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This article in SSSAJ

  1. Vol. 56 No. 5, p. 1500-1504
     
    Received: Apr 7, 1990
    Published: Sept, 1992


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doi:10.2136/sssaj1992.03615995005600050027x

Nitrogen Fixation by Alfalfa with Two Substrate Nitrogen Levels under Sodium Chloride Stress

  1. M. Zhou,
  2. T. C. Tucker,
  3. M. Pessarakli  and
  4. J. A. Cepeda
  1. Contribution from the Dep. of Soil and Water Science, Univ. of Arizona, Tucson, AZ 85721

Abstract

Abstract

Nitrogen fertilizer is rarely applied to alfalfa (Medicago sativa L.) fields because high yields are attained with symbiotic N2 fixation between alfalfa and Rhizobium meliloti. The growth and N2 fixation by one alfalfa cultivar with low salt tolerance (‘Mesa-sirsa 83CL’) and two selections that are salt tolerant at germination (‘Mesa-sirsa Cycle 3’ and ‘Cycle 5’) were investigated at four NaCl salinity levels (0, −0.3, −0.6, and −1.2 MPa added osmotic potentials, OP) in a greenhouse. Automatically recirculated nutrient solution with 5 mg NO3-N L−1 was used during the growth at first cutting and 1 mg NO3-N L−1 was provided for the regrowth of the second cutting. A second N2-fixation study was conducted with two salt levels (0 and −0.6 MPa added OP) and two NO3-N levels (1 and 5 mg L−1). The NaCl salinity resulted in substantial reductions in growth, N2 fixation percentage, and total fixed N2. The effect of salinity was more pronounced for the second cuttings than the first ones. The percentages of total N2 fixed by plants were substantially decreased by increasing NO3-N level in the nutrient solution and the reduction was enhanced as the growth period progressed. The amount of fixed N2, however, did not decrease with increasing NO3-N availability. Fixed N2 was between 86 and 93% for the 1 mg NO3-N L−1 level in the nutrient solution, whereas this value ranged between 50 and 60% for the 5 mg NO3-N L−1 level. The alfalfa cultivar and the selections did not differ in either growth or N2 fixation. The combination of high NO3-N level and salinity, however, significantly decreased the percentage of fixed N2 in the plants.

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