Objective  The study aimed to explore the phytoextraction remediation effectiveness and mechanism by using Trichoderma harzianum with organic fertilizer for strongly acidic heavy metal contaminated soil, in consideration of the function of microbial (Trichoderma harzianum) passivation and Brassica chinensis (Brassica rapa L. Chinensis Group.) extraction, combined with organic fertilizer application.

  Method  In the pot experiment, the separate and combined treatments of Trichoderma harzianum passivation and Brassica chinensis extraction were designed, together with the application of organic fertilizer. A blank control was set up and each treatment has three replicates, making a total number of 24 treatments.

  Result  Compared with the control treatment, the soil pH increased by 14.05%-34.60% and the organic matter content increased by 10.11%-99.42% in the treatment of Trichoderma harzianum and organic fertilizer. Under the treatment of Trichoderma harzianum, the soil available potassium and ammonium nitrogen content increased by 51.02% and 10.31%. Under the treatment of organic fertilizer, the soil available phosphorus and available potassium were increased by 451.84% and 433.69%. The aboveground biomass of Brassica chinensis increased by 414.29% in the combination of Trichoderma harzianum and organic fertilizer; The aboveground biomass of Brassica chinensis has significant negative correlation with soil total Cd. The aboveground transfer factors and bioconcentration factors of Brassica chinensis increased by 25.58% and 21.29% compared with that of control; Soil total Cd content decreased by 43.83% and the acid extractable Cd content of soil decreased by 87.41%. Both aboveground and root Cd in Brassica chinensis has significant negative correlation with soil acid extractable Cd.

  Conclusion  The combination of Trichoderma harzianum and organic fertilizer has the potential to strengthen the phytoextraction efficiency and remediation of acidic Cd contaminated soil, which provide a theoretical basis and practically guide for heavy metal-contaminated soils in mining areas.