Soil applied biochars and foliar applied nanoparticles improve wheat growth in cadmium contaminated soil

We studied the interactive effects of soil-applied algal-biochar (ABC) and sorghum-biochar (SBC) with foliar applications of iron oxide nanoparticles (FeO-NP) and zinc oxide nanoparticles (ZnO-NP) on the growth and accumulation of cadmium (Cd) by wheat grown in a cadmium-contaminated soil (previously irrigated with sewage water). Algal and sorghum BCs were prepared using Kon-Tiki and analyzed prior to experimentation. Soil was amended with 1% biochar (ABC or SBC) and filled into pots in which wheat was grown to maturity. FeO-NP and ZnO-NP (5 g L⁻¹) were applied foliarly. The results demonstrated a positive and significant influence of biochar and nanoparticles on agronomic parameters such as plant height, fertile tillers, grain yield, and straw yield. The agronomic attributes were highest in ABC-amended soil with FeO-NP foliar application. Grain Zn concentration increased significantly with ZnO-NP, while Cd concentrations in grain and straw decreased significantly with FeO-NP in SBC-amended soil. Soil pH and ECe were unaffected by NPs. However, ABC and SBC amended treatments showed a significant decrease in DTPA-extractable Cd, compared to No-BC treatments. The uptake of Cd by wheat grains decreased by 33% with the foliar application of FeO-NP and ZnO-NP, respectively, in the absence of biochar (no-BC), while reductions of 34% and 25% were observed when SBC was applied to the soil in combination with FeO-NP foliar application. The study demonstrated that combined biochar and nanoparticle applications can mitigate Cd uptake, enhance Zn accumulation, and improve wheat growth in contaminated soils, with ABC and FeO-NP showing the most promising results. • Combined application of biochar and nanoparticles significantly improved wheat growth, yield, and metal homeostasis in contaminated soil. • Foliar application of FeO-NP with biochar (especially sorghum biochar, SBC) reduced grain Cd uptake by up to 33%, demonstrating effective Cd mitigation. • ZnO-NP foliar spray increased grain Zn concentration, highlighting its potential for biofortification in wheat. • Biochar amendments (ABC and SBC) reduced DTPA-extractable Cd in soil, with SBC showing greater efficacy in Cd immobilization. • Green-synthesized nanoparticles and biochar derived from waste materials (algae and sorghum) provide a sustainable solution for managing heavy metal-contaminated soils.