WINTER HARDINESS OF ALFALFA VARIETIES DEPENDING ON A TEMPERATURE AT THE ROOT COLLAR
An investigation was conducted to study winter hardiness of sickle and changeable alfalfa varieties depending on conditions of overwintering on frozen soils of Yakutia. According to the meteorological analysis during overwintering, the sum of negative temperatures for two periods of the experiment was 5282, on the average. The 5-year average root-collar temperature for the first trial plantation made up –12.4 °C with the ground surface average air temperature of –54.1 °C and snow depth of 36 cm. For the second plantation, these figures were –10.30 °C, –53.60 °C and 42 cm, respectively. It has been found that the root-collar temperature is more dependent on snow depth rather than on a ground surface air temperature. Of the nine alfalfa varieties studied, Yakutskaya Zheltaya and Syulinskaya cultivars showed guaranteed winter hardiness and productivity of green mass and seeds under conditions of Yakutia. Vega and Flora cultivars showed low resistance to overwintering conditions, they died in their first winter. Winter hardiness of Kanskaya, Onokhoiskaya 18, Severnaya Hybrid, Flora 2 and Flora 4 cultivars reduced with each overwintering regardless of air temperature and snow depth.