Dung and urine patches on grasslands are hotspots of greenhouse gas (GHG) emissions in temperate regions, while its importance remains controversial for tropical regions as emissions seem to be lower. Here we investigated N2O, CH4 and CO2 emissions from urine and dung patches on tropical pastures in Kenya, thereby disentangling interactive and pure water, dung or urine effects. GHG fluxes were monitored with automated chambers for 42-59 days covering three seasons (short rainy season, long rainy season, dry season) for six treatments (Control; +1 L water; +1 kg dung; 1 L urine; 1 L water +1 kg dung; 1 L urine +1 kg dung). Cumulative CO2 emissions did not differ among treatments in any of the seasons. Water or urine addition alone did not affect CH4 fluxes, but these were elevated in all dung-related treatments. Scaled up on the total area covered, dung patches halve the CH4 sink strength of tropical pastures during the dry season, while during the rainy season they may turn tropical pastures into a small CH4 source. For N2O, both dung and urine alone and in combination stimulated emissions. While the N2O emission factor (EFN2O) from dung being constant across seasons, the EFN2O for urine was greater during the short rainy season than during the dry season. Combined application of urine + dung was additive on EFN2O. While the mean dung EFN2O in our study (0.06%) was similar to the IPCC Guidelines for National GHG Inventories EFN2O for dry climate (0.07%), the urine EFN2O we measured (0.03-0.25%) was lower than the IPCC value (0.32%). In addition, the IPCC Guidelines assume a urine-N: dung-N ratio of 0.66:0.34, which is higher than found for SSA (<0.50:0.50). Consequently, IPCC Guidelines still overestimate N2O emissions from excreta patches in SSA.
Keywords: Emission factor; Excreta; Methane; Nitrous oxide; Ratio dung - urine N; Seasonality.
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