Nitrous oxide emissions following incorporation of improved-fallow residues in the humid tropics

N. Millar, J. K. Ndufa, G. Cadisch, E. M. Baggs

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The rotation of crops with fast-growing tree, shrub, and herbaceous N2-fixing legume species (improved fallows) is a central agroforestry technology for soil fertility management in the humid tropics. Maize yields are increased following improved fallows compared with continuous maize cropping or traditional natural-fallow systems consisting of broadleaved weeds and grasses. However, the effect of these improved-fallow systems on N availability and N2O emissions following residue application has yet to be determined. Emissions from these systems not only have a detrimental effect on the environment, but are of additional concern in that they represent a potentially significant loss of N and a reduction in N-use efficiency. Emissions of N20 were measured from improved-fallow agroforestry systems in western Kenya, being characteristic of agroforestry systems in the humid tropics. Emissions were increased after incorporation of fallow residues and were higher after incorporation of improved-fallow legume residues (Sesbania sesban, Crotalaria grahamiana, Macroptilium atropurpureum) than natural-fallow residues (mainly consisting of Digitaria abyssibica, Habiscus cannabinus, Bidens pilosa, Guizotia scabra, Leonotis nepetifolia, Commelina benghalensis). Following incorporation of Sesbania and Macroptilium residues (7.4 t dry matter ha-1; 2.9% N) in a mixed fallow system, 4.1 kg N2O-N hat was emitted over 84 days. The percentages of N applied emitted as N2O following residue incorporation in these tropical agroforestry systems were of the same magnitude as in temperate agricultural systems, N2O (loge) emissions were positively correlated with residue N content (r = 0.93; P < 0.05), and thus the residue composition, particularly its N content, is an important consideration when proposing management practices to mitigate N2O emissions from these systems.

Original languageEnglish
Pages (from-to)GB1032 1-9
JournalGlobal Biogeochemical Cycles
Issue number1
Publication statusPublished - Mar 2004


  • Agroforestry
  • Humid tropics
  • Improved fallows
  • Nitrous oxide
  • Residue quality
  • Soil mineral nitrogen

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