Long-Term Effects of Paper Mill Biosolids and Liming Materials On Soil Properties, Trace Metals Availability and Distribution in a Loamy Soil.

Residues from pulp and paper Kraft mills contain crop nutrients and trace metals that can harm the environment when applied in large amounts to agricultural lands. This study investigated the effects of annual applications over nine years of paper mill biosolids (PB) and liming materials (LM) on the chemical forms of four trace metals (TM), namely cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn). This study was conducted (2000-2008) near Trois-Rivières, QC, Canada (46°17' N; 72°50' W) on a loamy soil receiving 30, 60, and 90 t ha^–1 of PB (wet basis) and 3 t ha^–1 of three liming materials (lime mud, wood ash, and calcitic lime) in combination with 30 t PB ha^–1. Soil samples were collected every three years after the crop harvest (grain corn in 2002 and 2008, soybean in 2005) and submitted to a sequential extraction to fractionate TM into five operationally defined groups: exchangeable, carbonate, Fe-Mn oxide, organic, and residual. Results showed an increase in soil pH when applying liming materials, specifically with lime mud with an elevation of 1.3 units after nine years of repeated application. The residual fraction was the most abundant pool for Cu, Ni and Zn with 42-61%. By contrast, the pools considered as readily and potentially bioavailable (exchangeable and carbonate), represented between 3-12 % for Cu, Ni and Zn. Cadmium showed a different pattern being mostly bound to exchangeable fraction (36-63 %). The addition of LM reduced the mobility factor for all metals examined, especially for Cd (12-18 %). Overall, the application of PB in combination with LM contributed to decrease TM in the most mobile fractions compared with the untreated control plots. Lime mud showed a great potential to reduce the bioavailability of TM in soil under field conditions.