Jianhui Zhang
Institute of Mountain Hazards and Environment,
Chinese Academy of Sciences & Ministry of Water Conservancy in Chengdu, China

Tillage has a long history in agricultural areas of the Upper Yangtze River Basin, with a purpose of loosing surface, improving soil physical properties, enhancing soil fertility, incorporating chemicals or amendments and controlling weed growth. However, a major concern arises from tillage when it becomes intense and continuous in the sloping field, which drastically overturns and pulls the loose soil material in the downslope direction. Intensive tillage translocates soil, and redistribute soil downhill along the lower landscape positions, and there cause soil erosion.

Tillage erosion is far from negligible in agricultural ecosystems and is the dominant process of soil redistribution in agricultural landscapes of the Upper Yangtze River Basin. Water erosion usually occurs in middle to lower back-slope positions on individual hillslopes, whereas tillage erosion largely causes soil loss in convexities such as shoulder slope and crests or downslope sides of the field boundary. Typically, tillage erosion is most intense in convex slope positions and downslope sides of the field boundary (where water erosion is weakest, while tillage-induced soil accumulation is present in depression positions (where water erosion is most intense). As a consequence, there are different patterns of water erosion and tillage erosion along the transect of the slope. Unlike water erosion that transports the soil off the field and over a long distance, tillage erosion moves the soil within the field and over a short distance in the course of each event.

The process of tillage erosion may create an accelerating mechanism of soil erosion by water, resulting in more severe soil losses. Tillage erosion rates in non-mechanized agriculture areas may be comparable to those in mechanized agriculture areas, as a result of much steeper slope of the former. Consequently, tillage erosion is an important process of soil degradation on sloping cultivated land in the Upper Yangtze River Basin. 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. Simulated experiments showed that intensive tillage results in a gradual smoothening of the slopes. Tillage erosion playing a dominant role in the process of soil erosion within a landscape can increase SOC stocks. However, SOC depletion take place in situations where the two processes of tillage and water erosion are both important and tillage erosion acts as a delivery mechanism for water erosion. Consequently, tillage erosion plays a dual role: enhancing carbon storage at depositional positions, and accelerating carbon depletion through water erosion if it is a key delivery process for soil in the same landscape.