Dynamic changes of CH4 and CO2 emission from grazing sheep urine and dung patches in typical steppe

The contribution of livestock excreta to greenhouse gases (GHGs) emissions by sheep grazing in a typical steppe system in Guyuan county, Hebei province of the People's Republic of China was evaluated. Changes of methane (CH4) and carbon dioxide (CO2) fluxes from urine and dung patches excreted by sheep on grassland were measured for the first 144 h during July, August, September and October in 2011. CH4 fluxes from dung patches significantly increased (P < 0.05) within the first 4-8 h, and CO2 fluxes from urine patches significantly increased (P < 0.05) within the first 8 h. Urine patches cumulated the highest CO2 emission (188.89 g m−2) in the first 144 h in August. Cumulative CH4 emissions from urine patches and dung patches were −0.19 to 1.00 and −8.01 to 30.25 mg m−2 during the measurement period, and the control grassland was a net CH4 sink (−14.66 to −0.29 mg m−2). Dung induced the highest CH4 emission (23.46 μg g−2) in July. Significant positive correlations were found between soil temperature and GHGs fluxes (CH4 in grassland: R2 = 0.32, P < 0.01; CO2 in urine patches: R2 = 0.20, P < 0.05). Based on our measurement, the CH4 emission produced by the daily excreta per adult sheep grazing in summer was estimated at 15.07 ± 4.90 mg.