Landform change due to soil redistribution by intense tillage based on high-resolution DEMs

Abstract

Tillage erosion is considered to be one of the most widespread forms of soil erosion on sloping agricultural land, yet little attention has been paid to the impact of tillage erosion on landform change. This study assessed the rates of tillage erosion caused by manual hoeing and evaluated the impacts of medium-term tillage erosion on landform change on slopes with linear and complex forms in the Three Gorges Reservoir region, China. To quantify the tillage erosion rate without the influence of water erosion, a series of tillage experiments were set up and an on-site survey was conducted during the dry season of 2008. The tillage erosion rates on the linear and complex slopes were assessed using high-resolution digital elevation models (DEMs), a step profile method and a tillage erosion model. The erosion rates from the step profile method were 16.8 and 36.6Mgha−1 tillage pass−1 on the linear and complex slopes, respectively, and those deduced from the tillage erosion model were 17.6 and 41.7Mgha−1 tillage pass−1. After intense tillage, the most notable changes in soil depth occurred at the summit and toe positions, with a decrease of 100% at the 0-m position (summit) and an increase of 13.1% and 30.9% after 5- and 15-operation tillage, respectively, at the toeslope position on the linear slope. On the complex slope, a 100% reduction in soil depth was observed at the summit; the largest increase in soil depth appeared at the toeslope position after 5- and 15-operation tillage by 23.1% and 48.2%, respectively; and a significant decrease in soil depth at the shoulder slope also occurred. For the linear slope, the slope gradient gradually decreased due to intense tillage, and the landform could be referred to as slow-forming terraces where no severe water erosion occurred at the lower slope positions. Additionally, insignificant changes in the slope gradient occurred at the flat summit slope positions, whereas significant soil accumulation at the toeslope positions caused an obvious reduction of the slope gradients on the complex slope. This indicates that intensive tillage results in a gradual smoothening of the slopes. Furthermore, tillage erosion altered the soil profiles leading to the truncation, the mixing of soil profiles and the formation of new soil profiles at different slope positions. Overall, these results clearly indicate that tillage erosion is one of the important soil redistribution processes, and hoeing tillage plays a dominant role in landform change.