Effects of half-ridge planting on soil erosion in the Mollisol region of China

Half-ridge planting is a new soil and water conservation measure for sloping farmland. However, its effectiveness in controlling soil erosion remains unclear. In this study, half-ridge planting was monitored on-site in the field and simulated by designing soil bulk densities of contour ridges using soil pans (2.0 m long × 0.5 m wide × 0.5 m deep). Simulated rainfall (intensities of 75 mm h –1 and 100 mm h –1 ) and inflow (inflow rates of 1.25 L min –1 and 1.67 L min –1 ) experiments were conducted to study the effects of half-ridge planting on soil erosion, ridge morphology, and hydrodynamic characteristics under 5° and 7° slope gradients. The treatments with different soil bulk densities included all looseness (1.00 g cm –3 , Loose), upper looseness + lower compaction (1.00 and 1.20 g cm –3 , Loose-Compact), upper compaction + lower looseness (1.20 and 1.00 g cm –3 , Compact-Loose) and all compaction (1.20 g cm –3 , Compact). Field experiments revealed that corn root residue had soil-stabilizing capacity in both years. Compared with the Loose state, Compact-Loose and Compact states reduced soil erosion by 17.9–52.5% (from 4.03–7.89 to 1.92–6.05 t ha –1 ) in rainfall experiments. An exception occurred at 5° and 75 mm h –1 . All three configurations reduced soil erosion by 18.3–60.8% (from 0.46–1.24 to 0.21–0.91 t ha –1 ) in inflow experiments. Morphologically, these treatments maintained wider ridges and deeper, narrower furrows compared with the Loose treatment. Multivariate analyses ranked erosion susceptibility as Loose > Loose-Compact > Compact-Loose > Compact. Ridge morphology directly suppressed soil erosion and mediated the effects of rainfall intensity, whereas hydrodynamic parameters dominated runoff variation. In summary, optimizing soil bulk density configurations effectively mitigates soil erosion on contour ridges. This makes half-ridge planting a practical strategy for controlling erosion on sloping farmland with thin soil layers.