MEASUREMENT AND CONTROL OF WATER POTENTIAL IN A SOIL-PLANT SYSTEM

Water potential gradients were measured in soil-grown pepper plants. In one test where plants were equilibrated at low water potentials, the root zone water potential agreed well with water potential measurements in the plant stem and plant leaves. On the other hand it was found that the water potential in root-free soil adjacent to the root zone was higher than that in the root zone and that the observed gradient increased with decreasing root zone water potential. This increased gradient was attributed to decreased soil water conductivity in the root-free soil and to increased flow resistance across a millipore membrane separating the root-free soil and the root zone. In another test the total water potential in the root zone was controlled at three different levels by adding polyethylene glycol solution directly to the root zone. In this test the water potentials and water potential gradients responded in a reasonable fashion to the applied osmotic stress indicating that control of water potentials in soilplant systems is possible with polyethylene glycol.