Effect of wildfires on soil properties of agricultural lands of Mediterranean-climate region in Chile

The frequency and severity of wildfires in Mediterranean climate regions have increased in the last decades due to changes in climatic conditions and land use. This change in the fire regime has increased the threat to forest, shrublands and agricultural lands. To evaluate to what extent wildfires could affect agricultural soils, we evaluated 40 properties of soil samples collected at two depths (0-5 and 5-10 cm) in areas affected by moderate severity wildfires 14 mo prior, and the immediately neighboring unburned area. The overall most relevant soil properties to differentiate between burned and unburned soil, regardless its sampling depth, were selected as soil quality indicators and used to compute a soil quality index. Accordingly, carboxylesterase activity, available soil moisture, pH, Ca, P, Fe, B, S and Cu were selected using a two-way ANOVA. The results showed that carboxylesterase activity decreased from 0.49 +/- 0.18 to 0.26 +/- 0.16 mu mol g-1 dry soil, and available soil moisture was reduced from 9.85 +/- 0.83 to 8.33 +/- 0.52 cm in burned soils. Also, pH significantly decreased from 7.30 +/- 0.14 to 6.27 +/- 0.23 which affected the subsequent nutrient availability. Thus, Ca and P decreased from 6.50 +/- 1.78 to 3.95 +/- 0.91 cmol(+) kg-1 and from 10.72 +/- 2.84 to 7.44 +/- 0.91 mg kg-1 respectively, whereas Fe increased from 3.89 +/- 0.97 to 16.75 +/- 3.13 mg kg-1, Cu and S availability doubled, and B content increase by 29%. The overall soil quality index revealed a nonsignificant decreased between unburned (0.59 +/- 0.03) and burned (0.55 +/- 0.04) soils 14 mo after the fire.