A simulated effect of wetting and drying periods for two textural soils amended with biochar at a catchment scale

Biochar is considered as an option to ameliorate soil functions, by improving soil physical and hydraulic soil properties. This study investigated the effect of biochar and of wetting and drying cycles on the water infiltration at laboratory and at a hypothetical watershed scenario. In the laboratory, test samples with 2.5% and 5% (by dry mass) of a mango-wood biochar were added to a sandy and sandy loam soil material. Cumulative infiltration was determined after simulated intense wetting and drying cycles, by drying the samples at 30°C for three consecutive days. Additionally, biochar amended soil hydraulic parameters, obtained at the laboratory, were used to simulate the water discharge of a hypothetical watershed, with the Soil and Water Assessment Tool (SWAT). It was established that biochar addition and repeated wetting and drying cycles decreased cumulative infiltration and enhanced soil rigidity. At watershed scale, pore size distribution, in terms of hydraulic conductivity, played a key role to predict surface runoff and subsurface flow under fully and partially saturated conditions. These results contribute to understand better the effect of biochar amendments as a soil conservation management option on the watershed hydrology.