Freundlich, Langmuir and Temkin Isotherms for Assessing Boron Adsorption-Desorption in Different Soil Types in Tunisia

Understanding the distribution of soil boron (B) is crucial for grasping its dynamics and interactions with soil properties, ultimately ensuring enough boron availability for optimal plant growth and crop yield. This research investigates the adsorption and release of B in Tunisian soils. Six soil profiles, including Cambisol, Vertisol, Fluvisol, and three Luvisols, were sampled and analyzed through batch equilibrium experiments across a range of B concentrations. The retention and release of B were modeled using the Freundlich, Langmuir, and Temkin adsorption isotherms. Results indicated that B adsorption capacity varies significantly with soil type and depth. The Bt horizon of the Cambisol (k = 13.77) and the B horizon of the Vertisol (k = 13.07) showed the highest adsorption, due to favorable traits like high clay content, neutral to alkaline pH, and high cation exchange capacity. In contrast, Luvisol (Balta), with its acidic pH and sandy subsoil, exhibited low adsorption and released more B. The Freundlich isotherm best describes both adsorption (R2 = 0.78–0.96) and desorption (R2 = 0.97–1.00), confirming that B retention is heterogeneous and multilayered. The Temkin model further revealed that chemisorption is the dominant mechanism, with adsorption energy values exceeding 20 kJ mol–1 across all horizons. However, the Langmuir model poorly captured the sorption behavior in most horizons, especially at higher B levels. These results emphasize the importance of soil-specific B management strategies in Tunisian soils. Applying isotherm modeling enhances the understanding of B behavior and supports more efficient fertilization practices tailored to specific soil types and land uses.