Impact of Grazing on Soil in the Southern Guinea Savanna Zone of Nigeria A.O. AWETO and D.O. ADEJUMOBI* Department of Geography, University of Ibadan, Ibadan, Nigeria. Summary This study examines the effects of traditional sedentary grazing on soils in the southern guinea savanna ecosystem in Nigeria. The characteristics of soil in grazed plots are compared with those of similar soil in ungrazed plots in a savanna "forest' reserve in a nearby locality, in order to infer the effects of grazing. In the 0-10 cm layer of the soil, organic carbon, total nitrogen, exchangeable calcium, magnesium, potassium, sodium, cation exchange capacity and available phosphorus levels are significantly lower in the grazed plots. Decline in the organic carbon and nutrient levels of the grazed plots is mainly due to soil exposure resulting from grazing and savanna burning and the attendant processes of accelerated organic matter decomposition and nutrient loss through leaching and erosion. Low soil nutrient levels in the grazed plots will reduce primary production and hence the rate of herbage production for livestock. It could also lead to some adverse ecological changes in the ecosystem with the disappearance of certain plant species. The ecosystem consequently becomes less diverse and resilient as soil nutrient status becomes increasingly impoverished. It is suggested that herdsmen should practise rotational grazing and that livestock should be fed with a supplementary fodder of legumes, such as Gliricidia sepium and Leucaena leucocephala planted in natural grazing areas, in order to minimise the problems of overgrazing which are frequently experienced during the dry season. * Dr A.O. Aweto is a Senior Lecturer in Biogeography in the Department of Geography at the University of Ibadan, and Mr D.O. Adejumobi is a geographer serving on the Nigerian National Youth Service Corps. Introduction As with the other savanna lands of the tropics, livestock production is an important feature of the agricultural economy in the savanna zones of Nigeria. The bulk of Nigeria's livestock are kept in the drier Sudan and Sahel savanna zones which are freer from tsetse fly infestation than the more humid guinea and derived savanna zones (Fig.l). The two former savanna zones experience a much longer dry season towards the end of which grasses die off and fresh grazing for livestock becomes scarce. During this period, large numbers of cattle are driven by herdsmen to the wetter guinea savanna zone where the growing season is longer and forage resources are more abundant (Agboola, 1979). Until quite recently the guinea savanna zone served mainly as a dry season grazing area for cattle from the drier Sudan and Sahel savanna zones. Consequent on very rapid population growth rates coupled with frequent droughts in the drier savanna lands of the north which decimate livestock numbers, Nigeria is experiencing a shortage of livestock products. In order to meet a growing demand the government is intensifying efforts to produce livestock and to make the country self-sufficient in animal products (Federal Ministry of Agriculture, Water Resources and Rural Development, 1988). In order to achieve this end, the government has encouraged increased utilisation of the country's forage resources, including those of the wetter guinea savanna. Partly in response to government initiative and encouragement and to the perceived potentials of keeping livestock permanently in the wetter guinea savanna, a number of herdsmen from the drier savanna lands of the north have migrated into, and settled permanently in the guinea savanna zone where they rear livestock. Volume 11, Number 1, (1991) 27