Vol. 8, Issue 12, Part G (2025)
Abstract
Rice (Oryza sativa L.) is the staple food for more than two-thirds of the Indian population and plays a pivotal role in food security and the national economy. Long-term fertilizer management significantly alters soil physicochemical properties and microbial diversity, which in turn influences nutrient cycling and crop productivity. The present study was conducted at RARS, Jagtial, using soil samples from a 20-year long-term fertilizer experiment to investigate the microbial diversity and plant growth promoting (PGP) traits of rhizospheric isolates under organic (100% FYM) and inorganic (100% NPK) fertilization practices. Soil samples were collected from the rhizosphere at a depth of 15-30 cm and serial dilutions were plated on selective media for isolation of bacteria, fungi, and actinomycetes. A total of 48 microbial isolates were obtained, of which 43 were purified and characterized based on morphological, cultural, biochemical, and physiological traits following Bergey’s Manual. Among these, 42 were Gram-positive and one Gram-negative, with diverse pigmentation and colony morphology. Screening for enzymatic activities revealed that 27 isolates exhibited protease activity, 13 urease production, and 26 hydrocyanic acid (HCN) production, whereas none showed detectable chitinolytic activity under plate assay conditions. Further, PGP screening showed that 17 isolates solubilized phosphate (halo zones 3.7-14.8 mm), 24 isolates solubilized potassium (3.2-15.6 mm), and 19 isolates solubilized zinc (3.2-15.6 mm). Thirteen isolates produced siderophores, 27 produced ammonia, and the majority (22 isolates) synthesized indole acetic acid (IAA), with varying intensities. Notably, isolates RB 40, RB 39, and RB 1 exhibited superior phosphate, potassium, and zinc solubilization respectively, while RB 2, RB 19, RB 37, RA1, and RA2 were strong siderophore producers. The results highlight that long-term nutrient management exerts a significant influence on the rhizospheric microbial community and its functional potential. Several isolates demonstrated multiple beneficial traits, suggesting their potential as biofertilizer candidates to enhance nutrient availability and reduce dependence on chemical inputs. This study emphasizes the importance of integrating microbial inoculants in sustainable rice cultivation systems to improve soil health and crop productivity while minimizing environmental impacts of continuous chemical fertilizer use.
