Effect of wheat straw-derived biochar on rape growth and cadmium uptake in an alkaline soil

We explored the effect of wheat straw-derived biochar on remediation of alkaline cadmium(Cd)contaminated soil by conducting the sequential batch adsorption experiment and pot experiment. The results showed that the sorption isotherm of Cd on biochar was highly nonlinear, indicating that the surface sorption of Cd on biochar was dominant. The distribution coefficient(Kd)of Cd on biochar was 1.5~3.0 times more than that on soil. Biochar application(1%, m/m)to soil promoted the sorption of low-concentration Cd by soil and increased the Kd value by 19.5% at the equilibrium concentration of 0.1 mg·L-1. In contrast, biochar inhibited the sorption of high-concentration Cd by soil and decreased the Kd value by 37.2% at the equilibrium concentration of 10 mg·L-1. Biochar application to soil had no significant effect on soil pH. Biochar alleviated the inhibitory effect of Cd on rape growth, which biomass in rape was increased by 45.0%. In addition, biochar application decreased the uptake of Cd by 40.6% in rape. There was a strong correlation between the amount of Cd extracted by CaCl2, Mg(NO3)2, NH4OAC, HCl, DTPA, and BCR1, and the amount of Cd in the aboveground part of rape(R2>0.8). In conclusion, wheat strawderived biochar is beneficial in reducing the Cd bioavailability in alkaline soil; however, this effect is not achieved via increasing soil pH and adsorption capacity.