Nitrogen fertilizer application lecture
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Control the amount of nitrogen fertilizer should minimize the amount of nitrogen fertilizer application and the number of applications to reduce the nitrate content in vegetables. The amount of mu should be controlled under the standard nitrogen of 20 kg. The high-fertility vegetable field should be controlled under 10 kg or no nitrogen fertilizer should be used. 70% to 80% of nitrogen fertilizer is used as the base fertilizer for deep-seated application, 20% to 30% for top-dressing application, and medium-term application of human and animal manure.
The application of ammonium nitrogen fertilizers and the use of ammonium nitrate nitrogen fertilizers applied to vegetables generally have less pollution, lighter hazards, and less rotten vegetables. Nitrate nitrogen fertilizers, however, can lead to the accumulation of nitrates in vegetables, which is harmful to the human body. Therefore, in addition to the control of the amount of nitrogen fertilizer in vegetables, it should also pay attention to the application of ammonium bicarbonate, ammonium sulfate, ammonia and other ammonium nitrogen fertilizer, avoid application of ammonium nitrate and compound fertilizer containing nitrate nitrogen.
The deep application of nitrogen fertilizers and avoidance of applying nitrogenous fertilizers on the surface or shallow layers may increase the chance of direct contact with air and sunlight, resulting in loss of nitrogenous fertilizers. Should generally be applied 12 to 15 cm deep. Soybean roots and root vegetables with developed roots should also be applied to the root distribution layer beyond 15 cm.
Topdressing advocates that the nitrate content of vegetables in early-applied vegetables will gradually decrease with the time after top-dressing, so topdressing with nitrogen fertilizer should be sooner rather than later. In particular, leafy vegetables and vegetables with short growing periods must not be topdressed with nitrogenous fertilizers during the late growth period. Generally, they should be applied at the seedling stage, and nitrogen fertilizers should be stopped 25 days before harvest.
Leafy vegetables avoid spraying foliar nitrogen fertilizer vegetable long-term spray nitrogen fertilizer solution, vegetables tender, good color, high yield. However, after nitrogen fertilizer is applied on the leaves, the ammonium ions can easily be converted into nitrate ions when exposed to air. The ions are directly absorbed by the leaf stomata, and the leafy vegetables have a shorter growing period, and the nitrate content in the leaves tends to increase exponentially. Therefore, it is best not to spray nitrogen fertilizer on foliar vegetables.