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Taking natural root-soil composite of corn Shennong 46 as test material, cutting mechanical tests were carried out in the universal test machine and homemade pressure system around specimen. The results showed that moisture content was the key natural factor influencing ultimate shear stress, which increased with moisture content. The ultimate shear stress in vertical profile 20 mm away from root center was the largest, and the secondary was in vertical profile through root center. For vertical profiles more than 20 mm away from root center, the longer distance, the smaller ultimate shear stress. Combining with ridge-till specifications, reasonable cutting section for stubble-cutting disc was 40 cm away from ridge center. In the vertical section, the greatest shear stress existed at a depth of 20~60 mm from the surface of earth, was about 5.20~7.15 MPa. The maximum power was consumed in this depth range for rootstalk cutting mechanism.