Combined effects of tillage direction and slope gradient on soil translocation by hoeing

Few studies have dealt with tillage erosion processes under the combined action of tillage direction and slope gradient, while effects of the two factors were independently examined. This study aims to elucidate the variation of soil translocation at different tillage directions and slope gradients. The magnetic tracer method was used to measure the soil translocation caused by downslope (0 degrees), oblique downslope (45 degrees), contour (90 degrees), oblique upslope (135 degrees) and upslope (180 degrees) tillage under different slope gradients (0.087 to 0.577 m m(-1)). The net downslope displacement of soil (NDDS) was closely related to tillage direction and slope gradient. However, the relationship between the NDDS and tillage direction varied with slope gradient. For gentle slopes (0-0.30 m m(-1)), the NDDS showed three clear changes: slow decrease (0 degrees to 45 degrees), rapid decrease (45 degrees to 135 degrees) and little change (135 degrees to 180 degrees). Meanwhile, the NDDS decreased rapidly from 0 degrees to 135 degrees and changed little from 135 degrees to 180 degrees on the moderate slopes (0.30-0.45 m m(-1)), while it decreased rapidly from 0 degrees to 90 degrees and varied little from 90 degrees to 180 degrees on the steep slopes (0.45-0.60 m m(-1)). A binary trigonometric function equation could be used to express the changes in NDDS with the combined action of tillage direction and slope gradient. Applying 135 degrees and 90 degrees hoeing tillage directions to gentle and moderate slopes, and steep slopes, respectively, may be an important alternative in reconciling the contradiction between soil conservation optimization and labor saving.