During the vegetative growth period, the stem of onion becomes shorter, forming an oblate conical stem disk. The lower part of the stem disk is the heel of the stem disk, and the upper part of the stem disk is surrounded by cylindrical leaf sheaths and branches and buds, and fibrous roots grow below. The heel tissue of mature bulb shrinks and hardens, which can prevent water from entering the bulb. Therefore, the heel can control the premature growth of roots or the premature germination of bulbs. In the reproductive growth period, plants are affected by low temperature and long sunshine, and the growth cone begins to differentiate into flower buds, which are tubular and hollow, with wax powder and inflorescences at the top, and can blossom and bear fruit. Due to the degradation of flowering period, onion bulbs form aerial bulbs in buds.
The leaves of onion are composed of leaf body and leaf sheath, forming pseudostems and bulbs. The leaves are dark green, cylindrical and hollow, and there is a concave groove in the abdomen (this is one of the morphological signs that distinguish them from green onions at seedling stage). The tubular leaves of onion grow vertically, with small leaf area and thick wax powder on the surface, which is an ecological feature of drought resistance.
Scape is stout, as high as 1m, hollow and cylindrical, expanding below the middle, tapering upward, and the lower part is covered by leaf sheath; Involucre 2-3-lobed; Umbellies are spherical with many dense flowers; Pedicel is about 2.5 cm long. Pollen white; Tepals with green midvein, oblong-ovoid, 4-5 mm long and 2 mm wide; Filaments are the same length, slightly longer than perianth segments, and combine at the base of 1/5. 1/2 is attached to the lower part of the joint, the base of the inner filament is extremely expanded, and there are 1 teeth on both sides of the expanded part, and the outer wheel is conical; [1] Ovary: nearly spherical, with curtain at the base of abdominal seam; The style is about 4mm long. Flowering and fruiting period may-July.
growing environment
(1) temperature
Onions are very adaptable to temperature. Seeds and bulbs can germinate slowly at 3 ~ 5℃ and start to germinate at 65438 02℃. The suitable temperature for seedling raising is 12 ~ 20℃, the leaf is 18 ~ 20℃, and the bulb is 20 ~ 26℃. Strong seedlings can tolerate the low temperature of ~ 6 ~ 7℃. Bulbs need higher temperature to expand, and bulbs can't expand below 15℃. The optimum growth temperature is 2 1 ~ 27℃. If the temperature is too high, it will grow and decline and enter dormancy.
(2) Lighting
Onion is a long-day crop, which needs more than 14 hours of long-day sunshine during bulb expansion and bolting flowering. Under the condition of high temperature and short sunshine, only leaves grow and onions cannot form. The suitable light intensity of onion is 20000 ~ 40000 lux.
(3) Moisture
Onion should get sufficient water supply during germination, seedling growth and bulb expansion. However, water should be controlled at seedling stage and before overwintering to prevent seedlings from growing white and suffering from freezing injury. Irrigation should be controlled before harvest 12 weeks to enrich bulb tissue, accelerate maturity and prevent bulb cracking. Onion leaves are drought-tolerant, suitable for 60% ~ 70% humidity, and diseases are easy to occur if the air humidity is too high.
(4) Soil and nutrition
Onion has strong adaptability to soil and is suitable for using fertile, loose and well-ventilated neutral loam. Sandy loam is easy to obtain high yield, while clayey loam has full bulbs, good color and storage resistance. The root system of onion has a weak ability to absorb fertilizer, so it needs sufficient nutritional conditions to achieve high yield. Every1000kg onion needs to absorb 2kg nitrogen, 0.8kg phosphorus and 2.2kg potassium from the soil. The application of trace elements such as copper, boron and sulfur can significantly increase the yield.