Simultaneous in-situ remediation and fertilization of Cd-contaminated weak-alkaline farmland for wheat production

In-situ remediation of heavy metal-contaminated farmland mainly focuses on acidic soil, however, weak-alkaline farmland widely exists in north China. Meanwhile, fertilization is usually ignored, but it may influence remediation efficiency as well as grain production. In this paper, field experiments were carried out to investigate in-situ simultaneous remediation and fertilization of Cd-contaminated weak-alkaline soil by microbial agent mixed with fulvic acid (MFA), wheat straw biochar, sepiolite and their mixture. Results showed that addition of these conditioners decreased the soil available Cd by 39.86%–71.33% and the wheat Cd by 41.94%–87.10%. The decrease order of soil available Cd followed sepiolite > mixture > biochar > MFA, while the decrease order of wheat Cd was mixture > sepiolite > biochar > MFA. With addition of mixture, the wheat Cd reduced to 0.08 mg/kg, lower than the Cd limit of 0.1 mg/kg in Contaminant Limit in Food of National Food Safety Standards (GB2762-2017), and the highest wheat yield reached 7590 kg/hm2. The MFA had significant effects on improvement of soil organic matters, nutrients and rhizosphere microbes; the biochar was prominent in improving soil organic matters, inhibiting wheat Cd and soil available Cd; the sepiolite had obvious advantages in reducing wheat Cd and soil available Cd; and the mixture had a more balanced effect on soil remediation and fertilization. Correlation study showed that soil available Cd significantly affected the uptake of Cd by wheat, and wheat yield was significantly positively correlated with soil organic matters, available N. Therefore, reducing soil available Cd, increasing soil organic matters and nutrients are the keys to simultaneous remediation and fertilization of Cd-contaminated weak-alkaline soil for wheat production.