Study On Mixed Sowing Mode Of Annual Grass-Legume Artificial Grassland And Yield Formation Mechanism In Alpine Region

In recent years,the natural grassland in the alpine pastoral area of the Qinghai-Tibet Plateau has been seriously degraded,the forage yield has decreased drastically due to various factors such as climate change and human activities,which not only hinder the development of local animal husbandry and the improvement of the living standards of herders,but also threaten the ecological function of the alpine ecosystem.Therefore,the establishment of artificial grassland in this area is an inevitable choice to alleviate the grazing pressure of grassland,increase the supply of forage,curb grassland degradation,and adhere to green development.At present,the most important artificial grassland in the alpine pastoral area is the mixed sowing of the annual leguminous plant common vetch and the gramineous oat,but the forage yield is still not high.At the same time,due to the different mixing modes(mixed sowing of species,ratio of grass-legume,sowing method and density),many researches of forage yield vary widely,and there are few studies on ecological mechanism in this region.So,it is of great theoretical and practical significance to further study the suitable mixed sowing mode for high-yield and high-quality forage in the alpine pastoral area of the Qinghai-Tibet Plateau.In this study,the annual leguminous plant common vetch,broad bean and oat in the alpine pastoral area were used,which mixed sowing by grass-legume on the yield.We analyzed the effects of different sowing modes on forage yield and quality,and then comprehensively evaluated the yield and quality of forage by Grey Relation Analysis.We also explained the formation mechanism of forage yield under different treatments from specific competition(group competition and individual functional traits strategy).In addition,the main factors affecting the total yield of forage under different mixed sowing species were also discussed.Our research found that the mixed species had a significant effect on the total yield.The total yield under the combination of oat+broad bean was about 50%higher than that of oat+common vetch,and the compatibility between the legume and grass was better.Both intra-specific competitions were greater than inter-species competitions,and the combination of oat and broad bean was significant,the result of competition was that leguminous forage limited the population expansion of grasses,and the combination of oat and common vetch was significant,which is related to slim stalk of common vetch that rely on oats to grow up.At the same time,the abundance,plant height and specific leaf area of grasses were significantly affected by the mixed species.The ratio of grass-legume had a significant effect on the total yield of mixed sowing and the optimum ratio varies according to the mixed species.The mixed effect of oat+common vetch combination is best at 7:3,and the oat+broad bean combination is at 80:2.And with the increase of the ratio of legume,its relative yield showed an increasing trend,but most of the individual traits did not show significant differences.The mixed method had no significant effect on the total output,but sowing in stripe was more advantageous,and had lesser inter-specific competition.The aboveground biomass,underground biomass and root dry weight of broad bean were also significantly larger than the spreading.Each treatment had no significant effect on soil physical and chemical properties.In addition,sowing density had no significant effect on the total yield and forage quality,and the ratio of the grass-legume had a significant effect on some of the quality.Through the Gray Relation Analysis and the actual comprehensive consideration,when the total density is 1000 grains/m~2,oats and broad beans are planted at 980:20(numbers of seeds),and the forage yield and overall quality performance are relatively high,the yield is 578.98 kg per mu,which is increased by 63.55%compared with oats unicast,and the sowing is simple and easy.It is suitable for local cultivation.The multivariate regression of mixed planting and traits showed that the plant height of common vetch and the specific leaf area of broad bean showed a significant positive linear relationship with the total mixed yield,indicating that legumes have a great influence on the productivity of annual grass-bean mixed grassland in alpine region,and the main environmental factors affecting total yield is illumination.