Summary
A quantitative estimate is made of the amount of nitrogen symbiotically fixed by a legume crop growing under normal field conditions. The method involves simultaneous determinations of the “AN” values by the legume and a non-nodulating crop, using15N-labelled nitrogen fertilizer. The fertilizer is applied at a low rate to the legume crop to avoid interference with the symbiotic N fixation process, but at a normal rate to the non-nodulating crop.
The amount of symbiotically fixed nitrogen expressed in kg N/ha is calculated by multiplying the difference in A value between the legume and the non-nodulating crop with the % utilization of fertilizer N by the legume crop.
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Fried, M., Broeshart, H. An independent measurement of the amount of nitrogen fixed by a legume crop. Plant Soil 43, 707–711 (1975). https://doi.org/10.1007/BF01928534
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DOI: https://doi.org/10.1007/BF01928534