Increasing Efficiency of Liquid Fertilizer via Incorporating Beneficial Microorganisms

Abstract

The growing trend in organic agriculture has boosted the public awareness of organic fertilizer. The present study focused on isolating plant growth promoting microorganisms from the soil samples and incorporating beneficial plant growth promoting microbial (PGPM) strains to a provided liquid organic fertilizer to improve the efficiency of current formula. After isolating plant growth promoting microorganisms, experiments were conducted qualitatively and quantitatively to evaluate the efficacy of those species. Five phosphorous solubilizing bacteria and fungi, one potassium solubilizing bacteria, one potassium solubilizing fungi, six free living nitrogen fixing bacteria from different regions including Hambanthota, Mahiyanganaya, Galaha, Welimada, Rathnapura Sri Lanka were isolated using serial dilution plating on specific growth media and screened for various plant growth-promoting traits. The highest phosphate solubilization (67.8 mg/ml) was exhibited in PH.1 which also exhibited the highest phosphorous solubilization index (PSI) of 2, isolated from the soil sample received from Hambanthota district. Alginate encapsulation as small beads were produced from bacterial inoculum of PH.1 phosphorous solubilizing bacteria with sodium alginate, cellulose, and calcium chloride. A series of different percentages of cellulose (3% - 6%) was used during bead formation to evaluate the effect of cellulose on encapsulation efficiency of beads. Alginate beads were applied to the liquid fertilizer, incubated, and plated periodically to evaluate the efficiency of this formulation. The number of released cells of PH.1 reached 7.36 X 10 6 CFU/ml after 48 hours of incubation in the 0.25 X diluted liquid fertilizer which resulted from the bead formulation of 4% (w/v) Alginate + 3% (w/v) cellulose. The cellulose supported the entrapment of bacterial cells (plant growth-promoting bacterium) PH.1 as biofertilizer in the matrix, which reduced cell loss. The highest entrapment efficiency of 5.441% was obtained at 3% (w/v) cellulose, Overall, the appropriate content of cellulose mixed with alginate is conducive to changes in the morphology of microcapsules and increases the amount of biological encapsulation. This indicates that the beads-based biofertilizer can partially replace chemical fertilizers.