Abstract Soil chemical properties and soil mesofauna composition were assessed at a forest site in northern Austria, where 20 years earlier an amelioration treatment had been performed. The site had been treated with limestone, a high P slag, and ammonium nitrate to replace the poorly growing pine (Pinus sylvestris) forest with a Norway spruce (Picea abies) stand. This treatment was at that time a common means for the amelioration of nutrient-poor forest soils with recalcitrant forest floor layers. After treatment, a dense cover of a nitrophilic stinging nettle (Urtica dioica) developed. Most likely, the site had been over-fertilized, and inadvertently, an experiment with extreme N enrichment had been conducted. The abundance of collembolans increased, and dominance structure shifted from Isotomiella minor, Lipothrix lubbocki, and Isotoma notabilis at fertilizer treatment to Friesea mirabilis, Isotomiella minor, and Sphaeridia pumilis in the control, but the abundance of soil mesofauna generally decreased in the fertilizer treatment. Fertilization reduced the mass of the litter layer from 7.6 to 2.4 kg/m2. The total carbon pool in the soil was reduced due to reduction of the litter layer. However, the content of soil organic matter in the upper mineral soil was significantly increased. A part of the applied and mineralized nitrogen had been lost from the soil, but N retention in the upper mineral soil was still considerable. Soil pH and the base saturation were sustainably increased. Carbon losses upon mineralization of the litter layer were not offset by the increase in C content of the mineral soil. Presently, the C pool in the soil of the fertilized treatment is lower than in the control. However, the overall nutrient enrichment of the soil may facilitate C sequestration in the fertilized site in the future.