Studies on nitrogenase activity of diazotrophic isolates from different rice production systems
The present study was carried out to evaluate the nitrogen fixing ability of diazotrophs isolated from the rhizosphere soils of rice which were grown in three different rice growing systems. A total of hundred and ten isolates obtained were subjected to Acetylene Reduction Assay (ARA) and ninety eight isolates recorded significant amount of nitrogenase activity in a range of 185.73 to 3794.55 nmoles of ethylene mg of protein 1 h 1. The highest nitrogenase activity was recorded by Derxia (3794.55 nmoles of ethylene mg of protein 1 h 1) isolated from Trichy (lowland) Among the three different rice production systems, isolates obtained from lowland rice (Derxia aEUR" 3794.5 nmoles of ethylene mg of protein 1 h 1) recorded higher nitrogenase activity followed by Aerobic (Pseudomonas 2194.89 nmoles of ethylene mg of protein 1 h 1) and SRI (Azotobacter 1971.85 nmoles of ethylene mg of protein 1 h 1) rice isolates. The results revealed marked variation in the ARA of the diazotrophic isolates obtained from lowland, SRI and Aerobic rice. The nitrogenase activity of diazotrophs from rice fields have been reported earlier but the nitrogenase activity of diazotrophs from three different rice production systems from various parts of Tamil Nadu is reported for the first time from India.