The importance of proton supply in phosphate rock dissolution: Comparative study of three phosphate rocks from sub-Saharan Africa

The dissolution in hydrochloric acid of three phosphate rocks (PRs) from sub-Saharan Africa was studied in the laboratory and their agronomic effectiveness compared using soils from Tanzania, Ivory Coast, Kenya and Netherlands. The objective was to investigate the potential of the PRs in supplying phosphorus under conditions of limited and unlimited supply of protons (H+). The test crop was maize (Zea mais var. LG11). Results show that calcium carbonate content is an important factor determining differences between the PRs with respect to their effectiveness. They also show that (i) differences in the dissolution of the PRs manifested more at low than at high acid concentration, (ii) availability of enough protons is an important factor in PR dissolution, (iii) low rates of PRs should be more desirable than high rates and (iv) soil and plant factors have an important role in the effectiveness of a PR.