Greenhouse gas emissions from sheep excreta deposited onto tropical pastures in Kenya

The findings of new research study, published in Agriculture, Ecosystems and Environment, contribute to more robust estimates of greenhouse gas emissions from African livestock systems. These estimates are fundamental to develop targeted mitigation strategies.

The study was carried out by scientists from the International Livestock Research Institute, Karlsruhe Institute of Technology, the University of Aarhus and Agroscope.

To improve the estimate of greenhouse gas emissions from tropical rangelands in sub-Saharan Africa, the researchers measured greenhouse gas emissions from sheep excreta over two periods of 51 days on a Kenya rangeland.

In addition, they measured greenhouse gas emissions from potential hotspots in the landscape linked to sheep grazing: overnight enclosures (locally referred to as ‘bomas’), where sheep are kept at night to protect them from theft and predators, the areas surrounding sheep bomas, and areas surrounding watering troughs.

Results showed a short pulse of CO2 fluxes after sheep urine application and a rapid increase of CH4 fluxes following sheep dung application in both rainy and dry season.

However, only small increases of N2O fluxes were observed after dung and urine applications compared to controls without excreta. Elevated N2O fluxes mainly coincided with heavy rainfall.

Overall, N2O emission factors did not vary across excreta type or seasons, but mean N2O emission factors for dung (0.01%) and urine patches (0.02%) were only one tenth of the default emission factors from the 2019 IPCC Refinement for dry climate.

However, they found that bomas and watering troughs were sites of herd concentration that are important sources of greenhouse gas emissions in the landscape, and that emissions in these locations can remain elevated for months to years, especially when soil moisture is high.

Citation

Zhu, Y., Butterbach-Bahl, K., Merbold, L., Oduor, C.O., Gakige, J.K., Mwangi, P. and Leitner, S.M. 2024. Greenhouse gas emissions from sheep excreta deposited onto tropical pastures in Kenya. Agriculture, Ecosystems and Environment 359: 108724.

Photo: Boran women with sheep and goats at a traditional deep well water source, Garba Tulla, Isiolo, Kenya (ILRI/Fiona Flintan).