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

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Abstract
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 N2 fixed to C2H4 produced was 1:2.31. It was concluded that the acetylene reduction assay as performed provided at least a moderately accurate measure of N2 fixation in pasture turfs.