Element budgets of two afforested mine sites after application of fertilizer and organic residues

Abstract

The effects of mineral fertilizer, sewage sludge and compost application on soil solution chemistry and element fluxes at two mine spoils were studied in a field trial. The two sites differed in substrate composition: (a) a pyrite and lignite containing spoil (WEB site); and (b) a pyrite and lignite free spoil (SEE site). Soil solution was continuously sampled at 20 and 130 cm soil depth over a 2-year period, and analyzed for all major elements, pH, and electrical conductivity. At the WEB site, major elements in soil solution at 20 cm depth were Ca, Mg, Al and SO 4-S. In the unameliorated subsoil, Fe was detected in high concentrations. Pyrite oxidation caused massive element fluxes of up to 6 t Fe ha −1 year −1 and 14 t SO 4-S ha −1 year −1. At the SEE site, major elements in soil solution were Ca, Mg and SO 4-S. Maximum element fluxes measured 1 t Ca ha −1 year −1 and 1 t SO 4-S ha −1 year −1. Application of mineral fertilizer and organic residues increased NO 3, NH 4, K, and Cl concentrations and fluxes. Thirty to 40% of the applied mineral fertilizer was leached below 20 cm within 4 weeks. Sewage sludge application led to N fluxes in 20 cm depth of 56 kg N ha −1 (2 years) −1 at the SEE site and 94 kg N ha −1 (2 years) −1 at the WEB site, equivalent to 5 and 10% of N applied with sewage sludge, respectively. At the SEE site, NO 3-N fluxes were increased down to 130 cm soil depth after application of sewage sludge. At both sites, compost plots showed lower N fluxes (25 and 14 kg N ha −1) compared with the control plots (35 and 24 kg N ha −1). In contrast, potassium fluxes were significantly increased after compost application. However, the overall effects on soil solution chemistry from application of mineral fertilizer and organic residues were small relative to the effects from mining only.