Introduction, Allen V. Barker and David J. Pilbeam Essential Elements-Macronutrients Nitrogen, Allen V. Barker and Gretchen M. Bryson Phosphorus, Charles A. Sanchez Potassium, Konrad Mengel Calcium, David J. Pilbeam and Philip S. Morley Magnesium, Donald J. Merhaut Sulfur, Silvia Haneklaus, Elke Bloem, Ewald Schnug, Luit J. de Kok and Ineke Stulen Essential Elements-Micronutrients Boron, Umesh C. Gupta Chlorine, Joseph R. Heckman Copper, David E. Kopsel and Dean A. Kopsell Iron, Volker Roemheld and Miroslav Nikolic Manganese, Julia M. Humphries, James C.R. Stangoulis, and Robin D. Graham Molybdenum, Russell L. Hamlin Nickel, Patrick H. Brown Zinc, J. Benton Storey Beneficial Elements Aluminum, Susan C. Miyasaka, N.V. Hue, and Michael A. Dunn Cobalt, Geeta Talukder and Archana Sharmaz Selenium, Dean A. Kopsell and David E. Kopsell Silicon, George H. Snyder, Vladimir V. Matichenkov and Lawrence E. Datnoff Sodium, John Gorham Vanadium, David J Pilbeam and K Drihem Conclusion, Allen V. Barker and David J Pilbeam

Handbook of plant nutrition

Publisher Summary The direct application of phosphate rock (PR) to soils as a source of fertilizer phosphorus (P) is a practice that has been employed with varying degrees of popularity over the years. Experimental results have shown that PR is most effective when used on acid soils that are extremely deficient in P. This chapter evaluates systematically the various factors related to the utilization of PR as a source of P for plants. However, PR may be a suitable source of P in extensive agricultural systems where suboptimum yields are expected because of limits on additional inputs; in these cases, the relative amounts and costs of PR and soluble P fertilizers required to obtain the desired yield need to be compared. This chapter discusses factors affecting the agronomic effectiveness of PR. The availability of the P in PR is influenced by (1) the inherent differences among PR sources, (2) the soil environment to which the PR was applied, and (3) the crop for which the PR fertilizer was used.

The Use of Phosphate Rock for Direct Application to Soils

Publisher Summary This chapter evaluates the degree to which phosphate rocks (PR) and partially acidulated phosphate rocks (PAPR) are suitable for use in tropical agriculture. Considerable research has been conducted in search of alternative means of supplying phosphorus (P) for crop production in tropical soils. The use of PR combined with soluble forms of P, such as PAPR, represents a highly efficient means of utilizing indigenous PR resources. The research on these combinations throughout Latin America, Africa, and Asia has shown that the response curves for products with only 40– 50% of the phosphorus applied in a water-soluble form are similar to those of highly soluble phosphorus fertilizers, thus suggesting that both the soluble and insoluble fractions contribute to the plant response. This approach offers expanded opportunities for utilizing indigenous resources that possess properties unsuited for production of fully acidulated products and for use with soils and crops where PR alone is unreliable. This is especially the case in soils characterized by high phosphorus retention capacity, where the soluble fraction of the fertilizer treatment is relied upon only for the early stages of growth and the unacidulated fraction continues to dissolve during the longer term.

Agronomic Value of Unacidulated and Partially Acidulated Phosphate Rocks Indigenous to the Tropics

Phosphorus fixation is generally understood as the transformation of soluble forms of P into less soluble ones after they react with the soil. Although this is a common occurrence in soils, it becomes a major management consideration in certain soils because of the large amounts of fertilizer P needed to meet crop requirements. Phosphorus fixation is most frequently a problem in acid soils high in finely divided sesquioxides, less frequently a problem in calcareous soils, and rarely a problem in soils that are neither high in free sesquioxides nor calcareous. A P-deficient soil which can be corrected by an application of 20 to 50 kg of P Iha is not a problem soil, but a soil which requires 300 to over 1,000 kg of P Iha needs a different management for profitable crop production. A considerable proportion of the world's potentially arable but presently unused land has this limitation. The purpose of this chapter is to examine the occurrence and magnitude of high P fixation and the management practices designed to cope with this situation. No attempt is made to give a full literature review on P fixation, rather we attempted to illustrate management concepts with specific examples. Our discussion is confined to acid soils where the problem is most severe. For example, Olsen and Watanabe (1957) reported that representative acid soils of the United States fixed more than twice the amount of added P per unit of surface area than a similar group of neutral or calcareous soils. They also found that the P fixed was held with five times more bonding energy in acid soils as compared to calcareous soils.

E. O. McLean

Papers

Sources of Phosphorus for Plants Grown in Soils with Differing Phosphorus Fixation Tendencies