Nitrogen runoff under simulated rainfall from a sewage-amended lateritic red soil in Fujian, China

Sewage sludge (SS) is used on sloping land, as a soil amendment, because of its organic matter (OM) and nutrient content. However, the presence of nitrogen (N), in acidic soils amended with sludge, and its transport in runoff can lead to eutrophication of downstream surface water. This study assesses the effects of different application methods on N transport, via runoff from plots amended with SS (0 and 120 Mg ha−1). A lateritic red soil (pH 5.2) was selected for this study, using simulated rainfall conditions. When sludge was broadcasted and mixed with surface soils (BM), the concentrations and mass losses of total N in the mixed sample (MTN), total N in the settled sample (STN), total particulate N (TPN), total suspended N (TSN), total dissolved N (TDN) and NH4+-N, in runoff water, were highest at 1 or 18 d after application. BM treatments showed initial pollution risks to surface waters, which diminished gradually with time. Whereas the concentrations and mass losses of NO3−-N, in all sludge plots, appeared to have a declining trend, after an initial ascent. Hole-application (HA) and broadcast application with hay mulch (BH) treatments prevented N loss effectively, the runoff losses coefficient of MTN increased in the order BM (0.43%) > HA (0.15%) > BH (0.03%). For sludge treatments, N was largely lost in dissolved species, while a large portion of NH4+-N was lost in particulate fraction. Nitrogen (N) losses in runoff were greatly affected by the transformation of sludge N in the soil and the modification of soil properties, induced by sludge amendment. The risk associated with the application of sludge to sloping fields, in areas of acidic soil, is an important research subject that merits further study.