Index >> Rhizobium and Legume Root Nodulation >>Acetylene Reduction Technique

The advantage of the technique includes facility for large number of in situ assays, economy, simplicity, effective gas exchange prior to incubation, easy removal of the gaseous end products and sensitive analysis with a flame ionization detection system after separation by gas chromatography. The technique is 10³ times mote sensitive than ¹⁵N tracer technique.

Samples to be tested are incubated in serum vials, syringes, plastic bags or suitable containers with purified acetylene (C₂H₂) under standard temperature, incubation period and illumination. At the end of incubation, the gas from the container is removed for ethylene (C₂H₄) analysis by gas chromatographic fractionation followed by detection by flame ionization or colorimetry. After correction for the small amount of C₂H₂ present as an impurity in C2H4 the amount of nitrogen fixed is determined by the extent of reduction of C₂H₂ to C₂H₄. Moles of N₂ fixed is obtained by division of moles of C₂H₂ reduced to C₂H₄ by a factor of 3. This factor is based on the ratio of the requirement of 6 electrons for reduction of N₂ and 2 for C₂H₂. The method is extremely useful for routine field evaluations.