Brieuc Hardy

Long-term effect of biochar on the stabilization of recent carbon: soils with historical inputs of charcoal

This study was set up to identify the long‐term effect of biochar on soil C sequestration of recent carbon inputs. Arable fields (n = 5) were found in Belgium with charcoal‐enriched black spots (>50 m2; n = 14) dating >150 years ago from historical charcoal production mound kilns. Topsoils from these ‘black spots’ had a higher organic C concentration [3.6 ± 0.9% organic carbon (OC)] than adjacent soils outside these black spots (2.1 ± 0.2% OC). The soils had been cropped with maize for at least 12 years which provided a continuous input of C with a C isotope signature (δ13C) −13.1, distinct from the δ13C of soil organic carbon (−27.4 ‰) and charcoal (−25.7 ‰) collected in the surrounding area. The isotope signatures in the soil revealed that maize‐derived C concentration was significantly higher in charcoal‐amended samples (‘black spots’) than in adjacent unamended ones (0.44% vs. 0.31%; P = 0.02). Topsoils were subsequently collected as a gradient across two ‘black spots’ along with corresponding adjacent soils outside these black spots and soil respiration, and physical soil fractionation was conducted. Total soil respiration (130 days) was unaffected by charcoal, but the maize‐derived C respiration per unit maize‐derived OC in soil significantly decreased about half (P < 0.02) with increasing charcoal‐derived C in soil. Maize‐derived C was proportionally present more in protected soil aggregates in the presence of charcoal. The lower specific mineralization and increased C sequestration of recent C with charcoal are attributed to a combination of physical protection, C saturation of microbial communities and, potentially, slightly higher annual primary production. Overall, this study provides evidence of the capacity of biochar to enhance C sequestration in soils through reduced C turnover on the long term.

Evaluation of the long-term effect of biochar on properties of temperate agricultural soil at pre-industrial charcoal kiln sites in Wallonia, Belgium

Research on biochar has increased, but its long-term effect on the fertility of temperate agricultural soil remains unclear. In Wallonia, Belgium, pre-industrial charcoal production affected former forested areas that were cleared for cultivation in the nineteenth century. The sites of traditional charcoal kilns, largely enriched in charcoal residues, are similar to soil amended with hardwood biochar more than 150 years ago. We sampled 17 charcoal kiln sites to characterize their effect on soil properties compared with adjacent reference soils. Charcoal-C content was estimated by differential scanning calorimetry. The kiln soil contains from 1.8 to 33.1 g kg−1 of charcoal-C, which markedly increases organic C:N and C:P ratios. It also contains slightly more uncharred soil organic carbon (SOC) than the reference soil, which accords with larger total N content. We measured a small increase in nitrates in the kiln soil that might relate to greater mineralization and nitrification of organic N. Frequent application of lime raised the pH to values close to neutral, which offset the residual effect of charcoal production on soil acidity. A cation exchange capacity (CEC) of 414 cmolc kg−1 was estimated for charcoal-C, whereas that of uncharred SOC was 213 cmolc kg−1. Despite the large CEC of the kiln soil, exchangeable K+ content was no different from the adjacent soil, whereas exchangeable Ca2+ and Mg2+ contents were considerably larger. Charcoal enrichment has little effect on available, inorganic and total P, but it can form strong complexes with Cu, which reduces the availability of the metal. Biochar is very persistent in soil; therefore, long-term implications should not be overlooked. Highlights Charcoal kiln soil contains from 1.8 to 33.1 g kg−1 of charcoal-C, which raises C:N and C:P ratios. Charcoal-C content was estimated by differential scanning calorimetry. We estimated a CEC of 414 cmolc kg−1 for charcoal-C and 213 cmolc kg−1 for uncharred SOC. Retention of exchangeable K+ remained unaffected by charcoal but that of Ca2+ and Mg2+ increased.

Estimation des besoins en charbon de bois et en superficie forestière pour la sidérurgie wallonne préindustrielle (1750-1830) Deuxième partie : les besoins en superficie forestière

The wood for the charcoal kilns to produce charcoal came from coppices whose rotation period is estimated to be some twenty years. A coppice of this age on medium soil would typically produce in the range of 80 to 100 steres per hectare, so forested surface area needs are estimated to be 4 444 ha on average per furnace. Considering the number of furnaces operating in Wallonia, it is realistic to estimate the overall surface area needed by the pre-industrial steel sector to be in the range of 325 000 ha of forests, i.e. nearly three quarters of the Wallonia forests of the time.

Estimation des besoins en charbon de bois et en superficie forestière pour la sidérurgie wallonne préindustrielle (1750-1830) Première partie : les besoins en charbon de bois

Just as in neighbouring areas, huge demands were made on the Walloon forests to supply the charcoal required by the steel sector prior to the switch to coal during the 19th century. Steel production using wood reached a peak in Wallonia between 1750 and 1830. Charcoal was used not only to melt the ore but also to refine the cast iron produced, and to a far lesser extent, to craft iron in the forges. On the basis of very early statistics, it has been established that some three tons of charcoal were required to produce and refine one ton of cast iron. At that time, a furnace could produce between 500 and 550 tons of cast iron per year. Charcoal needs are estimated to be roughly 1 600 tons per year and per furnace, i.e. the equivalent of 20 000 steres of wood. With over 70 furnaces in production in Wallonia, overall charcoal requirements came to approximately 115 000 tons per year, i.e., more than 1 400 000 steres of wood.

La gestion patrimoniale des forêts anciennes de Wallonie (Belgique)

Thierry Kervyn1 | Jean-Pierre Scohy2 | Didier Marchal2 | Olivier Collette3 | Brieuc Hardy4 Laurence Delahaye1 | Lionel Wibail1 | Floriane Jacquemin5 | Marc Dufrêne5 | Hugues Claessens5 1 Département d’Étude du Milieu naturel et agricole (DGARNE, SPW) 2 Département de la Nature et des Forêts (DGARNE, SPW) 3 Département du Patrimoine (DGATLPE, SPW) 4 Earth and Life Institute (UCL) 5 Gembloux Agro-BioTech (ULiège)