Salt damage in greenhouse vegetable cultivation is an important factor affecting the yield, therefore, it is imperative to solve the problem of controlling salt damage in greenhouses. The long-term use of chemical fertilizers, including inorganic salts such as nitrogen, phosphorus, potassium, and trace elements, is the main cause of salt damage in greenhouses. In the absence of organic matter in soil, long-term blind overuse of chemical fertilizers will inevitably result in the deposition of chemical elements in the soil, which is bound to cause salt damage. Salt pollution in greenhouses is a symptom that is comprehensively manifested by differences in soil types, irrigation quality, improper application of chemical fertilizers, and salt tolerance of planted crops, which can lead to crop wilting, dead trees, and infertility in growth and development.
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Salt damage is judged by the severity of soil salt damage. Commonly used ground observation and laboratory analysis are two methods to judge: In the initial stage of salt damage, there is green frost and then develops to green moss. At this time, the total soil salt test is 0.189-0.255. %, Shetian crops are still normal; when the soil salt is heavy, white crystal “salt cream†appears on the ground, and dead trees appear at seedling stage. At this time, the test soil salt content is 0.255-0.315%, when the local surface appears “red frost†During the middle period of crops in the shed, crops appeared wilting. At this time, the chemical analysis of soil salinity reached 0.315-0.378%. When Tantian conjoined with wilting death, the total salt amount was as high as 0.378-0.441%. The osmotic pressure of the soil solution was high. The whole root system was like a bubble in a pickle jar and could easily cause root water reflux, reverse osmosis, red roots, and stem atrophy. The crop roots are rotted and dehydrated and die. In general, vegetables are wilting at noon and recover sooner or later. Similar to wilt disease, the stem base is atrophic, roots are red and black, and the absorption function of the root system is destroyed. This will inevitably cause nutrient imbalance, which will lead to root diseases and lead to deficiency of the disease. Potassium deficiency and boron deficiency are prone to fungal diseases; calcium deficiency, magnesium deficiency, and copper deficiency are easily caused by bacterial diseases; zinc deficiency and molybdenum deficiency are easily obtained viruses. Too much potash reduces the effectiveness of calcium, magnesium, and boron. Too much phosphorus reduces the effectiveness of calcium, zinc, and boron.
Control measures First, adjust the proportion of organic fertilizer, chemical fertilizer and microbial fertilizer applied in Shetian. Organic fertilizer accounted for 65% of the demand for crops in the greenhouse, chemical fertilizer accounted for 30% of the fertility requirement, and microbial fertilizer accounted for 5% of the total growth period. Livestock and poultry organic fertilizers were changed to organic fertilizers such as fermented soybean meal and cottonseed meal. Chemical fertilizers should be based on the physiological needs of different crops and reduce chlorine and sodium content. Microbial fertilizers are always involved in the whole process of base fertilizers, top dressings and red fertilizers. Secondly, the application of 100-150 kg/mu special fertilizer for saline-alkali soil in the salt-damaged shed fields has a very significant effect. Under the initiative of Wang Daichun, an expert in soil and fertilizer, the vegetable sheds in Shexian County used salt-alkali land special fertilizers to stop the occurrence and spread of soil “salt damageâ€. Low-yield sheds gradually became medium and high-yielding sheds and were welcomed by vegetable farmers. The third is to select salt-tolerant vegetable varieties such as cucumber Jinyou No. 1; melon rhubarb skin, black netting; cherry tomatoes; winter breeding of summer cucurbits; The fourth is to control the amount of chemical fertilizers. In particular, nitrogen fertilizers should not be excessive, and organic fertilizers must be fermented and decomposed. The fertilization in greenhouses should be conducted according to the amount of fertilization, and a small number of fertilization methods should be used. Prevent excessive use of fat once. Generally, urea does not exceed 10kg per mu and ammonium sulfate does not exceed 20kg per mu. Pay attention to proper watering after application to keep the soil moist and reduce the concentration of soil solution, which is beneficial to the exertion and absorption of fertilizer effects. Fifth, a reasonable choice of fertilizer types. The ranking order of salinity of commonly used fertilizers from high to low is: ammonium chloride> potassium chloride> ammonium nitrate> potassium sulfate> urea> ternary compound fertilizer> binary compound fertilizer. It can be seen that the salinity of chlorinated fertilizers is strong, and special attention must be paid to the application of greenhouse soil, followed by nitrate and sulfate fertilizers.