P-32 ISOTOPIC TECHNIQUES FOR EVALUATING THE AGRONOMIC EFFECTIVENESS OF ROCK PHOSPHATE MATERIALS

Tropical soils are often low in available P and therefore require inpu ts of P fertilizer for optimum plant growth and production of food and fiber. The cost of applying imported or locally produced, water-solub le, P fertilizers is often greater than utilizing indigenous phosphate rock. Therefore quantifying the P availability of soils amended with phosphate rock-based products in a variety of crop management and envi ronmental conditions in developing countries is desirable for making r ecommendations on best type and rate of fertilizers to use to obtain m aximum agronomic and economic benefits. One adequate approach for eval uating the agronomic effectiveness of rock phosphate materials is thro ugh the use of P-32/P-33 isotopic tracers. The present paper describes the principles and assumptions of the P-32 isotopic techniques common ly used in the field and greenhouse for the agronomic evaluation of ro ck phosphate materials. An overview of the applications of these techn iques is also given.