Reclamation of Calcareous Sodic Soil by Brevibacterium sp. SOTI06, a Calcite Dissolving Bacteria

Soil degradation due to sodicity is a major constraint to agricultural development in arid and semi-arid regions. The accumulation of exchangeable Na⁺ ions affects soil physicochemical properties, which subsequently increases pH, thus reducing crop yield and nutrient availability. Several practices have been followed for revitalizing salt-affected soils, such as the addition of inorganic or organic amendments. Since most of these soils are calcareous (CaCO₃) in nature, they can serve as a cationic source to release Ca²⁺ to replace the Na⁺ from the clay-complex. Though CaCO₃ is poorly soluble, dissolution can be easily achieved by calcite dissolving bacteria. The present study aimed to evaluate the efficiency of Brevibacterium sp. SOTI06, in reclaiming calcareous sodic soil, along with organic and inorganic inputs through a soil incubation study. The reduction in pH, Na⁺, ESP (Exchangeable sodium percent), and free CaCO₃ during the incubation period confirms the efficiency of amendments. The pH was drastically reduced from 9.10 to 8.20 in gypsum-applied soils. The combined effect of bacterium and press mud reduced higher rates of CaCO₃ in soil (16.6 to 14.5%), with a rise of Ca²⁺ ions (23.5 to 28.7 meq 100 g soil^-1). The mean calcite dissolution was higher in bioinoculant and gypsum-applied soils (9.04%). The SEM (Scanning Electron Microscopy) images confirmed the colonization and calcite dissolution potential of Brevibacterium sp. SOTI06 by pit formation in calcite stones. Hence, this study revealed that the combined application of bioinoculants with organic and inorganic amendments can effectively reclaim calcareous sodic soils.