What is khaira disease and why it occurs?

It is the disease which usually occurs in rice due to zinc deficiency at the nursery stage. The tip of the zinc deficient leaves first become yellow and then dry and plant remained stunted. It can be identified by the appearance of rust coloured or brownish red coloration on the surface of the outer leaves. It can be managed by spraying of @ 5 kg zinc sulphate at nursery stage or foliar spray of 0.5 percent Zinc sulphate in early stage of crop.