Contribution of livestock effluent management to the soil greenhouse gas emission in a Sahelian agropastoral region

Abstract. The assessment of greenhouse gas (GHG, i.e., CO₂, CH₄ and N₂O) emissions from soils is a major component of the carbon footprint of the agro-pastoral ecosystems in the Sahelian region. For this purpose, CO₂ emissions were measured in the district of Dantchandou in Niger using a portable analyzer EMG-5 over the annual cycle at nineteen sites from three land use types: shifting crop fields, manured crop fields, and fallow, as well as from three livestock concentration spots: livestock corrals, areas near pastoral ponds and near a pastoral well. Furthermore, CH₄, and N₂O emissions were measured using a static chamber on a subsample of three land uses and in five different months. The daily and seasonal emission dynamics are defined. The CO₂ emissions measured with the EMG-5 are consistently lower at the beginning and end of the day, higher in the early afternoon in un-manured sites, and in the late morning in manured sites. Mean daily CO₂ emissions increase with the first rains in June, peak at the beginning and end of the rainy season, and fall sharply following the end of the rains in October. The average daily CO₂ emissions from livestock concentration spots reaches during the rainy season 2.64±1.35 gCO₂ m^-2 d^-1 in vicinity of the pond, 24.99±15.73 gCO₂ m^-2 d^-1 in corralling field and 75.09±28.34 gCO₂ m^-2 d^-1 close to the pastoral well, compared to respectively 1.53±1.35, 1.68±0.65 and 4.68±0.75 gCO₂ m^-2 d^-1 during the dry season. The rainy season averages from shifting, manured and fallow fields are 4.3±2.72, 13.8±5.76 and 4.7±2.62 gCO₂ m^-2 d^-1 respectively and only 1.3±0.41, 1.8±0.48 and 1.2±0.35 gCO₂ m^-2 d^-1 during the dry season. The annual mean CO₂ emissions are very high in livestock corrals and near pastoral wells (respectively 34.0±10.9 and 92.5 MgCO₂ ha^-1 y^-1) and higher in manured fields (21.2 ±3.9 MgCO₂ ha^-1 y^-1) than in shifting fields, fallow and around ponds (8.3±2.5, 8.7±1.5 and 9.9±3.7 MgCO₂ ha^-1 y^-1 respectively). To account for that spatial variability in assessing the annual emissions at the scale of the district, emissions were weighted by the areas of each land use or livestock concentration spots in the territory. As a result, annual emissions from soils in the district are estimated at 16.5 MgCO₂ ha^-1 y^-1, 175 kg CH₄ ha^-1 y^-1 and 36 kg N₂O ha^-1 y^-1. The gap in CO₂ emissions between manured and un-manured sites is used to estimate the contribution of the livestock effluent deposit to the annual CO₂ emissions in the territory. In average over the year this contribution amounts 0.48 gCO₂ m^-2d^-1 or 15.3% of total soil CO₂ emissions.