Integrated Application of Organic Amendments with Alcaligenes sp. AZ9 Improves Nutrient Uptake and Yield of Maize (Zea mays)

Bacterial species in the plant-beneficial-environmental branch of Alcaligenes characterize an important part of rhizosphere microbes. The effects of plant growth-promoting Alcaligenes sp. AZ9 (accession #KU494828) on soil status and maize (Zea mays L.) performance were evaluated in single or combined applications with soil amendments, such as biochar (BC) prepared through pyrolysis of maize straw at 300 oC, rock phosphate enriched compost (CM), and humic acid (HA) in two wirehouse experiments under natural environment. Qualitative P solubilization of Alcaligenes sp. AZ9 revealed the appearance of a halo zone up to 19.1 mm in agar medium with P solubilizing index 4.27 and P solubilizing efficiency 327%. Alcaligenes sp. AZ9 showed solubilization of P up to 30.85 µg mL−1 by lowering pH of medium from 7.0 to 5.25. The application of Alcaligenes sp. AZ9 significantly improved soil biological attributes, such as bacterial colony forming unit by 20.5%, soil organic carbon by 10.3%, soil organic matter by 5.1%, and water content of saturated soil by 5.7%. The combined application of Alcaligenes sp. AZ9 with either BC, CM, or HA or with their mixture (BC plus CM plus HA) significantly increased the above biological attributes of soil than the application of Alcaligenes sp. AZ9 alone. Moreover, the integrated application of Alcaligenes sp. AZ9 with BC, CM, and HA significantly improved growth and yield attributes of maize in terms of root length (26%), plant height (39%), shoot fresh biomass (31%), shoot dry biomass (32%), root fresh biomass (30%), root dry biomass (34%), 100-grains weight (26%), stover yield (28%), and grain yield (19%). Similarly, the integrated application of Alcaligenes sp. AZ9 with BC, CM, and HA promoted N, P, and K in maize grain concentration by 12%, 11%, and 11%, respectively, compared with the application of organic amendments without Alcaligenes sp. AZ9. Combined application of Alcaligenes sp. AZ9 with BC, CM, and HA could be an effective strategy to improve plant growth, nutrients uptake, and yield of maize in the context of sustainable agriculture. In future research, the effects of integrated application of Alcaligenes sp. AZ9 with BC, CM, and/or HA should be further evaluated under field conditions.