REDUCTION IN SOIL LOSS FROM EROSION-SUSCEPTIBLE SOILS AMENDED WITH HUMIC SUBSTANCES FROM OXIDIZED COAL

Soils that pose high risk of erosion require amendment with either nat ural or synthetic soil conditioners to reduce soil loss hazards. The o bjective of this study was to evaluate the potential of using coal-der ived humic substances (as soil conditioners) to reduce runoff erosion on erosion-susceptible soils, Surface (0-20 cm) samples of severely de graded soils from Principina in Tuscany (Orthic Xerofluvent) and Bovol one in Venice (Udic Ustochrept) in Italy were used to assess the effec ts of five rates (0, 0.05, 0.10, 0.50 and 1.00 g/kg) of humic acids (H A) on soil loss and other hydrological parameters. A rainfall simulato r was used to apply approximately 40 mm/h intensity rain for 1 h on so il beds of dimensions 2 m X 0.5 m X 0.01 m, packed at a bulk density o f 1.20 Mg/m(3) and inclined at a slope of 15%. The amount of soil erod ed (E) and the time to initiate runoff (Rt) and drainage (Dt) were rel ated to changes in the water-holding capacity and aggregate stability of the soils following the HA treatments, In the control treatments, t he values of E, Rt and Dt were higher in the Principina than Bovolone soil. Increasing HA rates generally delayed Rt, accelerated Dt and red uced 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 mag nitude of reduction was achieved with 0.10 g/kg (200 kg/ha) of HA. Imp rovements 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 o f these soils accounted for the reduced runoff erosion. These results show that amending erosion-susceptible soils with low rates of coal-de rived humic substances is a potentially effective soil management prac tice for reducing erosion rates. (C) Elsevier Science B.V. All rights reserved.