Abstract
There is a lack of long-term field approach investigating biochar impact on soil properties and vegetation, particularly in forest ecosystems. Relic charcoal hearths (RCHs), the result of the historical charcoal production in the forests, preserve a charcoal-enriched topsoil horizon, thus representing a suitable proxy for studying the long-term effect of biochar addition to soil. In this study, we analyzed the chemical properties of a soil as impacted by charcoal accumulation in three RCH plots in southern Wallonia (Belgium) compared to the soil outside RCHs. We further evaluated the effects of RCHs soil properties on the growth performances of silver birch and European beech as well as the leaves’ nutrient concentration of the latter. RCHs soil stored much more carbon and nitrogen than the reference ones. Most of the C in RCHs derived from charcoal (70‒94% of total organic carbon), which would correspond to a total input of 342 tons of biochar per hectare in these soils. Such an accumulation of charcoal still affects nutrient status of soil even after 150 years since charcoal hearths abandonment: CEC and K, Ca, Mg, Na, Mn and Zn concentration remained higher in RCHs soil compared to the reference one. In spite of a seemingly higher fertility of RCHs soil, elemental concentrations of European beech leaves grown in RCHs did not show any significant difference compared to the reference plots, except for C and Mn concentration, higher and lower, respectively, in the leaves of European beech trees grown inside than outside RCHs. Overall, RCHs soil chemical properties were not a decisive factor in significantly improving tree growth. On the contrary, tree ring width average values of both tree species was slightly lower in RCH plots, suggesting to better investigate the potential long-term detrimental effect of a large biochar addition to soil on forest trees.
Highlights
The interest and the use of biochar, a pyrolysis derived C-rich material used as a soil amendment, increased dramatically in the last decade (Lehmann and Joseph, 2015; Novotny et al, 2015; Tan et al, 2017)
Texture of soil was quite uniform in Relic charcoal hearths (RCHs) and reference plots, between loam and silt loam (Table 1)
These values are consistent with some studies (e.g., Criscuoli et al, 2014; Hardy and Dufey, 2017), but quite higher than others (e.g., Borchard et al, 2014; Kerré et al, 2016; Mastrolonardo et al, 2018) reporting contribution to total organic carbon (TOC) from charcoal-C
Summary
The interest and the use of biochar, a pyrolysis derived C-rich material (namely charcoal) used as a soil amendment, increased dramatically in the last decade (Lehmann and Joseph, 2015; Novotny et al, 2015; Tan et al, 2017). In contrast with annual crops, where a short-term experiment can monitor the complete plant cycle, field experiments of several years are intrinsically required to investigate the effect of biochar on tree growth. Previous studies on this topic generally covered a time period limited to 2 or 3 years (e.g., Pluchon et al, 2014; Glisczynski et al, 2016; Wrobel-Tobiszewska et al, 2016), which allows to investigate at most the response of tree seedlings to biochar addition or the yield of biomass in a short rotation forest plantation. It is crucial to examine the long-term fate and impact of biochar on soil properties and vegetation, in forest ecosystems (Li et al, 2018), which have been rarely investigated so far (Gundale et al, 2016; Luo et al, 2016)
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