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.

Some soil heavy metal pollution, such as As (Arsenic) and Cd (cadmium), in the black shale areas of western Zhejiang, exhibits significant geological background characteristics, yet the migration patterns and bioavailability are unclear. This study systematically integrated geochemical investigations of the rock-weathered soil–water–soil system to reveal the migration mechanisms and the species of the potentially toxic elements (PTEs) in black shale regions. The results showed that strongly acidic drainage (pH = 3.9) released from black shale weathering led to significant enrichment of Cd and As in soils. The mean Cd concentration (0.84 mg/kg) was 3.3 times higher than the Zhejiang background value, with active speciation (exchangeable fraction and humic acid-bound fraction) dominating during migration. This research provides a scientific basis for PTE prevention and control in geologically high-background regions.

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.