Biochar-based metal oxide nanocomposites of magnesium and manganese improved root development and productivity of safflower (Carthamus tinctorius L.) under salt stress

Biochar-based metal oxide nanocomposites (BNCs) are the new classes of soil amendment materials, which combine the benefits of biochar with nano-materials. This research was conducted to evaluate the possible effects of biochar-based nanocomposites (25 g biochar kg −1 soil; 25 g BNC-MgO kg −1 soil; 25 g BNC-MnO kg −1 soil and 12.5 g BNC-MgO + 12.5 g BNC-MnO kg −1 soil) on phenology, morphology and productivity of safflower plants ( Carthamus tinctorius L.) under salt stress (non-saline, 6 and 12 dSm −1 NaCl salinities). Soil had a silty loam texture with low organic matter, neutral pH and 18.80 cmol kg −1 cation exchange capacity. Application of biochar and particularly BNCs increased the pH and cation exchange capacity of soil, growth of main and lateral roots (especially lateral roots), root density, plant height, shoot diameter, leaf area, chlorophyll content and stability, branches and flowers per plant, potassium, magnesium and manganese contents, duration of reproductive stage, plant biomass, seed and oil yields of safflower under salt stress. The sodium content and duration of vegetative stage in safflower plants were reduced by biochar and BNCs treatments. In general, BNC-MgO in individual and combined forms with BNC-MnO were the superior treatments for enhancing safflower root and shoot growth and productivity under salt stress through improving the phenological (reproductive stage) and morphological parameters of plants. • Biochar-based nanocomposites (BNCs) reduced sodium content of plants. • BNCs improved cation exchange capacity of a silty loam soil with low organic matter. • BNCs increased root and shoot growth parameters at saline and non-saline conditions. • The impacts of BNCs on lateral root growth were more noticeable than the main root. • Nutrient contents, seed and oil yields were improved by BNCs treatments.