Chemical and microbiological properties of alpine forest soils: Effects of pelletized ashes in a short-term trial

The application of wood ash to forest soils has been used to compensate nutrient loss and avoid soil and water acidification. Using ashes in a non-stabilized form might negatively affect forest ecosystems. Bearing this in mind, together with landscape restrictions and socio-economic parameters, it underlines the importance of using pelletized ashes as soil additives in alpine areas. Therefore, in this study we evaluated the effects of pelletized ashes on the chemical and microbiological properties of four soils representative for the central Alps [rendzic Leptosol (L), fibric Histosol (H), haplic Podzol (P), and dystric Cambisol (Cm)] in a microcosm trial during 22 weeks. The following ash-pellet treatments were at a ratio equivalent to 2 Mg ha(-1): pellets without any additive (A); or in combination with bark, compost, and digestate (B-D). A control without ashes (Ct) was also included. Weekly measurements of pH and electrical conductivity (EC) from the soil leachates were performed. A higher pH, relative to Ct, was found in treatment A for Podsol. Additionally, treatments B and C led to a pH rise in Leptosol. Electrical conductivity, total C and N, and inorganic N forms were not significantly affected by the pelletized treatments regardless the soil type. A similar trend was recorded for pH and EC levels from the leachate samples. A lower metabolic quotient (qCO(2)), relative to Ct, was recorded in Podsol following treatment A. However, when pellet ashes were applied in combination with digestate, a higher qCO(2) than that in Ct was found for this type of soil, which might indicate a lower microbial C utilization efficiency and/or microbial stress. This latter treatment also resulted in a lower dehydrogenase activity in Podsol, whilst soil protease activity and N mineralization were not affected in any of the studied soils. We conclude that ash amendment in pellets form on certain soils improves their acidity levels without causing extreme effects. (C) 2015 Elsevier B.V. All rights reserved.