Inoculation of Earthworms and Plant Growth-Promoting Rhizobacteria (PGPR) for the Improvement of Vegetable Growth via Enhanced N and P Availability in Soils

A pot trial was conducted to investigate the single, dual, and triple inoculation of earthworms or plant growth-promoting rhizobacteria (PGPR), including nitrogen-fixing bacteria (NFB) (Azotobacter chroococcum HKN-5) and phosphate-solubilizing bacteria (PSB) (Bacillus megaterium HKP-1), on the growth of Brassica parachinenesis and nitrogen (N) and phosphorus (P) availability in soils. All of the five inoculation treatments significantly (P < 0.05) increased the shoot growth of B. parachinenesis. The greatest shoot and root biomass were recorded in the triple inoculation of earthworm, NFB, and PSB. All of the five inoculation treatments significantly (P < 0.05) increased the concentrations of ammonium (NH₄ ⁺)-N, NO_x-N, and sodium bicarbonate (NaHCO₃)-extractable P in soils. Based on plant growth and availability of N and P in soils, the present study suggested that the triple inoculation may be a promising approach for reducing the need for chemical fertilizers in growing vegetables.