Soil Organic Matter Management: The Roles of Residue Quality in C Sequestration and N Supply - Sustainable Management of Soil Organic Matter - page 116

amended treatments. Emissions from the Kenyan clay soil in the second
experiment were higher ( P < 0.1) than from the Chitedze sandy clay loam
in the first experiment. This may have been due to the development of
anaerobic microsites in the Kenyan soil, as a result of its higher clay content
(48% as opposed to 28%).
Incorporation of Sesbania resulted in rapid N release and very high,
but short-lived (2 days), fluxes of N 2 O (data not shown). Such rapid N
release from Sesbania is undesirable in improved fallow systems as the
N availability is often asynchronous with crop demand (Handayanto et al .,
1997) and therefore can result in large, immediate gaseous losses. Over 29
days, there was no significant difference in total N 2 O emissions from the
Sesbania and Macroptilium treatments. Grinding (< 2 mm) as opposed to
chopping (< 7 mm) of high-quality Sesbania leaves had no significant effect
on N 2 O emissions. Jensen (1994) found that decomposition of high-quality
residues of different sizes varied only slightly. Greater difference between
grinding and chopping could be expected following incorporation of
low-quality material, by increasing the accessibility of moderately available
C to microbial attack.
This work has shown N 2 O production to be influenced by residue
polyphenol content and its ability to bind proteins. There is the potential
for these losses to be controlled and N to be retained within the system by
regulating N release and improving synchrony of N supply with crop
demand by manipulating the quality of organic inputs using varying
combinations of plant material of differing qualities, prunings of different
ages from the same plant and varying combinations of inorganic and
organic N sources. This will be examined in future experiments, and N 2 O
losses will also be equated with losses by NH 3 volatilization, NO 3 − leaching
and total denitrification. The relative contributions of nitrification and
denitrification to the N 2 O fluxes are unquantifiable without the use of
selective nitrification inhibitors, or stable isotope techniques. Further
process-based studies will be undertaken to verify this.
Acknowledgements
We wish to thank the Rockefeller Foundation for funding part of this work,
and Jon Fear for analysis of plant material.
References
Baggs, E.M., Rees, R.M., Smith, K.A. and Vinten, A.J.A. (2000) Nitrous oxide
emissions from soils after incorporating plant material. Soil Use and Manage-
ment 16, 42-48.