Studies On Soil Phosphorus Transformation Characteristics And Rhizosphere Microecological Effects Of Rape / Common Vetch Intercropping System

Phosphorus is an essential nutrient element for crop growth.It is reported that 25%of the phosphorus absorbed by plants comes from fertilizer,but it is easy to be absorbed and fixed after the application of phosphate fertilizer,resulting in a decrease in fertilizer utilization and an increase in ineffective cumulative phosphorus.Therefore,how to fully tap the existing soil phosphorus pool resources has become the focus of attention.Rape（Brassica napus L.）and common vetch（Vicia sativa L.）are high quality forages,and both of them are phosphorus efficient crops.In this experiment,rape and common vetch were taken as the research objects to explore the forage quality,nutrient absorption and efficient phosphorus utilization of intercropping system under P0(0 kg·hm^-2),P1(45 kg·hm^-2)and P2(90 kg·hm^-2).Combined with pot experiments with different root separation methods,the changes of root configuration,root exudates and soil microecological environment were studied.1.Intercropping and application of phosphate fertilizer significantly increased the aboveground biomass and P1(45 kg·hm^-2)of rape（R）and common vetch（CV）.The fresh grass yield and hay yield of intercropping rape（IR）and intercropping common vetch（ICV）increased by 31.26%,33.46%and 10.80%,40.31%,respectively.The crude protein yield of IRCV-P1 treatment was 3.92%and 142.27%higher than that of rape and monoculture common vetch,respectively.The neutral detergent fiber of intercropping rapeseed at P1 and P2 levels decreased by 3.47%and 4.08%compared with that at the same phosphorus application level,and the acid detergent fiber content of intercropping rape at P1 level was significantly lower than that at P0 and P2 levels by 25%and 15.29%,respectively.The relative feed value of intercropping rape and common vetch was 8.15%and 7.09%higher at P1 and P2 levels than at P0 level,respectively.Phosphorus application promoted the absorption of nitrogen and phosphorus by crops,and the apparent recovery rate of phosphate fertilizer in rape was significantly higher than that in common vetch.The agronomic utilization efficiency of rape at P1(45 kg·hm^-2)level was significantly higher than that in common vetch,and the land equivalent ratio（LER）of intercropping treatment was more than 1,indicating that rape and common vetch intercropping had advantages.2.Fertilization increased the content of soil total phosphorus and available phosphorus,and the total phosphorus content of monoculture rape,monoculture common vetch and intercropping treatments at P2 level was significantly higher than that of P0 by 25.05%,38.85%and 24.96%,respectively.The content of available phosphorus in rape and common vetch intercropping treatment under P1 and P2 was significantly higher than that of P0 by33.39%and 19.14%.At the level of P1(45 kg·hm^-2),intercropping between rape and common vetch significantly increased the contents of Resin-Pi,Na HCO₃-Pi and Na HCO₃-Po in soil,and the content of 1M HCl-Pi,conc HCl-Pi,conc.HCl-Po decreased with the increase of planting years,indicating that intercropping improved the availability of phosphorus.Compared with CV and R,the soil bulk density of IRCV treatment decreased by 6.18%and 8.21%,respectively,and the soil p H of IRCV-P1 decreased by 0.29 units compared with P0,and the content of organic matter increased with the increase of fertilizer application,which was related to the good soil fertilization effect of rape and common vetch as green manure crops.3.The content of soil microbial biomass carbon,nitrogen and phosphorus increased with the increase of phosphorus application.The intercropping of rape and common vetch（IRCV）increased by 2.22%,17.35%,12.26%and 10.84%,21.05%and 33.71%,respectively,compared with the corresponding monoculture rape（R）and single cropping of common vetch（CV）under P0,P1 and P2 levels.The soil microbial biomass nitrogen content of IRCV-P1 treatment was 6.58%and 32.87%higher than that of IRCV-P2 and IRCV-P0,and 7.31%and 41.88%higher than that of R and CV at the same phosphorus application level,respectively.The phosphorus content of soil microbial biomass treated by IRCV was 39.96%,42.55%and 36.03%and 32.68%higher than that of R and CV at P0,P1 and P2 levels,respectively.The application of phosphate fertilizer had no significant effect on the activities of sucrase and urease.The relative abundance of Proteobacteria in the bacterial community treated with IRCV increased by 1.26%and 3.60%compared with R and CV treatment,which enhanced the potential of soil organic phosphorus mineralization,inorganic phosphorus dissolution and the availability of phosphorus.Phosphorus application reduced the relative abundance of Firmicutes,indicating that intercropping and phosphorus application could regulate the structure of soil microbial community.4.Phosphorus application increased the aboveground and underground biomass of rape and common vetch intercropping system.The fresh weight of stem and leaf of rape without separation treatment was significantly increased by 13.44%and 21.72%compared with nylon separation treatment and plastic separation treatment.At P0 and P45 levels,the fresh weight of rape without separation treatment（NB）was 16.38%,26.38%and 22.39%,32.26%higher than that of nylon separation treatment（MB）and plastic separation treatment（SB）,respectively.The root fresh weight of common vetch unseparated（NB）was significantly higher than that of MB and SB by 39.39%and 17.95%,respectively.Rape and common vetch intercropping improved the root configuration and promoted the transformation from moderately active phosphorus and stable phosphorus to active phosphorus in soil,and p H decreased after intercropping,which was related to the content of organic acid secreted by roots,increased the content of microbial biomass carbon,nitrogen and phosphorus in soil,and increased the relative abundance of eutrophic bacteria such as Proteobacteria,Actinobacteria and Chloroflexi.To sum up,intercropping between rape and common vetch improved soil physical and chemical properties,and then affected the change of phosphorus composition.In order to meet the phosphorus absorption of intercropping system,it changed the root configuration and stimulated the content of organic acids secreted by roots.intercropping improved the structure of soil microbial community,further affected the type and content of secreting organic acids,promoted the activation of insoluble phosphorus in soil,and improved the utilization efficiency of phosphate fertilizer.It promoted the increase of aboveground yield.