The Effects On The Growth Of Soybean By Simulation Of Shading In Apple-Soybean Intercropping System In Loess Region Of Western Shanxi Province

Fruit-crop-intercropping is one of the typical models in agroforestry systems in loess region of west Shanxi.Soybean is a common crop which farmers adopt to plant under the fruit. Competition for light in this system would influence the growth of soybean which is atypical kind of short-day crop which favors temperate weather. In order to explore the influence mechanism of low-light stress on soybean growth, this study investigated the effects of different light intensities on photosynthetic characteristics and yield characters of soybean during each key phonological period by four kinds of light treatment.(Transmittance was CK (100%), T1(70%), T2(50%) and T3(30%) respectively.) The main results are as follows:1. Microclimate was obviously changed after shading. With the decrease of light intensity, there was a decreasing trend in photosynthesis active radiation, near-surface air temperature and ground temperature. And air relative humidity increased at the same time. It could be concluded that shading can decrease temperature and photosynthesis active radiation and increase humidity.2. Shading treatment influenced soybean photosynthetic characteristics. With the decrease of light intensity, content of chlorophyll in leaves and soil water content increased while net photosynthetic rate, Transpiration Rate and water use efficiency all decreased. Light compensation point and light saturation point decreased as well. It suggested that this kind of soybean could tolerant shade. Leaf stomatal conductance decreased after shading but intercellular CO2concentration increased. It can be inferred that non-stomatal limitation resulted in decrease of crop photosynthetic rate.3. Stem-leaf biomass and yield of soybean were influenced by low light. Soybean height, the stem-leaf biomass and leaf area index increase and later decrease with the increase of shading degree. When transmittance was lower than50%, both soybean growth and the above-ground biomass decreased obviously. It indicated that this kind of soybean could adapt to low light environment but over shading would inhibit plant growth. Leaf height, specific leaf weight and yield of soybean decreased evidently after shading. It illustrated that low light could weaken soybean productivity and the weakening effects were more obvious than crop adaptability.The result showed that the decrease of net photosynthesis rate of bean directly caused decline of bean production.While the main factor that brought out the decrease of net photosynthesis rate turn out to be the weakening of photosynthetically active radiation after shading.