Orange peel biochar: An effective amendment to improve the maize resilience by regulating the soil enzymatic activities, nutrient uptake, and ionic homeostasis under salinity stress

The conversion of organic waste into biochar offers innovative solutions for soil remediation. Globally, salinization is a major threat to agricultural productivity, significantly contributing to soil degradation. The application of orange peel (OP) waste could provide a better solution for sustainable crop productivity. The study investigated the influence of OP and orange peel biochar (OPB) at varying doses (0.5 %, 1 %, and 2 %) on soil enzymes and maize growth under different salinity levels (1.66, 4, and 8 dS m^–¹). The results indicate that OPB was more effective than OP, with promising outcomes even at lower rates. At 8 dS m^–1, 1 % OPB significantly enhanced shoot length (30.7 %), root length (21.9 %), grain yield (3-fold), relative water content (14.2 %), protein content (32.1 %), chlorophyll value (51.9 %), carotenoid content (31.5 %), and grain N, P, and K contents (27.5 %, 54.0 %, and 17.8 %), while significantly reducing Na contents in roots (16.6 %) and shoots (27.8 %) compared to the control. Furthermore, 1 % OPB was an optimal rate for enhancing soil enzymatic activities, including urease (55.4 %), acid phosphatase (37.8 %), and alkaline phosphatase (47.4 %), outperforming the control at 8 dS m^–1. The structural equation model (SEM) revealed that improving soil enzymatic activities was the main mechanism accelerated by OPB to improve the maize growth and yield. Adding 1 % OPB to soil is an efficient and effective approach for alleviating the toxic effects of salinization to improve maize growth, physiology, and yield. These findings will advance OP recycling as a cost-effective solution for sustainable agriculture and mitigating salinity stress.