Degradation of soil physicochemical quality by ephemeral gully erosion on sloping cropland of the hilly Loess Plateau, China

• EGE caused significant degradation of soil quality on the sloping crop land.
• Soil degradation progress caused by EGE was related with soil profile layers.
• The descent of SQI was 10.6%, 27.7% and 36.6%, respectively, in a three-step progress.
• Soil physical properties were more susceptible and fragile to EGE than soil nutrients.
• Key factors that respond to soil quality degradation were identified.

Ephemeral gully erosion (EGE) is a common type of shallow linear erosion that exerts a major threat to the productivity and sustainability of agricultural systems. The objective of this study was to evaluate the impact of EGE on soil physicochemical properties that determine soil quality. It was hypothesized that sites with EGE exhibit significant changes in soil physiochemical properties compared with sites without EGE. This study used a paired sampling method to compare the soil physiochemical properties of soil at 0–2, 2–5, and 5–10 cm depth of ephemeral gully bottoms to inter-gully areas (CK) in croplands of the hilly Loess Plateau of China. The results showed that EGE posed a threat to soil physicochemical properties and thus the soil quality index was progressively reduced as EGE increased. Reductions in soil quality index were observed as stages of EGE (depth of gully) increased. Three critical EGE stages were defined by <10 cm and ≥30 cm depths of gully where the soil quality index decreased significantly. Compared with the CK, the 0–2 cm depth of the gully bottom was essentially a net soil deposition layer, especially for the first erosion stage (gully < 10 cm deep). Soil nutrient loss was greatest in the 2–5 cm depth. Soil physical properties were more susceptible and fragile to EGE than soil nutrients. Degradation of soil physical-dominated properties occurred in the first erosion stage, with key factors being erodibility (K value), silt content, specific surface area (SSA) and mean weight diameter of aggregates (MWD), whereas soil degradation was mainly caused by losses of soil available nutrients during the subsequent erosion stages. This approach of combining field ground-truth survey with laboratory analysis to study the in-situ impact of ephemeral gully erosion on soil physicochemical properties aids in understanding the features of soil degradation caused by EGE.