低量施氮对小青菜生长和氮素损失的影响

采用田间试验和微区试验相结合,研究了低量施氮对小青菜(Brassica.chinensis)产量、氮肥利用率和氮素损失的影响,其中氮素总损失用15N示踪法测定,氨挥发用通气密闭室法测定,反硝化损失用乙炔抑制-原状土柱培养法测定,不加乙炔测定N2O排放。结果表明,施用氮肥显著增加了小青菜的产量和吸氮量,在75和150kg/hm2氮肥水平下,氮肥利用率分别为46.8%和39.4%。由于试验地土壤pH低(5.38),各处理的氨挥发均很低且差异不大,施用氮肥没有增加氨挥发。试验地土壤反硝化损失和N2O排放量较高,分别为N4.34kg/hm2/sup和N2.65kg/hm2,施用氮肥没有增加反硝化损失和N2O排放,表明氮源不是反硝化作用的限制因子。在N75和150kg/hm2两个施氮水平下,氮素回收率分别为103%和91.3%,并且土壤残留氮主要累积在020cm土层,表明肥料氮损失很少,这与氨挥发、反硝化损失较低的结果相吻合。

Effects of low rate nitrogen application on Brassica chinensis growth and N losses

Understanding N-cycling in the soil-plant-atmosphere system is essential to maximize nitrogen use efficiency (NUE) and optimize nitrogen budget for crop production. Most researches on N loss and its environmental consequence mainly focused on the soil cultivated with field crop, however, few researches were carried out on the vegetable field. This study aimed to the effects of N fertilization on the fate of nitrogen and green cabbage (Brassica chinensis) growth. A field and a microplot experiment were combined to investigate the changes of green cabbage yield, NUE and nitrogen losses subjected to a low rate application of N fertilize. Labeled ()~(15)N technique, enclosure method, and acetylene inhibition-soil core incubation technique were used to measure total nitrogen loss, ammonia volatilization, denitrification loss and nitrous oxide emission, respectively. Results showed that yield and N uptake capacity of green cabbage increased significantly due to the application of nitrogen fertilizer. NUE was 46.8% and 39.4% at rate of N 75 and 150 kg/ha, respectively. The increase of ammonia volatilization was negligible mainly due to low soil pH (5.38). Denitrification loss(N 4.34 kg/ha)and N_2O emission (N 2.65 kg/ha) in the soil without nitrogen supply were rather high, and it was not affected by the application of nitrogen. Total recovery of applied N at rate of 75 and 150 kg N/ha was 103% and 91.3%, respectively. The majority of residue ()~(15)N concentrated on 0-20cm layer, indicating fertilizer nitrogen losses were small, which coincided with the results of low ammonia volatilization and denitrification losses.