Spectral–Biogeochemical Integration for Vegetation Health and Soil–Plant Metal Dynamics in Wastewater‐Irrigated Agroforestry: Insights From Sadat Forest, Egypt

ABSTRACT

This study develops an integrated framework that combines Sentinel‐2 spectral indices with soil and plant geochemistry to evaluate vegetation health and soil–plant metal dynamics in Casuarina equisetifolia (7–10 years), Eucalyptus camaldulensis (7–10 years), and Sesbania sesban (1–3 years) plantations in Sadat Forest, Egypt. Vegetation indices (Normalized Difference Vegetation Index [NDVI], Simple Ratio Index [SR], Red Edge Index [RE], Anthocyanin Reflectance Index 2 [ARI2]) revealed clear age‐ and species‐specific differences, with younger S. sesban exhibiting higher canopy vigor, while older stands of Casuarina and Eucalyptus showed spectral signatures of stress and reduced productivity. Soil analyses indicated that most heavy metals (iron [Fe], chromium [Cr], manganese [Mn], cobalt [Co], nickel [Ni], copper [Cu], zinc [Zn], cadmium [Cd], lead [Pb]) remained within safe thresholds, though localized enrichment reflected long‐term wastewater irrigation. Bioaccumulation factor (BAF) calculations demonstrated species‐specific uptake strategies: Casuarina and Eucalyptus acted as effective accumulators of Mn, Cu, Zn, and Pb, whereas Sesbania enhanced nitrogen and boron enrichment through legume‐associated processes. Statistical analyses confirmed significant effects of species and plantation age on nutrient availability, while correlation patterns highlighted nutrient synergies (potassium [K]–calcium [Ca]–magnesium [Mg], phosphorus [P]–trace elements) and antagonisms (Mn with multiple nutrients). These findings underscore the importance of species selection, plantation age, and mixed‐species design in sustaining soil fertility and ecological resilience. By linking spectral stress signals with biochemical uptake mechanisms, this work provides a novel, integrative approach for monitoring and managing wastewater‐irrigated agroforestry systems under anthropogenic stress.