THE INFLUENCE OF CULTURAL AND ENVIRONMENTAL FACTORS ON THE TIME OF MATURITY OF BULB ONION CROPS

The extent of year to year and site to site differences in onion bulb maturity date is described and discussed in relation to cultural practices, and the physiological processes that underly these differences. Year to year differences in maturity date correlate closely with differences in accumulated thermal time during the summer months. This is explained by experiments in constant photoperiods which show that bulbs develop more rapidly at higher temperatures.

Cultural practices which establish a large leaf area index early in the season result in early maturity. The larger the leaf area index the larger the decrease in red: far-red ratio in the leaf canopy. Controlled experiments have shown that the lower this ratio the sooner bulb scales initiate and the more rapidly onions bulb and mature. The effect of many cultural practices on bulb maturity date can be understood in terms their influence on leaf canopy development.