Combined application of biochar and nanoparticles (silicon and boron) effectively reduced the metal toxicity of sweet basil (Ocimum basilicum L)

Biochar and nanoparticles (NPs) are potential strategies for increasing plant yield and minimizing the negative effects of toxic metals on sweet basil (Ocimum basilicum L). The current study aims to reduce the access of toxic elements to the oil extracted from basil plants growing in polluted soils by biochar and NPS of silicon (Si) and boron (B). Sweet basil plants were grown in contaminated soil that contained cadmium (Cd) and lead (Pb) at concentrations of 58 and 800 mg kg⁻¹, respectively. The experiment included two doses of biochar (0 and 1%, w/w) and four foliar combinations of Si and B nanoparticles at the dose of 100 mg L⁻¹ of Si and/or B. Cd and Pb availability were reduced by 44 and 48%, respectively, compared to the control. The soil pH raised significantly (p < 0.05) as a result of biochar addition. Furthermore, biochar addition at the dose of 1%, (w/w) caused a 14% increase in the soil organic matter. The highest growth parameters of basil plants were obtained from the biochar treatment with Si + B NPs foliar application. The treatment that was amended with biochar and sprayed with Si + B showed the greatest significant values of nitrogen (N), phosphorus (P), potassium (K), and calcium (Ca) content in basil plants. The chlorophyll content of basil leaves rose along with the synthesis of proline and soluble carbohydrates after the addition of biochar to the polluted soil and Si + B spraying. Biochar minimized Cd in the leaf and oil by 48 and 49%, respectively, compared to the control, while Pb concentrations were reduced by 29 and 49%, respectively. The oil extracted from the basil plants grown in the soil amended with biochar contained 50–52 and 23–26 μg kg⁻¹ of Cd and Pb, respectively. Adding biochar to the contaminated soil increases the oil yield of sweet basil and reduces its content of toxic elements, while spraying the basil plant with silicon and boron nanoparticles increases the plant’s resistance to metal toxicity.