Chemically activated biochar for enhancing Zea mays germination: An integrated biochar–ultrasonic seed priming approach

Abstract

In response to the challenges of climate change and the growing need for sustainable agricultural solutions, this study aimed to develop and evaluate chemically activated soybean seed-derived biochar as a biostimulant for Zea mays seeds, applied through ultrasonic priming, to promote seed germination and early seedling growth. The biochar was produced by pyrolyzing soybean seeds and was chemically activated with KOH, ZnCl₂, or NaBH₄. The synthesized materials were characterized by textural, structural, thermal, spectroscopic, and microscopic techniques. Among the materials tested, the biochar activated with NaBH₄ (BNaBH₄) exhibited superior performance, significantly enhancing germination rate (88%), root length (112.9 mm), and shoot length (71.8 mm), compared to the control. Subsequent trials with different concentrations of BNaBH₄ (0, 1, 25, 50, and 75 mg/L) showed a hormetic pattern: intermediate concentrations promoted early seedling growth. Emergence tests confirmed these findings by showing an increased emergence speed index, a reduced mean emergence time, and greater biomass accumulation at tested concentrations of 1 and 25 mg/L (with regression models predicting optimal responses within the 10–25 mg/L range). Regression analysis revealed a nonlinear, dose-dependent response, reinforcing the observed hormetic behavior and highlighting the need for studies to determine the optimal dose for each biochar type and target crop. These findings highlight that using NaBH₄-activated soybean biochar, combined with ultrasonication, is a promising approach to promoting early vigor in Zea mays seedlings at optimal concentrations.