| dc.description.abstract | The experiment involved comparing three types of
grasses when used as filter strips for soil and water
conservation on cropland. The slope of the land was
approximately 8%. The soils were the eutric nitosols
developed from the Nairobi trachytes (Ga chene , 1989).
These soils are deep and well drained.
The three grasses tested were the napier grass
(Pennisetum purpureum), Nandi setaria (Setaria anceps)
and the tall signal grass (Brachiaria ruz t z Iens Ls ). The
experimental design used was the completely randomised
block design (CRBD). This comprised of three blocks
that were 3 m apart. Each block comprised of four plots
that were 2 m wide, 11.6 m long and 0.5 m apart. The
four treatments (the control and the three types of
filter strips) were randomly distributed within each
block using random number tables. The grass filter
strips (0.5 m wide) were established at the lower end
of the plots using splits from the nearby grass bulking
site. Pure stand crops of maize and beans were planted
during the long and short rains respectively.
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The run-off and eroded sediments call ection and storage
involved a collector unit at the downstream side of
each pi at. From the call ector, the run-off and the
sediments were conveyed to the main run-off storage
tank (approximately 1 m3) through a pvc pipe. The pipe
was 3 m long and 6.4 cm in diameter. A small drum of
approximately 0.09 m3 was put inside the main run-off
storage tank. The small drum was for storing run-off
from I ight storms an d also most of the eroded sediments
were stored here for ease of removal and measurement.
Apart from run-off and soi I loss, other parameters
measured were the crop height, crop yields, so i I
moisture and the fodder potential of the grasses.
The four treatments showed no significant difference in
run-off and soil loss reduction during the long rains
of 1990. This was well shown by the low soil loss
reduction efficiencies. The efficiency during this
season was 2.6, 4.0 and 13.6% for the napier, setaria
and brachiaria respectively. This improved during the
short rains of the same year whereby, the napier filter
strip attained 17.7%. The setaria only improved to 5.9%
while the brachiaria had 58.8%. During the long rains
of 1991, the napier strip gave a run-off reduction
efficiency of 40.5%, the setaria filter strip had 29.7%
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while the brachiaria one had 68.9%.
Similarly, the treatments had no significant difference
in soil loss reduction during the long rains of 1990
but improved with time as in the case of run-off
reduction. The napier, setaria and brachiaria strips
had a soil reduction efficiency of 3.8%, 7.9% and 19.0%
respectively during the long rains of 1990. For the
short rains of the same year, the napier strip had a
soil reduction efficiency of 93.0%, the setaria strip
had 81.9% while the brachiaria one attained 94.7%. The
strips maintained high efficiency in soil loss
reduction during the long rains of 1991 whereby, the
napier filter strip had an efficiency of 75.6%. The
setaria and brachiaria strips had 67.5% and 92.8%
respectively. In overall run-off reduction efficiency,
the filter strip of brachiaria was the most effective
followed by the napier and lastly the setaria filter
strip.
The filter strips were noted to have minimal adverse
ef fects on the nearby crop. I t was on I y the napi er
which was observed to a substantial adverse effect on
the first one or two rows of the adjacent crop. Where
a filter strip was planted, one row of maize or two
x xi
rows of beans were foregone. In overall crop yields,
the treatments had no significant difference. Though
the filter strips were found to utilize the soil
moisture around them, they conserved more a short
distance away from the strip edge.
In the case of fodder potential, the strips of napier,
setaria and brachiaria had an annual dry matter yield
of 8.8, 2.5 and 2.7 Kg/m2 respectively. This was from
green fodder- y i e ld s of 46.7, 12.4 and 11.7 Kg/m2 for
the napier, setaria and brachiaria respectively.
Together with important nutrients content, the napier
was the most superior fol lowed by the brachiaria. The
benefits of the fodder and the conservation of the soil
and water were found to compensate for the crop area
taken up by the grass filter strips. | en |
