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This article in AJ

  1. Vol. 70 No. 6, p. 1027-1032
    Received: July 30, 1977

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Influence of Percent NO3−/NH4+ on Growth, N Absorption, and Assimilation by Lima Beans in Solution Culture1

  1. William S. McElhannon and
  2. Harry A. Mills2



Application of the appropriate quantity and form of N in proportion to the rate of plant uptake and assimilation could significantly increase the utilization of applied N fertilizers. The objective of this study was to determine the influence of various percentages of NO3 to NH4+ and N concentration on N absorption, assimilation, growth, and yield for lima beans (Phaseolus lunatus L.) when grown in solution culture. Nitrogen was supplied as Ca(NO3)2 and/or (NH4)2SO4 at three N concentrations and five percentages of NO3 to NH4+. Peak absorption periods for NO3 and NH4+ were observed when NH4+ supplied 50% of the N. Two peak absorption periods for NO3 occurred, the first at the initiation of inflorescence and the second during pod filling. Peak periods of NH4+ absorption occurred during initiation of the inflorescence, pod development, and pod filling.

Dry weights of all plant parts were consistently higher when NO3 was 75% or more of the N. Lima bean root morphology was altered at all N concentrations when NH4+ was more than 50% of the N. Plant N content was highly influenced by the form and level of N available for assimilation and may not be an accurate indicator of the N available for pod development.

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