Abstract:
n sub-Saharan Africa, agriculture can account for up to 66% of anthropogenic greenhouse
gas (GHG) emissions. Unfortunately, due to the low number of studies in the region there is still
much uncertainty on how management activities can affect these emissions. To help reduce this
uncertainty, we measured GHG emissions from three maize (Zea mays) growing seasons in central
Kenya. Treatments included: (1) a no N application control (C); (2) split (30% at planting and
70% 1 month after planting) mineral nitrogen (N) applications (Min—100 kg N ha−1); (3) split
mineral N + irrigation (equivalent to 10 mm precipitation every three days—MI); (4) split mineral
N + 40 kg N ha−1 added as manure (MM—total N = 140 kg ha−1); and (5) split mineral + intercropping
with faba beans (Phaseolus vulgaris—MB). Soil CO2 fluxes were lower in season 1 compared to seasons
2 and 3 with fluxes highest in Min (p = 0.02) in season 2 and lowest in C (p = 0.02) in season 3. There
was uptake of CH4 in these soils that decreased from season 1 to 3 as the mean soil moisture content
increased. Cumulative N2O fluxes ranged from 0.25 to 2.45 kg N2O-N ha−1, with the highest fluxes
from MI during season 3 (p = 0.01) and the lowest from C during season 1 (p = 0.03). The average
fertilizer induced emission factor (0.36 ± 0.03%) was roughly one-third the default value of 1%. Soil
moisture was a critical factor controlling GHG emissions in these central Kenya highlands. Under
low soil moisture, the soils were CH4 sinks and minimal N2O sources.
