Nutrient Flow Characteristics And Policy Empirical Analysis Of Typical County In Crop-livestock Systems In The Black Soil Region

The integration of crop and livestock production promotes agricultural green development under the guarantee of food security in Black Soil Region in Northeast China.In this study,Nong’an County,Jilin Province,located in Black Soil Region in Northeast China,was selected as the study boundary.Quantitative studies for nitrogen and phosphorus flows,utilization efficiency as well as environmental losses in crop-livestock systems from 1990 to 2020 were conducted through field research,statistical data and literature,combined with the NUFER model(NUtrient flows in Food chains,Environment and Resources use).We also analyzed the potential of chemical fertilizer reduction and manure substitution in the region through scenario analysis for two measures: balanced fertilizer application and organic substitution;and further analyzed the effect evaluation of organic fertilizer subsidy policy on grain yield and nitrogen and phosphorus emission using Synthetic Control Method empirically,in order to provide theoretical basis for realizing the strategies and ways of agricultural green development in the region.The main results of this study are as follows:1.Based on the analysis of nutrient flow characteristics,the main reasons for environmental damage are the indiscriminate use of large amounts of chemical fertilizers and the unregulated discharge of animal manure.In 2020,compared to 1990,nitrogen and phosphorus inputs in crop-livestock systems decreased by 41% and 20%,respectively,with chemical fertilizer application being the biggest input item.The nitrogen and phosphorus use efficiency in crop system and crop-livestock systems in Nong’an County have fluctuated and increased,while those in the livestock system has decreased and tended to stabilize.The overall nitrogen loss in the crop-livestock systems in Nong’an County has decreased by 41%,while the phosphorus loss has increased by 29%.Ammonia volatilization from farmland is the main way nitrogen is lost,accounting for 44% of the total nitrogen loss,a decrease of 45% compared to1990.Animal manure discharged into water or stacked improperly is the main way phosphorus is lost,accounting for 63% of the total phosphorus loss,an increase of 98% compared to 1990.In 2020,the nitrogen and phosphorus losses per unit of crop-livestock products were reduced by60% and 13%,compared to 1990.2.Based on balanced fertilizer application and organic substitution scenario analysis it is clear that chemical fertilizer reduction and organic fertilizer substitution for chemical fertilizer are important measures to address the current high consumption of organic and inorganic nutrient resources.In 2020,the nitrogen and phosphorus nutrients produced by livestock manure in Nong’an County were 22.9 Gg and 5.0 Gg respectively.The nitrogen and phosphorus carrying capacity indices of the county’s fecal nitrogen and phosphorus were 0.52 and 0.59,respectively.If all were used for crops,they could replace 27% of chemical fertilizers.The total amount of nitrogen and phosphorus chemical fertilizers applied in the current planting system is101.6 Gg,which is 1.5 times the theoretical demand.Based on meeting the nutrient requirements of crops and reducing the amount of chemical fertilizer input(balanced fertilization scenario),the county has a potential reduction of 40% for nitrogen fertilizer and80% for phosphorus fertilizer.By reducing the amount of chemical fertilizer input and replacing the reduced amount of chemical fertilizer with organic fertilizer with equal nutrient content(organic substitution scenario),the county has a potential reduction of 50% for nitrogen fertilizer and 80% for phosphorus fertilizer.The nitrogen and phosphorus loss rate of the organic substitution strategy is 26.4% and 83.3% lower than that of the balanced fertilization strategy,respectively.3.Based on the analysis of the effect of organic fertilizer subsidy policy,it was found that the implementation of organic fertilizer subsidy could increase grain yield and promote nitrogen and phosphorus emission reduction with a certain time lag of synergistic effect.Since the implementation of the policy in 2009 in Nong’an County,the increase in grain yield has been shown after 2012,with an average annual increase of 10.3% compared to the unimplemented policy,and the policy has increased grain yield by 8.5% by 2020.Organic fertilizer subsidy policy has a better effect on phosphorus emission reduction than nitrogen emission reduction.The decrease in nitrogen and phosphorus emission intensity is shown after 2016 and at the beginning of the policy implementation,with an average annual decrease of 15.3% and 17.6%,respectively,compared with the unimplemented policy,and the policy reduces nitrogen and phosphorus emission intensity by 13.5% and 12.4% by 2020.And it still holds after the robustness test.The implementation of the organic fertilizer subsidy policy is mainly influenced by the density of livestock and poultry breeding,the type of subsidized organic fertilizer and the willingness of farmers to accept it.The development of organic fertilizer substitution technology in the Black Soil Area should increase policy support in non-pilot areas and tap the advantages of modern farming scale,management and technology to achieve synergistic and optimal development of crop-livestock systems.