Abstract
Abstract. Few field studies examine greenhouse gas (GHG) emissions from African agricultural systems, resulting in high uncertainty for national inventories. This lack of data is particularly noticeable in smallholder farms in sub-Saharan Africa, where low inputs are often correlated with low yields, often resulting in food insecurity as well. We provide the most comprehensive study in Africa to date, examining annual soil CO2, CH4 and N2O emissions from 59 smallholder plots across different vegetation types, field types and land classes in western Kenya. The study area consists of a lowland area (approximately 1200 m a.s.l.) rising approximately 600 m to a highland plateau. Cumulative annual fluxes ranged from 2.8 to 15.0 Mg CO2-C ha−1, −6.0 to 2.4 kg CH4-C ha−1 and −0.1 to 1.8 kg N2O-N ha−1. Management intensity of the plots did not result in differences in annual GHG fluxes measured (P = 0.46, 0.14 and 0.67 for CO2, CH4 and N2O respectively). The similar emissions were likely related to low fertilizer input rates (≤ 20 kg N ha−1). Grazing plots had the highest CO2 fluxes (P = 0.005), treed plots (plantations) were a larger CH4 sink than grazing plots (P = 0.05), while soil N2O emissions were similar across vegetation types (P = 0.59). This study is likely representative for low fertilizer input, smallholder systems across sub-Saharan Africa, providing critical data for estimating regional or continental GHG inventories. Low crop yields, likely due to low fertilization inputs, resulted in high (up to 67 g N2O-N kg−1 aboveground N uptake) yield-scaled emissions. Improvement of crop production through better water and nutrient management might therefore be an important tool in increasing food security in the region while reducing the climate footprint per unit of food produced.
Highlights
Increased atmospheric concentrations of greenhouse gases (GHGs: CO2, N2O and CH4) over the last century have been correlated to increasing mean global temperature (IPCC, 2013); while N2O is the primary ozone-depleting anthropogenically emitted gas (Ravishankara et al, 2009)
This study indicates that soil GHG fluxes from low-input, rain-fed agriculture in western Kenya are lower than GHG fluxes from other tropical or subtropical agricultural systems with greater management intensities (e.g., China and Latin America)
Given that GHG emissions are often associated with soil moisture and that much of eastern Africa is drier than the climate at this study site, baseline emissions of GHGs across eastern Africa may be extremely low
Summary
Increased atmospheric concentrations of greenhouse gases (GHGs: CO2, N2O and CH4) over the last century have been correlated to increasing mean global temperature (IPCC, 2013); while N2O is the primary ozone-depleting anthropogenically emitted gas (Ravishankara et al, 2009). Previous studies in Africa were limited in scope, measuring emissions from a low number of sites (generally less than 10) for a short time period (i.e., less than 1 year), often with low temporal resolution This shortage of baseline data makes it impossible for many developing countries to accurately assess emissions from soils used for agriculture or to use Tier 2 methodology, which requires the development and documentation of country or regionally specific emission factors, to calculate GHG inventories (IPCC, 2006). Because most of the research behind the development of the Tier 1 methodology has been completed in temperate zones, the differences in climate, soils, farm management and nutrient balances (Vitousek et al, 2009) seem to result in consistent overestimates of GHG fluxes (Hickman et al, 2014b; Rosenstock et al, 2013b) This likely translates to inflated national agricultural GHG inventories in SSA that may result in incorrect targeting and inefficient mitigation measures
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