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[Objective] This study explored the effects of alfalfa soil extract on physiological characteristics and tuber yield of continuous cropping potatoes to provide basis for alleviation of continuous cropping obstacles and improvement of tuber yield. [Method] The Qingshu 9 potato and soil from 5-year continuous potato cropping field were selected for potting experiment. Soil extracts were collected after mixing 0, 20, 40, 60, 80 and 100 g of clear water alfalfa with 0-20 cm root zone soil from 3 years continuous cropping field with 1 L of distilled water to irrigate potted potatoes. The effects of different mass concentrations of alfalfa soil extracts on plant growth, whole plant dry matter quality, root morphology, enzyme activity, osmotic adjustment substance content and yield were then studied. [Result] During the starch accumulation period, plant height, stem diameter and dry matter quality of potato treated with 60 g/L were increased by 14.0%, 33.3% and 32.3% compared with CK. Total root length, root surface area, root volume, root diameter, root tip number and root vitality were significantly increased. The SOD activity of leaves was significantly enhanced, while contents of MDA and Pro were significantly reduced. Alfalfa soil extract treatments also increased yield of potatoes, with the largest increase of 39.4% in T3. Correlation analysis showed that potato yield per plant had extremely positive correlation with dry matter quality of whole plant. [Conclusion] Alfalfa soil extract effectively improved the growth of continuous cropping potatoes and increased potato yield. The treatment with 60 g/L alfalfa soil extract was the best. [ABSTRACT FROM AUTHOR]