What is the reason behind the yellow colour of paddy crop?

Question

turning of the colour of the paddy leaf into yellow

Answer 1

if u r talkin of the normal ripening prcess, i wud answer it in the form of increase in concentration of carotenoids and xantophylls bcoz of the senescing promoting action of ethylene, aba etc. but if ur askin for immature yellowing, its a sign of drought, either natural or physiological, which may be due to some pathogen which is obstructing its xylem system or taking all the water from it.salinity of the soil may b another reason.sometimes, due to overuse of urea too, u cn see symptoms like that.