| This paper selects Caijiachuan watershed as the research area which located in loess hilly gully region. There are various agroforestry systems in research area, but this paper chooses fruit-wheat intercropping as study object. According to study roots characters of young and old apple and apricot tree at the level trench on separated slope, it investigates the soil moisture and nutrition and analyses distribution law and fractal structureof root system and the research results are as follows:(1) From investigation during July and August, it showed that soil moisture content around apple and apricot descent with the decline of soil depth. The rainfall only can supply the surface layer of soil, because the rainfall was enough but it didn't last long time.The results also showed that apple trees use water in 60-100cm soil depth, and apricot trees use water in 80-100cm soil depth.(2) With analyzing soil nutrients, it showed that the amounts of soil available potassium and phosphorus were at normal level, but the content of total N and organic matter were at low level. So it is important to add nitrogen fertilizer artificially in order to improve soil fertilizer.(3) According to analyzing moisture content of root system, the results showed that moisture content of root system were affected by the age of fruit trees, so the moisture content of root system of young tree was higher than that of old tree. Then with the differences among the distribution of soil moisture content, the maximum and minimum moisture content of root system appeared at site B in gentle slope and site A in steep slope. But in different root diameters and soil depth, the moisture content of root system didn't appear obviously disparity.(4) The study results of distribution characters of apple root system showed that young apple trees roots can't distribute in the lower ridge of contour ditch, but it reached the 0.5H distance from the upper ridge of contour ditch and the 60-80cm soil layer. However, old apple trees roots grew every part of the level trench on separated slope, and existed at the 80-100cm soil layer. It is suggested that apple roots system will extend to each part of the land space, so its effect to crop will be obvious and will use the water and nutrition of deeper soil layer.(5) The study results of distribution characters of apple root system suggested that apricot trees roots mostly distributed at 20-40cm soil layer and the deepest layer is 80-100cm soil layer. It was found that absorbing roots mostly occurred at 0-20cm soil layer, but this phenomenon showed that apricot roots could not use the deep soil water and nutrition.(6) Based on the results of biomass of root system, the biomass of root system are concentrated in 40-60cm, 60-80cm soil depth. Meanwhile it is higher than that in gentle slope, and biomass of root system of young tree is lighter than that of old tree.(7) Studying on root fractal, it showed that fractal dimension of apple root is higher than that of apricot root. This appears that apple tree has much more absorbing root. Also results of fitting on is higher than that of apricot tree, so using the model of fractal model of root system biomass and DBH and Height of apple tree can accurately estimate the biomass of root system and provide theory for fruit-wheat intercropping system.
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