Soil-bin experiment on effects of contour ridge tillage for controlling hillslope soil erosion in black soil region

Abstract: Ridge tillage is the most common tillage method in Mollisol region of Northeast China, and contour ridge tillage is one of the practices to promote soil and water conservation on the farmland. However, the effects of contour ridge tillage for controlling hillslope soil erosion and its erosion process under different rainfall intensities have not been fully investigated. Studying the hillslope soil erosion controlling effects of contour ridge can provide basic information for designing hillslope soil conservation practices. A simulated rainfall experiment was designed to study the effects of contour ridge tillage for controlling hillslope soil erosion in balck soil region of northeast China, three rainfall intensities (50, 75 and 100 mm/h), one slope gradient (5°), two surface treatments of contour ridge tillage and flat tillage were conducted, and a soil box with 8 m long and 3 m wide was used in this study. The results showed that contour ridge tillage has a significant effect on erosion prevention under rainfall intensity of 50 mm/h, and there was almost no runoff and soil loss compared with flat hillslope. In 75 and 100 mm/h treatments, the runoff and soil loss processes on contour ridge hillslope obviously had abrupt changes before and after the ridge failure. Compared with the flat tillage hillslope, before contour ridges failure, the contour ridge tillage reduced more than 97.7% of runoff and soil loss, runoff intensities and erosion rates were 0.01 - 0.06 times and 0.01 - 0.02 times lower than that of flat hillslope, respectively, and water storage capacities for contour ridge hillslope under three rainfall intensities were greater than 97.2%, which indicated that contour ridge tillage had a satisfactory effect for controlling hillslope soil erosion. However, when contour ridges failure occurred, soil loss greatly increased and correspondingly effects of contour ridge tillage for controlling hillslope sharply decreased. Hillslope soil loss was closely responding to runoff rate after ridges failure. The runoff and soil loss after ridges failure increased by 23.3- 25.9 and 136.8-171.5 times than that before ridges failure, respectively; and water storage capacity respectively decreased 50% and 10% under 75 and 100 mm/h rainfall intensities, while soil loss increased by 63.7% and 35.8%. Hillslope soil loss of the treatment with contour ridge tillage was 2.7 - 3.6 times higher than the flat tillage under the rainfall intensities of 75 and 100 mm/h. Contour ridge tillage might have a better effects for controlling hillslope soil erosion under the rainfall intensities less than 50 mm/h, but contour ridges failure occurred frequently under the high rainfall intensities, resulting in a dramatic decrease of the erosion control effect. Although ridge failure occurred under large rainfall intensity treatments, the water volume intercepted (including infiltration and impoundment) was still remarkable. It was found that the ridge stability improved in wide-ridge tillage system in field survey, and the popularization of the wide-ridge tillage was expected to further improve the effect of erosion control. Therefore, the future work should be focused on the improvement of contour ridge tillage to better control the hillslope erosion in Mollisol region of northeast China, and more research should be conducted on contour ridges failure to better understand and predict this process in ridge tillage systems of the balck soil region.