Ash as a phosphorus fertilizer to reed canary grass: effects of nutrient and heavy metal composition on plant and soil EVA LINDVALL 1 , ANNE-MAJ GUSTAVSSON 1 , ROBERT SAMUELSSON 2 , TORD MAGNUSSON 3 andCECILIA PALMBORG 1 1 Department of Agricultural Research for Northern Sweden, Swedish University of Agricultural Sciences, Ume  a SE-90183, Sweden, 2 Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences, Ume  a SE-90183, Sweden, 3 Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Ume  a SE-90183, Sweden Abstract Fertilization effects and risks of heavy metal enrichment were studied in a field experiment, in which plots of reed canary grass (RCG) were treated annually with three different fertilizers: Ash from co-combustion of RCG and municipal wastes (mixed ash), pure RCG ash, and commercial fertilizer (control). RCG ash is a waste prod- uct that is currently expensive to dispose of. The amounts of nutrients applied annually were 100 kg ha À1 N, 15 kg ha À1 P, and 80 kg ha À1 K in all treatments. In the ash treatments, all P derived from ash, whereas N and part of the K were supplemented by fertilizers. The amount of heavy metals exceeded the limits set by the Swedish Environmental Protection Agency for all elements analyzed in the mixed ash and for Ni and Cr in the RCG ash. There were no significant differences between treatments in terms of RCG dry matter yield obtained at harvest in spring, or in heavy metal concentrations in the biomass. Soil samples from 0–5 cm, 5–10 cm, and 10–20 cm below the surface showed significant differences between treatments for the concentration of Cd, Cr, Cu, Pb, and Zn, with higher concentrations in plots fertilized with mixed ash than in the control. Neither spring yield nor soil available P was reduced by using ash instead of min- eral P fertilizer, suggesting that pure RCG ash can be used to complement commercial fertilizer, albeit less fre- quently than here. However, ash derived from co-combusting RCG with different waste materials (mixed ash treatment) should not be used in RCG production due to the high heavy metal content. Keywords: ash fertilization, element balance, heavy metals, Phalaris arundinacea, reed canary grass, spring harvest Received 28 May 2013; accepted 11 November 2013 Introduction Increasing local production of renewable energy from herbaceous crops on agricultural land is of great interest, since imported fossil fuels need to be replaced with sustainable energy sources. Since the mid-1980s, interest in the use of perennial grasses as energy crops has increased in the USA and in Europe (Lewandowski et al., 2003). Perennial grasses have many advantages over annual crops, since successfully established swards can be commercially viable for at least 8 years before they need to be reseeded (Saijonkari-Pahkala, 2001). Consequently, they require less tillage than annual energy crops. In addition, they require less pesticides and also less supplementary nutrients because some of the nutrients from the shoots are recycled to the rhi- zomes during autumn (Wrobel et al., 2009; Xiong et al., 2009; Heinsoo et al., 2011). Growing moderately tall grasses such as reed canary grass (Phalaris arundinacea L., RCG) also facilitates subsequent conversion into food production, since the costs of restoring the land are moderate, in our experience, relative to those incurred e.g., after growing Salix as a short rotation crop (SRC) or tree plantation. Furthermore, grass production tech- niques are familiar to farmers in potential cropping areas, and machinery and buildings are readily avail- able. Growing grasses, with the exception of some giant energy species such as Miscanthus, instead of Salix (SRC) or trees also preserves an open landscape, which is valuable in forest dominated areas. During the 1980s, several projects were initiated in Sweden to evaluate different crops and their potential for agro-industrial use. These studies identified RCG as one of the most interesting species for energy purposes in Sweden. Ongoing research in the Baltic countries (Kryzeviciene et al., 2008; Kukk et al., 2010) also shows RCG to be a promising crop, and large-scale projects in Correspondence: Eva Lindvall, tel. + 46(0)907 868 716, fax +46(0) 907 868 162, e-mail: eva.lindvall@slu.se © 2013 John Wiley & Sons Ltd 553 GCB Bioenergy (2015) 7, 553–564, doi: 10.1111/gcbb.12161