Nitrogenase activity was determined in situ by repeated assays at regular intervals to compare the patterns of diurnal variations occurring in a rice field, a grassland, and a peanut field. In the rice field only one peak occurred (mid-day), whereas the other systems exhibited typical two-peak patterns, which were suspected to be induced by climatic conditions or possibly by a specific rhythm of exudation. Observed data on diurnal variations in nitrogenase activity were fitted to different models of diurnal variation comprised of computed periodic curves.
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