The Impact of Organic Fertilizers on Growth, Yield, and Rhizospheric Bacterial Diversity in Black Turmeric (Curcuma caesia)

Background: Agricultural applications of organic manures are critical for enhancing soil health and producing higher-quality black turmeric, a plant used in various traditional medicines. Identifying and analyzing the biochemical activities of rhizospheric bacteria in different soil conditions can provide insights into sustainable agricultural practices. Method: A field study was conducted over three to four months by planting black turmeric rhizome samples in two different soil conditions: organic and conventional. Morphological features were extensively documented. UV-Vis spectroscopy was performed on organic rhizome methanolic extracts, while both organic and conventional aqueous extracts underwent XRF analysis. Antibacterial activity against eight pathogenic bacteria was tested using methanolic and aqueous rhizome extracts. Rhizobacteria were isolated from organic soil using a serial dilution procedure and identified through pure culture techniques. Various biochemical activities, including catalase production, starch hydrolysis, antibiotic sensitivity, pH tolerance, temperature tolerance, and gram staining, were performed to characterize the bacterial species. Results: The study showed distinct inhibitory zones for pathogenic bacteria in both methanol and aqueous extracts. UV-Vis spectroscopy identified a peak in the 200-250 nm range. XRF analysis revealed the presence of various elements in both soil and leaves, with differing concentrations. Gram-positive bacteria were identified, and these bacteria exhibited catalase activity, starch hydrolysis, and significant antibiotic sensitivity. Soil bacteria demonstrated pH tolerance and resistance to high temperatures. Rhizomes grown in organic soil exhibited better growth and development compared to those in conventional soil. Conclusion: Organic fertilizers positively influence the growth and quality of black turmeric. The role of soil bacteria in sustainable agriculture offers promising new techniques for managing plant diseases and enhancing soil health.