Screening and identification of beneficial soil bacteria: evaluating inoculation effects on plant growth with and without organic matter.

Plant growth-promoting bacteria (PGPB) play a vital role in enhancing crop productivity by improving nutrient availability, phytohormone production, and stress tolerance. While the individual effects of PGPB and organic matter on plant growth are well-documented, their combined influence remains less explored. This research aimed to investigate the effects of certain plant growth-promoting bacteria belonging to different genera on the growth of Corn when organic matter was added to the soil. Plant growth-promoting properties were measured using conventional methods, and the highest phosphate solubility (42.46 mg/L) and auxin production (3.36 mg/L) were observed in isolate Bacillus 2MDP-10, while the highest release of potassium was measured in isolate Azotobacter 3MDP-4 (6.73 mg/L). A greenhouse experiment was conducted using a factorial, completely randomized design. Results indicated that all measured growth parameters, including fresh and dry weight of roots and shoots, plant height, stem diameter, and chlorophyll index, were significantly higher in inoculated treatments compared to the non-inoculated treatment (negative control). Ensifer sp. 3MDP-1 improved Corn growth more effectively than the positive control. This isolate resulted in a 2.8-fold increase in shoot dry weight, a 2.4-fold increase in root dry weight, a 29% increase in plant height, and a 2.4-fold increase in chlorophyll index relative to the negative control. Our results demonstrated that the addition of organic matter in the form of manure significantly enhanced all measured parameters; however, no significant interaction was observed between manure addition and bacterial inoculation, except for root dry weight and nitrogen percentage. It is likely that bacterial colonization in the rhizosphere and the utilization of carbon released by the roots are key factors responsible for this response.