Inversion of low heavy metal content in Soil-Scutellaria baicalensis systems using optimized spectral indices and LSSVM

Heavy metal (HM) contamination of soil increasingly threatens the safety of Chinese herbal medicines. Hyperspectral remote sensing technology enables rapid, nondestructive monitoring of soil HM content. This study employs hyperspectral technology to indirectly monitor low Cr and Ni concentrations in the Soil- Scutellaria baicalensis (Huangqin)system using canopy spectra. Surveys and sampling, and data collection were conducted across five growth stages in two regions (Beijing and Hebei Province) of Scutellaria baicalensis (S. b.) . The migration, correlation, and accumulation Cr and Ni in the Soil- S. b. system were analyzed. Canopy spectra were analyzed to estimate Cr and Ni contents using optimized spectral indices and LSSVM-based full-band modeling. Finally, Cr and Ni contents in S. b. leaves were estimated using the optimal inversion model, and further inversions based on enrichment characteristics were performed. The results were as follows. (1) In the May samples, the average soil Cr and Ni contents were 59.35 and 19.87 mg/kg, respectively, which were lower than the soil background values in Beijing and Hebei. Cr and Ni contents in roots, stems and leaves (RSL) were 26.96, 34.81, 37.09 mg/kg and 2.66, 4.08, 3.89 mg/kg, respectively. From June to September, the average Cr and Ni contents in the RSL of S. b. were 1.40, 0.76, 1.09 mg/kg and 1.11, 0.70, 1.23 mg/kg, respectively. (2) A strong correlation existed between low concentrations of HM in the soil and S. b. different parts, reaching a highly significant level (p < 0.01), supporting the use of S. b. leaves to estimate Cr and Ni in different soil parts and S. b.. (3) For Cr and Ni , by modeling the preprocessed first derivative (FD) and second derivative (SD) spectra, the R c 2 = 0.98, RMSE c = 0.10 mg/kg, R v 2 = 0.55, and RMSE v = 0.33 mg/kg for Cr , and R c 2 = 0.99, RMSE c = 0.04 mg/kg, R v 2 = 0.48, and RMSE v = 0.34 mg/kg for Ni were obtained, demonstrating their strong ability to estimate Cr and Ni in S. b. leaves. (4) Using hyperspectral estimation of Cr and Ni in S. b. leaves, together with grouped inversion of enrichment characteristics, stems and roots exceeded 0.33. Therefore, canopy spectral analysis combined with enrichment patterns offers a practical method for monitoring Cr and Ni in Huangqin system, supporting the safety testing of Chinese herbal medicines.