Characteristics And Regulatory Approaches Of Nutrient Flows In Intensive "Crop-Livestock" Production Systems Of The Peri-urban Area Of China

A rapid development of intensive agriculture in terms of crop and animal production is anticipated in China, especially in peri-urban areas, in order to meet the increasing human demands for animal products and high-quality crop products. Meanwhile, this development also has linked to the negative effect on the utilization of resource and the environment. It is indicated that primary production of crop has been a key factor determining the secondary production such as animal production and vice versa. Consequently, linking cropping and animal production systems is very important to realize the improvement of nutrient use efficiency and reduction of resource use. Under this condition, there is an urgent need to investigate nutrient balances and flows of intensive"crop-livestock"production systems in peri-urban areas of China. Shunyi District of Beijing was selected to be the study area. The objectives of this study are described as follows: 1) analysis of nitrogen (N) and phosphorus (P) balances and flows in the"crop– livestock"production systems at the farm (including an intensive pig plant and an"ecological feeding gardens"), village (a village characterized by intensive pig breeding) and regional (three major cropping systems were considered) levels, respectively; 2) systematic evaluation of the risk of environmental pollution; 3) exploration of better management measures for utilization of nitrogen and phosphorus resources. The main results are shown as follows:(1) Feed purchased were considered as the main source of N and P inputs of"crop– livestock"production systems, which amounted to 96.0% (12469.0 kg N/(hm2·a)) of total N and 98.6% (2794.9 kg P/(hm2·a)) of total P inputs in the intensive pig farm. The corresponding values in the"ecological feeding gardens"were 97.6% (9268.5 kg N/(hm2·a)) and 98.9% (2179.6 kg/(hm2·a)).(2) The recycling of organic resources is an alterative measure to reduce the application rate of synthetic fertilizer. In the intensive pig farm, 82.7% and 99.4% of total N and P inputs of the cropping system were from synthetic fertilizers mainly due to the recycling of organic matter discharged from biogas plant was restricted. In contrast to the"ecological feeding gardens", 28.6% and 55.6% of manure N and P were incorporated into fields resulting in the recycled manure N and P occupied 90.4% and 99.4% of total inputs of the cropping system, hence, only 5.7% and 0.6% of total N and P inputs of the cropping system originated from synthetic fertilizer.(3) A relatively low N use efficiency (NUE) and P use efficiency (PUE) of"crop– livestock"production systems were found in the intensive pig farm with the value of 18.8% and 20.6%, and also in the"ecological feeding gardens"accounting for 24.9% and 26.3%, respectively. In balanced fertilization scenario, NUE and PUE of the cropping systems are significantly enhanced. In improved feed utilization scenario, NUE and PUE of the livestock system are markedly increased. Moreover, increases in nutrient use efficiencis of"crop– livestock"systems are higher in the latter scenario and less nutrient losses from animal manure also could be obtained.(4) Nutrient losses from animal manure in the process of storage and treatment as well as nutrient surpluses in cropping systems should be paid more attention. The amount and percentage of nutrient losses from animal manure were higher in the storage and treatment stage, comparing to these in the housing stage; An extremely high nutrient surpluses with the value of 1962.8 kg N/(hm2·a) and 837.0 kg P/(hm2·a) took place in the cropping system of"ecological feeding gardens". It concluded that an appropriate amount of cropland for animal manure recycling and proper animal stocking density in combination with the optimization of nutrient management are the keys to solve this issue.(5) At the village scale, nutrient inputs in the cropping system were mainly derived from the recycled nutrient in terms of animal manure and crop residues incorporated into fields. Contrarily, nutrient in feed imported to the livestock system were totally purchased from outside of the village. Furthermore, NUE and PUE of"crop– livestock"systems were only 20.1% and 26.3%, respectively. Basing on the scenario analysis, nutrient use efficiencies of"crop– livestock"production systems at the village level are able to be increased by the optimization of feed.(6) The positive nutrient (N and P) balances were found across all three cropping systems, especially in the vegetable system, in Shunyi District over the study period. The amount of N and P surplus were 528.4 N kg/(hm2·a) and 82.7 P kg/(hm2·a) in wheat/maize rotation systems, 719.6 N kg/(hm2·a) and 129.5 P kg/(hm2·a) in orchards as well as 1062.3 N kg/(hm2·a) and 491.8 P kg/(hm2·a) in vegetable systems, respectively. Moreover, differences in nutrient (N and P) inputs from fertilizers (synthetic fertilizer and animal manure) were statistically significant among these three cropping systems (P<0.05). Nutrient inputs in wheat/maize rotation systems were mainly contributed by the application of synthetic fertilizer, in contrast that in vegetable cropping systems animal manure were the major source of nutrient inputs.