Effect of legume intercropping on N2O emissions and CH4 uptake during maize production in the Great Rift Valley, Ethiopia

• Published in: Biogeosciences 2020-01, Vol.17 (2), p.345-359
• Main Authors: Shimelis Gizachew Raji, Dörsch, Peter
• Format: Article
• Language: English
• Subjects: Agricultural practices; Agricultural production; Agriculture; Biomass; Cereal crops; Climate-smart agriculture; Corn; Crop production; Crop yield; Crotalaria juncea; Digital agriculture; Emissions; Fertilizers; Flowering; Fluxes; Greenhouse effect; Greenhouse gases; Growing season; Hydroxyapatite; Intercropping; Lablab purpureus; Legumes; Leguminous plants; Methane; Nitrous oxide; Rift valleys; Seasons; Shading; Soil; Uptake; Zea mays
• ISSN: 1726-4170; 1726-4189
• DOI: 10.5194/bg-17-345-2020

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 (N2O) and methane (CH4) fluxes in minerally fertilized maize (64 kg N ha-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 N2O 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, N2O emissions were comparable with the fully fertilized control. Maize-yield-scaled N2O 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 N2O-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 CH4 uptake ranged from 1.0 to 1.5 kg CH4-C ha-1, with no significant differences between treatments or years but setting off the N2O-associated emissions by up to 69 %. Our results suggest that leguminous intercrops may increaseN2O 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.