Degree Type


Date of Award


Degree Name

Doctor of Philosophy




Three experiments were performed to evaluate the role of soil temperature in the rate of soybean (Glycine max (L.) Merr.) root extension;In the first experiment, a water bath system was designed to provide accurate root-zone temperature control and serial observation of taproot and lateral root development to a depth of 120 cm. The system consisted of a 137.2 x 100.3 x 121.9 cm deep constant temperature water bath, twelve 2.5 x 30.5 x 121.9 cm immersed acrylic plastic growth containers, movable lighting, and a derrick for removing the growth containers. The acrylic contaners were lifted from the bath in tiers of three, and data recorded with photographs;In the second experiment, Beeson, Hawkeye 63, Wayne, and Harosoy 63 soybean cultivars were grown at root-zone temperatures of 17(DEGREES)C, 21(DEGREES)C, 25(DEGREES)C, and 29(DEGREES)C to evaluate the effect of temperature on the development of the taproot and lateral roots. Temperature treatments were imposed upon the soybean cultivars with the constant temperature water bath system. The constant temperature bath was located in a temperature modified greenhouse. Serial measurements of taproot and lateral root location and frequency of primary nodes by depth were recorded on alternate days until 19 days after emergence. The rate of taproot extension increased with temperature, decreased with time and averaged over time was greater for the Beeson and Hawkeye 63 cultivars than for the Wayne and Harosoy 63 cultivars. The rate of lateral root extension increased with temperature, generally increased with time, and averaged over time was greater for the Beeson and Hawkeye 63 cultivars than the Wayne and Harosoy 63 cultivars at temperature treatments greater than 17(DEGREES)C. The frequency of primary nodes varied with depth, time and cultivar. The Beeson and Hawkeye 63 cultivars had fewer primary nodes than the Wayne and Harosoy 63 cultivars;In the third experiment, a two-dimensional soybean root growth stimulation model was developed for the root growth data. The major inputs were equations describing taproot and lateral root extension, primary node development, and the rooting angle as a function of time and temperature. The model predicts the extension of the taproot and 10 primary lateral roots. The rooting depths predicted by the model agree well with greenhouse and field experimental data.



Digital Repository @ Iowa State University,

Copyright Owner

James Allen Stone



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296 pages