Comparison of soil nutrient status of some rice growing environments in the major agro-ecological zones of Ghana

Soil fertility management and maintenance has been a major problem to crop production in Ghana, varying considerably across agro-ecological zones within the country. With an increasing intensity in the use of lowlands for rice cultivation, a random fertility survey was conducted within some watersheds in two major agro-ecological zones to ascertain their current fertility status and to possibly develop management options that can ensure their sustainable use for crop production, particularly rice. Types of lowlands encountered within these two watersheds were mainly inland valleys and river flood plains. Rectilinear valleys were encountered within the Jolo Kwaha watershed within the Savannah agro-ecological zone while convex valleys were observed within the Mankran watershed in the Forest agro-ecological zone. Concave valleys were, however, observed in both watersheds. Major soil types encountered were basically Gleysols and to a lesser extent Fluvisols in both watersheds. Volta and Lima series were prominent within the Jolo Kwaha while Oda, Kakum and Temang series were prominent within the Mankran watershed. Soil fertility levels, as observed for selected parameters were low across locations, particularly within the Jolo Kwaha watershed. Available phosphorus (P) was the most deficient nutrient within both watersheds with over 80% of both watersheds recording very low levels (<3 mg kg(-1)). Soils of Jolo Kwaha were also observed to be quite acidic. Exchangeable cations (K, Ca, Mg, Na) were quite moderate across locations within the Forest agro-ecology but relatively low across the Savannah, particularly Ca. Both total carbon and nitrogen levels, even though low, were comparatively higher for the Mankran than Jolo Kwaha watershed. Soils of lowlands within the Jolo Kwaha watershed are deeper than the relatively shallow soils of the Mankran watershed. The adoption of simple but effective eco-technologies such as the "Sawah" system would help to enhance and maintain nutrient availability for sustainable rice production within these lowlands.