Activated carbon amendments to soil alters nitrification rates in Scots pine forests

The influence of charcoal on biotic processes in soils remains poorly understood. Charcoal is a natural product of wildfires that burned on a historic return interval of similar to100 years in Scots pine (Pinus sylvestris L.) forests of northern Sweden. Fire suppression and changes in forest stand management have resulted in a lack of charcoal production in these ecosystems. It is thought that charcoal may alter N mineralization and nitrification rates, however, previous studies have not been conclusive. Replicated field studies were conducted at three late-succession field sites in northern Sweden and supporting laboratory incubations were conducted using soil humus collected from these sites. We used activated carbon (AC), as a surrogate for natural-occurring fire-produced charcoal. Two rates of AC (0 and 2000 kg ha(-1)), and glycine (0 and 100 kg N as glycine ha(-1)) were applied in factorial combination to field microplots in a randomized complete block pattern. Net nitrification, N mineralization, and free phenol concentrations were measured using ionic and non-ionic resin capsules, respectively. These same treatments and also two rates of birch leaf litter (0 and 1000 kg ha(-1)) were applied in a laboratory incubation and soils from this incubation were extracted with KCl and analyzed for NH4+ and NO3-. Nitrification rates increased with AC amendments in laboratory incubations, but this was not supported by field studies. Ammonification rates, as measured by NH4+ accumulation on ionic resins, were increased considerably by glycine applications, but some NH4+ was apparently lost to surface sorption to the AC. Phenolic accumulation on non-ionic resin capsules was significantly reduced by AC amendments. We conclude that charcoal exhibits important characteristics that affect regulating steps in the transformation and cycling of N. (C) 2004 Elsevier Ltd. All rights reserved.