Effect of applying fertilizer on nitrate accumulation in vegetables

The nitrate content in vegetables in Fuzhou City was studied in this experiment．The results show that the content of nitrate in vegetables are between 59．5 and 3743．1 mg／kg under the condition of common applying fertilizers．The order of nitrate content in defferent vegetables is leaf vegetable> Chinese cabbage>onion> rhizome> melon>bean>eggplant．According to the evaluation standard of WHO／FAO，the nitrate content of leaf vegetable，Chinese cabbage，and onion exceed the quota．Under the condition of applying pure nitrogen of 450 kg／hm²．85％ nitrate accumulated in vegetables comes from nitrogen fertilizers，the contributive order of different kinds of nitrogen fertilizers to nitrate accumulated in vegetables is NH₄NO₃>NH₄HCO₃>CO(NH₂)₂>(NH₄)₂SO₄>NH₄C1．The doses and ways of applying nitrogen fertilizers are greatly relative to nitrate accumulated in vegetables．On the one hand，the positive relations are shown on applying nitrogen fertilizers and negativity one are shown on applying dicyan diamide．At the same dose of nitrogen fertilizers applied，the nitrate accumulated in vegetables is decreased with the reducing of the amount of base manure and in crea sing of the addition manure，and applying organic fertilizers cooperated may reduce the nitrate content in vegetable．With the results of the above statements，the following countermeasures are put forward including regulating breeds of vegetable and structures of fertilizer；adding proper dicyandiamide and preventing from applying exceeding amount of nitrogen fertilizers；applying high ratio nitrogen fertilizers in early stage，and low ratio nitrogen fertilizers in middle and late stages．