Suo - Mires and peat vol. 56 no. 3 | 2005

Phosphorus and potassium deficiencies are common in Scots pine stands growing on drained peatlands. In this study, the foliar nutrient concentrations and stand growth were monitored after the application of phosphorus and potassium fertilisers of different solubility in four experiments on thick-peated drained peatlands in northern central Finland. The studied stands involved three fertilisation treatments: (i) unfertilised control, (ii) rock phosphate and potassium chloride, and (iii) apatite and biotite. The growth of stands was monitored 20–25 years after the fertilisation. Needles were sampled four times: 4–9, 11–14, 16–19 and 21–24 years after the fertilisation. According to foliar analyses, the trees on the control plots suffered from severe phosphorus and potassium deficiencies. Rock phosphate and apatite fertilisation increased the foliar phosphorus concentrations above the deficiency limit, and the effect was still noticeable 21–24 years after the application. Both potassium sources, that is, the slowly soluble biotite and the water-soluble potassium chloride increased the foliar potassium concentration to an adequate level. Potassium chloride increased the concentrations faster and stronger than biotite during the first years (4–9) after the applications. The situation was reversed when 11–14 years or more had passed from the fertilisation: the biotite fertilised stands had higher potassium concentrations. The fertilisation treatments decreased the foliar nitrogen, zinc, manganese, copper and boron concentrations. The fertiliser applications increased the stand volume growth considerably. Raw phosphate and potassium chloride increased the volume growth significantly already during the first five-year period. The effect of the apatite and biotite treatment was weaker during the first 10 years, but became stronger with time. During the period 19–24 years after the fertilisation, the stand growth on the biotite plots was equal to that of the plots fertilised with potassium chloride. However, during the whole study period the differences between the treatments remained insignificant. The results showed that slowly soluble apatite and biotite are suitable sources of phosphorus and potassium for pines on drained peatlands. However, to avoid boron deficiency, also boron should be added simultaneously.

• Moilanen, Finnish Forest Research Institute, Muhos Research Station, Kirkkosaarentie 7, FIN-91500 Muhos, Finland Sähköposti: ei.tietoa@nn.oo
• Pietiläinen, Sähköposti: ei.tietoa@nn.oo
• Issakainen, Sähköposti: ei.tietoa@nn.oo

The effects of potassium (K) fertilisation on the nutrient status and growth of Scots pine (Pinus sylvestris L.) stands on drained peatlands were studied on three field experiments in northern central Finland. The Scots pine stands were at a sapling or pole stage with a dominant height of 3–8 m when the experiments were set up. The stands differed from each other in their nutritional status, for example, the foliar K concentration varied considerably between the experiments. The experiments were fertilised with potassium chloride, rock phosphate (P 42kg ha-1) and urea (N 46kg ha-1) between 1979 and 1980. The potassium doses in terms of elemental K, were 50, 100, 200 and 400kg ha-1. The foliar samples were taken three times during the study period: 7–9 years, 14–15 years and 19–20 years after fertilisation. The stand measurements were done 19–22 years after the fertilisation. The rate and magnitude of stand response due to fertilisation depended essentially on the nutritional status of the trees. The strongest effect of PK-fertilisation was obtained on a nitrogen-rich peatland, where the stands suffered from severe phosphorus and potassium deficiencies (foliar P concentration < 1.2 mg g-1, K concentration < 3.5 mg g-1). During the study period, the annual stand volume growth on fertilised plots ranged from 3.9 to 5.4 m3 ha-1 a-1, and that of the unfertilised plots was 0.78 m3 ha-1 a-1. In other sites, where the lack of phosphorus and potassium was not so drastic, nor did the trees suffer from shortage of nitrogen, the effect of PK-treatment on tree growth was weak or almost non-existent. The foliar K concentrations rose with the amount of potassium chloride applied. The fertilisation effect of the dose of 100kg K ha-1 lasted 15–20 years, after which the foliar K concentration dropped close to the deficiency limit. The effect of the larger doses (200–400kg K ha-1) on the needle K concentration was more pronounced and still visible at the end of the study period. However, the stand growth responses gained with larger potassium applications were not essentially greater than those with the 100 kg ha-1 dose.

• Pietiläinen, Finnish Forest Research Institute, Muhos Research Station, Kirkkosaarentie 7, FIN-91500 Muhos, Finland Sähköposti: ei.tietoa@nn.oo
• Moilanen, Sähköposti: ei.tietoa@nn.oo
• Vesala, Sähköposti: ei.tietoa@nn.oo

Water table measurements were obtained in a treed fen that was drained in 1987 and harvested for timber in 1997. The water table level was quantified at five different distances from the ditch for three ditch spacing. Water table levels were compared between pre-drainage, post-drainage and post-removal of the canopy. The phenomenon of watering-up after clear-cutting did not occur where a drawdown of at least 10 cm was caused by the drainage. This lowering was observed across the 20 m ditch spacing and within the first 6 m from the ditch, in the 40 and the 60 m spacing. The water table fluctuations were also reduced after harvesting.

• Jutras, Forest Biology Research Centre, Université Laval, Sainte-Foy, QC G1K7P4 Canada Sähköposti: ei.tietoa@nn.oo
• Plamondon, Sähköposti: ei.tietoa@nn.oo