Abstract

The over-reliance on inorganic fertilizers in crop cultivation poses environmental concerns, necessitating the search for sustainable alternatives. This study evaluated the effect of soil amendment with Klebsiella oxytoca on the growth, yield, and soil properties of Capsicum annuum. Soil samples were collected from the Botany Garden of Rivers State University, while seedlings were obtained from the Teaching and Research Farm of Rivers State University, Port Harcourt, Nigeria. Klebsiella oxytoca were isolated from soil, and identified through phenotypic and genotypic characterization. Broth cultures of the bacterium were prepared and standardized. Seedlings were divided into three treatments: control (water only), Klebsiella oxytoca–amended (alternating water and broth culture), and NPK fertilizer (water plus fertilizer), and transplanted into sandy loam soil in polythene bags. Growth results showed that Klebsiella oxytoca significantly increased plant height (39.76 ± 16.42 cm) compared to NPK (38.72 ± 2.13 cm) and control (18.82 ± 1.71 cm) (p < 0.05). NPK significantly enhanced number of leaves (55.40 ± 22.51) and leaf breadth (44.15 ± 10.51 cm²) relative to Klebsiella oxytoca (49.80 ± 3.63 leaves; 25.86 ± 7.80 cm²) and control (16.60 ± 4.98 leaves; 19.26 ± 5.04 cm²) (p < 0.05). Stem caliper showed no significant difference (p > 0.05), though NPK plants recorded the thickest stems (2.24 ± 0.59 cm) compared to Klebsiella oxytoca (1.68 ± 0.23 cm) and control (1.28 ± 0.11 cm). Fruit production was limited to NPK (0.60 ± 1.34 fruits), with no significant differences (p > 0.05). Total Heterotrophic Bacteria increased from 5.63 × 10⁶ to 8.02 × 10⁶ CFU/g in control soil, while higher counts were recorded in Klebsiella-amended (9.30 × 10⁶ CFU/g) and NPK-treated soils (9.50 × 10⁶ CFU/g) after cultivation. Klebsiella spp. counts remained relatively stable in the control soil (5.51 × 10⁴–5.53 × 10⁴ CFU/g) but increased in Klebsiella-amended (6.55 × 10⁴ CFU/g) and NPK-treated soils (8.05 × 10⁴ CFU/g). Fungi counts decreased in the control (5.54 × 10⁴ to 2.98 × 10⁴ CFU/g) and Klebsiella-amended soils (3.60 × 10⁴ CFU/g), while remaining relatively unchanged in NPK-treated soil (5.54 × 10⁴ to 5.56 × 10⁴ CFU/g). In conclusion, soil amendment with Klebsiella oxytoca showed promising potential as a sustainable biofertilizer by enhancing vegetative growth of Capsicum annuum; however, it does not improve fruit yield.