| dc.description.abstract | The influence of rainfall, vegetative cover and soil
characteristics on runoff and soil loss were
investigated on the semi-arid area of Mukogodo,
Laikipia District, Kenya. This study was carried out
between July 1992 and August 1993. Two site conditions
with respect to vegetation cover and two management
systems were the treatments. They were designated as
Perennial Enclosed (PE), Perennial Open (PO), Bare
Enclosed (BE) and Bare Open (BO). Three runoff plots
(each 2 by 10 metres) were designed and set up in each
of the above treatments.
Rainfall parameters (amount and intensity) were
measured. storm kinetic energies and erosivities were
determined using the formula E = 11.9 + 8.7 * log I
(Wischmeier et aI, 1958). Runoff and sediment yield
from each plot were measured after each rainfall
event. Soil moisture was monitored in each treatment
using a Neutron probe up-to 75 cm deep. Vegetative
cover and soil surface condition were also monitored
in all the plots.
Over the study period, the Bare plots (BE and BO) lost
over 50% of rainfall as runoff. The Perennial plots
(PE and PO) had runoff less than half the runoff from
the Bare plots. Total runoff values for BE and BO were
not significantly different at p<O.Ol, and thus
closure to grazing did not reduce rainwater loss from
the Bare plots. There was a significant difference
(p<O.Ol) between total values of runoff for the PE and
PO plots. This showed that closure to grazing reduced
rainwater loss from the Perennial plots.
The total values of soil loss for the Bare plots were
above the acceptable limit of 10 t/ha/yr (Hudson ,
1981), while the Perennial plots recorded acceptable
soil loss values. Closure to grazing did not lead to
an improvement in vegetative cover in the Bare plots.
A fast cover recovery was observed in the Perennial
plots after the short rains. High crust strength
values were recorded in this study. The Bare plots had
crust strength values which were 15-30% higher than
the crust strength values recorded in the Perennial
plots.
In all treatments, available soil water was between
25% of Available Water Capacity (AWC) and 2% of AWC
most of the time. As compared to the Bare plots, the
Perennial plots had higher total available soil water
at the beginning of each season. Soil moisture results
also showed that very little water (less than 2 mm)
was recorded below the 50 cm depth for all the treatments.
Multiple regression analysis revealed that rainfall,
erosivity and vegetative cover accounted for 65% of
the variability in rainwater loss. Similarly,
rainfall, erosivity, and runoff accounted for 72% of
variation in the in the soil lost. Vegetative cover
significantly (p<O.05) reduced runoff, while the
impact on soil loss was not statistically significant.
Important implications for developing a strategy to
reclaim denuded land arise from the results of this
study. The results show that vegetative cover reduces
runoff. It can be expected that a reduced runoff will
lead to a reduced soil loss. This means that
vegetative cover should be encouraged as a means to
improve denuded land. From the results, zones with
some cover of perennial grasses will recover by
closure alone. The high runoff from the Bare areas
shows that easy recovery is impossible unless some
measures are taken to get water into the ground | en |
