Abstract
The influence of seasonal variation on nitrogenase (N2-ase) activity of undisturbed soil-plant cores ofPanicum maximum var.trichoglume was measured using the C2H2 reduction assay. The largest N2-ase activity in the field, 14.7 g N ha−1 day−1, occurred in spring when soil moisture was high, soil temperature was low and nitrogenous fertiliser influence was at a minimum. The potential N2-ase activity of the cores, measured under controlled conditions, reached a maximum of 27.2 g N ha−1 day−1 and averaged 26.3 g N ha−1 day−1 over the 14 month sampling period. N2-ase activity was positively correlated (P=0.05) with field soil moisture and negatively correlated with field soil temperature (r=0.59 and −0.78 respectively). Multiple regression showed that 69% of the variation of N2-ase activity in the field was associated with the combined effects of soil moisture and soil temperature. Nitrogen fixing bacteria were isolated from the roots ofP. maximum and based upon morphology, biochemical tests and fluorescent antibody reaction, were found to be closely related toAzospirillum lipoferum.
Published Version
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