通过盆栽试验，采用随机区组设计和根系分隔技术研究了施氮和根系分隔方式对玉米/紫花苜蓿间作体系中紫花苜蓿根系形态和固氮能力的影响，为玉米/紫花苜蓿间作体系氮素管理和化肥减量增效提供科学依据。结果表明，施氮能增加紫花苜蓿不同茎级根长、根表面积、根体积，增幅分别为22.4%、18.4%、16.9%；降低根瘤数、根瘤干质量、固氮率、固氮量、豆血红蛋白含量，降幅分别为33.8%、64.5%、29.4%、17.0%、55.4%。在不施氮条件下，与塑料板分隔（PSS）处理相比，根系不分隔（NS）和根系尼龙网分隔（NNS）处理紫花苜蓿不同茎级的根长、根表面积、根体积分别降低 26.1%、29.1%、36.9%和13.6%、12.9%、23.5%，根瘤数、根瘤干质量、固氮率、固氮量、豆血红蛋白含量分别增加69.5%、76.4%、148.2%、52.9%、73.3%和49.3%、61.4%、66.0%、41.9%、43.3%；与NNS处理相比，NS处理使紫花苜蓿不同茎级的根长、根表面积、根体积分别降低14.0%、18.8%、19.5%，根瘤数、根瘤干质量、固氮率、固氮量、豆血红蛋白含量分别增加13.5%、9.3%、49.5%、7.8%、20.9%。在施氮条件下，与PSS处理相比，NS和NNS处理紫花苜蓿不同茎级的根长、根表面积、根体积分别降低 23.9%、28.3%、32.3%和12.6%、15.3%、23.5%，根瘤数、根瘤干质量、固氮率、固氮量、豆血红蛋白含量分别增加45.5%、97.6%、105.5%、30.0%、42.6%和42.8%、45.5%、58.6%、26.2%、18.2%；与NNS处理相比，NS处理使紫花苜蓿不同茎级的根长、根表面积、根体积分别降低12.9%、15.4%、18.1%，根瘤数、根瘤干质量、固氮率、固氮量、豆血红蛋白含量分别增加1.9%、35.8%、29.6%、2.9%、20.7%。综上，施氮和根系分隔均会促进玉米/紫花苜蓿间作体系中紫花苜蓿不同茎级根系的生长，但会抑制紫花苜蓿的固氮能力。

In this study,pot experiments were conducted to study the effects of nitrogen application levels and root separation patterns on the root morphology and nitrogen fixation ability of alfalfa in the maize/alfalfa intercropping system using random block design and root separation technology,so as to provide a scientific basis for reduction and efficiency enhancement of chemical fertilizer in the maize/alfalfa intercropping system. The results showed that nitrogen application increased the root length,root surface area and root volume of the alfalfa at different diameter-class by 22.4%, 18.4% and 16.9%, but decreased the number of nodules,dry weight of the nodules,the rate of nitrogen fixation,fixed amount and the leghemoglobin content by 33.8%, 64.5%, 29.4%, 17.0% and 55.4% respectively.Under no nitrogen fertilizer(N0) treatments, compared with plastic sheet separation (PSS) treatment, the root length,root surface area and root volume of alfalfa at different diameter-class of no separation(NS) and nylon net separation (NNS)treatments were reduced by 26.1%,29.1%,36.9% and 13.6%,12.9%,23.5%,and the number of root nodules,dry weight of root nodules,nitrogen fixation rate,fixed amount and the content of leghemoglobin of NS and NNS treatments were increased by 69.5%,76.4%,148.2%,52.9%,73.3% and 49.3%,61.4%,66.0%,41.9%,43.3%,respectively;Compared with the NNS treatment,the root length,root surface area and root volume of alfalfa at different diameter-class of NS treatment were reduced by 14.0%,18.8% and 19.5%,and the number of alfalfa nodule,dry nodule weight,nitrogen fixation rate, fixed amount and the content of leghemoglobin of NS treatment were increased by 13.5%,9.3%,49.5%,7.8% and 20.9%respectively.Under nitrogen fertilizer (N1) application treatment,compared with PSS treatment,the root length,root surface area and root volume of alfalfa at different diameter-class of NS and NNS treatments were reduced by 23.9%,28.3%,32.3% and 12.6%,15.3%,23.5%,and the number of root nodules,dry weight of root nodules,nitrogen fixation rate,fixed amount and the content of leghemoglobin of NS and NNS treatments were increased by 45.5%,97.6%,105.5%,30.0%,42.6% and 42.8%,45.5%,58.6%,26.2%,18.1%,respectively;Compared with the NNS treatment,the root length,root surface area and root volume of alfalfa at different diameterclass of NS treatment were reduced by 12.9%,15.4% and 18.1%,and the number of alfalfa nodule,dry nodule weight,nitrogen fixation rate,fixed amount and the content of leghemoglobin of NS treatment were increased by 1.9%,35.8%,29.6%,2.9% and 20.7%,respectively.Therefore,both nitrogen application and root separation promote the growth of root at different diameter-class in the maize/alfalfa intercropping system,while inhibite the nitrogen-fixing ability of alfalfa.