First, the choice of onion planting varieties
When selecting varieties, we must choose varieties suitable for local light conditions, and most of the northern regions cultivate long-day varieties; However, most varieties cultivated in autumn and winter in southern China are short-day varieties. This requires us to introduce from areas close to our own latitudes, rather than from areas with very different latitudes.
Onion varieties can be divided into yellow onion, white onion and red onion according to the color of skin. Different varieties have different characteristics, so onion farmers must choose onion varieties according to local consumption habits and climate characteristics.
Second, management during onion sowing and seedling raising
1, sowing time
Whether the sowing date is suitable or not has a great influence on the yield and quality of onion. The lowest temperature in winter in Northeast China is below -20℃, which is usually planted in late summer and early autumn, and transplanted and planted in the next spring. Autumn sowing and transplanting before winter are mostly used in central and southern North China, East China and Central China. Sowing is generally carried out in late autumn in South China. Let's take East China and Central China as examples to see the cultivation techniques of onions.
2. Soil preparation and fertilization before sowing
Choose a field with fertile soil, convenient irrigation and far away from industrial waste, and apply base fertilizer appropriately about one week before sowing in the seedbed, and the amount of base fertilizer should not be too much to prevent the seedlings from growing too fast. Apply about 2000㎏ of organic fertilizer and 40㎏ of calcium superphosphate to each mu of seedbed, spread it out, and then carry out deep ploughing, the ploughing depth should be greater than 20. After ploughing, make a border, the width of which is about 1 m, and the distance between two ridges.
Step 3: sow.
The sowing amount of onion has a certain relationship with seed germination rate, planting area and number of plants per unit area. In actual planting, the eliminated part should be considered, and the seed quantity should be increased by 20%. Generally, the sowing amount per mu should be controlled at about 5㎏, and sowing can be done. After sowing, the seed surface should be covered with fine sand, and the covering thickness is about 2㎝. Build a small arch shed after sowing to keep the temperature of onion nursery.
4. Seedling management
After sowing onions and before the seedlings are unearthed, the following management work should be done:
Temperature management: after sowing, keep it at 20℃~25℃ during the day and 65438 03℃ at night; When all the onion seedlings sprout, the temperature should be properly lowered to prevent the seedlings from overgrowth, and kept at 15℃~20℃ during the day and 10℃ at night. When the onion grows above 15㎝, the small arch shed can be removed to make the seedlings adapt to the natural temperature change. Water and fertilizer management: Water management at seedling stage is extremely important, and soil moisture should be kept at about 60%. When the seedbed is found to be dry, it should be watered immediately to prevent soil hardening from affecting seed germination and emergence; Fertilization at seedling stage is the key to cultivate strong seedlings, and the application of farmyard manure supplemented with other inorganic fertilizers can basically meet the growth needs of seedlings. Weeding and thinning: When the seedlings grow 2-3 true leaves, weeding and thinning should be done in time. Interplanting should follow the principle of removing the weak and retaining the strong, removing the small and retaining the big, so as to ensure the uniformity of the seedlings and prevent the slow growth caused by the dense seedlings. Third, onion colonization
It is very important to apply base fertilizer before planting. The type and amount of fertilization have great influence on onion growth and bulb size. Here, I introduce some knowledge about onion growth to my onion farmers.
1, bolting characteristics of onion
The onion bulb has the characteristics of bolting early after expansion, which not only reduces the onion yield, but also seriously affects the onion quality. There are two factors in early bolting of onion: one is that it needs a certain low temperature, which is the leading factor to induce flower bud differentiation of onion. Most varieties can complete vernalization and start bolting and flowering after 40~70 days at the low temperature of 2~5℃. The second factor is the size of onion seedlings. If the thickness of onion leaf sheath is more than 0.6㎝, vernalization bolting and flowering can be completed in about 40 days.
From the above two factors, we can see that in North China, Central China and Northeast China, onions must not grow too vigorously before freezing in winter if they want to get full bulbs and achieve high yield.
2. Fertilization and soil preparation before planting
In East and Central China, it can be transplanted and planted in late autumn and early winter. Never apply too much fertilizer before planting, let alone nitrogen fertilizer, in case onions grow too vigorously before freezing in winter. In addition, in order to adapt to the characteristics of onion fibrous roots, the base fertilizer used must be fully decomposed, and manure decomposition, shallow application and uniform application are the technical points of using base fertilizer. Because onion is a shallow root crop, the root system is mainly concentrated in the soil layer with a depth of 20-30 ㎝. Therefore, when fertilizing and preparing soil, the soil should be turned deep, and the depth is generally about 50㎝, so as to ensure that the root system is easy to grow.
3. Ridge the ridge to make the bed
After the land is leveled, ridging can be carried out. The width of the boundary field is slightly larger. Generally speaking, the width of each border field is about 1.5 m, the ridge height is about 20 cm and the ridge width is about 25 cm.
4. Water and plastic film mulching
The day before planting, water 1 time in the field to ensure that the seedlings have enough water after planting. After underwater infiltration, spray herbicide 1 time, and then cover with plastic film. The plastic film on both sides of the border field should be tightened and compacted to ensure that the plastic film mulching can maintain the temperature and humidity of the soil.
Step 5 raise seedlings
In late autumn and early winter in East China and Central China, when the onion seedlings grow to 3-4 leaves, they can be transplanted and planted. When picking up seedlings, it is required to pick up seedlings with a shovel or shovel, and classify the picked seedlings according to large, medium and small. The standard of medium-sized seedlings is to have 3-4 true leaves, the plant height is about 30㎝, the leaf sheath diameter is 6-7 ㎜, and the weight of a single plant is 4-6 grams, and then plant them separately to facilitate future management.
Step 6 plant
Onion is suitable for close planting because its plants are upright and its leaves are less shaded. Generally speaking, the row spacing of onion planting is 15~ 18㎝, and the plant spacing is 10~ 13㎝, and about 30,000 plants are planted per mu. The planting depth shall be based on burying small bulbs and not dropping seedlings after watering.
The slow seedling stage of onion is 15 days after planting. After the slow seedling stage, it is clear which seedlings are thriving and which seedlings are not alive. At this time, weak and dead seedlings can be replaced by strong seedlings by replanting.
After the slow seedling stage, the weather in northern China is getting colder. From this period until it turns green in spring, the growth of onion is relatively slow, mainly accumulating nutrients to supply the growth of root system. Therefore, this period is also called squatting seedling period by onion farmers. Before the soil freezes in winter, you must water it once. After watering the frozen water, there is no need for other management.
Winter goes to spring, and with the recovery of spring, onions quickly enter the rapid growth period. They began to grow roots and leaves one after another, and the absorption capacity of plants increased. During this period, fertilizer and water management should keep up in time.
Fourth, the management of onion vegetative growth period
After the arrival of spring, onions have entered a rapid growth period.
Water management: Generally speaking, only when the soil temperature at the depth of 10㎝ is stable above 10℃ can green water be watered. Starting from watering green water, according to the climate and soil quality, it needs to be watered 1 time every 6~9 days. Fertilizer management: after the onion turns green, the plant enters the vigorous growth period of leaves. During this period, some nitrogen fertilizer can promote the growth of leaves, and urea 15~25㎏ and potassium sulfate 15~20㎏ can be applied per mu. Five, onion bulb expansion period management
The period from leaf sheath expansion to harvest is called onion bulb expansion period. With the increase of temperature and sunshine hours, the nutrients accumulated by onion began to be transported to the leaf sheath, which expanded to form bulbs.
1, water management in bulb expansion period
The water demand during bulb expansion period is gradually increasing, and timely watering according to climate and soil conditions is still the focus of management. During this period, water of 1 time should be poured every 5-7 days to keep the water content of the soil between 60% and 80%.
2. Top dressing at bulb expansion stage
Apply 5 ~10 potassium sulfate and10 ~15 urea per mu, and water them in time after fertilization to promote the absorption of nutrients by onions. It is wrong for many onion farmers to use too much nitrogen fertilizer during onion expansion. If nitrogen fertilizer is used too much, onions will be greedy and grow vigorously, which will affect bulb development.
3, pest control
Onion swelling period is also a high incidence period of diseases and insect pests, so we should pay attention to the occurrence of various diseases and insect pests in field management. Once diseases and insect pests occur, we should take the method of combining physical, biological and chemical control in time to ensure the healthy growth of onion seedlings. The common diseases of onion are downy mildew and gray mold, and the pests are mainly the damage of ground maggots.
Downy mildew: mainly harms onion leaves. At first, onion leaves will have oval lesions. The color of these places will become lighter, yellow-green, and gradually turn gray. In the later stage, onion leaves often dry up and die.
When the temperature is between15 and 20℃, downy mildew of onion is in a high incidence period. If downy mildew is found, it can be controlled by spraying agents such as aluminum fosinate, chlorothalonil and propamocarb, every 7~ 10 day 1 time, 2~3 times in a row.
Gray mold: white oval or nearly round spots appear on the leaves when it occurs, which mostly develop downward from the tip of the leaf and gradually connect into pieces, causing the onion leaves to curl and die. Gray mold is easy to spread when the soil humidity is too high in spring, and it can be prevented by spraying carbendazim and thiophanate-methyl.
Ground maggot: general term for fly larvae. Ground maggots that harm onions are the larvae of flies. If there is harm of ground maggots, it can be controlled by root irrigation with 40% phoxim EC 1000 times.
Six, onion harvest
Onion lodging is a sign of bumper harvest. When the leaves gradually turn yellow and begin to lodging, the outermost 1~3 scales of onion bulbs begin to dry and shrink, and can be harvested like a film. Sunny weather should be chosen for harvesting, and the harvesting period of onions varies greatly in different regions, which should be determined according to the growth of onions.
In addition, considering the weather conditions at that time, it is best to have a few sunny days to dry after harvest. When harvesting, hold the onion plant with your hands and gently lift the plant, and the onion will be taken out. Be careful not to hurt the onion when harvesting, otherwise the onion wound infection will cause rot.
Picked onions can't be transported in a hurry, so they must be fully aired. Onion bulbs can only be stacked and stored when they are dry. Generally, it needs to be aired 10 days or so. When they are aired, they must be protected from rain and finally stored or sold.
In recent years, the market demand for onion is increasing. Onion has become a characteristic industry in many places because of its strong adaptability, high yield and storage resistance. If you want to grow onions well, you should learn from experienced onion growers according to the local actual situation, so as to better apply the experience to actual production.