Quantitative assessment of tillage erosion on typical sloping field in black soil area of northeast China

Abstract: Massive research on soil erosion in northeastern China has focused on quantifying the rates and patterns of water erosion. Soil transportation caused by farming equipments or tillage erosion, however, has largely been overlooked as a significant geomorphic process in the black soil region. The objectives of this study, therefore, were to 1) quantatively determine tillage translocation value due to moldboard plowing, which was the predominant implement of soil preparation in this area; 2) to examine the effect of slope gradient and tillage direction on tillage translocation; and 3) to investigate the spatial distribution of tillage erosion in a typical sloping cultivated land. Tillage translocation process was determined by labeling method in this study. White quartz gravel with 6-12 mm in diameter was used as the tracer for all the plots. A summation curve was generated to calculate mean soil movement based on tracer redistribution along the path of tillage. Tillage operations were conducted in both up and down direction of the sloping field separately, and the mean slope was 3.6° with maximum up to 7.2°. Speed and depth of tillage were set as 13.6 km/h and 25 cm, respectively. Prior to tillage operation, the terrain following coordinates and elevation of study area were measured at 20 m intervals along 7 transects, and these data were to produce digital elevation model of study area (320 m×120 m). The results showed that the ratio of tracers recovered after tillage operations to that applied ranged from 95.54% to 98.15%, with an average of 96.96%, showed that the tracer recovery rate was high. And tillage depth estimated by summation curve was 24.9 cm which was consistent with pre-set tillage depth (25.0 cm). These evidences indicated that the technique used in this experiment could appropriately estimate tillage translocation. The average experiment error (4.83%) was lower than reported tillage translocation and erosion studies, which credited to the accurate sampling process. A further analysis was conducted to the first plot (slope gradient 5.02%) with the highest error of 13.34%. We found that variability within the original tracer-labeled plot contributed to the high experiment error. Moldboard plow operation moved great quantities of soil resulting to potential erosive. Tracer concentration at 0-20 cm within plots maintained at a high level in upslope tillage direction while the tracer concentration at 0-20 and 50-150 cm were both higher in downslope direction, indicating that tillage implements translocated more soil and took it far away in downslope direction. Mean soil translocation varied from 10 to 34 m and translocation in mass ranged from 32.68 to 134.14 kg/m. Tillage translocation was significantly affected by slope gradient, especially for upslope tillage. The rate of tillage erosion depended on the interval length of 20 m flocculated in 0.4-11.0 Mg/(hm2·a). Severer tillage erosion was observed on back-slope, shoulder positions and the greater slope positions, comparing to summit and toe-slope positions. The slope gradient of cultivated lands in black soil area is generally smaller, but the tillage erosion could be serious because of the higher tillage depth and speed of equipment operations. Results from this research can be of benefit to set targeted measures to reduce soil loss and maintain soil fertility in this area.