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

N Millar, J K Ndufa, G Cadisch, Elizabeth Baggs

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Abstract

[1] The rotation of crops with fast-growing tree, shrub, and herbaceous N-2-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 N2O 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 ha(-1) 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 (log(e)) 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
Article numberGB1032
Number of pages9
JournalGlobal Biogeochemical Cycles
Volume18
Issue number1
DOIs
Publication statusPublished - 26 Feb 2004

Keywords

  • agroforestry
  • humid tropics
  • improved fallows
  • nitrous oxide
  • residue quality
  • soil mineral nitrogen
  • land use change
  • denitrification rates
  • soil emissions
  • release
  • lignin
  • mineralization
  • legumes
  • carbon
  • litter
  • decomposition

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