FLUIDIZED-BED COMBUSTION BOTTOM-ASH EFFECTS ON INFILTRATION AND EROSION OF VARIABLE-CHARGE SOILS

Highly weathered soils generally maintain low electrolyte levels (EC) in soil solution, which, along with raindrop impact, causes aggregate dispersion and enhanced erosion. This study was conducted to determine if application of fluidized bed combustion bottom ash (FBCBA) could c ontrol erosion of variable-charge soils. Seven highly weathered soils (six Oxisols and one Ultisol) were prewetted and then subjected to hig h-intensity rainfall (110 mm h(-1)) for 2 h. The FBCBA was surface app lied at a rate of 5 Mg ha(-1). Infiltration, runoff, and erosion were measured throughout the rains. The FBCBA increased EC and pH of the so il solution, because it contained CaO (23%), Ca(OH)(2) (3%), and CaSO4 (73%). Steady-state infiltration rates (I-s) ranged from 7.2 to 54.8 mm h(-1) for the control and from 9.5 to 44.4 mm h(-1) for the FBCBA. The FBCBA had either a favorable, an unfavorable, or no effect on the parameters tested, depending on the soil. On soils with a favorable re sponse to FBCBA, I-s was increased by 1.7 to two times, total runoff r educed by two times, and total erosion reduced by 2.2 to 2.4 times. On soils with an unfavorable response, I-s was decreased by 1.2 to 1.6 t imes, total runoff increased by 1.2 to 1.6 times, and erosion increase d by 1.6 times. The increased infiltration and reduced erosion and run off occurred only for soils that had low pH(Delta pH less than or equa l to 0.6) and negative charge(less than or equal to 2.0 cmol(c) kg(-1) ). Unfavorable responses were found when Delta pH was > 2.1, charge in crease was at least 6.8 cmol(c) kg(-1), and final pH was > 9.