Abstract: Field experiments were conducted to investigate the changes in soil nitrogen forms and nitrate accumulation in vegetables under single and continuous applicatiof dicyandiamide (DCD).
The results showed that compared with the sole application of chemical fertilizer, during the long-term growth of cabbage, the single application of DCD increaseoil ammonium nitrogen content by 21.3%-339.4%, while soil nitrate nitrogen and vegetable nitrate contents decreased b4%-80.2% and 4.4%-58.3%, respectively; at the harvest of short-term leafy vegetable water spinach, soil ammonium nitrogen content incresed by 299.4%, while soil nitrate nitrogen and vegetable nitrate contents decreased by 26.2% and 31.7%, respectively.
In the "cabbage-sater spinach-radish cabbage" cropping system with continuous application of DCD, soil ammonium nitrogen, nitrate nitrogen, and vegetable nitrate contents all showed an accumulative tree soil ammonium nitrogen content under DCD application developed from slightly higher than the chemical fertilizer treatment (44.0%) to significantly higher than the chemical fertilizer treaent (392.5%, P<0.01); soil nitrate nitrogen content developed from significantly lower than the chemical fertilizer treatment (-68.2%, P<0.01) to santly higher than the chemical fertilizer treatment (146.6%, P<0.05); and vegetable nitrate content developed from significantly lower than the chemical fertilizer tratment (-30.2%, P<0.05) to significantly higher than the chemical fertilizer treatment (40.4%, P<0.01).
Therefore, the single apication of DCD can significantly reduce vegetable nitrate content, while the soil with continuous application of DCD can maintain a certain level of ammonium nitrogen, and these surplus ammonium nogen will be further converted into nitrate nitrogen remaining in the soil, which may pose a risk of vegetable nitrate accumulation.