Root distribution variation of crops under walnut-based intercropping systems in the Loess Plateau of China.

Efficient managing practices require an understanding of the root distribution of crop in walnut (Juglans regia)-crop intercropping systems, a field study was conducted in the Loess Plateau of China to examined the vertical distribution and horizontal variation of roots for soybean (Glycine max) and peanut (Arachis hypogaea) grown with walnut trees. Crop roots were sampled to 60 cm depth at five distances from the tree row using stratified digging method. The results showed that 72.7% of total root length density (RLD) for intercropped soybean distributed in the 0-10 cm soil layer and sole soybean roots in the first soil layer were determined to 54.3% of total RLD. The RLD of intercropped peanut primarily located in the 0-10 cm soil layer, reaching the average of 52.8 cm dm -3 for the five distances from the tree row. While the maximum RLD of 62.1 cm dm -3 for sole peanut was achieved in the 10-20 cm soil layer. The RLDs of both intercropped soybean and peanut increased with distance from the tree row, but the corresponding values at 1-1.5 m and 1.5-2 m from the tree row were significantly less than those at other distances. In addition, although the depths of root vertical barycenter (RVB) for both intercropped soybean and peanut tend to move downward with distance from the tree row, they were always shallower than sole soybean and peanut. Greater proximity to the tree row reduced crop roots and, furthermore, compelled crop roots to highly concentrate in the upper soil layer (0-10 cm), especially within the range of 1-2 m from the tree row.