CHEMICAL FERTILITY ASPECTS INFLUENCED BY THE MINERALOGICAL COMPOSITION OF SOME ACID TROPICAL SOILS OF THE FOREST ZONE IN CENTRAL CAMEROON

The mineralogical composition of mixed topsoil samples (0-20 cm) from different sites, Mbalmayo (Mb), Mengang (Me) and Nkolbisson (Nk), loca ted in the forest zone of Central Cameroon was determined in order to draw inferences related to chemical fertility. The chemical fertility was assessed on the basis of CEC, nutrient reserves (Ca, Mg and It) in the mineral fraction and P adsorption isotherms. Quartz is the major component in sand and silt fractions while the clay fraction of all so ils studied is dominated by kaolinite and Fe oxides (goethite). Weathe rable minerals still present are: diopside, enstatite, feldspars and m ica. The dominance of kaolinite and Fe oxides is responsible for the l ow CEC. Nutrient release by the mineral fraction follows the order Ca> Mg>K, although the soils are poor in Ca-bearing minerals. Phosphorus a dsorption becomes more important with an increase in clay content and DCB extractable Fe. Adsorption maxima range from 1100 to 2160 mu g P/g . Since in this area, agricultural utilization of lime and P fertilize rs is financially prohibitive for the small farmer which is the main c rop producer, improvement of the chemical fertility of these soils req uires a management strategy that allows the increase of CEC, Ca and P supply possibly through the use of wood industry by-products (wood ash or pulp).