Growth and Survival of Young Plant Roots in Dry Soil

Considerable controversy exists about the ability of plant roots to grow into dry soil when part of the root system is in wet soil. Much of the research on this subject was conducted before the development of accurate methods of measuring soil water potentials between −1 and −60 bars. An experiment was conducted to determine growth of corn (Zea mays L.), and tomato (Lycopersicon esculentum Mill) roots from wet soil into soils at various water potentials. Roots grow more rapidly at high (less negative) than at low (more negative) water potentials but some growth occurs at water potentials more negative than - 40 bars. For practical purposes root growth probably stops when soil water potential decreases below −50 to −100 bars, but some root tips may remain alive even in air-dry soil if they are less than 3 to 5 mm from moist layers. These root tips will rapidly elongate if the soil around them again becomes wetted.