Study On Productive Features Of Annual Grass-legume Community In The Western Sichuan Plain

Sowing grass with legume plays important role reducing chemical N application,forage production cost and subsequently environmental stress in winter leisure land.The sowing ratios between grass and legume determined the potential for enhancement on the quantity and quality of forage.In this study,annual ryegrass?Lolium multifolum Lamk?was separately mixed with common vetch?Vicia sativa L.?,mutagenesis of burclover?Medicago polymorpha L.?and milk vetch?Astragalus sinicus L.?,with grass-legume rations of 100:0,75:25,50:50,25:75 and 0:100,and harvested for four times,respectively.The mixtures were evaluated from the aspects of field growth traits,forage nutrient quality,root morphology,soil available nutrients,soil enzyme activity and soil bacterial community structure and composition,to explore productive features of annual grass-legume community.The main results were as follows:1.The cumulative dry matter yield?DMP?,cumulative crude protein yield?CCPP?and cumulative digestible dry matter yield?CDDMP?were analyzed by DTOPSIS method.The dominant mixtures included HC₃?25%annual ryegrass+75%mutagenesis of burclover?,HJ₂?50%annual ryegrass+50%common vetch?,HC₂?50%annual ryegrass+50%mutagenesis of burclover?in the Western Sichuan Plain.Compared with single sowing with annual ryegrass,the dry material production,crude protein production and digestible dry material production increased by 12.28%to 14.43%,34%to 45.67%and10.41%to 18.76%,respectively.2.Grass/legume ratio had a significant effect on the root morphology of mixtures?P<0.05?.Compared with single sowing with annual ryegrass,root dry weight and root volume of mixtures decreased by 11.48%to 72.36%and 11.23%to 70.01%,respectively.Compared with single sowing with annual legume,the root dry weight and root volume of mixtures increased by 123.73%to 1341.67%and 53%to1431.71%,respectively.The root of mixtures with HC₁?75%annual ryegrass+25%mutagenesis of burclover?,HC₂,HC₃,HJ₂,and HZ₁ had strong competitive effects.Root dry weight was negatively?P<0.05?correlated to accumulative cumulative dry matter yield,cumulative crude protein yield and cumulative digestible dry matter yield.In addition,cumulative crude protein yield was negatively correlated to root area,root diameter and root vlume?P<0.05?.3.The concenations of organic matter,available nitrogenand available phosphorus from soils samples in mixtures with common veth and burclover were increased following the increase of legume ratios,and mixtures with HJ₂ and HC₃surstained more soil nutrients.However,the concentrations of organic matter content,available nitrogen and available phosphorus from soil samples in mixtures with milk vetch decreased following the increase of legume ratio and mixtures with HZ₁surstained most soil nutrients.In this situation,soil available P was negatively?P<0.01?correlated to root dry weight and root area;soil available K was negatively?P<0.05?correlated to root dry weight;both soil organic matter and avlabile N were negatively?P<0.05?correlated to root length and root tillers;both root volume and root diameter were negatively?P<0.05?correlated to soil available P and available K.4.Grass/legume ratio and cutting had significant effects on soil enzyme activity?P<0.05?.Both soil urease activity and soil nitric acid reductase activity firstly increased and then decreased following the increase of cut times.Soil acid protease activity gradually decreased.Soil nitiric acid reductase activity was positively?P<0.05?correlated to soil available P,but negatively?P<0.05?correlated to root dry weitht and root volume;soil urease activity was positively?P<0.05?correlated to soil organic matter,root dry weight,root diameter and root volume.5.A total of 276406 OTUs were obtained from soil samples in mixtures,with a similarity greater than 96%.The diversity index?Shannon?,the richness index?Chao1and ACE?and the PD whole tree diversity index?PD whole tree index?of soil samples were 8.82¹0.56,3836.69⁹250,3703.13⁹9.28.85 and 213.51³43.10,respectively.Legume ratios in mixtures had no significant effect on the soil bacterial alpha diversity index,but cutting had significant effect on the Chao 1 index and the PD whole tree diversity index?P<0.05?.Proteobacteria,Acidobacteria and Actinobacteria are dominant soil bacterial phyla in mixtures,with relative abundance of 59.1%⁶9.8%.The analysis of PCoA and NMDS showed that cutting?not grass/legume ratio?had significant effect on soil bacterial community structure?P<0.05?.Soil sample at the first,second and forth cut tended to gather together in mixtures,with high similarity of community structure.Generally,Sowing with annual ryegrass+legume was an effective measure in winter.It improved the yield and quality of forge,changed the root form,enhanced soil fertility and affected soil bacterial community structure.25%annual ryegrass+75%burclover,50%annual ryegrass+50%common vetch,50%annual ryegrass+50%burclover were the recommended mixutred in the Western Sichuan Plain,and the practice with three cutting times had best effects.