三峡库区肉牛养殖环境承载力研究

肉牛养殖业规模化扩张给我国农村带来了潜在的环境风险,环境约束已成为制约肉牛产业良性发展的主要瓶颈。以三峡库区丰都县为例,通过调查访谈知情人和畜牧局提供的统计资料,分析了当地肉牛养殖与排泄物处理方式的特点,并以此为依据设置了4种情景,分别探讨耕地畜禽粪便负荷、氮负荷、磷负荷约束下肉牛养殖的环境承载力。结果表明,耕地磷负荷是最紧的约束指标,肉牛养殖的环境承载力随规模化饲养污染资源化利用率的增加而提高。当牛粪资源化利用率分别为0%、13%、30%、50%时,如果不考虑化肥施用与种植制度的影响,肉牛养殖的阈值数量分别为26.2万头、30.1万头、37.4万头、52.4万头。在复种指数为1.61、化肥施用占60%的条件下,肉牛阈值则分别为16.9万头、19.4万头、24.1万头、33.8万头。建议环保部门与农业部门加强合作,将环境约束论证纳入养殖业发展规划,由追求"吨位"向"品位"转变,以养殖少量的高端品种替代大宗普通品种,开展养殖业的合同环境服务创新模式,增强敏感流域养殖污染可持续防治的能力。

Environmental Carrying Capacity of Beef Cattle in the Three Gorges Reservoir Area

The large-scale expansion of concentrated beef cattle feedlots has brought potential environmental risks to rural China and environmental constraints have restricted development of the beef cattle industry. Fengdu County in the Three Gorges Reservoir area was chosen for a case study in which the characteristics of beef cattle feedlot operation and manure treatments were analyzed and the data were collected through survey interviews or provided by the local Animal Husbandry Bureau. Four operational patterns of beef cattle feedlot were set up and the corresponding environmental carrying capacity for each was discussed, based on loading restrictions for livestock manure, nitrogen and phosphorus. We found that phosphorus loading was the most tightly restricted. The environmental carrying capacity of beef cattle would increase with improved manure utilization, as would the beef market capacity. When recycling rates of cattle manure were 0%, 13%, 30% and 50%, the corresponding thresholds for beef cattle populations were 262, 301, 374 and 524 thousand, respectively, without considering the impacts of chemical fertilizer application and cropping system. The thresholds decreased to 169, 194, 241 and 338 thousand, respectively, when the multiple cropping index was 1.61 and the chemical fertilizer application rate was 60%. We suggest that environmental agencies and the agriculture sector strengthen cooperation to realize the win-win situation of local economic benefit and environmental sustainability, and that the theory of environmental constraint be added to planning in the livestock industry. In addition, it is important to move the beef cattle breeding pattern from quantity to quality, from high qualified beef species in exchange for normal species. The environmental contract service pattern should be promoted to increase sustainability by strengthening livestock pollution control in sensitive watersheds.