Acacia tumida prunings as source of nutrients for soil fertility improvement in Niger: biochemical composition and decomposition pattern

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Limited sources of organic amendments for increasing nutrient availability for crop growth is a major challenge in Niger. Reports on the role of organic material in soil fertility improvement in the Sahelian zone of Niger have been focused merely on limited range of organic amendments such as animal manure and crop residues. There is however little information on the use of agro-forestry leaves for soil fertility improvement in Niger. The current study was therefore designed to (i) evaluate the quality of Acacia tumida prunings, (ii) determine the decomposition and nutrient release patterns of Acacia tumida prunings (iii) assess the factors that influence the decomposition and nutrient release patterns of organic materials under Sahelian conditions. Litterbag experiment was conducted in a Randomized Complete Block Design (RCBD) with three replications. The treatments consisted of a factorial combination of (a) three types of organic amendments (Acacia tumida pruning, millet straw and cattle manure), and (b) two levels of insecticide application (with and without insecticide). The litterbag experiment was conducted on sandy and crusted sandy soil types. The percentage composition of N, P and K in Acacia tumida prunings were 2.30, 0.14 and 1.50, respectively on a dry weight basis. The decomposition of Acacia tumida pruning was faster (k/day = 0.014) than that of cattle manure (k/day = 0.012). On the average, 45 and 34 % of organic materials decomposed in the litterbags free of insecticide and litterbags treated with insecticide respectively. The contribution of termites to organic amendment decomposition was estimated to be 36 % for millet straw and 30 % for manure. The highest N release constant (k/day = 0.025) was recorded for millet straw whereas the highest P release constant (k/day = 0.035) was documented for manure. The highest potassium release constant (k/day = 0.114) was recorded for Acacia tumida pruning. This study has contributed to knowledge regarding the decomposition of Acacia tumida prunings which has an important implication for diversifying the source of nutrients for soil fertility improvement in Niger. Moreover, the results of this study indicate that the presence of termites and the intrinsic quality of the organic material play crucial roles in the decomposition of organic materials in the Semi-arid environment of Niger.
A Thesis presented to the Department of Crop and Soil Sciences, Faculty of Agriculture, College of Agriculture and Natural Resources, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana, in partial fulfilment of the requirements for the award of the Degree of Master of Philosophy in Soil Science.