Use efficiency and emission spatial-temporal variability of nitrogen and phosphorus for pig production in Beijing

To meet the growing demand of livestock products, the rapid development of intensive livestock production system in peri-urban area has brought many serious environmental problems. However, little is known about the quantitative information of livestock production in peri-urban environments. In this study, we analyzed the nitrogen and phosphorus use efficiency and losses and the temporal-spatial variation of pig breeding, using the data of a comprehensive survey conducted on 92 pig farms during 2012-2013 and calculated with the NUFER-animal model(nutrient flows in food chains, environment and resources-animal model). The NUFER model is a deterministic model with large databases that calculates the flows, use efficiencies, and emissions of N and P in the food chains in 31 regions of China and the national level on an annual basis. It uses a mass balance approach with detailed amount of the partitioning of nitrogen and phosphorus inputs and outputs. Then, 5 kinds of feed and manure management optimization measures were proposed using scenario analysis. From 1980 to 2013, the nitrogen use efficiency at the fattening level (fattening pigs only) increased from 17.8% to 19.0%, and the phosphorus use efficiency increased from 32.0% to 35.8%; the nitrogen use efficiency at the herd level (fattening pigs plus sows and boars) increased from 16.0% to 16.7%, and the phosphorus use efficiency decreased from 29.5% to 23.4%; the nitrogen use efficiency at the system level (soil-feed-pig breeding system) decreased from 18.5% to 11.4%, and the phosphorus use efficiency decreased from 41.6% to 17.1%. In 2013, the total nitrogen and phosphorus losses were 4.2×104 and 0.65×104 t, respectively, increasing by 56.9% and 97.0% comparing with that in 1980. The reason for this change was that the breeding mode of pig breeding changed from family and traditional mode to intensive mode. For the proportion of the feed utilization, the family was rapidly decreased, which led to the efficiency decreasing at system scale. However, due to the precision feeding and manure management, the nutrient use efficiency was increased at animal and herd level. At the same time, the government proposed many policies, laws and regulations, standards and norms since 2000, so that the nutrient use efficiency first decreased and then increased and the environmental losses first increased and then decreased from 1980 to 2013. The result also showed that the proportion of different feed sources of pig breeding in peril-urban area changed a lot in 2013. Feed gradually shifted from local production to import from abroad, and feed input conversed from the by-product feed to the main product feed. The results of spatial distribution variation showed that the environmental losses were rapidly decreased at urban and suburban area, and rapidly increased at outer suburb of Beijing. These spatial-temporal changes were mainly attributed to the urbanization and the urban development planning. Insights from pig breeding systems in peri??urban region of Beijing provide relevant guidance to the sustainable livestock production in cities of rapidly developing countries.