Short-term effects of experimental burning on soil nutrients in the Cantabrian heathlands

The aim of this study is to determine the short-term effects of fire on nitrogen and phosphorus soil concentration in heathland sites dominated by Calluna vulgaris in the Cantabrian Mountain range (NW Spain). Three C. vulgaris heathlands sites (San Isidro, Riopinos I and Riopinos II) were selected. In June 2005, one plot (20 m × 20 m) per site was subjected to an experimental fire and the other was used as a control. Immediately after the fire, ten ash samples and ten soil samples (at a depth of 5 cm) were collected and thoroughly mixed. Soil moisture, temperature, total N, NH₄⁺, NO₃^?, total P, available P and pH were determined in each sample. The quantity of ashes deposited was 300 g/m², with a pH of 9, low N content but higher P concentrations. Significant differences in temperature and soil moisture were detected between the fire-treated and control plots. No significant differences for soil pH, total and available P, total N and NO₃^? concentration were found between the treatments. However, the concentration of ammoniacal-N indicated a significant increase 11 months post-fire and was produced by the changes in environmental soil conditions after the fire. Our results show that low intensity fires do not modify the concentration of N and P in the soil. However, post-fire conditions favour an increase in ammoniacal-N one year later.