CRITICAL AUTUMN HARVEST PERIOD FOR ALFALFA IN THE ATLANTIC REGION BASED ON GROWING DEGREE-DAYS

Abstract

Air temperature normals (1951–1980 period) were analyzed for over 200 locations in the Atlantic region to estimate spatial and temporal variations in the critical autumn period during which alfalfa (Medicago sativa L.) should not be harvested to allow plants to reach adequate winter hardiness by accumulating sufficient food reserves in the roots. Data are presented which show that the starting date of the critical harvest period could be estimated from the average date when 450 growing degree-days above 5 °C remain in autumn (F450). F450 compared well with starting dates determined experimentally in 3 yr of field tests at three locations in Ontario. F450 varied from before 10 Aug. in northwestern New Brunswick and parts of Newfoundland to after 4 Sept. in southwestern Nova Scotia. Annual differences in climate cause F450 to vary with a standard deviation of about 5–6 days at a given location. A zonation map describing spatial variation in the rest period was prepared as a general guide for cutting management.Key words: Alfalfa, Medicago sativa L., cutting management, winter survival, climate zonation