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

Abstract

Abstract. 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 increase N2O 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.

Combination of Compost and Mineral Fertilizers as an Option for Enhancing Maize (Zea mays L.) Yields and Mitigating Greenhouse Gas Emissions from a Nitisol in Ethiopia

“…In the context of climate-smart agriculture (CSA), soil management should balance the three CSA pillars of mitigation, adaptation, and productivity [1]. Considering type and amount of fertilizer as well as application time and technique can improve the productivity while reducing nutrient imbalances and nutrient losses from agricultural fields [2,3]. Applying organic fertilizers was shown to have positive yield effects in a broad range of cropping systems [4][5][6][7][8] and also has environmental benefits, as evaluated in a life cycle assessment study [9].…”

“…Although, improper application of organic fertilizers can result in considerable releases of greenhouse gases (GHG) [14,17], combining organic and mineral fertilizers was frequently described as a viable option to reduce nitrogen (N) losses and emissions of GHGs, especially carbon dioxide (CO 2 ) and nitrous oxide (N 2 O) in different cropping systems [3,[18][19][20]. The potential to reduce GHG emissions depends largely on the type of the organic amendments and their effects on soil microbial community structure and functions [14].…”

“…This is the main cropping season with WFPS values of about 90% and average temperatures above 20 • C [38], which favor GHG emissions. On a global perspective, Ethiopia emitted relative low amount of GHG with about 150 Mt CO 2 equivalents in 2015, of which about 61% came from agriculture, mainly livestock [3,40]. Because of the low amount of N applied to cropping fields in Ethiopia during the last decades, N fertilizers were not a main driver of GHG emissions [40].…”

Nitrous Oxide Emissions from Smallholders’ Cropping Systems in Sub-Saharan Africa

“…Ortiz-Gonzalo et al [43] showed that maize (Zea mays) intercropped with beans (Phaseolus vulgaris) in central highlands of Kenya emitted N 2 O in the range of 0.18 to 0.27 kg ha −1 . Inorganically fertilized maize crops intercropped with lablab (L. purpureus) and Crotalaria (C. juncea) in Ethiopia emitted between 0.17 and 0.33 kg N 2 O-N ha −1 yr −1 [47]. Intercropping or rotating cereals with legumes provides synergies in managing soil nutrients in the field and may result in relatively lower N 2 O emissions.…”

Fertilizer Management Strategy to Reduce Global Warming Potential and Improve Soil Fertility in a Nitisol in Southwestern Ethiopia

“…Based on the global average value Ethiopia is contributing an insignificant amount of GHGs (0.03%) emissions as a global warming potential, from all agricultural activities [4][5][6]. GHGs emitted from fertilized crop fields are not well investigated and understood in Ethiopia.…”