Onions are native to Central Asia or West Asia, and there are many different varieties, which have been used in food all over the world.
As a vegetable, onion has many functions. For example, in addition to the vitamins and minerals that ordinary vegetables have, it also has the effect of lowering blood pressure and blood fat. Onions contain allicin, which can stimulate gastric acid secretion and increase appetite. At the same time, it can play a certain role in controlling blood lipids and blood pressure. Onions also contain allicin, which also has the antibacterial and anti-inflammatory properties of garlic.
Onions are highly adaptable to temperature. Seeds and bulbs can germinate slowly at 3 to 5 °C, and robust seedlings can withstand low temperatures of -6 to 7 °C. Bulb expansion requires a higher temperature, bulbs can not expand below 15 ℃, 21 ~ 27 ℃ growth is the best. If the temperature is too high, it will grow and decline and go dormant.
Onion has strong adaptability to soil, and it is suitable for fertile, loose, and well-ventilated neutral loam soil. Sandy loam soil is easy to obtain high yield, but clay loam soil has full bulbs, good color and good storage resistance. The onion root system has a weak ability to absorb fertilizer, and sufficient nutrient conditions are required for high yield. Every 1000 kilograms of onion needs to absorb 2 kilograms of nitrogen, 0.8 kilograms of phosphorus and 2.2 kilograms of potassium from the soil. The application of copper, boron, sulfur and other trace elements can significantly increase production.
Onions should supply sufficient water during the germination stage, the seedling growth stage and the bulb expansion stage. However, in the seedling stage and before overwintering, the water should be controlled to prevent the seedlings from growing too long and suffering from freezing damage. Irrigation should be controlled 12 weeks before harvest to enrich bulb tissue, accelerate maturation, and prevent bulb cracking. Onion leaves are drought tolerant and suitable for 60% to 70% humidity. Too high air humidity is prone to disease.
