Evaluation of soil amendment effect on foliar nutrient composition as basis for developing predictive technologies for forest stand response

This study evaluated the impact of soil amendments – ammonium nitrate (NH₄NO₃) and wood ash – on the chemical composition of tree needles and leaves, focusing on essential macro- and micronutrients (nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg)) critical for forest growth. Tree crown material from Scot’s pine, lodgepole pine, Norway spruce and silver birch was collected after fertilizer application. Foliar samples were taken from multiple experimental plots, with three first-stratum trees sampled in each plot, concentrating on the upper third of the tree crowns. This approach ensured representative data for nutrient concentration changes over time. The response varied depending on the forest site type and fertilizer type. The statistically significant differences observed in conifer forests with drained organic soils indicate that NH₄NO₃ fertilization could affect N concentrations in plant tissues, possibly as a result of the nutrient dilution effect, where higher biomass may lead to a decrease in N concentration in the needles. Wood ash, either alone or combined with NH₄NO₃, had a more pronounced positive effect on K and P in conifer stands, with its impact remaining site-specific. It also increased Ca concentrations, particularly in conifer forests on dry upland and drained mineral soils, while its effect in deciduous stands was limited to forests with drained mineral soils. Mg concentrations in fertilized plots were higher in deciduous stands with drained mineral soils, whereas coniferous stands showed more varied responses. Given the role of nutrient availability, soil properties, and dilution effects in determining foliar nutrient concentrations, ongoing monitoring and repeated sampling before thinning are recommended to assess long-term fertilization impacts and prevent nutrient imbalances.