| dc.description.abstract | Effects of the rainfall variability on soil moisture (SM) over crop growth periods is
a prerequisite for assessing and developing better soil moisture conservation practices in
semi-arid areas. It was therefore necessary to quantify soil moisture variability as affected
by rainfall availability for crop productivity. This lead to an investigation into hydrologic and
subsequent crop responses. The study was based on data collected for Kalalu, Laikipia
District during the short and long rains periods of 1988 and 1989 respectively. Maize and
beans under three soil moisture management practices, namely tied ridging (TR),
conventional tillage (CT) and residue mulch (RM) were studied.
Data on rainfall, soil moisture and crop yields were used. An estimate of soil moisture
and crop yields were used. An estimate of soil moisture variability in the rhizosphere by
Land Use Specific Analysis (LUSA) method, crop evapotranspiration by Crop Water
Requirement estimation Program (CROPWAT), Available Soil Moisture Index (ASI) and
LUSA Methods were made. Potential crop yields were estimated through Wageningen and
Agro-Ecological zone Methods for maize and beans respectively. Actual yields were
estimated through CROPWAT, YES and Doorenbos Methods. Comparison between rainfall,
soil moisture, available soil moisture, crop evapotranspiration and crop yields under the three
tillage practices and the two crops were made.
Increasing trends in soil moisture during both short and long rains period for the three
tillage types were observed. The trend was more for the 1989 long rains season. Soil
moisture during the short rains period in the three treatments reached their maximum within
18 days and remained constant for the next 20 days before declining with TR having the
lowest declining rate. During the long rains, SM in both RM and CT reached their maximum
within 43 days before declining while TR had a lower increasing rate reaching a maximum
within 53 days before declining at a lower rate than the other two. Generally SM during the
short rains period was higher than that of the long rains.
Rainfall amount and distribution before and after tillage coupled with the tillage
practices enhanced soil moisture with rainfall having more impact. There was little significant
difference in cumulative crop water used under the three treatments. CROPW AT
overestimated the crop water used during the long rains season. There was an overestimate
of bean yields due to the unexpected high measured soil moisture. Major reduction in yield
was due to water deficit. Water and temperature limitations were two major factors that
reduced maize yields from 8.9tons/ha to 1.2tons/ha.
These analyses showed that quantification of soil moisture and consequent crop water
used within the crop growth stages will facilitate the choice of appropriate tillage practices.
Early tillage especially after harvesting was necessary for soil moisture retention and
availability to the crop. A combination of residue mulch and tied ridging will facilitate better
soil moisture distribution necessary to reduce water deficits and improver crop | en |
