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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 product 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 mineral P fertilizer, suggesting that pure RCG ash can be used to complement commercial fertilizer, albeit less frequently 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.

In two field experiments in northern Sweden, we investigated if intercropping reed canary grass (RCG; Phalaris arundinacea L.) with nitrogen-fixing perennial legumes could reduce N-fertilizer requirements and also if RCG ash or sewage sludge could be used as a supplement for mineral P and K. We compared biomass production, N uptake and N-fixation of RCG in monoculture and mixtures of RCG with alsike clover (Trifolium hybridum L.), red clover (Trifolium pratense L.), goat's rue (Galega orientalis Lam.) and kura clover (Trifolium ambiguum M. Bieb.). In one experiment, RCG was also undersown in barley (Hordeum vulgare L.). Three fertilization treatments were applied: 100 kg N ha À1, 50 kg N ha À1 and 50 kg N ha À1 + RCG ash/sewage sludge. We used a delayed harvest method: cutting the biomass in late autumn, leaving it on the field during the winter and harvesting in spring. The legume biomass of the mixtures at the inland experimental site was small and did not affect RCG growth negatively. At the coastal site, competition from higher amount of clover biomass affected RCG growth and spring yield negatively. N-fixation in red clover and alsike clover mixtures in the first production year approximately covered half of recommended N-fertilization rate. Goat's rue and kura clover did not establish well at the costal site, but at the inland site goat's rue formed a small but vital undergrowth. RCG undersown in barley gave lower yield, both in autumn and spring, than the other treatments. The high N treatment gave a higher spring yield at the inland site than the low N treatments, but there were no differences due to fertilization treatments at the coastal site. For spring harvest, there were no yield benefits of RCG/legume intercropping compared with RCG monoculture. However, intercropping might be more beneficial in a two-harvest system.Keywords: ash fertilization, biofuel, delayed harvest, Galega orientalis, intercropping with legumes, nitrogen fixation, Phalaris arundinacea, sewage sludge, Trifolium spp. Received 11 January 2012; revised version received 24 February 2012 and accepted 28 February 2012 IntroductionReed canary grass (Phalaris arundinacea L., hereafter RCG) has been evaluated since the mid-1980s as a perennial crop for biofuel production in both Europe and the United States (Lewandowski et al., 2003). Perennial grasses have many advantages over annual crops. Successfully established swards of perennial grasses can have lifetimes of at least 8-10 years before they need to be reseeded, and thus require less cultivation. Furthermore, they have lower requirements for pesticides and nutrients. Some of the nutrients from the shoots are recycled to the roots during autumn (Wrobel et al., 2009;Xiong et al., 2009;Heinsoo et al., 2011). Grass fields can also easily be converted to food production without substantial restoration costs, unlike for instance short-rotation Salix coppices or tree plantations. In addition, grass production techniques are well known among farmers in potential cropping areas, and ...