Abstract:This study investigated the effect of mixed planting ratio and planting method on the productivity and interspecific relationship of Elymus sibiricus and alfalfa in mixed planting system.The experiments included different planting ratios of E.sibiricus and alfalfa (2∶1,5∶2,3∶1,7∶2 and 4∶1,denoted by 1,2,3,4 and 5) and planting methods (inter line and same line,denoted by A,B).The number of branches/tillers,grass yield,relative density (RD),relative yield of population (RY),relative yield total (RYT) and interspecific competition rate (CR) of mixed grassland in the second year of establishment were measured.The influence of mixed seeding ratio and seeding method on the inter-species relationship was analyzed using gray correlation analysis.Furthermore,the optimal mixed planting ratio and planting method for mixed planting of E.sibiricus and alfalfa in the Loess Plateau were determined.The results showed that the annual grass yield of mixed grassland was the highest under treatment B1.For both the first cutting or the second cutting,the RYT was the highest in A3 (RYT＞1).The gray correlation analysis showed that the comprehensive population advantage of alfalfa was better under the alfalfa and E.sibiricus ratio of 1:2 than other ratios;the comprehensive population advantage of E.sibiricus was better with the E.sibiricus and alfalfa ratio of 1:4.The results suggest that the two mixed forages could avoid competition to a certain extent,and there could be niche separation.The results also showed that the competitiveness of alfalfa gradually decreased after the first mowing,and the competitiveness of E.sibiricus gradually increased.The optimal treatment was intercropping mixture with the alfalfa to E.sibiricus ratio of 1∶2 in the inter line.