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Effect on Plant Growth of Constricting Forces Applied to the Upper Part of Roots¹

Contraction forces developed by soils as they dry may compress roots and reduce growth. In order to evaluate this effect on growth, plants were placed with their up per roots between two rigidly fixed adjacent plastic tubes that could be inflated against the roots with 0 to 15 bars air pressure. Root and top growth of corn (Zea mays L.), oats (Avena sativa L.), and western wheatgrass (Agropyron smithii Rydb.) decreased gradually as a constricting force on the upper part of the roots was increased from about 4 to 15 bars. At pressures lower than about 4 bars, growth was larger than growth of the plants in loose sand, which applies little if any constricting force on roots. When wet puddled soil was dried around the upper roots of corn or oat seedlings, growth was decreased in some experiments and increased in others possibly because the pressure was larger or smaller, respectively, than 4 bars. The effect that drying of poor soil structure has on compressing roots and reducing plant growth needs to be investigated.

Key Words: Soil structure and plant growth • Soil tilth • Soil desiccation forces

² Professor of plant science (soils), South Dakota State Univ., Brookings, SD 57006.

Received for publication January 24, 1976.