Abstract:

The climate in the north of Xinjiang Province is cold and extreme snowfall often occurs in winter that contributes to alfalfa cold injury and freezing injury with a decline in alfalfa stand production and consequent reduction in animal production potential. This study explored the variation in cold resistance， overwintering survival rate and hay yield of alfalfa （Medicago sativa） varieties with different fall-dormancy scores and with different snow-cover-thickness treatments in Northern Xinjiang. Alfalfa varieties tested were： AC Caribou （Dormancy score 1）， Concept （Dormancy score 3）， Magnum 551 （Dormancy score 5）， Sardi 7 （Dormancy score 7）， and WL656HQ （Dormancy score 9） and the experiment included snow cover thickness treatments of 0， 10， and 15 cm， achieved using plastic frames and addition or removal of snow to control snow depth on the experiment plots. Data collected included daily soil temperature in the root cap and in the surface layer （1-10 cm）， average water content in the surface layer （0-15 cm）， plant physiological indexes of cold resistance in the root and neck and overwintering survival rate of alfalfa plants. It was found that winter snow helped to maintain the temperature balance of the soil layer around the cap and neck of root of alfalfa， and the overwintering survival rates of alfalfa varieties with high fall dormancy were significantly increased under snow cover （P<0.05）. Compared with no snow covering， malondialdehyde content of alfalfa decreased， while soluble protein， water soluble carbohydrate content and hay yield increased with snow covering. Principal component analysis indicated that under 15 cm snow cover， Magnum 551 with fall-dormancy score 5 had excellent overall score for overwintering survival rate， cold resistance index and hay yield. Hence this variety is recommended as suitable for cultivation in northern Xinjiang.

Key words: alfalfa, fall dormancy, snow cover thickness, winter survival rate, cold-resistance index