Reduction of nutrient losses with eroded sediments by post-fire soil stabilisation techniques

After an experimental fire in steep shrubland in a temperate-humid region (north-west Spain), the effects of two post-fire stabilisation treatments (grass seeding and straw mulching) on the chemical properties of eroded sediments, and the amount of nutrients lost with them, were evaluated relative to control burnt soil, over a period of 13 months. Total C and N concentrations, and delta C-13, indicated that sediments were mainly contributed by charred plant and litter material. The highest concentrations of extractable base cations in the sediments occurred during the first 3 months following fire, especially for Na and K. As treatments had little or no effect on nutrient concentration in sediments, differences in nutrient losses were due to the 10-fold lower sediment production in mulching compared with other treatments. In control and seeding treatments, the accumulated amounts of nutrients lost with sediments were 989-1028 kg ha(-1) (C), 77 kg ha(-1) (N), 1.9-2.4 kg ha(-1) (Ca), 0.9-1.1 kg ha(-1) (Mg), 0.48-0.55 kg ha(-1) (NH4+-N), 0.39-0.56 kg ha(-1) (K), 0.19-0.34 kg ha(-1) (Na) and <0.1 kg ha(-1) (P and NO3--N). These values accounted for 22-25% (total C and N) and 5-12% (NH4+-N, Ca, P and Mg) of available nutrients in ash, and 1.0-2.4% of those in ash+topsoil. As nutrient and sediment losses were strongly correlated, the reduction of the latter by mulching application leads to an effective decrease of post-fire nutrient losses.