Section 2
Chapter 1,284

A comparison between the acetylene reduction method, the isotope dilution method and the total nitrogen difference method for measuring nitrogen fixation in lucerne (Medicago sativa L.)

Martensson, A.M.; Ljunggren, H.D.

Plant and Soil 81(2): 177-184


ISSN/ISBN: 0032-079X
DOI: 10.1007/bf02197149
Accession: 001283951

An application of the acetylene-reduction technique was developed. The technique, consisting of a plastic bag incubation system, using propane as an internal standard of the apparent volume, made it possible to carry out repeated incubations on the same plant system. The evaluated technique included studies of the diffusion of ethylene and propane in a soil column, as well as studies of the optimal substrate concentration and grade of purity of the substrate. In addition, the conversion factor between amounts of reduced acetylene as compared with reduced dinitrogen was determined by 15N2 incubations to be 4.41. The developed in situ acetylene-reduction technique was compared wth an isotope dilution method and a total N difference method. A comparison of the derived total N fixation values from each with the value derived from the acetylene-reduction method showed that the values differed significantly. The acetylene-reduction method gave the highest N fixation values, the isotope dilution the lowest values and the total N difference method was intermediate. No statistical significant difference existed between the 2 different reference crops [lucerne with a commercial inoculant, and fescue] used in the isotope dilution method.

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