Latest potential sowing time of galega (Galega orientalis Lam.) for successful cultivation in the extreme winter conditions of northern Japan

Mixed seeded plots of timothy (Phleum pratense L.) and galega (Galega orientalis Lam.) were established in multiple seeding times from 2014 to 2017 to determine the latest sowing limit in the Konsen region, northern Japan, where growing conditions are severe. Although low yields were observed in some cases when the soil freezing depth was deeper than average, the dry matter yield of the first crop of galega in the year after sowing was higher under conditions that ensured pre-overwintering plant length growth of 30 cm or more, as compared with growth of less than 30 cm. Galega rhizomes were observed under conditions of pre-overwintering plant length of 28 cm or more, but not under conditions of less than 28 cm in length. Therefore, achieving 30 cm plant length prior to overwintering is desirable when sowing galega in the Konsen region. Furthermore, the effective cumulative temperature (ECT) required for pre-overwintering galega to reach 30 cm in plant length was 1079°C, for which seeding dates were calculated to be July 10 and June 29 in terms of calendar days, with 80% and 90% probability. In the Konsen region, galega should be sown earlier than in other regions of Hokkaido to ensure the growth rate because of the effects of soil freezing on overwintering performance.