Effects of biochar combined with nitrogen fertilizer on ryegrass remediation of cadmium-contaminated soil

In order to reduce the harm of cadmium (Cd) in soil, the effects of biochar combined with nitrogen fertilizer (NO3--N) on Cd enrichment in ryegrass were studied. In this study, soil contaminated with 0.3 mg/kg, 3 mg/kg and 5 mg/kg Cd was subjected to 6 treatments (CK: Neither NO3--N nor shell biochar; BC: 5% shell biochar; BNX: shell biochar + X mg/mL NaNO3 solution, X = 1, 2, 5, 10), the remediation effect of biochar combined with NO3--N on Cd-contaminated soil was investigated. A single application of biochar can effectively fix free Cd in the soil. Under different concentrations of Cd pollution, the maximum removal rates of Cd under different NO3--N levels could reach 30.23%, 36.06%, and 30.90%, respectively. In addition, it was found that the organic matter of medium and low Cd-polluted soil was positively correlated with the available Cd content. In contrast, in the case of higher Cd pollution, organic matter has less influence on the effective Cd content. Combined with correlation analysis, pH plays a key role in Cd morphological change and Cd enrichment. When the mass ratio of NO3--N and biochar is about 5:1 similar to 10:1, Cd in soil can be reduced more effectively and quickly, the phytoremediation period can be shortened, and the biological removal rate and Cd enrichment can be increased.