Comparison of isotherm equations for boron adsorption and desorption on soils with fertilizer applications.

Adsorption and desorption of boron (B) was investigated in soils receiving different fertilizers such as mineral (21 % N), organic mineral (10% N), mycorrhizas inoculums, wine-producing residues (three different formula: distiller's residue 2.2% N; anaerobic digestate 2.8% N; the same plus mycorrhizas inoculum), and compost by farm residues (2.0% N). The soil samples, collected after a triennial lettuce (Lactuca sativa L. cv Bacio) cultivation, were equilibrated using six B concentrations (0, 1, 5, 20, 50, 100 mg B L -1 , as H 3 BO 3 ). Sorption processes were fitted to linear forms of the Freundlich, Langmuir and Temkin equations. Boron adsorption data were well described by Freundlich and Langmuir isotherms, while the Temkin showed a lowest fit. All fertilized plots showed higher intensity of adsorption (Freundlich 1/n range 0.617-0.765 L kg -1 ), and applications of distiller's residue plus anaerobic digestate and organic-mineral fertilizer to soils increased the maximum adsorption and buffering capacity, with the Langmuir and Temkin models, respectively. The Freundlich intensity of adsorption 1/n was positively correlated with the Langmuir maximum adsorption Xm and Temkin buffering capacity b. Boron desorption data fitted well with the Freundlich isotherm (high R 2 values), and the desorption intensity coefficients, 1/n 1 , increased with the application of fertilizers. Comparison of desorption to adsorption Freundlich isotherms showed that there was a total reversibility of adsorbed boron for all fertilized plots, well explained by the desorption index values <1. Freundlich isotherm proved more effective in describing B desorption in soils as compared to Langmuir and Temkin equations.