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This article in AJ

  1. Vol. 70 No. 6, p. 999-1004
     
    Received: Jan 9, 1978
    Published: Nov, 1978


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doi:10.2134/agronj1978.00021962007000060027x

Diurnal Changes in Plant Water Potential and Canopy Temperature of Wheat as Affected by Drought1

  1. W. L. Ehrler,
  2. S. B. Idso,
  3. R. D. Jackson and
  4. R. J. Reginato2

Abstract

Abstract

The diurnal courses of plant water potential (ψplant and temperature (canopy-air) (ΔT) were determined for 4 days for a wet soil (six levels of water content, θv, corresponding to values of soil water potential (ψm) of −0.1 to −0.5 bars) as compared with a dry soil (six values of ψm, from −1.6 to −18.0 bars), established by withholding irrigations. In wet soil, ψplant decreased from near zero at predawn to −16 bars from solar noon until 1600 hours, and then returned to near zero shortly after sunset. For this treatment, ΔT increased from an initial negative value (−2 to −9 C, depending on the saturation deficit) to either the least negative or a slightly positive value near 1000 hours, and then it gradually decreased and was negative at 1400 hours in five of the six wet plots.

For dry soil, the ψplant curve reasonably paralleled that for a well watered crop, but was more negative and did not necessarily return to the predawn value after sunset. For dry soil, ΔT increased rapidly after sunrise, peaked near solar noon (rather than at 1000 hours) and decreased only slightly by 1400 hours, and was positive (0.7 to 7.0 C) in all six dry plots.

Because typical diurnal curves for ΔT differed in shape depending on soil water content, canopy temperatures of plants on wet and dry soils differed most near 1400 hours. Thus, it is feasible to use ΔT measured at this time to represent the whole day. Such ΔT measurements can lead to routine monitoring capabilities by remote sensing techniques.

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