Explanation:

Zinc is an essential micronutrient. Zinc deficiency causes Khaira disease in rice grown in the calcareous soil of north India. 
The important symptoms of Khaira disease are-
(1) Discoloration of lower leaves (brown streaks and blotches) occurring two weeks after transplanting. 
(2) The midrib at the base of growing leaves is sometimes chlorotic. 
(3) Plants are stunted, and roots are scanty. 
(4) The disorder becomes apparent after several years of rice cropping the following reclamation. 
(5) The symptoms became more severe when bright sunny days prevail. 
(6) The affected plants show some recovery six weeks after transplanting.