Assessment of Soil Injection Treatments in Street Tree Beds: Impacts on Soil Microclimate and Foliar NDVI

This study evaluated the effects of soil injection treatments, including aeration, hydrogel application, and mycorrhizal inoculation, on the soil hydrothermal regime and foliar NDVI of young street trees (Prunus serrulata) under real urban conditions. The experiment was conducted during three growing seasons (2023–2025) at two sites with contrasting soil structural properties. Soil moisture, temperature, and leaf-level NDVI were monitored to assess treatment effects and temporal variability. Soil moisture responses to the treatments were site-dependent, with Aeration and the combined Mycorrhiza + Hydrogel treatment showing contrasting responses between the two sites. Aeration showed site-dependent effects, improving soil moisture conditions in compacted clay soils, but providing limited benefits in coarse-textured soils. The amendment treatments, all of which included Aeration, showed variable responses relative to Aeration alone. Soil temperature responses were less consistent, with no significant effects of Site, Treatment or their interaction. Differences in NDVI associated with the combined Mycorrhiza + Hydrogel treatment were detected during the following two growing seasons. The results highlight that soil injection treatments can contribute to urban tree management; however, their effects are site-dependent and should be evaluated through long-term monitoring.