两种典型养鸡模式的能值分析

畜禽养殖的有机化过程被认为是实现养殖业持续发展与保障食品安全的重要途径.运用能值分析方法对两种典型养鸡模式——家庭有机饲养和林地散养进行了系统分析,并结合Castellini等人对意大利所做的同类研究(工业规模化笼养和草地散养)进行了横向对比.结果表明,林地散养生产系统的能值产出率为1.11,与家庭有机饲养系统相近,而在环境负载率和可持续发展能力方面的表现,均差于家庭有机饲养生产系统,说明林地散养模式尽管通过提高系统生产空间,理论上接近畜禽养殖的有机化理念,但由于大量的禽舍建筑、医药及其饲料等方面的外部资源输入,反而使得系统的环境负载率提高,可持续性大大下降.与意大利的结果比较发现,我国两个养殖系统的社会经济成本高、对外部不可再生资源的依赖程度较高,有机化目标并没有很好的实现.因此,我国现有的有机化畜禽养殖方式和外部制度都有待进一步改进和创新.

Emergy-based analysis of two chicken farming systems: a perspective of organic production model in China

The organic production model is regarded as an important way to ensure food safety and achieve agricultural sustainable development. Presented in this paper is an emergy-based analysis of two typical popular chicken rearing systems in China, i.e., family operated organic rearing system and field rearing system in orchard, from the perspective of production efficiency, environmental impact and the overall sustainability. Emergy analysis capable of accounting for both economic aspect and the natural contribution to production on a common basis, allowing meaningful comparison across different systems, has been applied in many cases and proved to be a powerful tool to assessment of ecological economic systems and processes, with special focus on the agricultural field. According to the new development of emergy methodology, new emergy parameters, i.e., the renewability factor of each item was incorporated in this study to improve emergy accounting. System indices such as the emergy yield ratio (EYR), environmental load ratio (ELR) and environmental sustainability index (ESI) were applied to characterize the resource use, environmental impact and the overall sustainability of the studied systems. In addition, the similar evaluation results conducted in Italy(scatter rearing system in grassland and conventional scale rearing system)were also introduced for reference and comparison. The indices calculated for family operated organic system and scattering system in orchard respectively are as follows: the transformation, 4.24×10⁶ sej/J and 2.20×10⁶sej/J; EYR, 1.10 and 1.11; ELR, 3.10 and 3.44; ESI, 0.36 and 0.32. In consideration of the two concerned systems in China, it can be found that the lower transformity indicates that the family operated system is less efficient in food taking and consequently has lower efficiency in emergy conversion compared with scatter rearing system in orchard. The emegy yield ratio (EYR) for the two production system are both very low and close to 1, which simply means that each process only converts resources from outside into product without much addition from local resources. However, as indicated by ELR and ESI, family operated organic systems produces lower ecosystem stress and pressure on environment and correspondingly is more sustainable than scatter rearing system in orchard. Nevertheless, despite being close to the concept of organic production practice in consideration of rearing space for exercise and food taking, the field rearing system has a relative poor performance with regard to overall sustainability, which is attributable to large amount input of external purchased resources, e.g. the building materials, drugs, food and so on. Further comparison with systems in Italy shows that due to longer life cycle, chicken systems in China have relatively lower production efficiency and higher economic cost. With regard to environmental load and overall sustainability, their performance has already been better than conventional scale rearing system in Italy, but still far from the practice of scatter rearing system. Anyway, two so-called organic production systems concerned in this paper still heavily rely on purchase industrial resource and are less efficient in exploring the local resource and far from the real practice of organic production. Additionally, higher economic cost results in less competitive in world market. Therefore innovation in production techniques and institutional reforms associated with organic pattern are urgently needed in China.