|Sourcebook of Alternative Technologies for Freshwater Augmentation in Africa (International Environmental Technology Centre - United Nations Environment Programme, 1998, 182 p.)|
|Part B - Technology profiles|
|1. Agricultural technologies|
|1.1 Fresh water augmentation|
Terracing of grazing land is generally considered to be too expensive and labour intensive in relation to the expected returns. However, eroded grazing lands may be revegetated economically by building small, interlocking mini-catchments using a pitting and ridging technique coupled with reseeding with native grasses and legumes.
Pitting should start at the top of an eroded slope below a cutoff drain which will intercept runoff from above. Pits should be dug to form interlocking catchments, each about 2 m2 in area, varying in shape with the micro topography.
Pitting can be extended down the slope as convenient and necessary. Final embankments should be about 30 cm high, around crescent-shaped trenches, 15 cm deep and 20 cm wide. Cow peas, or other ground cover crop, should be sown on the ridges, and cattle excluded, during the first growing season to allow vegetation cover to establish and soil to compact (Figure 4).
Extent of Use
Crescent-shaped pits have been used to restore eroded lands in Kenya.
Operation and Maintenance
There are limited operation and maintenance requirements. In particular, over-grazing should be avoided so as not to cause a return to a previously denuded condition. Cutoff drains also are to be maintained.
Level of Involvement
Local community inputs or hired labour is generally used to construct the pits and cutoff trench.
Costs are primarily related to labour costs of about $100 to $150/ha. To establish a ground cover crop, fertilisers may be needed, especially where severe loss of topsoil has occurred. However, these costs can be offset, in part, by growing a cash crop during the first year after construction. For example, a first year cow pea cash crop can offset the cost of construction and fertiliser.
Effectiveness of the Technology
Surface runoff is reduced with the result that soil moisture content is greatly increased and available for use in growing both grain and forage legumes. Cow peas, grown during the first season, have been reported to yield 750 to 900 kg/ha. Notwithstanding, weeds and grasses tend to dominate in the second season, unless additional management practices are adopted. Pasture yields of 3 to 4 t/ha/season are achievable, with a legume content up to 50%. Total dry matter production on Katumani-treated land increased by a factor of 5 to 10 compared to untreated land.
This technology is appropriate for the rehabilitation or conservation of grazing lands in regions with 500 to 800 mm rainfall.
Positive benefits are the rehabilitation of degraded lands, and stabilisation of soils. Use of native vegetation can also contribution to the maintenance of biodiversity.
Improved fodder production and grazing capacity, and agricultural products from a planted tree crop (e.g., fruits, nuts or firewood), are likely outcomes of adopting this technology.
Adopting this technology is labour-intensive.
No adverse cultural problems have been recorded.
Further Development of the Technology
The challenge is to extend the Katumani pitting technique to a larger group of farmers, soil types and environments in the region.
Simiyu, S.C., E.M. Gichangi, J.R. Simpson, and R.K. Jones 1992. Rehabilitation of Degraded Grazing Lands Using the Katumani Pitting Technique. In: M.E. Probert (Editor), A Search for Strategies/or Sustainable Dryland Cropping in Semi-arid Eastern Kenya. ACIAR Proceedings No. 41, 138 p.