practice. Since organic matter plays a crucial role in
maintaining the productivity of poorly buffered upland
soils, attempts should be made to use production
systems that have relatively high surface soil
organic matter levels. The results of long-term observations
on high base status soils show that this is
more effectively achieved with alley cropping than sole cropping (Table 2). Even after 5 years of continuous
cropping, the organic C level under the
hedgerows was 1.23%~the same as that observed at
the start of the trial. The alleys also showed higher
organic C levels than the control treatment. The
microsite soil enrichment under the hedgerows probably
results from partial shading, litter fall and higher
fauna1 activities.
The manurial effect of hedgerow prunings depends
on their chemical composition, nutrient yield
and management practices. The amount of nutrient
yield varies with species (Table 3). Nitrogen fixing
species such as Gliricidia and Leucaena have high
N-yields of 225 and 300 kg N ha- ’ year-‘, respectively.
Despite the high amount of N yieId from
Gliricidia (128 kg N ha- ’ > and Leucaena (232 kg N
ha-’ ) during the main growing season, the associated
maize crop in this trial still responded to N
application, due to low N-use efficiency from the
prunings (Mulongoy and Van der Meersch, 1988).
Kang (1988) estimated the N contribution from Gliricidia
and Leucaena prunings to an associated maize
crop to be about 40 kg N ha- ‘. Incorporation of
N-fixing leguminous hedgerows does reduce the N
requirement for crop production with alley cropping
to some extent. Further research is needed to assess
the contributions of other nutrients in the prunings to
the associated crops.