Study On The Competitive Ability Of Soybean In The Walnut-soybean Agroforest Systems Based On SPAD

Shi Guangyao ABSTRACT: The object of agroforestry is to reduce interspecies competition and increase mutualism through ecological principles.Interspecific competition ability is an important index to explain interspecific relationship.Competitive ability is often used to represent crop growth status in composite mode.In this study,the 5-year-old walnut soybean complex system low hilly area in North China was taken as an example.The analysis of chlorophyll content,SPAD,plant height,breast diameter and photosynthetic effective radiation of soybean leaves was used to study the spatial and temporal distribution characteristics of the interspecific competition relationship of walnut soybean composite system,and to understand the growth status of soybean under the agroforestry model,and it provide theoretical basis for model optimization and regulation of management.The main results are as follows:1.The leaf area index of walnut in the intercropping pattern showed a tendency of increasing firstly,and decreasing from July to September.During the experiment perid of walnut was in the order of August(1.86)> July(1.69)> September(1.50)respectively.2.Through the correlation analysis of SPAD and chlorophyll content of soybean leaves,SPAD and chlorophyll content had a very significant positive correlation,which further verified the feasibility of SPAD instead of traditional method to determine chlorophyll content.3.Through the analysis of the correlation between chlorophyll,plant height and breast diameter of soybean leaves,both of them have reached a significant level.Therefore,the change of chlorophyll can be used to reflect the change of plant height and the diameter of the breast,thus it can reflect the variation of biomass.4.In the spatial distribution of soybean sprout period,the SPAD of soybean was basically maintained at the same level.In the leaf spreading period,the trend of the general trend of soybean in the leaf spreading period was " double peak".At the exit stage,the SPAD of soybean achieved a certain extent,but the rising degree slowed down.The SPAD in the flowering period of soybean tended to be stable,and the SPAD in the pod period of soybean showed a downward trend.5.The photosynthetic active radiation of walnut-soybean composite model showed a "single peak" trend,the whole growing season of soybean under the forest space(range from 0.5 m of walnut tree)was a competitive disadvantage,the growth was inhibited and the photosynthetic active radiation was between 350-400 W/m2,and the tree margin space(range from 0.5-1.5 m of walnut tree),the competitive advantage of soybean was obvious.In the process,the competitive advantage is occupied,indicating that the region is the most suitable for the soybean,at the first gradient of competitive advantage,the photosynthetic effective radiation is between 450-500 W/m2,the space of the tree(range of walnut tree 1.5-2.5 m)is located at the second gradient of competitive advantage,and the photosynthetically effective radiation is between 650-700 W/m2.