Evaluation of Phosphorus Nutrient Status in Seedling Lettuce1

Lettuce seedlings were grown in a modified Hoagland’s solution, with 9 treatments ranging from 0.06 to 16.0 mM/liter of H 2 PO 4 . In the low P solutions the deficiency symptoms shown by lettuce seedlings consisted of leaves showing a darker green and reduced growth. Tissue levels of soluble PO 4 –P in these deficient seedlings dropped to a low of 379 ppm PO 4 –P and a high of 13770 ppm PO 4 –P for plants well supplied with P. The critical level for the evaluation of the P nutrient status of seedling lettuce plants in the conductive, lamina, and root tissue were respectively: 780, 600, 580 ppm soluble PO 4 –P on a dry wt basis.