To prevent the application of nitrate nitrogen fertilizers, nitrate-nitrogen fertilizers such as ammonium nitrate and potassium nitrate can easily accumulate nitrates in vegetables; it is also not suitable to use chlorinated fertilizers. Chloride ions can reduce the content of starch and sugar in vegetables and cause deterioration of the quality of vegetables. Lower, and chloride ions will remain in the greenhouse soil, can cause acidification of the soil, easily lead to calcium deficiency in the soil. When potassium chloride, ammonium sulfate and other chemical fertilizers are applied to the soil, ammonia ions and acid ions are not easily absorbed by the crops and remain in the soil, which will increase the concentration of the soil solution and damage the normal growth of the crops. Therefore, greenhouse fertilizer should use urea, ammonium phosphate, diammonium phosphate, superphosphate and special fertilizers.
Preventing the fertilization of vegetables under drought conditions is a happy crop. Fertilizing when the soil is dry, not only can the fertilizer effect not be fully exerted, but also the concentration of soil solution can suddenly increase, causing the roots of the vegetables to burn. Therefore, when fertilizing vegetables, they should be combined with irrigation, and they should be fertilized in the trenches, bury the fertilizer in solid water and then apply water, or apply fertilizer in the water.
To prevent shallow fertilization greenhouses due to a better degree of confinement, shallow fertilization or spread fertilization materials, it is easy to make the fertilizer volatile, both to reduce fertilizer efficiency, but also easy to produce ammonia hazards. When topdressing, it should be done with acupuncture points or strips, with a depth of 5-6 cm, preferably 8-10 cm from the roots of vegetables, which can reduce the accumulation of nitrates in vegetables and increase the utilization rate.
To prevent excessive application of unfamed organic fertilizers to excessively apply organic fertilizers such as pigs, cattle, and sheep manure, the ammonia gas and nitrous acid gas generated during the decomposition process will harm the vegetables. For example, when the ammonia concentration exceeds the limit, cucumbers and tomatoes will suffer damage. The initial leaves will be burned as if they were burned by boiling water. After drying, they will become brown. When the concentration of nitrous acid exceeds the limit, it will cause damage to susceptible vegetables such as eggplant and pepper, and when the leaves are severe, it will become white. And dead. The use of a large amount of cake fat that has not been sufficiently cooked causes localized high temperatures and high concentrations of ammonia and organic acids to easily burn roots.
To prevent excessive fertilization in greenhouses, we must strictly follow the principle of “a small number of times†to prevent excessive fertilization. The limit of application of chemical fertilizer to different soils per acre is as follows: urea does not exceed 0.6 kg per mu; 25 kg of diammonium phosphate sandy loam, 35 kg of clay and loam; 40 kg of superphosphate-based sandy loam, 50 kg of loam and clay. Once improper fertilization is found, when the harmful gas content in the greenhouse is too high, ventilators should be opened to ventilate when the temperature is high at noon to reduce the concentration of harmful gases so as to ensure the normal growth of vegetables.
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