Effects of Physicochemical Properties of Calcareous Soils on Boron Adsorption-Desorption Reactions

Understanding the processes that control the activity of boron (B) in the soil solution is important for maintaining water quality and soil fertility management. Since these processes are influenced by the physical and chemical properties of soil, in this research, the effects of soil properties on B adsorption-desorption reactions and the degree of reversibility were studied. For this purpose, B adsorption and desorption isotherms were measured in 14 calcareous soils. Adsorption isotherms were described by using the empirical models and the effects of soil properties were analyzed by using the multi-variables regression. Results showed that B adsorption followed Langmuir equation with maximum adsorption in the range of 3-14 mmol.kg^-1. Calculations indicated that soil cation exchange capacity (CEC) and reactive calcium carbonate equivalent (CCE_r) were primarily responsible for B retention in the calcareous soils. Organic carbon, CCEr, and aluminum oxide described about 94% variability inthe average coefficient of boron distribution (CCE_r and CEC were directly related to the degree of reversibility (hysteresis) of adsorption reactions. The two-surface Langmuir isotherms indicated that adsorption maximum could be useful in predicting B availability in soil. On the contrary, the binding energy coefficients in both high and low B concentrations failed to show any practical benefit. Regression model (as a function of CEC and adsorption equation coefficients) confirmed the practical use of Freundlich and Langmuir coefficients to predict B availability in calcareous soils.