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This article in AJ

  1. Vol. 63 No. 6, p. 901-904
     
    Received: Mar 18, 1971


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doi:10.2134/agronj1971.00021962006300060024x

Soil Water Suction and Root Temperature Effects on Nitrogen Fixation in Soybeans1

  1. Tsungmin Kuo and
  2. L. Boersma2

Abstract

Abstract

The effect of soil water suction and root temperature on rates of nitrogen fixation, transpiration, and net photosynthesis of soybeans (Glycine max (L.) Merr.) was studied in laboratory experiments. The range of root temperature and soil water suction considered was 15.6 to 37.8 C and 0.30 to 2.50 bars, respectively. With increasing root temperature rates of nitrogen fixation, transpiration and photosynthesis increased slowly at first and then rapidly until an optimum temperature was reached followed by a decrease at higher temperatures. Optimum temperatures were 27, 30, and 27 C for rates of nitrogen fixation, transpiration, and net photosynthesis, respectively. Rates of the three paralneters decreased with increasing soil water suction. The amount of nitrogen fixed per unit of CO2 absorbed was highest at a root temperature of 23.9 C and lowest at 37.8 C. This ratio decreased with increasing soil water suction at all temperatures considered. Changes in transpiration rate resulting from changes in soil temeprature were attributed to temperature effects on viscosity and metabolic activity.

Effects of soil water suction and soil temperature on nitrogen fixation indicated in this study emphasize the complex symbiotic nature of the process. Mechanisms by which the two environmental parameters might affect the rate of fixation were indicated but not clearly elucidated by the results of the experiments.

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