GROWTH RESPONSE OF ALFALFA VARIETIES OF DIVERSE GENETIC ORIGIN TO DIFFERENT ROOT ZONE TEMPERATURES

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Abstract
Twenty alfalfa varieties, representing a broad cross-section of alfalfas from different climatic zones, were grown in a greenhouse at soil temperatures of 5°, 12°, 19°, and 27 °C to determine the effect of root zone temperatures on herbage and root growth. The air temperature varied between 15° and 32 °C. The photoperiod was extended to 16 hours by supplemental lighting. There were marked varietal differences in root development at different soil temperatures. Varieties of Medicago sativa generally yielded more herbage and roots than those of Medicago falcata. However, varieties of M. falcata produced the most herbage per weight of roots. Growth of alfalfa was greatly affected by root zone temperature; the most herbage was produced at 27 °C and the most root and nodular tissue at 12 °C. Soil temperature affected the shape and color of nodular tissue. Nitrogen and phosphorus increased in herbage as the root zone temperature increased, with P increasing more than N. Time to reach the flowering stage was not appreciably affected by root zone temperature.

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