the increase in planting area,yield and other agricultural inputs.Linear optimal model simulations show that adjusting rice,wheat and maize supplement with the ratios of 37.6%,20.9%and 39.0%can meet 2030 grain demand（400 kg/capita/year）and minimize resource consumption and environmental emissions,while keeping current grain acreage unchanged.Integrated management measures based on adjusted supply ratios could further increase annual per capita cereal supply to 420 kg/capita/year,while reducing nutrient resource consumption by 10.1%,reactive nitrogen losses by 27.8%and greenhouse gas emissions by 44.4%.（4）The rapeseed yield in YRB increased significantly from 2001 to 2020,with the average yield reaching 2.08 t/ha in the past five years.There was no significant change in N,P,and total fertilizer input,which were 142 kg N/ha,57.5 kg P₂O₅/ha and 233 kg/ha on average in the past 20 years,while K fertilizer input increased significantly（49.0 kg K₂O/ha）.The nitrogen partial productivity（PFP-N）of rapeseed was significantly increased,and it was higher in the middle and upper sub-regions than that in the lower sub-region,but it was much lower than that in developed countries.In the past 20 years,the N surplus of rapeseed decreased and gradually tended to nutrient balance state,while the P surplus remained stable after increasing,and the K surplus was negative,and the average deficit reached 78.5 kg K₂O/ha in the past 5 years.At the same time,yield-scaled Nr loss,CF,EP,and AP all decreased,which was highest in the lower sub-region,followed by the upper sub-region and the middle sub-region.Scenario analysis showed that the comprehensive management measures that taking into account nutrient（input,fertilization time,fertilizer form and fertilization location）,sowing date and density in2030 could improve the rapeseed yield,while reducing the yield-scaled Nr loss,CF,EP,and AP to 35.8%,59.5%,45.2%and 50.7%respectively of 2020.（5）In the past 20 years,the planting area of oil crops in YRB was stable（on average918×10⁴ ha）,and the total vegetable oil production and annual supplement per capita of vegetable oil increased significantly,which was 745×10⁴ t and 12.4 kg/capita/year in the past five years,respectively.The proportion of vegetable oil supplement was stable,with soybean oil,canola oil and peanut oil accounting for 11.1%,63.6%and 25.4%respectively.From 2001 to 2020,the resource and environmental indicators of vegetable oil production in YRB showed a significant improvement.The consumption of land,N fertilizer,P fertilizer and total fertilizer per ton of vegetable oil production decreased significantly by 10.3%,19.2%,12.7%and 7.57%,respectively.The yield-scaled Nr loss and GHG emission of vegetable oil production decreased significantly by 17.1%and9.34%,respectively.The results of factor decomposition analysis model showed that the increase of yield and fertilizer efficiency contributed to the decrease of yield-scaled GHG emision of vegetable oil production in the past 20 years,while the input of diesel inhibited this process.Compared with other regions,the annual supply per capita of vegetable oil is only 79.0%of that in the north China,the land consumption per unit ton vegetable is1.33 times of that in the south China,and the fertilizer consumption,yield-scaled Nr loss and GHG emission are significantly higher than those in the south China and the north China.In the future,the self-subsistence of vegetable oil can be realized through the development and utilization of winter fallow fields to expand the oil crops in YRB.If combined with the comprehensive optimization management strategy,the land consumption of 50×10⁴ ha can be reduced,and the nutrient input,Nr loss and GHG emission can be reduced by 20.5%,61.0%and 37.7%.