Reduction in soil loss from erosion-susceptible soils amended with humic substances from oxidized coal

Abstract

Soils that pose high risk of erosion require amendment with either natural or synthetic soil conditioners to reduce soil loss hazards. The objective of this study was to evaluate the potential of using coal-derived humic substances (as soil conditioners) to reduce runoff erosion on erosion-susceptible soils. Surface (0–20 cm) samples of severely degraded soils from Principina in Tuscany (Orthic Xerofluvent) and Bovolone in Venice (Udic Ustochrept) in Italy were used to assess the effects of five rates (0, 0.05, 0.10, 0.50 and 1.00 g/kg) of humic acids (HA) on soil loss and other hydrological parameters. A rainfall simulator was used to apply approximately 40 mm/h intensity rain for 1 h on soil beds of dimensions 2 m × 0.5 m × 0.01 m, packed at a bulk density of 1.20 Mg/m³ and inclined at a slope of 15%. The amount of soil eroded (E) and the time to initiate runoff (Rt) and drainage (Dt) were related to changes in the water-holding capacity and aggregate stability of the soils following the HA treatments. In the control treatments, the values of E, Rt and Dt were higher in the Principina than Bovolone soil. Increasing HA rates generally delayed Rt, accelerated Dt and reduced E substantially on both soils. On the Principina soil a reduction of about 36% in soil loss was obtained by adding only 0.05 g/kg of HA (equivalent to 100 kg/ha). On the sandier Bovolone soil, the same magnitude of reduction was achieved with 0.10 g/kg (200 kg/ha) of HA. Improvements in Rt and Dt from the HA amendments explained between 58 and 81% of the variation in E from both soils. Furthermore, improvements in the water retention capacity more than in the aggregate stability of these soils accounted for the reduced runoff erosion. These results show that amending erosion-susceptible soils with low rates of coal-derived humic substances is a potentially effective soil management practice for reducing erosion rates.