Evaluation of grass strips performance in soil and water conservation
Abstract
Although grass strips for soil and water conservation offer several advantages such as ease
of establishment, low cost, effective means of soil erosion control, and as a source of fodder,
they are not widely used. The study aimed at assessing the potential and actual performance
of eight grass species in terms of formation of terraces, moisture conservation, protection of
terrace banks, source of fodder, competition for water, and harbouring pests and diseases.
The study had two components: technical evaluation of grass strips performance in soil and
water conservation and an evaluation of farmers' perception on the use of grass strips.
Technical evaluation of grass strips performance in soil and water conservation was
undertaken on grass strips established at Kabete Steepland Research Site in 1989. It involved
measurement of ground slope changes, soil moisture gradient, effect of grass establishment
on adjacent crop yields, fodder potential of different grass species and bank stability. A field
survey was carried out in Gatundu to assess the farmers' perception on the use of grass strips
as a soil and water conservation measure. In addition to farmer interviews, the survey
included measurements of width and spacing of grass strips, grass strip barrier continuity and
fodder yield, and the resulting embankment height.
In terms of terrace formation, the results from the Steepland Research Site, showed that grass
strips planted for a period of 5 years since 1989, resulted in slope reductions of 30%, 8.3 %,
38%,36%,25%,20% and 20% for tall signal, makarikari, donkey, creeping signal, bana,
guatemala and tall guinea grass respectively. This was as a result of sediment deposition on
the upper side of the strips leading to the formation of forward sloping bench terraces. Bana
and guinea grasses increased soil moisture storage by trapping runoff during rainy periods
but reduced the same during dry spells due to high water use. Some significant soil moisture
depletion by these grasses was observed within 0.5 m from the strip edge. It was also
observed that competition between bana grass and the bean crop was higher in the first row
than the third row. The bean yields were 0.33, 0.5, and 0.8 kg for the first, second and third
row respectively. However, the competition effect of these grasses was compensated by their
higher fodder yields. Fodder yields were 3.81 kg/m2, 2.63 kg/rrr", 2.28 kg/m2, 2.24 kg/m2,
1.49 kg/rrr', and 1.07 kg/rrr', for bana, guatemala, guinea, donkey, creeping signal and tall
signal grasses respectively.
Tall signal, creeping signal and donkey grasses provided barrier continuity above 90% while
bana and guinea grasses had 84.5 and 86.5 % respectively. Their banks were well stabilised
with minimum rills on gaps caused by their tufted growth. Due to their overgrowth, these
grasses were found to harbour rodents like rats and squirrels. Makarikari and guatemala
grasses gave poor ground barrier continuity of below 60% throughout the period. This was
as a result of pests attack and tufted growth respectively.
Farmers in Gatundu division perceived grass strips as a better alternative to mechanical
structures due to their less labour requirement in establishment and their potential as a source
of fodder to livestock. The use ~f grass strips was found on 54.4 % of the farms surveyed in
the division. Napier grass tPennisetum purpureum) was the most common grass found to be
grown on 98 % of the farms with grass strips due to its fodder potential. Land size,
percentage level of other soil conservation measures and land slope were the main factors
affecting grass strip adoption in Gatundu division. However, 14.6% of the farmers cited
competition for moisture and nutrients by grass strips established from napier and its related
species. In terms of design and maintenance, it was observed that many grass strips were
poorly aligned and spaced thus leading to more erosion on the downhill side.
Citation
Siteki, R.O(1996). Evaluation of grass strips performance in soil and water conservationSponsorhip
University of NairobiPublisher
Department of Agricultural Engineering, University of Nairobi,
Description
Msc-Thesis