Rate of Aerobic Nitrogen Transformations in Six Acid Climax Forest Soils and the Effect of Phosphorus and CaCO₃

Nitrogen transformations (mineralization, nitrification, and nitrous oxide production) were evaluated in acid forest floor soils collected from six climax forest sites on Blackhawk Island, Wisconsin. Soils' acidity (CaCl 2 ) ranged from pH 3.9 to 5.1, and organic matter concentrations varied from 2.4 to 59.0 percent. The samples were incubated aerobically for 4 weeks at 30°C under field moist conditions. Treatments were: control; 100 mg P (as KH 2 PO 4 ) kg -1 soil; CaCO 3 ; and P with CaCO 3 . Nitrification of mineralized N ranged from nearly complete in the SM Alfisol to almost non-existent in the Histosol. Addition of P had little effect on ammonification or nitrification. Liming, however, greatly enhanced ammonification on nonnitrifying or slowly nitrifying soils and both ammonification and nitrification in nitrifying soils. Adding P and lime together did not affect N transformations compared to liming alone. Nitrous oxide emission rates in the soils were related to nitrification. From 0.03 to 0.3 percent of the NH 4 -N nitrified was released as N2O-N. Phosphorus addition had little effect but liming increased N 2 O emission rates in soils where nitrification was also enhanced. Forest Sci. 31:680-684.