Dynamic changes of CH_4 and CO_2 emission from grazing sheep urine and dung patches in typical steppe

摘要

The contribution of livestock excreta to greenhouse gases (GHG_s) 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 (CH_4) and carbon dioxide (CO_2) 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. CH_4 fluxes from dung patches significantly increased (P ＜ 0.05) within the first 4-8 h, and CO_2 fluxes from urine patches significantly increased (P＜0.05) within the first 8 h. Urine patches cumulated the highest CO_2 emission (188.89 gm~2) in the first 144 h in August. Cumulative CH_4 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 CH_4 sink (-14.66 to -0.29 mg m~(-2)). Dung induced the highest CH_4 emission (23.46 μg g~(-2)) in July. Significant positive correlations were found between soil temperature and GHGs fluxes (CH_4 in grassland: R~2 = 0.32, P ＜ 0.01; CO_2 in urine patches: R~2 = 0.20, P ＜ 0.05). Based on our measurement, the CH_4 emission produced by the daily excreta per adult sheep grazing in summer was estimated at 15.07 ± 4.90 mg.