中文摘要：

豆科和禾本科混播草地是人工草地的主要建植方式之一,探究其间的产量表现和竞争作用,对于维持混播草地的稳定生产具有重要意义。以禾本科牧草柳枝稷和豆科牧草苜蓿为试验材料,按照不同种植密度进行混作盆栽控制试验,测定柳枝稷和苜蓿各生长特征指标的变化,以相对竞争指数（RCI）与相对总产量指数（RYT）揭示二者之间的竞争作用和混作产量表现。结果表明：不同种植密度和种植方式下柳枝稷和苜蓿株高变化不明显,即种内和种间竞争作用对株高的影响较小。柳枝稷的分蘖数和地上部分生物量随种植密度的加大持续降低,而相同种植密度下,二者在单作和混作处理下无显著差异（P〉0.05）,表明上述2个指标主要受种内竞争的作用。而柳枝稷的地下部生物量和苜蓿的茎粗、根粗、地上地下部生物量等指标同时受种内和种间竞争的约束,尤其是低、高密度混作时根冠比显著下降,表明柳枝稷和苜蓿的种间竞争主要体现在地下部分。柳枝稷RCI值在中低混作密度下均低,而苜蓿在各混作密度下均较高,表明苜蓿生长受到柳枝稷的抑制作用。柳枝稷与苜蓿混作虽然存在种间竞争作用,但在二者之间的互补效应下该模式可获得较高的生物量（RYT〉1）。上述结果可为优化人工草地栽培制度,提高牧草产量、土地利用率及维持草地生产力,提供新思路和参考。

英文摘要：

Legumes and grass mixed planting is one of the main patterns of pasture.To understand the yield performance and competition of mixed pasture is significant for maintaining its stabile productivity.Switchgrass（Panicum virgatum L.）and alfalfa（Medicago sativa L.）were mixed planting at different densities in this pot experiment.Growth indexes of switchgrass and alfalfa were measured.Relative competition indices（RCI）and relative yield totals（RYT）were calculated to assess the effects of competition and production when the two species mixed planting.The results showed that the height of switchgrass and alfalfa had insignificant differences among planting density and forms which indicated slight effect from intra-and interspecific competition.The tiller number and aboveground biomass of switchgrass were decreasing with increase of planting density,but had insignificant difference between monoculture and mixed planting treatment under the same planting density（P〉0.05）,showing that the above two indicators mainly affected by intraspecific competition.The belowground biomass of switchgrass,as well as stem diameter,root diameter,above-and belowground biomass of alfalfa were bounded by intraspecific and interspecific competition.Especially the root-shoot ratio of switchgrass and alfalfa,which dramatically decreased under low and high mixed planting density,indicated that the interspecific competition mainly impacted underground part of switchgrass and alfalfa.The RCI values of switchgrass were relatively small under low and medium mixed planting densities,while the RCI values of alfalfa were high under each density,suggesting that the growth of alfalfa was suppressed by switchgrass.Although there was interspecific competition between the two species in their mixtures,there was some degree of resource complimentarity（e.g.RYT〉1）.In conclusion,the results observed in the study should provide a new insight in optimizing the cultivation of artificial grasslands and facilitate prediction of biomass produ