MICROBIAL AND PHYSICOCHEMICAL QUALITIES OF RICE CULTIVATED SOILS IN AULE, AKURE, NIGERIA

Abstract

Rice (Oryza sativa L) is the seed of the monocot plant of the genus Oryza and of the grass family Poaceae (formally Graminae). The family include twenty wild species and two widely cultivated, Oryza sativa L (Asian rice) and Oryza glaberrima (African rice). Ten soil samples were collected from a rice farm of about 2 hectares, at a distance of 50 meters apart using a garden trowel at a depth of 0 – 15 cm during the raining season and analysed for microbial, physical and chemical properties. A total of fourteen microorganisms were isolated consisting of nine bacteria and five fungi. The bacteria were Bacillus thuringensis, B. pumilus, Lactobacillus fermentum, B. cereus, B. anthracis, Paenibacillus taichungensis, Staphylococcus lentus, B. subtilis and Pseudomonas putida, while the fungi included Aspergillus flavus, Rhizopus stolonifer, Saccharomyces cerevisiae, Penicillium sp, and P. chrysogenum. The soil had an average microbial count of 8.13 × 105 cfu / g for bacteria and 5.9.0 × 103 sfu/g for fungi, while the control soil (vegetable cultivated soil) had a microbial count of 7.31 × 104 cfu/g and 4.20 × 103 sfu/g respectively for bacteria and fungi. The isolates were screened for enzyme production using agar plate methods. The ability of the soil microorganisms to produce amino acids and ascorbic acid (vitamin C) was carried out using submerged fermentation method. The supernatants obtained at 24 hour, 48 hour and 72 hour of fermentation were centrifuged and filtered using Millipore filters (0.45 μm pore size). The filtrates were analysed for lysine, aspartic acid, glutamic acid, alanine, valine and phenylalanine qualitatively using paper electrophoresis. The vitamin C content of the filtrates were further determined by a chemical method using ascorbic acid as the reference compound. The colour of the soil varies from grey black to whitish black, while its texture ranges from sandy loamy to clay loam. The soil of study has a moisture content of about 19.02 %, the water holding capacity of about 28.0 % and temperature of 31 0C. The chemical properties revealed that soil pH was 6.55, organic carbon of 1.02 %, organic matter of 1.20 %, total nitrogen of 0.30 % and organic nitrogen of 0.05 %. The mineral analysis revealed sodium (0.07 cmol/kg), potassium (0.04 cmol/kg), calcium (1.28 cmol/kg), magnesium (0.17 cm ol/kg) and phosphorus (0.02 cmol/kg) were present in the sampled soils. The sample soils could be a reservoir of microorganisms that could be exploited for some useful metabolites.