Response Of Yield And Quality Of Italian Ryegrass To Nitrogen Fertilizer And Microbial Fermentation Mechanism

In order to make full use of forage resources in southwest China,the production and quality of Italian ryegrass treated with three nitrogen levels(N1:150 kg/hm~2、N2:300kg/hm~2、N3:450 kg/hm~2)and five topdressing rates(A1:1:1:1、A2:1:2:0、A3:1.5:1.5:0、A4:2:1:0、A5:3:0:0)were investigated.At the same time,the bacterial community determined via Pac Bio single molecule,real-time sequencing technology(SMRT)and the fermentation characteristics of Italian ryegrass(IR,82%moisture)silage prepared with corn stover(CS)were investigated.A selected strain of Lactobacillus plantarum(L694)and a commercial inoculant stain of Lactobacillus plantarum(LP)were used as additives.The results shows as follow:1.The production and quality of Italian ryegrassThe plant height,SPAD and yield of Italian ryegrass were significantly increased with nitrogen fertilizer levels(P<0.05),and Italian ryegrass treated N2A2 had highest yield(P<0.05).The content of crude protein(CP)of Italian ryegrass was increased with the increase of nitrogen levels,whereas the acid detergent fiber(ADF)and neutral detergent fiber(NDF)content were decreased(P<0.05).In the same nitrogen level,the CP content of Italian ryegrass in first and third cutting were increased as nitrogen fertilizer increased.In second cutting,there was no significant difference of CP content between the topdressing rate of A2and A3,but both of which were significantly higher than those of others(P<0.05).The Italian ryegrass treated with A2 topdressing rate had lower fiber content(P<0.05).The content of nitrate were increased with the increase of nitrogen level(P<0.05).At 150kg/hm~2 pure N,the nitrate content of each topdressing rate reached the safe level;At 300kg/hm~2 pure N,the A1,A2 and A3 treatment had lower nitrate content;however,at 450kg/hm~2 pure N,the nitrate content of each topdressing rate exceeded 0.25%.2.Fermentation quality and bacterial community of silageLactic acid bacteria(LAB)effectively improved silage quality.Carnobacterium were the dominant genus in both forages before ensiling,while Lactobacillus were the prevalent genus in silages after 42 days of fermentation,and the relative abundance of Lactobacillus in LAB-inoculated silage was as high as 94.98%.Lactobacillus plantarum was the dominant species in IR+LP and IR+L694 treatments,which led to higher(P<0.05)lactic acid and lower(P<0.05)butyric acid production.Lactobacillus plantarum,Lactobacillus hammesii,Lactobacillus brevis,and Lactobacillus coryniformis were abundantly present in IR+CS+LP and IR+CS+L694 treatments,and acetic acid contents of these were higher(P<0.05)than those of other silages.Besides,the abundance of Lactobacillus coryniformis were exceeded3%in mixture silages,which had lower butyric acid content than that of Italian ryegrass silages.Thus,from yield,quality and the fertilizer cost consideration,the application level of300 kg/hm~2 pure N with the topdressing rate of 1:2:0 is better for Italian ryegrass.Addition of CS and LAB can change the microbial community and influence the silage fermentation of IR.