An Economic Evaluation Of Soil Conservation Measures In Zvimba And Chirau Communal Lands
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Soil erosion is an increasingly important problem in Zimbabwe. Whitlow (1988) states that 4.7% of the country or 1.8 mio hectares of land are actually eroded, the bulk (1.5 mio hectares) located in the Communal Lands. Arable and grazing lands are equally effected by erosion. The influence of human factors, especially population density and tenure system explained most of the variations of erosion in the Communal Lands (Whitlow 1988). At present most of the arable lands are more or less protected against rill and gully erosion through countor ridges, mostly built in the late sixties. Contours, however, do not sufficiently reduce . sheet erosion so that high soil losses from arable land still occur. The farmers crops are thereby not only affected by the loss of fertile topsoil and fertilizers washed away but the infiltration capacity of the soil is reduced and water-runoff increases, leaving the crops with less water to grow. Also, the structural stability of the soil may collapse (Elwell,l989). Stocking (1986) estimates that in average 75 t/ha of topsoil are lost every year from the communal grazing areas and about 50 t/ha from the arable lands in communal areas. If the loss of top soil is calculated in terms of nutrients, farmers would yearly lose nitrogen and phosphorus worth Z$ 120 from grazing lands and Z$ 80 from cropland, calculated in 1985 fertilizer prices. This is more than the average application of fertilizers that amounted up to Z$ 55/ha in 1989/90 and often more than the gross margin per hectare (MLARR 1990). Erosion presents a major hidden farming cost not only for future farming but also for current agricultural enterprises.