Nutrient supply to reed canary grass as a bioenergy crop : intercropping with legumes and fertilisation strategies for phosphorus and potassium

Sammanfattning: Growing energy demand and global warming are promoting research into potential new sources of renewable energy. Fossil fuels need to be replaced with sustainable energy sources to decrease emissions of greenhouse gases. Production of bioenergy from herbaceous crops on agricultural land is one alternative. In Sweden, reed canary grass (Phalaris arundinacea L.) is considered an interesting species for this purpose, as it is perennial and well-adapted to the northern climate. This thesis evaluated different approaches to reduce the mineral fertiliser requirement in reed canary grass (RCG) production for bioenergy purposes in a spring harvesting system. Fertilisation effects and the risk of heavy metal enrichment were studied in a field experiment involving annual applications of ash for seven years. Three different treatments were applied: ash from co-combustion of RCG and municipal waste (mixed ash), pure RCG ash and, as a control, PK fertilisers. There were no significant differences between treatments in terms of RCG dry matter yield or biomass concentrations of heavy metals. Samples from the uppermost soil layer (0-5 cm) differed between treatments in terms of cadmium, chromium, copper, lead and zinc concentration, with higher concentrations in the mixed ash treatment compared with the control. The effects of intercropping RCG with different nitrogen (N)-fixing perennial legumes were examined in three field experiments, in combination with various fertilisation treatments. Two levels of N fertilisation combined with RCG ash or sewage sludge were applied in a delayed harvest system, which involved cutting the biomass in late autumn, leaving it on the field during winter and harvesting in spring. The estimated N fixation rate in red clover and alsike clover was high enough to compensate for lower N fertilisation. However, in most cases growth of the RCG in monoculture was not N-limited at half the recommended N fertilisation rate and intercropping with legumes was not beneficial. In order to determine the P and K requirements of RCG in a delayed harvest system, different levels of phosphorus (P) and potassium (K), supplied by mineral fertilisers or RCG ash are being compared in an ongoing study. No differences in biomass yield between treatments have been found after two harvest years.