Nitrous oxide and methane fluxes from urine and dung deposited on Kenyan pastures

Livestock keeping is ubiquitous in tropical Africa. Urine and dung from livestock release greenhouse gases (GHGs), such as nitrous oxide (N2O) and methane (CH4), to the atmosphere. However, the extent of GHG’s impact is uncertain due to the lack of in situ measurements in the region. Here we measured N2O and CH4 emissions from cow urine and dung depositions in two Kenyan pastures that received different amounts of rainfall using static chambers across wet and dry seasons. Cumulative N2O emissions were greater under dung+urine and urine-only patches (P < 0.0001), more than three times higher in the wet compared with the dry season (P < 0.0001), and higher in the farm receiving higher rainfall overall (P < 0.0001). Cumulative CH4 emissions differed across treatments (P = 0.012), driven primarily by soil CH4 uptake from the urine-only treatment. Cumulative N2O emissions were positively related to N input rate in excreta. However, the relationship was linear during the dry season (r2 = 0.99; P = 0.001) and exponential during the wet season (r2 = 0.99; P < 0.0001). Nitrous oxide emission factors were 0.05% (dry season) and 0.18% (wet season) of N in urine and dung+urine, which is less than 10% of the IPCC Default Tier 1 emission factor of 2%. We predict that emissions from cattle urine in Kenya are approximately 1.7 Gg N2O–N yr−1 (FAO estimates 11.9 Gg N2O–N yr−1). Our findings suggest that current estimates may overestimate the contribution of excreta to national GHG emissions and that emission factors from urine and dung need to account for agroecosystems with distinct wet and dry seasons

Is conservation agriculture ‘climate-smart’ for maize farmers in the highlands of Tanzania?

Conservation agriculture (CA) is promoted extensively to increase the productivity and environmental sustainability of maize production systems across sub-Saharan Africa and is often listed as a climate-smart agriculture (CSA) practice. However, the impacts of CA on food security, resilience/adaptive capacity and climate change mitigation are location-dependent and it is unknown whether CA can simultaneously address CSA’s multiple objectives. Here we evaluate four variations of CA: reduced tillage plus mulch (mulch), reduced tillage plus mulch and leguminous cover crop (Lablab), reduced tillage plus mulch and leguminous trees (CAWT), and reduced tillage plus mulch and nitrogen fertilizer (CA + F)—for their effect on CSA-relevant outcomes in highland Tanzania maize production. By comparison to conventional practice in the region, intensification of maize production by Lablab, CAWT, and CA + F significantly increases yields by 40, 89 and 77 %, respectively. Likewise, rainfall use efficiency was highest in these three treatments and significantly greater than conventional practices in 7 of 12 comparisons. Seasonal and annual greenhouse gas fluxes were similar across all treatments; however, yield-scaled global warming potential (Mg CO2 eq Mg grain−1) was lower in CAWT (2.1–3.1) and CA + F (1.9–2.3) than conventional practice (1.9–8.3), averaging 62 and 68 % of the emission intensity of conventional practice, respectively. The findings demonstrate that CA can deliver benefits consistent with the objectives of CSA for farmers in this region, particularly when soil nitrogen limitation is alleviated, providing other constraints to adoption are removed