Experimental investigation of the spatial movement law of straw–root–soil complexes during slope contour rotational tillage operations based on the tracer method

Abstract

During contour rotary tillage on sloping terrain, the migration characteristics of the straw–root–soil complex directly affects the effectiveness of straw return and soil sustainability, but the underlying mechanisms remain unclear, hindering the development of specialized rotary tillage equipment. This study uses a self-developed bench test platform for rotary tillage on sloped terrain in hilly and mountainous regions and tracer method to systematically investigate the effects of slope gradient (5°, 10°, 15°), blade shaft rotational speed (200–300 r/min), forward farming speed (0.2–1.0 km/h), and straw content (0.4–1.2 kg/m²) on the migration characteristics of soil aggregates. The test results demonstrate that the forward farming speed is the most effective controllable parameter for suppressing the horizontal and lateral displacement of soil complexes. Increasing the speed from 0.2 km/h to 1.0 km/h can reduce the lateral displacement of straw by 65.3%. An increase in the rotational speed of the blade shaft intensifies the migration of the complex mass, with a notably increased displacement toward the downhill side under steep slope conditions (15°). The slope gradient is the dominant natural factor driving the asymmetric movement of the complex along the lower side of the slope. When the slope increases from 5° to 15°, the lateral displacement of the straw increases by 166%. Straw mulching effectively mitigates tillage-induced soil erosion. When the straw content increases from 0.4 kg/m² to 1.2 kg/m², the lateral soil displacement is reduced by 37.7% to 51.9%. Through orthogonal experiments and response surface analysis, the hierarchical order of the factors influencing soil complex transport was determined. In terms of soil lateral displacement, the primary influencing factor is the slope gradient. With respect to soil horizontal displacement, the dominant factor is the forward farming speed. Corresponding regression prediction models were developed. This study provides the first systematic evaluation of the transport mechanisms governing the straw–root–soil complex on sloped terrain under contour rotary tillage conditions, thereby establishing a theoretical foundation for designing specialized tillage equipment for hillside agriculture and performing quality control in the incorporation of crop residue.