Influence of plant species on bacterial and fungal activities in the rhizosphere of modified soil

This study evaluated the influence of plant species on bacterial and fungal activities in the rhizosphere of modified soil. Experimental plots were demarcated and beds of 1 m × 1 m were constructed with alleys of 0.75 m between replicates and 0.5 m between beds. Three plant species—Solanum lycopersicum (tomato), Cucumis sativus (cucumber), and Solanum melongena (garden egg)—were cultivated. Fresh animal dung obtained from an abattoir was cured and used to modify the soil. A total of eight soil samples (four modified and four unmodified) were collected in triplicate. Modified soils were incubated for two weeks before planting. Microorganisms were isolated using the serial dilution technique on Nutrient Agar Medium (NAM) and Sabouraud Dextrose Agar (SDA). Results revealed that bacterial counts in modified soils ranged from 3.2 × 10⁵ to 3.6 × 10⁶ Cfu/g, while unmodified soils ranged from 2.6 × 10⁴ to 3.0 × 10⁴ Cfu/g. Fungal counts in modified soils ranged from 1.9 × 10⁵ to 2.6 × 10⁵ cfu/g compared to 1.3 × 10⁴ to 2.1 × 10⁴ Cfu/g in unmodified soils. Bacterial isolates included Pseudomonas, Micrococcus, Klebsiella, Citrobacter, Bacillus, Erwinia, and Lactobacillus spp., while fungal isolates were Cladosporium, Pichia, Aspergillus, and Fusarium spp. The presence of fast-growing copiotrophic species such as Citrobacter and Erwinia in modified soils indicates that animal dung enriched the rhizosphere with additional microorganisms. The study concludes that while animal dung improves soil microbial diversity, it may also introduce undesirable species; thus, microbial screening of organic amendments is recommended prior to use.