Residual effects of direct application of Burkina Faso phosphate rock on rice cultivation in Ghana

Abstract

Soil phosphorus deficiency is a critical constraint in crop production in Sub-Saharan Africa (SSA). Although phosphate rock (PR) deposits have been found in the region, they have not been well-utilised due to low reactivity, limited markets, lack of effective extension systems and other factors. However, previous studies indicate that direct application of these PRs are effective for lowland rice cultivation, although the residual effects of this application on rice yields have not been fully examined. We research the residual effects of PR direct application on rice yields in two typical agro-ecological zones for lowland rice cultivation in SSA: Guinea Savannah (GS) and Equatorial Forest (EF). PR residual effects differ between the GS and EF regions. Residual effects in GS varied due to annual changes in environmental conditions such as soil water content, while EF showed high reproducibility, most likely because of irrigation management. Residual effects were higher after a 2-year consecutive application than after a single application. Residual effects of PR application continued for at least 2 years, suggesting that a single PR application can produce a positive effect on three rice crops. In GS, where rice is grown under rain-fed cultivation, PR application was effective, but its direct and/or residual effects were influenced by conditions such as water shortages, which could adversely affect PR solubilisation. In EF, where rice is irrigated in inland valleys, the effect of PR direct application is consistently positive over 2 years, likely due to the inherent phosphorous contribution.