Soil fertility status and potential organic inputs for improving small holder crop production in the interior savanna zone of Ghana

Abstract

Soil fertility decline is a major problem facing small-scale farming in Sub-Saharan Africa. To optimize the productivity of fertilizer usage, it is imperative that the fertility status of the soil is known. This study was conducted to evaluate the fertility status and potential organic inputs that can be used alone or in combination with mineral fertilizers for increased crop production in the interior savanna zone of Ghana. A survey of the availability of potential organic inputs in the region identified cow dung, refuse compost, and some plant residues with potential for enhancing soil productivity. Soil, household refuse, cow dung, and plant samples were collected from 40 farming communities and analyzed using standard protocols. The decomposition and nutrient release patterns of the organic materials were further investigated in laboratory incubation studies and in litter bags for 12 weeks. Results of the physico-chemical analysis revealed that soils in the interior savanna zone are coarse textured with low exchange capacity. The majority of the soils have low organic matter contents (1.0 ±0.4%) and low levels of the major plant nutrients. Available P in particular was very low with most of the soils having values less than 5.0 ppm. Elemental analysis of the materials revealed that they contained appreciable quantities of macro and micronutrients. The N contents of all the plant materials were higher than the critical level of 20.0-25.0 mg g-1 below which net N immobilization from the soil would be expected. The P contents of all the materials were above the critical level of 2.5 mg g-1 for P mineralization. The C/N ratios of all the materials were below 25, which indicate rapid mineral N release during decomposition. The decomposition of the materials indicated the high potential of the materials to supply NPK to crop plants within the experimental period. This suggests that the application of these materials to soil alone or in combination with mineral fertilizer ould improve nutrient availability to crop plants. Since results obtained may differ under field condition where mineralization tends to be complicated by environmental factors, field studies using a test crop such as maize are recommended to establish the relationship between nutrient release from the materials and crop demand. © 2005 by The Haworth Press, Inc. All rights reserved.