How can chemical fertilizer pollution of vegetables be reduced?
In recent years, due to long-term heavy use, part of the chemical fertilizer entering the soil has not been absorbed and utilized by crops and has transferred into groundwater, causing pollution.So how can chemical fertilizer pollution of vegetables be reduced?
To reduce vegetable pollution from fertilization, attention should be paid to the following points in fertilization:
1. Apply organic fertilizer heavily. Organic fertilizer will not cause the accumulation of nitrate in vegetables and can also improve vegetable quality. Organic fertilizer is best applied after high-temperature composting or biogas fermentation and decomposition, which can kill pathogens and insect eggs, reduce the amount of pesticide applied, and improve vegetable yield and quality. Vegetables grown with biogas fertilizer are the best pollution-free vegetables.
2. Do not apply nitrate nitrogen fertilizer, or apply it sparingly. Nitrate nitrogen fertilizer and compound fertilizer containing nitrate nitrogen easily cause vegetables to accumulate nitrate, so they are not suitable for use on vegetables. Ammonium nitrogen fertilizer and amide nitrogen fertilizer can be selected, such as ammonium sulfate, ammonium bicarbonate, urea, etc.
3. Control the amount of nitrogen fertilizer. The accumulation of nitrate in vegetables increases with the increase in the amount of nitrogen fertilizer applied. The amount of nitrogen applied per mu should be controlled within 30 kg, of which 70%-80% should be applied deeply as base fertilizer, and 20%-30% should be applied deeply as seedling fertilizer.
4. Nitrogen fertilizer should be applied early and deeply. Applying nitrogen fertilizer as base fertilizer or seedling-stage topdressing is beneficial for vegetables to grow early and quickly, and helps reduce the accumulation of nitrate in the soil and in vegetable tissues. Applying nitrogen fertilizer deeply into the 10-15 cm soil layer can reduce nitrogen loss and improve nitrogen fertilizer use efficiency. In deep soil, the soil air is in anaerobic conditions, nitrification is slow, and the accumulation of nitrate by vegetables can be reduced.
5. Fertilize according to the site and season. In soil with high fertility and rich organic matter, vegetables easily accumulate nitrate, so nitrogen fertilizer should be prohibited or applied sparingly. In low-fertility vegetable fields, the nitrate accumulated by vegetables is relatively light, and nitrogen fertilizer and organic fertilizer can be applied to build up soil fertility. In general vegetable plots, if balanced fertilization based on soil testing is adopted, it is beneficial for high quality and high yield, makes it less easy for vegetables to accumulate nitrate, and also helps build up soil fertility. In summer and autumn, when temperatures are high, nitrate accumulation is not favored, so nitrogen fertilizer can be applied in appropriate amounts. In winter and spring, when temperatures are low and light is weak, nitrate reductase activity declines, and nitrate is easily accumulated, so nitrogen fertilizer should not be applied or should be applied sparingly.
6. Fertilize according to the vegetable. Different types of vegetables absorb and accumulate nitrate to different degrees. Chinese cabbage types and leafy green vegetables easily accumulate nitrate, so nitrate nitrogen fertilizer must not be used; solanaceous fruiting vegetables, fruit vegetables, and root vegetables accumulate relatively little nitrate, so it can be applied appropriately, but application of nitrate nitrogen fertilizer should be stopped 15-30 days before harvest.
7. Leafy vegetables must never be given foliar nitrogen fertilizer. When nitrogen fertilizer is used as a foliar fertilizer, it directly contacts the air, and ammonium ions easily become nitrate ions that are absorbed by the leaves, increasing nitrate accumulation. Therefore, in pollution-free leafy vegetable production, foliar application of nitrogen fertilizer should be prohibited, especially within 1 month before harvest.
8. Do not irrigate with sewage. Irrigating vegetables with sewage easily causes pollution. Sewage discharged from factories and mines contains relatively high amounts of toxic substances such as chlorine, arsenic, tin, and lead, and must be prohibited for watering vegetables. Urban domestic sewage should be harmlessly treated, and after killing pathogens and insect eggs, mixed with clean water before use.