Boron characterization and distribution in particle-size fractions and humic substances in forest and agricultural Tunisian soils

Boron (B) is vital for optimal crop growth and soil health, with its distribution influenced by several factors such as soil properties, environmental conditions, and land management practices. Therefore, understanding its distribution is crucial for developing effective soil management strategies. Currently, there is a lack of information regarding the status of B in Tunisia, highlighting the need for research into its distribution and the factors affecting its availability in Tunisian soils. This study aimed to quantify B fractions and investigate the distribution of available B in particle-size fractions, as well as total B in humic substances, at different depths of soils located in northwest Tunisia. Four agricultural soil types (Luvisol, Vertisol, Cambisol, Fluvisol) and two forest soil types (Luvisol) were selected and analyzed for physicochemical properties and B fractions (Rs-B, Ox-B, Org-B, Res-B, total-B). Additionally, particle size (sand, silt, clay) and humic fractionation (fulvic acid, humic acid, humin) were conducted to quantify B content in each fraction. The results revealed that forest soils exhibited higher available B content, particularly in deeper layers, while agricultural soils (sedimentary rock) had higher total B amounts compared to forest soils (igneous rock), indicating the influence of soil parent material. The distribution of B forms followed Res-B > Org-B > Ox-B > Spa-B > Rs-B, with dynamic equilibrium observed. Moreover, available B predominated in silt fractions, and total B in humic acid fractions. These findings provide insights into B dynamics concerning soil properties and land use, with implications for optimizing crop production and soil fertility in northwest Tunisia, contributing to sustainable agricultural development.