Enteric methane emission estimates for Kenyan cattle in a nighttime enclosure using a backward Lagrangian Stochastic dispersion technique

This study provides methane (CH$_{4}$) emission estimates for mature female African beef cattle in a semi-arid region in Southern Kenya using open-path laser spectroscopy together with a backward Lagrangian Stochastic (bLS) dispersion modeling technique. We deployed two open-path lasers to determine 10-min averages of line-integrated CH$_{4}$ measurements upwind and downwind of fenced enclosures (so-called bomas: a location where the cattle are gathered at night) during 14 nights in September/October 2019. The measurements were filtered for wind direction deviations and friction velocity before the model was applied. We compared the obtained emission factors (EFs) with the Intergovernmental Panel on Climate Change (IPCC) Tier 1 estimates for the Sub-Saharan African (SSA) countries, which were mostly derived from studies carried out in developed countries and adapted to the conditions in Africa. The resulting EF of 75.4 ± 15.99 kg year$^{-1}$ and the EFs calculated from other studies carried out in Africa indicate the need for the further development of region-specific EFs depending on animal breed, livestock systems, feed quantity, and composition to improve the IPCC Tier 1 estimates

Nitrous oxide emission factors for cattle dung and urine deposited onto tropical pastures: A review of field-based studies

Livestock excreta on pastures is an important source of nitrous oxide (N2O) emissions, however studies measuring these emissions in tropical regions, particularly Africa, remain limited. Therefore we measured N2O emissions from different quantities of dung patches during three observation periods (dry, wet and transition from dry to wet season) and different volumes of urine patches during wet and dry seasons. Dung patches did not stimulate soil N2O emissions in any of the three observation periods, while urine application stimulated soil N2O emissions during both seasons, with higher emissions observed during the wet season. The dung EFs (0.00–0.03%) and the urine EFs (0.04–0.40%) showed no detectable effects of dung quantity or urine volume. We further synthesized observations from other studies in wet and dry tropical regions, which indicated that the excreta N2O EFs were similar to the default values provided in the IPCC 2019 refinement (0.11% vs 0.07% for dung and 0.41% vs 0.32% for urine in dry climates, and 0.13% vs 0.13% for dung and 0.65% vs 0.77% for urine in wet climates). However, sub-Saharan African (SSA) studies had consistently lower EFs, possibly due to the lower urine-N: dung-N ratio in SSA compared with the other tropical regions, suggesting that the refinement may still overestimate excreta emissions in SSA. Moreover, considering the large variations in the summarized tropical excreta N2O EFs, from -0.01 to 1.77% for dung and 0.00 to 4.90% for urine, more studies under diverse conditions across tropical regions are recommended

Identification of temporary livestock enclosures in Kenya from multi-temporal PlanetScope imagery

The use of night-time livestock enclosures, often referred to as “bomas”, “corrals”, or “kraals”, is a common practice across African rangelands. Bomas protect livestock from predation by wildlife and potential theft. Due to the concentration of animal faeces inside bomas, they not only become nutrient-rich patches that can add to biodiversity, but also hotspots for the emission of nitrous oxide (N$_{2}$O), an important greenhouse gas, especially when animals are kept inside for long periods. To provide an accurate estimate of such emissions for wider landscapes, bomas need to be accounted for. Moreover, initial experiments indicated that more frequent shifts in the boma locations could help to reduce N$_{2}$O emissions. This stresses the need for better understanding where bomas are located, their numbers, as well as when they are actively used. Given the recent advances in satellite technology, resulting in high-frequent spectral measurements at fine spatial resolution, solutions to address these needs are now within reach. This study is a first effort to map and monitor the appearance of bomas with the use of satellite image time series. Our main dataset was a dense times series of 3 m resolution PlanetScope multispectral imagery. In addition, a reference dataset of boma and non-boma locations was created using GPS-collar tracking data and 0.5 m resolution Pléiades imagery. The reduction of vegetation cover and increase of organic material following boma installation result in typical spectral changes when contrasted against its surroundings. Based on these spectral changes we devised an empirical approach to infer approximate boma installation dates from PlanetScope\u27s near infrared (NIR) band and used our reference dataset for setting optimal parameter values. A NIR spatial difference index resulted in clear temporal patterns, which were more apparent during the wet season. At landscape scale our approach reveals clear spatio-temporal patterns of boma installation, which could not be revealed from less frequent sub-meter resolution imagery alone. While further improvements are possible, we show that small-sized (150–500 m$^{2}$) temporary surface changes, such as those that occur when pastoralists use mobile bomas, can be detected with dense image time series like those offered by the PlanetScope constellation. In future, this could lead to better assessment of a) spatio-temporal livestock distribution, b) the contribution of bomas to N$_{2}$O emissions and soil fertility at landscape scale, and c) the uptake of enclosure rotation practices at large spatial scales

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

To improve the estimate of greenhouse gas emissions (GHG) from tropical rangelands in sub-Saharan Africa, we measured GHG emissions from sheep excreta over two periods of 51 days on a Kenya rangeland. In addition, we measured GHG emissions from potential hotspots in the landscape linked to sheep grazing: overnight enclosures (“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 CO$_2$ fluxes after sheep urine application and a rapid increase of CH$_4$ fluxes following sheep dung application in both rainy and dry season. However, only small increases of N$_2$O fluxes were observed after dung and urine applications compared to controls without excreta. Elevated N$_2$O fluxes mainly coincided with heavy rainfall. Overall, N$_2$O emission factors (EFs) did not vary across excreta type or seasons, but mean N$_2$O EFs for dung (0.01%) and urine patches (0.02%) were only one tenth of the default EFs from the 2019 IPCC Refinement for dry climate. We did, however, find that bomas and watering troughs are sites of herd concentration that are important sources of GHG emissions in the landscape, and that emissions in these locations can remain elevated for months to years, especially when soil moisture is high. This study contributes to more robust estimates of GHG emissions from African livestock systems, which are fundamental to develop targeted mitigation strategies

Soil greenhouse gas emissions from a sisal chronosequence in Kenya

Sisal (Agave sisalana) is a climate-resilient crop grown on large-scale farms in semi-arid areas. However, no studies have investigated soil greenhouse gas (GHGs: CO2, N2O and CH4) fluxes from these plantations and how they relate to other land cover types. We examined GHG fluxes (Fs) in a sisal chronosequence at Teita Sisal Estate in southern Kenya. The effects of stand age on Fs were examined using static GHG chambers and gas chromatography for a period of one year in seven stands: young stands aged 1-3 years, mature stands aged 7-8 years, and old stands aged 13-14 years. Adjacent bushland served as a control site representing the surrounding land use type. Mean CO2 fluxes were highest in the oldest stand (56 +/- 3 mg C m(-2) h(-1)) and lowest in the 8-year old stand (38 +/- 3 mg C m(-2) h(-1)), which we attribute to difference in root respiration between the stand. All stands had 13-28% higher CO2 fluxes than bushland (32 +/- 3 mg C m(-2) h(-1)). CO2 fluxes in the wet season were about 70% higher than dry season across all sites. They were influenced by soil water content (W-S) and vegetation phenology. Mean N2O fluxes were very low (Peer reviewe

Effect of feeding practices and manure quality on CH4_{4} and N2_{2}O emissions from uncovered cattle manure heaps in Kenya

Countries in sub-Saharan Africa (SSA) rely on IPCC emission factors (EF) for GHG emission reporting. However, these were derived for industrialized livestock farms and do not represent conditions of smallholder farms (small, low-producing livestock breeds, poor feed quality, feed scarcity). Here, we present the first measurements of CH$_{4}$ and N$_{2}$O emissions from cattle-manure heaps representing feeding practices typical for smallholder farms in the highlands of East Africa: 1) cattle fed below maintenance energy requirements to represent feed scarcity, and 2) cattle fed tropical forage grasses (Napier, Rhodes, Brachiaria). Sub-maintenance feeding reduced cumulative manure N$_{2}$O emissions compared to cattle receiving sufficient feed but did not change EF$_{N2O}$. Sub-maintenance feeding did not affect cumulative manure CH$_{4}$ emissions or EF$_{CH4}$. When cattle were fed tropical forage grasses, cumulative manure N$_{2}$O emissions did not differ between diets, but manure EF$_{N2O}$ from Brachiaria and Rhodes diets were lower than the IPCC EF$_{N2O}$ for solid storage (1%, 2019 Refinement of IPCC Guidelines). Manure CH$_{4}$ emissions were lower in the Rhodes grass diet than when feeding Napier or Brachiaria, and manure EF$_{CH4}$ from all three grasses were lower than the IPCC default (4.4 g CH$_{4}$ kg$^{-1}$ VS, 2019 Refinement of IPCC Guidelines). Regression analysis revealed that manure N concentration and C:N were important drivers of N$_{2}$O emissions, with low N concentrations and high C:N reducing N$_{2}$O emissions. Our results show that IPCC EFs overestimate excreta GHG emissions, which calls for additional measurements to develop localized EFs for smallholder livestock systems in SSA