The Rengen Grassland Experiment: soil contamination by trace elements after 65 years of Ca, N, P and K fertiliser application

The Rengen Grassland Experiment (RGE) was established in the Eifel Mts. (Germany) on a low productive Nardetum in 1941. Since then, the following fertiliser treatments have been applied along with a two cut system: unfertilised control, Ca, CaN, CaNP, CaNP-KCl and CaNP-K2SO4 with basic slag (syn. Thomas phosphate) as the only P fertiliser. The effect of long- term fertilisation on plant-available (extracted with 0.01 mol l(-1) CaCl2), easily-mobilisable (extracted with 0.05 mol l(-1) EDTA), potentially-mobilisable (extracted with 2 mol l(-1) HNO3) and total concentrations of trace elements (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in the top 0-10 and 10-20 cm of soil were investigated in 2006. According to redundancy analysis (RDA), the effect of treatment on the concentrations of risk elements was significant and explained 82.3 and 90.6% of the variability in the data in the 0-10 and 10-20 cm soil layers, respectively. Basic slag supplied the soil with considerable amounts of As, Cr, Cu, Fe, Mn and Zn. Following 65 years of fertiliser application the concentrations of risk elements in the soil profile had increased substantially, especially with basic slag. However, threshold limits for total trace element concentration in soil permitted by Czech national legislation were exceeded only in the case of As. The increase in plant-available As concentrations was most critical as it increased the potential uptake of As by plants in plots fertilised with P. Although P treatments received more than 300 g of Cr ha(-1) annually, no effect on plant-available Cr soil content was detected. This contrasted with the accumulation of total Cr in the 0-10 and 10-20 cm soil layers. Furthermore, plant availability of Cd, Fe, Mn and Zn was affected by soil pH and generally decreased with the application of quick lime. Plant availability of these elements was not correlated with amounts supplied by fertilisers.