Poinsettia ( Euphorbia pulcherrima Willd. ex Klotz) in nutrient culture developed Mg deficiency symptoms at 0, 1 and 2 ppm Mg in the solution. A high K level caused a depression of leaf Mg concentration and the appearance of deficiency symptoms with 5 ppm Mg in the solution. The Mg concentration of leaves from 3 stem positions reflected changes in Mg supply. The results emphasize the importance of recognizing the K –Mg relationship when interpreting results of soil and foliar nutrient analyses.
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Cox et al. (1980) studied this question.