(2) Soil preparation and fertilization Onion seedling stage is long, and sufficient base fertilizer should be applied. Generally, 32,500-45,000 kg of decomposed organic fertilizer or soil miscellaneous fertilizer is applied per hectare, and the furrow is leveled by shallow raking. When conditions permit, 375 kg of calcium superphosphate can be added. When underground pests are serious, poison valley can be used to control them. Before sowing, soil conditioner should be sprayed without deep ploughing, and 200 grams per 667 square meters should be added with water 100 kg. Spraying on the ground can loosen the soil, which is beneficial to root system development and water storage and prevent drought in winter and spring.
③ The suitable effective growth period of onion seedlings at sowing date is 80-90 days, which can meet the planting standard. When planting winter onions, we should first decide whether to sow in autumn or spring according to the local climate conditions. Generally, autumn sowing is needed in areas with frost-free period below 180 days; Areas with more than 200 days are suitable for spring sowing; In areas where the frost-free period is between 180-200 days, you can sow in spring and autumn. This is because the growth period is insufficient and plants cannot fully develop; However, if the growth period is too long, premature aging will easily occur in the vigorous growth period of leaves, and the goal of high yield cannot be achieved. The vast areas in the north are mainly planted in autumn. Autumn sowing in North China should be in late September, earlier in cold areas and later in warm areas. In Shandong province, seeds were sown in 10. The standard for determining the sowing date is that the seedlings have a growth period of 40-50 days before overwintering, and can grow into 2-3 true leaves, with a plant height of about 10 cm and a stem diameter of less than 4 mm, so that the physiological seedlings can safely overwinter and reduce the phenomenon of early bolting in the next year. When sowing in autumn, the ten-day average temperature is 16.5- 17℃, and the effective growth accumulated temperature (above 7℃) is 660-700℃. Sow early in autumn, and bolting is serious early in the following year; It is too late, the seedlings are too small, and it is easy to freeze to death in winter. Sowing in spring should be as early as possible. In North China, topping sowing should be carried out from the end of February to the beginning of March. The later sowing, the smaller the seedlings; The lower the output. When transplanting, spring-sown scallion seedlings in Shandong are smaller than autumn-sown scallion seedlings, with light leaf color, thin mesophyll, short scallion and insufficient yield.
(4) Sowing method The suitable density of onion seedlings is 6.5438+0.5 million plants per hectare, and the number of seedlings sown in autumn should be no less than 3 million plants, so as to prepare for weak seedlings in winter and a small number of thinning seedlings. Spring sowing should have 2.25 million seedlings per hectare to prepare for thinning and a small number of natural dead seedlings. The germination rate of onion seeds is generally not high, about 75%. According to the calculation of germination rate and emergence rate, the seeds for autumn sowing are 30-45 kg per hectare, and the seeds for spring sowing are 15-22.5 kg. Sowing is usually used for seeds that are not treated before sowing. In some areas, seeds are soaked in warm water at 50-55℃ for 20-30 minutes before sowing; Or soak the seeds in 0.2% potassium permanganate solution for 20-30 minutes, and then rinse with clean water to kill the germs on the surface of the seeds. The soaked seeds can be unearthed 1-2 days in advance. There are two sowing methods: sowing and drilling. Sowing is to raise a layer of fine soil as covering soil in the sowing bed first. Fill the border with enough water, then spread the seeds evenly, and then cover with soil 1- 1.5 cm. This method has the advantages of good water content, no soil hardening, uniform soil covering and high seedling emergence rate. When the soil moisture is good, there is no need to water it. Sow first, then cover the soil and step on it. This is called dry sowing. Drilling is to open a shallow ditch with a depth of 1.5-2 cm in the border according to the row spacing of about1.5 cm, sow the seeds in the ditch, hold the border flat and step on it.
⑤ Management of seedlings before winter. All seedlings can emerge in 6-8 days after autumn sowing. Sowing in early spring took 15-25 days to be unearthed because of the low temperature and slow germination. During this period, the soil moisture should be kept sufficient and the surface should not become hard. Before emergence, the border can be lightly raked once to protect soil moisture and prevent hardening. If the soil is dry, water it. When conditions permit, cover with plastic film after sowing to keep moisture and increase temperature, and pull it out in time when seedlings emerge. In the pre-winter growth period of seedlings, the temperature is getting lower and lower and the growth is slow. At this time, we should control the water and fertilizer to prevent the seedlings from growing too big or white. Generally, 1-2 water can be poured before winter. After all the seedlings emerge, water them once, and water them once for the winter before the soil freezes. Water should be carried out according to the soil moisture, if the soil is not dry, water can be omitted. After watering with frozen water, two layers of fine horse manure, soil mixed fertilizer or plant ash 1-2cm thick are thinly sprinkled on the edge of the seedlings, which can keep out the cold and keep moisture, and the seedlings can safely overwinter. The cover should not be too thick, otherwise the seedlings will rot due to heat. The normal standard of onion seedlings before overwintering is: average plant height 10 cm, with two true leaves, heart leaf1; The diameter of bulb base of seedlings is less than 0.3 cm; Miao Zhuang is prosperous. The seedlings are too large and bolting is serious in the early second year; Too small is easy to freeze to death.
⑥ Field management at seedling stage In spring, when the average temperature of the day reaches 65438 0 3℃, the broken grass covered on the seedbed is pulled out of the seedbed and then watered with green water. Greening water should not be watered too early to avoid lowering the ground temperature. When conditions permit, combine with watering green water and applying decomposed organic fertilizer, with 4500-7500 kg per hectare. Then intertillage, interplanting and weeding. When thinning seedlings, pull out the weak dense seedlings and keep the seedling spacing 7-8 cm. After the autumn sowing seedlings are watered with green water, they should squat for 10- 15 days to make the seedlings grow sturdily and lay the foundation for the next stage of growth. After squatting, the seedlings entered the vigorous growth period and the growth was obviously accelerated. It is necessary to increase the number of watering and keep the soil moist. In the early stage of vigorous growth of seedlings, the first fertilizer was applied in North China from late April to early May, and the second fertilizer was applied in the middle stage of vigorous growth of onion seedlings in late May, with urea100-150kg/ha each time. When applying fertilizer for the first time, spray brassinolide Shuofeng 48 1 100mg/kg solution to promote plant cell division and accelerate the rapid growth of seedlings. Sow seedlings in spring, and keep the soil moist when they emerge, so as to facilitate the emergence of seedlings. Water the seedlings in time after they come out together, and control the watering when they grow to three true leaves to promote the root system development. After the third leaf stage, use sufficient water and fertilizer to accelerate the growth of seedlings. When the onion seedlings are 50 cm high and 8-9 leaves long, and 10- 15 days before planting, the watering should be stopped and the seedlings should be exercised to make the leaves healthy and the pseudostems bear fruit, which is beneficial to slow transplanting. The planting area of onion seedlings per hectare is 5-8 hectares. The standard of strong seedlings when planting is: the average weight of a single plant is about 40 grams; About 50 cm high; Scallion is about 25 cm long; Onion is about 1 cm thick; Tubular leaves are dark green, with no less than 5-6 pieces per plant; It has the typical characteristics of this breed.