Residual effects of N fertilization on soil-water chemistry and ground vegetation in a Swedish Scots pine forest

Abstract

A study was made of soil-water chemistry and ground vegetation in a previously established N fertilization experiment in a Scots pine forest in central Sweden. Plots had been fertilized two, three or four times during a 15-year-period, each time with 150 kg N ha −1. The fertilizer used was initially pure ammonium nitrate, but at the latest fertilization made 4–8 years before the study, a minor dose of lime was also included. The aim of the study was to reveal possible residual affects of the previous fertilization. Soil water was sampled six times during a nine-month-period. Water samples were analyzed with respect to inorganic N, pH, Al, base cations and Cd. The only statistically significant treatment effect was that the concentration of base cations decreased with increasing total N dose in one of the two replicate blocks. Both fertilized plots and control plots had very low concentrations of inorganic N (<10 μg/l). Few species in the ground vegetation appeared to be affected by the previous N fertilization. Cladina rangiferina, the most abundant lichen species, had a much lower cover on plots that had been fertilized four times than on all other plots. Also, the other lichens tended to be less abundant on plots that had received fertilizer four times. The lower abundance of lichens on these plots resulted in a change in vegetation type from lichen types to dwarf shrub types. The experiment studied is situated in a region where deposition of N is larger than the critical load. Despite this, an extra addition of 600 kg N ha −1, corresponding to 40 kg N ha −1 year −1, had no consistent long-lasting effects on soil-water chemistry. At this dose, but not at the lower doses tested, there was a change in the plant community.