Nitrogen mineralization and nitrification in amended colliery spoils.
Mineral nitrogen concentrations were greater in acid spoils (pH<5) than in limed or neutral spoils. In acid spoils, the predominant form was NH4-N. Addition of ammonium sulphate with limestone to bare acid spoil was followed by a temporary accumulation of NO2-N. Large populations of Nitrosomonas and Nitrobacter were found in neutral spoils and in acid spoils which had received limestone and NPK amendments. Limed and neutral spoils, amended with shoddy and sewage-sludge two years previously, released little mineral nitrogen when incubated for forty days. Acid spoils (pH<4.5), similarly ameliorated, released more mineral nitrogen, especially if incubated with calcium carbonate, but released less than unfertilized acid grassland soil.