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Unclear soil layer coupling failure characteristics on natural grassland impeded the design and optimization of appropriate tillage tools. The coupling failure characteristics including surface disturbance and profile, disturbed cross-section area, soil over-turning rate, and coupling forces between the soil layer of natural grassland and selected passive subsoiler-type openers were investigated in this paper. Three single-shoot openers (i.e. CO, AO and WAO) and a test unit were designed, and furrow opening experiments under different working depths were conducted. Results showed that, along the passages, U-shaped disturbed cross-sections were usually created with soil-root clods overturned along the furrows. The roots were usually broken in a pulling or dragging way underground. Both disturbed cross-section area and draft force values increased with the working depth increasing linearly (R2≥0.93), contrary to the tendency of the specific draft force with the depth. Winged opener (i.e. WAO) had larger draft forces and disturbed soil layer cross-section areas than no-winged openers (i.e. AO and CO). The soil layer failure processes of the natural grassland were affected by its composite soil layer structure and the geometry parameters of the openers. The results provide original references for designing novel furrow openers applicable to improve degraded natural grassland.

Novel tillage tools with high working performance are desired in improving degraded natural grassland tillage system. This paper aimed to find the influence of various geometry structures of very narrow tines on related soil disturbance characteristics and tillage resistances. Four shank-type tillage tines with different cutting head shapes, and the test bench were designed and manufactured. Field experiments under different working depths were conducted. The working depth uniformity, soil over-turning rate, cross-section area of disturbed soil layer, and related forces were obtained, analysed, and compared. Results showed that, the working depth uniformities were above 70%, and soil overturning rates did not exceed 5%. Furrows with V-shaped cross-section were formed. The tine with an arc-shaped cutting edge (AT) obtained a lower draft force value, and the tine with chamfer structure (TTD) presented big differences on the draft force and soil disturbance compared to the tine with blunt cutting edge (TT). Both the draft force and the area of disturbed soil cross section had a good linear relationship with the working depth, and the specific draft force increased with the working depth increasing. Using a very narrow tine with chamfers to split and break the soil layer on the natural grassland without pulling or dragging the roots could be an appropriate tillage method applied for improving degraded natural grassland, but still need further surveys.