After prolonged use of chemical fertilizers, many regions—including vegetable farmers in western Sichuan—have become heavily reliant on them. This overuse has led to soil degradation and raised concerns about the safety of produce. To address these issues, the production of pollution-free vegetables requires strict adherence to proper fertilization principles.
The key to producing safe, high-quality vegetables lies in controlling the levels of harmful substances such as nitrates and other carcinogens. By following the right fertilization strategies, farmers can ensure that these substances remain within acceptable limits.
The main fertilization principles for pollution-free vegetable production include: using mainly organic fertilizer with supplementary chemical inputs; applying multi-component fertilizers rather than single-element ones; and prioritizing base fertilizers like "Shiji" while using top-dressing as a supplement.
When using chemical fertilizers, it's crucial to avoid nitrate-based nitrogen fertilizers. If they must be used, the dosage should not exceed 25 kg per acre. Fertilizers should always be combined with organic materials in a 2:1 ratio. The last application of chemical fertilizers should occur at least 30 days before harvest to allow time for any harmful compounds to break down.
In practice, several important considerations should be taken into account:
1. Human feces and urine must be fully fermented and decomposed before being applied. After fermentation, they should be diluted with water and then used as a top dressing.
2. Fertilizers should be deeply applied early in the growing season to reduce volatilization and improve nitrogen efficiency. Applying ammonium nitrogen below 6 cm and urea below 10 cm helps optimize nutrient uptake.
3. It’s recommended to use biological nitrogen fertilizers alongside increased phosphorus and potassium. These help prevent soil compaction and improve plant resilience against environmental stress.
4. Fertilization should be adjusted based on the type of vegetable and growing conditions. Leafy vegetables tend to accumulate more nitrates than fruit-bearing ones. Climate also plays a role—nitrates build up more under low light and cold conditions. Farmers should adjust their practices accordingly to keep nitrate levels within safe limits.
It's important to note that base fertilizers are the most critical component in this process. They should make up more than 70% of the total fertilizer applied. Organic sources like compost, crop residues, and ash are ideal for base fertilizers, with some chemical fertilizers added in moderation.
When determining the type and amount of base fertilizer, special attention should be given to:
1. Avoiding fertilizer concentration barriers. Over-application of chemical fertilizers can create high-concentration zones that harm plants. Organic fertilizers, however, are less likely to cause this issue due to their slow release and buffering capacity.
2. Using minimal amounts of nitrate and ammonium nitrogen fertilizers. These can leach easily from the soil and cause imbalances. Urea is a better choice, and only 30% of nitrogen should be applied as top-dressing, with 70% as base fertilizer.
3. Applying all phosphate fertilizer as a base. Vegetables require a lot of phosphorus early in their growth cycle. A lack of phosphorus during the seedling stage can reduce yield even if it's added later.
Fertilization and pest control are equally important in vegetable farming. Improper practices can lead to contamination and health risks. By adopting these principles, farmers can produce safer, healthier crops while maintaining sustainable agricultural practices.
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