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Water Potential Evaluation of Three Germination Substrates Utilizing Polyethylene Glycol 20,000¹

Numerous problems exist in controlling substrate water potentials for germination investigations. Therefore, an evaluation of three germination substrates was conducted at four water potentials maintained by various concentrations of polyethylene glycol 20,000 (PEG). The substrates were: 1) PEG saturated paper (paper), 2) paper on PEG saturated vermiculite (vermiculite), and 3) paper on foam floating on PEG solution (foam). A water vapor seal was placed on half of the trays prior to placement in a controlled environment. Germination substrate water potentials were measured with a thermocouple psychrometer every 2 days for a 2-week period. Germination substrate water potentials never fully equilibrated with the solution water potentials. Germination substrate water potential in the nonvapor sealed trays decreased 0.8 MPa within a 2-day period while vapor sealed trays showed no appreciable decrease. At the end of the 12-day period substrate water potentials had decreased 0.15 and 1.85 MPa for the vapor sealed and nonsealed trays, respectively. When both vapor-sealed and non-vapor sealed trays were considered, vermiculite and foam substrates exhibited a significantly higher water potential than paper. When only the vapor-sealed trays were considered, the influence of type of germination substrate was reduced, although vermiculite exhibited a higher water potential than the foam. The foam substrate was considered most desirable because of ease of preparation and tendency to avoid accumulation of free-standing solution.

Key Words: Vapor sealed trays • Paper substrate • Vermiculite substrate • Foam substrate

² Graduate research assistant and assistant professor, Range Science Dep., Texas A&M Univ., College Station, TX 77843.

Received for publication June 8, 1981.