Erodibility of biochar from a sandy soil in Denmark

In recent years, the influence and effect of biochar on soil properties has been intensively investigated, particularly in the context of its potential to mitigate the effects of anthropogenic climate change by acting as a net carbon sink. However, a lack of evidence to support the influence and positive effects of biochar on physical and chemical processes in edaphic ecosystems represents a major limitation in its viability as a ‘soft’ geo-engineering option to contribute to ameliorating anthropogenic climate change. One major question that remains unanswered concerns the mobilization, fate and erodibility of biochar in the landscape. Since biochar has a lower bulk-density than soil, its susceptibility to erosion is expected. This lack of information is important and could have profound economic implications for farmers committed to its use, since a high net annual loss of biochar by erosion could exceed any net annual economic gain in terms of increased TOC stocks, as well as any potential increase in soil quality and concomitant land capability. Crucially, therefore, any positive gain to biogeochemical recycling of nutrients and to edaphic ecosystem processes largely depends on the amount of biochar that is not eroded and remains within the upper soil matrix. The overall objectives of this study were to explicitly investigate the erodibility of biochar if erosion events occur directly or soon after its application, to estimate the financial value of the eroded biochar and to analyse its cost-effectiveness if applied to whole field scales. The investigation was conducted on a recently cultivated field located in the predominantly agricultural region of Jutland, north Denmark. Biochar was applied to the soil surface of three plots on three different slope positions at a concentrations equivalent to 1.5-2 kg m-2 and manually incorporated within the till-zone. A 30 min. erosion simulation was conducted on each plot using the 2.2 m-2 Portable Wind and Rainfall Simulator. The preliminary results of this study showed that a fair amount of biochar can be eroded from the fields within the first rainfall event after biochar application to the soil. In order to provide guidelines for its application, for its post-application management to reduce the discharge of biochar, and of the likely costs that this would incur for farmers in environments such as arid and semi-arid regions that frequently experience extreme erosion events, further investigations are needed.