苜蓿即使单播,也会因多次刈割、土壤害虫损伤根系、收割机的轮压及其它因素的影响而缺苗.据调查,在根沙尔斯克流域,单播苜蓿生长到第一年底缺苗率为24.1%,混播的因密度不同缺苗率为25.2—41.0%;苜蓿生长到第二年和第三年,其密度为每公顷58万和47万株.这样,在晚秋和早春季节,苜蓿田内便有相当大的面积为野草丛生. Alfalfa, even unicast, will also lack seedlings due to multiple mowing, root damage by soil pests, wheel pressure on harvesters and other factors.According to the survey, in the Gansu Karst Valley, unicast alfalfa grows to the end of the first year The lack of seedling rate was 24.1%, mixed planting density due to the different lack of seedling rate of 25.2-41.0%; alfalfa growth to the second and third years, the density of 580,000 per hectare and 470000. Thus, in late autumn and early spring Season, alfalfa fields there is a considerable area of ​​weeds.