The main aim of the study was to investigate the retention pattern of atmos
pherically deposited NH4+ plus NO3- in podsolized forest soils in southern
Sweden during the period 1985-1994. Nitrogen budgets were calculated for 37
coniferous forest sites dominated by Norway spruce (Picea abies (L.) Karst
.) or Scots pine (Pinus sylvestris L.). Total deposition of NH4+ plus NO3-
was obtained by adding bulk deposition and dry deposition. Dry deposition w
as calculated by using regional data on air concentrations of particulate a
nd gaseous N compounds and previously established deposition velocities in
stands of Norway spruce and Scots pine. Nitrogen leaching was obtained by c
ombining measured NH4+ and NO3- concentrations with the amount of percolati
ng soil water. The latter was chiefly estimated from the Cl- balance, assum
ing that the flux in throughfall was equal to the Cl- flux in the soil wate
r. Nitrogen uptake by the trees was estimated by inserting data on diameter
growth in empirical biomass functions and then applying typical N concentr
ation values gained from the literature. The average N deposition was 13.3
+/- 7.4 kg N ha(-1) yr(-1) (+/-SD). Nitrogen leaching, estimated annual soi
l N retention (maximum N immobilization), ecosystem N retention and bole N
accumulation (N uptake in bole wood + bole bark) were positively correlated
with N deposition. Bole N accumulation and ecosystem N retention were also
negatively correlated with stand age. The seven stands that showed a measu
rable amount of N leaching had a total N deposition of >15 kg N ha(-1) yr(-
1) and were all situated in the southernmost part of the investigated area.
The average value of the estimated soil N retention, 8.5 +/- 6.0 kg N ha(-
1) yr(-1), was close to the range of default values used in estimates of cr
itical N loads to European forest ecosystems.