Abstract
In monocropped cereal systems, annual N inputs from non-fertilizer sources may be more than 30 kg ha-1. We examined the possibility that these inputs are due to biological N2 fixation (BNF) associated with roots or decomposing residues. Wheat was grown under greenhouse conditions in pots (34 cm long by 10 cm diameter) containing soil from a plot cropped to spring wheat since 1911 without fertilization. The roots and soil were sealed from the atmosphere and exposed to a15N2-enriched atmosphere for three to four weeks during vegetative, reproductive or post-reproductive stages. This technique permitted detection of as little as 1 μg fixed N plant-1 in plant material and 40 μg fixed N plant-1 in soil. No fixation of15N2 occurred during either of the first two labelling periods. In the final labelling period, straw returned to the soil was significantly enriched in15N, especially in a pot with a higher soil moisture content. Total BNF in this pot was 13 μg N plant-1, or about 30 g N ha-1. In a separate experiment with soil from the same plot, we detected BNF only when soil was amended with glucose at a high soil moisture content. Measured associative BNF was insufficient to account for observed N gains under field conditions.
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Lethbridge Research Centre contribution no. 3879488.
Lethbridge Research Centre contribution no. 3879488.
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Bremer, E., Janzen, H.H. & Gilbertson, C. Evidence against associative N2 fixation as a significant N source in long-term wheat plots. Plant Soil 175, 13–19 (1995). https://doi.org/10.1007/BF02413006
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DOI: https://doi.org/10.1007/BF02413006