Abstract
Boron is essential for crop growth but needed in very small amounts. The range between boron deficiency and toxicity for plants is quite narrow. These stress conditions gravely reduce yield and quality of many crop species. Therefore, understanding the factors and the reactions affecting boron availability in soil is necessary. Against this framework, our research aims to determine the available boron status in a semiarid soil of Dour Ismail irrigated perimeter (North Tunisia). The objectives are also to investigate boron distribution in different particle-size fractions throughout the soil profile and to understand boron adsorption-desorption mechanisms according to some soil properties. For this purpose, one soil profile was dug in the field plot that had not received any previous boron fertilization. Soil samples were gathered from the different horizons of the profile and analyzed for the main physicochemical properties. Our results showed that the studied soil is Stagnic Fluvisol (clayic). The highest boron amounts were recorded in deep horizons and were greatly affected by soil salinity, organic matter, and clay contents. However, the increase in the pH level and the high percentage of total lime significantly diminished the available boron amounts in surface layers. The investigation of depth boron distribution in the different particle-size fractions indicated a considerable contribution of the silt (2–50 µm) fraction (52% of the soil total available boron), while the coarse (>50 µm) and clay (<2 µm) fractions seem to play a less important role. The adsorption data were fitted to Freundlich adsorption isotherm. It revealed that adsorption of boron increased with the increase of boron concentrations in soil solution. Desorption isotherm denotes that the accumulated boron in soil was not easily released. Adsorption and desorption of boron in soil were greatly affected by soil properties, such as pH, salinity, sand content, clay content, total organic carbon, total nitrogen, and cation exchange capacity.
Highlights
Boron (B) is a necessary micronutrient for the growth of all crops [1]
The electrical conductivity (EC) values increased as we moved from the surface (1.36 dS/m) to deep layers (2.08 dS/m). e soil texture was dominated by claysilt fractions (≈60%) throughout the pro le. e TCaCO3 percents decreased with the increase in depth. e Ap surface horizon of the studied soil exhibits the highest organic matter (OM) contents with 1.23% of total organic carbon (TOC) and 1.12% of total nitrogen (TN). ese values decreased with depth and reached 0.61% and 0.60%, respectively. e cation exchange capacity (CEC) has the same behavior as the TOC and TN. e values varied from 30.67 meq/100 g top to 17.33 meq/100 g bottom
Mahajan et al [16] and Kumari et al [17] reported a similar relationship. e examination of B distribution in the studied soil showed an increase in the available B content as we moved from surface horizon Ap (0.64 mg/kg) to the deep horizon C2 (0.74 mg/kg). e low B values recorded in surface layers may be explained by a slight increase in the pH level (8.30) and a relatively high TCaCO3 (13.16%) amount
Summary
Boron (B) is a necessary micronutrient for the growth of all crops [1]. It plays a key role in a diverse range of plant functions including cell division and sugar transport. B content evolves and must be monitored frequently because of the narrow range between the levels of B deficiency and toxicity as compared to other nutrients [3]. B deficiency is prevalent in coarse-textured acidic soils developed mainly in high rainfall zones. Soils with low OM content and high adsorption capacity (e.g., soils with high soil pH level and rich in clay minerals) are generally B deficient [5]. B toxicity symptoms are often observed in arid and semiarid regions owing to the use of irrigation waters high in B
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