What are the key techniques for lettuce cultivation in spring?

Spring lettuce mainly refers to lettuce planted every other year and listed in the following spring.

(1) Variety selection There are many varieties of lettuce, and the suitable varieties should be selected according to the local climate, season, variety characteristics and uses. Spring lettuce supplied in early spring should be cold-resistant and early-maturing varieties, such as Beijing crucian carp and winter melon bamboo shoots, Nanjing white skin fragrance, Shanghai small pointed leaves, Hangzhou pointed leaves, Chongqing red lettuce and so on. For spring lettuce supplied in late spring, it is advisable to choose mid-late maturity varieties with high yield and difficult bolting, such as Beijing willow bamboo shoots, purple leaf bamboo shoots, Yanling bamboo shoots, Nanjing green skin incense, purple skin incense, round leaf white skin incense, Shanghai big round leaf, Shanghai big pointed leaf, Hangzhou round leaf, Chongqing Wannianchun and so on. When processing, Hefei pointed leaf lichen, Pizhou pointed leaf lichen, Yangguoqiu lichen and Tongguan iron lettuce should be selected.

(2) During sowing, lettuce needs a cool climate. Although the seedling stage is cold-resistant, it will not be cold-resistant when it enters the stalk hypertrophy stage, so it is necessary to avoid high temperature and heat. Lettuce seeds are small, so they are transplanted with seedlings. The optimum growth temperature of lettuce succulent stems is 1 1 ~ 18℃, so sowing must be timely, and the specific time varies with local climate and characteristics. For example, in the south of the Yangtze River basin, lettuce can overwinter in the open field, and winter seeds should be sown in autumn, so that when the seedlings grow slowly before winter, they are in a physiological state of 6-8 leaves, developed roots and developed foliage, and they can accumulate certain nutrients, so that they can safely overwinter, and when the soil is slowly thawed next spring, they can recover in advance. At a lower temperature, the roots and rosette leaves grow slowly, so the roots are deep and leafy, the leaves are thick, the accumulated nutrients are more, and the fleshy stems are fat and brittle, which can be supplied to the vegetable market in spring, and the prices are generally higher in the morning and lower in the evening. If the autumn sowing is too late, the growth period before winter is short, the seedlings are small, and the accumulated nutrients are few, so it is easy to suffer from freezing injury during wintering. Even the surviving seedlings will have shorter vegetative growth period, fewer leaves and less accumulated nutrients, resulting in small stems, late marketing, low yield and low price. However, if sowing in autumn is too early, it will prolong the growth period before winter, resulting in larger seedlings and early flower bud differentiation, resulting in less leaf number differentiation and easy bolting in the next year. If bolting is carried out before winter, plants are vulnerable to freezing injury in winter.

It is unsafe to overwinter in the open field, such as Beijing, Yinchuan and Lanzhou. Seeding and seedling raising in cold bed (sunny bed) was postponed to the middle and late June of 65438+ 10, or seedling raising in greenhouse was postponed to the middle and late June of 65438+ 10, and then planted in the open field in the following spring.

(3) Generally, the robust spring lettuce is cultivated by seedling raising and transplanting. Seedbed is selected from loose fertile soil, which has strong fertilizer efficiency and water retention. First, apply decomposed organic fertilizer or human and animal manure as base fertilizer. Generally, organic fertilizer1500 ~ 2,000 kg or NPK compound fertilizer (15- 15)30 ~ 50 kg is applied per mu. Lettuce should be sown by wet sowing. Water it first, then dry the seeds, and then cover them with fine soil, with a thickness of about 0.5 cm. If the soil moisture is good, you can also dry the seeds when the soil moisture is good, and then hoe them shallowly and into the soil.

If the seedlings of spring lettuce are thin, the seedlings are slow after planting, the growth before winter is poor, and the disease resistance is poor, which is one of the important reasons for the death of seedlings in winter and the decline of yield and quality. In addition to the general requirements, special attention should be paid to the following two points in cultivating strong seedlings of spring lettuce:

First, the sowing amount should be appropriate. The sowing amount per mu of nursery land is about 0.6 kg, and the ratio of seedbed area to sowing area is about 1∶20. It is necessary to interplant seedlings in time. Generally, when cotyledons are flattened and there are 1 ~ 2 true leaves, the spacing between seedlings should be kept at about 5 cm, so that each seedling can get enough sunshine and nutrition, prevent overgrowth and promote seedling qi and Miao Zhuang. In wintering areas, seedlings need to be protected in sunny places or plastic greenhouses. When the seedlings grow 3 ~ 4 true leaves, the distance between seedlings should be kept 6 cm.

Secondly, after applying sufficient organic fertilizer or compound fertilizer to the seedbed, nitrogen fertilizer is generally not applied at the seedling stage, and at the same time, watering is properly controlled to keep the soil in a state of "dry and wet" and "alternate dry and wet", and the seedlings are cultivated into strong seedlings with strong leaves, developed roots and strong rhizomes. If there is too much nitrogen fertilizer and water, it is easy to form fine seedlings.

(4) Planting 1) Planting time: Lettuce should be planted before overwintering in a safe area in the open field, so that the root system can develop well and recover quickly after turning green in the next spring, which can be put on the market early and increase the yield. If the sowing date is late, the seedlings are small when sowing, or the sowing is delayed, and the quality of seedlings is poor, it will cause more dead seedlings before the delay.

In areas that can't survive the winter in the open field, lettuce should be planted as soon as possible after the land is thawed in the second year, so as to delay the growth and development of seedlings. If sowing is delayed, the temperature will rise rapidly, the seedlings will grow white and the young stems will grow tall, and immature bolting will affect the yield and quality.

2) Preparation before planting: Mainly applying sufficient base fertilizer and fine soil preparation. Spring lettuce is planted before winter and harvested in spring, and the growth period is about 5 months. Before planting, we should try our best to use decomposed organic fertilizer, properly apply ternary compound fertilizer of nitrogen, phosphorus and potassium (15-15), and generally apply 2000 ~ 3000 kg of organic fertilizer and compound fertilizer (65438) per mu. For those planted before overwintering, the whole layer shall be ploughed 10 ~ 15 days before planting; After overwintering, it can be planted in the soil before winter. The quality of soil preparation is related to whether the seedlings can survive the winter safely. The soil preparation is extensive, there are many clods in the ground, there is a gap between the soil and the root system after planting, and cold air hits the root system directly in winter, which is prone to freezing injury and causes seedling shortage. In areas where spring lettuce can overwinter in the open field, it is best to adopt high ridge cultivation extending from east to west. When planting, plant the seedlings at the south base of the ridge. Because of the high soil temperature on the south side of the ridge, the seedlings recover to grow faster after sowing, the root system develops well, and there are fewer dead seedlings during the winter, which can be put on the market about 10 days earlier than ordinary flat farming.

3) Correctly master the planting technology: when digging seedlings from seedbed, try to bring clods, the main root is 6 ~ 7 cm long, and the main root is too short, which will affect the growth of slow seedlings and plants after slow seedlings; The main root is left too long, and the root bends in the soil when planting seedlings, which also affects the growth of lateral roots and seedlings. The depth of planting seedlings can be flexibly controlled according to the climatic conditions of planting. Winter planting is slightly deeper than spring planting. When planting in winter, the roots should be buried in the soil, but not in the heart leaves and growing points of the stems, and then the soil should be compacted to make the roots closely connected with the soil for rooting. When planting, the soil moisture is good, and less water can be used when planting. After sowing, under the condition of suitable soil humidity and temperature, the seedlings can quickly send out new roots and start to grow after delaying emergence.

Seedlings should grow healthily, and the number of leaves is appropriate, generally about 5 true leaves, with normal leaf color and no pests and diseases. Large and small seedlings should be planted separately to facilitate future management and harvest. We should also eliminate those seedlings that are thin, tall, white, with few leaves and diseases and insect pests.

(5) Strengthening field management For spring lettuce planted in winter and spring, the central task of field management should be determined according to different growth processes and different climate characteristics. The field management of lettuce planting before overwintering can be divided into two stages: overwintering period and turning green period.

1) field management in overwintering period: The main goal is to make lettuce form developed roots and strong foliage, enhance the cold resistance of seedlings and ensure safe overwintering. A large number of lateral roots are easy to appear after the main roots of lettuce are cut off. After delaying the emergence of seedlings, lightly water lettuce once to promote the increase of leaf number and leaf area, then intertillage, control water and squat seedlings to make lettuce form developed roots and rosette leaves. If you water too much, the seedlings will grow in vain, and the cold resistance will be reduced, which is easy to cause freezing injury. In the next spring, the fleshy stems will grow slowly, resulting in thin and long fleshy stems.

2) Field management in greening period: The main goal is to correctly handle the relationship between leaf growth and fleshy stem hypertrophy, ensure stable growth and prevent channeling.

After turning green, the growth of leaves is the main factor. At this time, it is necessary to cultivate more soil moisture, raise ground temperature, promote the expansion of leaf area, thicken and darken leaves, and accumulate nutrients for succulent stems. If you water in a hurry just after turning green, the ground temperature will drop, the heart leaves of plants will turn yellow, the leaf area will increase slowly, the leaves will become thinner, and the stems will stretch upward before they grow thick, resulting in the phenomenon of "jumping seedlings". In addition, the climate changes greatly in early spring, and if it is cooled by cold current after watering, the leaves that grow after turning green are also easy to freeze.

When the leaves of plants grow completely and the stems begin to swell rapidly, topdressing should be carried out. If the soil moisture is good, it can be applied in the hole without watering. If the soil is dry, it should be fertilized and watered. Generally, urea 10 ~ 15 kg and potassium chloride 7.5 ~ 10 kg are applied per mu. Pay great attention to soil moisture during the hypertrophy of lettuce succulent stems, and don't let the soil dry and wet alternately; Keeping the soil moist often can not only make the succulent stems swell rapidly, but also make them not easy to crack. Stop watering and topdressing 7 ~ 10 days before harvesting to prevent fleshy stems from cracking.

(6) The most suitable harvesting time of lettuce is when the growth point at the top of the main stem of lettuce is flush with the top of the highest leaf.