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This article in AJ

  1. Vol. 80 No. 5, p. 789-793
    Received: Oct 8, 1987

    * Corresponding author(s):
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Decreased Rates of Nitrate Uptake During Pod Fill by Cowpea, Green Gram, and Soybean

  1. John Imsande  and
  2. D. G. Edwards
  1. D ep. of Genetics, Iowa State Univ., Ames, IA 50011
    D ep. of Agriculture, Univ. of Queensland, St. Lucia, Queensland, Australia 4067



Grain legumes derive their seed-N from soil-N uptake, remobilization of plant-N, and N2 fixation. To establish the profile of nitrate uptake and the contribution made by soil-N uptake during pod fill, non-nodulated plants were grown in solution culture, and net rates of nitrate-N uptake were measured throughout the plant growth cycle. Green gram [Vigna radiata (L.) Wilzek cv. Berken], cowpea [Vigna unguiculata (L.) Walp. cv. Ife Brown], and soybean [Glycine max (L.) Merr. cvs. Bragg and Harosoy] were utilized in these studies. At physiological maturity, plants were harvested and dry weight and N content were measured. For the determinate legumes, green gram and Bragg soybean, seeds represented approximately 25% of the total plant dry weight and contained approximately 45% of the total plant-N. For the indeterminate cowpea and Harosoy soybean, seeds accounted for approximately 35 to 40% of the total plant dry matter and contained approximately 50 and 70%, respectively, of the total plant-N. The fraction of nitrate-N taken up after the onset of pod fill ranged from approximately 20% for the determinate to 30% for the indeterminate cultivars. Thus, it can be calculated that a maximum of approximately 50% of the total seed-N for each of the four cultivars was derived directly from nitrate-N uptake during pod fill, and the remaining 50% came from mobilization of N in vegetative tissue.

Contribution from the Dep. of Agriculture, Univ. of Queensland, and the Iowa Agric. and Home Econ. Exp. Stn., Ames. Project no. 2619. Research supported in part by a grant to the senior author from the Iowa State Biotechnology Council.

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