Harnessing biochar and plant growth‐promoting bacteria for sustainable crop production under reclaimed water irrigation: A review

Global agriculture accounts for approximately 72% of total freshwater consumption and accelerating water scarcity from population growth, and climate change is intensifying pressure on this supply, particularly in arid and semi-arid regions. Reclaimed water (RW) has emerged as a strategically important supplementary irrigation source that can alleviate freshwater competition and partially offset synthetic fertilizer demand. However, long-term RW application introduces compounding risks including soil salinity accumulation, sodicity, accumulation of potentially toxic elements, and inputs of pharmaceutical residues and microbial contaminants that threaten soil health and crop safety. This review critically examines the co-application of biochar and plant growth-promoting bacteria (PGPB) as an integrated amendment strategy for mitigating RW-induced multi-stressor challenges while enhancing crop productivity and soil biological health. Biochar improves soil aggregation, water retention, cation exchange capacity, and toxic ion immobilization, while PGPB enhance nutrient acquisition, phytohormone production, and plant stress tolerance. Critically, biochar functions as a protective carrier that extends PGPB persistence and colonization, producing synergistic outcomes that neither component reliably achieves alone. Drawing on saline irrigation, heavy metal, and water-deficit studies where RW-specific studies is limited, this review identifies mechanistic gaps, limitations, and priority research directions for advancing sustainable RW reuse in agriculture.