Existing unsaturated zone soil water samplers have several deficiencies that jeopardize their utility for field sampling. Suction cups function only when a vacuum is applied, and sample from an unknown volume of soil. Pan samplers sample only saturated flow. A capillary‐wick sampler was developed to overcome these problems and was tested in both the laboratory and field to evaluate its performance. Breakthrough curves for selected inorganic ions and organic chemicals were established in the laboratory. No adsorption/desorption of these chemicals was found for the capillary‐wick sampler made entirely of glass. Banks of eight capillary‐wick samplers were installed in field plots of Padina sand (loamy, siliceous, thermic, Grossarenic Paleustalf), Weswood silt loam (fine‐silty, mixed, thermic Fluventic Ustochrept), and Lufkin clay (fine, montmorillonitic, thermic Vertic Albaqualf) soils. Saturated soil Br breakthrough curves were determined at each location and used to estimate the number of samplers required to characterize the flow of contaminants. To achieve 95% confidence in the chemical data from the three soils and plot sizes tested, 31 samplers were required for the sandy soil, six for the silt loam soil, and only two for the clay soil. The wick‐activated sampler collected soil solution samples from soils having soil water potentials ranging from 0 to −6.0 kPa. The capillary‐wick sampler collected samples continuously across this range of water potentials without the need for a continuous vacuum and is thus an improvement over existing samplers. While the capillary‐wick samplers usually collected sample volumes representative of the flux at potentials of −5 kPa, samples collected at greater and lesser potentials were not representative of the flux.

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Young growth‐chamber‐grown cotton plants were subjected to a series of eight periods of soil water stress, which served as a preconditioning treatment. After preconditioning, water was withheld and changes in the stomatal resistance and leaf water potential were determined and compared with similar well watered control plants. The stomatal response of stress preconditioned plants adjusted such that the diffusion resistance of the lower surface of the leaf did not reach a value greater than 20 s cm−1 until the leaf water potential dropped 14 bars below that required to reach the same resistance on previously unstressed plants. The resistance—leaf water potential relation for the adaxial surface was unaltered by the preconditioning treatment. Adjustment of the osmotic potential of the guard cells on the abaxial surface provides at least a partial explanation of this change in response. The lack of adjustment of stomatal response on the adaxial surface of the leaves was correlated with a lack of adjustment in osmotic potential of guard cells on that surface.

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