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Root Water Uptake and Soil Water Distribution: Test of an Availability Concept¹

ABSTRACT

An experimental test was made of the hypothesis that the fractional water uptake by the root system from a soil layer is proportional to the root density and to the difference between the water potential in that layer and the mean leaf water potential. This theory adequately explained the water uptake by a cotton root system that was divided over a wet and a dry soil compartment. It was also established that the absolute rate of water uptake from each compartment could be accurately calculated from the measured potential difference between soil and plant leaf, and from a separately measured plant hydraulic resistance, which was shown to have a value of 0.67 x 10⁹ s, independent of transpiration rate.

¹ Contribution from the Texas Agric. Exp. Stn., Texas A&M Univ., College Station, TX 77843.

² Research Associate and Professor, respectively, Dep. of Soil and Crop Sciences, Texas Agric. Exp. Stn.

Received for publication May 16, 1983. Accepted for publication October 11, 1983.