Avoid applying nitrate nitrogen fertilizers like ammonium nitrate and potassium nitrate, as this can easily lead to nitrate accumulation in vegetables. It's also not advisable to use chlorinated fertilizers. Chloride ions can lower the starch and sugar content in vegetables, reducing their quality. These ions can linger in greenhouse soil, potentially causing soil acidification and calcium deficiency. After applying fertilizers like potassium chloride and ammonium sulfate, ammonia ions and acid ions may not be fully absorbed by plants and could remain in the soil, increasing the soil solution’s concentration and harming crop growth. Therefore, it’s better to use urea, ammonium phosphate, diammonium phosphate, superphosphate, and specialized fertilizers in greenhouse farming.
Avoid fertilizing under drought conditions. Vegetables are high-water-demand crops. Applying fertilizer when the soil is dry can not only hinder the full effectiveness of the fertilizer but also cause a sudden spike in soil solution concentration, leading to plant damage. Thus, fertilization should always be paired with irrigation. Ditches should be dug for fertilization, followed by irrigation, or topdressing with water.
Prevent shallow fertilization due to the greenhouse's airtight environment. Shallow fertilization can lead to fertilizer volatilization, reducing efficiency and potentially causing ammonia hazards. When topdressing, apply fertilizer into holes or strips, burying it about 5-6 cm deep, ideally 8-10 cm away from the vegetable roots to minimize nitrate buildup and improve vegetable nutrient uptake.
Avoid excessive application of uncomposted organic fertilizers like pig, cow, and sheep manure. During decomposition, these can release ammonia and nitrous acid gases, which can harm vegetables. Excess ammonia can turn cucumber and tomato leaves brown, while high nitrous acid levels can damage sensitive plants like eggplant and peppers, causing them to die. Using large amounts of incompletely decomposed cake fertilizers can generate high temperatures, ammonia concentrations, and organic acids, easily burning roots.
Prevent over-fertilization in greenhouses. Follow the principle of "small amounts multiple times" to avoid excessive fertilization. The maximum recommended chemical fertilizer application per acre: no more than 0.6 kg of urea per acre; 25 kg of diammonium phosphate for sandy loam, 35 kg for clay and loam; 40 kg of superphosphate for sandy loam, 50 kg for loam and clay. If improper fertilization is detected, and harmful gas levels rise, open the greenhouse vents during midday to exchange air and reduce harmful gas concentrations, ensuring healthy vegetable growth.
Author: Gu Youjiang
Source: Shaanxi Science and Technology News
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In addition to the above guidelines, it's essential to monitor the pH level of your greenhouse soil regularly. Soil acidity can fluctuate due to excessive fertilization, impacting nutrient availability for plants. Consider using lime or other soil amendments to maintain optimal pH levels. Furthermore, rotate different types of fertilizers to avoid nutrient imbalances and promote healthier plant growth. Always test the soil before planting to understand its current nutrient status and adjust fertilization practices accordingly.
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