Use of phosphate rocks for sustainable agriculture

This publication deals with the direct application of phosphate rock (PR) sources to agriculture. Phosphorus (P) is an essential plant nutrient and its deficiency 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). The Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture initiated a Coordinated Research Project called 'The use of nuclear and related techniques for evaluating the agronomic effectiveness of phosphatic fertilizers, in particular rock phosphates'. This was implemented by institutes of developing and industrialized countries from 1993 to 1998. The results obtained yielded new information on: chemistry of soil P; tests for available soil P; phosphate nutrition of crops; agronomic effectiveness of PR products; and P fertilizer recommendations with particular emphasis on PR use. Within the framework of the integrated plant nutrition systems promoted by the Land and Water Development Division (AGL), FAO, and the national action plans for soil productivity improvement under the Soil Fertility Initiative for sub-Saharan countries, PRs are considered as potentially important locally available P sources. AGL has instituted several studies on the agro-economic assessment of PRs for direct application in selected countries. Results of practical utility and policy guidelines can be drawn from these studies. Several organizations have conducted extensive research on the utilization of indigenous PR deposits in tropical soils in Latin America, Africa, Asia and elsewhere. In the past decade, considerable progress has been made in the utilization of PR sources for direct application in agricultural cropping systems worldwide. A wealth of information is now available but scattered in several publications. Recognizing the need for the wider dissemination of the available information, the Joint FAO/ IAEA Division of Nuclear Techniques in Food and Agriculture together with the AGL convened a Consultants' Meeting in Vienna in November 2001 in order to review advances in this fi eld of research and development, and to elaborate a proposal for the production of this technical bulletin