Annual methane budgets of sheep grazing systems were regulated by grazing intensities in the temperate continental steppe: A two-year case study

Methane (CH4) emission from animal husbandry accounts for a large percentage of anthropogenic contributions to CH4 emissions. Fully understanding of grazing management effects on the CH4 budget is essential for mitigating CH4 emissions in the temperate grazing steppe systems. Annual CH4 budgets for the sheep grazed steppes at various grazing intensities, un-grazing (UG, 0 sheep ha(-1)year(-1)), defer grazing (DG, 1.0 sheep ha(-1) year(-1)), moderate grazing (MG, 1.43 sheep ha(-1)year(-1)), and heavy grazing (HG, 2.43 sheep ha(-1)year(-1)) were assessed across 2012-2014 in the agro-pastoral region of northern China. Annual soil CH4 uptake averaged across 2012-2014 were 1.1 +/- 0.1, 2.4 +/- 0.2, 2.2 +/- 0.2, and 1.3 +/- 0.1 kg CH4-C ha(-1) for UG, DG (only 2013-2014), MG and HG sites. Non-growing season CH4 uptake comprised 50.0 +/- 4.3% of annual CH4 uptake in 2012-2013 and 37.7 +/- 2.0% in 2013-2014. DG and MG significantly promoted annual soil CH4 uptake (P < 0.05), while there was no difference between HG and UG (P > 0.05). Bell-shaped relationship was presented between stocking rates and soil CH4 uptake (r(2) = 0.59, P < 0.05). Annual soil CH4 uptake significant linearly and positively correlated with root biomass (r(2) = 0.30, P < 0.05). Annual CH4 budgets for the grazed grasslands were -1.1 +/- 0.1, 5.7 +/- 0.6, 11.5 +/- 1.5 and 15.5 +/- 1.3 kg CH4-C ha(-1) year(-1) in UG, DG (only 2013-2014), MG and HG across 2012-2014. Soil CH4 uptake could offset 29.7 +/- 5.6, 15.9 +/- 4.3 and 6.8 +/- 1.0% of total annual CH4 emissions from sheep, sheepfold and faeces in DG, MG, and HG. All grazed steppes are sources for atmospheric CH4 and the magnitude is regulated by grazing intensities. Sheep CH4 emissions for 1-g liveweight gain were 0.21, 0.32 and 0.37 g CH4-C in DG, MG and HG, respectively. DG is the recommended grazing management in this region to achieve greater herbage mass, higher sheep performance and lower CH4 emissions simultaneously.