氮素形态、用量及施用时期对小青菜产量和硝酸盐含量的影响

采用田间试验研究了氮素形态、用量及施用时期对小青菜产量和硝酸盐含量的影响。结果表明，等氮量施肥下，产量最高的是硝酸钙，尿素+微量元素处理；尿素，有机无机复混肥和碳酸氢铵处理间无显著差异，DMPP处理产量最低；追施微量元素能提高小青菜的产量。硝酸盐含量随着收获时期的延后而降低，有机无机复混肥处理则略有升高，但未达到显著水平；收获期取样时，不同氮肥对硝酸盐的积累是:硝酸钙＞DMPP＞尿素＞有机无机复混肥＞尿素+微量元素＞碳酸氢铵。配施微量元素及氮磷钾的协同吸收均能降低硝酸盐含量。综合考虑产量和品质指标，以有机无机复混肥处理效果较好。小青菜产量和Vc含量随着施氮量的提高而提高，但硝酸盐含量也随之提高；小青菜产量和Vc含量随着施氮时期的延后而降低，硝酸盐含量高峰出现在追肥后20d左右。

Effects of form, rate and time of N fertilizer application on yield and nitrate content of greengrocery

The effects of different types and application methods of N fertilizer on greengrocery (Brassica campestris L. ssp. Chinnesis) yield and nitrate content were investigated in a field experiment. Results showed that: ① At the same N fertilizer application rate, yield was highest with the Calcium nitrate and urea + micronutrient treatments. The yield difference among urea, organic-inorganic fertilizer mixture and ammonium bicarbonate treatments was not significant, and the DMPP （3，4-dimethylpyrazole phosphate）treatment had the lowest yield among the six treatments. Top-dressing of micronutrients could enhance yield. The nitrate content declined with harvesting time, except the organic-inorganic fertilizer mixture treatment. At harvesting, underground-plant samples from the six treatments showed the following order of nitrate accumulation ability: calcium nitrate> DMPP > urea> organic-inorganic fertilizer mixture >urea + micronutrients> ammonium bicarbonate. The synergistic absorption of N with P and K could reduce nitrate content in plants. Considering the yield and quality together, the organic-inorganic fertilizer mixture treatment would be the best; ② Greengrocery yield and Vc content increased with N fertilizer rate, so was nitrate content; ③ Greengrocery yield and Vc content declined as the fertilization time was delayed. The accumulation peak of nitrate content in plants is 20days after N fertilizer application.