Iris Lewandowski

The development and current status of perennial rhizomatous grasses as energy crops in the US and Europe

Perennial grasses display many beneficial attributes as energy crops, and there has been increasing interest in their use in the US and Europe since the mid-1980s. In the US, the Herbaceous Energy Crops Research Program (HECP), funded by the US Department of Energy (DOE), was established in 1984. After evaluating 35 potential herbaceous crops of which 18 were perennial grasses it was concluded that switchgrass (Panicum virgatum) was the native perennial grass which showed the greatest potential. In 1991, the DOEs Bioenergy Feedstock Development Program (BFDP), which evolved from the HECP, decided to focus research on a “model” crop system and to concentrate research resources on switchgrass, in order to rapidly attain its maximal output as a biomass crop. In Europe, about 20 perennial grasses have been tested and four perennial rhizomatous grasses (PRG), namely miscanthus (Miscanthus spp.), reed canarygrass (Phalaris arundinacea), giant reed (Arundo donax) and switchgrass (Panicum virgatum) were chosen for more extensive research programs. Reed canarygrass and giant reed are grasses with the C3 photosynthetic pathway, and are native to Europe. Miscanthus, which originated in Southeast Asia, and switchgrass, native to North America, are both C4 grasses. These four grasses differ in their ecological/climatic demands, their yield potentials, biomass characteristics and crop management requirements. Efficient production of bioenergy from such perennial grasses requires the choice of the most appropriate grass species for the given ecological/climatic conditions. In temperate and warm regions, C4 grasses outyield C3 grasses due to their more efficient photosynthetic pathway. However, the further north perennial grasses are planted, the more likely cool season grasses are to yield more than warm season grasses. Low winter temperatures and short vegetation periods are major limits to the growth of C4 grasses in northern Europe. With increasing temperatures towards central and southern Europe, the productivity of C4 grasses and therefore their biomass yields and competitiveness increase. Since breeding of and research on perennial rhizomatous grasses (PRG) is comparatively recent, there is still a significant need for further development. Some of the given limitations, like insufficient biomass quality or the need for adaption to certain ecological/climatic zones, may be overcome by breeding varieties especially for biomass production. Furthermore, sure and cost-effective establishment methods for some of the grasses, and effective crop production and harvest methods, have yet to be developed. This review summarizes the experience with selecting perennial grasses for bioenergy production in both the US and Europe, and gives an overview of the characteristics and requirements of the four most investigated perennial rhizomatous grasses; switchgrass, miscanthus, reed canarygrass and giant reed.

Combustion quality of biomass : practical relevance and experiments to modify the biomass quality of Miscanthus x giganteus

Abstract A catalogue is set up describing the quality characteristics relevant for the combustion of biomass to be used as solid fuel. The practical relevance of these characteristics is discussed. The main characteristics are water concentration, the concentration of chloride and ash, the heating value and the concentration of volatiles and remaining coke. Further quality criteria are the concentrations of nitrogen, sulphur, potassium and calcium. In multifactorial field trials at three locations, the influence of location, fertilizer application and harvest date on the quality of Miscanthus biomass from 3- and 4-year-old plantations was tested. The concentrations of water, minerals and ash, all three of which should be as low as possible, were higher in biomass from the cool and humid than in biomass from the warm location. The application of potassium fertilizer led to increases in the ash and potassium concentrations. Harvesting Miscanthus in February instead of December led to an improved biomass quality because the concentrations of ash, minerals and especially of water had declined. Compared to other lignocellulose plants Miscanthus biomass has a very good combustion quality. In February the stems of Miscanthus had a water concentration of only 16–33%. The mineral concentrations were also low, with 0.3–2.1 g kg−1 for chloride, 0.9–3.4 g kg−1 for nitrogen and 3.7–11.2 g kg−1 for potassium.

Delayed harvest of miscanthus—influences on biomass quantity and quality and environmental impacts of energy production

One important aim of this paper is to investigate the effect of delayed harvest of miscanthus on biomass yield and quality. Miscanthus field trials were therefore carried out at three locations in south Germany. The plants were harvested at different dates, and the yields and chemical composition of the biomass were measured. Another aim is to investigate the effects of delayed harvest of miscanthus on the net primary energy balance, total emissions of greenhouse gases, and total emissions of acidifying gases in the case of a large-scale heat generation from this biomass. Thus, life cycle assessment (LCA) for a theoretical large-scale heat generation from this specially grown and harvested miscanthus was carried out. Since no standard data set was available, two different model approaches (A and B) were applied within LCA to describe the energy consumption of biomass drying. Results of the field trials show an energy yield of 187–528 GJ ha−1 harvest from miscanthus in December. With delayed harvest, bioenergy yields decreased by 14–15% between December and February and by a further 13% between February and March. This was accompanied by a significant decrease in water content and in the concentrations of ash, nitrogen, chloride and sulphur in the biomass. The decline in energy yield, however, cannot be traded off by a reduced total primary energy consumption due to a reduced need for drying. The amount of total CO2 equivalent emissions of theoretical heat generation from miscanthus varies between 10.3 and 36.1 kg CO2 equivalents GJ−1 depending on the harvest time, production site and drying process model used. A clear effect of delayed harvest on total CO2 equivalent emissions per GJ was not found. The amount of total SO2 equivalent emissions varied between 44 and 213 g GJ−1. Here, results of both drying models show a clear decrease of SO2 equivalents with delayed harvest. In addition, energy generation from miscanthus emits less CO2 and SO2 equivalents than conventional heat generation from light heating oil. It can be concluded that an early harvest of miscanthus maximises energy yield and finite primary energy savings per hectare. It may also maximise CO2 equivalent savings per energy yield when energy consumption of the drying processes can be kept low. To gain certainty on this point, more robust data bases for the LCA are needed. On the other hand, late harvest reduced total SO2 equivalent emissions of an energetic use of miscanthus and it also recommended for economic reasons.

Quantity and quality of harvestable biomass from Populus short rotation coppice for solid fuel use—a review of the physiological basis and management influences

Abstract Woody biomass from poplar and aspen ( Populus sp.) short rotation coppice (SRC) has good combustion properties compared to non wood solid bio fuels and fossil solid fuels. This review compiles and discusses relevant literature on fuel quality and yield for Central European conditions. The most problematic quality parameter of woody biomass from Populus SRC is its high water content at harvest time (55–60%). Storing unchipped material on the field during summer is an efficient tool to lower it. In order to control other quality parameters—mainly nitrogen (N), potassium (K) and heavy metal contents but also yield—one has to take into account the physiological background of SRC. Important features are species/clone, age of sprouts, growth pattern, site and nutrient cycling. Maximum mean annual increment (MAI) occurs later than in willows. Therefore rotations should be longer than in willow: at least 6–7 years for poplars and,—due to differences in growth pattern,—10 to 12 years for aspen. Both results in MAIs of 10– 12 o.d.t. ha −1 yr −1 and reduced nutrient concentrations due to a lower share of branches and twigs in the harvested biomass. However, with elongated rotations costs rise because yet no automated (and thus cheap) harvest methods for large stem diameters were developed. Although sometimes ignored poplars are demanding concerning site characteristics. Basic requirements are good water (minimum 350 mm rainfall during growing season) and nutrient supplies, deep soils and favourable climatic conditions (average air temperature between June and September at least 14°C). Only aspen are partly suited for poorer conditions. For Populus -SRC in general weed control during establishing phase is essential.

The modelled productivity of Miscanthus×giganteus (GREEF et DEU) in Ireland.

Abstract The contribution of Miscanthus biomass to an energy or fibre industry in Ireland can only be estimated if the potential productivity is predicted on a regional basis. In order to parameterise a model to predict dry matter production, growth and climatic measurements were carried out in 1994 and 1995 on a Miscanthus field trial, planted in 1990 in southern central Ireland. These were used to derive relationships between: (i) leaf canopy light interception and thermal time calculated from air temperatures; and (ii) radiation intercepted and above ground biomass. These relationships were used to parameterise an empirical productivity model in which water and nutrient supplies are assumed non-limiting. The output from this model was incorporated into a geographical information system (GIS) to map the predicted potential production of M.×giganteus throughout Ireland, using 10 year daily air temperatures and incident radiation from 23 climatic stations. Across the island, potential biomass yields at the end of the growing season, ranged between 16 and 26 t DM ha−1. The model approach and its predictions are discussed.

Screening Miscanthus genotypes in field trials to optimise biomass yield and quality in Southern Germany

Field experiments to test the biomass production from the C4 perennial grass Miscanthus have concentrated on one triploid genotype, namely M.×giganteus. Several limitations to production from M.×giganteus including insufficient winter rhizome cold tolerance demonstrated the need to broaden the genetic base. This paper presents results from a field trial in Southern Germany planted with 15 Miscanthus genotypes including M.×giganteus, M. sacchariflorus, wild M. sinensis and bred M. sinensis hybrids over 3 years. Under field conditions, establishment from micro-propagation was high and all genotypes survived the first winter (losses<6%). Genotype growth characteristics were determined by measurements of height, shoot density, stem diameter, flowering time and autumn senescence rate. Increasing plant age was associated with higher yields (2, 6, and 17 t dry matter ha−1 in autumn of years one to three, respectively) and better biomass qualities for combustion. Delaying harvest time from autumn until spring in the second and third years reduced harvestable yields but increased combustion quality by lowering moisture, ash, Cl and N contents for all genotypes. Yields were highest for the M.×giganteus and some newly bred M. sinensis hybrids, but biomass qualities were best in the pure M. sinensis genotypes. These trials showed that new hybrids between M. sacchariflorus and M. sinensis should be developed that have many growth characteristics similar to M.×giganteus but with improved rhizome freeze tolerance in winter. As the biomass yield and quality of a particular genotype after 1 year of growth does not always relate to that measured in subsequent years, identification of the most suitable genotypes requires at least 2 years.

CO2-balance for the cultivation and combustion of Miscanthus

Miscanthus ‘Giganteus’ is a perennial C4-grass from East Asia. The biomass yield-potential of Miscanthus has been investigated in Germany since 1987. The combustion of biomass offers a possibility for lowering emissions of the greenhouse gas CO2. The CO2 which is set free during combustion has previously been fixed by the plants. The study analyses the demand for energy and the CO2-emissions which are involved in the production of Miscanthus, beginning with propagating the plants to transporting the biomass to the power station. Energy demand and CO2-emissions are compared with those of the provision and combustion of hard coal. The energy content of Miscanthus biomass harvested from one hectare, about 20 t of dry matter, corresponds to the energy content of 12 t hard coal. For each gigajoule of hard coal, 96.6 kg CO2 are emitted during provision and combustion. By combusting Miscanthus instead of hard coal 90% of CO2-emissions can be saved.

Propagation method as an important factor in the growth and development of Miscanthus×giganteus

Abstract The morphological development of Miscanthus×giganteus plants propagated either by rhizome division or by micropropagation was studied in two field and two pot trials. Significant differences were found for the thickness of the rhizome branches as well as the number and strength of the shoots. Rhizome propagated plants had a lower number but stronger shoots and thicker rhizome branches than micropropagated plants. In the field those plants micropropagated directly by in vitro tillering developed more slowly than those micropropagated through somatic embryogenesis, both in terms of total dry matter (DM) and share of the rhizome of total DM. The analysis of the chemical composition of shoots and rhizomes showed a tendency of higher N, P, K and sugar contents in rhizomes from rhizome propagated plants. Morphological differences between propagation variants were found to last until the third ratoon although these differences diminish with increasing age of the plantation. Directly micropropagated plants have thinner stems, making them more susceptible to lodging. As no chilling occurred in any of the trials, no immediate conclusions can be drawn about differences in chilling resistance between the propagation variants.

Progress in upscaling Miscanthus biomass production for the European bio-economy with seed-based hybrids

Field trials in Europe with Miscanthus over the past 25 years have demonstrated that interspecies hybrids such as M. × giganteus (M × g) combine both high yield potentials and low inputs in a wide range of soils and climates. Miscanthus hybrids are expected to play a major role in the provision of perennial lignocellulosic biomass across much of Europe as part of a lower carbon economy. However, even with favourable policies in some European countries, uptake has been slow. M × g, as a sterile clone, can only be propagated vegetatively, which leads to high establishment costs and low multiplication rates. Consequently, a decade ago, a strategic decision to develop rapidly multiplied seeded hybrids was taken. To make progress on this goal, we have (1) harnessed the genetic diversity in Miscanthus by crossing and progeny testing thousands of parental combinations to select several candidate seed‐based hybrids adapted to European environments, (2) established field scale seed production methods with annual multiplication factors >1500×, (3) developed the agronomy for establishing large stands from seed sown plug plants to reduce establishment times by a year compared to M × g, (4) trialled a range of harvest techniques to improve compositional quality and logistics on a large scale, (5) performed spatial analyses of yield potential and land availability to identify regional opportunities across Europe and doubled the area within the bio‐climatic envelope, (6) considered on‐farm economic, practical and environmental benefits that can be attractive to growers. The technical barriers to adoption have now been overcome sufficiently such that Miscanthus is ready to use as a low‐carbon feedstock in the European bio‐economy.

The influence of nitrogen fertilizer on the yield and combustion quality of whole grain crops for solid fuel use.

Whole grain crops can be suitable for the production of solid biofuels because they have a high biomass yield and can be harvested with a low water concentration. The concentrations of water, ash, nitrogen (N), sulphur (S), chlorine (Cl) and potassium (K) in solid biofuels should be as low as possible and calcium (Ca) concentrations high to avoid technical problems and environmentally harmful emissions during the combustion process. Since N fertilization can negatively influence the combustion quality of biomass, a conflict between yield and quality aims can arise. The aim of this study is to investigate the influence of the dosage of N fertilization on the yield and quality of the whole crop biomass of triticale, rye and wheat. In 1996 and 1997, field trials with winter triticale, winter rye and winter wheat were conducted at three locations in South-West Germany. N fertilizer doses were varied from 0 to 70 and 140 kg N ha−1 a−1. All N doses were applied between March and May. The whole crop biomass was harvested. The water concentrations and concentrations of ash, N, K, Cl and Ca in straw and grain were measured. A dose of 70 kg N significantly increased the yield of all cereal species, but yield increases at 140 kg N were not always significant when compared with 70 kg N. At 70 kg N the energy yields reached 137–249 GJ ha−1, for wheat, 142–263 GJ ha−1 for rye and 182–250 GJ ha−1 for triticale. The water concentration of the biomass, mainly of the straw, was significantly increased by N fertilization when the harvest was performed early at comparatively high water concentrations. For all cereal species a significant increase of N concentrations, especially in the grain, was measured at increased N fertilizer levels. The K concentrations of the straw and the Ca concentrations of straw and grain of all cereal species were also increased by N fertilization. N fertilization had little or no effect on the ash and Cl concentrations, which slightly decreased with increased N fertilization. N fertilization can, therefore, be used as a tool to influence the concentrations of N and K in the biomass. When combining yield and quality aims, 70–100 kg ha−1 a−1 N fertilizer was the best dosage for the whole grain crops at the southwestern German locations tested here.