Assessment of biochar from poplar SRC biomass carbonization for improving water retention in sandy soils

This study examined the effects on water content profiles of coarse soils amended with biochar produced from poplar short‑rotation coppice biomass. Biochar was generated in the laboratory by carbonizing biomass under nitrogen at 300 °C, 400 °C, 500 °C and 600 °C, and characterized through proximate analysis, FTIR spectroscopy, EDX elemental analysis, mercury intrusion porosimetry, and BET gas‑adsorption. Biochars were mixed at 0%, 10%, 25% and 50% with pure sand and coarse soil, and moisture content was quantified at matric potentials of ∼0 (saturation), −100 hPa (field capacity, FC), −3300 hPa and −15000 hPa (wilting point, WP). Increasing carbonization temperature produced typical volatilization patterns, with oxygen loss, carbon enrichment, and functional‑group evolution toward more stable hydrophobic amorphous and turbostratic chars. The predominance of macroporosity in the biochars resulted in water‑content gains at FC, WP and in available water content, AWC, for both sand–biochar and coarse‑soil–biochar mixtures. The highest relative AWC gains per unit percentage of added biochar, calculated relatively to the corresponding unamended substrate, occurred in coarse-soil mixtures: 2.1%, 1.8% and 1.4% with 10%, 25% and 50% of Biochar-400 and 1.8%, 1.3% and 1.6% with 10%, 25% and 50% of Biochar-600. These findings improve understanding of biochar’s role in soil water storage and carbon sequestration in drought‑prone environments, considering carbonization temperature, porosity, soil texture and amendment concentration.