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This article in CS

  1. Vol. 44 No. 2, p. 484-492
     
    Received: July 3, 2004


    * Corresponding author(s): lpurcell@uark.edu
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doi:10.2135/cropsci2004.4840

Soybean N2 Fixation Estimates, Ureide Concentration, and Yield Responses to Drought

  1. Larry C. Purcell *a,
  2. Rachid Serrajb,
  3. Thomas R. Sinclairc and
  4. A. Dea
  1. a Dep. of Crop, Soil, and Environmental Sci., 1366 W. Altheimer Drive, Univ. of Arkansas, Fayetteville, AR 72704
    b International Crops Research Institute for the Semi-Arid Tropics, Patancheru 502 324 Andhra Pradesh, India
    c USDA-ARS, Univ. of Florida, Agronomy Physiology and Genetics Laboratory, IFAS Building no. 350, 2005 SW 23rd Street, P.O. Box 110965, Gainesville, FL 32611-0965

Abstract

Increasing N2 fixation tolerance to drought has been hindered by the labor and costs of quantifying N2 fixation using 15N methodologies. The relative abundance of ureides (RAU) in plant tissues has been used for estimating N2 fixation in soybean [Glycine max (L.) Merr.] grown under well-watered conditions, but it has not been evaluated for drought conditions. The present research evaluated the response of N accumulation to N fertilization, the ability of the RAU technique to predict N2 fixation under drought conditions, and the response of yield to N fertilization under well-watered and drought conditions. Under drought, shoot N accumulation rate during vegetative growth approximately doubled as the amount of N fertilizer was increased from 10 to 200 kg N ha−1, indicating a greater sensitivity of N2 fixation to drought than uptake and assimilation of inorganic N. Under well-watered conditions, the relationship between estimates of N2 fixation made by 15N-dilution and RAU agreed within 15% of published reports. Under drought conditions, however, this relationship was greatly different (13 to 43%) from published reports. Fertilization with inorganic N in 1 yr increased grain yield 15 to 25% for the drought treatment and 12 to 15% for the well-watered treatment. In a second year, N fertilization increased yield of both drought and well-watered treatments approximately 9%. This research indicates that the RAU technique for estimating N2 fixation under drought conditions may be invalid without further refinement, that N2 fixation is more sensitive to drought than the uptake and assimilation of inorganic soil N, and that increasing the tolerance of N2 fixation to drought would likely result in yield increases.

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