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Water Transfer through Cotton Plants Connecting Soil Regions of Differing Water Potential

USDA-ARS, Dep. of Soil Science, 1991 Upper Buford Cir., Univ. of Minnesota, St. Paul, MN 55108
Dep. of Soil and Crop Sciences, Texas A&M Univ., College Station, TX 77843

^* Corresponding author.

Several studies have shown that water can move through plant root systems from wet to dry soil during periods of low evaporative demand. It has been suggested that such movement could be important in alternate furrow or drip irrigation systems, where water is applied in a discrete or nonuniform manner. This study was undertaken to examine this question, using a physical experiment and computer simulation. A growth chamber experiment was conducted with three rows of cotton (Gossypium hirsutum L.) plants. The outer row plants were grown over vertical barriers such that half of their root systems shared a volume of soil with the center row plants, while the other half was hydraulically isolated in separate soil compartments. The center compartment was allowed to dry, while the outer compartments were watered daily. Soil moisture was measured throughout all compartments twice daily by gamma densitometry. When the potential gradient between center and outer compartments reached 1.0 MPa, the gamma readings showed overnight movement of water from wet to dry soil that could only have taken place through the root systems of the outer row plants. The overnight transfer of water, while significant, was not sufficient to fully supply the daytime transpiration demand of the unirrigated center row plants. It was also less than that predicted by computer simulation, unless the latter reflected the inability of the xylem water potential of cotton plants to equilibrate with soil water potential during periods of low evaporative demand. Regardless, the results suggest that water transfer by root systems should not be excluded in simulations of water movement in the soil-plant-atmosphere system.

Received for publication January 25, 1988.