Toposequnential variation in soil fertility and limiting nutrient for rice growth in the white volta floodplain of northern Ghana.

Integrated floodplain resource management for rice cultivation is imperative to satisfy the growing demand of rice in West Africa. Irrigated pot experiments were conducted with different fertilizer treatments to identify toposequential variation in soil fertility and limiting nutrient for rice growth within the White Volta floodplains in Ghana. Eighteen experimental soils were examined across a riverside to upland gradient, ranging from 898 to 4200 m in distance from the main riverside, from 73 to 106 m in elevation, and from 0.7 to 2338.1 m in distance from water sources. The soil analysis revealed close correlation between N-mineralization rates and carbon contents of the soils, which were exponentially decayed with distance from water sources. In the non-fertilized treatments, plant N uptakes at maturity also decreased along the same transect from the water sources. However, the dry matter production was little relevant to this toposequential factor. Various fertilizer treatments identified remarkable effect of sulfur on rice growth, which was more significant on soils closer to waster sources. NPK application without S increased only N concentration and N: S ratio in plant tissues but not biomass production. The results indicated that sulfur is the primary limiting element for rice growth, and its supplementation would be more beneficial as closer to water sources so as to effectively utilize greater Nsupplying capacity of this agro-environmental soils.