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This article in CS

  1. Vol. 27 No. 4, p. 742-745
    Received: Aug 18, 1986

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Effects of High Temperatures and Starter Nitrogen on the Growth and Nodulation of Soybean1

  1. A. K. La Favre and
  2. A. R. J. Eaglesham2



Until recently it was believed that soil temperatures in excess of 30°C are likely to inhibit the establishment of root nodules on soybean [Glycine max (L.) Merr.]; however, using diurnally cycling thermoperiods rather than constant-temperature techniques, we previously found that a root temperature of 45°C is required to suppress soybean nodulation. Considering that the level of soil N also affects growth and nodulation, in this work we examine the effects of daily maxima of 30 to 45°C in combination with different levels of N (KNO3) applied at planting, using sand-cultured ‘Wilkin’. Plant growth, on combined N or symbioticaily fixed N, was severely inhibited by temperature maxima >41°C, but was improved by 36°C maximum for 9 h daily. With 21-day-old plants, maxima >6° adversely affected nodulation only in the presence of combined N, and after depletion of N excellent nodulation was obtained. Growth and nodulation at 35 days were less adversely affected by temperature stress when a small (e.g., 90 mg N plant-1) application of N had been made at planting than under N-free conditions. The results show that inhibition of nodulation of soybean by high temperature is exacerbated by: (i) the presence of available N, and (ii) the complete absence of applied N.

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