Rhizosphere borne beneficial microbes for promoting plant growth in calcareous and sodic soils– An overview

Sodic and calcareous soils are characterized by high sodium and calcium carbonate content. Excess sodium in sodic soils leads to surface crusting and dispersion of clay particles. The presence of calcium carbonate in calcareous soil results in higher soil pH, poor soil structure, low phosphorus availability and low fertility, all of which significantly reduce crop productivity. Effective management of these soils is highly essential for improving soil fertility and ensuring crop productivity, particularly in India, as 6.73 M ha of land are salt affected, whereas 229 M ha are calcareous. Bio-augmenting this problem soil with salt-tolerant beneficial microorganisms has emerged as a promising strategy for addressing these issues. Salt-tolerant bacteria can withstand salt concentrations up to 30 % by accumulating ideal solutes for osmoregulation, producing extracellular proteases and stimulating Na+/ H+ antiporters. These beneficial microorganisms can improve soil structure, increase nutrient availability, promote the leaching of excess salts and solubilize calcium carbonate by producing organic acids. Salt-tolerant plant growth-promoting bacteria could alleviate stress in plants through various mechanisms and this review paper provides an overview of salt-affected soils and the importance of rhizosphere-borne microbes in alleviating salt stress. Integration of microbial strains with traditional soil amendments provides an eco-friendly and effective approach for restoring soil health and promoting sustainable agriculture in sodic and calcareous soils.