Detailed Explanation of Key Points for Spring Management Techniques of Onions

I. Watering: Onions are generally not watered during the overwintering period, and there are no pests or diseases. In March to April, water lightly once with green-returning water; when entering the vigorous leaf growth period, appropriately increase irrigation; about 10 days before bulb expansion, carry out seedling control to suppress leaf growth; when there are 6 functional leaves, water thoroughly once, then control seedlings for 10 days to prevent excessive plant growth from affecting bulb expansion. After seedling control, the bulb begins to expand, which is the key period for topdressing and watering. However, because the temperature rises during this period, evaporation and plant growth are large, and it is the period with the highest water demand, watering should be frequent, often keeping the field moist, and irrigation should preferably be done in the morning and evening. If premature bolting is found, the entire flower stalk should be removed immediately, and bulbs can still form. Reduce watering frequency before maturity, and stop watering 1 week before harvest.

II. Topdressing: When onions enter the vigorous leaf growth period, from green return to before bulb expansion, the fertilizer requirement is the highest. Apply 1 to 2 heavy topdressings, with 15 kg of urea and 5 to 7 kg of potassium sulfate per mu; appropriately increasing phosphate and potassium fertilizer is beneficial to bulb development. When small bulbs grow to 2 cm, apply about 15 kg of ternary compound fertilizer per mu, and supplement fertilizer appropriately during the peak bulb expansion period, applying 15 to 20 kg of urea per mu, with an interval of 10 to 15 days between the two fertilizations.

III. Timely prevention and control of pests and diseases: The main pests and diseases harming onions are gray mold and leafminer, and attention should be paid to applying the right remedy.

IV. Harvest: The harvest period is when onion bulbs are enlarged, most plants have lodged, the lower 1 to 2 leaves are yellow, and the tips of the 3rd to 4th leaves have turned yellow. Harvesting should be done on a sunny day, and after harvest, dry in place for 3 to 5 days. When drying, dry only the leaves and not the heads (the leaves of the back row can be used to cover the bulbs of the front row); after drying, it can promote bulb after-ripening and dry the epidermis, which is beneficial for storage.