Ten-year application of cattle manure contributes to the build-up of soil organic matter in eroded Mollisols

Purpose: Amendment of animal manures into eroded soils is an important approach to improving nutrient status and increasing the concentration of soil organic carbon (SOC). However, the contribution of the manure carbon to SOC and its variation along soil profile has not been quantified. Materials and methods: We simulated soil erosion in a mollisol by removing the top soils of 0-, 5-, 10-, 20-, and 30-cm depth and compared SOC in soil profiles 10 years after either chemical fertilization alone or combined with cattle manure application. Results and discussion: Increasing erosion depth decreased SOC concentration and weakened soil aggregation. Compared to the chemical fertilization only, the addition of cattle manure significantly increased SOC accumulation and soil aggregation, which mainly occurred in 0–40-cm depths. The greatest effect of manure application was observed in the 10-cm erosion treatment. The application of cattle manure increased the 13C abundance in aggregates and bulk soil in the top 40 cm of soil profile. Using the natural 13C abundance method, we quantified the contribution of the cattle manure to SOC at 0–40-cm depths ranging from 1.1 to 8.4% across erosion treatments. Conclusions: The greatest contribution of the manure-C to SOC occurred in surface layer with 10 cm of soil removal. The application of animal manures was recommended for restoring severely eroded soils.