Published online November 15, 2018 Crop Residue Workshop
Unraveling Crop Residue Harvest Effects on Soil Organic Carbon Douglas L. Karlen,* Marty R. Schmer, Stephen Kaffka, David E. Clay, Michael Q. Wang, William R. Horwath, Alissa Kendall, Alan Keller, B. John Pieper, Stefan Unnasch, Tom Darlington, Fred Vocasek, and Alan G. Chute Abstract Crop residues protect soil resources, sustain soil organic carbon (SOC), cycle nutrients, support microbial communities, and provide bioenergy feedstock. Herein we (i) summarize the origin of the “Crop Residues for Advanced Biofuels: Effects on Soil Carbon” workshop; (ii) review the workshop structure; and (iii) present consensus points, unanswered questions, and outcomes of the workshop. Initiated by a farmer/ethanol investor’s letter to the American Society of Agronomy (ASA) President, an ASA Working Group (WG) was established to make a recommendation to the ASA Board on how to respond. The WG concluded a Tri-Society sponsored workshop involving farmers, ethanol production and marketing groups, agronomists, crop scientists, soil scientists, engineers, non-governmental organizations, life cycle analysis (LCA) experts, and regulatory personnel was needed to address the complex question that had been posed and to ensure all viewpoints were fully represented. The WG was expanded to an ASA Task Force who organized the workshop in Sacramento, CA. Eighty workshop attendees identified four consensus areas (crop residue management [CRM]; severity of soil erosion; tillage, CRM and erosion linkages; and the importance of simulation [LCA] models) and four unresolved themes (carbon sequestration, CRM effects on SOC stocks, changing climate effects, and the need to focus on ecosystem services rather than single endpoints). The workshop resulted in three direct outcomes: (i) development of a stakeholder funded SOC database, (ii) LCA and SOC model improvements, and (iii) development of this special section in Agronomy Journal. Dale and Ong (2014) concluded that large scale, renewable energy systems are no longer just a “good idea”; but essential, and during the next few decades society must develop systems capable of producing clean energy at the multi-terawatt scale. Crop residues such as corn (Zea mays L.) stover, and other cellulosic materials were identified as potential feedstocks to meet this demand and have been rigorously evaluated for the past decade (e.g., Perlack et al., 2005; U.S. Department of Energy, 2011 and 2016). However, it is also well established that crop residues have important ecosystem service and productivity functions (Larson, 1979; Johnson, 2018; Ibrahim et al., 2018).
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he ASA-CSSA-SSSA sponsored workshop, “Crop Residues for Advanced Biofuels: Exploring Soil Carbon Effects” that is being highlighted by this special section, was prompted by a June 2016 letter to then ASA President Paul Fixen from Ron Alverson, a South Dakota farmer/corn grain ethanol investor. Mr. Alverson was seeking ASA support for a letter he was preparing for the California Air Resources Board (CARB), asking if corn grain and stover derived ethanol deserved different Low Carbon Fuel Standard and carbon intensity (CI) values. Currently, the CI value of cellulosic ethanol from corn stover is 21.6 g CO2 MJ–1 while the average Midwest corn grain ethanol CI value is ~75 g CO2 MJ–1. The CI values have economic consequences in the California transportation fuel market, with January 2018 Low Carbon Fuel Standard CO2 prices averaging US$107 Mg–1. Furthermore, cellulosic-based fuels are still required under federal regulations and have a high (D7) renewable identification number value. Mr. Alverson’s argument was that although removing corn stover could provide shortterm economic gains for farmers, doing so may decrease long-term, sustainable crop production if soil organic carbon (SOC) stocks are depleted.
Published in Agron. J. 111:1–6 (2019) doi:10.2134/agronj2018.03.0207 Available freely online through the author-supported open access option
D.L. Karlen, USDA-Agricultural Research Service (ARS), National Lab. for Agriculture and the Environment (NLAE), 1015 N. University Boulevard, Ames, IA 50011-3611; M.R. Schmer, USDA-ARS, Agroecosystem Management Research Unit, 251 Filley Hall/Food Ind. Complex, UNL, East Campus, Lincoln NE 68583; S. Kaffka, Univ. of California– Davis (UCDavis), Dep. of Plant Sciences, 281 Hunt Hall, Davis, CA 95616; D.E. Clay, South Dakota State Univ., Room 214, Agronomy, Horticulture & Plant Science, Box 2207A, Brookings, SD 57007; M.Q. Wang, Argonne National Lab., 9700 Cass Ave, Lemont, IL 60439; W.R. Horwath, UC-Davis, Dep. of Land, Water and Air Sciences, Room 3226, Plant and Environmental Sciences Building, Davis, CA 95616; A. Kendall, UC-Davis, Dep. of Civil and Environmental Engineering, 3167 Ghausi Hall, One Shields Avenue, Davis, CA 95616; A. Keller, POET-DSM Advanced Biofuels LLC, Emmetsburg, IA 50536; B.J. Pieper, DuPont BioSciences Inc., 59219 W. Lincoln Hwy., Nevada, IA 50201; S. Unnasch, Life Cycle Associates, LLC, 884 Portola Rd, Portola Valley, CA 94028; T. Darlington, Air Improvement, 10820 Boyce Road, Chelsea, MI 48118; F. Vocasek, Servi-Tech Laboratories, 1816 E Wyatt Earp Blvd, Dodge City, KS 67801; A.G. Chute, Iowa Agricultural Bio Fibers, 1918 900th Street, Harlan Iowa 51537. Received 26 Mar. 2018. Accepted 10 Sept. 2018. *Corresponding author (
[email protected]).
Copyright © 2019 by the American Society of Agronomy 5585 Guilford Road, Madison, WI 53711 USA This is an open access article distributed under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Abbreviations: ASA, American Society of Agronomy; CA, conservation agriculture; CARB, California Air Resources Board; CI, carbon intensity; CRM, crop residue management; LCA, life cycle analysis; SOC, soil organic carbon; WG, working group.
Core Ideas • The workshop demonstrated ASA-CSSA-SSSA capabilities to address complex problems. • Corn is an important crop with regard to soil organic carbon (SOC) stocks. • Crop residue management (CRM) effects on SOC stocks are complex and multi-dimensional. • Quantifying CRM effects on SOC is very important. • Accurate but simple on-farm measurement and monitoring techniques for SOC are needed.
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Crop residues including corn stover have many different roles including protecting soil resources, sustaining SOC stocks, cycling nutrients, supporting microbial communities, and now providing feedstock for bioenergy or bio-product production. Negative impacts of excessive crop residue harvest on SOC stocks (Johnson et al., 2014; Johnson, 2018) and potential soil degradation (Karlen and Rice, 2015) are well documented. Alverson argued that stover harvest will cause soil resources to be degraded and atmospheric CO2 to increase. He also stated that it was his perception that the modeling currently used to determine CI of grain- and cellulosic-based ethanol did not account adequately for changes in SOC stocks or greenhouse gas emissions. These questions are neither new nor answered simply as evidenced by publications from the 1970s and 1980s. Examples include Lockeretz (1981), who stressed the importance of coordinating soil conservation policies when developing public policy concerning renewable energy programs; Epstein et al. (1978), who emphasized that alternative uses for crop residues should be considered only when needs for soil protection and productivity have been met; and Larson (1979), who concluded that removal of a portion of crop residues should not be objectionable to the agricultural community if soil productivity, could be maintained. Karlen et al. (2014) summarized results from 28 research sites in seven states (IA, IL, MN, NE, PA, SC, and SD) and reported that average no-till corn grain yield was significantly lower than with conventional tillage when stover was not removed, but equivalent or even slightly higher when it was harvested. They attributed the positive stover harvest response to mitigation of potential residue management problems, such as N immobilization and reduced spring soil temperature. Clay et al. (2012, 2015) concluded that findings from those and other studies suggest that stover removal may be sustainable within high yielding no-tillage systems. However, stover harvest was NOT recommended at all 28 locations summarized by Karlen et al. (2014). At those sites and in other published studies where land slope is high (>5%), annual average corn yields are 11 Mg ha–1 or 175 bu ac–1) the amount of crop residue created through photosynthesis generally exceeds the amount required for SOC maintenance and preservation of soil aggregates or structure. Finally, the workshop provided a very effective way to demonstrate the capability of ASA-CSSA-SSSA members to help multiple society sectors understand and address complex problems such as carbon sequestration, greenhouse gas emissions, and development of more sustainable agricultural practices. The success of this accomplishment is confirmed by the collection of well written contributions within this special issue of Agronomy Journal. References Clay, D.E., J. Chang, S.A. Clay, J. Stone, R. Gelderman, C.G. Carlson, K. Reitsma, M. Jones, L. Janssen, and T. Schumacher. 2012. Corn yields and no-tillage affects carbon sequestration and carbon footprints. Agron. J. 104:763–770. doi:10.2134/agronj2011.0353 Clay, D.E., G. Reicks, C.G. Carlson, J. Miller, J.J. Stone, and S.A. Clay. 2015. Residue harvesting and yield zone impacts C storage in a continuous corn rotation. J. Environ. Qual. 44:803–809. doi:10.2134/ jeq2014.07.0322 Dale, B.E., and R.G. Ong. 2014. Design, implementation, and evaluation of sustainable bioenergy production systems. Biofuel. BioProducts and Biorefining 8:487–503. doi:10.1002/bbb.1504 Epstein, E. J.E. Alpert, and C.C. Calvert. 1978. Alternative use of excess crop residues. In: W.R. Oschwald, editor, Crop residue management systems. Special Publication No. 31., American Society of Agronomy, Madison, WI. p. 219–230.
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Ibrahim, M.A., T. Chua-Ona, M. Liebman, and M.L. Thompson. 2018. Soil organic carbon storage under biofuel cropping systems in a humid, continental climate. Agron. J. 110:1748–1753. doi:10.2134/ agronj2018.03.0204 Johnson, J.M.F., J.M. Novak, G.E. Varvel, D.E. Stott, S.L. Osborne, D.L. Karlen, J.A. Lamb, J.M. Baker, and P.R. Adler. 2014. Crop residue mass needed to maintain soil organic carbon levels: Can it be determined? BioEnergy Res. 7:481–490. doi:10.1007/s12155-013-9402-8 Johnson, J.M. 2018. A “Soil Lorax” perspective on corn stover for advanced biofuels. Agron. J. 110:1–4. doi:10.2134/agronj2018.02.0093 Karlen, D. L., S. J. Birrell, J. M. F. Johnson, S. L. Osborne, T. E. Schumacher, G. E., Varvel, R. B. Ferguson, J. M. Novak, J. R., Fredrick, J. M., Baker, J. A., Lamb, P. R. Adler, G. W. Roth, and E. D. Nafziger. 2014. Multilocation corn stover harvest effects on crop yields and nutrient removal. BioEnergy Res. 7:528–539. doi:10.1007/ s12155-014-9419-7 Karlen, D.L., and C.W. Rice. 2015. Soil degradation: Will humankind ever learn? Sustainability 7:12490–12501. doi:10.3390/su70912490 Larson, W.E. 1979. Crop residues: Energy production or erosion control. J. Soil Water Conserv. 34(2):74–76. Lockeretz, W. 1981. Crop residues for energy: Comparative costs and benefits for the farmer, the energy facility, and the public. Energy Agric. 1:71–89. Perlack, R.D., L.L. Wright, A.F. Turhollow, R.L. Graham, B.J. Stokes, and D.C. Erbach. 2005. Biomass as feedstock for a bioenergy and bioproducts industry: The technical feasibility of a billion-ton annual supply. DOE/GO-102005-2145 and ORNL/TM-2005/66. https:// www1.eere.energy.gov/bioenergy/pdfs/final_billionton_vision_ report2.pdf (accessed 5 Sept. 2018). U.S. Department of Energy. 2011. U.S. billion-ton update: Biomass supply for a bioenergy and bioproducts industry. R.D. Perlack and B.J. Stokes, Leads, ORNL/TM-2011/224. Oak Ridge National Laboratory, Oak Ridge, TN. https://www1.eere.energy.gov/bioenergy/ pdfs/billion_ton_update.pdf (accessed 5 Sept. 2018). U.S. Department of Energy. 2016. 2016 billion-ton report: Advancing domestic Rresources for a thriving bioeconomy, volume 1: Economic availability of feedstocks. M. H. Langholtz, B. J. Stokes, and L. M. Eaton, Leads, ORNL/TM-2016/160. Oak Ridge National Laboratory, Oak Ridge, TN. doi:10.2172/1271651. http://energy.gov/eere/ bioenergy/2016-billion-ton-report (accessed 5 Sept. 2018).
Agronomy Journal • Volume 111, Issue 1 • 2019
