[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 1 600 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.