Biochar application alters soil Ni fractions and phytotoxicity of Ni to pakchoi (Brassica rapa L. ssp. chinensis L.) plants

Abstract

Soil contamination with nickel (Ni) from anthropogenic activities can have serious environmental impacts. The consequences of Ni contamination on the Ni fractional distribution in the soil, their potential phytotoxicity, and the possible use of biochar are least deliberated. A greenhouse experiment was conducted to determine the effect of selected Ni contamination levels and kunai grass biochar on soil Ni fractions and crop growth response. A bulk soil in polythene bags was spiked with NiCl 2 solution at 0, 56, 100, and 180 mg Ni kg −1 soil. Another set of bags received kunai grass ( Imperata cylindrica ) biochar at 0.75% on a dry weight basis. The treatments were replicated 3 times and planted with pakchoi seeds. Results indicated dose-dependent variations in the distribution of Ni fractions namely, exchangeable and acid-soluble, oxidizable, and residual Ni upon fractionation of soil samples drawn on days 30 and 60. As the level of Ni contamination increased, a significant enhancement of soil exchangeable and acid-soluble portion of Ni and oxidizable Ni with concomitant failure of pakchoi seedling growth. The biochar application significantly (p < 0.05) decreased exchangeable and acid-soluble Ni (58%) and enhanced residual Ni pools in low Ni contaminated soils (56 mg) thereby relieving pakchoi plants from toxic effects of Ni. Biochar incorporation to the soil decreased the Ni uptake by pakchoi plants and decreased bioaccumulation factor from 1.81 to 1.20 in low Ni contaminated soil only. Chemical transformation of Ni fractions due to biochar application can effectively reduce toxicity to crop plants, and Ni uptake thus a safe option to manage soil contaminant Ni. • Biochar application investigated in spike Ni contaminated soils under pakchoi plants. • Biochar @ 0.75% transformed exchangeable Ni to more stable residual Ni fraction. • Reduced phytotoxicity , and Ni uptake coupled with decreased Ni bioaccumulation. • Soil incorporation of biochar is potentially safe approach in Ni contaminated soils.