The principles that control effectiveness of rock phosphates as fertilizer are now fairly well understood so that the potential effect of a material can be predicted with some confidence from laboratory analysis of the raw material. Soil characteristics, especially acidity, and calcium and phosphate status, are important: if these are not conducive to dissolution, crop response to rock phosphate is small. Some crop characteristics, especially the extent of root systems and whether they are infected with mycorrhizae, also affect utilization of rock phosphate. Dissolution of rock phosphates may be too slow for rapidly growing crops but may be adequate for perennial crops.
Such factors limit the use of rock phosphates for direct application, so that much greater knowledge of the characteristics of the phosphates, soils and crops, and their interactions, is necessary for their successful use than for the soluble phosphates. Economic considerations are important also. Because the phosphate content is less than that of concentrated soluble fertilizers, the cost of transporting rock phosphates, per unit of phosphorus, may not be economic. However, for acid and calcium deficient soils the larger amounts of calcium that rock phosphates supply may be an advantage and may lessen or eliminate the need for lime, especially for crops that require relatively large amounts of calcium.
Fosfatos de roca en la agricultura