| dc.description.abstract | To the east and south of the central highlands
of Kenya lies an area whose agricultural production
is based on a low and unreliable rainfall. There
are two cropping seasons in a year of roughly equal
duration. The rainfall duration of each season
seldom exceeds two months and heavy rain usually
occurs during the first month from the start of rains.
This, combined with structurally weak and rapidly
capping, sandy clay or sandy loam soils, results in
the loss of considerable amounts of rainfall as
runoff. With little or no rainfall occuring after
two months from the onset of the rains, it means
that crops of three to four months duration have to
reach maturity mainly with moisture stored in the
soil, Hence crop failures are quite frequent.
In this research project, selected tillage
practices and cropping sequences were investigated
to determine their'effectiveness in conserving
rainfall. The research project was carried out at
Katumani Agricultural Research Station, Machakos,
which is situated within the target area. Minimum,
conventional, cloddy and tied-ridge tillage
methods were tried. It was expected that the different
methods would have different effects on the
infiltration capacity of the soil and hence on the
proportion of rain which would be lost as runoff and
that which would infiltrate into the soil. The
cropping sequences included maize/maize, beJ3,ns/maize
and bare fallow/maize, and it was expected that the
d~fferent sequences would conserve varying amounts of
residual moisture at the end of the first season.
The residual moisture would be carried over to aug -
ment of rainfall received during the second season,
and so help to obtain a better crop yield. The
project was carried out during the long (April) and
the short (November) rainy seasons of 1976 and the
long rains of 1977.
The data presented show that with low rainfall
similar to thereceived during the long and the short
rains of 1976(200mm or less) the deeper layers of the
soil profile under the different tillage methods
remained dry throughout the rainy season, because only
a few of the daily showers were large enough to wet the
soil deeper than 15-20cm. However significantly
higher moisture contents were obtained under tied-ridges
as compared to the other tillage methods following
a wet period in Field M, hence demonstrating the
superiority of tied ridges in conserving rainfall.
Crop establishment was satisfactory on the minimum
and the conventionally tilled seedbeds but less so on
the cloddy and the tied ridge seedbeds. Subsequent
growth was satisfactory on minimum, conventional and
the tied ridge seedbeds but, adversely affected on the
cloddy seedbed.Since the rain stopped too early for
maize to reach maturity in either the long or the
short rain of 1976 the dry matter was harvested. Thei
drymatter yields were lowest on the cloddy seedbed
and significantly higher on tied ridges in the long
rains but not superior in the short rains of 1976.
During the 1977 long rains, which were substantially
above average (507.3mm) maize on tied ridges gave
significantly higher grain yields while that minimum
,tillage gave the lowest. There was no difference
between the maize yields from the conventional and the
cloddy seedbeds. Bean yields were lowered signifi
cantly on the cloddy seedbed compared to other seedbeds
during the relatively dry long rains of 1976,
but were highest on the cloddy seedbed during the
wet long rains of 1977. Bean yields from the tied
ridges were lowest during the long rains of 1977
though the differences were not significant probably
because the tied ridges were too wet for the beans.
With such low rainfall as occurred during the
long rains of 1976 the water content of the soil
profile under the different cropping sequences did
not increase significantly. Thus at the end of the
long rains, and after a maize or bean crop or after
a bare fallow, the soil profile was still at or below
the permanent wilting point. However, the profiles
under previous crops (maize or beans) were slightly
drier than the profile under a previous bare fallow.
Although the differences in drymatter yields of the
following maize crop during the short rains of 1976,
were not significant, the differences in cob
number and grain yield were highly significant, with
preceding fallowing giving higher cob number and
grain yield than preceding cropping.
No firm conclusions could be reached, since the
research project extended over only three seasons of
which two were virtual crop failures. Nevertheless,
the results obtained suggest that the tied ridge
tillage method may be a very promising method of
rainfall conservation, especially as most of the
cropping seasons are usually intermediate between the
relatively dry seasons of 1976 and the wetter long
rains of 1977. Similarly, the evidence from the
short rains of 1976 suggests that fallowing could
store sufficient water in the soil which might
significantly improve crop yields of the following
season. It is therefore recommended that further
trials should be carried out on the tied ridge method
of tillage and the use of fallow period in the
cropping sequence before firm recommendations for
farmers could be made. | en |
