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E.M.Baggset al.
Effect of Residue Quality on N
2
O Emissions
3.2
Effect of Residue Quality on
N
2
O Emissions from Tropical
Soils
E.M. B
AGGS
, N. M
ILLAR
, J.K. N
DUFA AND
G. C
ADISCH
Department of Biology, Imperial College at Wye, Wye,Ashford,
Kent TN25 5AH, UK
Introduction
One of the potential benefits of N
2
-fixing trees in agroforestry systems is
the recycling of nutrients through litter fall or prunings, which become
available to crops after decomposition. The quality of the prunings or litter
is important in determining nutrient supply and soil organic matter
formation. However, crop N recovery from prunings is often < 20% (Giller
and Cadisch, 1995), with a lack of synchrony between N release and crop
demand, and the potential for substantial N losses. Previous work in
temperate systems has shown that incorporation of plant material can
significantly increase N
2
O emissions from soils. The magnitude of
emissions varies depending on the quality and biomass of added plant
material, and also with soil temperature, moisture content, aeration, soil
type and cultivation. Greater N
2
O emissions are usually measured after
incorporation of material with a low C : N ratio, than material with a high
C : N ratio (Baggs
et al
., 2000). However, for tropical agroforestry residues,
lignin and polyphenol contents have a strong influence on determining
the availability of N for release (Handayanto
et al
., 1994) and hence
nitrification and denitrification. Emissions from agroforestry systems are of
concern, not only due to the loss of valuable N resource from the system,
but also due to the role of N
2
O in the greenhouse effect and the destruction
of stratospheric ozone.
We report here the results of controlled environment experiments in
which N
2
O emissions and N release were measured following amendment
of tropical soils with prunings and residues from alley cropping and
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