Nitrification and urea hydrolysis in deciduous woodland soils from a site exposed to heavy atmospheric pollution

Laboratory studies of nitrification and urea hydrolysis were performed using soils obtained from sites exposed to pollution from a coking works and from a relatively unpolluted site. No net production of nitrate occurred in either soil when amended with ammonium sulphate alone, or together with CaCO(3) at 0.05% w/w. However, nitrate accumulated in both soils when 5% w/w CaCO(3) was added, with this amount of lime increasing the pH of both soils from around pH4 to pH7. Under these conditions, nitrification in the polluted soil occurred at about half the rate found in the relatively unpolluted soil. Urea hydrolysis occurred at a similar rate in both soils and was not impaired by exposure to coking pollution. Little nitrification of the ammonium liberated by urea hydrolysis occurred in either soil, however, presumably because, although the soil pH increased due to urea hydrolysis, it did not become sufficiently alkaline to support rapid nitrification. The relatively unpolluted soil used here was obtained from an area away from the coking works, but was exposed to generalised atmospheric pollution (wet and dry deposited acidity, greater than 1.0 and 2.4 kg H(+) ha(-1) yr(-1), respectively). Nitrification and urea hydrolysis occurred in these soils, so these processes were not inhibited by exposure to these relatively high background levels of air pollution.