Factors affecting the agronomic effectiveness of phosphate rock for direct application

Phosphorus (P) is critically needed to improve soil fertility for sustainable crop production in large areas of developing countries. In recent years, phosphate rock (PR) for direct application has been tested in tropical acid soils as a potential alternative to conventional water-soluble P fertilizers like single superphosphate (SSP) and triple superphosphate (TSP). Some developing countries have PR deposits which, if used to supplement other imported P fertilizers, would allow a saving of much needed foreign exchange. Solubility of P fertilizers is not the only criterion in selection of the most suitable P fertilizer. This paper discusses the results of experiments to compare the relative agronomic effectiveness (RAE) of various PR sources with respect to SSP or TSP as influenced by four important factors: PR sources, soil properties, management practices, and crop species. Under certain conditions, PRs can be agronomically effective.