Synergistic Effects of Organo-Mineral Fertilization and Phosphorus-Solubilizing Bacteria on Soil Biological Activity and Eggplant Growth in Calcareous Soil

Abstract

This study was conducted to investigate the effects of a commercial microbial fertilizer containing Bacillus megaterium, Pantoea agglomerans and Pseudomonas fluorescens on soil biological properties and plant growth during eggplant (Solanum melongena L.) cultivation under greenhouse conditions in calcareous soils. While 70% of the phosphorus (P) requirement was supplied via fertigation, the remaining 30% was provided through organo-mineral basal fertilization at four reduction levels (0%, 25%, 50%, 100%) combined with microbial inoculation. Soil samples collected prior to the experiment and at 4 different growth stages were analyzed for physical, chemical, and biological properties, while plant samples collected at the end of the harvest were evaluated for pomological and physiological traits. The results indicated that microbial treatments substantially enhanced soil biological activity. Specifically, the full-dose P + microbial treatment (100+) produced the highest urease, alkaline phosphatase, β-glucosidase activities, and total bacterial count. The 100+ treatment also yielded the most pronounced improvements in soil EC, organic matter, total nitrogen, and available P. Plant parameters, including fruit length, peduncle length, dry biomass, soluble solids content, and chlorophyll concentrations, responded positively to P–microbial combinations. The highest leaf phosphorus concentration was obtained from the 100+ treatment, while the maximum total yield was achieved in both the 100 and 100+ treatments. These findings demonstrate that microbial inoculants create a strong synergy with mineral fertilization by enhancing P bioavailability and nutrient use efficiency. Consequently, it was determined that an integrated microbial-chemical fertilization strategy is an effective method for sustainable eggplant production in calcareous soils.