Use of Bacillus as a Plant Growth-Promoting Rhizobacteria to Improve Phosphate and Potassium Availability in Acidic and Saline Soils

Abstract

Bacillus is a rhizobacterium that can help with the nutrient cycle in the soil. Plant growth-promoting rhizobacteria (PGPR) can be found in the rhizosphere of many plants. This research was divided into two parts: (1) a test of the ability of Bacillus genus isolates to withstand various NaCl concentrations in saline and acidic soils; and (2) quantification of the secondary metabolites produced by the rhizobacteria in the form of hormones and organic acids. Bacillus valezensis (BPF2), which can dissolve phosphate, Bacillus sp (BPK1), and Bacillus subtilis (BPK2), which can dissolve potassium, were the isolates tested. Bacillus increased the availability of phosphate and potassium in the saline and acidic soils and the secondary metabolites produced, such as organic acids and the hormone indole acetic acid. The results showed that the three isolates could still dissolve phosphorous and potassium with a 3% NaCl addition, but the concentration decreased as the incubation time increased to H+15. On the 30th day, Bacillus valezensis inoculation improved soil phosphate availability by up to 88% in the acidic soil and 73% in the saline soil compared to the control. On the other hand, Bacillus sp. and Bacillus subtilis raised the potassium concentration in the acidic soil until day 10, reaching a maximum of 0.37 me.100g−1. The three PGPRs (Bacillus valezensis, Bacillus sp., and Bacillus subtilis) produced 13.25, 11.97, and 14.97 g.mL−1 of indole acetic acid metabolites, respectively. Acetic, lactic, citric, malic, and oxalic acids were among the organic acids produced. Bacillus valezensis produced the most lactic acid at 4.94 mg.L−1, while Bacillus sp. and Bacillus subtilis produced the most acetic acid, at 2.91 and 2.55 mg,L−1, respectively.