Disease management
Soil: Onions can be grown on all types of soil such as
sandy loam, silt loam and heavy clay soils. However, deep friable, highly
fertile sandy loam to clay soil rich in humus is considered as ideal. Sandy
soil needs frequent irrigation and favours early maturity. Whereas heavy
soils restrict the development of bulbs and the crop matures late as
compared to light soils. A pH range between 5.8-6.5 is considered as
optimum. Good drainage is essential as water-logging results in total
failure of the crop.
Climate:
The
onion is cool season crop, tolerant to frost in the young stage but less
sensitive to heat. It is well adapted to a temperature range of 13-25
oC. A temperature range of 15-21 oC before bulbing is required for its good
vegetative growth whereas a temperature of 20-25 oC is considered ideal for
bulb development. Very low temperatures in the beginning favours
physiological disorder called bolting. Sudden rise in temperature favours
early maturity of the crop in rabi and results in small size of bulbs. At
least 10 hours light with favorable temperature is essential for growth,
development and bulbing. Onion thrives well in places, which receive an
average rainfall of 750-1000 mm during monsoon.