Nitrogen mineralization in coal mine spoil and topsoil

Summary N mineralization was compared in fresh topsoil, stockpiled topsoil, coal-mine spoil, and in various mixtures of soil and mine spoil, with and without sludge amendment. N mineralization was slightly lower in stockpiled topsoil than in fresh topsoil or mine spoil. Differences between stockpiled and fresh topsoil were small and were attributed to changes in the relative proportions of readily degradable versus slowly degradable organic fractions. Sludge amendment increased N mineralization, but straw amendment immobilized N through 12 weeks of incubation. More N was leached from mixtures of mine spoil and soil than from soil or mine spoil alone, but net N mineralization decreased with increasing mine-spoil-to-soil ratios, probably as a result of greater denitrification losses. Mixing mine spoil with soil can increase plant available N more than soil or spoil alone, because spoil contributes mineralizable organic N while soil improves the physical and chemical environment of the mine spoil.