Growth and nutrition of coniferous forests on acidic mineral soils - status and effects of liming and fertilization

Deposited air-borne S- and N -containing pollutants acidify forest soils in southern Sweden. It has been suggested that this may severely affect forest yield. Liming and/or application of specific nutrients, e.g. phosphorus (P) and potassium (K), have been proposed as countermeasures. The influence of such measures, and of nitrogen (N) addition, was investigated in two experimental series over 5-10 years. Stem growth and needle element concentrations were assessed, predominantly in high-yielding Norway spruce [Picea abies (L.) Karst.] and Scots pine (Pinus sylvestris L.) stands, 30-60 years old, growing on acidic mineral soils in southern Sweden. The effect on crown transparency was also evaluated in some of the Norway spruce stands. In all experiments a randomized block design was used. The treatments included liming (500-6,000 kg ha1), and N addition at low annual doses (2x10 kg N ha1) and in single shots (150 kg N ha1). Combinations of lime+N, lime+PK and lime+PKN were also tested. The effects were generally weak or negligible, except that growth was significantly increased by N fertilization in the Scots pine stands, and by lime+PKN in some of the Norway spruce stands. In another study, the survival and growth of Norway spruce seedlings were found to be more or less unaffected when planted in pre-harvest acidified, limed or N fertilized soil, although the Ca and Zn concentrations in their needles rose after liming, while those of Mn and A1 declined. In closed-canopy stands of Norway spruce and Scots pine with N concentrations of more than 15-16 mg (g DM)'1 in current-year needles, N fertilization was indicated to not necessarily stimulate increased growth. Other indicators of highly N-rich forests (e.g. elevated arginine levels) also start to appear above this level. The closed-canopy stands growing on the most acidic soils showed no signs of severe damage or nutrient deficiencies. These findings, together with the small or negligible effects of the tested countermeasures against soil acidification, suggest that as regards stem growth, needle-element concentrations or crown transparency, there seems to be no acute need for liming and/or PK addition in SW Sweden in Norway spruce stands on sites similar to those examined