In order to form a solid basis for an effective fertilization mode in saline-alkali soils,a field experiment was conducted to determine the effects of different levels of nitrogen on soil microoganisms and sunflower yield in Hetao Irrigation District in Inner Mongolia.Six treatments were designed including five nitrogen fertilizer levels,viz.,75 kg·hm-2(N1),150 kg· hm-2(N2),225 kg· hm-2(N3),300 kg· hm-2(N4),375 kg· hm-2 (N5) and a control (CK).The results indicated that:(1) Applying nitrogen fertilizer could significantly increase the number of microorganisms and the diversity of flora in the root zone.The order of soil microorganisms at 0 ～ 20 cm soil depth arranged was N4 ＞ N3 ＞ N5 ＞ N2 ＞ N1 ＞ CK.(2) Applying nitrogen fertilizer could promote the growing and development of sunflower as well as yield.The growth vigor and dry matter of sunflower increased gradually and yield varied parabohcally with nitrogen application rates.Therefore,the yield of five nitrogen fertilizer levels treatments were higher than CK by 0.06％,36.27％,61.95％,105.36％ and 85.03％,respectively.(3) Appropriate nitrogen application rate could reduce soil salinity of 0 ～ 40 cm depth.After harvest,the order of salt accumulation arranged was N2 ＞ CK ＞ N5 ＞ N3 ＞ N1 ＞ N4.(4) There is a significant positive correlation between the numbers of soil microorganisms,advantage bacteria flora and nitrogen application,root dry matter.However,there is a significant negative correlation between the numbers of soil microorganisms,advantage bacteria flora and soil salt content,salt accumulation.In summary,the appropriate nitrogen application rate is 300 kg·hm-2 for sunflower on the moderate saline-alkali soils in Hetao Irrigation District in Inner Mongolia.%在内蒙古河套灌区盐碱食葵田进行大田试验,以不施氮肥为对照(CK),设置了75 kg· hm-2(N1)、150kg·hm-2(N2)、225 kg·hm-2(N3)、300 kg·hm-2(N4)、375 kg·hm-2(N5)五个氮肥施用水平,研究了不同氮肥施用量对土壤微生物区系和食葵产量的影响.结果表明:(1)盐碱地施用氮肥可提高土壤微生物数量和细菌优势菌菌群多样性,各处理0～20 cm土层根区土壤微生物数量大小顺序为N4＞ N3＞ N5＞ N2＞ N1＞ CK,各施肥处理较CK差异极显著(P＜0.01);(2)盐碱地施用氮肥可促进食葵生长发育,提高产量,随氮肥施用量由低到高,食葵长势和干物质积累呈逐渐增加趋势,产量与施氮量呈抛物线型关系,各处理产量分别较CK提高0.06％、36.27％、61.95％、105.36％和85.03％;(3)适量施氮可抑制土壤积盐,食葵收获后,各处理积盐量大小顺序为N2＞ CK＞ N5＞ N3＞ N1＞N4;(4)土壤微生物的数量和优势茵菌群数与氮肥施用量、食葵根干重呈正相关关系,与土壤含盐量和积盐量呈负相关关系.综合试验结果,内蒙古河套灌区中度盐碱地食葵生产中氮肥适宜施用量为300 kg·hm-2.
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