CHEMICAL CHARACTERIZATION OF SOILS OF A TROPICAL HUMID FOREST ZONE - A METHODOLOGY

A methodology, based on a combination of routinely performed analyses and investigation of fundamental charge and anion sorption properties, was used to characterize the soils of the humid forest zone of Camero on, In general, the soils have about 2 cmol kg(-1) permanent negative charge, with about 1 cmol kg(-1) from variable-charge sources at curre nt soil pH values, Furthermore, they are impoverished with respect to Ca, Mg, and K, while Al frequently dominates the exchange complex. Thu s, the ability of these soils to retain base cations is more limited t han is suggested by the cation-exchange capacity (CEC), Therefore we p ropose the concept of a degradation index (DI) defined as: DI = 100(CE C5.5 - sum of basic cations)/CEC5.5, where CEC5.5 is the CEC measured at pH 5.5, This index encompasses degradation a soil may have experien ced from natural or man-made causes, Extractable PO4 concentrations ar e considered very low and the soils have a moderate to high capacity t o fix added PO4. Surface soil SO4 concentrations are considered margin al to deficient for plant growth, though adequate reserves of SO4 are held in the subsoil by SO4 sorption, The approach used demonstrated th at the five morphologically different soil profile classes identified in the zone have similar chemical characteristics. Thus, the results o f experimentation conducted on one of the soil profile classes will be applicable throughout the zone, Furthermore, the approach has provide d a means of identifying comparable soil types in other parts of the w orld and will guide technology transfer, The analytical methods used i n this study are relatively simple and require no specialized equipmen t, and are therefore within the capabilities of many laboratories in t he developing world.