| The interspecific relationship is a key issue in theoretical researches and production practices in agroforestry system, it determines the functions and benefits of agroforestry system. However, some questions and problems in the current studies of the interspecific relationship, lacked systematic analysis for spatial and temporal distribution simulation of solar radiation under canopy, unclarified and unqualified effects of solar radiation under canopy on crops, severely restrict the researches and regulations of interspecific relationship coupling of water, nutrients, light and other factors together. Against the key scientific issue in this field, this study takes typical economic trees and crop in the Loess Plateau, apple trees (Malus pumila) and soybean (Glycine max), as research objects, will focus on building canopy projection model of single apple tree according to projected geometry and deriving crowns projection of apple trees and its movement trajectory to analyze the spatial and temporal dynamic of scope of canopy shade, simulating solar radiation intensity under trees to analyze the spatial and temporal dynamic of intensity of canopy shade, clarifying and quantifying the influences of shading on crops by establishing mathematic relation between crops’productivity and solar radiation and other microclimatic factors and analyzing economic benefits of soybean, determining the appropriate intercropping area for soybean under apple trees by means of above results, based on monitoring form and structure of canopy, solar radiation and other microclimatic factors and crops’growth, productivity and economic benefits. Details were listed as followed:(1) For the shading scope of apple trees, a theoretical model was developed in the rectangular plane coordinate system, which took canopy shape, tree height, height below branch, canopy radius, longitude, latitude, altitude, solar altitude, solar azimuth, date and time into account to describe coordinate position and shadow boundary of canopy of single apple tree:as 0≤h<β, canopy projection was oval model; as β≤h< α, canopy projection was model of combining graphic of oval and circular; as α≤h<90, canopy projection was circular model. The model was based on the apparent motion rules of the sun, geometrical optics theory. The precision and error sources of model was analyzed after eliminating penumbral effect of tree-shading, this model showed a quite effective in simulating the canopy projection.Shading scopes of 4-year-old and 6-year-old apple trees were strip areas. In 08:00 and 16:00 of day, the shading area was repeated shading by adjacent trees distributed in 1.2-1.4m from the tree row under 4-year-old apple trees at grain filling stage of soybean,0.6-1.lm from the tree row under 6-year-old apple trees at seeding stage of soybean,0.7-1.lm from the tree row under 6-year-old apple trees at flowering stage of soybean, 1-2.2m from the tree row under 6-year-old apple trees at grain filling stage of soybean. The shading strip ranged from 0.7m south of the tree row to 1.5m north of the tree row for 4-year-old apple trees and from 1.2m south of the tree row to 2m north of the tree row for 6-year-old apple trees at seeding stage of soybean, ranged from 0.8m south of the tree row to 1.6m north of the tree row for 4-year-old apple trees and from 1.3m south of the tree row to 2.1m north of the tree row for 6-year-old apple trees at flowering stage of soybean, ranged from 0.6m south of the tree row to 1.9m north of the tree row for 4-year-old apple trees and from lm south of the tree row to 2.5m north of the tree row for 6-year-old apple trees at grain filling stage of soybean.(2) For the shading intensity of apple trees, the models of direct and diffuse of absorbed photosynthetically active radiation (PAR) under apple trees were established respectively. The results of simulation test showed that the precisions between the accumulative total of measured values and calculated of direct and diffuse radiation at different time has a high simulating precision.The closer the distance from the tree, the stronger the shading intensity, and shading area under 6-year-old apple trees had a stronger shading intensity than under 4-year-old apple trees. The shading intensity had a smooth variation between trees in the same row and a sharp variation between tree rows, resulting that the shading intensity of the north of trees was stronger than the south.(3) For the influences of shading on soybean, the effects of intercepted light, dropped temperature and increased humidity, and the comprehensive effect of microclimate of the intercropping systems are gradually strong with the increase of shading intensity. Photosynthetic characteristics, water use efficiency, biological characteristics and productivity of soybean were reduced by shading, but content of chlorophy II in leaves and leaf area index were increased within 50% shading. The PAR were most for net photosynthetic rate (Pn) and yield of soybean compared to other factors of microclimate, and its contribution rate on Pn and yield reached 58.9% and 60.9% respectively. Economic benefits of soybean were decreased with the increasing of shading intensity, and occurred deficit when shading intensity was more than 61%.(4) The technique of spatial configuration and structure of apple-soybean intercropping systems based on light environment was designed. The model of boundary of canopy projection and the models of direct and diffuse of absorbed PAR under apple trees was applied to calculate shading scope and shading time and daily and growing seasonally accumulative radiation in this design. And then, integrated with light adaptability of soybean, grade separation of shading scope and intensity was divided, the appropriate intercropping area for soybean were determined based on above results: anywhere under 4-year-old apple trees was suitable for intercropping soybean, the area from 0.3 south to 0.5 north of the tree row was not favorable for intercropping soybean. |
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