VOLUME 19 (Supplement)

Multi-elemental and stable isotope characterization of soil from selected Carabao mango orchards in the Philippines

Mango productivity in the Philippines is challenged by declining yields and site-specific soil constraints. These challenges highlight the need to assess site conditions and identify key indicators that are associated with mango productivity. In this study, we evaluated the soil characteristics of selected orchards in six major mango-producing provinces in the Philippines using multi-elemental and stable δ¹³C and δ¹⁵N isotope techniques to determine the governing geochemical processes related to location and depth interactions, the nutrient status, and historical land-use changes. Location proved to be a major driver of soil parameter variation, while depth exerted a less significant influence. Redox-driven nutrient cycling, particularly involving Mn–Fe–C–N interactions, was identified as an important geochemical process influencing soil elemental dynamics across sampling sites. Stable isotope analysis revealed a distinct shift in soil δ¹³C values from C4 to C3-derived signatures, indicating progressive enrichment of δ¹³C with depth and confirming the historical transition from C4 grasslands to long-term C3 mango monocultures. Meanwhile, δ¹⁵N values varied significantly among provinces, with depleted δ¹⁵N signatures indicating a greater reliance on synthetic N fertilizers, whereas enriched δ¹⁵N values reflected long-term organic matter inputs and enhanced microbial N transformations. These findings demonstrate that the combined application of stable isotopes and multi-elemental analysis is an effective approach for assessing the nutritional status and land use history of mango orchard soils. The results also provide valuable baseline information for developing site-specific nutrient management strategies and recommendations to improve mango productivity in the Philippines.