When planting off-season vegetables, not only the hardware facilities such as plastic greenhouses and solar greenhouses should be ready, but also the fertilization technology is crucial. There are still some differences between the fertilizer application methods for off-season vegetables and seasonal vegetables. Through practice, this paper introduces the key points of fertilizer application technology for off-season vegetables: magnesium sulfate monohydrate

1. It is necessary to determine the economic fertilization amount, select the appropriate fertilizer varieties, determine the appropriate fertilization period, fertilization methods and other contents. The amount of fertilizer applied shall be calculated according to the yield level and soil fertility level on the premise of meeting the vegetable demand. If the supply of nitrogen, phosphorus and potassium nutrients in the soil can meet the vegetable demand, the amount of fertilizer applied shall be 20%~40% of the vegetable yield to ensure the fertilizer supply intensity. Under the current fertility level, the fertilization principle should be to control nitrogen, reduce phosphorus, stabilize potassium, and apply micro fertilizer targeted.

Generally, chlorine type fertilizer and volatile nitrogen fertilizer should not be used, and nitrate nitrogen fertilizer should be controlled as far as possible. Generally, for vegetables with short growth period or harvested from roots, stems and leaves, 12%~13% nitrogen fertilizer, all phosphorus, potassium and microelement fertilizer can be used as base fertilizer, and the other nitrogen fertilizer can be used as topdressing in several times during the high growth period. For melons and fruits, 13% nitrogen fertilizer, 23% phosphorus and potassium fertilizer, and all micronutrients can be used as base fertilizer, and the other nitrogen fertilizer, phosphorus and potassium fertilizer can be used as topdressing in several times. If the salt content is 0.2%~0.3%, chemical fertilizer should not be used as base fertilizer.

2. Heavy application of organic fertilizer and year by year deep cultivation of soil. The decomposed high-quality organic fertilizer is selected to be applied as the base fertilizer about one month before the shed is covered. The application amount is generally 1~1.5 times of that of the field, that is, 3000~10000 kg per mu. It is further cultivated year by year, and the cultivation layer is thickened to achieve the integration of soil and fertilizer and improve the physical and chemical properties of the soil.

In order to prevent ammonia and nitrite gas poisoning, organic fertilizer should be decomposed, especially chicken manure. It is required to be decomposed to a high degree and applied in advance. It is strictly prohibited to stack in the shed for a long time. Organic fertilizer and inorganic fertilizer can be used together. If a part of inorganic fertilizer is taken out for foliar spraying, it will be more economical.

3. Select better irrigation methods for different soils. Different vegetables have different requirements for soil moisture. Vegetables with shallow roots, such as cucumber, pepper, cauliflower, celery, lettuce, like wet soil, so the amount and frequency of irrigation should be increased appropriately. Vegetables with deep roots, such as watermelon, melon, loofah, tomato, zucchini, have strong drought resistance, so the amount and frequency of irrigation should be reduced as much as possible. Different growth stages have different requirements on soil moisture. The root system has weak water absorption capacity at seedling stage, which requires higher soil moisture. In the growing stage, it is necessary to control water and squat seedlings to promote roots; In the peak period of the results, the hygrophilic vegetables should be watered frequently, and the relative humidity of the topsoil layer should be kept at about 85%; For drought tolerant vegetables, too much water should not be supplied at this stage.

In plastic greenhouse, how to determine the appropriate irrigation period, temperature, amount and method is the key to achieve reasonable irrigation. The temperature of water for greenhouse irrigation should be maintained at 20 ℃~25 ℃. If the temperature exceeds 28 ℃, the root system of vegetables will be damaged, causing greenhouse vegetable diseases.

4. Effectively solve the salt hazard. For the plot where salt damage has occurred, it can be solved by selecting cabbage, spinach, pumpkin, celery, cauliflower and other salt tolerant vegetables and applying organic fertilizer. It is also an effective method to change soil and clean up salt or irrigate and soak the field.

Solar greenhouses and plastic greenhouses are often overfertilized and there is no natural rainfall to take a shower, resulting in rising salt concentrations in the soil. Standardized fertilization is an effective way to prevent salt accumulation in greenhouse.