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This article in AJ

  1. Vol. 74 No. 4, p. 667-673
    Received: Oct 8, 1981
    Published: July, 1982



Diurnal Relationship Between Evapotranspiration and Leaf Water Potential of Field-Grown Soybeans

  1. D. C. Reicosky,
  2. T. C. Kaspar and
  3. H. M. Taylor



Research is needed to describe the effect of management practices on plant water stress and water use efficiency. This study investigated the diurnal relationship between evapotranspiration (ET) and leaf water potential (Ψ1) for field grown soybeans [Glycine max (L.) Merr.] as affected by row spacing and irrigation on an Ida silt loam [fine, silty, mixed (calcareous) mesic family of Typic Udorthents]. ET and Ψ1 were determined in detail on 2 days in the 1979 growing cycle, one just preceding canopy closure (11 July) and the second at the midpod fill stage (1 August), Ψ1 was measured by using a pressure chamber technique, and ET was measured by using a portable chamber. On both days, the relationship between Ψ1 and ET was similar for both row-spacing treatments. The nonirrigated treatments, however, demonstrated a slight hysteresis in the Ψ1-ET relationship, whereas the irrigated treatments did not. The ET at a given Ψ1 was much greater on 1 August than on 11 July, probably because of an increase in soil evaporation caused by a recent rainfall and an increase in transpiration due to the increased leaf area index. The Ψ1-ET relationship seemed to be affected more by irrigation than by row spacing. The simplified Ohm's Law analogy does not seem to adequately describe the relationship of plant water flux to resistance and potential difference under field conditions.

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