Methane Emission and Uptake from Soils as Influenced by Excreta Deposition from Grazing Animals
- S. Yamulki *,
- S. C. Jarvis and
- P. Owen
There have been only a few recent field-based measurements to estimate the impact of excreta from grazing animals on methane (CH4) exchange. We report measurements of CH4 exchange from cattle dung and urine deposited in a simulated seasonal grazing pattern. Dung and urine samples were deposited on six separate experimental plots at different times of the year to simulate different stages of normal grazing under UK conditions to study the effects of environmental factors on CH4 exchange rates. During all the experiments, dung pats were the main emitter of CH4 with an estimated mean daily rate of 0.72 (range 0.21 to1.46) g CH4-C per cow. Both net emission and consumption of CH4 from urine patches, however, were observed during the different experiments with a negligible mean daily emission of 0.02 (range −0.05 to 0.15) g CH4-C per cow. Significant variations were observed between the experiments, despite the similarity of application rates and the composition of the excreta. These variations were mainly due to climatic differences when excreta were deposited: ambient temperature and rainfall were the most important factors. The estimated total annual emission of CH4 from cattle excreta deposition during the grazing season in the UK ranged between 0.42 and 3.26 (mean = 1.57) kt CH4-C. Our work confirms other studies that suggest that excreta patches are insignificant sources of CH4 compared to the rumens of grazing cattle, and that climatic factors have a significant impact on CH4 emissions.
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