Soil erosion alters the composition of soil nitrogen and induces nitrogen immobilization along a sloping agricultural landscape

Soil erosion transports and redistributes sediment across the landscape, altering soil organic carbon (SOC) and nitrogen (N) availability and stocks. However, the effect of erosion on soil N remains largely unclear. In this study, SOC, soil total N (TN), mineral N ( and ), dissolved organic N (DON) and total dissolved N (TDN) were evaluated in 100‐cm soil profiles in different sites (including the non‐erosion flat site, erosional site and depositional site) to examine the responses of the concentration and composition of soil N to different erosional intensity. Additionally, N mineralization and microbial biomass nitrogen (MBN) were determined to evaluate the bioavailability of soil N. Our results showed that erosion depleted TN in the erosional sites while enriching it in the depositional site throughout the soil profile. The erosion, rather than the deposition, altered the composition of dissolved N, with TDN (DON and mineral N) dominating deeper soil profiles (40–100 cm, accounting for 18%–50% of TN). The wide soil C:N ratio in the erosional site altered microbial metabolism to mine N to maintain their growth rather than mineralizing organic matter into soil bioavailable forms. This was supported by the net N mineralization (Nm), which exhibited a significant negative correlation with MBN and soil C:N ratio. The imbalanced loss of SOC and TN caused by the erosion induces soil N limitations. Collectively, our results suggested that erosion decreased TN concentrations and altered the composition of dissolved N, inducing N immobilization and decreasing soil bioavailable N.