| dc.description.abstract | A 24 year rainfall data study was done for Mutomo,
southern Kitui. Seasonal rainfall was found inadequate
in 71% and 57% of the dry "long" and "short" rains,
respectively.
be tween years,
Mon th Iy ra in fa II
with coefficient
was highly variable
of variation often
above 100%; there were also many small storms compared
to big ones as evidenced by large data skewness. The
"long" rains last shorter than the "short" rains, and
by virtue of seasonal total, the former was classified
as unfavourable for a crop like maize. On average, 58%
and 67% of rainfall in April and November were found
to be potentially runoff-producing. These results
justified water harvesting for supplementing rainfall
to improve maize production in the area.
A water harvesting experiment for maize production was
conducted at the Mutomo site in the "short" rains of
1990 on a field of 5% slope. The experimental area
consisted of twelve plots in three blocks of four
plots each. Treatments were 0 (control), 13.6, 19.6
and 27.2 m2 of sloping catchment areas above each 16 m2
level cropped area. The soil was deep with no apparent
restriction within 150 cm. The soil texture was sandy
clay for the top 60 cm and clay below this depth. Bulk
densities varied from 1490 for the top 15 cm to 1540
kgm-3 from 60-105 cm. Infiltration tests conducted with
double ring
infiltration
xv
infiltrometer gave a range
rat es 0 f 14 .2 t0 75 .5 mm h-1•
of final
The mean
organic matter content was 3.68%. The soil was high in
base saturation and low in macro nutrients especially
ni trogen and phosphorus, but showed no hazards of
salinity or sodicity.
Soil sampling for moisture determination was done to
105 cm depth every ten days. A water balance was done
for each treatment for 82 days of the rainfall season.
Runoff simulation was done using a portable rainfall
simulator. Computer generated daily runoff values were
determined for each rainfall event. The rainfall was
606.3 mm and pan evaporation was 341.9 mm. High
intensity rainfall resulted in a high mean runoff of
61%. Computer generated runoff ranged from 8.5% to 84%
early in the dry and in the wettest periods of the
season, respectively, showing high sensitivity to
"antecedent mois~ure. The total runoff was estimated at
287.0, 259.7, 185.9 and 0 mm and the percolation below
root zone at 368.5, 341.9, 268.6 and 84.4 mm for the
27.2, 19.6, 13.6 and 0 m2 catchments, respectively.
Soil moisture increased to saturation in the wet
period, and reduced to 183 mm at the end of the
season. Yields of Katumani maize grown at the
experimental site were not significantly different at
P=0.05, a fact attributed to the above average
rainfall In the season. | en |
