Standardized high-yield cultivation techniques of lettuce in spring

Letterhead lettuce is stem lettuce, its stem meat is crisp and tender, delicious, can be fried, cold, blanched soup, pickled, etc., is a consumer favorite vegetable. Lettuce, also known as lettuce, is a variety of lettuce species in the Compositae family that can form succulent tender stems and is an annual herb. Alias stem lettuce, lettuce shoots, green shoots, cabbage. Date of birth: 1-4 months. Native to central or northern China. The stem on the ground can be eaten, the stem skin is white and green, the stem meat is crispy and tender, the young stem is green, and it turns white and green after maturity. The main edible fleshy tender stems, can be eaten raw, cold, fried, dried or pickled, tender leaves can also be eaten.

Morphological characteristics of lettuce

The stem looks like a circle, like a bamboo shoot. Straight roots, most lateral roots after transplantation, shallow and dense, mainly distributed in 20-30cm soil layer. Stems shortened. Leaves alternate, lanceolate or long oval, etc., color light green, green, dark green or purple, leaf spreading or ruffled, entire margin or notch. The shortened stem gradually elongates and thickens with the growth of the plant. After the flower bud differentiation at the stem end, the stem thickens and grows at the same time as the flower stem elongates, forming a rod-shaped fleshy tender stem. Light green, emerald green or yellowish green. Panicle head, pale yellow flowers, each inflorescence has about 20 flowers, self-pollinated, sometimes cross-pollinated. Achene, black-brown or silvery-white, with crested hairs.

The problems of lettuce spring cultivation:

1. In the middle stage of growth, the fleshy stem is slender, the leaf internodes are elongated, the leaves are thin and small, the skin is thick and the meat is less, the edible value is not high, and it is easy to bolt and bloom. This phenomenon is commonly known as "channeling". There are four reasons for "channeling": one is insufficient water supply and soil drought; the other is insufficient fertilizer supply and poor nutritional growth; the third is high temperature, high respiratory intensity, high nutrient consumption, low distribution rate of dry matter to edible parts; and the fourth is excessive watering.

2. Cracks in lettuce fleshy stem expansion late, fleshy stem longitudinal crack, deep to the middle of the stem, crack part is yellow brown, perishable, reduce the edible value. The causes of cracking: one is related to variety; the other is related to uneven supply of water and fertilizer, sudden drought and sudden waterlogging, especially when the fleshy stem is mature, the outer skin has been lignified, at this time, a lot of watering, the fleshy stem suddenly expands, and the epidermis cannot expand and crack.

3. Immature bolting spring lettuce planting too late, affected by high temperature and long sunshine, rapid flower bud differentiation and bolting flowering. In addition, too large or excessive seedling planting is also easy to occur late bolting phenomenon.

Standardized high-yield cultivation of lettuce in spring

In view of these problems, we should take necessary measures for high yield cultivation.

1. Variety selection should choose varieties that are not easy to crack. Generally, purple leaf lettuce has large water content, high yield and is most easy to crack. Green leaf lettuce has relatively light cracks.

2. Sowing at appropriate time should be done as early as possible to make its roots and leaf clusters fully grow at lower temperatures, so as to accumulate a large amount of dry matter for rapid hypertrophy of fleshy stems. Sowing in greenhouse in our area is generally done from early to late February. If sowing is too late, flower stems are in hypertrophy period, and the respiratory intensity is large in case of high temperature, so it is easy to "run".

3. Cultivation of strong seedlings 667 square meters (mu) lettuce seedbed area of 15 square meters, with 50 grams of seed, seed bed soil to be prepared into nutrient soil in advance. The nutrient soil proportion is: 7 parts of mature soil without planting vegetables, 3 parts of high-quality decomposed organic fertilizer, and inorganic fertilizer, 50 grams of compound fertilizer per cubic meter, fully mixed and sieved. Then spread the nutrient soil into the seed bed, generally 6-7 cm thick, and use about 100 kg of nutrient soil per square meter.

When the seedbed is ready, sow immediately. Before sowing, the seeds should be treated, first drying the seeds for 2-4 hours, then soaking them in water at 20 ° C for 3 - 4 hours, washing and draining the water, then sowing, or placing the soaked seeds in an environment of 15 ° C-20 ° C for germination, and sowing after 2-3 days of germination.

Sowing method generally adopts broadcasting method, on the flat bed soil, pour water before sowing, after the water infiltrates, mix the seeds or buds with 4 - 5 times the volume of wet fine sand, evenly sprinkle into the ridge surface, cover 0.5-1 cm thick fine soil after sowing, lay plastic film after covering soil, which is conducive to heat preservation and moisture retention. Under the temperature condition of 15 ° C-20 ° C, when most of the seedlings are top soil in 1 - 2 days, the mulch film is removed in time.

After sowing, the temperature is controlled at 20℃-25 ℃ during the day and 15℃ at night, and the seedlings can be harvested in 3-5 days. After emergence, the temperature is kept at 18℃-20℃ in the daytime and about 1 - 2 ℃ at night. When the seedlings are 2 - 3 leaves, the seedlings are placed in a cold shed with a distance of 5-7 cm. After the seedlings are divided and slowed down, the foliar micro-fertilizer is sprayed 1-2 times, and chlorothalonil and thiophanate are sprayed for disease prevention. Water management is based on the principle of keeping the soil moist and not watering it. Too dry or too wet easily causes aging or excessive growth of seedlings.

4. lettuce planting root system developed, root group dense, shallow root system, poor absorption capacity, need to apply more organic fertilizer, generally 667 square meters of high-quality organic fertilizer more than 5000 kg, ammonium phosphate 50 kg, potassium sulfate 15 kg, as base fertilizer, and then soil preparation for the bed, bed width 1.2 meters.

From mid-April to late April, seedlings are planted in time when 4-5 true leaves are planted, row spacing is 40 cm, plant spacing depends on varieties, generally 25 - 30 cm, 4 rows are planted per plot, and generally about 6000 seedlings are planted in 667 square meters.

One day before planting, spray water on the seedbed to make the bed soil moist. When digging seedlings, try to bring more soil and less damage to roots. Because the outside temperature is low when planting, it should be carried out in warm weather with no wind after cold weather. The planting depth is appropriate to bury the roots completely in the soil. Do not press the heart leaves too deep. The soldiers should press slightly to make the roots fully close to the soil.

5. Field management after planting: control water between 2-3 leaf rings to promote root development and rosette leaf development. When the leaves are flush with the rosette leaves, the stems begin to plump. Water and apply quick-acting nitrogen fertilizer and potassium fertilizer. Change from "control" to "promotion" in time. This water and fertilizer must be timely, too early or too late for the growth of succulent stems are unfavorable. After starting watering, the hypertrophy speed of the stem is accelerated, the amount of water and fertilizer required is increased, the ground is slightly dry, the watering should be uniform, the amount of water should be moderate, and flood irrigation should be strictly prevented. When the ground can enter, shallow loose soil to break hardening, combined with watering, and then topdressing 1-2 times, each time every 667 square meters of urea about 20 kg, fertilizer should not be too large, in case of stem cracks.

6. Pest and disease control According to the observation of cultivation in recent two years, the main diseases of lettuce in our area are downy mildew and leaf spot, which can be controlled alternately by chlorothalonil, mancozeb, thiophanate and pulick.

The main pests are aphids, whitefly, Kudzu winter moths, red spiders and so on. Aphids and whiteflies were controlled with aphids and Wanling. The winter moth of lettuce was controlled with trichlorfon, dipterone and Bt emulsion. Red spider is controlled with amaranth, methomyl, etc.

7. Harvest in due time When the top of the main stem of lettuce and the leaf tip of the highest leaf are flat, the harvest is suitable, at this time the fleshy stem has fully expanded, and the quality is crisp and tender. Staged harvest can be removed top growth point, to prevent "channeling" seedlings or cavity aging. However, the interval period should not be too long. In addition, lettuce should be harvested early when it is found to have slight cracks. Generally, the yield of 667 square meters is 2500-3000 kg.