Nutrient conditions in drained peatlands along a north-south climatic gradient in Sweden

Soil nutrient conditions were investigated in a series of five peatland aff orestation trials (established 1971) along a noah-south gradient in Sweden. AII areas were drained low-sedge mires and planted with Scots pine (Pinus sylvestris (L.)). Soil samples from the topsoil (0-20 cm) were collected 22 years after drainage with two ditch spacings (7.5 and 60 m) and PK-fertili zation with three fertilization regimes. Total and available nutrient conce ntrations were determined. Results indicated that pH and total concentratio ns of N, P and Ca in the topsoil of extensively drained areas increased wit h decreasing temperature sum in similar site types. Concentrations of K and Mg were not correlated to temperature sum. Tree height and volume were pos itively correlated to concentrations of P, K and Ca, but not to N, and only for temperature sums greater than or equal to 950 d.d. (day degrees). Henc e, it appeared that P and/or K directly or through their effects on N miner alization, limited tree growth in the south, whereas another growth factor was Limiting in the north. We examined the available/total concentration ra tios for the soil nutrients, with the intention to reveal possible climate- dependent trends in those ratios. The available/total ratios of P and Ca we re found to increase with increasing temperature sum. For Ca in southern ar eas the ratios were higher in intensively drained and PR-fertilized plots t han in the extensively drained and unfertilized treatment, possibly indicat ing that peat mineralization had been more intensive. The Ca-ratios for the two northernmost areas, which showed little or no tree growth reaction, di d not increase even in the intensively drained and fertilized treatments. W e hypothesise that the treatment-induced changes in available/total Ca rati o along the climate gradient also reflect post-drainage intensity of N-mine ralization. Hence, the absence of increased Ca-ratios at temperature sums b elow 950 d.d. may indirectly indicate that tree growth is limited by the mi crobial release of organically bound N. (C) 2000 Elsevier Science B.V. All rights reserved.