Forest Ecology and Management 261 (2011) 105–110 Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco Recycled iron phosphate as a fertilizer raw material for tree stands on drained boreal peatlands Mika Nieminen a,∗ , Ari Laurén b , Hannu Hökkä c , Sakari Sarkkola a , Harri Koivusalo d , Taina Pennanen a a Finnish Forest Research Institute, Vantaa Research Unit, P.O. Box 18, FI-01301 Vantaa, Finland b Finnish Forest Research Institute, Joensuu Research Unit, P.O. Box 68, FI-80101 Joensuu, Finland c Finnish Forest Research Institute, Rovaniemi Research Unit, P.O. Box 16, FI-96301 Rovaniemi, Finland d Aalto University School of Science and Technology, Department of Civil and Environmental Engineering, P.O. Box 15200, FI-00076 Aalto, Finland article info Article history: Received 20 July 2010 Received in revised form 21 September 2010 Accepted 21 September 2010 Keywords: Apatite Hydrochemistry Iron phosphate Peatland forestry Phosphorus abstract Fertilization of drained peatland forests with easily soluble or slow-release apatite fertilizers can increase phosphorus (P) export to water courses, especially when the soil is low in aluminum (Al) and iron (Fe) hydroxides and oxides. Application of Al and Fe together with P increases P adsorption to the soil and decreases the risk of leaching. The aim of this study was to investigate the use of recycled iron phos- phate (rFePO 4 ) as forest fertilizer raw material from environmental and forest production perspectives. Trial fertilizers with different mixtures of rFePO 4 and Russian Kola apatite (Kap) were applied on 15 mini-catchments (area 100 m 2 ), where the discharge at the outlet was collected, sampled and analyzed throughout the about 4-year measurement period. The foliage P content and height growth of the trees on the mini-catchments were measured. The biomass growth of the extramatrical mycorrhizal mycelia (EMM) was studied with a separate in-growth mesh bag experiment conducted on the same site. The results indicated no increase in phosphorus export to surface waters after application of rFePO 4 and 25/75 and 50/50 mixtures of rFePO 4 and Kap. In contrast to earlier studies showing a relatively high P export with different types of apatite fertilizers, the Kap fertilizer showed only minor phosphorus export. The height growth measurements and needle analyses of the juvenile Scots pine stands indicated poor P availability from pure rFePO 4 , but the P availability from the 50/50 and 25/75 mixtures of rFePO 4 and Kap was similar to pure Kap. The mixtures of Kap and rFePO 4 enhanced the EMM biomass by 2- to 3- fold, whereas Kap and rFePO 4 alone, and high P availability (superphosphate) had no significant effect compared to non-P controls. The increase in EMM biomass as induced by concurrent application of Kap and rFePO 4 was not clearly reflected in tree growth and P acquisition. However, longer follow-up studies than in this one may be needed in order to verify the effect of increased EMM biomass on mycorrhizal mycelia mediated nutrient uptake and tree growth. © 2010 Elsevier B.V. All rights reserved. 1. Introduction In the boreal and temperate zones about 15 million hectares of peatlands and wetlands have been drained for forestry (Paavilainen and Päivänen, 1995), and the drainage has substantially increased the tree stand growth of the peatland forests. On many drained peatland sites a sustainable tree biomass production requires one or more fertilizations with phosphorus (P) during the stand rotation (Moilanen, 1992; Veijalainen, 1992). The tree growth response to easily soluble and slow-release apatite fertilizers has long been a ∗ Corresponding author. Tel.: +358 50 391 2399; fax: +358 10211 2206. E-mail addresses: mika.nieminen@metla.fi (M. Nieminen), ari.lauren@metla.fi (A. Laurén), hannu.hokka@metla.fi (H. Hökkä), sakari.sarkkola@metla.fi (S. Sarkkola), harri.koivusalo@tkk.fi (H. Koivusalo), taina.pennanen@metla.fi (T. Pennanen). subject of active research (e.g. Kaunisto et al., 1993; Silfverberg and Hartman, 1999). Easily soluble fertilizers result in a rapid growth response, but the total growth over 30–40 years is not affected by the fertilizer-solubility because of a longer response to slow-release fertilizers. Slow-release fertilizers are used in operational forestry, because they are cheaper than acidulated easily soluble products. Although apatite fertilizers increase the tree production on drained peatlands, their present use in operational peatland forestry is limited. One reason for the low fertilization activity is the concern that fertilization may increase P export to surface and ground waters, thus causing eutrophication in recipient water courses. A high rate of P export occurs after fertilization of drained peatland forests when using acidulated, easily soluble fertilizers (Nieminen and Ahti, 1993) or non-acidulated, slow-release apatite products (Harriman, 1978; Kenttämies, 1981; Ahti, 1983; Malcolm and Cuttle, 1983; Saura, 2002). An increased P export is typical in soils with low contents of Al- and Fe-hydroxides and -oxides 0378-1127/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2010.09.036