Mineral deficiencies in leaves. Illustration of the leaves of a plant, showing the effect of excessive use of fertiliser versus various mineral deficiencies. The growing seedling (at centre right) should have sufficient room in its pot to grow and absorb fertiliser nutrients. At top, a surplus of fertiliser will cause green leaves to curl under. At centre left, nitrogen deficient leaves become pale in colour. Phosphorus deficiency is manifested in curled leaves with purplish undersides (lower left). While a leaf suffering a lack of potassium develops bronze edges (at bottom right).