Comparing methane emissions from different sheep-keeping systems in semiarid regions: A case study of Syria

摘要

Sheep husbandry represents a significant source of methane (CH"4) in semiarid grassland regions such as Syria. However, the contribution of sheep to CH"4 emissions in Syria is still unknown. This study was designed to quantify CH"4 emissions and identify possible mitigation strategies for their reduction. Methodology developed by the Intergovernmental Panel on Climate Change (IPCC) was used to estimate CH"4 emissions. A survey was conducted on 64 farms from different locations in Syria in 2009. Data were collected concerning sheep-keeping systems (SKSs), body mass, milk and wool yield, farm locations, feed rations, periods of grazing on the Steppe, the duration of pasturing on agricultural residuals and time periods when sheep were kept in stables. Using a linear statistical model, the influence of SKS, geographical region and sheep body mass on emitted CH"4 were analysed. The results showed that the geographical region, SKS and sheep body mass had significant effects (P<0.05) on CH"4 emissions. According to the model, the mean values of estimated CH"4 emissions from extensive, semi-intensive and intensive SKSs were 26+/-0.9, 22.5+/-1.3 and 13.5+/-1.7kg/sheepyear, respectively. In comparing differences between the least square means of CH"4 emissions, the extensive and semi-intensive SKSs produced 92% and 66% higher CH"4 emissions compared to intensive SKS. The differences in CH"4 emissions within the distinct SKSs were attributed to dietary composition. Extensive SKS used a less concentrated feeding regime (98+/-17day/year) than semi-intensive SKS (114+/-47day/year), and intensive SKS employed concentrated feeding year round. Furthermore, it was observed that sheep with the same body mass produced higher CH"4 emissions in extensive SKS than in semi-intensive and intensive SKSs. Moreover, the semi-intensive SKS occupied more natural pastures than extensive SKS, which caused an overuse of the Steppe. Therefore, an effective mitigation strategy involves the use of more digestible feed, which would be accomplished by increasing the quantity of concentrated feed. Owing to unfavourable farming conditions, low-cost nonconventional feeds such as the residuals of wheat and cotton should be used to improve sheep management practices to reduce Steppe overgrazing in the extensive and semi-intensive SKSs of Syria and other semiarid areas.