Temporal and spatial characteristics of nitrogen and phosphorus cycling and environmental losses in the "soil-feed-dairy" production system in Beijing

With the increasing of urbanization rate and income, the food demand and food consumption structure has been changed greatly in China, especially for the dairy products. However, the environmental risk of livestock production is also growing quickly under the rapid increase of dairy population and intensification rate. Currently, dairy production is mainly concentrated around the peri-urban area in the big cities on the purpose of access to the market. However, there is little information about the nutrient flow and losses of peri-urban dairy production yet. Increasing understanding of this information is useful for policy makers to regulate the size and location of dairy production, and to achieve a crop-dairy integrated and environmental friendly dairy production system. Here, the performance of nitrogen (N) and phosphorus (P) flow, use efficiency and losses of peri-urban dairy farms in Beijing was assessed, using data of a comprehensive survey conducted on 28 dairy farms during 2012-2013 and calculations with the NUtrient flows in Food chains, Environment and Resources (NUFER) model. The feed formula and feed intake, feeding days and other parameters of the production system were derived from survey data for the year 2012 and 2013, and were derived from NUFER model for the period of 1980-2011. Our results showed that, nitrogen use efficiency (NUE) at the animal level (only lactating dairy cow) increased from 14.9% to 21.2% from 1980 to 2013, and phosphorus use efficiency (PUE) increased from 13.8% to 27.3% during the same period. At the herd level (including calves, breed cows, heifers and dry cows), NUE increased from 14.5% to 18.2%, and PUE increased from 15.8% to 24.9% for the past 33 years. Similarly, both the NUE and PUE increased at the system level (soil-feed-cow chain) during the period of 1980-2013, e.g., NUE increased from 11.3% to 15.8%, and PUE increased from 13.3% to 22.3%. NUE was decreased from 1980 to 1985 at all the three production level, however, steadily increased since 1985. Differed with that of NUE, PUE was steadily increased at all the three production level from 1980. The total nitrogen losses increased from 1 516 t N in 1980 to 16 973 t N in 2013, and the total phosphorus losses increased by 1 649 t P, from 114 t P to 1 763 t P during the same period. The average N or P losses to produce 1 kg N or P in products decreased greatly since 1980. In conclusion, the characteristics of N and P flow thorough the "soil-feed-dairy" production system have been greatly changed in Beijing. The nutrient use efficiency and total environmental losses are increasing. The reasons for these changes are the increasing of animal number, the transformation from the traditional to the intensive farming and the improvement of the environmental management measures. Therefore, it is necessary to improve the sustainable development of urban dairy farming by the adjustment of dairy production from quantity to quality, precision feeding technology, and waste management.