Increasing levels of nitrogen deposition will push soils to a toxic level of acidification in which iron becomes more soluble, and plant growth is reduced, according to a study published online in Nature Geoscience.
A long history of human-influenced nitrogen deposition associated with industry and agriculture has left soils in the western Tatra Mountains of Slovakia highly acidic. William Bowman and colleagues reveal that increasing the nitrogen load in the region triggers the release of soluble iron into alpine grassland soils. This iron release is indicative of extreme soil acidification, analogous to conditions seen in soils after acid mine drainage.
On the basis of these results, the authors warn that high levels of nitrogen deposition in Europe and North America over the past half century may have rendered many soils susceptible to a new stage of acidification where iron, rather than calcium or aluminum, is the main buffer.