MICROBIAL POPULATION ASSOCIATED WITH SOIL DEPTH ON A FARMLAND AROUND THE FACULTY OF SCIENCE, UNIVERSITY OF DELTA, AGBOR

This study investigates the vertical distribution of microbial populations in relation to soil depth, total organic carbon (TOC), and total nitrogen (TN) in agricultural farmland at the University of Delta, Nigeria. Soil samples were collected from three depth intervals (0–15 cm, 15–30 cm, and 30–45 cm) and analyzed for physicochemical properties (pH, EC, TOC, TN, available P, and texture) and microbial composition (bacteria and fungi). Microbial enumeration was performed using serial dilution and plate count techniques on Nutrient Agar and Sabouraud Dextrose Agar for bacteria and fungi, respectively. Isolates were identified using Gram staining and biochemical tests. Results revealed a decline in microbial biomass (MBC, MBN) and organic carbon with increasing depth, consistent with global trends. The dominant bacterial isolates included Escherichia coli, Staphylococcus sp., and Klebsiella sp., while fungal species such as Aspergillus fumigatus and Rhizopus sp. were prevalent. Statistical analysis confirmed significant positive correlations between microbial abundance, TOC, and TN, supporting the hypothesis that nutrient availability governs microbial stratification. The study highlights the importance of depth-specific soil management to enhance microbial activity and nutrient cycling in tropical agroecosystems. Findings contribute to localized agricultural strategies for sustainable soil fertility and productivity. Keywords: Soil microbial biomass, total organic carbon, total nitrogen, soil depth, agricultural soils, microbial diversity.