Chapter 1 The Biosphere Chapter 2 The Anthroposphere Introduction Air Pollution Water Pollution Soil Plants Chapter 3 Soils and Soil Processes Introduction Weathering Processes Pedogenic Processes Chapter 4 Soil Constituents Introduction Trace Elements Minerals Organic Matter Organisms in Soils Chapter 5 Trace Elements in Plants Introduction Absorption Translocation Availability Essentiality and Deficiency Toxicity and Tolerance Speciation Interaction Chapter 6 Elements of Group 1 (Previously Group Ia) Introduction Lithium Rubidium Cesium Chapter 7 Elements of Group 2 (Previously Group IIa) Beryllium Strontium Barium Radium Chapter 8 Elements of Group 3 (Previously Group IIIb) Scandium Yttrium Lanthanides Actinides Chapter 9 Elements of Group 4 (Previously Group IVb) Titanium Zirconium Hafnium Chapter 10 Elements of Group 5 (Previously Group Vb) Vanadium Niobium Tantalum Chapter 11 Elements of Group 6 (Previously Group VIb) Chromium Molybdenum Tungsten Chapter 12 Elements of Group 7 (Previously Group VIIb) Manganese Technetium Rhenium Chapter 13 Elements of Group 8 (Previously Part of Group VIII) Iron Ruthenium Osmium Chapter 14 Elements of Group 9 (Previously Part of Group VIII) Cobalt Rhodium Iridium Chapter 15 Elements of Group 10 (Previously Part of Group VIII) Nickel Palladium Platinum Chapter 16 Elements of Group 11 (Previously Group Ib) Copper Silver Gold Chapter 17 Trace Elements of Group 12 (Previously of Group IIb) Zinc Cadmium Mercury Chapter 18 Elements of Group 13 (Previously Group IIIa) Boron Aluminum Gallium Indium Thallium Chapter 19 Elements of Group I4 (Previously Group IVa) Silicon Germanium Tin Lead Chapter 20 Elements of Group 15 (Previously Group Va) Arsenic Antimony Bismuth Chapter 21 Elements of Group 16 (Previously Group VIa) Selenium Tellurium Polonium Chapter 22 Elements of Group 17 (Previously Group VIIa) Fluorine Chlorine Bromine Iodine

Anion Adsorption in Ferruginous Tropical Soils1

Trace elements in soils and plants

Publisher Summary This chapter reviews the work done with soils and with hydrous oxides of iron and aluminum, with particular reference to mechanisms and structural aspects of anion adsorption. Anion adsorption on clay minerals and calcium carbonate is also discussed. The determination of adsorption isotherms is one of the most useful experimental procedures in the study of the interaction of anions with hydrous oxides or soils. Anion adsorption involves an electrostatic interaction and some chemical interaction between the surface and the ion. The Langmuir model is incomplete in describing this adsorption because it takes no account of charge. The adsorption of anions is dependent on pH, with maximum adsorption usually occurring for fully dissociated ions at low pH where the surface becomes positively charged, owing to protonation of surface M·OH groups. Maximum adsorption of anions of incompletely dissociated acids occurs at a pH value close to the pK of the acid. Anion adsorption reactions in soil are complicated by competition for adsorption sites from anions, including carboxylates, and also by the presence of cations, such as calcium and aluminum.

Anion Adsorption by Soils and Soil Materials

Reactions of phosphate fertilizers in soils

Summary

The two main motivations for studying equations which describe adsorption of phosphate are to understand the processes involved, and to summarize many results by a few numbers. If more than one hypothesis about the process is tenable, appropriate statistical procedures should be used both to choose between them and to obtain the best summary of the results with a given equation. Equations most likely to be successful in describing adsorption are those in which the affinity for adsorption decreases as the amount of adsorption increases. This effect is inherent in the process of phosphate adsorption and occurs because specific adsorption of anions increases the negative charge on the adsorbing surface. It is included in the complex equations of Bowden, and in simpler fashion in the Freundlich equation. Because the simpler equation can only approximately describe the true situation, a perfect fit over a wide range of concentrations should not be expected. Equations for which the affinity for adsorption is constant — such as the Langmuir equation — are not consistent with our knowledge of the adsorption process. This difficulty is not avoided by the multi-surface Langmuir equations: such equations may also be difficult to justify on statistical grounds.

The description of phosphate adsorption curves

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.

Anion Adsorption in Ferruginous Tropical Soils1

Citations

Trace elements in soils and plants

Anion Adsorption by Soils and Soil Materials

Reactions of phosphate fertilizers in soils

The description of phosphate adsorption curves

Management Considerations for Acid Soils with High Phosphorus Fixation Capacity

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