放牧阉牦牛提前出栏甲烷排放强度减排潜力探讨

以阉牦牛提前出栏项目活动为例,按照2006年IPCC国家温室气体清单优良做法指南的计量方法,在同等牧草利用量的前提下,分别对4岁和7岁阉牦牛一生CH4排放总量和单位体重CH4排放量(即排放强度)进行了初步比较分析.发现在同等牧草利用量的基础上,由于饲养一头7岁阉牦牛一生所消耗的牧草量相当于可饲养2.1头4岁的阉牦牛所消耗的牧草量,所以从CH4排放总量而言,前者一生排放CH4总量比后者少86.3 kg.然而,由于后者总体重比前者重192 kg,所以,后者的单位体重CH4排放强度(以CH4/体重计)只有0.973 kg·kg-1,而前者为1.374 kg·kg-1.根据排放强度的概念,在同等牧草消耗量的基础上,如果将一头7岁阉牦牛替代成饲养2.1头4岁的阉牦牛,可以多生产192 kg的活体重,在同样生产192 kg活重的基础上,利用替代法估算后者饲养方式比前者饲养方式可以实现77 kg CH4减排量,即相当于总减排1.6 t CO2当量.因此,基于排放强度减排而不是总量减排的概念,提前出栏有较大的CH4减排潜力.

Discussion on Reduction Potential of CH4 Emission Intensity for Early Off-take Practice of Grazing Yak

The case study preliminarily compared the CH₄ reduction potential and CH₄ emission intensity of 7 year-old and 4 year-old grazing yak after early off-take practice based on the 2006 IPCC GHG inventory guidelines and under the premise of equal herbage consumption. Our results showed that the total CH₄ emission was greater by about 86.3 kg for 2.1 4-year yaks compared with 7 years old yak during their life assuming that their total herbage consumption was the same, because total herbage consumption for a 7-year yak was equal to that of 2.1 4-year yaks. However, CH₄ emission per unit body weight (1.374 kg·kg^-1) for a 7-year yak (i.e. emission intensity) was higher than that of 2.1 4-year yaks (0.973 kg·kg^-1) because total body weight of 2.1 4-year yaks was higher by 192 kg than that of a 7-year yak. According to CH₄ emission intensity, change of the early off-take practice from 7-year to 4-year yak could reduce 77 kg CH₄ if producing 192 kg body weight through 2.1 4-year yaks compared with a 7-year yak, i.e. reduction potential was about 1600 kg CO₂ equivalent under the same consuming forage. Therefore, for grassland-based animal husbandry, early off-take practice for grazing animals had a great reduction potential in the intensity of greenhouse gases (GHGs) emissions per unit output rather than total emissions of GHGs.