Comparative Analysis of Compost Manure and Inorganic Fertilizer on the Bacterial Population Density of Cocoa Seedling Rhizosphere

Abstract

Soil quality has been known to have a strong effect on cocoa tree growth
and the interactions of plant and microbe in the rhizosphere influence
plant health, productivity and soil fertility. In this study, the rhizospheres
of cocoa seedlings were analyzed for bacterial density population after
soil amendment. Cocoa seedlings were self-grown in nursery located at
the Orchard of the Faculty of Agriculture, University of Benin and
Amelonado variety Tc1-Tc8 pods were used. The seeds were prepared,
pre-germinated and planted in bags containing 5 kg top soil. Organic
fertilizers (compost poultry manure and cow dung) and inorganic
fertilizer was applied to the soil surrounding the seedlings at one month
after planting. The sowing soil and the rhizosphere of the cocoa seedlings
at one month to four month were collected and analyzed. Serial dilution
method was used for culturing and bacterial isolates were identified by
Gram staining and various biochemical methods. The isolates were
further characterized by DNA extraction, PCR and sequencing. All
isolates belong to the phyla Proteobacteria, save one which belongs to the
phylum Firmicutes; all of which are predominately found in the soil. The
result revealed that the rhizosphere of seedlings amended with inorganic
fertilizer recorded the least bacterial activity (2.35 x 105
– 3.05 x 105
cfu/g), while that of poultry manure recorded the highest (8.20 x 105
–
1.17 x 106
). The application of poultry manure showed a significant
difference in the bacterial population.