Biophysical Baseline Information For The Nyando Catchment Area

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Date
2003
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Ministry Of Agriculture
Abstract
The River Nyando Catchment is one of the seven major catchments within the Kenyan side of the Lake Victoria drainage basin and covers an area of approximately 3550 km2 ,comprising parts of Kericho, Kisumu, Nyando and Nandi South Districts. This catchment together with River Nzoia catchment contributes more than 50% of the Kenyan waters into the lake. The physiography of the catchment comprises highlands and lowlands areas and falls under agroclimatic zones II - IV with mean annual rainfall ranging from less than 1000 mm to over 1600 mm. Land use varies with topography and agroclimatic conditions. The highland zones are under fallow/grazing, woodlots, natural forest and cultivation of tea, coffee and annual crops, while lowland zones are dominated by grazing lands, marshes/swamps, cultivation of sugarcane and annual crops. The reconnaissance soil mapping established fourty two (42) mapping units covering the highland and lowland zones of the catchment. Soils on the highlands are well drained, deep to very deep, are of moderate to low fertility, have shallow humic topsoil, stable soil aggregates and include Nitisols, Alisols, Luvisols, and Cambisols. The soils found in degraded hills and volcanic footridges, however, are shallow, rocky and bouldery and include Leptosols and Cambisols. Lowland soils are moderately deep to deep, have impeded drainage, sodic subsoil and less stable aggregates and include Vertisols, Luvisols, Gleysols and Fluvisols. The soils within the catchment are adequately supplied with plant nutrients Ca, K and Mg. Mg occurs in excess amounts in all the landform units while Ca is excess in the lake side beach ridges. P is excessive in parts of the piedmont plains, lacustrine plains, lake side beach ridges and alluvial plains. P is deficient in parts of the mountain, hills, volcanic footridges, footslopes, upland, plateau and lacustrine plains. Except in the mountain and the lake side beach ridges, parts of all the other units indicates deficiencies in N. Low to very low levels of OM occur in parts of the hills, footslopes and piedmont plains, while high levels are in parts of the mountainous areas, volcanic footridges, upland and plateau! Erosional plains. Areas with very severe erosion hazard occur on mountainous and hilly areas and cover about 5%, severe hazard areas occur on the hills, foot ridges and foot slopes and cover 17%, high hazard areas occur on lower parts of the footslopes, upland and upper piedmont plains and cover 51 %, moderate hazard areas occur on the plains covering 24% and low hazard areas cover 4% of the catchment area. Much of the upper catchment area has hitherto been conserved either under appropriate cover crops, natural! Plantation forestry, pasture or range. Human activities including recent permanent settlements and encroachment into the forest reserves, introduction of annual crops in the steep forest or tea areas, opening up for arable cultivation of formally grazing lands and continued overstocking in the lowland areas has enhanced erosion hazard. Integrated farmer initiated conservation measures such as terracing; grass strips, trash and stone lines in the highland areas are more successful than structural/ mechanical measures in the lowland areas
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