Abstract: 【Objective】To reveal the effects of potassium deficiency on the growth and development of Lactuca sativa L..【Methods】The soil-less substrates were used for cultivation,and morphological indexes such as number of leaves,root length,leaf length,leaf width,underground fresh weight,above-ground fresh weight,underground dry weight,above-ground dry weight,leaf area and root-crown ratio were determined under the treatment of no potassium deficiency（CK）,50% potassium deficiency and 100% potassium deficiency.【Results】The effects of different degrees of potassium deficiency on the growth status of lettuce was most obvious on the 28^th day.The lettuce grown with no potassium nutrient solution had the best growth,with the largest number of leaves,leaf length,leaf width,leaf area,root length,weight,and the highest water content. Lactuca sativa L. treated with 100% potassium deficiency nutrient solution had the smallest plant,the smallest number of leaves,the largest leaf length,leaf width,leaf area, root length,weight,and the smallest water content.The plant growth of lettuce that was treated with 50% potassium deficiency nutrient solution was in the middle.【Conclusion】Potassium could promote the growth and development of Lactuca sativa L.,and increased the root length,leaf length,leaf width,leaf area,weight,and lettuce is sensitive to potassium.

Key words: Potassium fertilizer, Lactuca sativa L., Nutrient solution, Substrate cultivation