Enhancing Maize Drought Resilience with Agrichar Soil Amendments and Nanobiochar Foliar Sprays: Effects on Physio–Biochemical Responses

Drought stress poses a threatening impact on maize growth, demanding the need for sustainable strategies to enhance plant resilience. This study investigated the effect of agrichar (AC) and nanobiochar on three maize plant hybrids subjected to three water levels (100%, 80%, and 60%), with treated groups receiving nanobiochar foliar spray (NBFS) with or without soil AC doses (0 t/ha (T), 5, and 10), while the control group received no NBFS and AC. Results demonstrated that the 5 and 10 T AC improved membrane stability index-(MSI) by 35% and 82%, respectively. The combined treatment significantly enhanced antioxidant activities as superoxide dismutase activity was enhanced by 11% in NBFS combined with agrichar treatment compared to no-NBFS and AC. Application of NBFS significantly enhanced catalase activity under 100%, 80%, and 60% water level (WL) by 9.1%, 7.5%, and 7.1%, respectively, compared to no-NBFS and AC. The enhancement in yield kg/ha with 5 and 10 T AC supplemented soil by 23% and 43.7%, respectively, at 60% WL. The combined application led to improvement in growth parameters, photosynthetic pigments, and grain yield. The improved agronomic performance observed under AC and NBFS application was further supported by molecular docking, which revealed a strong binding affinity of tartaric acid (an active metabolite present in plants as well as in AC) with antioxidant enzymatic protein (ascorbate peroxidase). In conclusion, these findings demonstrated that the combined application of 10 T/ha AC and NBFS caused an average improvement of 40% in maize yield under limited irrigation.