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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.

Paper mill sludge is characterized by high concentrations of organic matter and lime and very low concentrations of heavy metals and organic chemicals. Interest in the recycling of paper mill residuals in developing countries is vital because the use of lime and fertilisers by small farmers is financially prohibitive. The effects of paper pulp sludge and lime on the dynamics of soil nutrients was studied in the laboratory using columns of mixed samples of top soil from three tropical acid soils (Kandiudult). The soil columns were leached over a period of 90 days with de-ionized water in amounts equivalent to the annual rainfall of the sampling site. To assess the amount of nutrient that may become available to plants, NH 4 OAc-EDTA pH 4.65 soil extractant was used. For all soils, application of paper pulp sludge or lime to tropical acid soils generally resulted in an initial flush and increased concentrations of Ca, Mg, SO 4 , dissolved organic carbon (DOC) and inorganic carbon in soil leachates. Compared with liming, application of paper pulp sludge reduced NO 3 leaching. The amount of leached Ca, DOC and inorganic carbon (mainly HCO 3 -) increased substantially with the addition of paper pulp sludge or lime. In relation to nutrients, the most meaningful amendment effect that persisted after leaching was a substantially increased available Ca in the treated soil. In addition to increasing Ca levels, the addition of paper pulp sludge increased the concentrations of leached and available Ca. To sustain yield increase with paper pulp sludge, calculation of the optimum quantity to be returned to the soil should be based on losses of Ca by leaching and by plant uptake.

Paper mill sludge is characterized by high concentrations of organic matter and lime and very low concentrations of heavy metals and organic chemicals. Interest in the recycling of paper mill residuals in developing countries is vital because the use of lime and fertilisers by small farmers is financially prohibitive. The effects of paper pulp sludge and lime on the dynamics of soil nutrients was studied in the laboratory using columns of mixed samples of top soil from three tropical acid soils (Kandiudult). The soil columns were leached over a period of 90 days with de‐ionized water in amounts equivalent to the annual rainfall of the sampling site. To assess the amount of nutrient that may become available to plants, NH4OAc‐EDTA pH 4.65 soil extractant was used. For all soils, application of paper pulp sludge or lime to tropical acid soils generally resulted in an initial flush and increased concentrations of Ca, Mg, SO4, dissolved organic carbon (DOC) and inorganic carbon in soil leachates. Compared with liming, application of paper pulp sludge reduced NO3 leaching. The amount of leached Ca, DOC and inorganic carbon (mainly HCO3‐) increased substantially with the addition of paper pulp sludge or lime. In relation to nutrients, the most meaningful amendment effect that persisted after leaching was a substantially increased available Ca in the treated soil. In addition to increasing Ca levels, the addition of paper pulp sludge increased the concentrations of leached and available Ca. To sustain yield increase with paper pulp sludge, calculation of the optimum quantity to be returned to the soil should be based on losses of Ca by leaching and by plant uptake.

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