GREENHOUSE GAS MITIGATION AND CARBON SEQUESTRATION IN AGRICULTURAL LANDSCAPES

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 1001464
• Project Start Date: Nov 1, 2013
• Project End Date: Oct 31, 2018
• Program Code: [(N/A)]- (N/A)

Recipient Organization
MICHIGAN STATE UNIV
(N/A)
EAST LANSING,MI 48824

Performing Department
Plant, Soil and Microbial Science

Non Technical Summary
Nitrogen availability is critical for crop production yet excess nitrogen poses a significant environmental threat. The threat to groundwater and surface waters is well recognized and understood; the threat to air quality is more poorly recognized but no less real. Nitrogen trace gases can significantly affect regional / global climate over long time scales, as can other trace gases such as methane. Agricultural landscapes may play a critical role in global balances of these greenhouse gases, and the inclusion of perennial biofuel crops in the landscape may represent a mitigation option. Our research is showing that crop management can significantly affect nitrous oxide (N2O) production and methane (CH4) consumption in Michigan corn-soybean-wheat rotations. Importantly, low-input management strategies do not necessarily affect gas fluxes less than high-input management - in fact, systems in which leguminous cover crops substitute for inorganic fertilizers can have higher N2O fluxes, and similar CH4 fluxes. Specific modern management practices in general may, however, have less of a long-term impact than the simple historical effect of original land-use conversion. This means that the transient seasonal fluxes of gases from row-crops may occur on top of a baseline flux that is already elevated due to original forest clearing and, in highly productive systems, is since supported by high cycling rates of added organic and/or inorganic nitrogen. Because of the importance of these gas fluxes to global climate change, and the potential for changes in environmental policy and emerging biofuel markets that could affect future crop management potentials (IPCC 2007, Robertson et al. 2008, 2011), it is important to better understand the nature of elevated fluxes in row-crops - from the standpoints of both long-term legacies related to land use change as well as contemporary management impacts. Our research is designed to address these questions by measuring fluxes in different agricultural systems, conducting experiments to identify the controls on fluxes, and testing mitigation opportunities in a whole-system context. Research findings will help to allow agriculture to play a positve role in climate change mitigation.

Animal Health Component

10%

Research Effort Categories

Basic

90%

Applied

10%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
133	0199	1070	100%

Knowledge Area
133 - Pollution Prevention and Mitigation;

Subject Of Investigation
0199 - Soil and land, general;

Field Of Science
1070 - Ecology;

Keywords

greenhouse gases

row-crop agriculture

nitrous oxide

methane

carbon dioxide

bioenergy

Goals / Objectives
The objectives of the project are: To evaluate long-term field level fluxes of N2O and CH4 in row-crop ecosystems and to relate fluxes to management intensity (including high chemical vs. organic-based regimes, and annual grain vs. perennial biofuel crops) and to the historical effect of original land clearing. To evaluate fine-scale temporal dynamics of trace gas fluxes in annual (corn, soybean, wheat) cropping systems fertilized at different rates and in a variety of cellulosic cropping systems. To examine major controls on N2O fluxes as well as on the sources of N2O from soil: nitrification vs. denitrification in particular.

Project Methods
Objective 1 A field flux-chamber sampling program is now in place on the Long-Term Ecological Research (LTER) site at KBS. This long-term program (in place since 1992) allows us to evaluate objective 1 - to what degree management intensity affects long-term trace gas fluxes. On this site are 8 replicated 1 ha treatment plots corresponding to 8 different ecosystems found in agricultural landscapes: (T1) corn-soybean conventional tillage rotation managed with standard tillage, fertilizer, and herbicide levels; (T2) same as (T1) but no-till; (T3) reduced-input corn-soybean-wheat rotation conventionally tilled with winter cover crops; (T4) same as (T3) but managed organically; (T5) Poplar trees on a 10 year rotation cycle; (T6) alfalfa; (T7) early successional old-field; and (T8) same as (T7) but on a never-plowed, higher organic matter soil profile. Three old-growth deciduous forest (DF) plots nearby (on the same soil series) provide a historical reference site for addressing the conversion-legacy question. Additionally, a set of 8 different biofuel cropping systems were installed in 2008: (G1) continuous corn, (G2) corn-soybean-canola (now corn-soybean with cover crop), (G3) switchgrass, (G4) miscanthus, (G5) native grass polyculture, (G6) short-rotation poplar, (G7) old-field, and (G8) native prairie. Objective 2 Fine-scale temporal dynamics of trace gas fluxes are being evaluated with a near continuous trace gas measurement system now in place on a nitrogen fertilizer gradient experiment fertilized at 9 different nitrogen rates, from 0 to 290 kg N/ha for corn years, to 180 kg N/ha for wheat years, and no fertilizer for soybean years. This automated system measures fluxes from nine flux chambers four times per day during non-frozen soil conditions (ca. 280 days/year). This system has been in continuous operation for the several years and will be maintained for several more years in order to capture a full range of climatic variability. As flux data accumulate, the information gathered will be used to parameterize and test quantitative trace gas models being developed with collaborators at the Queensland University of Technology. Objective 3 We are observing changes in the 15N2O isotopomer ratio to examine controls on the source of N2O in soil: nitrification vs. denitrification. This work is being conducted with N. Ostrom of the MSU Isotope Geochemistry Laboratory. We are particularly interested in identifying changes in sources through different soil wet-dry regimes.

Progress 11/01/13 to 10/31/18

Outputs
Target Audience:Our primary audiences for this work have been the scientific community, which uses our findings to further inform the fundamental understanding of greenhouse gas fluxes in agriculture, and policymakers and other interested in agricultural mitigation opportunities. The primary form of knowledge transfer has been via peer-reviewed publications as well as presentations at scientific meetings and in other professional settings. Additionally findings have been disseminated through presentations to undergraduate and graduate students, K-12 teachers, extension educators, and working professionals including farmers. Press releases and radio and video interviews allowed us to provide results of our work to the general public. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project supported in part or in whole the research training of 4 postdoctoral scholars, 6 graduate students, and 10 undergraduates.Undergraduate research training was performed as part of summer internships as part of NSF and DOE -supported Research Experience for Undergraduates program. We have also provided professional development for teachers via the KBS school-year science education workshops and for extension educators and crop advisers via occasional workshops and field days in cooperation with other projects. How have the results been disseminated to communities of interest?We have disseminated findings from this research program to a variety of audiences. Our primary audience is the scientific community, with whom we communicate results via participation in national meetings and the various conference proceedings and peer-reviewed publications noted elsewhere in this report. We also communicate our findings to other communities of interest, in particular K-12 educators and students, university students, working agricultural professionals, and public media. These efforts include tours of research sites, curriculum materials for K-12 classrooms, class field trips, and presentations at workshops. Literature Cited: Abraha, M., S. K. Hamilton, J. Chen, and G. P. Robertson. 2018. Ecosystem carbon exchange on conversion of Conservation Reserve Program grasslands to annual and perennial cropping systems. Agricultural and Forest Meteorology 253-254:151-160. Hoben, J. P., R. J. Gehl, N. Millar, P. R. Grace, and G. P. Robertson. 2011. Nonlinear nitrous oxide (N2O) response to nitrogen fertilizer in on-farm corn crops of the US Midwest. Global Change Biology 17:1140-1152. Gelfand, I., R. Sahajpal, X. Zhang, R. C. Izaurralde, K. L. Gross, and G. P. Robertson. 2013. Sustainable bioenergy production from marginal lands in the US Midwest. Nature 493:514-517. Gelfand, I., I. Shcherbak, N. Millar, A. N. Kravchenko, and G. P. Robertson. 2016. Long-term nitrous oxide fluxes in annual and perennial agricultural and unmanaged ecosystems in the upper Midwest USA. Global Change Biology 22:3594-3607. Gelfand, I., T. Zenone, P. Jasrotia, J. Chen, S. K. Hamilton, and G. P. Robertson. 2011. Carbon debt of Conservation Reserve Program (CRP) grasslands converted to bioenergy production. Proceedings of the National Academy of Sciences USA 108:13864-13869. IPCC (Intergovernmental Panel on Climate Change). 2007. Climate change 2007: Synthesis report. IPCC, Geneva, Switzerland. IPCC (Intergovernmental Panel on Climate Change). 2013. Climate change 2013: The physical science basis. Cambridge University Press, Cambridge, UK and New York, NY, USA. McSwiney, C. P. and G. P. Robertson. 2005. Nonlinear response of N2O flux to incremental fertilizer addition in a continuous maize (Zea mays sp.) cropping system. Global Change Biology 11:1712-1719. Millar, N., G. P. Robertson, A. Diamant, R. J. Gehl, P. R. Grace, and J. P. Hoben. 2012. Methodology for quantifying nitrous oxide (N2O) emissions reductions by reducing nitrogen fertilizer use on agricultural crops. American Carbon Registry, Winrock International, Little Rock, Arkansas, USA. Millar, N., G. P. Robertson, A. Diamant, R. J. Gehl, P. R. Grace, and J. P. Hoben. 2013. Quantifying N2O emissions reductions in agricultural crops through N fertilizer rate reduction. Verified Carbon Standard, Washington, DC, USA. Millar, N., G. P. Robertson, P. R. Grace, R. J. Gehl, and J. P. Hoben. 2010. Nitrogen fertilizer management for nitrous oxide (N2O) mitigation in intensive corn (Maize) production: an emissions reduction protocol for US Midwest agriculture. Mitigation and Adaptation Strategies for Global Change 15:185-204. Millar, N., A. Urrea, K. Kahmark, I. Shcherbak, G. P. Robertson, and I. Ortiz-Monasterio. 2018. Nitrous oxide (N2O) responds exponentially to nitrogen fertilizer in irrigated wheat in the Yaqui Valley, Mexico. Agriculture, Ecosystems and Environment 261:125-132. NRC (National Research Council). 2010. Toward sustainable agricultural systems in the 21st Century. National Academies Press, Washington, D.C., USA. Pryor, S. C., D. Scavia, C. Downer, M. Gaden, L. Iverson, R. Nordstrom, J. Patz, and G. P. Robertson. 2014. Chapter 18: Midwest. Pages 418-440 in J. M. Melillo, T. C. Richmond, and G. W. Yohe, editors. Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program. doi:10.7930/J0J1012N. Richter, D. and M. L. Mobley. 2009. Monitoring earth's critical zone. Science 326:1067-1068. Robertson, G. P., V. H. Dale, O. C. Doering, S. P. Hamburg, J. M. Melillo, M. M. Wander, W. J. Parton, P. R. Adler, J. N. Barney, R. M. Cruse, C. S. Duke, P. M. Fearnside, R. F. Follett, H. K. Gibbs, J. Goldemberg, D. J. Mladenoff, D. Ojima, M. W. Palmer, A. Sharpley, L. Wallace, K. C. Weathers, J. A. Wiens, and W. W. Wilhelm. 2008. Sustainable biofuels redux. Science 322:49-50. Robertson, G. P., S. K. Hamilton, S. J. Del Grosso, and W. J. Parton. 2011. The biogeochemistry of bioenergy landscapes: carbon, nitrogen, and water considerations. Ecological Applications 21:1055-1067. Robertson, G. P., S. K. Hamilton, B. L. Barham, B. E. Dale, R. C. Izaurralde, R. D. Jackson, D. A. Landis, S. M. Swinton, K. D. Thelen, and J. M. Tiedje. 2017. Cellulosic biofuel contributions to a sustainable energy future: Choices and outcomes. Science 356:eaal2324d. Ruan, L., A. K. Bhardwaj, S. K. Hamilton, and G. P. Robertson. 2016. Nitrogen fertilization challenges the climate benefit of cellulosic biofuels. Environmental Research Letters 11:064007. Ruan, L. and G. P. Robertson. 2013. Initial nitrous oxide, carbon dioxide, and methane costs of converting Conservation Reserve Program grassland to row crops under no-till vs. conventional tillage. Global Change Biology 19:2478-2489. Ruan, L. and G. P. Robertson. 2017. Reduced snow cover increases wintertime nitrous oxide (N2O) emissions from an agricultural soil in the upper U.S. Midwest. Ecosystems 20:917-927. Ruan, L. and G. P. Robertson. (in review). No-till substantially improves the climate benefit of cellulosic biofuel crops established on marginal lands. Shcherbak, I., N. Millar, and G. P. Robertson. 2014. Global metaanalysis of the nonlinear response of soil nitrous oxide (N2O) emissions to fertilizer nitrogen. Proceedings of the National Academy of Sciences USA 111:9199-9204. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? This research contributed to our understanding of the ecological basis for greenhouse gas fluxes to the atmosphere. The role of agriculture in these fluxes - whether as a source or sink - is important to know in order to develop effective greenhouse gas mitigation strategies at a national level. The development of carbon credit trading, expanded to include other greenhouse gases, depends on a sound scientific understanding of these issues. Long-term research aids the discovery and methodologies for creating credits and is an important part of this national endeavor. We made progress towards all of the objectives outlined above. OUTCOMES AND IMPACTS: We have made measurements of the radiatively important trace gases nitrous oxide (N2O) and methane (CH4) at biweekly to monthly intervals through the year at the KBS Long-term Ecological Research site. These measurements are included in an on-going assessment of the overall impact of farming activities on atmospheric chemistry. The global warming impacts (GWIs) of 11 different cropped and natural ecosystems are calculated using information on soil carbon sequestration, fertilizer, lime, fuel inputs, and the production of N2O and consumption of CH4 in these systems. N2O production continues to be the largest single source of GWP in all annual crop ecosystems, followed by nitrogen fertilizer manufacturing when nitrogen fertilizer is used. Carbon sequestration in all cropping and successional systems has been sampled to 1.2 m soil depth and shows substantial differences among cropping systems. In particular, soil carbon sequestration is significant in no-till surface soils and in soils from systems with legume cover crops. The analysis of N2O fluxes across 9 different fertilizer levels, conducted in part with a near-continuous automated chamber system, showed a nonlinear response of N2O flux to fertilizer inputs regardless of crop (corn vs. wheat vs. soybean). A meta-analysis of all available studies showed that this relationship is global in scope (Shcherbak et al. 2014). CH4 oxidation is affected by fertilization but not by tillage in noncropped sites; in cropped sites CH4 oxidation is already low and is not further affected by tillage or N fertilizer. These and other results offer significant promise for reducing the global warming impact of agricultural systems, whether for grain or cellulosic biomass. We have published extensively in the area of greenhouse gases in row crop agriculture and our research is having an impact both in public policy (Richter and Mobley 2009) and the voluntary carbon markets, where our N2O abatement protocol (Millar et al. 2010) was the first to be adopted by all three major US carbon registries (Millar et al. 2012, 2013). In particular, our discovery of a nonlinear (exponentially increasing) relationship between nitrogen fertilizer use and N2O production (McSwiney and Robertson 2005, Hoben et al. 2011, Shcherbak et al. 2014, Millar et al. 2018) has provided impetus for converting fertilizer rate reductions into tradable carbon offset credits. While significant deployment awaits the emergence of a carbon compliance market, now under development for California, our work lays the groundwork for providing farmers an incentive for applying nitrogen fertilizer more precisely, thereby reducing both N2O and other reactive forms of nitrogen in the environment such as nitrate. In 2014 the first carbon credit for N2O abatement was issued to a Michigan farmer by the American Carbon Registry and purchased and retired by The Climate Trust. We are currently working with a CIMMYT wheat agronomist to make 500,000 acres of irrigated wheat in the Yaqui Valley eligible for carbon payments. We found that for 2013 and 2014, reducing the current N fertilizer rate to the economic optimum rate could have avoided 84-138 Gg CO2eq per year in this region (Millar et al. 2018). When coupled with carbon payments, a more precise N use could result in reduced agricultural N2O emissions and increased farmer income--both while maintaining current high wheat productivity. We have also assessed 20 years of measured N2O fluxes in 11 different ecosystems at the KBS LTER site (Gelfand et al. 2016) and found that average N2O emissions a) increased in the order unmanaged ecosystems < non-leguminous perennial cropping systems < fertilized annual grain and N-fixing cropping systems; and b) did not differ among annual cropping systems over the entire corn-soybean-wheat rotation but did differ among crops (rotation phase) within the different systems. Daily soil N2O fluxes were poorly predicted by the variables measured; annual cumulative fluxes were related to soil nitrate pools in perennial systems but not in annual cropping systems where they were confounded with management differences. The future development of a cellulosic biofuels market also promises significant greenhouse gas mitigation and thus climate benefits (NRC 2010), but only if managed in a way that ensures the greenhouse gas balance of future biofuel cropping systems is as negative (climate mitigating) as possible (Robertson et al. 2017). This includes the need to minimize carbon debt - both the greenhouse gases (CO2 and N2O) released upon establishment of the cellulosic cropping system and as well the indirect land use cost of establishing cellulosic cropping systems on land now used for crops, which forces new land elsewhere into more intensive management with concomitant greenhouse gas release. Our previous work has addressed both issues. First, we've shown experimentally that direct carbon debt can be substantial unless steps (such as no-till cultivation) are taken to protect existing soil carbon (Gelfand et al. 2011, Abraha et al. 2018), especially when the land under conversion has been in the USDA's Conservation Reserve Program. In fact plowing creates so much carbon debt that it is unlikely to be repaid within a century (Ruan and Robertson 2013); much of this debt can be avoided with no-till establishment (Ruan and Robertson, in review). Second, we have estimated the capacity of marginal lands in the US Midwest to produce cellulosic biofuels (Gelfand et al. 2013), whereby carbon debt is avoided a) by harvesting existing perennial successional or CRP vegetation and b) by avoiding the use of land now in annual crop production. There is also the question of fertilizer impact with cellulosic crops - and we have now documented the same exponentially increasing response of N2O to fertilizer (Ruan et al.2016) as has been documented for annual crops. Additionally we've shown that this exponential relationship also holds for nitrate leaching (Ruan et al. 2016). The amount and duration of snow cover in the northern hemisphere has tended to decrease with increasing global temperatures over the past few decades, and this trend is likely to continue (IPCC 2013). Moreover, the frequency of mid-winter thaws is expected to increase in US Midwest soils (Pryor et al. 2014), and freeze-thaw cycles can affect carbon and nitrogen dynamics, including N2O emissions. In a snow removal experiment in an annual cropping system, we showed using automated flux chambers that cumulative wintertime N2O fluxes increased upon snow removal by up to three times over ambient snow cover. Less snow cover led to lower soil temperatures, due to a lack of snow-cover insulation, and more frequent freeze-thaw cycles that broke up soil aggregates and accelerated nitrogen turnover (Ruan and Robertson 2017). Winters with less snow cover may thus accelerate N2O fluxes from agricultural lands in this region; a more conservative N use that decreases reactive N in soils would serve as a general strategy to reduce these wintertime fluxes.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Abraha, M., I. Gelfand, S. K. Hamilton, J. Chen, and G. P. Robertson. 2017. Carbon debt of CRP lands converted to annual and perennial bioenergy crops. AGU Fall Meeting, New Orleans, LA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Bowles, T. M., A. S. Grandy, F. Calderon, M. A. Cavigelli, S. W. Culman, B. Deen, C. F. Drury, A. G. Garcia, W. S. Harkcom, R. M. Lehman, S. L. Osborne, G. P. Robertson, M. R. Schmer, and J. S. Strock. 2017. Crop rotation diversity and yield resilience: Evidence from 11 long-term experiments in North America across a precipitation gradient. ASA, CSSA, and SSSA 2017 Annual Meeting, Tampa, FL.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Hussain, M. Z., S. K. Hamilton, A. Bhardwaj, B. Basso, and G. P. Robertson. 2017. Leaching export of dissolved organic carbon and dissolved nitrogen from agricultural soils in southern Michigan. ASA, CSSA, and SSSA 2017 Annual Meeting, Tampa, FL.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Izaurralde, R. C., W. B. McGill, J. R. Williams, C. D. Jones, R. P. Link, D. H. Manowitz, D. E. Schwab, X. Zhang, G. P. Robertson, and N. Millar. 2017. A model to simulate microbial denitrification with EPIC: Description, evaluation, and applications. ASA, CSSA, and SSSA 2017 Annual Meeting, Tampa, FL.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Kahmark, K., K. R. Glanville, S. Bohm, and G. P. Robertson. 2017. Evaluating QCL-based absorption spectroscopy technology for chamber-based flux measurements of nitrous oxide in agricultural landscapes. ASA, CSSA, and SSSA 2017 Annual Meeting, Tampa, FL.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Millar, N., D. G. Baas, and G. P. Robertson. 2017. The influence of winter cover crops on nitrous oxide (N2O) emissions from Midwest row-crops. ASA, CSSA, and SSSA 2017 Annual Meeting, Tampa, FL.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Paul, Z., W. C. Hockaday, C. A. Masiello, G. P. Robertson, and M. E. Gallagher. 2017. Quantifying biochemical and energetic reservoirs in soil organic matter under fertilization and harvest treatments. ASA, CSSA, and SSSA 2017 Annual Meeting, Tampa, FL.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Robertson, G. P. 2017. GHG mitigation by lignocellulosic bioenergy cropping systems: Potentials and pitfalls. ASA, CCSA and SSSA Annual Meeting, Tampa, FL.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Zhang, X., S. LeDuc, I. Gelfand, I. Sahajpal, C. M. Clark, R. C. Izaurralde, K. L. Gross, and G. P. Robertson. 2017. Using marginal lands to produce cellulosic bioenergy feedstocks in the US Midwest: Production Capacity, greenhouse gas emissions, and environmental impacts. ASA, CSSA, and SSSA 2017 Annual Meeting, Tampa, FL.
• Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Abraha, M., S. K. Hamilton, J. Chen, and G. P. Robertson. 2018. Evapotranspiration of annual and perennial biofuel crops. American Geophysical Union, Washington, DC.
• Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Castro Vega, D., K. Glanville, and G. P. Robertson. 2018. Impact of changing rainfall patterns on denitrification nitrous oxide reductase lag. Ecological Society of America, New Orleans, LA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Chicoine, T., S. S. Roley, G. P. Robertson, and S. Evans. 2018. Soil-and root-associated microbiomes across twelve switchgrass cultivars. DOE Genomic Science, Tysons, VA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Gelfand, I., M. Abraha, D. Pan, J. Tang, J. Chen, M. Zondlo, and G. P. Robertson. 2018. Evaluation of field based quantum cascade lasers for measuring N2O fluxes from static chambers and eddy covariance towers. EGU General Assembly 2018, Vienna, Austria.
• Type: Other Status: Published Year Published: 2018 Citation: Abraha, M., S. K. Hamilton, J. Chen, and G. P. Robertson. 2018. Data from: Ecosystem carbon exchange on conversion of Conservation Reserve Program grasslands to annual and perennial cropping systems. Dryad Digital Repository, https://doi.org/10.5061/dryad.sc41rn3.
• Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Glanville, K. and G. P. Robertson. 2018. Consequences of extreme rainfall patterns on nitrous oxide fluxes in Midwest cropping systems. Ecological Society of America, New Orleans, LA.
• Type: Other Status: Published Year Published: 2017 Citation: Austin, E. E., K. Wickings, M. D. McDaniel, G. P. Robertson, and A. S. Grandy. 2017. Data from: Cover crop root contributions to soil carbon in a no-till corn bioenergy cropping system. Dryad Digital Repository. https://doi.org/10.5061/dryad.bb458.
• Type: Other Status: Published Year Published: 2018 Citation: Abraha, M., I. Gelfand, S. K. Hamilton, J. Chen, and G. P. Robertson. 2018. Data from: Legacy effects of land use on soil nitrous oxide emissions in annual crop and perennial grassland ecosystems. Dryad Digital Repository, https://doi.org/10.5061/dryad.17g36j4.
• Type: Other Status: Published Year Published: 2018 Citation: Hamilton, S. K., M. Z. Hussain, C. Lowrie, B. Basso, and G. P. Robertson. 2018. Data from: Evapotranspiration is resilient in the face of land cover and climate change in a humid temperate catchment. Dryad Digital Repository, https://doi.org/10.5061/dryad.6fm52.
• Type: Other Status: Published Year Published: 2018 Citation: Roley, S. S., D. S. Duncan, D. Liang, A. Garoutte, R. D. Jackson, J. M. Tiedje, and G. P. Robertson. 2018. Data from: Associative nitrogen fixation (ANF) in switchgrass (Panicum virgatum) across a nitrogen input gradient. Dryad Digital Repository, https://doi.org/10.5061/dryad.60bn81v.
• Type: Other Status: Published Year Published: 2018 Citation: Sprunger, C. D. and G. P. Robertson. 2018. Data from: Early accumulation of active fraction soil carbon in newly established cellulosic biofuel systems. Dryad Digital Repository, https://doi.org/10.5061/dryad.7jq46.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Millar, N., A. Urrea, K. Kahmark, I. Shcherbak, G. P. Robertson, and I. Ortiz-Monasterio. 2018. Nitrous oxide (N2O) responds exponentially to nitrogen fertilizer in irrigated wheat in the Yaqui Valley, Mexico. Agriculture, Ecosystems and Environment 261:125-132.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Abraha, M., I. Gelfand, J. Chen, S. K. Hamilton, and G. P. Robertson. 2018. Legacy effects of land use on soil nitrous oxide emissions in annual crop and perennial grassland ecosystems. Ecological Applications 28:1362-1369.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Abraha, M., S. K. Hamilton, J. Chen, and G. P. Robertson. 2018. Ecosystem carbon exchange on conversion of Conservation Reserve Program grasslands to annual and perennial cropping systems. Agricultural and Forest Meteorology 253-254:151-160.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Basso, B., B. Dumont, B. Maestrini, I. Shcherbak, G. P. Robertson, J. R. Porter, P. Smith, K. Paustian, P. R. Grace, S. Asseng, S. Bassu, C. Biernath, K. J. Boote, D. Cammarano, G. De Sanctis, J.-L. Durand, F. Ewert, S. Gayler, D. W. Hyndman, J. Kent, P. Martre, C. Nendel, E. Priesack, D. Ripoche, A. C. Ruane, J. Sharp, P. J. Thorburn, J. L. Hatfield, J. W. Jones, and C. Rosenzweig. 2018. Soil organic carbon and nitrogen feedbacks on crop yields under climate change. Agricultural & Environmental Letters 3:180026.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Hamilton, S. K., M. Z. Hussain, C. Lowrie, B. Basso, and G. P. Robertson. 2018. Evapotranspiration is resilient in the face of land cover and climate change in a humid temperate catchment. Hydrological Processes 32:655-663.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Sprunger, C. D. and G. P. Robertson. 2018. Early accumulation of active fraction soil carbon in newly established cellulosic biofuel systems. Geoderma 318:42-51.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Roley, S. S., D. S. Duncan, D. Liang, A. Garoutte, R. D. Jackson, J. M. Tiedje, and G. P. Robertson. 2018. Associative nitrogen fixation (ANF) in switchgrass (Panicum virgatum) across a nitrogen input gradient. PLoS ONE 13:e0197320.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Spiegal, S., B. T. Bestelmeyer, D. W. Archer, D. J. Augustine, E. H. Boughton, R. K. Boughton, M. A. Cavigelli, P. E. Clark, J. D. Derner, E. W. Duncan, C. Hapeman, D. H. Harmel, P. Heilman, M. A. Holly, D. R. Huggins, K. King, P. J. A. Kleinman, M. A. Liebig, M. A. Locke, G. W. McCarty, N. Millar, S. B. Mirsky, T. B. Moorman, F. B. Pierson, J. R. Rigby, G. P. Robertson, J. L. Steiner, T. C. Strickland, H. M. Swain, B. J. Wienhold, J. D. Wulfhorst, M. A. Yost, and C. L. Walthall. 2018. Evaluating strategies for sustainable intensification of US agriculture through the Long-Term Agroecosystem Research network. Environmental Research Letters 13:034031.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Sprunger, C. D., S. W. Culman, G. P. Robertson, and S. S. Snapp. 2018. How does nitrogen and perenniality influence belowground biomass and nitrogen use efficiency in small grain cereals? Crop Science doi: 10.2135/cropsci2018.02.0123.
• Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Liang, D. and G. P. Robertson. 2018. Nitrification-derived nitrous oxide (N2O) emissions from annual and perennial cropping systems in southwest Michigan. International Society for Microbial Ecology Conference, Leipzig, Germany.

Progress 10/01/16 to 09/30/17

Outputs
Target Audience:Our primary audiences for this work have been the scientific community, which uses our findings to further inform the fundamental understanding of greenhouse gas fluxes in agriculture, and policymakers and other interested in agricultural mitigation opportunities. The primary form of knowledge transfer has been via peer-reviewed publications as well as presentations at scientific meetings and in other professional settings. Additionally findings have been disseminated through presentations to undergraduate and graduate students, K-12 teachers, extension educators, and working professionals including farmers. Press releases and radio and video interviews allowed us to provide results of our work to the general public. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?OUTPUTS: We have made measurements of the radiatively important trace gases nitrous oxide (N2O) and methane (CH4) at biweekly to monthly intervals through the year at the KBS Long-term Ecological Research site. These measurements are included in an on-going assessment of the overall impact of farming activities on atmospheric chemistry. The global warming potentials (GWPs) of 11 different cropped and natural ecosystems are calculated using information on soil carbon sequestration, fertilizer, lime, fuel inputs, and the production of N2O and consumption of CH4 in these systems. N2O production continues to be the largest single source of GWP in all annual crop ecosystems, followed by nitrogen fertilizer manufacturing when nitrogen fertilizer is used. Carbon sequestration in all cropping and successional systems has been sampled to 1.2 m soil depth and shows substantial differences among cropping systems. In particular, soil carbon sequestration is significant in no-till surface soils and in soils from systems with legume cover crops. The analysis of N2O fluxes across 9 different fertilizer levels, conducted with a near-continuous automated chamber system, showed a nonlinear response of N2O flux to fertilizer inputs regardless of crop (corn vs. wheat vs. soybean). CH4 oxidation is affected by fertilization but not by tillage in noncropped sites; in cropped sites CH4 oxidation is already low and is not further affected by tillage or N fertilizer. These and other results offer significant promise for reducing the global warming potential of agricultural systems, whether for grain or cellulosic biomass. How have the results been disseminated to communities of interest?We have published extensively in the area of greenhouse gases in row crop agriculture and our research is having an impact both in public policy (Richter and Mobley 2009) and the voluntary carbon markets, where our N2O abatement protocol (Millar et al. 2010) was the first to be adopted by all three major US carbon registries (Millar et al. 2012, 2013). In particular, our discovery of a nonlinear (exponentially increasing) relationship between nitrogen fertilizer use and N2O production (McSwiney and Robertson 2005, Hoben et al. 2011, Shcherbak et al. 2014) has provided impetus for converting fertilizer rate reductions into tradable carbon offset credits. While significant deployment awaits the emergence of a carbon compliance market, now under development for California, our work lays the groundwork for providing farmers an incentive for applying nitrogen fertilizer more precisely, thereby reducing both N2O and other reactive forms of nitrogen in the environment such as nitrate. In 2014 the first carbon credit for N2O abatement was issued to a Michigan farmer by the American Carbon Registry, and purchased and retired by The Climate Trust. We are currently working with a CIMMYT wheat agronomist to make 500,000 acres of irrigated wheat in the Yaqui Valley eligible for carbon payments. The future development of a cellulosic biofuels market also promises significant greenhouse gas mitigation and thus climate benefits (NRC 2010), but only if managed in a way that ensures the greenhouse gas balance of future biofuel cropping systems is as negative (climate mitigating) as possible. This includes the need to minimize carbon debt - both the greenhouse gases (CO2 and N2O) released upon establishment of the cellulosic cropping system and as well the indirect land use cost of establishing cellulosic cropping systems on land now used for crops, which forces new land elsewhere into more intensive management with concomitant greenhouse gas release. Our previous work has addressed both issues. First, we've shown experimentally that direct carbon debt can be substantial unless steps (such as no-till cultivation) are taken to protect existing soil carbon (Gelfand et al. 2011), especially when the land under conversion has been in the USDA's Conservation Reserve Program. In fact plowing creates so much carbon debt that it is unlikely to be repaid within a century (Ruan and Robertson 2013). Second, we have estimated the capacity of marginal lands in the US Midwest to produce cellulosic biofuels (Gelfand et al. 2013), whereby carbon debt is avoided a) by harvesting existing perennial successional or CRP vegetation and b) by avoiding the use of land now in annual crop production. There is also the question of fertilizer impact with cellulosic crops - and we have now documented the same exponentially increasing response of N2O to fertilizer (Ruan et al.2016) as has been documented for annual crops. What do you plan to do during the next reporting period to accomplish the goals?Continue existing field experiments and observations.

Impacts
What was accomplished under these goals? This research contributed to our understanding of the ecological basis for greenhouse gas fluxes to the atmosphere. The role of agriculture in these fluxes - whether as a source or sink - is important to know in order to develop effective greenhouse gas mitigation strategies at a national level. The development of carbon credit trading, expanded to include other greenhouse gases, depends on a sound scientific understanding of these issues. Long-term research aids the discovery and methodologies for creating credits and is an important part of this national endeavor. We made progress towards all of the objectives outlined above, as noted in OUTPUTS, below.

Publications

• Type: Journal Articles Status: Published Year Published: 2016 Citation: Millar, N. and G. P. Robertson. 2016. Managing nitrogen fertilizers in the field to reduce greenhouse gases. Fertilizer Focus September/October:54-57.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Austin, E. E., K. Wickings, M. McDaniel, G. P. Robertson, and A. S. Grandy. 2017. Cover crop root contributions to soil carbon in a no-till corn bioenergy cropping system. GCB Bioenergy 9:1252-1263.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Izaurralde, C., W. B. McGill, J. Williams, C. Jones, R. Link, D. Manowitz, D. Schwab, X. Zhang, G. P. Robertson, and N. Millar. 2017. Simulating microbial denitrification with EPIC: Model description and initial evaluation. Ecological Modelling 359:349-362.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Ruan, L. and G. P. Robertson. 2017. Reduced snow cover increases wintertime nitrous oxide (N2O) emissions from an agricultural soil in the upper U.S. Midwest. Ecosystems 20:917-927.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Sanford, G. R., R. D. Jackson, L. G. Oates, G. P. Robertson, S. Roley, and K. D. Thelen. 2017. Biomass production a stronger driver of ethanol yield than biomass quality. Agronomy Journal 109:1-12.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Sprunger, C. D., S. W. Culman, G. P. Robertson, and S. S. Snapp. 2017. Perennial grain on a Midwest Alfisol shows no sign of early soil carbon gain. Renewable Agriculture and Food Systems doi:10.1017/S1742170517000138.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Reimer, A., J. E. Doll, B. Basso, S. T. Marquart-Pyatt, G. P. Robertson, D. Stuart, and J. Zhao. 2017. Moving toward sustainable farming systems: Insights from private and public sector dialogues on nitrogen management. Journal of Soil and Water Conservation 72:5A-9A.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Sprunger, C. D., L. G. Oates, R. D. Jackson, and G. P. Robertson. 2017. Plant community composition influences fine root production and biomass allocation in perennial bioenergy cropping systems of the upper Midwest, USA. Biomass and Bioenergy 105:248-258.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Kravchenko, A. N., S. S. Snapp, and G. P. Robertson. 2017. Field-scale experiments reveal persistent yield gaps in low-input and organic cropping systems. Proceedings of the National Academy of Sciences USA 114:926-931.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Kravchenko, A. N., E. R. Toosi, A. K. Guber, N. E. Ostrom, J. Yu, K. Azeem, M. L. Rivers, and G. P. Robertson. 2017. Hotspots of soil N2O emission enhanced through water absorption by plant residue. Nature Geoscience 10:496-500.
• Type: Other Status: Published Year Published: 2016 Citation: Ruan, L., A. K. Bhardwaj, S. K. Hamilton, and G. P. Robertson. 2016. Data from: Nitrogen fertilization challenges the climate benefit of cellulosic biofuels. Dryad Digital Repository http://dx.doi.org/10.5061/dryad.f1b82.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Robertson, G. P., S. K. Hamilton, B. L. Barham, B. E. Dale, R. C. Izaurralde, R. D. Jackson, D. A. Landis, S. M. Swinton, K. D. Thelen, and J. M. Tiedje. 2017. Cellulosic biofuel contributions to a sustainable energy future: Choices and outcomes. Science 356:eaal2324.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Valdez, Z. P., W. C. Hockaday, C. A. Masiello, M. E. Gallagher, and G. P. Robertson. 2017. Soil carbon and nitrogen responses to nitrogen fertilizer and harvesting rates in switchgrass cropping systems. BioEnergy Research 10:456-464.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Yang, Q., X. Zhang, M. Abraha, S. Del Grosso, G. P. Robertson, and J. Chen. 2017. Enhancing the soil and water assessment tool model for simulating N2O emissions of three agricultural systems. Ecosystem Health and Sustainability 3:e01259.
• Type: Other Status: Published Year Published: 2016 Citation: Ruan, L. and G. P. Robertson. 2016. Data from: Reduced snow cover increases wintertime nitrous oxide (N2O) emissions from an agricultural soil in the upper U. S. Midwest. Dryad Digital Repository http://dx.doi.org/10.5061/dryad.9c7s3.
• Type: Other Status: Published Year Published: 2017 Citation: Kravchenko, A. N., E. R. Toosi, A. K. Guber, N. E. Ostrom, J. Yu, K. Azeem, M. L. Rivers, and G. P. Robertson. 2017. Data from: Hotspots of soil N2O emission enhanced through water absorption by plant residue. Dryad Digital Repository, http://dx.doi.org/10.5061/dryad.83150.
• Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Abraha, M., I. Gelfand, S. K. Hamilton, C. Shao, Y.-J. Su, G. P. Robertson, and J. Chen. 2016. Ecosystem carbon budgets under contrasting land use histories using eddy covariance and deep core methods. AGU Fall Meeting, San Francisco, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Chicoine, T., S. S. Roley, G. P. Robertson, L. Tiemann, M. Friesen, and S. Evans. 2016. Variation in microbial communities and nitrogen transformation rates among switchgrass varieties. Keystone Symposium Conference, Santa Fe, NM.
• Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Gelfand, I., A. N. Kravchenko, S. K. Hamilton, R. Jackson, K. Thelen, and G. P. Robertson. 2016. Climatic impacts of managed landscapes for sustainable biofuel feedstocks production. AGU Fall Meeting, San Francisco, CA.
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Glanville, K. R. and G. P. Robertson. 2016. Consequences of changing rainfall patterns on nitrous oxide fluxes in continuous corn vs. switchgrass cropping systems. ASA, CSSA, and SSSA 2016 Annual Meeting, Phoenix, AZ.
• Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Hess, L., E. S. Hinckley, G. P. Robertson, and P. A. Matson. 2016. The effects of more extreme rainfall patterns on nitrogen leaching from a field crop system in the upper Midwest, USA. AGU Fall Meeting, San Francisco, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Liang, D. and G. P. Robertson. 2016. Seasonal dynamics of soil ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA) in response to nitrogen fertilization. ASA, CCSA, and SSSA 2016 Annual Meeting, Phoenix, AZ.
• Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Millar, N. and G. P. Robertson. 2016. Nitrogen management for carbon credit. ASA, CSSA and SSSA Annual 2016 Meeting, Phoenix, AZ.
• Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Thelen, K. D., G. Sanford, G. P. Robertson, and R. Jackson. 2016. Bioethanol production potential of cellulosic biomass crops in North Central USA. ASA, CSSA, and SSSA 2016 Annual Meeting, Phoenix, AZ.
• Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Valdez, Z., W. C. Hockaday, C. A. Masiello, G. P. Robertson, and M. E. Gallagher. 2016. Impacts of N fertilizer and harvest rate on size and stability of switchgrass soil and C and N pools. ASA, CSSA, and SSSA 2016 Annual Meeting, Phoenix, AZ.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Cole, J. R., J. Guo, L. Tift, J. M. Tiedje, and G. P. Robertson. 2017. Methods for high-throughput massively parallel soil ecofunctional gene analysis. DOE Genomic Science Program Annual Meeting, Washington, DC.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Glanville, K. and G. P. Robertson. 2017. Consequences of changing rainfall patterns on nitrous oxide fluxes in continuous corn versus switchgrass cropping systems. ESA Annual Meeting, Portland, OR.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Glanville, K. R. and G. P. Robertson. 2017. Consequences of changing rainfall patterns on nitrous oxide fluxes in cropping systems. Soil Ecology Society Biennial Meeting, Fort Collins, CO.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Liang, D. and G. P. Robertson. 2017. Management intensities and seasons affect the relative contribution of ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA) to nitrification across a Midwest management gradient. 2017 Soil Ecology Society Biennial Meeting, Fort Collins, CO.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Liang, D. and G. P. Robertson. 2017. Partitioning ntrous oxide (N2O) emissions from ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA) in corn and switchgrass ecosystems. DOE Genomic Science Program Annual Meeting, Washington DC.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: S�nchez, R., K. Glanville, and G. P. Robertson. 2017. Effect of altered rainfall patterns at different topographical positions on N2O fluxes. ESA Annual Meeting, Portland, OR.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: O'Neill, B., T. M. Schmidt, G. P. Robertson, A. N. Kravchenko, and A. S. Grandy. 2017. Linking soil C and N cycling and trace gas fluxes with soil bacterial communities along a gradient of simple to complex crop rotations. 2017 Soil Ecology Society Biennial Meeting, Fort Collins, CO.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: O'Neill, B., C. D. Sprunger, J. Kerr, and G. P. Robertson. 2017. Aligning soil health testing and farmer knowledge for improved on-farm soil management. Soil Ecology Society Biennial Meeting, Fort Collins, CO.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Roley, S. S., D. S. Duncan, D. Liang, A. Garoutte, R. D. Jackson, J. M. Tiedje, and G. P. Robertson. 2017. Associative nitrogen fixation across a nitrogen input gradient. DOE Genomic Science Program Annual Meeting, Washington DC.

Progress 10/01/15 to 09/30/16

Outputs
Target Audience:Our primary audiences for this work have been the scientific community, which uses our findings to further inform the fundamental understanding of greenhouse gas fluxes in agriculture, and policymakers and other interested in agricultural mitigation opportunities. The primary form of knowledge transfer has been via peer-reviewed publications as well as presentations at scientific meetings and in other professional settings. Additionally findings have been disseminated through presentations to undergraduate and graduate students, K-12 teachers, extension educators, and working professionals including farmers. Press releases and radio and video interviews allowed us to provide results of our work to the general public. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?OUTPUTS: We have made measurements of the radiatively important trace gases nitrous oxide (N2O) and methane (CH4) at biweekly to monthly intervals through the year at the KBS Long-term Ecological Research site. These measurements are included in an on-going assessment of the overall impact of farming activities on atmospheric chemistry. The global warming potentials (GWPs) of 11 different cropped and natural ecosystems are calculated using information on soil carbon sequestration, fertilizer, lime, fuel inputs, and the production of N2O and consumption of CH4 in these systems. N2O production continues to be the largest single source of GWP in all annual crop ecosystems, followed by nitrogen fertilizer manufacturing when nitrogen fertilizer is used. Carbon sequestration in all cropping and successional systems has been sampled to 1.2 m soil depth and shows substantial differences among cropping systems. In particular, soil carbon sequestration is significant in no-till surface soils and in soils from systems with legume cover crops. The analysis of N2O fluxes across 9 different fertilizer levels, conducted with a near-continuous automated chamber system, showed a nonlinear response of N2O flux to fertilizer inputs regardless of crop (corn vs. wheat vs. soybean). CH4 oxidation is affected by fertilization but not by tillage in noncropped sites; in cropped sites CH4 oxidation is already low and is not further affected by tillage or N fertilizer. These and other results offer significant promise for reducing the global warming potential of agricultural systems, whether for grain or cellulosic biomass. How have the results been disseminated to communities of interest?We have published extensively in the area of greenhouse gases in row crop agriculture and our research is having an impact both in public policy (Richter and Mobley 2009) and the voluntary carbon markets, where our N2O abatement protocol (Millar et al. 2010) was the first to be adopted by all three major US carbon registries (Millar et al. 2012, 2013). In particular, our discovery of a nonlinear (exponentially increasing) relationship between nitrogen fertilizer use and N2O production (McSwiney and Robertson 2005, Hoben et al. 2011, Shcherbak et al. 2014) has provided impetus for converting fertilizer rate reductions into tradable carbon offset credits. While significant deployment awaits the emergence of a carbon compliance market, now under development for California, our work lays the groundwork for providing farmers an incentive for applying nitrogen fertilizer more precisely, thereby reducing both N2O and other reactive forms of nitrogen in the environment such as nitrate. In 2014 the first carbon credit for N2O abatement was issued to a Michigan farmer by the American Carbon Registry, and purchased and retired by The Climate Trust. We are currently working with a CIMMYT wheat agronomist to make 500,000 acres of irrigated wheat in the Yaqui Valley eligible for carbon payments. The future development of a cellulosic biofuels market also promises significant greenhouse gas mitigation and thus climate benefits (NRC 2010), but only if managed in a way that ensures the greenhouse gas balance of future biofuel cropping systems is as negative (climate mitigating) as possible. This includes the need to minimize carbon debt - both the greenhouse gases (CO2 and N2O) released upon establishment of the cellulosic cropping system and as well the indirect land use cost of establishing cellulosic cropping systems on land now used for crops, which forces new land elsewhere into more intensive management with concomitant greenhouse gas release. Our previous work has addressed both issues. First, we've shown experimentally that direct carbon debt can be substantial unless steps (such as no-till cultivation) are taken to protect existing soil carbon (Gelfand et al. 2011), especially when the land under conversion has been in the USDA's Conservation Reserve Program. In fact plowing creates so much carbon debt that it is unlikely to be repaid within a century (Ruan and Robertson 2013). Second, we have estimated the capacity of marginal lands in the US Midwest to produce cellulosic biofuels (Gelfand et al. 2013), whereby carbon debt is avoided a) by harvesting existing perennial successional or CRP vegetation and b) by avoiding the use of land now in annual crop production. There is also the question of fertilizer impact with cellulosic crops - and we have now documented the same exponentially increasing response of N2O to fertilizer (Ruan et al.2016) as has been documented for annual crops. What do you plan to do during the next reporting period to accomplish the goals?Continue existing field experiments and observations.

Impacts
What was accomplished under these goals? This research contributed to our understanding of the ecological basis for greenhouse gas fluxes to the atmosphere. The role of agriculture in these fluxes - whether as a source or sink - is important to know in order to develop effective greenhouse gas mitigation strategies at a national level. The development of carbon credit trading, expanded to include other greenhouse gases, depends on a sound scientific understanding of these issues. Long-term research aids the discovery and methodologies for creating credits and is an important part of this national endeavor. We made progress towards all of the objectives outlined above, as noted in OUTPUTS, below.

Publications

• Type: Journal Articles Status: Published Year Published: 2016 Citation: Abraha M, Gelfand I, Hamilton SK, Shao C, Su Y-J, Robertson GP, Chen J. 2016. Ecosystem water use efficiency of annual corn and perennial grasses: Contributions from land-use history and species composition. Ecosystems 19: 1001-1012.
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Gelfand I, Shcherbak I, Millar N, Kravchenko AN, Robertson GP. 2016. Long-term nitrous oxide fluxes in annual and perennial agricultural and unmanaged ecosystems in the upper Midwest USA. Global Change Biology. DOI: 10.1111/gcb.13426
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Gustafson D, Hayes M, Janssen E, Lobell DB, Long S, Nelson GC, Pakrasi HB, Raven P, Robertson GP, Robertson R, Wuebbles D. 2016. Pharaoh's dream revisited: An integrated US Midwest field research network for climate adaptation. Bioscience 66: 80-85.
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Ladoni M, Basir A, Robertson GP, Kravchenko AN. 2016. Scaling-up: cover crops differentially influence soil carbon in agricultural fields with diverse topography. Agriculture, Ecosystems and Environment 225: 93-103.
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Ladoni M, Kravchenko AN, Robertson GP. 2015. Topography mediates the influence of cover crops on soil nitrate levels in row crop agricultural systems. PLoS ONE 10: e0143358.
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Oates LG, Duncan DS, Gelfand I, Millar N, Robertson GP, Jackson RD. 2016. Nitrous oxide emissions during establishment of eight alternative cellulosic bioenergy cropping systems in the North Central United States. Global Change Biology Bioenergy 8: 539-549.
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Paustian K, Lehmann J, Ogle S, Reay D, Robertson GP, Smith P. 2016. Climate-smart soils. Nature 532: 49-57.
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Ruan L, Bhardwaj AK, Hamilton SK, Robertson GP. 2016. Nitrogen fertilization challenges the climate benefit of cellulosic biofuels. Environmental Research Letters 11: 064007.
• Type: Other Status: Published Year Published: 2015 Citation: Robertson GP. 2015. A sustainable agriculture? Daedalus 144: 76-89.
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Sanford GR, Oates LG, Jasrotia P, Thelen KD, Robertson GP, Jackson RD. 2016. Comparative productivity of alternative cellulosic bioenergy cropping systems in the North Central USA. Agriculture, Ecosystems and Environment 216: 344-355.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Abraha MG, Gelfand I, Chen J, Shao C, Su Y-J, Hamilton SK, Robertson GP. 2015. Land use history, ecosystem type and species composition drive water use efficiency in annual maize and perennial grasslands in a humid temperate climate. 2015 American Geophysical Union Annual Meeting. San Francisco, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Smith RG, Gross KL, Robertson GP. 2015. Crop diversity drives productivity and stability in annual row crops. ASA, CSSA, and SSSA 2015 Annual Meeting. Minneapolis, MN.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Gelfand I, Moyer R, Poe A, Pan D, Abraha M, Chen J, Zondlo M, Robertson GP. 2015. Diurnality of soil nitrous oxide (N2O) emissions. 2015 American Geophysical Union Fall Meeting. San Francisco, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Hussain MZ, Hamilton SK, Bhardwaj A, Basso B, Thelen K, Robertson GP. 2015. Evapotranspiration and water use efficiency in maize-soybean crops in the US Midwest. 2015 American Geophysical Union Fall Meeting. San Francisco, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Millar N, Baas DG, Robertson GP. 2015. The influence of potential biofuel cover crops on nitrous oxide (N2O) emissions from Midwest row-crops. ASA, CSSA and SSSA 2015 Annual Meeting. Minneapolis, MN.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Tao L, Pan D, Gelfand I, Abraha M, Moyer R, Poe A, Sun K, Robertson GP, Zondlo M. 2015. N2O fluxes over a corn field from an open-path, laser-based eddy covariance system and static chambers. 2015 American Geophysical Union Fall Meeting. San Francisco, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Walbridge M, Bestelmeyer B, Derner J, Harmel D, Heilman P, Huggins D, Kleinman P, Moorman T, McCarty G, Pierson F, Rigby J, Robertson GP, Sadler J, Sanderson M, Steiner J, Strickland T, Wienhold B. 2015. Development of the Long-Term Agro-Ecosystem Research (LTAR) Network: Current status and future trends. 2015 American Geophysical Union Fall Meeting. San Francisco, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Zhang X, Zhao K, Abraha M, Gelfand I, Izaurralde RC, Thomson AM, Hamilton SK, Chen J, Robertson GP, Xu M, Liang X-Z. 2015. Biogeochemical and biophysical climate regulation services from converting native grassland to bioenergy production in the US Midwest. 2015 American Geophysical Union Fall Meeting. San Francisco, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Roley SS, Duncan DS, Liang D, Jackson RD, Robertson GP. 2016. Nitrogen fixation in switchgrass responds to N fertilizer addition, plant N demand, and soil type. Ecological Society of America Annual Meeting 2016. Fort Lauderdale, FL.

Progress 10/01/14 to 09/30/15

Outputs
Target Audience:Our primary audiences for this work have been the scientific community, which uses our findings to further inform the fundamental understanding of greenhouse gas fluxes in agriculture, and policymakers and other interested in agricultural mitigation opportunities. The primary form of knowledge transfer has been via peer-reviewed publications as well as presentations at scientific meetings and in other professional settings. Additionally findings have been disseminated through presentations to undergraduate and graduate students, K-12 teachers, extension educators, and working professionals including farmers. Press releases and radio and video interviews allowed us to provide results of our work to the general public. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?OUTPUTS: We have made measurements of the radiatively important trace gases nitrous oxide (N2O) and methane (CH4) at biweekly to monthly intervals through the year at the KBS Long-term Ecological Research site. These measurements are included in an on-going assessment of the overall impact of farming activities on atmospheric chemistry. The global warming potentials (GWPs) of 11 different cropped and natural ecosystems are calculated using information on soil carbon sequestration, fertilizer, lime, fuel inputs, and the production of N2O and consumption of CH4 in these systems. N2O production continues to be the largest single source of GWP in all annual crop ecosystems, followed by nitrogen fertilizer manufacturing when nitrogen fertilizer is used. Carbon sequestration in all cropping and successional systems has been sampled to 1.2 m soil depth and shows substantial differences among cropping systems. In particular, soil carbon sequestration is significant in no-till surface soils and in soils from systems with legume cover crops. The analysis of N2O fluxes across 9 different fertilizer levels, conducted with a near-continuous automated chamber system, showed a nonlinear response of N2O flux to fertilizer inputs regardless of crop (corn vs. wheat vs. soybean). CH4 oxidation is affected by fertilization but not by tillage in noncropped sites; in cropped sites CH4 oxidation is already low and is not further affected by tillage or N fertilizer. These and other results offer significant promise for reducing the global warming potential of agricultural systems, whether for grain or cellulosic biomass. How have the results been disseminated to communities of interest?We have published extensively in the area of greenhouse gases in row crop agriculture and our research is having an impact both in public policy (Richter and Mobley 2009) and the voluntary carbon markets, where our N2O abatement protocol (Millar et al. 2010) was the first to be adopted by all three major US carbon registries (Millar et al. 2012, 2013). In particular, our discovery of a nonlinear (exponentially increasing) relationship between nitrogen fertilizer use and N2O production (McSwiney and Robertson 2005, Hoben et al. 2011, Shcherbak et al. 2014) has provided impetus for converting fertilizer rate reductions into tradable carbon offset credits. While significant deployment awaits the emergence of a carbon compliance market, now under development for California, our work lays the groundwork for providing farmers an incentive for applying nitrogen fertilizer more precisely, thereby reducing both N2O and other reactive forms of nitrogen in the environment such as nitrate. In 2014 the first carbon credit for N2O abatement was issued to a Michigan farmer by the American Carbon Registry, and purchased and retired by The Climate Trust. We are currently working with a CIMMYT wheat agronomist to make 500,000 acres of irrigated wheat in the Yaqui Valley eligible for carbon payments. The future development of a cellulosic biofuels market also promises significant greenhouse gas mitigation and thus climate benefits (NRC 2010), but only if managed in a way that ensures the greenhouse gas balance of future biofuel cropping systems is as negative (climate mitigating) as possible. This includes the need to minimize carbon debt - both the greenhouse gases (CO2 and N2O) released upon establishment of the cellulosic cropping system and as well the indirect land use cost of establishing cellulosic cropping systems on land now used for crops, which forces new land elsewhere into more intensive management with concomitant greenhouse gas release. Our previous work has addressed both issues. First, we've shown experimentally that direct carbon debt can be substantial unless steps (such as no-till cultivation) are taken to protect existing soil carbon (Gelfand et al. 2011), especially when the land under conversion has been in the USDA's Conservation Reserve Program. In fact plowing creates so much carbon debt that it is unlikely to be repaid within a century (Ruan and Robertson 2013). Second, we have estimated the capacity of marginal lands in the US Midwest to produce cellulosic biofuels (Gelfand et al. 2013), whereby carbon debt is avoided a) by harvesting existing perennial successional or CRP vegetation and b) by avoiding the use of land now in annual crop production. There is also the question of fertilizer impact with cellulosic crops - and we have now documented the same exponentially increasing response of N2O to fertilizer (Ruan et al., in prep) as has been documented for annual crops. What do you plan to do during the next reporting period to accomplish the goals?Continue existing field experiments and observations.

Impacts
What was accomplished under these goals? This research contributed to our understanding of the ecological basis for greenhouse gas fluxes to the atmosphere. The role of agriculture in these fluxes - whether as a source or sink - is important to know in order to develop effective greenhouse gas mitigation strategies at a national level. The development of carbon credit trading, expanded to include other greenhouse gases, depends on a sound scientific understanding of these issues. Long-term research aids the discovery and methodologies for creating credits and is an important part of this national endeavor. We made progress towards all of the objectives outlined above, as noted in OUTPUTS, below.

Publications

• Type: Journal Articles Status: Published Year Published: 2014 Citation: Robertson, G. P., P. R. Grace, R. C. Izaurralde, W. P. Parton, and X. Zhang. 2014. Correspondence: CO2 emissions from crop residue-derived biofuels. Nature Climate Change 4:933-934.
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Abraha, M., J. Chen, H. Chu, T. Zenone, R. John, Y.-J. Su, S. K. Hamilton, and G. P. Robertson. 2015. Evapotranspiration of annual and perennial biofuel crops in a variable climate. Global Change Biology Bioenergy doi: 10.1111/gcbb.12239.
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Basso, B., D. W. Hyndman, A. D. Kendall, P. R. Grace, and G. P. Robertson. 2015. Can impacts of climate change and agricultural adaptation strategies be accurately quantified if crop models are annually reinitialized? PLoS ONE 10:e0127333.
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Gelfand, I., M. Cui, J. Tang, and G. P. Robertson. 2015. Short-term drought response of N2O and CO2 emissions from mesic agricultural soils in the US Midwest. Agriculture, Ecosystem and Environment 212:127-133.
• Type: Book Chapters Status: Published Year Published: 2015 Citation: Gelfand, I. and G. P. Robertson. 2015. Mitigation of greenhouse gas emissions in agricultural ecosystems. Pages 310-339 in S. K. Hamilton, J. E. Doll, and G. P. Robertson, editors. The Ecology of Agricultural Landscapes: Long-Term Research on the Path to Sustainability. Oxford University Press, New York, New York, USA.
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Kravchenko, A. N. and G. P. Robertson. 2015. Statistical challenges in analyses of chamber-based soil CO2 and N2O emissions data. Soil Science Society of America Journal 79:200-211.
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Gelfand, I. and G. P. Robertson. 2015. A reassessment of the contribution of soybean biological nitrogen fixation to reactive N in the environment. Biogeochemistry 123:175-184.
• Type: Books Status: Published Year Published: 2015 Citation: Hamilton, S. K., J. E. Doll, and G. P. Robertson, editors. 2015. The Ecology of Agricultural Landscapes: Long-Term Research on the Path to Sustainability. Oxford University Press, New York, New York, USA.
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Hamilton, S. K., M. Z. Hussain, A. K. Bhardwaj, B. Basso, and G. P. Robertson. 2015. Comparative water use by maize, perennial crops, restored prairie, and poplar trees in the US Midwest. Environmental Research Letters 10:064015.
• Type: Book Chapters Status: Published Year Published: 2015 Citation: Millar, N. and G. P. Robertson. 2015. Nitrogen transfers and transformations in row-crop ecosystems. Pages 213-251 in S. K. Hamilton, J. E. Doll, and G. P. Robertson, editors. The Ecology of Agricultural Landscapes: Long-Term Research on the Path to Sustainability. Oxford University Press, New York, New York, USA.
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Oates, L. G., D. S. Duncan, I. Gelfand, N. Millar, G. P. Robertson, and R. D. Jackson. 2015. Nitrous oxide emissions during establishment of eight alternative cellulosic bioenergy cropping systems in the North Central United States. Global Change Biology Bioenergy doi: 10.1111/gcbb.12268.
• Type: Book Chapters Status: Published Year Published: 2015 Citation: Robertson, G. P. and P. M. Groffman. 2015. Nitrogen transformations. Pages 421-446 in E. A. Paul, editor. Soil microbiology, ecology, and biochemistry. Academic Press, Burlington, Massachusetts, USA.
• Type: Book Chapters Status: Published Year Published: 2015 Citation: Robertson, G. P. and S. K. Hamilton. 2015. Long-term ecological research in agricultural landscapes at the Kellogg Biological Station LTER site: conceptual and experimental framework. Pages 1-32 in S. K. Hamilton, J. E. Doll, and G. P. Robertson, editors. The Ecology of Agricultural Landscapes: Long-Term Research on the Path to Sustainability. Oxford University Press, New York, New York, USA.
• Type: Book Chapters Status: Published Year Published: 2015 Citation: Snapp, S. S., R. G. Smith, and G. P. Robertson. 2015. Designing cropping systems for ecosystem services. Pages 378-408 in S. K. Hamilton, J. E. Doll, and G. P. Robertson, editors. The Ecology of Agricultural Landscapes: Long-Term Research on the Path to Sustainability. Oxford University Press, New York, New York, USA.
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Stuart, D. L., B. Basso, S. T. Marquart-Pyatt, A. P. Reimer, G. P. Robertson, and J. Zhao. 2015. The need for a coupled human and natural systems understanding of agricultural nitrogen loss. Bioscience 65:571-578.
• Type: Book Chapters Status: Published Year Published: 2015 Citation: Swinton, S. M., N. Rector, G. P. Robertson, C. B. Jolejole-Foreman, and F. Lupi. 2015. Farmer decisions about adopting environmentally beneficial practices. Pages 340-359 in S. K. Hamilton, J. E. Doll, and G. P. Robertson, editors. The Ecology of Agricultural Landscapes: Long-Term Research on the Path to Sustainability. Oxford University Press, New York, New York, USA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Bhardwaj, A. K., L. Ruan, S. K. Hamilton, and G. P. Robertson. 2014. Water quality improvement, an important consideration to delineate sustainable fertilization and harvesting strategies for cellulosic bioenergy crops. 20th World Congress of Soil Science, Jeju, Korea.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Gelfand, I., C. Gallagher, B. C. G. Moneymaker, and G. P. Robertson. 2014. Relative importance of nitrous oxide vs. nitric oxide emissions from soils across a management intensity and biodiversity gradient. American Geophysical Union Fall Meeting, San Francisco, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Jones, C. D., R. C. Izaurralde, W. McGill, D. Manowitz, and G. P. Robertson. 2014. Evaluation of a microbial denitrification model in the environmental policy integrated climate model. ASA, CSSA, & SSSA International Annual Meeting, Long Beach, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Hussain, M. Z., S. K. Hamilton, A. K. Bhardwaj, B. Basso, M. G. Abraha, and G. P. Robertson. 2014. Water footprints of cellulosic bioenergy crops: Implications for production on marginal lands. American Geophysical Union Fall Meeting, San Francisco, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: D. G. Baas. 2014. Nitrous oxide emissions from midwest row-crops: comparing presence and absence of winter cover crops within and between conventional and organic management systems. ASA, CSSA, & SSSA International Annual Meeting, Long Beach, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Millar, N. and G. P. Robertson. 2014. Manual chamber sampling strategies to help account for temporal and spatial variability of N2O emissions from agricultural cropping systems. ASA, CSSA, & SSSA International Annual Meeting, Long Beach, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Robertson, G. P., I. Gelfand, and S. S. Roley. 2014. Ecosystem services from cellulosic biofuel production systems on marginal lands. ASA, CSSA, & SSSA International Annual Meeting, Long Beach, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Sprunger, C. D. and G. P. Robertson. 2014. Differences in active fraction soil carbon under annual and perennial biofuel crops. ASA, CSSA, & SSSA International Annual Meeting, Long Beach, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Thelen, K. D., K. E. Hadley, G. Sanford, R. Jackson, and G. P. Robertson. 2014. An analysis of bioenergy cropping systems in the Great Lakes Region. ASA, CSSA, & SSSA International Annual Meeting, Long Beach, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Abraha, M. G., I. Gelfand, J. Chen, S. K. Hamilton, Y.-J. Su, and G. P. Robertson. 2015. Water use efficiency of annual corn and perennial grasses.Ecological Society of America, Baltimore, MD
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Haddix, M. L., R. T. Conant, G. P. Robertson, S. J. Morris, K. Magrini-Bair, R. J. Evans, F. Calderon, J. Ernakovich, N. Mellor, and E. A. Paul. 2015. Development of a pyrolysis method to quantify the stabile fraction in soil.Soil Ecological Society Meeting 2015, Colorado Springs, CO.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Sprunger, C. D., G. P. Robertson, R. D. Jackson, and L. G. Oates. 2015. Differences in fine root production and C allocation among perennial cropping systems in contrasting soils of the upper Midwest.Ecological Society of America, Baltimore, MD.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Su, Y.-J., H.-Y. Hsieh, J. Chen, M. G. Abraha, C. Shao, R. John, S. K. Hamilton, and G. P. Robertson. 2015. Soil respiration variations respond to microclimate variations in biofuel crop ecosystems. Ecological Society of America, Baltimore, MD.

Progress 11/01/13 to 09/30/14

Outputs
Target Audience: Our primary audiences for this work have been the scientific community, which uses our findings to further inform the fundamental understanding of greenhouse gas fluxes in agriculture, and policymakers and other interested in agricultural mitigation opportunities. The primary form of knowledge transfer has been via peer-reviewed publications as well as presentations at scientific meetings and in other professional settings. Additionally findings have been disseminated through presentations to undergraduate and graduate students, K-12 teachers, extension educators, and working professionals including farmers. Press releases and radio and video interviews allowed us to provide results of our work to the general public. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? OUTPUTS: We have made measurements of the radiatively important trace gases nitrous oxide (N2O) and methane (CH4) at biweekly to monthly intervals through the year at the KBS Long-term Ecological Research site. These measurements are included in an on-going assessment of the overall impact of farming activities on atmospheric chemistry. The global warming potentials (GWPs) of 11 different cropped and natural ecosystems are calculated using information on soil carbon sequestration, fertilizer, lime, fuel inputs, and the production of N2O and consumption of CH4 in these systems. N2O production continues to be the largest single source of GWP in all annual crop ecosystems, followed by nitrogen fertilizer manufacturing when nitrogen fertilizer is used. Carbon sequestration in all cropping and successional systems has been sampled to 1.2 m soil depth and shows substantial differences among cropping systems. In particular, soil carbon sequestration is significant in no-till surface soils and in soils from systems with legume cover crops. The analysis of N2O fluxes across 9 different fertilizer levels, conducted with a near-continuous automated chamber system, showed a nonlinear response of N2O flux to fertilizer inputs regardless of crop (corn vs. wheat vs. soybean). CH4 oxidation is affected by fertilization but not by tillage in noncropped sites; in cropped sites CH4 oxidation is already low and is not further affected by tillage or N fertilizer. These and other results offer significant promise for reducing the global warming potential of agricultural systems, whether for grain or cellulosic biomass. How have the results been disseminated to communities of interest? We have published extensively in the area of greenhouse gases in row crop agriculture and our research is having an impact both in public policy (Richter and Mobley 2009) and the voluntary carbon markets, where our N2O abatement protocol (Millar et al. 2010) was the first to be adopted by all three major US carbon registries (Millar et al. 2012, 2013). In particular, our discovery of a nonlinear (exponentially increasing) relationship between nitrogen fertilizer use and N2O production (McSwiney and Robertson 2005, Hoben et al. 2011, Shcherbak et al. 2014) has provided impetus for converting fertilizer rate reductions into tradable carbon offset credits. While significant deployment awaits the emergence of a carbon compliance market, now under development for California, our work lays the groundwork for providing farmers an incentive for applying nitrogen fertilizer more precisely, thereby reducing both N2O and other reactive forms of nitrogen in the environment such as nitrate. In 2014 the first carbon credit for N2O abatement was issued to a Michigan farmer by the American Carbon Registry, and purchased and retired by The Climate Trust. The future development of a cellulosic biofuels market also promises significant greenhouse gas mitigation and thus climate benefits (NRC 2010), but only if managed in a way that ensures the greenhouse gas balance of future biofuel cropping systems is as negative (climate mitigating) as possible. This includes the need to minimize carbon debt – both the greenhouse gases (CO2 and N2O) released upon establishment of the cellulosic cropping system and as well the indirect land use cost of establishing cellulosic cropping systems on land now used for crops, which forces new land elsewhere into more intensive management with concomitant greenhouse gas release. Our previous work has addressed both issues. First, we've shown experimentally that direct carbon debt can be substantial unless steps (such as no-till cultivation) are taken to protect existing soil carbon (Gelfand et al. 2011), especially when the land under conversion has been in the USDA's Conservation Reserve Program. In fact plowing creates so much carbon debt that it is unlikely to be repaid within a century (Ruan and Robertson 2013). Second, we have estimated the capacity of marginal lands in the US Midwest to produce cellulosic biofuels (Gelfand et al. 2013), whereby carbon debt is avoided a) by harvesting existing perennial successional or CRP vegetation and b) by avoiding the use of land now in annual crop production. There is also the question of fertilizer impact with cellulosic crops – and we have now documented the same exponentially increasing response of N2O to fertilizer (Ruan et al., in prep) as has been documented for annual crops. What do you plan to do during the next reporting period to accomplish the goals? Continue existing field experiments and observations.

Impacts
What was accomplished under these goals? This research contributed to our understanding of the ecological basis for greenhouse gas fluxes to the atmosphere. The role of agriculture in these fluxes--whether as a source or sink--is important to know in order to develop effective greenhouse gas mitigation strategies at a national level. The development of carbon credit trading, expanded to include other greenhouse gases, depends on a sound scientific understanding of these issues. Long-term research aids the discovery and methodologies for creating credits and is an important part of this national endeavor. We made progress towards all of the objectives outlined above, as noted in OUTPUTS, below.

Publications

• Type: Book Chapters Status: Awaiting Publication Year Published: 2015 Citation: Gelfand, I. and G. P. Robertson. 2015. Mitigation of greenhouse gas emissions from cropping systems. In S. K. Hamilton, J. E. Doll, and G. P. Robertson, editors. The ecology of agricultural ecosystems: long-term research on the path to sustainability. Oxford University Press, New York, New York, USA. (in press).
• Type: Book Chapters Status: Awaiting Publication Year Published: 2015 Citation: Millar, N. and G. P. Robertson. 2015. Nitrogen transfers and transformations in row-crop ecosystems. In S. K. Hamilton, J. E. Doll, and G. P. Robertson, editors. The ecology of agricultural ecosystems: long-term research on the path to sustainability. Oxford University Press, New York, New York, USA. (in press).
• Type: Book Chapters Status: Awaiting Publication Year Published: 2015 Citation: Robertson, G. P. and S. K. Hamilton. 2015. Conceptual and experimental approaches to long-term ecological research at the Kellogg Biological Station. In S. K. Hamilton, J. E. Doll, and G. P. Robertson, editors. The ecology of agricultural ecosystems: long-term research on the path to sustainability. Oxford University Press, New York, New York, USA. (in press).
• Type: Books Status: Awaiting Publication Year Published: 2015 Citation: Hamilton, S. K., J. E. Doll, and G. P. Robertson, editors. 2015. The ecology of agricultural ecosystems: long-term research on the path to sustainability. Oxford University Press, New York, New York, USA. (in press).
• Type: Journal Articles Status: Awaiting Publication Year Published: 2014 Citation: Robertson, G. P., P. R. Grace, R. C. Izaurralde, W. P. Parton, and X. Zhang. 2014. Questionable conclusions about the CO2 cost of stover removal from Midwest soils. Nature Climate Change. (in press).
• Type: Book Chapters Status: Awaiting Publication Year Published: 2015 Citation: Swinton, S. M., N. Rector, G. P. Robertson, C. B. Jolejole-Foreman, and F. Lupi. 2015. Farmer decisions about adopting environmentally beneficial practices. In S. K. Hamilton, J. E. Doll, and G. P. Robertson, editors. The ecology of agricultural ecosystems: long-term research on the path to sustainability. Oxford University Press, New York, New York, USA. (in press).
• Type: Book Chapters Status: Awaiting Publication Year Published: 2015 Citation: Snapp, S. S., R. G. Smith, and G. P. Robertson. 2015. Designing cropping systems for ecosystem services. In S. K. Hamilton, J. E. Doll, and G. P. Robertson, editors. The ecology of agricultural ecosystems: long-term research on the path to sustainability. Oxford University Press, New York, New York, USA. (in press).
• Type: Journal Articles Status: Awaiting Publication Year Published: 2014 Citation: Robertson, G.P. 2014. Sustainable agriculture. Daedalus (in press).
• Type: Book Chapters Status: Published Year Published: 2014 Citation: Pryor, S. C., D. Scavia, C. Downer, M. Gaden, L. Iverson, R. Nordstrom, J. Patz, and G. P. Robertson. 2014. Chapter 18: Midwest. Pages 418-440 in J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, eds. Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program. doi:10.7930/J0J1012N.
• Type: Book Chapters Status: Published Year Published: 2014 Citation: Robertson, G.P. 2014. Soil greenhouse gas emissions and their mitigation. Pages 185-196 in N.K. Van Alfen, editor. The Encyclopedia of Agriculture and Food Systems. Volume 5. Elsevier, San Diego, CA.
• Type: Journal Articles Status: Published Year Published: 2014 Citation: Robertson, G. P., K. L. Gross, S. K. Hamilton, D. A. Landis, T. M. Schmidt, S. S. Snapp, and S. M. Swinton. 2014. Farming for ecosystem services: an ecological approach to production agriculture. BioScience 64:404-415.
• Type: Journal Articles Status: Published Year Published: 2014 Citation: Shcherbak, I., N. Millar, and G. P. Robertson. 2014. Global meta-analysis of the nonlinear response of soil nitrous oxide (N2O) to fertilizer nitrogen. Proceedings of the National Academy of Sciences USA 111:9199-9204.
• Type: Journal Articles Status: Published Year Published: 2014 Citation: Shcherbak, I. and G. Philip Robertson. 2014. Determining the diffusivity of nitrous oxide in soil using in situ tracers. Soil Science Society of America Journal 78:79-88.
• Type: Book Chapters Status: Published Year Published: 2014 Citation: Ogle, S. M., P. R. Adler, F. J. Breidt, S. Del Grosso, A. Franzluebbers, M. Liebig, B. Linquist, G. P. Robertson, M. Schoeneberger, J. Six, C. van Kessel, R. Venterea, and T. West. 2014. Chapter 3: Quantifying greenhouse sources and sinks in cropland and grazing land systems. Pages 3.1-3.141 in M. Eve, D. Pape, M. Flugge, R. Steele, D. Man, M. Riley-Gilbert, and S. Biggar, eds. Quantifying greenhouse gas fluxes in agriculture and forestry: Methods for entity-scale inventory. Technical Bulletin Number 1939. Office of the Chief Economist, U.S. Department of Agriculture, Washington, DC.
• Type: Journal Articles Status: Published Year Published: 2014 Citation: Syswerda, S. P. and G. P. Robertson. 2014. Trade-offs and synergies in ecosystem services along a management intensity gradient in upper Midwest US cropping systems. Agriculture, Ecosystems & Environment 189:28-35.
• Type: Journal Articles Status: Published Year Published: 2014 Citation: Werling, B. P., T. L. Dickson, R. Isaacs, H. Gaines, C. Gratton, K. L. Gross, H. Liere, C. M. Malmstrom, T. D. Meehan, L. Ruan, B. A. Robertson, G. P. Robertson, T. M. Schmidt, A. C. Schrotenboer, T. K. Teal, J. K. Wilson, and D. A. Landis. 2014. Perennial grasslands enhance biodiversity and multiple ecosystem services in bioenergy landscapes. Proceedings of the National Academy of Sciences USA 111:1652-1657.
• Type: Theses/Dissertations Status: Published Year Published: 2013 Citation: Shcherbak, I. 2013. Production and movement of N2O in the full soil profile. Dissertation. Michigan State University, East Lansing, Michigan.
• Type: Theses/Dissertations Status: Published Year Published: 2014 Citation: Ruan, L. 2014. Impacts of biofuel crops on greenhouse gas emissions from agricultural ecosystems. Dissertation. Michigan State University, East Lansing, Michigan, USA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Kahmark, K. A., N. Millar, S. Bohm, S. Sippel, N. DiPiazza, Y. Bukhman, and G. P. Robertson. 2013. A new integrated analysis procedure for processing large volumes of near-continuous greenhouse gas concentration data. ASA, CSSA & SSSA International Annual Meeting, Tampa, Florida.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Gelfand, I., I. Shcherbak, and G. P. Robertson. 2013. Agricultural management and environment controls long-term soil nitrous oxide fluxes. American Geophysical Union Fall Meeting, San Francisco, California.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Millar, N., D. G. Baas, S. R. Miller, G. P. Robertson, and D. R. Mutch. 2013. Nitrous oxide emissions from cover crop systems in the US Midwest under conventional and organic management. ASA, CSSA, & SSSA International Annual Meeting, Tampa, Florida.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Millar, N., K. S. Kahmark, and G. P. Robertson. 2013. Nitrous oxide emissions at varying N rates from rainfed and irrigated row crops in the US Midwest. ASA, CSSA, & SSSA International Annual Meeting, Tampa, Florida.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Ruan, L., K. A. Kahmark, and G. P. Robertson. 2013. The impacts of changes in snowfall on wintertime soil greenhouse gas emissions using an automated chamber system. ASA, CSSA, & SSSA International Annual Meeting, Tampa, Florida.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Su, Y.-J., J. Chen, C. Shao, W. Shen, T. Zenone, R. John, M. Deal, S. K. Hamilton, and G. P. Robertson. 2013. Response of soil respiration to climate across biofuel crops and land use histories. American Geophysical Union Fall Meeting, San Francisco, California.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Hess, L. J. T., P. Matson, and G. P. Robertson. 2014. Changes in simulated rainfall intensity affect nitrogen transformations and leaching potentials in agricultural soils from conventional, no-till, and organic systems. Ecological Society of America Annual Meeting, Sacramento, California.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Shcherbak, I., N. Millar, and G. P. Robertson. 2013. A meta-analysis of the nonlinearity of direct annual N2O emissions in response to nitrogen fertilization. ASA, CSSA, & SSSA International Annual Meeting, Tampa, Florida.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Iverson, L., S. C. Pryor, D. Scavia, C. Downer, M. Gaden, R. Nordstrom, J. Patz, and G. P. Robertson. 2014. Climate change and the Midwest United States. Ecological Society of America Annual Meeting, Sacramento, California.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Roley, S. S., C. Xue, J. M. Tiedje, and G. P. Robertson. 2014. Evidence for nitrogen fixation in switchgrass. Ecological Society of America Annual Meeting, Sacramento, California.