Switchgrass as an Alternative Energy Crop

There is an increasing interest in Europe in biomass crops as a source for renewable CO2-neutral energy, fuels, and chemicals and as a fibre source for the production of paper and other renewable materials. Many different plants are being considered for this purpose. For example trees such as willow, eucalyptus and poplar and annual crops such as hemp. Switchgrass (Panicum virgatum L.) is one of the perennial rhizomatous grasses being developed for the purpose of biomass production. Since the early 1990s the crop has been developed as a model herbaceous energy crop for ethanol and electricity production in the USA and in Canada and it is also being considered as a paper pulp production feedstock.  In this project a broad range of factors were investigated that determine the suitability of switchgrass as a lignocellulosic C4 biomass crop in Europe. The most important agronomic aspects like variety choice, nitrogen response, yield development, and establishment were evaluated together with specific energy and fibre applications. Information from literature, from small experiments conducted in Europe, and results from ongoing research on other perennial rhizomatous grasses served as a starting point for the project.

The GENERAL OBJECTIVE of this project was to evaluate switchgrass as a promising cost effective energy crop that will add to agricultural diversification in Europe and to generate sufficient data to be able to initiate large scale production trials and facilitate further development of switchgrass in Europe. Specific objectives were: (1) to identify existing switchgrass varieties that are adapted to specific geographical regions of Europe, (2) to determinate the potential dry matter production of switchgrass in small production plots, (3) to determine nitrogen fertiliser requirement of switchgrass, (4) to collect physiological data on switchgrass to explain biomass production and quality,  (5) to identify best seed establishment methods under European conditions, (6). to evaluate  winter hardiness of switchgrass under European conditions, (7). to develop a pilot model for switchgrass biomass production, (8) to determine the suitability of switchgrass for various thermal conversion processes (pyrolysis, gasification and combustion, (9) to evaluate switchgrass fibre quality, (10) to evaluate economic and environmental aspects of the use of switchgrass as an energy crop, a fibre crop, and a combined energy/fibre crop, (11) to compare switchgrass to other energy and fibre crops.

1. Switchgrass can be grown successfully in Europe. It can be used to produce inexpensive biomass under low input conditions and at a low environmental impact.
2. Switchgrass biomass can be used for thermal conversion to electricity and heat. It also has potential as a fibre source for paper pulp production where it can replace hardwood, or as a feedstock for lignocellulose for bioethanol production.  Other promising applications of switchgrass fibre include as re-inforcing and filling agent in thermoplastic materials.
3. It is necessary to gain further experience with switchgrass under large field conditions and over a longer period of time. In addition, switchgrass performance could increase significantly through breeding and optimisation of agronomic parameters such as timeliness of seeding, row spacing, nutrient requirements, etc.
4. Information on applications of switchgrass for energy and fibre uses could be expanded much further.

Are there existing varieties that are adapted to specific geographical regions of Europe? It is possible to find switchgrass varieties that are adapted to most regions of Europe. The latitude of origin of a variety is the most important aspect determining the area of adaptation of a variety. Generally the use of varieties originating at southern latitudes (Southern USA vs Northern USA and Canada) can increase DM yields but (in NW Europe) it will also increase the chance of establishment failures in the first year and a decline in yields over time. Furthermore the quality of the biomass will be reduced (high moisture and nutrient content) if the variety does not mature in the fall. The best variety for a given latitude or geographical area will be a compromise between yield, quality and winter survival. From the current data on switchgrass grown in Europe it appears that switchgrass may be grown further north than in North America. Specific recommendations for using varieties are given in Chapter 5 and 10.

What is the potential dry matter production of switchgrass in small production plots?  In the current project yields of up to 18 tonnes dry matter/ha were found in NW Europe and up to 25 tonnes dry matter/ha were found in Southern Europe. Under practical conditions these yields may be lower as field plot yields are often higher than practical yields. Accurate estimates will have to be obtained on large filed experiments over longer periods of time. Another aspect is the time it takes for a switchgrass stand to raech maximum yield potential. At most experimental sites yields increased from year to year and may have increased even more in following years.

What is the nitrogen fertiliser requirement of switchgrass? Nitrogen fertiliser requirements were generally found to be low as the crop failed to show yield response to fertiliser applications at 4 out of 5 experimental sites. The current research shows that between 0 to 50 kg N/ha/year is adequate for NW European sites while at higher productive sites in southern Europe 50 to 100 kg N/ha/year should be adequate. More specific recommendations for quantity of nutrients cannot be made because this will also depend on the fertility status of the site.

What determines the yield and biomass quality of switchgrass? Yield and quality of switchgrass are determined by a range of factors of which the origin of the variety is probably the most important (see discussion in Chapter 5).

Which seed establishment methods for European conditions are recommended? Seed establishment makes switchgrass a very attractive biomass crop since it is inexpensive and reduces financial risks. Experiments have shown that no-till establishment methods are suitable for switchgrass, (see Chapter 6 for details). Spring establishment dates and seeding rates were tesed indicating that as low as 200 Pure live seeds per square meter can be sufficient for establishing a good stand. Further development of establishment methods for specific regions and soil conditions (slopes) is possible to decrease establishment risk and cost.

Which factors determine winter survival for switchgrass varieties? Winter survival is mainly determined by the length of the growing season of switchgrass. If a variety fails to mature sufficiently when winter sets in severe winterdamage to the stand will occur. This is especially the case in the establishment year. Therefore late maturing varieties which originate at southern latitudes should not be used at sites too far north (see Chapter 5 for details).

For what types of thermal conversion systems is switchgrass biomass suited. Switchgrass biomass has been tested for thermal conversion (for details see Chapter 7). Many different factors determine suistablity for thermal conversions. Based on the contents of alkaline metals and chlorine, two of the most important factors determining suitability for thermal conversion, it is expected that switchgrass biomass is better suitable for thermal conversion than (wheat) straw and worse than wood.

For which non-energy applications can switchgras fibres be used? Switchgrass has been evaluated for paper pulp production and as a reinforcing fibre in polypropylene composites (for details see Chapter 8). It was concluded that switchgrass could replace a part of the hardwood pulps in printing and writing papers. Due to its high bulk it will especially be suitable for bulky printing papers. Mechanical pulping of switchgrass needs far less energy than mechanical pulping of aspen or other woods. The high productivity under low input conditions results in low cost per tonne of biomass making switchgrass a potentially cost effective replacement for hardwood pulps in printing and other paper types. The low price and the relatively good mechanical characteristics should make switchgrass an attractive fibre for filling and stiffening in thermoplastic composites. Further improvement of composite mechanical properties by improved pulping should be possible. The potential ethanol production yield when switchgrass is used as feedstock in a lignocellulose to ethanol system was calculated to be 262 kg ethanol/tonne dry matter. This yield is comparable to the theoretical ethanol yield from hard wood like willow.

Which conclusions can be drawn from economical and ecological analysis of switchgrass production and utilisation? The data was limited to 3 years while the typical (economic) life span of a switchgrass stand is expected to be 10 to 15 years. Furthermore only small plot experimental data was available. Based on extrapolation of this data and available literature some conclusions can be drawn. The cost prices for switchgrass for the different countries mentioned above varied between 24 and 62 Euro per tonne DM. Not taking into account the land costs. In general environmental parameters that affect Miscanthus are similar to those mentioned for switchgrass. With Miscanthus requiring more input in establishment than switchgrass because Miscanthus is propagated by rhizomes and switchgrass by seed. In order to make better comparisons in the future there is need for scaling up production field trials to determine actual commercial biomass yields and costs for switchgrass and other perennial grasses like Miscanthus.

This research has been partially funded by the European Community (DGVI) under the FAIR program (FAIR 5-CT97-3701) and by ETSU, UK. The information contained on this website does not necessarily reflect the European Commissions views or anticipate in any way its future policy in this area.

A number of research organisations from different EU countries participated in this research project.