Effect of wildfire ash on hydrological properties of coarse-textured soils

In a world where wildfires are becoming increasingly recurrent due to climate change and land use, sandy soils are prone to ash incorporation due to their high macroporosity and rainfall effects. To enhance understanding regarding the influence of ash type and dose on the hydrological properties of coarse-textured soils, a study was undertaken to evaluate the effect of incorporating Eucalyptus globulus and Quillaja saponaria ashes on the pore size distribution (PSD), soil water retention curve (SWRC) and saturated (K_s) and unsaturated (K_u) hydraulic conductivities. The study evaluated the effects of two doses of ash (2 % and 4 %) from each species on two coarse-textured soils from central Chile (SL: sandy loam and SCL: sandy clay loam). The measurements were compared among treatments but also to a control without application. Each soil-dose-species combination was implemented with 4 replicates. Results showed that the ashes’ particle size was in the range of silt and very fine sand, which, after being added to the soils, led to a significant decrease in K_s (up to 82 %). However, all treatments showed moderately high K_s values. Regarding the SWRC, the van Genuchten model fitting showed that ash incorporation significantly increased the soil water content at saturation (${\theta }_s$) and decreased the parameter α. Additionally, adding the ash increased the water content at field capacity (FC) in both soils (up to 39.2 %). The main change in PSD was a higher fine porosity (FP) in the range of 34.8–43.9 % for SL and SCL soils, respectively. These results estimate the change in some key hydrological properties of coarse-textured soils, which can be used for modeling or deciding on post-fire ash management strategies.