Detailed Explanation of Lettuce Planting Methods and Cultivation Techniques

    Lettuce, also known as leaf lettuce, belongs to the Asteraceae family, genus Lactuca. It is an annual or biennial herbaceous crop native to the Mediterranean coast. It was introduced to China around the 5th century and is mainly cultivated in South China. Lettuce is rich in vitamins and minerals, and during cultivation it is easy to obtain pollution-free products without using pesticides. It is increasingly welcomed by consumers, and the planting area is increasing year by year. The following is a brief introduction to lettuce cultivation techniques. 
 
    I. Seedbed Soil Preparation
 
    For seedling raising, beds can be made and seeds sown directly in the production field. The seedling bed soil consists of 50% garden soil and 50% decomposed farmyard manure. At the same time, add 50 grams of urea and 500 grams of superphosphate per cubic meter of bed soil. After mixing evenly and sieving, spread it evenly on the seedbed to a thickness of 5 cm (when pricking out seedlings, the seedbed soil should be spread to a thickness of 10 cm).
 
    II. Seedling Raising
 
    1. Seed treatment: Spring cultivation is generally from February to April, and dry seeds are sown directly for seedling raising. For summer and autumn cultivation, sowing is from June to August. When weather conditions make germination difficult, seeds need to be soaked and then germinated at 15°C-22°C before sowing.
 
    2. Sowing: Before sowing, water the seedbed thoroughly. After the water seeps down, scatter a 0.5 cm layer of fine soil, then sow. Generally, the sowing rate is 10 grams per square meter of seedbed. After sowing, cover with 1 cm of fine moist soil and cover with plastic film to retain moisture. After seedlings emerge in 3-5 days, remove the plastic film. For summer and autumn seedling raising, pay attention to rain protection and shading to lower the temperature. The seedbed temperature should be controlled at 18°C-20°C. When the nighttime temperature exceeds 15°C, seedling growth is adversely affected. When the seedlings grow one true leaf, they can be pricked out at a spacing of 6-8 cm between plants and rows, and the seedbed soil thickness for pricking out should be 10 cm. Throughout the seedling stage, prevent tall spindly seedlings caused by high temperatures and stiff seedlings with small cotyledons and short hypocotyls formed under drought conditions.
 
    III. Transplanting
 
    Lettuce has a shallow root system and absorbs nutrients through fibrous roots, requiring soil with good permeability. Before transplanting, prepare the land and apply fertilizer first. Apply 5000 kg of decomposed high-quality farmyard manure and 20 kg of compound fertilizer per mu. After broadcasting, plow 15-20 cm deep, then make raised beds 1 m wide with a bed height of 10-15 cm. In winter and spring, to increase ground temperature, cover with plastic film 15 days in advance to warm the soil. When the soil temperature stabilizes at 8°C, seedlings can be transplanted.
 
    When transplanting, leaf lettuce can be planted somewhat densely, with a row spacing of 20-25 cm, while heading lettuce should have a row spacing of 30-40 cm. Transplant with soil balls. The transplanting depth should be such that the soil ball is level with the ground surface. After planting, water thoroughly in time to promote rapid recovery. Generally, seedlings recover and survive 6 days after planting.
 
    IV. Field Management
 
    After the seedlings recover, topdressing and watering can begin. Heading lettuce can be subjected to appropriate root restriction for 5-7 days, then topdressing and watering should be carried out. Apply 10 kg of urea per mu, applied with irrigation water, keeping the soil moist. In addition, for heading lettuce, at the early stage of heart leaf curling, spray 0.2% urea and 0.2% potassium dihydrogen phosphate on the leaves.
 
    Lettuce is not tolerant of high temperature and high humidity. When the temperature exceeds 25°C, ventilation should be provided to lower the temperature or shading measures should be taken. At the same time, lettuce is also afraid of waterlogging, so water should not accumulate in the beds, and drainage should be done promptly after rain. After hot summer rain, cold water must be used for irrigation in time.
 
    In the middle and late stages of lettuce growth, to keep the rosette leaves from senescing and allow the head leaves to rapidly fold and grow into tight heads, continuous and uniform water supply is needed to avoid head cracking or open growth during heading. In potassium-deficient plots, pay attention to applying potassium fertilizer during this period. Stop watering 5 days before harvest.
 
    V. Timely Harvest
 
    When the leaves have fully grown, are green, thick, and crisp-tender, harvesting at this time yields high output and commercial value. For heading lettuce, if the head feels somewhat firm when pressed with force and the tightness is moderate, it can be harvested. Harvesting methods: For leaf lettuce, large leaves can be broken off while leaving small leaves, and the harvested leaves can be tied in bundles for market, or the whole plant can be cut off. For heading lettuce, cut from the ground surface at harvest, remove the outer old leaves, and leave 3-4 outer leaves around the head before packaging for market.
 
    VI. Pest and Disease Control
 
    1. Downy mildew
 
    ① Symptoms: It damages leaves. Diseased leaves have light yellow spots. When humid, white mold grows on the underside of the leaves. In the later stage, the spots merge together. When dry, the leaves turn yellow-brown and wither.
 
    ② Transmission routes and disease conditions: It is a fungal disease. Seeds and diseased plant residues can carry the pathogen, and the pathogen spreads through wind and rain. The pathogen can directly invade plant tissues through the epidermis or stomata. When the temperature is 15°C-20°C, with cloudy and rainy humid conditions and a water layer or water droplets on the plant surface, infection is very likely.