MOBILITY OF ELEMENTS IN SOIL UNDER STABILIZED DAIRY FEEDLOT SURFACES: A LABORATORY STUDY

Abstract

Accumulation of manure on dairy feedlot surfaces (DFS) generates great amounts of dissolved constituents that can impact surface water and groundwater quality. Application of fluidized bed combustion (FBC) residue has been suggested to stabilize DFS and to minimize the environmental impact on water quality. The objective of this study was to investigate the effect of using FBC residue (to stabilize DFS) on the mobility of elements in Lily loam soil (Typic Hapludult). Seepage generated from simulated dairy manure (DM)-, FBC-, or DM/FBC-feedlot surfaces was applied to 70-cm soil columns at 10 weekly intervals. Using FBC with DM decreased the amount of N, P, Si, Mg, K, Na, and organic C retained by the soil and increased the retention of Ca, S, B, and Cl. A large portion of elements (e.g., P, B, Ca, Mg, K, Na) was retained in the surface 20 cm of the soil and decreased with depth. However, using FBC with DM enhanced the release of native soil Al, Fe, and Mn. Mechanisms responsible for this depletion could include (i) dissolution of soil minerals by SO4, (ii) replacement of elements on exchangeable sites by Ca, (iii) reduction of high-valence elements to more soluble forms, and (iv) formation of soluble element-organic complexes. We concluded that two sets of reactions should be considered when evaluating the impact of the stabilization process on water quality: (i) reactions between DM and FBC constituents that control chemical composition of the seepage and (ii) reactions between the seepage and soil components that control elements attenuation and mobility.