Abstract:The application of earthworm casts has significant effects on soil infiltration and aggregate composition. This study was carried out in the test area of the idle farmland of the loess area. Earthworm casts were applied in two methods:(A) earthworm casts mixed with the soil of the (0-5 cm) surface layer and (B) mulched 5 cm of soil layer after broadcast application of earthworm casts. Different levels of earthworm casts were designed to study on sediment yield and nitrate nitrogen loss with the runoff under rainfall conditions. The results showed that:(1) Both application methods effectively delayed the time of runoff occurring. The time of runoff occurring under layer application of 800 g/m2 was delayed by 3.88 min compared with CK, and the delay effect was the most obvious. (2) The layer application of 800 g/m2 could significantly reduce the rate of runoff increase in the early stage and delay the time of entering the stable stage. The variation of cumulative runoff with time could be well described by a power function. (3) Under the mixed application and layer application at 800 g/m2, the sediment yield in the stable phase was significantly reduced by 79.61% and 86.74% than CK. The accumulated sediment yields could be well described by the power function with the time, and the initial sediment yield was significantly reduced with the increase of the amount of earthworm casts. (4) Mixed application could significantly reduce the nitrate concentration in runoff. When the amount of application was large and the application method was layer application, it could play a good role to prevent the sediment and chemical solute loss with runoff.