Tuesday, July 19, 2011

Switchgrass.


So,

I mentioned in my Biofuels post that I had a preferred feedstock for production of biofuels.  After a fair chunk of research on the topic (it has been a topic I've followed for ~3 years), I firmly believe that switchgrass should be the primary feedstock for biofuel production in Canada and the United States.  In the interest of full disclosure, I will say that the reading I have done has not been based solely on peer-reviewed literature, though said reading has supported the facts I have read from non-scholarly sources.  I will also say that the Wikipedia article on switchgrass is an excellent starting point for learning more on the subject.

Switchgrass is native to North America, and can be found east of the Rockies, west of Nova Scotia and south of the Territories.  It is a primary constituent of the tallgrass prairie ecosystem.  This ecosystem is present where there is enough water to support more than a short grassland, but periodically sees all above-ground biomass destroyed.  Reasons for destruction usually include buffalo and fires.  As an interesting note, the indigenous peoples would often start fires for increased fruit production of berry plants, which in turn allowed for the tallgrass prairie to thrive.  This ecosystem has since been repressed by human activities.  We, as a civilisation tend to suppress wildfires and turn tallgrass prairie into farmland (it makes for excellent soil).  Virgin Ontario tallgrass prarie, or what is left of it, tends to be located on rocky or sloped lands which could not be tilled or built upon.

The reason switchgrass does well with periodic above-ground destruction is its biomass distribution.  Just over half of the biomass of a switchgrass plant is below-ground.  It is worth noting that growing switchgrass may be viewed as not only carbon neutral, but also a carbon sink.  Since more than half of the plant biomass is below ground, it may sequester and store the carbon dioxide released from the burning of fossil fuels.  One season of growing sees the switchgrass send up stalks and grow seed in the warm season (as of this post, most switchgrass I have seen has begun seed production).  In the cool season, the plant focuses on building up its root system.  Switchgrass can be mowed twice a growing season and still maintain a healthy root system.  The plant is also perennial, meaning it will return every spring indefinitely.  Experimental plots of switchgrass that were planted in the mid to late 1980s still exist today after one planting.

It is for this reason, among others, that the Resource Efficient Agriculture Program (REAP), advocates for switchgrass as a biofuel.  Recent success by REAP has been to advocate for grass pellets as opposed to wood pellets for stoves.  Though grass pellets do not burn as cleanly as wood pellets do (stoves must be modified for this), they are a more reliable source as wood pellets are made from industrial waste and are thus subject to economic forces.  REAP also outlines how to efficiently harvest switchgrass in Ontario and Quebec.  After a full growing season, the grass may be mowed and gathered into windrows to winter in the field.  This allows for snow melt to wash most of the nutrients back into the soil, decreasing fertilisation requirements.  This is largely the only input of resources required for a stand (or plot) of switchgrass, making it incredibly efficient.

Even with these low inputs, switchgrass may still thrive.  While first generation ethanol production requires corn, which in turn requires good agricultural land, switchgrass may be grown upon what is known as marginal cropland.  This means that the soil, for whatever reason, has become degraded and will not allow for food crop production, mitigating a food vs fuel economy.  Not only will it grow there, but the land eventually benefits from the presence of switchgrass.  Some individual stalks and their roots will eventually die, which means said roots will decompose underground.  This increases the organic content of the soil, which makes it higher quality.  It is for this reason that switchgrass has been used previously in soil conservation efforts, and why there is a large base of scholarly knowledge on the plant.

While I cannot remember the math that goes into this, various sources note that the energy requirements of the average Canadian home for one year can be provided by the production of a single acre of switchgrass in a season.  A hectare of land, 2.47 acres, will produce about 18.8 oven-dried tonnes of plant material in said season.  Since the switchgrass is only planted once over the lifetime of the stand and requires minimal energy inputs (fertilizers and such), the energy payoff is quite substantial.  If the switchgrass yielded is burned directly, it is estimated that the crop yields a 20:1 energy payoff, where first generation biofuels will break even only under the best of circumstances.  Conversion to second generation liquid biofuel will (theoretically) return a 5:1 energy payoff.  This figure is theoretical, as no one is yet certain what the predominant second generation production method will be.

Unfortunately, switchgrass does require some special treatment as a crop.  The crop requires three years to establish, and fertilizers must be avoided during this time (it encourages competition from weeds).  A stand must also be burned every 3-5 years in order to discourage competition from other plant life.  Remember, tallgrass prarie only thrived under periodic destruction, especially in the eastern half of North America.  It has also been noted that any monoculture is ecologically undesirable.  Honestly, these are legitimate problems, but I feel they are more than made up for by the benefits of the plant.  It is also worth noting that the monoculture may be mitigated by including other grasses from the tallgrass prairie ecosystem, particularly big bluestem.  However, it is a less robust plant.  Switchgrass is tolerant to floods, drought, and comparatively high salinity [salt concentration in soil].

I could go on about this, but the post as it stands is fairly cluttered.  I may return to this topic, and probably will should I run out of other talking points.  Be it known that I feel switchgrass would be an excellent feedstock for biofuel production.

NM

P.S.  The picture which begins this post was taken after I received a tip on the location of an experimental stand of switchgrass.  It seems the response of switchgrass is being measured against amounts of fertiliser used, which may explain the stripes of different colours.  I wonder what the results will be!
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