Abstract: In order to explore the dynamic characteristics of nitrogen nutrition in legume/cereal intercropping at different growth stages and interspecific interaction, alfalfa and sweet sorghum simulated intercropping experiment of root separation in pot was carried out by using nutrient solution sand culture method. The nodulation and nitrogen fixation characteristics of alfalfa and nitrogen metabolism characteristics of alfalfa and sweet sorghum were investigated under different growth stages and root separation methods. The results showed that nodulation and nitrogen fixation characteristics of alfalfa at different growth stages were as follows: no separation>nylon mesh separation>plastic separation and monoculture. The activities of four nitrogen metabolizing enzymes in alfalfa monoculture were significantly higher than those in no barrier and nylon mesh separation at initial blooming stage(P < 0.05). The nitrogen metabolism characteristics of sweet sorghum were not separated at the initial flowering stage of alfalfa, which was significantly greater than that of sweet sorghum monoculture. Therefore, when the interspecific root system interaction between alfalfa and sweet sorghum is close, it is beneficial to the nodulation and nitrogen fixation of alfalfa, so as to strengthen the mutual feed utilization of nitrogen nutrition between alfalfa and sweet sorghum, and improve the nitrogen metabolism level of gramineous forage sweet sorghum. In addition, the mutual nitrogen feeding dynamics of alfalfa/sweet sorghum was increased with different growth stages.

Key words: Alfalfa, Sweet sorghum, Interspecific, Root separation pattern, Dynamic characteristics of nitrogen

摘要： 为探明豆/禾间作在不同生长阶段及种间互作的氮营养动态特征，本试验采用营养液砂培法进行了盆栽根系分隔模拟间作试验，通过根系分隔方式对紫花苜蓿(Medicago sativa)和甜高粱(Sorghum dochna)不同生育时期的氮代谢特性及紫花苜蓿结瘤固氮特性进行研究。结果表明：紫花苜蓿结瘤固氮特性在各生育时期下均表现为不分隔>尼龙网分隔>塑料分隔和单作；紫花苜蓿4个氮代谢酶活性在初花期时表现为紫花苜蓿单作显著大于不分隔和尼龙网分隔(P < 0.05)；甜高粱氮代谢特性均在紫花苜蓿初花期时均表现为不分隔显著大于甜高粱单作。因此，紫花苜蓿/甜高粱种间根系互作紧密时，有利于豆科牧草紫花苜蓿结瘤固氮，由此加强了紫花苜蓿/甜高粱种间氮营养的互馈利用，提高其中禾本科牧草甜高粱氮代谢水平。另外，紫花苜蓿/甜高粱在不同生长阶段种间氮营养互馈动态均表现为随着生长动态进程而增加。

关键词: 紫花苜蓿, 甜高粱, 种间, 根系分隔模式, 氮素动态特征