Alleviation of nickel toxicity and an improvement in zinc bioavailability in sunflower seed with chitosan and biochar application in pH adjusted nickel contaminated soil

This study demonstrates the reduction of nickel (Ni) toxicity and enhancing zinc (Zn) bioavailability from sunflower seed with biochar (BC) and chitosan (CH) application to Ni contaminated soil. The pH of experiment soil was adjusted to value 6.5 prior to its use in a greenhouse experiment. Acidified Ni contaminated soil was amended with Zn (4 mg kg⁻¹ soil), while BC and CH, both as alone [1% each (w/w)] and in combination [0.5% each (w/w)], were used as immobilizing agents for Ni. Significantly higher concentrations of Zn were found in seed receiving ZnSO₄ treatments. However, these results were more pronounced in the treatment (Zn+CH+BC) where Zn, CH, and BC were together applied. The Zn+CH+BC treatment improved seed quality parameters, phytate/minerals molar ratios, increased seed weight (per pot) up to 75%, Fe 41%, Zn 42% in seed, while reduced Ni concentration up to 17% in seed, over control. Similarly, Zn+CH+BC treatment significantly decreased oxidative stress by improving antioxidant defense system in sunflower. The results of this preliminary study suggest that further studies are obligatory to corroborate the extent of Ni immobilization in soil and enhancing Zn bioavailability from sunflower seed under field conditions with realistic and applicable rates of BC and CH.