BOOK OF ABSTRACTS 139 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Thursday, 27 August 2026 / Hall C Soil Organic Matter, Caustobiolites, and Biochar SL67 Thermal Modulation of Humic Acids Under Industrially Relevant Processing Conditions: Linking Analytical Characterization to Plant Biostimulant Activity Hiarhi Monda1*, Maria Jerzykiewicz 2, Davide Savy3, Altetia James1, Elisa Namdarian1, Akshara Bathini1, Ryan Fountain1, Rich T. Lamar1 1 Huma, Inc., Humic Lab Research Facility, 1350 W Harwell Rd, Gilbert, USA 85233 * Hiarhi.monda@huma.us 2 University of Wrocław, Zakład Podstaw Chemii, Wydział Chemii, ul. F. Joliot-Curie 14 50-383 Wrocław, Poland 3 Department of Agricultural Sciences, University of Naples Federico II, Piazza Carlo di Borbone 1, 80055 Portici, Italy In recent years the biostimulant movement has been witnessing a flourishing market with rapid growth, and the humic substances followed this trend, remaining among the most widely recognized and adopted organic inputs in agricultural practice owing to their proven long-standing use and more than a century of scientific and agronomic interest [1]. However, commercial humic-based products often undergo thermal processing during extraction, concentration, drying, or formulation, potentially altering their chemical properties and biological performances [2]. Despite the industrial relevance of these treatments, the relationship between heat-induced chemical modifications and plant bioactivity remains poorly explored. In this study, 4 different humic acids (NM, ALB, NDL, GAS HAs) were extracted from the main commercially sourced lignite and sub-bituminous ores available in North America and subjected to controlled thermal treatment at different exposure times (100°, 200°, and 300° C for 10, 30, 60 min up to 3H). The heattreated HAs were then investigated through a comprehensive analytical characterization (elemental composition, UV-fluorescence, TGA/DSC, FT-ATR, NMR, ESR, EAC/EDC, TEAC antioxidant assay) and plant bioassays (1 week, 2 weeks growth tests) in order to evaluate how temperature-driven chemical transformations affect their structural features and their capacity to elicit the biostimulant response. Both FT-ATR and NMR confirmed that moderate thermal treatments (up to 200° C) reorganize HAs without fully destroying them, leading to a greater relative definition in the IR fingerprint region and the predominance of the aromatic/carbonyl peaks. In contrast, at 300° C the HAs undergo a deeper transformation, with a strong decrease in aliphatic and O-alkyl/carbohydratelike components and a relative increase in signals associated with more oxygenated/condensed structures.
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