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

Summary

This study leverages >150-year-old charcoal kiln sites in Wallonia as natural experiments in long-term biochar persistence, finding that hardwood biochar residues dramatically increase soil cation exchange capacity and alter nutrient stoichiometry. Biochar-C showed a CEC of 414 cmol_c kg⁻¹ (double that of uncharred organic carbon), and markedly raised C:N and C:P ratios whilst increasing exchangeable Ca²⁺ and Mg²⁺. Despite biochar's persistence and high charge, available phosphorus was little affected, and copper availability was substantially reduced through complexation—a finding with implications for long-term soil amendment strategies in temperate regions.

UK applicability

The temperate climate, soil type, and historical land-use context of Wallonia are broadly comparable to parts of the United Kingdom, particularly southern regions. However, the study's findings on very long-term biochar effects (>150 years) should be cautiously extrapolated, as soil management, crop rotations, and environmental conditions may differ; UK agronomists should consider the copper complexation finding when biochar is proposed near sensitive crops.

Key measures

Charcoal-C content (differential scanning calorimetry); soil organic carbon (SOC); C:N and C:P ratios; total nitrogen; nitrate content; soil pH; cation exchange capacity (CEC); exchangeable Ca²⁺, Mg²⁺, K⁺; available, inorganic and total phosphorus; copper complexation

Outcomes reported

The study characterised soil properties at 17 pre-industrial charcoal kiln sites in Wallonia, Belgium, where biochar-enriched soils had persisted for >150 years, and compared them with adjacent reference soils. Measurements included charcoal-C content, organic matter, nutrient ratios, cation exchange capacity, and metal complexation.

Topic tags