Water repellency in forest soils affected by fires and agricultural soils with different agricultural management and abandonment

Soil water repellency determines the water available in the soil system, the runoff generation and the geomorphologic processes. This study examines the soil wettability during the summer of 2008 and 2009 in forest soils with different fire history, and in agricultural soils with different managements. Water repellency was assessed using the Water Drop Penetration Time test (WDPT). Results indicate that water repellency is more frequent and persistent in forest soils than in agricultural ones. In the former, water repellency is reduced a year after a fire and is not recovered during at least 12 years. In agricultural soils, it is found under no till treatment, whereas sites treated with herbicides or tillage were virtually unaffected. Water repellency is exhibited because of the increment of aboveground biomass and organic matter content as the vegetation is recovered following a wildfire or after abandoned crop fields, and after adding reaping or with green manure. In any case, water repellency levels are not either high or continuous enough to produce important runoff and erosion rates in the agricultural soils, although this can occur after forest fires if the soil it is not still protected by the vegetation recovery. Land abandonment trigger the water repellency on soils, and in our case fire reduce it for some years.