| dc.description.abstract | The study was carried out on 12 natural runoff plot sea c h -Being 2 wide and 11. 6m Ionging s t a I led at Kabete Field Station to assess the effect of surface cover in controlling erosion on an average slope of 8%. Four rates of surface cover (0% cover or control, 10%, 20% and 40% surface cover) with three repl ications of each rate were tested under the natural rainfal during the short rains of 1988, long rains of 1989 and on the simulated rainfal an d ave r Iand f 10 W •
Results showed that the different rates of surface cover were significantly affecting the erosion rate. Annual soil loss (total soil loss from October 1988 to August 1989) for the control plot was
318.5 t/ha, whi Ie for the 10%, 20% and l~O% surface covered plots the annual soil losses were
respectively 301.6, 258.4 and 214.8 t/ha. The soil
loss was highly reduced by the 40%
plots as compared to the other
surface covered
treatments. The
difference between the rates of s u r f ac e cover was statistically different at 95% confidence in controlling soil loss. The percent surface coverage
of the soil by the simulated stones was exponentially related to the soi I loss with a coefficient of determination (r2) of 98%.
The annual runoff was not significantly
influenced by the different rates of the covers. The total r a inf a l from October 1988 to June 1989 in which the runoff plots were monitored was 1370 mm whereas the total runoff, excluding the runoff from the two heavy storms of 07/05/89 and 18/05/89, was
140 mm from the control plot and 139,138 and 130 from
10% 20% and 40% surface covered plots. Excluding the runoff and the rainfal I from th2 two heavy storms, the runoff as percent of• the rainfall was 12% from the 40% surface covered plot and 13%, 12.9% and 12.8% from tbe bare (0%),10% and 2•0% surface covered plots respectively. The effect of the four rates of surface cover was not statistically different in cantrall ing runoff.
Soi I loss from 79 mmlh simulated rainfall for the one hour initial run, was 31.6, 30.3. 24.4 and
21.1 t/ha from the control, 10%, 20% and 40% surface covered plots Espectively. Simi larly runoff was 33,
37. 34 and 27 mm from t he cant r o I, 10%, 20% and 40%
surface covered plots respectively.
The ratios of soil loss from the 40% cover to the 50i I loss from the control plot were 67%, 56%,
57% and 51% r e s p e c t Lve l y from the dry, wet, 1st very wet and 2 nd ve r y wet run 5. Mar eo v e r the rat i a 5 oft he
runoff from the 40% surface covered plots to the
control plot were 82%,
dry. wet. 1st ve r y respectively.
77%. 72% and 93% during the wet and 2~ very wet runs
The analysis of particle size distribution of
the eroded sediment showed that the proportion of clay sized particles in the eroded sediment was low in the short rains but slowly increased in the long r~ins as the erosion process continued.
The cover and management C-factor values computed as the ratios of the annual soil loss from the surface covered plots to the control plot was
0.91, 0.81 and 0.65 for 10%, 20% and 40% surface covers respectively.
As a result of the experiment and field investigations it is concluded that increased surface
cover reduces erosion whereas removal of stones lead to an increase in runoff and s o i I loss. However, removal of stones may be desirable in place's where the soi Is are deep and have stones throughout the profile. | en |
