IFDC’s fifty years of research and development on the use of phosphate rock as fertilizer

Phosphate rock (PR) is the key raw material in phosphatic fertilizers. However, the phosphorus (P) in PR is generally unavailable for crop nutrition. Currently, direct application of PR (DAPR) to crops accounts for less than 1% of the global annual P consumption of 21.4 million metric tons (Mt) of P equivalent. This paper reviews the International Fertilizer Development Center’s (IFDC) fifty years of research on DAPR as an alternative or supplement to water-soluble phosphate (WSP) fertilizers in acidic soils of the sub-humid and humid tropics. It highlights the significant advancements IFDC made in identifying basic principles determining the effectiveness of PR fertilizers including mineralogy, chemical reactivity, surface area and influential soil and crop factors. It also summarizes agronomic outcomes and identified economic factors impacting PR use. Examples of the use of the PR decision support system (PRDSS) developed by IFDC to integrate soil, crop, PR source and site factors to predict the relative agronomic effectiveness (RAE) and economic feasibility of the PR source are presented. Finally, the paper summarizes specific farming strategies and ongoing research that will influence the direct application of PR in the future.