Evaluation of the Potassium Nutrient Status of Seedling Lettuce by Plant Analysis1

Lettuce seedlings were grown in a modified Hoagland’s solution at concentrations of 0.03 to 8.0 mM/liter of K. In the low K solutions the lettuce seedlings developed K deficiency symptoms which were atypical in that chlorosis followed by random necrotic lesions were the predominant symptoms while the typical symptom of marginal scorch did not develop. Tissue levels of K in 13 day-old deficient seedlings (thinning stage of development) dropped to a low of 0.3% K. The critical level for the evaluation of the K nutrient status in the conductive, lamina, and root tissue were respectively: 2, 1.8 and 1.3% K on a dry wt basis. Seedling lettuce was reduced in yield (weight) when the concentration of K remaining in the culture solution at harvest time was less than 0.01 mMK and they were unable to reduce the concentration of K below 0.001 mMK.