Measurement of atmospheric nitrogen fixation in legume‐based pasture turfs using the acetylene reduction assay

Successive acetylene reduction assays and legume N uptake measurements were made over a period of 23 weeks on 80 clover‐rye grass pasture turfs kept in a glasshouse. Assays involved incubating the intact turfs in 5–1 containers with acetylene and measuring the Ethylene produced in 24 h. There was a close linear relationship between ethylene production and legume N uptake, with an overall correlation coefficient of 0.946; the estimated molar ratio of N 2 fixed to C 2 H 4 produced was 1:2.31. It was concluded that the acetylene reduction assay as performed provided at least a moderately accurate measure of N 2 fixation in pasture turfs.