SOME FACTORS ASSOCIATED WITH INJURY TO ALFALFA DURING THE 1977–78 WINTER AT BEAVERLODGE, ALBERTA

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Abstract
During the 1977–78 winter, many perennial legumes were severely injured in northern Alberta and British Columbia. The winter was characterized by an early killing frost on 1 Sept. 1977. Air temperatures were −28 °C in late November and −43 °C in early December prior to any appreciable ground snow cover. This caused soil temperatures at 5 cm to drop to −19 °C. Field and laboratory experiments are described in which cold hardiness measurements (LT40), etiolated regrowth weight measurements of root food reserves and visual percent stand estimates were determined on various cultivars of Medicago sativa, M. media and M. falcata prior to, during and/or following the 1977–78 winter. Injury was first observed in plants collected from the field following the low soil temperatures in November and December. Fall cutting management studies indicated that alfalfa harvested during August or early September in 1977 suffered the most severe injury the following spring. In June 1978, first-cut yields of these plots were up to 50% lower than the yields from single-cut control plots or plots harvested after mid-September. M. sativa, M. media and M. falcata cultivars left for seed showed little evidence of winter injury. The results suggest that low fall food reserves which resulted from harvesting during August or early September and low soil temperatures in December and January were two primary factors associated with winter injury. M. sativa stands cut twice in 1977 were more severely injured than stands of M. media or M. falcata. Three-year-old stands of M. media were more severely injured than 2-yr-old stands.