In plants, the common symptom caused by the deficiency of K, P, Ca and Mg is the

In plants, the common symptom caused by the deficiency of K, P, Ca and Mg is the appearance of necrotic areas in the leaves.
Necrosis is the death of a circumscribed area of plant or animal tissue as a result of disease or injury. Necrosis is a form of premature tissue death, as opposed to the spontaneous natural death or wearing out of tissue, which is known as necrobiosis.
Deficiencies of the nutrients nitrogen, phosphorus, potassium, and magnesium result in chlorosis (yellowing) and eventual necrosis (death) of older mature leaves.