Deficiency symptoms on lower leaves are due to

Deficiency symptoms on lower leaves are due to deficiency of phosphate i.e. P₂O₅.
P₂O₅ is triple superphosphate, a concentrated form of superphosphate and it contains 46% of P₂O₅.
The deficiency of phosphorus tends to inhibit or prevent shoot growth. Leaves turn dark, dull, blue-green and may become pale in severe deficiency. At first, the old leaves from the lower parts are affected but they may be translocated to the younger leaves also.