Hassan Bismarck Nacro

Hydrolysable carbohydrate in tropical soils under adjacent forest and savanna vegetation in Lamto, Côte d'Ivoire

Carbohydrates represent 5–25% of the organic matter in soils. They constrain microbial activities and mineral nutrient production in soil and also reflect the whole microorganism community dynamic. The objective of this study was to determine the contents and composition of hydrolysable carbohydrates in soils collected in a forest–savanna mosaic landscape in the region of Lamto (Cote d’Ivoire). Capillary gas chromatography was used to identify and determine carbohydrates in soil profile under 4 tropical ecosystems: gallery and plateau forests, and grass and shrub tree savannas. Forest soils were higher in organic matter than savanna soils (0.50–2.96% C v. 0.53–1.22% C). The carbohydrate-C content of soils, expressed as percentage of total soil organic C, was low, a likely consequence of the tropical climate that promotes a rapid decomposition of surface plant debris. The carbohydrate-C content was higher under savanna soils (5–7%) than under forest soils (3–4%). Glucose, ribose, mannose, xylose, and galactose were the 5 most abundant extractable monosaccharides in all soils. Between them, only xylose and ribose are controlled by the vegetation type. The [(galactose + mannose) : (arabinose + xylose)] and [mannose : xylose] ratios suggested that most soil sugars derive from microbial biomass. The large abundance of microbial carbohydrates indicates intense microbial activities in the soil, and then rapid decomposition of soil organic matter favoured by the long wet season, with high temperatures and soil water availability at the site study. Results suggest clearly that the climate likely controls the amount and composition of carbohydrates in Lamto soils.

Effectiveness of combined application of Kodjari phosphate rock, water soluble phosphorus fertilizer and manure in a Ferric Lixisol in the centre west of Burkina Faso

ABSTRACT Increasing soil phosphorus and organic matter content for crop production while reducing the cost of production are required to facilitate the achievement of green revolution in Africa. Field and pot experiments were laid out during 2012 and 2013 to assess the effects of combined application of Kodjari phosphate rock (PR) and water soluble phosphorus on sorghum yields, P uptake and Lixisol characteristics in the centre west of Burkina Faso. Five P fertilizers treatments (zero P, 100% TSP (triple super phosphate), 100% PR, 50% PR + 50% TSP, 75% PR + 25% TSP) and two cow manure treatments (zero, 5 t ha−1) were tested. In field experiment, 50% PR + 50% TSP was as effective as 100% TSP in increasing sorghum yield above the control by 30% in 2012 and 50% in 2013 and P uptake by 30% in both years. Manure had an additive effect on phosphorus fertilizers in increasing sorghum yields and P uptake. In pot experiment, increases of Ca uptake, soil pH and microbial P were observed with the application of 50% PR + 50% TSP. Our results suggest that formulation of fertilizer combining phosphate rock and mineral P would improve sorghum yields and income of smallholders.