ASSESSMENT OF SOIL FERTILITY STATUS OF NPK AFFECTED BY MICROORGANISMS IN KASHIM IBRAHIM UNIVERSITY TEACHING AND RESEARCH FARM

Soil fertility is a critical determinant of agricultural productivity and sustainability, particularly in semi-arid regions where nutrient depletion and low biological activity limit crop yields. This study assessed soil fertility status with emphasis on nitrogen (N), phosphorus (P), and potassium (K) as influenced by soil microorganisms at the Teaching and Research Farm of Kashim Ibrahim University, Maiduguri. Soil samples were collected from two depths (0–15 cm and 15–30 cm) using standard sampling procedures. Microbiological analyses were conducted using serial dilution and plate count techniques on Nutrient Agar and Potato Dextrose Agar to determine total heterotrophic bacterial and fungal populations. Bacterial and fungal isolates were further identified using Gram staining and morphological characteristics. Results revealed a high and relatively uniform heterotrophic bacterial population across both depths, with mean values of 5.41 × 10⁸ CFU/g and 5.31 × 10⁸ CFU/g in the 0–15 cm and 15–30 cm layers, respectively. In contrast, fungal populations were significantly higher in the surface soil (2.20 × 10⁶ CFU/g) compared to the subsurface layer (0.65 × 10⁶ CFU/g), indicating strong depth-dependent variability. Identified fungal species included Aspergillus niger, Aspergillus versicolor, and Scopulariopsis fusca. Correlation analysis showed no significant relationships among microbial populations across depths. Planned chemical analyses for soil NPK could not be completed due to laboratory constraints, limiting direct evaluation of nutrient–microbe interactions. The study demonstrates that the soils of the Teaching and Research Farm possess a healthy and active microbial community capable of supporting nutrient cycling. It highlights the importance of incorporating biological indicators into soil fertility assessment and recommends integrated soil management practices to sustain microbial activity and long-term soil productivity.