Calcium-boron Interactions in Plant Nutrition: From Molecular Mechanisms to Agricultural Applications: A Review

Ca-B interactions in crop plants are essential in crop productivity, quality and stress-tolerance in a variety of agro-climatic conditions. This review discusses the complex processes behind Ca-B nutrition in plants, both at the molecular interaction level and in the field. Calcium ionically bridges with the pectin compounds at the cellular level and boron forms borate crosslinking with rhamnogalacturonan II (RG-II). The resulting B-RG-II complex that involves two molecules of boric acid and two Ca²⁺ ions is important to retain the cell wall integrity. The effect of these nutrients during the plant development is synergistic and when there is deficiency of boron, it leads to increased cytosolic Ca²⁺ and also calcium-regulated gene expression. Physicochemical properties of soil play a great role in Ca-B dynamics. Boron adsorption on clay minerals is enhanced as pH rises reaching a peak of about pH 9.0 in alkaline environment. The arable land of the world is estimated at around 50% of the global land, with 50% of this area being acid in nature making the availability of the two nutrients to be limited and thus requires strategic interventions. Optimised Ca-B nutrition leads to significant increases in yield of major crops. This can only be achieved through combined methods of soil testing, precise fertilisation and environmental concerns to facilitate good management. Nutrient management strategies are being transformed with the new technologies such as genomics, metabolomics, precision agriculture, mycorrhizal associations and machine learning algorithms. New areas of research should be directed towards new decision support systems, molecular level interventions, sustainable boron recovery of waste streams and mycorrhizal-mediated nutrient interactions.