The search for alternate energy sources is growing in economic importance as fossil fuel supply rapidly depletes and concerns about its environmental effects grow. Various forms of biofuel have been incorporated into the United States industry, especially ethanol and biodiesel derived from monocultures of corn and soybean. Another promising source of biofuel is high-diversity prairie biomass. On the surface, prairie biomass solves some of the problems posed by using corn and ethanol biomass. Where corn and soybeans use fertile cropland, and may encourage the conversion of wooded ecosystems to agricultural land, prairies grasses can grow on abandoned degraded agricultural land. Where corn and soybeans require large amounts of pesticides and fertilizers, diverse prairie communities are more resistant to pest invasion and legumes provide nitrogen. Where corn and soybeans need to be replanted annually, prairie grasses regrow from below-ground root systems. To further explore the viability of using prairie biomass as a biofuel source, and to compare its efficiency with corn and soybean biofuel, Cedar Creek scientists calculated the net energy gain from corn, ethanol, and prairie plots of varying biodiversity. They also calculated certain environmental effects, such as greenhouse gas reduction (Hill et al. 2006, Tilman et al. 2006).
Net energy gain for corn and soybean biofuels was calculated as estimated energy use subtracted from estimated energy yield. Energy use was estimated as the amount of energy used in crop production and in converting crops to biofuels. To estimate the amount of energy used in crop production, the study combined information from existing US Department of Agriculture data on fertilizer, soil treatment, and pesticide application; recent other studies’ estimates of energy needed to produce each of these agricultural inputs; energy use for operating agricultural equipment, manufacturing equipment, the construction of buildings used in crop production and for producing the corn or soybean seeds planted; and the energy used to sustain farm households. To estimate the amount of energy used in converting crops to biofuels, the study estimated energy used to build facilities used to convert crops to biofuels, the energy used to transport crops to these facilities, power these facilities, and transport biofuels to their point of end use; and the energy used to sustain industrial workers’ households. To estimate energy yield, this study added the amount of combustible energy gained to the energy equivalent coproduct values (e.g., livestock feed). To estimate greenhouse gas (GHG) reduction for corn and soybean biofuels, GHG emissions were added to the GHG savings from displacing fossil fuel.
Randomly selected combinations of 1, 2, 4, 8, or 16 perennial herbaceous grassland species were planted in 152 prairie plots. Plots were grown with low inputs, unfertilized, and irrigated only during establishment; all plots were burned in early spring to remove aboveground biomass before growth began. Aboveground biomass was harvested and sampled annually. Net energy gain was calculated as estimated energy use subtracted from estimated energy yield. Energy use was estimated as the amount of energy used in prairie biomass production and in converting prairie biomass to biofuel. Energy used in prairie biomass production was estimated assuming standard agricultural practices for growing, harvesting, and transporting prairie biomass. Energy used in converting prairie biomass to biofuel was modeled in three scenarios: co-fired with coal, converted to ethanol, or gasified and converted to both synfuel and electricity. To estimate GHG reduction, GHG emissions were added to the GHG savings both from displacing fossil fuel and from the net GHG sink that occurs when prairie grasses store carbon underground in deep root systems.
If done properly, biofuel practices using diverse native prairie grasses may simultaneously provide wildlife habitat. A project to determine proper management practices is being implemented at 6 field sites across Minnesota. This project is being established on lands with at least 16 species of native prairie plants that have been established for at least five years. In all 6 sites, four treatments are to be established: a control, with no harvesting; 75% of the land harvested; 90% harvested, and all of the land harvested. Unharvested land can provide a refuge for wildlife immediately following harvesting, but how much land may be left unharvested while sustaining wildlife populations remains undetermined. In 3 of the sites, scientists will monitor the nesting and habitat use of birds, browsing of white-tailed deer, the diversity and composition of insect populations, and the diversity and composition of small mammal populations. Ecosystem values will be calculated by soil samples, floral surveys, and other relevant measurements. In the remaining 3 sites, no monitoring will occur pending future acquisition of funds, but harvesting will occur. This project will examine wildlife benefits, biofuel values, and ecosystem values in the four treatment areas in order to determine proper management practices and develop standard protocol. See Wildlife Conservation and Biofuel Production on Restored Prairies.
The routine use of antibiotics in livestock production has adverse effects on our water supply. The majority of the antibiotics administered to cattle are excreted in their manure. Since manure is nitrogen and phosphorus rich, it is used abundantly as an organic fertilizer instead of chemical fertilizers. As much as 40% of our water supply is contaminated with trace amounts of antibiotics that originate from feed lots. Even trace amounts of antibiotics in the environment could potentially lead to treatment resistant forms of bacteria.The high concentrations of nitrogen and phosphorus in livestock manure also leads to contamination of our water supply. Higher levels of nitrogen and phosphorus promote the rapid growth of algae in lakes and ponds throughout developed areas. Excess nitrogen in drinking water can have negative effects on the health of infants. Further studies are being conducted to understand its other potential human health risks.
Experiment E246 at Cedar Creek Ecosystem Science Reserve looks at the ability of different plant communities to be used as biofuels and to absorb specific contaminants (nitrogen, phosphorus, and antibiotics) out of the ground. This experiment also looks at how ecosystem properties (i.e. hydrology, soil carbon content) will affect the fate of these contaminants. America needs uncontaminated drinking water supplies as well as sustainable fuel sources. LIHD biofuels may provide a viable solution to both of these issues. Soybean biodiesel and corn ethanol require many fertilizer inputs which can introduce contaminants into the groundwater. E246 is looking at the ability of native prairie and introduced hay communities to be alternative biofuel sources. This study will compare the biofuel potential between corn, (requiring a large amount of fertilizer inputs) prairie, and hay communities (both requiring low fertilizer inputs). It will also look at the affect these plant communities have on ground contaminants. It is our goal to compare the groundwater cleansing abilities provided by diverse native prairie communities, non-native hay, corn, and bare ground. In knowing this information, we could recommend certain plant communities be planted adjacent to fertilized crops. These crops could be both harvested for biofuels while still reducing contaminants out of the groundwater.
Ethanol from corn grain yields 25% and biodiesel from soybean yields 93% more energy than is invested in production (Hill et al. 2006). In contrast, high-diversity prairie biomass can yield up to 451, 444, or 709% more energy than invested in production if co-fired with coal, converted to ethanol, or gasified and converted to both synfuel and electricity, respectively (Tilman et al. 2006). • Prairie plots with higher species diversity yield a greater energy gain. Plots with 2, 4, 8, and 16 species yield 84, 100, 157, and 238 % more bioenergy, respectively, than monocultures (Tilman et al. 2006). • Relative to fossil fuels, ethanol reduces greenhouse gas (GHG) emissions by 12% and biodiesel reduces GHG emissions by 41%; but overall they are both net carbon sources (Hill et al. 2006). Prairie biofuel, on the other hand, is carbon negative because it sequesters carbon underground in deep root systems (Tilman et al. 2006). • Prairie plots with higher species diversity sequester larger amounts of carbon dioxide than monocultures. In monocultures, there is no significant net sequestration of carbon dioxide. In plots with 16 species, almost 13 times as much carbon dioxide is sequestered in the soil and plant roots than is released during biofuel production. These results suggest that high-diversity prairie biomass may be a viable biofuel alternative, with several advantages over corn ethanol or soybean biodiesel.
