BOOK OF ABSTRACTS 209 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Hall A Poster Session / NOM and Aquatic Systems P2.13 Biochar effects on dissolved organic carbon assessed by 1H-NMR in andosol and alluvial single-soil columns Álvaro F. Garcia-Rodriguez1, Nobuhide Fujitake2, Lorena Goretti2 and Heike Knicker1 * 1 Group of Interactions between Soils, Plants and Microorganisms, Department of Food Biotechnology, Instituto de la Grasa (IG-CSIC), Building 46, UPO Campus, Ctra. de Utrera km 1, 41013 Seville, Spain 2 Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada, Kobe, Hyogo, 657-8501, Japan * Corresponding author: heknicker@ig.csic.es Climate change is increasing the frequency and intensity of extreme rainfall events, driving greater carbon (C) losses from soils via dissolved organic carbon (DOC) leaching. In Japan, where such events occur regularly [1], understanding how they affect soil organic carbon (SOC) dynamics and DOC composition is particularly important. Biochar (BC) — a carbon-rich byproduct of biomass pyrolysis — is widely used as a soil amendment for its potential to improve soil fertility, enhance water retention, and promote long-term C sequestration. However, field and laboratory studies have shown that BC particles, especially fine fractions, can migrate downward through soil profiles under intense rainfall or irrigation, potentially compromising BC persistence in topsoil and disrupting subsurface biogeochemical processes such as nutrient transport and groundwater quality [2]. To investigate the effects of BC on SOC mobilization and DOC characteristics, we carried out a controlled 4-week single soil column experiment using Andosol and alluvial soil. Columns were subjected to high and moderate irrigation frequencies based on their water-holding capacity (WHC), with and without BC amendment. DOC concentrations were measured in soil leachates, and molecular composition was characterized by 1H-NMR spectroscopy to track changes in aromatic, aliphatic, and oxygenated functional groups associated with BC-derived and native SOC fractions [3]. Preliminary results reveal higher total organic carbon (TOC) in alluvial soils than in andosol. In the alluvial-BC treatment, ¹H-NMR spectra showed a marked decline in the O-alkyl region (52.1→34.0%) over 4 weeks, accompanied by increases in aliphatic (17.9→28.2%), carboxyl-associated (25.8→29.8%), and aromatic (4.2→7.9%) fractions. These findings offer mechanistic insights into how soil mineralogy governs the mobility and transformation of both BC-derived and native DOC
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