Studies
conducted on Alfisols
have shown that
combining no-tillage
and alley cropping
with Leucaena leucocephala
hedgerows results
in significantly
greater levels of
transmission pores,
soil moisture retention
and available plant
water capacity,
and lower soil bulk
density, penetrometer
resistance, water
runoff and soil
erosion (Kang and
Hulugalle 1992,
Lal 1989c). On a
newly-cleared Ultisol
of high-rainfall
area in southern
Cameroon, Hulugalle
and Ndi (1994) found
that exchangeable
calcium, effective
CEC and water infiltration
were greatly increased
in the alleys of
plots where either
Flemingia congesta
or Senna spectabilis
had been planted
within 3 years of
hedgerow establishment.
Increased soil cover
by mulching not
only protects surface
soil from the impact
of water splash
but also improves
microclimatic conditions
by lowering soil
temperature, minimizing
temperature fluctuations,
and increasing soil
moisture. Budelman
(1989) compared
the effect of mulches
from Leucaena
leucocephala,
Gliricidia sepium
and Flemingia
macrophylla
applied at a rate
of 5,000 kg dry
matter ha-1 over
a 60-day period
in Côte d'Ivoire
and found that all
three, especially
F. macrophylla,
influenced soil
temperature and
moisture content
favorably. Four
years of mulch application
in a study on taro
alley-cropped with
Calliandra calothyrsus
and Gliricidia
sepium hedgerows
in Western Samoa
measurably improved
the soil's water
holding capacity
and soil structure
(Rosecrance et al.
1992). Soil moisture
levels were consistently
higher and soil
temperature significantly
lower (as much as
10 C cooler in mid-afternoon)
in the alley plots
compared to the
controls throughout
the growth of the
crop. Noticeably
more macrofauna,
especially worms,
were found in the
alley plots than
in the controls.
Soil
erosion control
on sloping lands
The primary
function of alley
cropping on sloping
lands is erosion
control and soil
conservation. A
large number of
experimental results
and field projects
have confirmed the
efficacy of dense
planting of hedgerows
along contours on
steeply-sloping
lands in controlling
soil erosion. Soil
erosion is reduced
by two approaches:
the "barrier
approach" and
the "cover
approach" (Nair
1993). Contour-planted
hedgerows act as
permeable barriers
slowing the rate
of water flow so
that soil particles
are deposited and
infiltration of
water into the soil
is increased (Giller
and Wilson 1991,
Pellek 1992). The
build-up of soil
behind hedgerows
can gradually lead
to the formation
of terraces. Soil
cover by tree litter
and prunings can
effectively check
raindrop impact
and runoff for some
time until they
are decomposed.
This cover effect
is generally considered
to account for most
of the beneficial
effects of alley
cropping in controlling
soil erosion (Kang
1993, Nair 1993).
Paningbatan
(1990) provided
convincing evidence
for the efficacy
of alley cropping
in checking soil
erosion. In a study
on an Alfisol with
14% slope and a
total rainfall of
1,412 mm during
the 3-month study
period, maize alley-cropped
with contour hedgerows
of Desmanthus virgatus,
established at a
6-m interhedgerow
spacing, effectively
contained erosion.
The presence of
hedegrows combined
with zero tillage
and the prunings
applied as mulch
limited soil loss
to 0.2 ton ha-1,
a significant reduction
from 127 tons ha-1
in the control and
41 tons ha-1 with
hedgerow and contour
cultivation but
no mulch. Lal (1989a)
showed in a study
on an Alfisol in
Nigeria that in
plots tilled and
alley-cropped with
L. leucocephala
and G. sepium with
prunings used as
mulch, erosion was
reduced by 85% and
73%, respectively,
comparing to the
plow-tilled control
plots.
