Jurgensen, Martin F.; Harvey, Alan E.; Larsen, Michael J. 1981. Effects of prescribed fire on soil nitrogen levels in a cutover Douglas-fir/western larch forest. 1981. Res. Paper INT-RP-275. Fort Collins, CO: U.S. Department of Agriculture, Forest Service. Rocky Mountain research station.
The effects of a prescribed broadcast fire on soil nitrogen (N) levels and related soil properties were determined following the clearcutting of a 250-year-old Douglasfir/western larch stand in northwestern Montana. Soil N losses from burning amounted to slightly over 90 Ib/acre (100 kg/ha), all from the surface organic layers. This was 6 percent of the total N originally present in the surface 12 inches (30 cm) of soil. In contrast, soil ammonium concentration increased within 2 days following the fire. Rapid nitrification also occurred after a 3-week lag period. The higher nitrate levels were associated with increased populations of nitrifying bacteria. Both soil ammonium and nitrate concentrations returned to preburn levels by the end of the following summer. Soil acidity was decreased after the burn and had not yet returned to original levels in the organic horizons 4 years later. Organic matter content of the mineral soil was not affected by the fire. No long-term depletion of soil N reserves would result from this prescribed fire. Plant reestablishment on the site benefited by increased soil N availability.