Enteric Methane Emission of Cattle Grazing Rangeland Ecosystems of South Eastern Kenya
Abstract
Large herds of ruminant cattle grazing degraded rangeland pastures in Kenya are associated with enteric methane (CH4) emission, contributing to global warming potential (GWP). Yet the CH4 emissions and associated GWP are hardly quantified to inform emerging threats to sustainable use of grassland ecosystems. This study estimated enteric CH4 emission and the GWP from cattle grazing in Makueni County, a rangeland ecosystem in South Eastern Kenya. Estimation applied the intercontinental panel of climate change (IPCC) Tier I and Tier II approaches with Tier II incorporating seasonal differences in feed quality, dry matter intake and animal performance. Animal activity and production data for the year 2019 was obtained from the County livestock inventory reports while feed quality data was sourced from recently published literature. The resultant emission factors (EFs) (kg/year) were 47.1 for females >2 years; 27.2 for heifers 1-2 years; 46.5 for males > 2years; 32.9 for young males 1-2years; and 17.2 for calves <1year. These EFs were higher (7.7 to 14.9%) than those of Tier I for females >2years, young males 1-2years and for calves <1yr but lower (5.4 to 12.3%) for males > 2years and for heifers 1-2 years. The Tier II estimates were 4.4% higher than the estimates with Tier I approach for both total estimated enteric CH4 emission (9,279,526.80 vs 8,889,997 kg CH4/year) and GWP (259,826,750.4 vs. 248,919,916 kg CO2 eq). The results reflect uncertainty of EFs generated from Tier I approach, which necessitates development of region-specific EFs using data from local breeds of animals and feed resources. This will improve certainties of the enteric CH4 emissions and accuracy in reporting the Nationally Determined Contributions (NDCs).
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