Abstract: In order to determine the suitable autumn sowing time and varieties of alfalfa (Medicago sativa) in the cold area of North China,four alfalfa varieties were selected to study their growth characteristics and cold resistance physiological characteristics at different temperatures (-5℃,-10℃) and different growth times after sowing (45,60 and 75 d). The results showed that the root weight and root volume of "Longmu 801" were significantly higher than those of other alfalfa varieties (P<0.05). Under low temperature,the content of free proline and soluble sugar of "Longmu 801" and "WL343" was increased significantly,which was higher than that of other alfalfa varieties. In conclusion,the main root diameter,root weight and root volume of alfalfa were positively correlated with the survival rate. When was simulated wintering at -10℃,the contents of soluble sugar and free proline increased,and the comprehensive cold resistance of "Longmu 801" was the best. Under simulated wintering conditions of-5℃ and-10℃,the survival rates of four alfalfa varieties were very low when they grew 45 days after sowing;The survival rate of "Longmu 801" is only higher than 50% at 60 days and higher than 55% at -5℃ and -10℃at 75 days. Therefore,it is the safest for autumn sowing alfalfa in Northwest China to ensure the growth time of at least 75 days before winter. For some cold resistant varieties such as "Longmu 801",the autumn sowing time can be postponed appropriately,but it should also be sown 60 days before winter.

Key words: Alfalfa, Varieties, Autumn sowing, Sowing time, Overwintering

摘要： 为确定北方寒冷地区紫花苜蓿（Medicago sativa L.）适宜的秋播时间及适种品种，本研究选取4个紫花苜蓿品种，通过对其在不同温度（-5℃，-10℃）及播种后不同生长时间（45，60和75 d）下的生长特性及抗寒生理特性进行研究。结果表明："龙牧801"的根重、根体积显著高于其它紫花苜蓿品种（P<0.05）。低温条件下，"龙牧801"与"WL343"的游离脯氨酸与可溶性糖含量明显高于其它紫花苜蓿品种。紫花苜蓿的主根直径、根重和根体积与成活率均呈极显著正相关。在模拟-10℃越冬时，"龙牧801"的抗寒综合表现最佳。在模拟-5℃和-10℃越冬条件下，4个紫花苜蓿品种在播种后生长45 d，60 d时成活率均极低；在生长75 d时在-5℃和-10℃条件下的成活率均高于55%。因此，西北地区秋播紫花苜蓿在入冬前至少保证75 d的生长时间越冬最为安全，对于某些抗寒品种如"龙牧801"可适当推迟秋播时间，但也应在入冬前60 d之前播种。

关键词: 紫花苜蓿, 品种, 秋播, 播种时期, 越冬