Cultivation for early winter seeding of spring wheat in central Hokkaido -Relations between seeding date and winter survival

Cultivation for early winter seeding of spring wheat is tested to extend gr owing periods and to make the wheat mature earlier in central Hokkaido, whe re soils are covered by snow but don't freeze in winter. In varietal trials using winter and spring wheat varieties at Naganuma, when the plants emerg ed and grew 1 similar to 2 leaves before continuous snow covering, two wint er wheat varieties could survive 61.0 similar to 100% of seeding plants unt il spring, and three spring wheat varieties showed a large annual variation (0.4 similar to 54.9%) for their winter survivals. On the other hand, when the emergence did not occur before continuous snow covering, all five vari eties survived at a relatively high rate (36.1 similar to 81.4%). In seedin g date trials using spring wheat cv. "Haruyutaka" at 3 locations (Naganuma, Shibetsu, and Pippu), the mean values for accumulated soil temperature and accumulated air temperature from seeding to emergence in early winter seed ing was 140 degrees C and 115 degrees C, respectively. On a basis of the pa st climate trend at some points in central Hokkaido, we considered that an earliest limit of a seeding date for early winter seeding of spring wheat i f plants were to survive safely in winter was about 20 similar to 25 days b efore the average date of continuous snow covering.