Soil-solution Interactions and Adsorption Mechanisms of Calcium and Boron in Agricultural Soils: A Comprehensive Review

Abstract

Calcium (Ca) and Boron (B) are essential nutrients whose interactions within the soil-solution play a fundamental role in determining their availability in agricultural systems. This review consolidates current understanding of Ca-B soil chemistry, emphasizing solution equilibria, adsorption processes, and their interactive influences. Calcium mainly exists as Ca²⁺ engaged in cation exchange, whereas boron shows pH-dependent speciation between H₃BO₃ and B(OH)₄⁻. Adsorption mechanisms differ fundamentally: calcium predominantly forms outer-sphere complexes on permanent charge sites, while boron primarily establishes inner-sphere complexes through ligand exchange process. Maximum boron adsorption occurs at pH 9-10, which contrasts with calcium behavior, where adsorption characteristics vary differently across pH levels. Clay mineralogy significantly influences ion retention: 2:1 phyllosilicate offers high cation exchange capacity (CEC) for calcium, while oxide minerals primarily function as adsorption sites for boron. Interactive effects include calcium-induced boron deficiency, which occurs through pH modification and competitive adsorption interactions between the ions. Recent spectroscopic advances have revealed molecular mechanisms such as the formation of CaB(OH)₄⁺ ion pairs, enhancing our understanding of boron retention and interactions in soil systems. Agricultural implications emphasize the importance of integrated nutrient management strategies that consider factors such as soil pH, texture, and organic matter to optimize nutrient availability and crop productivity. Critical research needs encompass developing multi-surface modeling approaches and investigating the impact of climate change on calcium- boron (Ca-B) dynamics to better predict and manage nutrient interactions under changing environmental conditions. This review employed a systematic literature synthesis approach, integrating findings from multiple databases and specialized journals to provide researchers and practitioners with a comprehensive resource for understanding Ca-B dynamics and developing improved nutrient management strategies.