The source apportionment of pollutants is the key to preventing and controlling the pollution caused by heavy metals in soils. The aim of this study was to investigate the main sources of heavy metals in the soils of black shale areas in western Zhejiang, China. Based on geostatistical spatial analysis, this research employed positive matrix factorization (PMF) for the source apportionment of heavy metals in paddy soil. The results showed that contaminated arable soils were concentrated in the western and southern study areas. At least five major sources of heavy metals were screened in this study: natural sources (39.66%), traffic emissions (32.85%), industrial emissions (9.23%), agricultural activities (9.17%), and mining (9.10%). To be specific, Cd was mainly from mining; As originated from agricultural inputs such as fertilizers and pesticides; and Hg, as an industrial pollutant, was transported by atmospheric deposition in the study area. The accumulation of Pb, Zn, and Cu was mainly influenced by natural sources and anthropogenic sources, i.e., traffic emissions, while that of Cr and Ni was controlled by natural sources.

The objectives of this study were to evaluate the cadmium adsorption capacity of iron–organic associations (Fe-OM) formed by laccase-mediated modification and assess the effect of Fe-OM on the immobilization of cadmium in paddy soil. Leaf organic matter (OM) was extracted from Changshan grapefruit leaves, and then dissolved organic matter (Lac-OM) and precipitated organic matter (Lac-P) were obtained by laccase catalytic modification. Different Fe-OM associations were obtained by co-precipitation of Fe with OM, Lac-OM, and Lac-P, respectively, and the adsorption kinetics, adsorption edge, and isothermal adsorption experiments of Cd on Fe-OM were carried out. Based on the in situ generation of Fe-OM, passivation experiments on Cd-contaminated soils with a high geological background were carried out. All types of Fe-OM have a better Cd adsorption capacity than ferrihydrite (FH). The theoretical maximum adsorption capacity of the OM-FH, Lac-OM-FH, and Lac-P-FH were 2.2, 2.53, and 2.98 times higher than that of FH, respectively. The adsorption of Cd on Fe-OM is mainly chemisorption, and the -OH moieties on the Fe-OM surface form an inner-sphere complex with the Cd ions. Lac-OM-FH showed a higher Cd adsorption capacity than OM-FH, which is related to the formation of more oxygen-containing groups in the organic matter modified by laccase. The immobilization effect of Lac-OM-FH on active Cd in soil was also higher than that of OM-FH. The Lac-OM-FH formed by laccase-mediated modification has better Cd adsorption performance, which can effectively inactivate the activity of Cd in paddy soil.

To explore the phytoremediation effect of ornamental chrysanthemums on cadmium (Cd)-contaminated farmland soil, a 2-year field trial was conducted on 23 chrysanthemum cultivars in Cd-contaminated soil in Zhejiang Province, China. The biomass yields, Cd content of the plants, Cd enrichment coefficient, and remediation efficiency were evaluated. The aboveground biomass of the tested chrysanthemums was 67.10–166.08 g/plant, the aboveground Cd content was 1.97–5.92 mg kg⁻¹, and the Cd enrichment coefficient was 2.98–9.84. In a screening test of twenty-three chrysanthemum cultivars, six cultivars, such as marigolds, were characterized by high cadmium accumulation, with the average cadmium accumulation of chrysanthemums exceeding 0.6 mg per plant, and the remediation of rhizosphere-contaminated soils took only 4–5 years. Fourteen chrysanthemum cultivars have good multiple-cropping characteristics, and five multiple-cropping chrysanthemum cultivars, such as QX-yz, have high heavy metal tolerance. The multiple-cropping JL-yg cultivars with higher Cd accumulation could be recommended for the remediation of Cd-contaminated farmland. The application of bamboo vinegar to the chrysanthemum rhizosphere effectively promoted Cd absorption. After estimating the economic benefits of artificially planting five dominant varieties of chrysanthemums for polluted farmland remediation, it is concluded that the annual income of a worker can be slightly higher than the average annual income level of local residents.

To address the challenge of synergistically mitigating multiple constraints—structure, nutrients, and microorganisms—in newly reclaimed farmland, and to comprehensively improve soil quality and crop productivity, a field experiment was conducted. Treatments with different combinations and application rates of microbial agents, organic fertilizer, modified biochar, and minerals were established. The effects of these treatments on soil physicochemical and biological properties, as well as wheat growth, were analyzed to identify key synergistic measures and their mechanisms for rapidly enhancing soil quality and crop productivity. Results showed that the integrated treatment (MCN), which consisted of organic fertilizer at 6 t ha⁻¹, modified biochar at 1.5 t ha⁻¹, minerals at 0.75 t ha⁻¹, and an appropriate amount of Bacillus amyloliquefaciens agent, was the optimal scheme balancing improvement efficacy and economic benefits. MCN significantly improved soil physical structure and chemical nutrient status. Compared to other treatments, it reduced bulk density by 0.14–0.18 g cm⁻³, increased large aggregate content by the greatest margin (12 g kg⁻¹), raised field water-holding capacity by 13.0–22.7 g kg⁻¹, elevated pH by 0.41–0.87, and increased soil organic matter by 0.55–4.43 g kg⁻¹, while effectively enhancing phosphorus availability and calcium content. MCN also effectively reshaped the soil microbial community toward a healthier ecological state. Compared to other treatments, it markedly increased the absolute abundance of beneficial bacterial classes, with Fibrobacteria being 2.0–9.4 times more abundant. It also increased β-glucosidase activity by 14.4–73.9 nmol g⁻¹ h⁻¹ and markedly enhanced both α- and β-diversity. Meanwhile, MCN significantly promoted wheat growth indicators such as plant height and spike length, and the yield was more than 3.5 times that of the NPK treatment. This study constructed a cascading efficiency path for improving soil quality and crop productivity in newly reclaimed farmland using PLS-SEM: The integrated treatment improved soil physical structure and provided balanced chemical nutrients and energy, thereby promoting microbial community restructuring and enhanced activity. Subsequently, changes in the microbial community may have further improved soil physicochemical properties and strengthened positive soil–crop interactions, ultimately leading to simultaneous improvements in crop yield and plant growth. The model had a good fit (GOF = 0.70, R² = 0.90), and through RDA, PCoA, and Pearson correlation, the synergistic efficiency mechanism of four materials (fertilizer, organic fertilizer, biochar, and minerals) in improving soil quality and crop productivity was analyzed. Based on this, this study established a mechanism model for improving soil quality and crop growth in newly reclaimed farmland through integrated treatment, providing a theoretical basis and practical paradigms for improving soil quality and achieving crop yield increase in newly reclaimed farmland.