Potassium is an important nutrient for transporting sugar, which is necessary for plant health and for converting sugar into starch and oil. In potassium deficiency, the leaves begin to curl inwards and the outer parts turn yellow and become dry. The leaves become green with a blue tint, and as it is illustrated in the image, yellow and brown colors may be observed among the leaf veins. In the advanced levels of deficiency, these dry and yellowing symptoms are replaced by a dark brown color.