Enhancing corn stalk humification via DDQ-assisted ball milling for soybean drought resistance

DDQ-assisted ball milling is valid in oxidizing lignin and activating cellulose. • The pretreatment promotes corn stalk humification at relatively low temperatures. • DDQ serves as a nitrogen source to improve the nitrogen content in resultant A-HA. • The A-HA markedly enhances the soybean drought resistance. • The enhanced antioxidant capacity and osmotic regulation are drought contributors. The production of artificial humic acid (A-HA) via hydrothermal humification offers a promising route for the valorization of waste biomass. However, its practical application is often hindered by several limitations, including low yield, inadequate nitrogen content, and limited reactivity resulting from a deficiency in oxygen-containing functional groups. To address these challenges, this study developed a DDQ-assisted ball milling pretreatment to facilitate the corn stalk humification. After hydrothermal treatment at 105 °C for 24 h, the proposed method increased the artificial humic acid (A-HA) yield from 14.91% to 18.71% and artificial fulvic acid (A-FA) yield from 3.12% to 5.06%. This improvement was ascribed to DDQ’s role in selectively oxidizing lignin and activating cellulose, which consequently enhanced the depolymerization and conversion of these recalcitrant components, thus promoting humification. Moreover, DDQ also served as a nitrogen source, collectively leading to the formation of A-HA with a higher nitrogen content and more oxygen-containing functional groups. These modified characteristics contributed to the superior effectiveness of the resulting A-HA in improving soybean drought resistance over its unpretreated counterpart. This study established a circular model from “agricultural waste to synthetic humic acid and ultimately back to agricultural application”, providing a viable technical strategy for advancing sustainable agriculture. Download: Download high-res image (245KB) Download: Download full-size image