How to produce fertile vegetables for scientific fertilization
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In greenhouses, the extensive use of fertilizers combined with tight sealing during winter and spring leads to low temperatures and weak light. These conditions can reduce the activity of nitrate reductase in vegetables, making them more prone to nitrate accumulation. Managing this issue through proper fertilization is crucial for producing safe, pollution-free vegetables.
First, implementing a scientific fertilization plan is essential. This involves tailoring the application of nitrogen, phosphorus, potassium, and micronutrients based on the specific needs of different vegetables and the nutrient status of the soil. For example, cucumbers have peak nutrient demands 75–140 days after planting, tomatoes around 30–52 days, and sweet peppers between 30–60 days. The ideal N:P:K ratios are 1:0.67:1.83 for cucumbers, 1:0.38:1.75 for tomatoes, and 1:0.38:1 for sweet peppers. Micronutrients, though required in small amounts, play a vital role. Foliar sprays such as 0.1%–0.3% ferrous sulfate, 0.05%–0.2% zinc sulfate, 0.3%–0.5% borax, 0.02%–0.05% ammonium molybdate, and 0.02%–0.04% copper sulfate can be applied. These can be mixed with Bordeaux mixture for disease control while also boosting fertility. Urea (0.1%–0.4%) or potassium dihydrogen phosphate (0.2%–0.3%) may also be used. However, avoid spraying leafy vegetables directly to prevent increased nitrate levels.
Second, controlling the amount of nitrogen fertilizer is key. While nitrogen is essential, overuse increases nitrate accumulation. To meet safety standards, aim for about 10–12 kg of pure nitrogen per acre. Apply it deeply, along with phosphorus and potassium, or use compound fertilizers. After application, cover the soil promptly. It's best to apply fertilizers via drip irrigation under plastic film or through water channels to minimize losses and improve efficiency. Avoid top-dressing 20 days before harvest.
Third, avoid using nitrate-based fertilizers. Products like ammonium nitrate, ammonium sulfate, calcium nitrate, and other nitrate-containing compounds can increase nitrate levels in vegetables. Chloride-based fertilizers, such as potassium chloride, should also be avoided, as they can lower sugar and starch content, reducing quality and yield. They may also cause soil compaction and degradation over time. Sulfate-based fertilizers, like magnesium sulfate, may not be fully absorbed by plants, leading to long-term soil issues. Ammonium bicarbonate is not recommended due to its high ammonia volatility, which can damage crops.
Fourth, consider using ecological organic fertilizers. These are made from fermented livestock manure and can be tailored to supply specific nutrients. With up to 45% organic matter, they help fix nitrogen, solubilize phosphorus, and release potassium. They also break down pesticide residues and chemical fertilizers. 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, maintain a moisture level of around 45%, and let it ferment under an insulating cover. In warmer seasons, composting takes 5–6 days, while in winter it may take 7–10 days. Once matured, it becomes loose, dry, and covered with white fungal threads, ready for use after air drying.
Lastly, limit the use of growth hormones. Some farmers use substances like gibberellins, ethephon, and paclobutrazol to accelerate growth and ripening, but this often compromises vegetable quality. Long-term consumption of such products can be harmful to human health. Therefore, it's important to promote natural growth methods and avoid excessive chemical interventions.