Enhancement of Plant Growth with Plant-Based Compost and the Heterotrophic Azotobacter and Streptomyces Inoculation under Greenhouse Conditions

Abstract

Compost is a natural and sustainable way to improve soil fertility and enhance plant growth. Moringa leaves have high mineral, cytokinin, and vitamin content which are useful for growth so that they can be used as organic fertilizer. Azotobacter and Streptomyces are from soil and have many biological activities. This study aimed to detect the importance of bioagents formula with Moringa Compost (MC) to enhance plant growth in poor sterile soil and plants were irrigated with half strength of Hoagland nutrient solution. Moringa leaves were collected and cleaned, and organic compost was prepared and analyzed for microbial and chemical composition. The prepared MC was rich in nitrogen and minerals and had high content of bacteria and fungi. The two bioagents used were isolate MB5 and MB11 which were characterized and molecular identified as Azotobacter chroococcum MB5 and Streptomyces griseus MB11. The free-living A. chroococcum can fix atmospheric nitrogen while Streptomyces is a filamentous bacterium with a high ability to produce secondary metabolites. The addition of 20% MC to soil increased soil EC and microbial counts compared to MC-free soil. Moreover, inoculation of soil with either AZ or ST increased the microbial counts and soil EC and the clearest increase was in the case of inoculation of soil with MC+AZ+ST. It also found that MC extract alone with the bacterial filtrates increases seed germination of Phaseolus vulgaris L. (common bean), which is a herbaceous annual worldwide plant, grown for its edible dry seeds or green unripe pods. In this regard, inoculation of soil with inoculum of both A. chroococcum MB5, and S. griseus MB11, in the presence of MC has the most pronounced effect and enhances both the growth, fresh and dry weights, leaf number, plant height, and root length of P. vulgaris grown under greenhouse conditions for one month and chemical content of the plant protein carbohydrates, P, N, Ca++ and K+. In conclusion, the combined application A. chroococcum MB5 and S. griseus MB11, as a biofertilizers with Moringa compost is recommended to enhance P. vulgaris growth. The use of these biofertilizers can reduce the use of chemical fertilizers, which can have detrimental effects on soil and the environment. Therefore, further research on the inoculation and application of these microorganisms with MC is essential for sustainable agriculture.