| As an important grain production base in China, northeastern mollisol region plays a decisive role to ensure national food security. Due to unreasonable farmland management measures, severe soil erosion happened in the area, the average black soil layer thickness has decreased from 60–80 cm in the 1950 s to the present 20–40 cm, making a great threat to national food security. So, based on the simulated rainfall experiments, 20 treatments were designed, including three tillage measures(longitudinal ridge, horizon ridge and non–ridge tillage), 3 kinds of rainfall intensity(50, 75, 100 mm h–1), five different rain patterns(intensive type: rainfall intensity distribution was 50–75–100–125 mm h–1, reduced type: rainfall intensity distribution was 125–100–75–50 mm h–1, peak type: rainfall intensity distribution was 50–75–100–125–100–75–50 mm h–1, valley type: rainfall intensity distribution was 100–75–50–75–100 mm h–1, uniform type: rainfall intensity was 75 mm h–1), and one slope(5o which was the critical slope gradient of changing longitudinal ridge to horizon ridge), This paper analysised the the influence of different tillage measures on slope surface erosion process under different rainfall intensity and rainfall patterns, in order to provide scientific basis for prevention and control of slope erosion in mollisol region. Following conclusion was obetained:1. Non–ridge tillage slope soil erosion process was exhibited. When the rainfall intensity increase from 50 mm h–1 to 75 mm h–1 and from 75 mm h–1 to 100 mm h–1, non–ridge tillage slope runoff increased by 68.2% and 84.6% respectively, while hillslope erosion increased by 83.8% and 243.7% respectively. No obvious rainfall patterns impact on hillslope runoff was found, but rainfall patterns had significant influence on the hillslope erosion. The total soil loss was in the order of reduced type > intensive type > uniform type, the total soil loss in uniform type treatment was 37.36% of it in intensive type treatmemnt and 42.74% of it in reduced type treatment.2. Investigated the impact of longitude ridge on slope soil erosion process in different rainfall intensities and rainfall patterns. The result showed that hillslope runoff volume and soil loss increased with the increasing of rainfall intensity. Compared with the non–ridge tillage slope, runoff volume and total soil loss on the longitudinal ridge slope increased 1.2–1.7 times and 1.3–2.1 times respectively. Runoff intensity, erosion rate as well as sediment concentration in stable stage was 2.1–2.4 times, 4.5–5.2 times and 5.2–2.0 times higher than non–ridge tillage slope. No obvious rainfall patterns impact on hillslope runoff was found, but rainfall patterns have significant influence on the hillslope erosion. Total runoff of each rainfall pattern was in the order of intensive type > uniform type > peak type > reduced type > valley type, while the total soil loss was in the order of peak type > valley type > reduced type > uniform type > intensive type. Except for 125 mm h–1 rainfall intensity, rainfall intensity occurred at the initial stage of the rainfall pattern contributed more to total soil loss than the same rainfall intensity appeared at the middle stage and the end stage. Overland flow collection impact of longitude ridge increased runoff velocity, and erosion pattern was changed from sheet erosion dominated to rill erosion dominated, which caused more soil loss.3. This paper discussed the hillslope soil erosion processes before and after the broken of horizon ridge. When rainfall intensity was 50 mm h–1 and precipitation was 37.5 mm, horizon ridge slope runoff intensity and slope erosion rate decreased by 97.6% and 99.7%, respectively, showing great erosion control effect of the horizon ridge. When rainfall intensity was 75 and 100 mm h–1, horizon ridge was broken when accumulated precipitation was 32.5 and 36.6 mm, indicating that horizon ridge with 15 cm high and 65 cm distance can intercept 35.5 mm preicipitaion in extream erosive rainfall condition. And befor horizon ridge was broken, slope runoff intensity and erosion rate decreased by 98% and 97%.While after horizon ridge was broken, slope surface erosion rate increased sharply, its value increased by 13.2–25.6 times compared with non–ridge tillage slope. Total runoff of each rainfall pattern was in the order of reduced type > uniform type > intensive type, runoff volume in intensive type treatment was 64.4% of it in uniform type treatment, while runoff volume in reduce type treatment was 1.2 times of it in uniform type. Total soil loss was in the order of uniform type > reduced type > intensive type. Total soil loss in uniform type treatment was 2.1 times and 1.5 times of it in intensive type and reduce type. In the extream erosive rainfall condition, when runoff volume generated from rainfall exceeded the water storage capacity of horizon ridge, it would be broken, and then erosion pattern was changed from splash and sheet erosion dominated to rill erosion dominated, which caused more sediment yield. So, great attention should be paid to the selection of reasonable standard of horizon ridge for preventing horizon ridge from breaking in extream erosive rainstorm processes.4. Dfferent tillage measures were compared under different rainfall intensities. Before horizon ridge was broken, the soil loss rate was in the order of longitude ridge slope > non–ridge tillage slope > horizon ridge slope. And erosion rate on the longtitude ridge slope was 2.3–3.2 times and 350–890 times of it on non–ridge tillage slope and horizon ridge slope, respectively. While after horizon ridge was broken, when rainfall intensity was 75 mm h–1,the soil loss rate was in the order of horizon ridge slope >longitude ridge slope > non–ridge tillage slope, erosion rate on the horizon ridge slope was 13.2 times and 3.5 times of it on non–ridge tillage slope and longitude ridge slope, respectively; When rainfall intensity was 100 mm h–1, the soil loss rate was in the order of horizon ridge slope > longitude ridge slope > non–ridge tillage slope, erosion rate on the horizon ridge slope was 3.6 times and 1.6 times of it on non–ridge tillage slope and longitude ridge slope, respectively. |
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