Comparison of runoff and soil loss in different tillage systems in the Mollisol region of Northeast China

Longitudinal ridge tillage is the conventional tillage method in the cold, Mollisol region of Northeast China in which furrows are oriented up and down the slope. In part due to the use of this tillage system with large slope lengths, soil erosion is a serious problem in this region. Currently, it is unclear what the best tillage system and ridge orientation is for sustainable agriculture in this region. Thus to compare the runoff and soil loss in longitudinal (LRS) and contour ridge (CRS) systems to a flat tillage system (FTS), a series of simulated rainfall experiments were conducted. A large soil pan (8 m-long, 1.5 m-wide, and 0.6 m-deep) and a side sprinkler rainfall simulation system were used in this study with the three tillage systems (LRS, CRS, FTS) under three rainfall intensities (50, 75 and 100 mm h−1) at a 5° slope gradient. The results showed that runoff and soil loss in the LRS were larger than those in the CRS and FTS due to a shift in erosion pattern from sheet to concentrated flow erosion along furrows which led to shear stress increases. Contour ridge failures occurred in the 75 and 100 mm h−1 treatments by breaching of ridges when water stored in furrows exceeded their storage capacity. Breaching changed the runoff and soil loss by providing a large sediment source to the convergent flow. Water storage of CRS furrows was constant as rainfall intensity varied which led to overtopping during large storm conditions. Shifting conventional LRS to CRS with modifications to retain more rainwater during low to moderate rainfall events is highly recommended as this would reduce soil loss and enhance infiltration. The FTS exhibited the lowest runoff and soil loss which is recommended for the Mollisol region of Northeast China in large storm conditions.