Effects of fall dormancy of alfalfa on seed production at a northern latitude

The agri-climatic adaptation of an alfalfa variety in North America is categorized by its Fall Dormancy Rating (FDR1 = dormant to FDR9 = non-dormant). Presently, only relatively dormant, winter-hardy varieties (FDR1–4) are grown for seed and herbage at the northern latitudes of western Canada. However, there is considerably greater demand for seed of varieties that have FDR ≥ 4. A study was conducted in the Peace River region of north-western Canada to determine the relationship between FDR and seed production of alfalfa with FDR ≥ 4. Trials were established in each of two consecutive years with four varieties representing each of six FDR categories, FDR4–9. Growth characteristics were determined for two successive years of seed crops for each year of establishment. Seed yield (as a percentage of that for FDR4) was 84, 52, 40, 29 and 39% for FDR5 to FDR9, respectively, whereas total biomass at seed maturity was 89,73, 73, 57 and 57% for FDR5 to FDR9, respectively. Seed yield was more sensitive to changes in FDR than total biomass. Short rotations of specific alfalfa varieties with FDR ≥ 4 could be an option for seed growers in the northerly latitudes of western Canada, provided greater financial compensation is given for higher FDR varieties, and provided genetic drift can be retained within acceptable limits.