Nutrient flow characteristics analysis of typical county in crop-livestock systems in black soil region in Northeast China

The integration of crop and livestock production promotes agricultural green development and guarantee food security in black soil region in Northeast China. In this study, Nong’an County, Jilin Province, which is 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). The present study explored the impacts of climate and socio-economic factors on nitrogen and phosphorus emissions. Furthermore, two sets of scenarios of balanced fertilization (reduction of fertilizer application) and organic substitution (increase of organic material substitution) were set up to assess the county’s emission reduction potential. The results showed that, compared to 1990, nitrogen and phosphorus inputs to crop-livestock systems for Nong’an County in 2020 decreased by 45% and 23%, respectively, with chemical fertilizer application as the largest input. The nutrient utilization efficiency of crop system and crop-livestock systems increased fluctuatingly, while nutrient utilization efficiency of livestock system decreased and tended to remain stable. The nitrogen and phosphorus losses of crop-livestock systems decreased by 41% and increased by 29% compared to 1990, respectively. Ammonia volatilization from farmland, runoff and erosion, and livestock manure discharge were the major contributors to nutirent losses. Through balanced fertilization and organic substitution, it is predicted that by 2030, Nong’an County will have the potential to reduce the application of chemical nitrogen fertilizer by 80% and chemical phosphorus fertilizer by 85%, with low levels of soil nitrogen and phosphorus accumulation, and the environmental emissions will be reduced by 67%, the nutrient utilization efficiency of crop system and crop-livestock systems will increase by more than 50%. In conclusion, crop-livestock system of Nong’an County can enhance the potential for fertilizer reduction in the future by increasing the amount of straw and manure returned to the field. The black soil region in Northeast China should continue to deepen the policy of zero growth of chemical fertilizer, and promote the utilization of organic waste to guarantee a synergistically optimized crop-livestock systems.