Abstract:

This publication deals with the direct application of phosphate rock (PR) sources to agriculture.
Phosphorus (P) is an essential plant nutrient and its defi ciency restricts crop yields severely.
Tropical and subtropical soils are predominantly acidic, and often extremely P deficient with high P-sorption (fixation) capacities. Therefore, substantial P inputs are required for optimum plant growth and adequate food and fibre production. Manufactured water-soluble P fertilizers such as superphosphates are commonly recommended to correct P deficiencies, but most developing countries import these fertilizers, which are often in limited supply and represent a major outlay for resource-poor farmers. In addition, intensification of agricultural production in these countries necessitates the addition of P not only to increase crop production but also to improve soil P status in order to avoid further soil degradation. Hence, it is imperative to explore alternative P sources. Under certain soil and climate conditions, the direct application of PR, especially where available locally, has proved to be an agronomically and economically sound alternative to the more expensive superphosphates. PR deposits occur worldwide, but few are mined (for use mainly as raw materials to manufacture water-soluble P fertilizers).