How to produce fertile vegetables for scientific fertilization
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In greenhouses, where large amounts of fertilizers are used and the environment is tightly sealed during winter and spring, low temperatures and weak light can reduce the activity of nitrate reductase in vegetables, leading to the accumulation of nitrates. Controlling this nitrate buildup through proper fertilization is essential for producing safe, pollution-free vegetables. Here are five key strategies to achieve this:
First, implement a balanced fertilization plan based on the specific nutrient needs of different vegetables and the current fertility status of the soil. For example, cucumbers require the highest nitrogen, phosphorus, and potassium (NPK) between 75 to 140 days after planting, while tomatoes need it between 30 to 52 days, and sweet peppers between 30 to 60 days. The ideal NPK ratios vary: 1:0.67:1.83 for cucumbers, 1:0.38:1.75 for tomatoes, and 1:0.38:1 for sweet peppers. Although micronutrients are needed in small quantities, they play a crucial role. Foliar sprays with iron sulfate (0.1–0.3%), zinc (0.05–0.2%), borax (0.3–0.5%), ammonium molybdate (0.02–0.05%), and copper sulfate (0.02–0.04%) can help improve plant health. These can be combined with Bordeaux mixture to prevent diseases, enhance growth, and even include urea (0.1–0.4%) or potassium dihydrogen phosphate (0.2–0.3%). However, avoid spraying leaves of leafy vegetables to prevent increased nitrate levels.
Second, carefully control the amount of nitrogen fertilizer applied. While nitrogen is essential for vegetable growth, excessive use leads to higher nitrate content. To meet safety standards, aim for about 10–12 kg of pure nitrogen per acre. Apply nitrogen deeply, along with phosphorus and potassium, or use a complete compound fertilizer. After application, cover the soil promptly. It’s best to use drip irrigation or inject fertilizers into the furrow under plastic to minimize losses and increase absorption. Avoid top-dressing 20 days before harvest to allow the plants to metabolize nitrates effectively.
Third, avoid using nitrate-based fertilizers such as ammonium nitrate, ammonium sulfate, calcium nitrate, and other compounds that can easily lead to nitrate accumulation in vegetables. Chloride-containing fertilizers like potassium chloride and ammonium chloride should also be avoided, as they can lower sugar and starch content, reducing quality and yield. Sulfate-based fertilizers like magnesium sulfate and ammonium sulfate may leave residual sulfates in the soil, which can hinder plant growth. Ammonium bicarbonate is not recommended due to its high ammonia volatility, which can cause damage to plants.
Fourth, apply ecological organic fertilizers made from fermented livestock manure. These fertilizers are rich in organic matter (up to 45%) and can act as nitrogen-fixing, phosphorus-solubilizing, and potassium-releasing agents. They also help break down pesticide and chemical residue. A typical recipe includes 2–2.5 cubic meters of fresh chicken manure, 0.2–0.3 tons of straw powder, 5 kg of corn flour, and 8 kg of multi-dimensional complex bacteria. Mix the ingredients thoroughly, ensuring the moisture content is around 45%, then add the microbial culture and mix again. Pile the mixture and cover it with insulation film. In warmer seasons, it takes 5–6 days to mature; in winter, 7–10 days. Using a reactor can speed up the process by heating it to 80°C for 1–3 days, killing harmful pathogens and eliminating odors. Once the compost is loose, dry, and covered with white fungal threads, it's ready to use after drying slightly.
Fifth, limit the use of plant growth hormones. Some farmers use substances like gibberellins, ethephon, and paclobutrazol to accelerate growth and early harvest, but this often results in lower-quality produce. Long-term consumption of such vegetables can be harmful to human health. Therefore, it's important to promote natural growth methods and avoid unnecessary chemical interventions.