Potassium isotopes evidence reveals agricultural practices accelerate soil erosion

• This study extended the K isotopes dataset in soil under various land use types. • The δ 41 K values in soil showed a negative correlation with soil erodibility factor. • Soil erosion by tillage causes heavy potassium isotope depletion. Stable potassium (K) isotopes, denoted as δ 41 K, are increasingly utilized for tracing geogenic processes and anthropogenic effects in terrestrial ecosystems. However, little is known about soil K isotopes under diverse land uses, despite K is an important nutrient in crop productivity. Karst ecosystem with weak stability is widely spread and easily suffers from soil erosion under intensive agricultural disturbances in southwest China. This research examined the composition of K isotopes and soil erodibility factor in 16 soil samples, including topsoil (0–10 cm) and subsoil (25–30 cm) of three croplands (CPL), three abandoned croplands (ACL), and two natural lands (NTL). The results showed a heavy depletion of K isotopes as follows: natural land (0.08–0.19 ‰) > abandoned cropland (δ 41 K −0.10–0.18 ‰) > cropland (δ 41 K: −0.13 ‰ to −0.01 ‰), and the compositions of K isotopes are lighter in the topsoil than in the subsoil of both CPT and NVT. Meanwhile, the δ 41 K displayed a negative correlation with the soil erodibility factor. Lighter K isotopes and greater soil erosion in cropland, indicating soil erosion under tillage disturbance, caused the heavy depletion of K isotopes. This study reported soil K isotope compositions under various land uses and showed a close link between soil erosion and soil K isotopes, reflecting the potential application of K isotopes in the traceability of soil erosion due to agricultural activities.