Dynamics of soil organic carbon and soil nutrients following tillage and water erosion in an agricultural landscape

A mechanistic understanding of nutrient movement associated with the erosion process is required to formulate precision soil conservation measures. We explored the response of surface soil nutrients and soil organic carbon (SOC) fractions to tillage erosion and water erosion. Tillage and water erosion rates were estimated by the directional tillage erosion model and revised universal soil loss equation, respectively. One hundred and twelve surface soil samples (0–20 cm) were collected from a sloping farmland (3.6 ha) in the Mollisols region of China. Soils were analyzed for total nitrogen (TN), total phosphorus (TP), total SOC, particulate organic carbon (POC), dissolved organic carbon (DOC), and microbial biomass carbon (MBC). Results showed that no significant relation between TN and tillage or water erosion rates exists at any slope position. The TP distribution is more affected by water erosion than tillage erosion. Water erosion also played a greater role in controlling distribution of DOC than tillage erosion, whereas POC distribution was more sensitive to tillage erosion. In addition, we observed a contrasting relationship between MBC and water erosion for the mild erosion (r = −.43, P < .05) vs. intense erosion scenario (r = .38, P < .05). This shift indicates a possible dual role of microbes in SOC cycling associated with water erosion: mild erosion (averaged 17.4 t ha−1 yr−1) depletes microbial biomass and contributes to SOC mineralization, whereas intense erosion (averaged 54.6 t ha−1 yr−1) may lead to a shift in microbial structure thus promoting the dynamic replacement of SOC at eroding sites.