Abstract. Soil contamination by trace elements (TEs) is a major concern for
sustainable land management. A potential source of excessive inputs of TEs
into agricultural soils are organic amendments. Here, we used dynamic
simulations carried out with the Intermediate Dynamic Model for Metals
(IDMM) to describe the observed trends of topsoil Zn (zinc), Cu (copper), Pb (lead) and Cd (cadmium)
concentrations in a long-term (>60-year) crop trial in
Switzerland, where soil plots have been treated with different organic
amendments (farmyard manure, sewage sludge and compost). The observed ethylenediaminetetraacetic acid disodium salt (EDTA)-extractable concentrations ranged between 2.6 and 27.1 mg kg−1 for Zn, 4.9 and 29.0 mg kg−1 for Cu, 6.1–26.2 mg kg−1 for Pb,
and 0.08 and 0.66 mg kg−1 for Cd. Metal input rates were initially
estimated based on literature data. An additional, calibrated metal flux,
tentatively attributed to mineral weathering, was necessary to fit the
observed data. Dissolved organic carbon fluxes were estimated using a soil
organic carbon model. The model adequately reproduced the EDTA-extractable
(labile) concentrations when input rates were optimised and soil lateral
mixing was invoked to account for the edge effect of mechanically ploughing
the trial plots. The global average root mean square error (RMSE) was 2.7, and the average bias
(overestimation) was −1.66, −2.18, −4.34 and −0.05 mg kg−1 for Zn, Cu,
Pb and Cd, respectively. The calibrated model was used to project the long-term metal trends in field conditions (without soil lateral mixing), under
stable climate and management practices, with soil organic carbon estimated
by modelling and assumed trends in soil pH. Labile metal concentrations to
2100 were largely projected to remain near constant or to decline, except
for some metals in plots receiving compost. Ecotoxicological thresholds
(critical limits) were predicted to be exceeded presently under sewage
sludge inputs and to remain so until 2100. Ecological risks were largely not
indicated in the other plots, although some minor exceedances of critical
limits were projected to occur for Zn before 2100. This study advances our understanding of TEs' long-term dynamics in agricultural fields, paving the way to quantitative applications of modelling at field scales.
Accumulation and fractionation of trace metals in a Tunisian calcareous soil amended with farmyard manure and municipal solid waste compost