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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-303
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-303
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 13 Aug 2019

Submitted as: research article | 13 Aug 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Effect of legume intercropping on N2O emission and CH4 uptake during maize production in the Ethiopian Rift valley

Shimelis G. Raji1,2 and Peter Dörsch1 Shimelis G. Raji and Peter Dörsch
  • 1Faculty for Environmental Sciences and Resource Management, Norwegian University of Life Sciences (NMBU), 1432 Ås, Norway
  • 2College of Agriculture, Hawassa University, P.O, Box 05, Hawassa, Ethiopia

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 three or six weeks after maize. The legumes were harvested at flowering and half of the above-ground biomass was mulched. In the first season, cumulative N2O emissions were largest in 3-week lablab, with all other treatments being equal or lower than the fertilized maize monocrop. After reducing mineral N input to intercropped systems by 50 % in the second season, N2O emissions were at par with the fully fertilized control. Maize yield-scaled N2O emissions in the first season increased linearly with above-ground 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 and 0.11 to 0.20 % of the estimated total N input in 2015 and 2016, respectively. 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 global warming potential by up to 69 %. Our results suggest that high yielding leguminous intercrops entail some risk for increased N2O emissions when used together with recommended fertilization rates, but can replace part of the fertilizer N without compromising maize yields in the following year and thus support CSA goals while intensifying crop production in the region.

Shimelis G. Raji and Peter Dörsch
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Shimelis G. Raji and Peter Dörsch
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