| dc.description.abstract | In this study, maize yields at Katumani have been related to two sets of
weather indices. These indices, known as the water requirement satisfaction indices
were computed according to a model developed by Frere and Popov (1979). One
index was computed using crop coefficients given by Food and Agricultural
Organization (FAO, 1986) and-the other by Mugah and Stewart (1982). The indices
were set at 100 at the time of emergence and started reducing the moment the crop
underwent water stress.
The analysis showed that changes of available soil water during the flowering
to wax ripeness phenological phases were the most sensitive as they affected the final
maize yields the most. This was followed by the tasselling to flowering interphase.
When the ratio of the interphase available water to the interphase water requirement
was correlated to yields, the flowering to wax ripeness interphase showed the highest
correlation. Correlating the interphase soil water deficits to the yields, results showed
that the crops experienced water stress in the last three interphases i.e. tasselling to
flowering, flowering to wax ripeness and wax ripeness to full ripeness. Flowering to
wax ripeness interphases had the highest negative correlation, followed by tasselling
to flowering and finally wax ripeness to full ripeness.
A modification to this model was done with the aim of improving on the
correlation between the indices and yields. This modification took into consideration
the interphase( s) at which the crop experienced water stress during the computation
of the indices. Interphase weights or coefficients were developed and used in the
computation of the final indices. There was a considerable improvement both in the
correlation coefficients obtained between the indices and yield, and the coefficient of
determination. Much of the yield variation at Katumani seemed to be due to water
stress experienced at the tasselling to flowering and flowering to wax ripeness interphases.
The equations developed when maize yields (dependent variable) was
regressed against the interphase modified indices (independent variable) were used
to predict yields for 1989 to 1991.
This study also tested the suitability of cultivating Katumani Composite B maize
using the FAD criteria. The long rains were found to be suitable. The short rains were
just below the threshold probability of success for a good crop.
Also investigated in this study were the most appropriate sowing dates using
the modified indices. The results showed that the earlier the planting dates in a given
season, the higher the chances for a successful crop and hence, good yields to be
attained. | en |
