Field technique using the acetylene reduction method to assay nitrogenase activity and its association with the rice rhizosphere

Summary A plastic bag, used as a field assay chamber, assisted in the investigation of the acetylene reduction method as a technique to measure nitrogen-fixing activity in rice paddy fields. A study of the change in volume of the plastic bag and of the loss of acetylene and ethylene from the bag provided evidence that this plastic bag method was feasible in field assays. The field assay of rice at the grain ripening stage showed that the nitrogen-fixing activity increased linearly after a lag phase of 0 to 3 hours during a time-course experiment.Detachment of the aerial part of the rice plant from its root remaining in the field did not affect the nitrogen-fixing activity of the root.The markedly higher nitrogen-fixing activity in the planted areas of the field compared with the nonplanted areas between the plant rows indicated that the nitrogenase activity in the field is associated with the roots of the rice plant. re]19751204