Tanjong Karang is a rice growing area in Malaysia. Soil belongs to inceptisol order, pH around 4.5-5.0 and harbors a diverse group of nitrogen fixing bacteria. Beside nitrogen-fixing activity these diazotrophs produced phytohormones especially, indoleacetic acid which enhanced extensive root architecture and help plant to acquire more nutrients from the surrounding area. Higher population of diazotrophs found in the rhizosphere as plant root exudates provides required carbon sources for nitrogen fixation and growth of the bacteria. Diazotrophs have preferences of carbon source utilization....