Seventy-five years of fertiliser application: insights from the Steinach grassland experiment

Abstract Purpose Soil contamination by potentially toxic elements, especially heavy metals, poses risks to food security and human health. The long-term use of mineral and organic fertilisers may lead to the accumulation and mobilisation of such elements. This study investigates how different fertilisation regimes influence the total content, mobility, and bioaccessibility of risk elements in soils of a historical grassland trial. Methods The research was conducted within the Steinach Grassland Experiment (SGE), initiated in 1933 on an alluvial meadow featuring Alopecurus pratensis in Southeast Germany, which is one of the longest-running grassland fertiliser experiments in Continental Europe. Soil samples were collected from 75 plots treated with various nitrogen (N), phosphorus (P), and potassium (K) fertilisers. Element concentrations were analysed using four extraction methods: aqua regia (total), CaCl₂ (plant-accessible), EDTA (easily mobilisable), and diluted HNO₃ (potentially mobilisable). Results Phosphorus fertilisation led to a slight increase in Fe, Zn, Mn, As, Cr, and Cd concentrations. The modest enrichment of arsenic and chromium was likely related to the historical application of Thomas slag. Despite decades of fertiliser application, concentrations of risk elements did not exceed national regulatory thresholds. Conclusion Long-term fertilisation at the SGE site has not resulted in excessive accumulation of potentially toxic elements beyond regulatory limits established for agricultural soils. Nevertheless, elements such as As, Cd, and Cr require regular monitoring to prevent their potential accumulation beyond safe thresholds.