Straw mulching is not always a useful post-fire stabilization technique for reducing soil erosion

- Post-fire mulching does not affect nutrient concentrations in soil and sediments.
- Most macronutrients and trace elements of sediments decreased with time after fire.
- With moderate precipitation rates, straw mulching does not reduce post-fire erosion.
- Mo, Mn and Zn levels in sediments exceed reference levels for ecosystem protection.

Mulching is increasingly employed to stabilize burnt areas, making necessary to elucidate where and how it should be used. The effects of mulching and the efficiency of two straw application strategies in reducing nutrient losses were evaluated in a steep area (burnt with moderate severity) with twelve experimental plots split into three sets: control burnt plots (BS), burnt plots with straw mulching in narrow bands along the contour lines (NM, global dose 800 kg ha− 1) and in wide bands (WM, global dose 1000 kg ha− 1). None of the mulching strategies had a significant effect on most of the 16 soil and sediment variables analysed (pH, nutrient and trace element concentrations). The principal component analyses show that soil and sediment samples change with time after the fire regardless treatment, decreasing progressively the differences between successive sampling dates. In sediments, pHKCl, Ca, Mg, Mn and Zn fitted to curvilinear regression models with time after fire as independent variable, while the other variables showed no clear temporal trend. During the first post-fire year, < 500 kg ha− 1 of sediments were eroded and mulching had no effect on the total mass of lost sediments and nutrients. We conclude that the erosion rate was rather low that year due to moderate precipitation rates and therefore mulching did not significantly reduce soil erosion. Nevertheless, the concentration of Mo, Mn and Zn in sediments exceeded reference levels for ecosystem protection and can lead to deficiency problems for on-site vegetation and to soil and water pollution off-site.