Effect of legume intercropping on N.sub.2O emissions and CH.sub.4 uptake during maize production in the Great Rift Valley, Ethiopia

Intercropping with legumes is an important component of climate-smart agriculture (CSA) in sub-Saharan Africa, but little is known about its effect on soil greenhouse gas (GHG) exchange. A field experiment was established at Hawassa in the Ethiopian rift valley, comparing nitrous oxide (N.sub.2 O) and methane (CH.sub.4) fluxes in minerally fertilized maize (64 kg N ha.sup.-1) with and without Crotalaria (C. juncea) or lablab (L. purpureus) as intercrops over two growing seasons. To study the effect of intercropping time, intercrops were sown either 3 or 6 weeks after maize. The legumes were harvested at flowering, and half of the aboveground biomass was mulched. In the first season, cumulative N.sub.2 O emissions were largest in 3-week lablab, with all other treatments being equal to or lower than the fertilized maize mono-crop. After reducing mineral N input to intercropped systems by 50 % in the second season, N.sub.2 O emissions were comparable with the fully fertilized control. Maize-yield-scaled N.sub.2 O emissions in the first season increased linearly with aboveground legume N yield (p=0.01), but not in the second season when early rains resulted in less legume biomass because of shading by maize. Growing-season N.sub.2 O-N emission factors varied from 0.02 % to 0.25 % in 2015 and 0.11 % to 0.20 % in 2016 of the estimated total N input. Growing-season CH.sub.4 uptake ranged from 1.0 to 1.5 kg CH.sub.4 -C ha.sup.-1, with no significant differences between treatments or years but setting off the N.sub.2 O-associated emissions by up to 69 %. Our results suggest that leguminous intercrops may increase N.sub.2 O emissions when developing large biomass in dry years but, when mulched, can replace part of the fertilizer N in normal years, thus supporting CSA goals while intensifying crop production in the region.