Mulching and green manuring effects of prunings
depend on the quantity and quality of the prunings added. Low quality prunings have long duration
mulching effects. High quality mulches, characterised
by a low C/N ratio and low lignin content,
decompose readily, and have a short-term mulching
effect and serve better as green manure (Tian et al.,
1992). Application of prunings as mulch is known
to:
1. protect the surface soil from the impact of raindrops;
2. lower surface soil temperature;
3. increase soil moisture infiltration and retention:
4. improve physical soil properties;
5. increase soil microbial and fauna1 activities;
6. suppress weeds.
An important, but little studied aspect of alley
cropping/agroforestry is the effect on soil fauna.
Kang et al. (1990) reported higher casting activity by
earthworms (Hyperiodrifus africanus) in ahey
cropped plots than in control (no hedgerow) plots.
Although casting activities of this earthworm species
vary under different woody species, they are also
higher under the hedgerows than in the alleys. The
improvement of soil physical conditions With increased
earthworm activities, combined with the
mulching effect of the prunings and the physical
barrier effect of the hedgerows, can contribute to
reduce soil erosion and runoff with alley cropping on
sloping land (Paningbatan, 1990; Kang and Ghuman,
1991).
It is well known that the organic matter content of
surface soil declines rapidly following forest clearing
and cropping, and attains an equilibrium level depending
on the cropping system and management 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