288-hole tray for 3 ~ 4 leaf seedlings and 128-hole tray for 4 ~ 5 leaf seedlings.

(2) Preparation of matrix

The spare matrix of 288-hole seedling tray imported from the United States is 2.76 m3 per 1000 tray, and that of 288-hole seedling tray imported from the United States is 2.92 m3 per 1000 tray, and that of 28-hole seedling tray imported from the United States is 3.65m3 per 1000 tray, and that of Korea is 1000 tray.

(3) preparation of matrix

Peat: vermiculite is 2: 1, peat: vermiculite: perlite is 2: 1: 1, or peat: vermiculite: waste mushroom material is 1: 1, and the covering materials are all vermiculite.

(4) Fertilization method and dosage

When preparing the substrate, 0.7- 1.2 kg of ternary compound fertilizer of nitrogen, phosphorus and potassium is added per cubic meter, or 0.2-0.5 kg of urea and 0.3-0.7 kg of potassium dihydrogen phosphate are added per cubic meter of substrate, and the fertilizer and the substrate are evenly mixed for later use. After seedling stage 1 two leaves, combined with water spraying, foliar fertilizer was applied 1 ~ 2 times.

When raising seedlings in summer, 0.4-0.7 kg of ternary compound fertilizer of nitrogen, phosphorus and potassium is added to each cubic meter of substrate. (5) Diversity

Lettuce has been cultivated in Beijing for 10 years. Hu Da 659, Sa Lin Nasi or Qianwei 75 were selected for winter protective cultivation and spring open cultivation. In summer, lettuce is made by the emperor, Caesar and Olympia. In autumn, lettuce is chosen from Emperor or Sa Lin Nasi. In addition, erect beef lettuce can be planted all year round.

(6) sowing date

Using various types of protection facilities and supporting varieties, lettuce cultivation in Beijing has been achieved by stages every year and listed line by line. Lettuce is transplanted by seedling raising, and the seedling age varies greatly due to different seasons. For example, the seedling age of lettuce planted from April to September is about 20 days, and the seedling age of lettuce planted from 10 to March of the following year is 30-40 days. 4-5 leaves are suitable for planting, and the sowing date is suitable for users' needs.

(7) Seeding amount and pre-sowing treatment

Plug seedling adopts precision sowing, the germination rate of lettuce seeds is generally above 95%, the 1000-grain weight of lettuce seeds is 8 ~ 12 g, and the seed requirement per hectare for plug seedling is1500 g. Because seeds are prone to thermal dormancy in high temperature season, they should be stored in refrigerator at 0 ~ 5℃ for 7 ~ 10 days before sowing.

(8) Sowing depth

Lettuce seeds need light to germinate, so sowing should not exceed 0.5 cm. Cover the seeds with a thin layer of vermiculite after sowing, and the seeds should not be exposed after watering. After watering, every compartment is clearly visible.

(9) Water resources management

After the sowing and covering operation is completed, spray water on the seedling tray (water drips from the bottom hole of the plug tray) to make the maximum water holding capacity of the substrate reach more than 200%; Lettuce likes humidity. In case of high temperature and large evaporation in summer, we should pay attention to watering frequently, and also pay attention to preventing rotten heart and rain and waterlogging. At seedling stage, cotyledons spread to 2 leaves with 1 seed, and the water content was 75% ~ 80% of the maximum water capacity. Sanye 1 heart is sold to commercial seedlings with water content of 70% ~ 75%.

(10) temperature management

Lettuce likes cool and humid climate conditions, and the optimum germination temperature is 15 ~ 20℃, and the seedlings emerge in 3 ~ 4 days. The suitable temperature for seedling growth is 15 ~ 18℃ during the day and 10℃ at night, which is not lower than 5℃. When it exceeds 25℃, it germinates slowly and appears thermal dormancy.

(1 1) Disease control

The main pests and diseases are virus disease, whitefly and aphid. See question 69 for control measures.

(12) Replanting

Due to the influence of seed quality and environmental conditions in greenhouse, the emergence rate of lettuce precision sowing is sometimes only 70% ~ 80%. If 128 hole seedling tray is selected, the missing seedling holes should be filled when the second real leaf is unfolded.

(13) seedling age and commercial seedling standard

The commercial seedling standard of lettuce plug seedlings varies according to the plug size. Select 128 hole seedlings, the number of leaves is 4-5, the maximum leaf length is 10 ~ 12 cm, and the seedling age is 30-35 days. A 288-hole seedling tray with 3-4 leaves was selected, the maximum leaf length was about 10 cm, and the seedling age was 20-25 days.

288-hole seedling tray is recommended for lettuce seedling raising, which has the advantage that it is not easy to damage seedlings when pulling out seedlings.

(14) Sales of commercial seedlings

When the commercial seedlings reach the above standards, the roots tightly wrap the substrate, and when the seedlings are pulled out of the plug, there will be no shedding phenomenon. When users pick seedlings, they can put them in cartons or baskets row by row and layer by layer. If you water the seedlings once before taking them, the plug seedlings can be transported for a long distance, and the survival rate of the plug seedlings can reach 100%.