Granulated blast furnace slag stimulates the growth of downy birch seedlings in acidified soil conditions

A study was conducted to investigate the effect of granulated blast furnace slag on the growth of downy birch (Betula pubescens Ehrh.) seedlings in model acidified substrates (pH 4.2–5.2). The addition of slag, whose main components are calcium, silicon, magnesium, and aluminum oxides, was shown to effectively neutralize soil acidity. Substrate deacidification to pH ~6.0 significantly stimulated plant growth: seedling height increased by 74% in a slightly acidic substrate (pH 5.2), and stem diameter by 38% in a strongly acidic substrate (pH 4.2), compared to control plants without slag. Normalizing pH also contributed to an increase in photosynthesis intensity and chlorophyll content to control levels, while simultaneously reducing the activity of antioxidant enzymes, indicating mitigation of oxidative stress. The results demonstrate a triple environmental benefit: safe disposal of industrial waste, improvement of the quality of acidic forest soils, and stimulation of forest plant growth, which contributes to the decarbonization of the metallurgical industry.