Correlation between air permeability and saturated hydraulic conductivity: unburned and burned soils
Prior research has shown a log–log correlation between ex situ air permeability (ka) measured at a matric potential of –50 and –100 cm H2O and saturated hydraulic conductivity (Ksat) in agricultural soils. We examined the applicability of a previously established log ka vs. log Ksat predictive relation in unburned and burned woodland–chaparral and coniferous soils. Specifically, we measured in situ ka in the field using the soil corer air permeameter (SCAP) and measured laboratory Ksat on soil cores. To determine postfire soil physical changes, Ksat was transformed into water permeability, kw. Then ka and kw were compared in unburned and burned soils. The median ka was lower and median kw was higher in burned than unburned woodland–chaparral soils. The median ka and kw were both lower in burned than unburned coniferous soils. Despite these effects, the 95% prediction interval of the predictive relation includes 80% of the burned soils and 83% of all desert soils. The RMSE values of the predicted log Ksat and measured log Ksat were 0.371, 0.552, 0.588, and 0.511 m d–1 for unburned and burned woodland–chaparral and unburned and burned coniferous soils, respectively. In comparison, the RMSE for the predicted and measured log Ksat was 0.654 m d–1 for an agricultural data set. The overall RMSE for unburned and burned soils including the agricultural soils was 0.551 m d–1. This suggests that the predictive relation is applicable for unburned and burned desert soils for in situ ka measurements.