Professor Zhang Lining of Qingdao Agricultural University: It is difficult to produce lettuce, the main reasons are as follows:
One is the reason for the variety. The lettuce varieties with good ball formation in production are: Emperor, General, Caesar, Malac, Oriental Fuxing, Queen, Salinas, etc. If the selected semi-balloon or loose-leaved lettuce varieties such as American fast-growing, glass lettuce, lettuce king and other varieties, the ball is poor, and even does not pass the ball.
The second is the lack of fertilizer. When we talked with the vegetable farmers, many vegetable farmers were not sure about the amount of lettuce needed, and some simply did not use the base fertilizer. Most of them only used nitrogen fertilizer, but ignored the use of phosphorus, potassium and calcium fertilizer. Insufficient fertilizer, especially if the phosphorus, potassium and calcium fertilizers are lacking, it is easy to cause balling. Generally, when planting a mu of lettuce, the base fertilizer should use 5000 kg of high-quality decomposed organic fertilizer and 30-50 kg of compound fertilizer. In addition, it should also pay attention to proper topdressing. Generally, 15-20 kg of compound fertilizer should be applied per acre 15 to 20 days after planting. After 30 days, 15 kg of compound fertilizer or 10 kg of high-nitrogen and high-potassium should be applied per acre. In the middle and later stages, it is not advisable to use human waste urine for top dressing.
The third is improper temperature management. The lettuce is a cool climate with a suitable temperature of 15 to 20 ° C. It is suitable for environments with large temperature difference between day and night and low night temperature. The temperature of the ball is 10 ~ 16 ° C, the temperature exceeds 25 ° C, not only is not conducive to the ball, but also due to excessive temperature caused by heart leaf necrosis or decay.
Fourth, improper humidity management. Planting lettuce in protected areas, some vegetable farmers worry that watering will affect the gentle yield of the ground, so most watering is insufficient. The growth of the heading lettuce requires the most water, and the soil should be kept moist, especially before the ball is formed and when the ball is about to end. After the formation of the leaf ball, control the watering to prevent excessive moisture, causing cracked balls and rotten hearts.
Fifth, pests and diseases affect the ball. The lettuce produced by the protected land has a higher probability of occurrence than the open-planted lettuce pests and diseases. The main diseases are downy mildew, soft rot, viral disease, dry rot, and top rot. These diseases can affect the normal ball formation of lettuce. In addition, aphids, whitefly, and thrips are easy to spread viral diseases, and should be promptly prevented.
Sixth, the timing of harvesting is not allowed. The harvesting period of loose leaf lettuce is relatively flexible, and the general harvesting is not strictly required, and can be determined according to market demand. Harvesting of lettuce should be harvested according to different varieties and different cultivation seasons, and should not be harvested too early. Many vegetable farmers in production see better prices in the lettuce market, often harvested when the vegetable ball is not fully packaged, which in turn affects production and overall income. Generally, the ball is set to 50 to 70 days after the ball is set to form a leaf ball. It feels that it can be harvested by hand pressing it.
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