| dc.description.abstract | The aim of this work was to quantify the impact of a modified agroforestry microclimate on
water use of a cowpea crop as compared to a sole stand in the Arid and semi-arid lands
(ASALs). Agroforestry systems have been developed in the ASALs to help the local farmers
alleviate the myriad problems associated with water management in crop growth. However,
most of the past studies using the same system had emphasized on soil fertility and its
physical improvement. Equally, tree pruning associated with the system are simply too
important as a source of fodder to be returned to the soil. Under such circumstances the only
benefit from agroforestry is expected to be derived from a greater utilization of physical
resources such as micro meteorological variables and hence the importance of their study.
The agroforestry system adopted in this case was alley cropping using the Cassia siamea
tree. The experimental site was located at Kibwezi Dryland Field Station of the University of
Nairobi in Makueni District. The study was conducted during the short and long rainy
seasons of 1998 and 1999 respectively. However the amount received was inadequate as
compared to the seasonal mean.
Parameters assessed include, solar radiation, relative humidity, air temperature, wind speed
and wind direction, pan evaporation, sunshine duration, rainfall, soil temperature, soil
moisture, above-ground dry matter production, actual and potential evapotranspiration, and
water use efficiency (WUE). Determinations of these variables were made both at the site
and at a nearby agrometeorological station which was about 70 m to the south of the site.
Two alleys measuring 5 m by 1m and 70 m long were used. They were subdivided into three
blocks with each of them having two treatments measuring 20 m by 5 m. The hedgerows
were lopped to size of 1 m in one treatment (PS) and 2 m on the other (PT) in the same block.
These were replicated thrice. The control plot (CP) with the same dimensions was established
at the periphery of the agroforestry system (cf. Fig. 3). It was replicated twice. All the
treatments were planted with the same density of cowpea cultivar CY.TT945-2264-4.
Results indicated that in the entire microclimatic variables measured, only wind speed was
significantly less by approximately 50°'0 in the alleys Soil moisture varied very little between
I m and 2.5 m, and between PS and PT in the alley cropping. In the open crop, measured soil
moisture was more by 11%.
fIhe mean actual evapotranspiration at the sole stand was reduced by about 32 and 27% as
compared to agroforestry system in the first and second season respectively.
The values of crop water use as compared to potential evapotranspiration and rainfall
revealed that, in the first season, only the initial stage of the crop that received enough
rainfall. Subsequent growth stages had deficits. A similar scenario was observed during the
second season.
Cowpea dry biomass was the only yield obtained. No grain yield was obtained as the crop
failed to reach maturity due to lack of sufficient rainfall. The study indicated that, there was a
severe reduction in dry matter production in the alleys as compared to sole stand. During the
first and second season, mean biomass production in the agroforestry system was reduced by
47 and 56% respectively as compared to the sole stand.
Water use efficiency (\VUE) was generally very low and particularly in the alleys where it
ranged from 0.15 to 0.5 g/mm from the initial to the vegetative stage. In ttie'sole stand the
range was from 0.2 to 2.2 g/mrn. On the average, the monocultural stand outperformed the
alley cropping by about 69%.
Since there was insignificant modification in all parameters measured apart from wind speed,
the poor crop performance in the alleys could not be ascribed to microclimatic modification.
Therefore, as observed by other researchers, during the seasons of below average rainfall as
was in this case, competition for moisture between the trees and the crops severely reduced
crop yields.
Thus, it was conclusive that, intercropping of cowpea with Cassia Siamea does not benefit
the cowpea crop and in fact is serious to the crop when moisture is limiting. | en |
