栾城城郊型农牧系统养分流动与环境排放时空特征

Temporal and Spatial Changes of Nutrient Flows and Losses in the Peri-Urban Crop-Livestock System in Luancheng

【目的】改革开放以来中国种植业和畜牧业生产模式及农牧系统结合程度都发生了很大改变,这种改变对农牧体系养分流动以及环境排放都产生了较大影响。论文以河北省石家庄市栾城区为例,分析其1985—2014年农牧系统生产结构、养分流动和损失时空变化特征,确定农牧系统养分损失的关键节点和影响因素,为栾城区以及其他县级行政区的农业可持续发展提供理论依据。【方法】采用食物链养分流动模型(NUFER模型:nutrient flow in food chain,environment and resources use)并结合实地调研,定量栾城区氮磷养分流动特征和影响因素。NUFER模型综合考虑了作物生产系统、畜禽生产系统、食品加工系统和家庭消费系统的氮磷养分流动、利用率和环境损失。实地调研采用面对面的问卷调研方式收集信息,调研内容包括农田养分输入输出、生产管理和养殖户农场养分输入输出、生产管理及粪尿管理等。【结果】2014年种植业蔬菜水果播种面积占总播种面积的比例达到25%,每公顷耕地氮和磷(折纯,下同)投入量分别为763和335 kg,单位面积氮和磷盈余量分别为132和237 kg·hm^(-2);畜牧业养殖密度达到18 LU/hm^2,饲料进口率达到75%,畜牧业源外源氮磷投入分别占农牧体系外源氮磷投入量的57%和39%,畜牧业源氮磷主产品输出占农牧体系氮磷主产品输出的60%和33%,是典型的高环境负荷的城郊型农牧生产体系。1985—2014年,畜牧业畜禽粪尿氮素还田率由59%降至35%。种植业氮利用率从45%降至43%,磷利用率从32%降至23%;畜牧业氮利用率从14%增至30%,磷利用率从4.4%增至10%;农牧系统氮利用率从41%降至36%,磷利用率从27%降至16%。2014年生产1 kg作物产品氮的平均氮损失为0.66 kg,生产1 kg作物产品磷的平均磷损失为0.11 kg;生产1 kg畜禽产品氮的平均氮损失为1.4 kg,生产1 kg畜禽产品磷的平均磷损失为1.8 kg;生产1 kg农牧系统产品氮的平均氮损失为1.5 kg·kg^(-1),磷损失为0.75 kg·kg^(-1)磷产品。农牧体系氮损失的主要途径是氨挥发,农牧体系磷损失的主要途径是粪尿直接水体排放。【结论】受城镇化驱动和农牧系统生产结构改变的影响,经过近30年发展,栾城区成为高投入、高产出、低氮磷利用率、畜牧业占主导地位的高环境负荷的城郊型农牧生产体系。当前农牧系统养分利用率偏低、损失偏高主要源自过高的畜禽养殖密度、农牧分离以及农牧体系养分管理措施的不合理。因此,确定栾城区合理的畜禽养殖承载量,加强饲养管理,实行粪尿全链条管理等农牧结合措施将对农牧系统可持续发展具有重要意义。

【Objective】 Crop-livestock production structure and their integration rate has been changed greatly in China since the reform and opening policy. These changes have large impacts on the nutrient flows and environmental losses in the crop-livestock production chain. Here, Luancheng District of Hebei Province was used as an example to analyze the temporal and spatial changes of crop-livestock production structure and impacts on nutrient flows and losses from 1985 to 2014, and to determine the key impacting factor of nutrient losses in crop-livestock system. These results can be used to improve the understanding of sustainable agriculture not only for Luancheng District, but also for other counties which faced the same situation with Luancheng District. 【Method】 The nutrient flows in Luancheng District were analyzed by using NUFER（nutrient flow in the food system, environment and resource） model and field survey. The NUFER model calculated nitrogen（N） and phosphorus（P） flow, use efficiency and environmental losses of crop production system, livestock system, food processing system and household consumption system. Field surveys were conducted through the face-to-face questionnaires to collect information about the nutrient management. The contents of the questionnaires include the production practices and nutrient input-output of crop system, livestock feeding management and manure management practices, manure recycle to crop land and nutrient input-output of the livestock system. 【Result】 In 2014, the percentage of vegetable and fruit sown area to the total sown area was 25%, N and P inputs of agricultural land were 763 kg N·hm-2 and 335 kg P·hm-2, the average surplus of N and P were 132 kg N·hm-2 and 237 kg P·hm-2 agricultural land, the livestock density reached up to 18 LU/hm2 agricultural land, feed import rate reached to 75%, input of external N and P from livestock production accounted for 57% and 39% of the total external input in crop-livestock system, and output of N and P as main animal products accounted for 60% and 33% of the output in crop-livestock system. All of these indicators indicated that Luancheng District was a typical high environmental loads peri-urban production system. From 1985 to 2014, manure N recycled rate decreased from 59% to 35%. Meanwhile, the nitrogen use efficiency（NUE） decreased from 45% to 43%, and the phosphorus use efficiency（PUE） decreased from 32% to 23% in the crop production during the same period. However, different with that of crop production, the NUE in animal production was increased from 14% to 30%, and the PUE of animal production was increased from 4.4% to 10%. For the whole crop-livestock production system, the NUE decreased from 41% to 36%, and the PUE decreased from 27% to 16%, respectively. In 2014, when 1 kg N was delivered into the crop products, 0.66 kg N lost to environment. Similarly, when 1 kg P was delivered into the crop products, 0.11 kg P lost to environment. The average N and P losses were 1.4 kg N and 1.8 kg P when 1 kg of N and P was retained in animal body, respectively. At the crop-livestock production level, the average N and P losses was 1.5 kg N·kg-1 and 0.75 kg P·kg-1. Ammonia was the major N loss pathway both in crop and livestock production, however, manure direct discharge was the main P loss pathway in the crop-livestock production system.【Conclusion】Driven by the urbanization and structure changes of crop-livestock system, the crop-livestock system in Luancheng District has been defined as the high input, high yield, low nutrient use efficiency, livestock dominated, high environmental risk typical and high environmental loads peri-urban production system during the past 30 years. The low nutrient use efficiency and high nutrient losses were due to the high livestock density, decoupled crop-livestock production and irrational nutrient management practices. Therefore, it is important to determine the reasonable livestock production capacity and improve the feed management and implement the whole chain manure management practices to achieve the sustainable crop-livestock production in Luancheng District.