The use of phosphate fertilizers and lime to mitigate P deficiencies and Al toxicities in Kenya has not been effective due to their high cost. Organic materials (OMs) are therefore being tested as cheaper alternatives but there are knowledge gaps on how they interact with soil to increase crop yields in acid soils. The effect of two OMs; farmyard manure (FYM) and Tithonia diversifolia (tithonia) green manure, and agricultural lime, each when applied alone or in combination with triple superphosphate (TSP), on selected soil chemical properties related to fertility and nutrient uptake by maize, was tested in a greenhouse experiment. Only the lime and FYM treatments significantly increased the soil pH. Lime was the most effective amendment in reducing the exchangeable Al followed by tithonia and FYM but TSP when applied alone did not reduce exchangeable acidity. The OMs and lime, when applied alone or in combination with TSP reduced the P sorption capacity of the soil but TSP on its own did not. Although TSP when applied alone gave the highest amounts of plant available P, this did not translate to the highest nutrient uptakes implying that some other factor, likely Al toxicity, was limiting their uptake. A reduction in exchangeable Al by application of OMs or lime led to higher nutrient uptakes compared to TSP. It is concluded that OMs can play the dual role of providing nutrients and mitigating the deleterious effects of soil acidity and in this respect are, therefore, likely to be more cost effective than lime.
