Nitrogen (N) fixation by legumes and nitrogen transfer to cereals have been considered as important pathways for overyielding and higher N use efficiency in cereal/legume intercropping systems. However, the extent to which root morphology contributes to N fixation and transfer is unclear. A two-factorial greenhouse experiment was conducted to quantify the N fixation, transfer and root morphology characteristics of the maize/alfalfa intercropping system in two consecutive years using the ¹⁵N-urea leaf labeling method, and combining two N levels with three root separation techniques. N application could inhibit N fixation and transfer in a maize/alfalfa intercropping system. Irrespective of the N application level, compared with plastic sheet separation (PSS), no separation (NS) and nylon mesh separation (NNS) significantly increased the total biomass (36%) and total N content (28%), while the N fixation rate also sharply increased by 75 to 134%, and the amount of N transferred with no root barrier was 1.24–1.42 times greater than that with a mesh barrier. Redundancy analysis (RDA) showed that the crown root dry weight (CRDW) of maize and lateral root number (LRN) of alfalfa showed the strongest associations with N fixation and transfer. Our results highlight the importance of root contact for the enhancement of N fixation and transfer via changes in root morphology in maize/alfalfa intercropping systems, and the overyielding system was achieved via increases in maize growth, at the cost of smaller decreases in alfalfa biomass production.

豆类固氮 (N) 和向谷物转移氮被认为是谷物/豆类间作系统中超产和提高氮利用效率的重要途径。然而，根形态对固氮和转移的贡献程度尚不清楚。为了量化玉米/苜蓿间作系统连续两年的固氮、转移和根系形态特征，使用¹⁵N-尿素叶标记方法，结合两个N水平和三个根分离技术。施氮可抑制玉米/苜蓿间作系统中的氮固定和转移。无论施氮水平如何，与塑料片分离（PSS）相比，不分离（NS）和尼龙网分离（NNS）显着增加了总生物量（36%）和总氮含量（28%），而固氮率也急剧增加了 75% 到 134%，并且没有根障碍的 N 转移量是有网状障碍的 1.24-1.42 倍。冗余分析（RDA）表明，玉米的冠根干重（CRDW）和苜蓿的侧根数（LRN）与固氮和转移的关联最强。通过玉米/苜蓿间作系统根系形态的变化，而超产系统是通过增加玉米生长实现的，代价是苜蓿生物量产量的下降幅度较小。