Controlling soil water matric potential in root disease studies

Abstract

Soil contained in 5.6 × 2.0 × 10.5 cm Plexiglas soil containers was separated from solutions of polyethylene glycol (PEG) 6000 by a Pellicon ultrafiltration membrane glued over the inside of 3.8-cm-diameter holes in two sides. Flow rate through the membrane was 4.4 ml day−1 cm−2 for a 1.0-bar potential difference across the membrane. At the end of 2 weeks, the average matric potential in the soil adjacent to the membranes for soil cells immersed in −0.2-, −1.0-, and −2.0-bar PEG solutions was −0.3, −1.1, and −2.3 bars respectively. The relatively constant potential and vigorous plant growth during the period indicated that sufficient water was passing through the membrane to meet the plant's water requirements. The Pellicon membrane's tolerance to microbial deterioration will permit the use of this technique in longer term studies than previously has been possible.