UC Riverside

Increases in Zn and Cu concentrations in soils amended with pig slurry (PS) can be described using numerical models. Our main objective was to validate that the HYDRUS-1D model is able to numerically describe profile concentrations and long-term vertical transport of Zn and Cu in a clay soil (Oxisol) cultivated under annual cropping in a no-till system and contaminated by successive doses of PS amendments. We first used a modeling approach that had previously been validated for an Alfisol. Then, we additionally also evaluated the effects of root growth and root water uptake on the transport of trace metals (TMs). Finally, we carried out 50-yr-long prospective simulations for different doses of PS amendments. Consideration of root growth and root water uptake processes in HYDRUS-1D simulations improved the description of measured field Zn concentrations. Although the correspondence between simulated and measured Cu concentrations was not as good as for Zn, we performed prospective simulations for both elements. Future scenarios that considered large PS doses showed large increases in concentrations of both TMs in the soil surface layer. The feasibility of using PS amendments on agricultural Oxisols will be limited by Cu because the soil Cu threshold concentration is exceeded in approximately 29 yr. Moreover, the total loads of both TMs allowed on agricultural soils are reached very fast when large rates are used, especially for Cu (19 yr), indicating that the long-term disposal of PS on agricultural soils should be done at low doses. These conclusions are probably conservative because our model did not consider potential leaching of TMs from the surface soil into deeper soil layers by dissolved organic C facilitated transport.