Viable Biomass for Hawaii

March 12, 2017 |

By Gretchen Miller

Special to The Digest

Meghan Pawlowski crawled through the tall, dense sugarcane jungle, glass vials in hand, searching for her next sample site while she kept her eye out for the scurry of cane spiders.  Up to four inches across, these usually harmless creatures are nonetheless an unpleasant one-on-one encounter while tangling in the thick undergrowth of the cane fields.  The eight long legs of the cane spider wrap adeptly around cane stalks; crossing paths with a human intruder, these legs will wrap around arms and legs instead.

Meghan Pawlowksi, a graduate student at the University of Hawaii Manoa’s College of Tropical Agriculture, crawled around her field site on the last sugarcane plantation in Hawaii, Maui’s Hawaiian Commercial & Sugar Company, or HC&S, collecting field data for two years.  Her study was unique because it was the first in-depth study of tropical grasses as a biofuel option for Hawaii; she was hoping to determine the best biofuel crop to grow in Hawaii.  Last month, she published the results of her long days in the field with her advisor, Dr. Susan Crow, UH Assistant Professor of Soil Ecology, in a peer reviewed scientific journal called PLOS ONE.

In January 2017, at the same time their article was published, HC&S closed, marking the end of 150 years of plantation agriculture in Hawaii.  The citizens of Hawaii, landowners, policymakers, and researchers are sitting with the question of what the best uses for thousands of acres of old plantation fields are for future generations.  Pawlowski, Crow, and their research team, investigated the potential these lands have for both biomass fuel production and reducing green house gases in our atmosphere by sequestering, or holding, carbon in thousands of acres of agricultural soils.

The team investigated two tropical grasses: sugarcane and Napier grass, to see which was best to grow on fallow sugarcane lands for biomass energy production. Results of two years of field data show that Napier grass grows very quickly with relatively low levels of water to produce biomass fuel material, and is also extremely effective at holding carbon in the soil to reduce global warming.  Dr. Crow explained,  “Carbon is being held in the soil itself.  The plant roots are the conduits to transfer it back to the soil. Then it’s stabilized … and will continue to hold the carbon in the soil for a very long time with zero-tillage, or zero-plowing, practices.  When you work to accumulate carbon in the soil, you’re rebuilding the quality of the soil.  Over time we rebuild soil health; as the soil heals we can also reduce the amount of water and fertilizer needed for Napier grass cultivation,” Dr. Crow said.  One major criticism of biomass energy production is that it often uses more energy to create the biomass fuel than it actually produces, adding to green house gases in our atmosphere instead of reducing them.  The field data on Napier grass shows it sequesters, or holds, so much carbon in the soils, and requires so little water to grow, that overall, Napier grass reduces green house gases in the atmosphere, making it a viable green house gas reduction as well as biofuel crop.

Napier grass has the potential to play an important role in the future of energy sovereignty for Hawaii.  In Governor Ige’s January 2017 State of the State Address, he reconfirmed Hawaii’s commitment to its Clean Energy Mandate, with the goal of generating one hundred percent of Hawaii’s electricity from renewable sources by 2045.  Dr. Crow explained that most of Hawaii’s renewable energy portfolio will be made up of a combination of wind, solar, and geothermal energy.  Biomass could be helpful “… on cloudy, windless days, where supply is low and demand is high.  We could use pelletized biomass on days of high need,” Dr. Crow said.  “The grasses could also be feedstock for a digester to produce methane, which we can burn for fuel.  Waste products from this methane production can then be returned to the soil by composting.”  Dr. Crow emphasized that closing energy loops such as these, by returning waste products to the soil to enrich agricultural lands, is essential for Hawaii to gain energy independence.

Joelle Simonpietri, Energy Program Manager at UH’s Applied Research Lab, addressed another of the controversies surrounding biofuel production directly, “Quite often there’s a food versus fuel question or conflict.  A better question is:  How can we most effectively use our landscape to produce food and fuel for a sustainable Hawaii?  There’s plenty of land for everything if we start planning now with the buy-in of prominent land-owners and farmers.”  Reframing the common food versus fuel debate to a food and fuel conversation could help Hawaii move towards an integrated food and fuel system for greater food and fuel security.

“[The] paper shows how dedicated energy crops can have long-term benefits for the planet and for the state.  It helps to inform the land use policy debate … and helps to inform landowners with their decisions about land use,” said Simonpietri.  To further inform Hawaii’s land use policy debate, Dr. Crow is currently working on analyzing her team’s four-year data set that is just coming out now, and searching for a field site where she can conduct a longer-term study on Napier grass.  She is also collaborating with a group of UH economists and engineers on a systems-level approach for optimizing land use on the state level, including how biomass can contribute to the state energy portfolio.

Sources

  1. 1. Crow, Susan, PhD, Assistant Professor of Soil Ecology, College of Tropical Agriculture, Department of Natural Resources, University of Hawaii at Manoa, personal phone interview, 2/2/17.  1910 East-West Road, Sherman 101, Honolulu, HI 96822.  808-956-7530, [email protected].
  1. 2. Pawlowski, MN, Crow, SE, et al. (2017) Field-Based Estimates of Global Warming Potential in Bioenergy Systems of Hawaii: Crop Choice and Deficit Irrigation.  PLOS ONE 12(1): http://journals.plos.org/ploseone/article?id=10.1371/journal.pone.0168510
  1. 3. Pawlowski, Meghan, former graduate student, College of Tropical Agriculture, Department of Natural Resources, University of Hawaii at Manoa, personal phone interview, 2/9/17.  1910 East-West Road, Sherman 101, Honolulu, HI 96822.  808-956-7530, [email protected].
  1. 4. Simonpietri, Joelle, Energy Program Manager, Applied Research Lab, University of Hawaii at Manoa, personal phone interview, 2/9/17.  2800 Woodlawn Drive, Suite 170, Honolulu, HI 96822. 808-956-0425, [email protected].

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