Harvest of grass for combustion in late summer and in spring

Swedish studies concerning the production of grass for combustion during the 1980s demonstrated that it was impossible to produce fuel guaranteed to be of acceptable hygienic quality at a reasonable cost. In those studies, the grass was harvested during summer using conventional haymaking methods. To avoid the problems involved with a summer harvest, it was proposed in 1989 that the grass be harvested during the winter or spring following the growing season. Since then, a system based on this delayed-harvest concept has been evaluated with regard to biological yield, losses during winter, harvesting technology, losses during harvesting and fuel characteristics. The crop used has been reed canary grass (Phaláris arundinácea L.). In contrast to harvest in late summer, a spring harvest was found to be of practical value. It provides a usable fuel of higher quality than that of grass from summer harvesting. The delay in the harvest leads to reduced concentrations of most elements that are undesirable in combustion, e.g. nitrogen, sulphur, chlorine or potassium. An exception is silica, the concentration of which increases during winter. A valuable effect of spring harvesting is that the initial ash deformation temperature is increased. Furthermore, the need for fertilizer with delayed harvest is low owing to the low content of nutrients in the harvested material. The main disadvantage is that there are major losses of material during the autumn and winter.