A Critical Review of Straw Derived Biochar for Managing Antimicrobial Resistance in Sandy Agricultural Soils

Antimicrobial resistance (AMR) in agricultural soils involves antibiotic residues, resistant bacteria, intracellular and extracellular resistance genes, and mobile genetic elements. Sandy soils can facilitate off-site transport through rapid drainage and limited sorption, although mobility alone does not establish greater AMR proliferation or human exposure. This structured critical review evaluates straw-derived biochar as a risk-management amendment, distinguishing direct evidence from mechanistic inference. The literature reports biochar-associated outcomes ranging from increases or negligible changes for individual genes to substantial reductions approaching 90% in particular experimental systems. No pooled effect was calculated because studies differed in feedstock, production conditions, amendment rate, soil and analytical methods. Evidence is strongest for sorption of selected antibiotics, metal retention and altered contaminant transport. Suppression of horizontal gene transfer and consistent resistome modification remain context dependent. No universal optimum pyrolysis temperature is supported; performance depends on contaminant and soil properties, and aging can improve or weaken retention. Field evidence in sandy profiles remains limited, particularly for deep transport, groundwater connectivity and crop exposure. Straw-derived biochar therefore represents a conditional AMR-management option requiring target-specific characterisation and validation. Future studies should integrate contaminant mass balances, absolute and relative gene abundance, mobile-element markers, metagenomics, culture-based measurements and multi-year field monitoring.