Soil erosion is a serious problem in subtropical China where hillslope red soils (Ultisols in US soil taxonomy) are intensively cultivated. Manure and amendments have been reported to improve crop growth and soil structural stability in long-term experiments so the objective of this study was to determine the effect of different organic amendments on soil aggregate stability, agronomic performance, runoff, and erosion. Four treatments consisted of inorganic NPK fertilizer (NPK), NPK fertilizer plus rice straw mulch (NPK + Str), NPK fertilizer plus rice straw-derived biochar (NPK + BC), and NPK fertilizer plus swine manure (NPK + OM) located on land with a 9–14% slope planted with peanut (Arachis hypogaea L.). During the peanut season, soil erosion ranged from around 2600 ton km− 2 with just inorganic NPK fertilizer down to 627 ton km− 2 with fertilizer plus swine manure, while addition of swine manure also increased the above-ground biomass and SOC (P < 0.05). In contrast, rice straw-derived biochar did not improve soil acidity, crop growth, and aggregation (P > 0.05) except the SOC, because biochar was susceptible to erosion (2115 ton km− 2). The least erosion was observed in the straw mulch treatment (225 ton km− 2), while it improved the above-ground biomass (P < 0.05) but not the C stock. The results indicated that the application of organic manure was a more appropriate practice for hillslope Ultisols management than using biochar.