Unfolding boron dynamics at the scale of soil-water-fertilizer-crop systems in the tropics: from soil availability to plant requirements

Boron (B) is an essential element that limits crop productivity and quality in tropical regions due to its low availability. Rainfall regime influences B dynamics in soil, which, in turn, affects crop responses to B. Tropical soils are considered low in B if concentrations are less than 0.20 and 0.60 mg kg-1 for annual and perennial crops, respectively. The B availability in soil is governed by the soil's pH, texture, organic matter (OM) content, cation exchange capacity, and source material. Plants' uptake of B occurs passively, although it varies according to its availability in the soil solution. The presence of low-affinity (BOR1 gene) and high-affinity (NIP5;1 gene) transporters has been characterized. B deficiency can impair crop development due to its role in cell metabolism at the molecular, physiological, anatomical, and morphological levels. Both B deficiency and toxicity affect plant growth, highlighting the importance of monitoring B availability by assessing soil fertility to optimize crop performance and quality. Further study should examine the nutritional management of economically important crops using B sources with different solubility in water, application rates, particle sizes, placement, forms, and timing. The speculation that the range between B deficiency and toxicity is narrow may be misunderstood, especially when foliar diagnosis is still neglected. This review aims to understand B dynamics in tropical soils, its functions in higher plants cultivated in these regions, and how its deficiency and/or toxicity can affect agricultural production.