Renewable energy from restored prairie plots in ...€¦ · Renewable energy from restored prairie...

Renewable energy from restored prairie plots in southeastern Minnesota, USA

B. Borsari1, I. Onwueme2, E. Kreidermacher3 & T. Terril4 1Department of Biology, Winona State University, Winona, MN, USA 2College of Natural & Applied Sciences, Missouri State University, Springfield, MO, USA 3Pork & Plants, Altura, MN, USA 4Winona County Soil & Water Conservation District, Lewiston, MN, USA

Abstract

Although prairies occupied most of North America prior to European settlement, an extirpation of these habitats has inevitably occurred since the expansion of intensive, agricultural systems. In recent years, however, a renewed interest in prairie restoration has spurred increasing efforts for looking at prairies as possible sources of renewable energy. The purpose of our work was to establish a prairie community on marginal farmland with the goal of producing pellets from its biomass to be burned on site for heating greenhouses, instead of relying on corn (Zea mays) as a biomass source. Plots of grass only and plots of mixtures of forbs and grass species were planted in 2007 on a farm in southeastern Minnesota. In its second year of growth, the biomass produced was compared to what was obtained from corn stover cultivated at the farm. The biomass yield data produced from the different plots of equal hectarage were analyzed through a one-way ANOVA and Scheffe’s test to verify significant differences among the three different cropping conditions (grass, grass and forbs, corn). Our data indicated that prairie plots with mixtures of grass species can be the most productive for biomass production. This preliminary work is of value in this part of the world and should inspire more farmers in the Midwest region of the U.S. to restore prairies on marginal lands. Keywords: biofuel, forb, grass, pellet production, prairie, renewable energy, sustainability.

Energy and Sustainability II 137

www.witpress.com, ISSN 1743-3541 (on-line)

© 2009 WIT PressWIT Transactions on Ecology and the Environment, Vol 121,

doi:10.2495/ESU090131

1 Introduction

The extirpation of American prairies allowed for an expansion of gigantic agricultural systems, dominated by corn (Zea mays) monocultures cultivated in rotation with soy beans (Glycine max) to support a highly centralized, fossil fuel dependent food system. In more recent times however, a chronic agricultural crisis has been affecting US agriculture and the current fluctuation in oil prices upon which modern agriculture depends remains a chronic threat to large scale agriculture, both economically and environmentally [1]. The recent enthusiasm for producing ethanol from corn as a new source of renewable energy has not contributed to aid U.S. agriculture, nor to alleviate the compelling need for employing renewable fuels as alternatives to petroleum, although Mielenz [2] contends that there is great potential for corn and more plant species in the emerging world of bioenergy, through an application of biotechnological approaches and genetic engineering. Thus, U.S. economy remains heavily reliant on oil and other non renewable fuels while the effort to produce ethanol from corn remains challenged in its reductionist attempt to resolve the current energy crisis. This effort has contributed to amplify visions and ideas about the obsolescence of an agricultural paradigm, which demands instead a more careful consideration to be designed to fulfil the needs of 21st century society with more sustainability in mind and a higher level of commitment to stewardship.

2 A quest for developing more sustainable energy systems

The challenge of designing renewable and more sustainable energy systems is often hampered by several barriers, including the difficulty of evolving farming systems from large annual monocultures to perennial polycultures. To this end, Fargione et al. [3] have demonstrated that a conversion of natural ecosystems into agricultural monocultures for biofuel production like ethanol releases a much larger amount of CO2 in the atmosphere than the one that can be offset by biofuel use, and thus proving a major fallacy for making this and similar approaches feasible. On the other hand, recent studies [4, 5] have suggested that perennial, rhizomatous grasses like switchgrass (Panicum virgatum) and many other species possess great attributes to be grown for energy purposes [6]. Concurrently, opportunities wait to be further explored in the agro industry of North America when herbaceous feedstock is converted into pellets to be burned for heating purposes [7]. We remain critical however that the emerging biofuel model of production be constructed with the similar approaches that led to the design of annual monocultural systems but rather, we envision agroecosystems of perennial polycultures dominating the future landscape of our bioregion. As a matter of fact, at the opposite end of this epistemological spectrum, low-input polycultures of native grasses and forbs appear to possess even higher potential for renewable biofuels production [8] and for attenuating the gas emissions during the conversion process. Inspired by this approach, we decided in 2007 to verify the initial findings of Tilman and his collaborators by establishing prairie patches on a larger scale than the typical size of a few squared meter plots. The

138 Energy and Sustainability II



intent of this endeavour consisted in developing an on-farm biomass production system, capable of weaning itself from propane and corn combustion for heating its greenhouses [9]. The purpose of this study focused on assessing the yields of prairie biomass from mixed perennial grasses, and grasses with forbs when these were compared to corn (Zea mays) stover for the production of pellets that were going to be used on site, thus attempting to achieve a greater level of sustainability for the farm. The need for this study was spurred by the increasing necessities of developing more sustainable and renewable energy systems, especially after the disappointing outcomes of ethanol production from corn in recent years. There may be significant opportunities for farmers interested in developing markets for agropellets as the estimated 500,000 pellet burning stoves and furnaces in North America [10] provide an indication for a viable market niche from biomass in most of the USA. In addition to this, there is an increasing need to restore the ecological equilibria and services that regulate food production systems and enterprises [11] as fast anthropogenic changes upon the landscape continue to obliterate the natural attributes of the same [12]. The Canadian experience in producing pellets from prairie biomass appears to have already made major steps forward in developing an efficient pellet production system, while identifying promising plant species, best management practices and while proposing viable solutions to technical challenges for employing native perennial plants as biofuels. A similarity of environmental conditions and resources to the above mentioned Canadian studies provided us with another significant stimulus to work towards the development of a renewable energy system feasible for our bioregion.

3 Materials and methods

In the early summer of 2007, 7.9 hectares of a 16.2 hectare farm (Pork &Plants), located in south eastern Minnesota (Winona County), were planted with mixed grasses (4.7 Ha.) and mixtures of grass with forbs species (3.2 Ha.), fig. 1. This approach stemmed from the idea of reducing reliance on corn and propane gas, which are burned on-site for heating purposes [9]. The seed was drilled into the soil with equipment already available at the farm and no other inputs were used to establish the prairie plots. Adjacent fields were planted to corn and raised with the standard inputs for corn production in Minnesota. Toward the end of the first growing season (2007) an evaluation of prairie establishment was conducted to assess prairie establishment and species richness in the grass with forbs plots, when these were compared to the grass only plots [9]. For the three cropping conditions (corn, grass polyculture, grass with forbs polyculture) we considered 1-acre parcels (0.405ha) as our units of analysis. Thus, we collected 10 biomass weights from the corn field, 8 from the grass polyculture field (these plots were harvested twice). Twenty four sample weights were collected from 9.7ha of adjacent prairie of the Minnesota Department of Natural Resources (MNDNR), which has been restored for 15 years. The decision of harvesting the DNR prairie was made in order to collect more reliable data from the grass with forbs cropping system since the one




planted at Pork & Plants in 2007 was flooded in the summer of 2008 and thus, mostly inaccessible. In 2008 the prairie plots were harvested and biomass yield data were collected in order to verify which one of the three systems was most productive and thus substantiate or refute experimental data obtained in Minnesota a few years ago by Tilman and his collaborators [8]. The harvest took place in mid-November 2008. Plots planted with a mixture of prairie grasses (4.7 Ha) were harvested in August in addition to the autumn harvest. The biomass was mowed and subsequently baled with a rotobaler.

Figure 1: Aereal photograph of Pork & Plant Farm, showing the five prairie plots that were established in the early summer of 2007. The grid in the lower left corner shows the location of the farm in Winona County (south eastern Minnesota).




4 Results and data analysis

Biomass yields (Mg/ha) were measured as the fields were harvested in the summer and autumn of 2008. A summary of quantitative and qualitative data for the three different types of fields are reported in table 1.

Table 1: Summary statistics for yields, plot type and crop species.

Plot Mean Yield (Mg/ha)

Crop type Land type (agricultural vs.

marginal)

Number of Harvests

Grasses and forbs

1.14+0.78 polyculture Marginal Autumn

Prairie grasses

2.17+0.87 polyculture Marginal Summer and autumn

Corn 3.15+0.68 Corn Agricultural Autumn A description of biomass yield (Mg/ha) for the three different cropping systems is reported in figure 2. In addition to this, the data were analysed with a one-way ANOVA in order to identify any significant difference [10].

Figure 2: Biomass yields for each plot (0.405ha) and for the three cropping systems (grass with forbs polyculture, corn, grass polyculture).

Although the mean biomass yield was the highest in the corn stover plots (fig. 3), the analysis of the variance (ANOVA) indicated that the type of vegetation composition (monoculture versus polyculture) had a significant effect on biomass yield, F (2, 39) = 149, p < 0.01. Furthermore, a post hoc test (Scheffe’s test) was also employed to identify differences among pairs of bioenergy cropping systems [13, 14]. This analysis




did not indicate any significant difference between the biomass yields of prairie grasses versus those of grasses and forbs, nor between those of prairie grasses with forbs and those from the corn stover crop. However, the data provided sufficient evidence to suggest that there was a difference between the grass mixture plots versus the corn fields. Our findings did not support entirely the data of Tilman and his collaborators [8]. However, these preliminary results indicate that there is a realistic match with those data (fig. 3) and that these will emerge with greater emphasis as more yield measurements will be taken in future growing seasons.

Figure 3: Mean biomass yields for the three cultivation conditions (grass with forbs polyculture, corn, grass polyculture) and standard errors.

5 Discussion

The mean biomass yield from corn stover was higher than yields obtained from 0.405ha plots where mixed perennial grasses and grasses with forbs were grown. For this reason the skepticism for producing biofuels from low-input high-diversity (LIHD) grassland biomass remains consistent and in favour of corn cultivation rather than perennial polycultures. However, it must be pointed out that corn cultivation requires several off-farm inputs such as: 148 kg/ha of nitrogen, 23 kg/ha of phosphorus, 50 kg/ha of potassium on a yearly basis [15], in addition to water for irrigation and the inevitable loss of topsoil due to erosion and leaching of nutrients into underground aquifer and other water reservoirs [11]. In addition to this, corn must be grown on fertile soils whereas prairie plant communities can be productive on marginal land and be successful without the inputs necessary to grow corn and other annual agronomic crops. Thus, the




lower the inputs and fertility conditions, the better the relative performance of the prairie grasses compared to corn. Finally, our experiment yielded data from one growing season only since establishment of native vegetation plots at the farm. An unusually rainy summer in 2008 affected harvesting operations and did not allow the first of the two planned harvests. Concurrently, a variety of grass species have been identified as possible crops for pellet production [4, 6, 7, 16, 17] and are studied to be genetically modified so that they may acquire the desirable traits to be grown on a large scale and to yield pellets of superior quality, that burn completely and leave minimum ash residue in the burner, after combustion [7, 10]. A long-term field study by Varvel et al [16] to compare the potential for ethanol production between corn (Zea mays) and switchgrass (Panicum virgatum) indicated that the potential of switchgrass was superior to the annual grass (corn) and did not require the costly inputs normally used to achieve successful yields. However, the challenge of cultivating native, perennial species consists in utilizing marginal soils and minimum inputs in order to achieve a positive carbon balance between productivity and crop growth. Prairie restoration requires normally a three to five year time frame for the plant community to become sufficiently established and diverse in its floral composition. At Pork & Plants we were in the second year since the restoration effort began in 2007 and thus, despite our ability to substantiate only partially the experimental outcomes obtained by Tilman and co-workers in 2006, we remain convinced that similar results will be achieved as the perennial polycultures at Pork & Plants will enter their fourth, or fifth year since restoration commenced. Ultimately, we remain optimistic that harvests in future years will favour the high diversity plots as supported by the literature.

5.1 Conclusion and implications for future research

Wes Jackson envisions a new agricultural paradigm (Natural Systems Agriculture) that relies more and more on perennial species and on a model of food production that mimics the ecological processes and services of the prairie; he foresees this knowledge to become the framework for a 50-year Farm Bill in the U.S. [1]. The compelling need of conserving biodiversity and a more sustainable employment of resources demands an inevitable reconciliation between agriculture and resource use [18]. The prospects of a flourishing agro-pellet industry in the near future appear to be feasible for large agricultural regions of Canada and the Midwestern region of the U.S. [7]. However, several technical aspects remain to be resolved as prairie biomass contains a high amount of alkali and thus leaves a higher ash residue after combustion than the one left by other types of biomass. Although delaying harvest to late autumn or to the following spring seem to reduce the amount of unwanted elements (as these are translocated into the underground root system), more technical and management issues need to be resolved [2, 7]. A minimization of biomass loss during baling is of great importance also to possible pellet producers, in addition to a development of local market niches. It would be paradoxical to develop such a new agroindustry upon the similar tenets that rule the commercialization of present agricultural commodities, as a majority of the environmental benefits




of this enterprise would evaporate inevitably, because of transportation costs. Rather, we envision the feasibility of an agro-pellet production enterprise with prairie biomass for North American territories where a restoration of farmland to prairie is achievable with success, reduced off-farm inputs, and major environmental benefits for the agrarian landscape. This approach is also in tune with present conservation needs of the agricultural environment to limit soil erosion as a loss of topsoil continues to affect the sustainability of agriculture [19] even when the best agronomic practices are employed [20]. Therefore, a cultivation of perennial polycultures is to be encouraged instead of researching the benefits of annual, non-perennial, non-native species like Miscanthus [17] and others, regardless of their potential as bioenergy crops. The next 50 years of land management in the U.S. will require the greatest wisdom to achieve sustainability and to ensure that future generations may continue to enjoy a comparable quality of life and prosperity with a clearer understanding about the finiteness of our natural resource base [1]. To this end, we support the vision of prairie farming to be embraced by farmers in Minnesota and in several other states of the of the U.S. Midwest region.

Acknowledgements

We are grateful to the Department of Natural Resources (DNR) of Minnesota for granting access to its land and for allowing us to harvest biomass from its prairie. Daryl Buck of the Soil and Water Conservation Service of Winona County, Minnesota was generous in donating seed and technical service for prairie establishment at Pork & Plants.

References

[1] Jackson, W., The Prairie Meets the Farm: The Next 50 Years on the American Land-Perennializing Policy and the Landscape. Proc. of the 21st North Am. Pr. Conf., eds. B. Borsari, N. Mundahl, L. Reuter, E. Peters & P. Cochran, Winona State University: Winona, MN (in press).

[2] Mielenz, J.R., Bioenergy for ethanol and beyond. Current Opinion in Biotechnology, 17(3), pp. 303-304, 2006.

[3] Fargione, J., Hill, J., Tilman, D., Polasky, S. & Hawthorne, P., Land Clearing and Biofuel Carbon Debt. Science, 319(5867), pp. 1235-1238, 2008.

[4] Lewandowski, I., Scurlock, J.M.O., Lindvall, E. & Christou, M., The development and current status of perennial rhizomatous grasses as energy crops in the US and Europe. Biomass and Bioenergy, 25(4), pp. 335-361, 2003.

[5] McLaughlin, S.B. & Walsh, M.E., Evaluating environmental consequences of producing herbaceous crops for bioenergy. Biomass and Bioenergy, 14(4), pp. 317-324, 1998.




[6] Schmer, M.R., Vogel, K.P., Mitchell, R.B., Moser, L.E., Eskridge, K.M. & Perrin, R.K., Establishment Stand Thresholds for Switchgrass Grown as a Bioenergy Crop. Crop Science, 46, pp. 157-161, 2006.

[7] Samson, R., Mani, S., Boddery, R., Sokhansanj, S., Quesada, D., Urquiaga, S., Reis, V. & Ho Lem, C., The potential of C4 perennial grasses for developing a global BIO-HEAT industry. Critical Review in Plant Science, 24, pp. 461-495, 2005.

[8] Tilman, D., Hill, J. & Lehman, C., Carbon-Negative Biofuels from Low-Input High-Diversity Grassland Biomass. Science, 314(5805), pp. 1598-1600, 2006.

[9] Borsari, B. & Onwueme, I., A New Lease on Life for Marginal Farmland: Convergence of Prairie Restoration with Biofuel Production. Proc. of the 16th IFOAM Organic World Congress, eds. D. Neuhoff, N. Halberg, T. Alföldi, W. Lockeretz, A. Thommen, I.A. Rasmussen, J. Hermansen, M. Vaarst, L. Lueck, F. Caporali, H.H. Jensen, P. Migliorini & H. Willer, ISOFAR: Bonn, vol.2, pp. 608-611, 2008.

[10] PFI (Pellet Fuels Institute), http://www.pelletheat.org [11] Brown, L.R., Plan B 3.0-Mobilizing to Save Civilization. W.W.Norton &

Company Inc., New York, NY, 2008. [12] Tilman, D. & Lehman, C., Human-caused environmental change: Impacts

on plant diversity and evolution. PNAS, 98(10), pp. 5433-5440, 2001. [13] Huck, S.W. & Cormier, W.H., Reading Statistics and Research,

HarperCollins Publishers Inc.: New York, 1996. [14] Patten, M.L., Understanding Research Methods. An Overview of the

Essentials, Pyrczak Publishing: Glendale, CA, 2002. [15] Tilman, D., Hill, J. & Lehman, C., Response to Comment on “Carbon-

Negative Biofuels from Low-Input High Diversity Grassland Biomass. Science, 316(5831), pp.1567, 2007.

[16] Varvel, G.E., Vogel, K.P., Mitchell, R.B., Follett, R.F. & Kimble, J.M., Comparison of corn and switchgrass on marginal soils for bioenergy. Biomassand bioenergy, 32(1), pp. 18-21, 2008.

[17] Heaton, E.A., Dohleman, F.G. & Long, S.P., Meeting US biofuel goals with less land: the potential of Miscanthus. Global Change Biology, 14(9), pp. 2000-2014, 2008.

[18] Ceroni, M., Liu, S. & Costanza, R., Ecological and Economic Roles of Biodiversity in Agroecosystems, pp. 446-472 In: Managing Biodiversity in Agricultural Ecosystems, eds. Jarvis, D.I., Padoch, C. & Cooper, H.D., Columbia University Press, 2007.

[19] Kort, J., Collins, M. & Ditsch, D., A review of soil erosion potential associated with biomass crops. Biomass and Bioenergy, 14(4), pp. 351-359, 1998.

[20] Zentner, R.P., Lafond, G.P., Derksen, D.A., Nagy, C.N., Wall, D.D. & May, W.E., Effects of tillage method and crop rotation on non-renewable energy use efficiency for a thin Black Chernozem in the Canadian Prairies. Soil and Tillage Research, 77(2), pp. 125-136, 2004.




Renewable energy from restored prairie plots in ...€¦ · Renewable energy from restored prairie...

Documents

Transcript of Renewable energy from restored prairie plots in ...€¦ · Renewable energy from restored prairie...