Assessment of certain soil properties related to different land-use systems in the Kaya watershed of the humid forest zone of Cameroon

A field survey was conducted in the Kaya watershed of the humid forest zone of Cameroon to assess changes in particle size distribution and chemical soil properties related to different land-use systems. The strongly acid soils are mainly composed of sand and clay, and are poor in organic carbon, total nitrogen, mineral nutrients and effective cation exchange capacity (ECEC), with the major portion of nutrients stored in the topsoil, together with organic matter. Land-use systems significantly affect the sand and the clay fractions and have high proportions of sand in soils of cropped fields, secondary forest and river valleys and high clay percentages under dense forest and fallows. Soil pH and exchangeable Al in the topsoil and the subsoil, organic carbon, available P, base saturation and Al saturation in the topsoil and ECEC in the subsoil significantly differ with the land-use systems. Soils of food-crop fields and river valleys presented a higher fertility level than under secondary and dense forests. Permanent vegetation coverage and/or exposure to heavy rains of the soils, disturbance due to land preparation, organic matter supplied by the vegetation, nutrient cycling, nutrient restitution and nutrient uptake could be differentiation factors. For agricultural development, utilization of residue from harvest to cover the soil surface, liming and P fertilization appeared as the first and the most important management options. Nitrogen and K fertilization could be added according to crop requirements. Since farmers cannot afford to buy lime and mineral fertilizers and agroforestery is hardly practised, the utilization of cheap and widely available wood ash as a liming agent and supplier of P and K is a promising option. Field trials at the farmer level are proposed to evaluate this. Copyright (C) 2002 John Wiley Sons, Ltd.