Impact of Water Holding Capacity and Moisture Content of Soil Substrates on the Moisture Content of Wood in Terrestrial Microcosms

Terrestrial microcosms (TMCs) are frequently used for testing the durability of wood and wood-based materials, as well as the protective effectiveness of wood preservatives. In contrary to experiments in soil ecology sciences, the experimental setup is usually rather simple. However, for service life prediction of wood exposed in ground, it is of imminent interest to better understand the different parameters defining the boundary conditions in TMCs. This study focused, therefore, on soil–wood–moisture interactions. Terrestrial microcosms were prepared from the same compost substrate with varying water holding capacities (WHCs) and soil moisture contents (MCsoil). Wood specimens were exposed to 48 TMCs with varying WHCs and MCsoil. The wood moisture content (MCwood) was studied as well as its distribution within the specimens. For this purpose, the compost substrate was mixed with sand and peat and its WHC was determined using two methods in comparison, i.e., the “droplet counting method” and the “cylinder sand bath method” in which the latter turned out advantageous over the other. The MCwood increased generally with rising MCsoil, but WHC was often negatively correlated with MCwood. The distance to water saturation Ssoil from which MCwood increased most intensively was found to be wood-species specific and might, therefore, require further consideration in soil-bed durability-testing and service life modelling of wood in soil contact.

Performance of Copper and Non-Copper Based Wood Preservatives in Terrestrial Microcosms

Summary The use of wood preservatives based on copper, chromium and arsenic (CCA) has become restricted in several countries due to environmental concerns. As a consequence, several chromium and arsenic free preservatives based on fungicides, regarded as more environmentally acceptable, have been developed. Most of these preservatives have only been tested in the laboratory against pure cultures of basidiomycetes and their long term effectiveness in practice is in many cases unknown. The effectiveness of six different preservatives, representing different types and combinations of fungicides, against mixed natural populations of micro-organisms, was evaluated during one year in terrestrial microcosms with soils known to provide high activity of different types of wood destroying micro-organisms. Of the fungicides tested, copper compounds provided the best protection against wood destroying micro-organisms. Copper free preservatives provided good protection against pure cultures of brown- and white rot fungi, but were ineffective when treated stakes were exposed in unsterile soils.