What are the key techniques for high-yield onion cultivation?
1. Raising strong seedlings. Generally, sowing and seedling raising are best done from late September to mid-October. For the seedling bed, choose loose and fertile sandy loam or new land with convenient drainage and irrigation that has not grown onions or garlic. Before sowing, prepare the soil finely, apply enough base fertilizer, and form flat beds for sowing. Before sowing, soak the seeds in warm water for 24 hours, dry them, mix them with dry crushed soil, and sow evenly. Each mu requires 70-75 grams of seed sown in the seedling bed. After sowing, cover the surface with fine soil, then cover with weeds to prevent rain erosion and direct sunlight. After covering with grass, drench with diluted manure water, and scatter insect-prevention chemicals around the bed. Remove the covering weeds after the seedlings emerge. During the seedling period, drench with diluted decomposed manure water once every 5-6 days. After about 40 days of seedling growth, they can be transplanted.
2. Land selection and fertilization. Onions should not be grown continuously. For the planting site, choose a base where the previous crop was solanaceous fruits, melons and beans, or late-season rice, especially loose and fairly fertile sandy loam or newly reclaimed land.
Before planting, use 25 kg of lime per mu to disinfect the soil, and use 1500-2000 kg of high-quality decomposed farmyard manure as base fertilizer. Form beds for planting, with a bed surface width of 80-100 cm and a bed height of 25-30 cm. The soil layer on the bed surface should be loose, fine, and level.
3. Scientific planting. Generally, plant from mid-November to early December, so that the seedlings grow rapidly before "Great Cold" and are not damaged by freezing.
The planting specifications are: plant spacing 10-12 cm, row spacing 14-16 cm, planting depth 2-3 cm, and about 8000 plants per mu. After planting, water thoroughly to settle the roots and help survival.
4. Timely topdressing. Seven days after transplanting, apply one application of thin human and livestock manure water. After another 7-8 days, apply one application of burnt soil or high-quality farmyard manure to promote rooting and enhance cold resistance.
In the severe cold season, onion seedlings grow relatively slowly, so topdressing can be paused. By late February of the following year, when the bulbs enter the expansion stage, apply 1-2 heavy fertilizer applications, with 10-12 kg of urea plus 5-6 kg of potassium sulfate per mu.
In late March, the bulbs expand rapidly. Apply another 1250 kg of decomposed human manure per mu, and stop fertilizing 25 days before harvest.
5. Reasonable watering. Onions like moisture but are prone to waterlogging. In the early stage, the seedlings are small and the temperature is relatively low, so water demand is relatively small; keeping the bed soil moist is enough.
After spring warms up, the temperature gradually rises, onions grow faster, and the bulbs form in large numbers and enter the expansion stage, so water demand is greater and they need sufficient watering. However, when there is more rain in spring, drain the ditches promptly to prevent water accumulation in the field.
Stop watering 10 days before harvest to facilitate harvest and avoid high water content in the bulbs, which makes them less suitable for storage.
6. Disease control. The diseases that commonly occur in onions are soft rot and stem rot.
(1) Apply decomposed fertilizer to prevent the fertilizer from carrying pathogens. During the growing period, control the amount of nitrogen fertilizer applied, and apply nitrogen, phosphorus, and potassium together. (2) During bulb formation, pay attention to timely drainage to avoid long-term water accumulation. (3) Before disease onset, use the following agents: 72% agricultural streptomycin 4000-fold solution and 405 Fuxing emulsifiable concentrate 8000-fold solution, applied alternately.
7. Timely harvest. When the plant leaves gradually turn yellow and the basal leaves begin to dry up, the onion bulbs have stopped growing and expanding, so they should be harvested promptly. At harvest, cut off the onion seedlings and try not to damage the bulbs, so as to facilitate storage and transportation.