Progress 04/15/11 to 04/14/16

Outputs
Target Audience:The target audience for this project was both scientists and practitioners, including extension agents and direct interactions with producers. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Training for 4 graduate students, one MS student who as a result of this work now works within the dairy industry; 1 MS who is now currently pursuing a PhD at Cornell University; 1 PhD student who is now a Research Scientist at ARS; and 1 MS student at UFL. An example of the outreach training includes a high school student from Hull, Georgia was involved in this project in partnership with the Young Scholars Program of the University of Georgia. He aided in field sampling, processing, and data analysis throughout the month of June 2013. This outreach effort exposed data from the project to the student involved, as well as introducing him to routine soil analysis methods and experimental design and implementation. He organized a poster and presented to other students and parents involved in the program. This presentation included summary data from experiments he conducted on MiGD soil samples. His experiments evaluated proposed methods found in the soil science literature to assess biological soil quality. How have the results been disseminated to communities of interest?We deployed a multi-level outreach effort that incorporates the following: (a) extension publications; (b) meetings/field-days with stakeholders and producers; (c) classroom instruction and site visits by college students; and (d) scientific presentations and publications. Results from this project were incorporated into our outreach/Extension activities. This includes routine in-service training for county Extension Agents by Dr. Dennis Hancock and communications with the GA/FL Grazing Dairy Network, a group of ~25 MiGD producers in Georgia and Florida who meet 2-3 times per year for educational trainings and peer-to-peer learning experiences on member farms. We estimate that in total we have referenced the research supported by this grant in at least 50 separate extension/outreach presentations to county, regional, and statewide producers/stakeholders. Our statewide extension specialist speaks on this work in approximately 30% of the presentations he conducts in 2016. This research is also routinely highlighted at extension conferences and field days for agribusinesses/producers working on pasture-based livestock systems throughout Southeast U.S. For instance, this research was highlighted at the Mid-Atlantic Dairy Conference, which was held in Moltre, GA in 2014. Participants in the conference toured two MiG Dairies and associated cheese and yogurt production facilities. Drs. Hancock and Thompson both gave field demonstrations of carbon accumulation associated with this emerging agricultural system. Dr. Hancock was responsible for the overall conference organization and planning. At the University level we have disseminated information from our field measurements in a Forage Management class taught to senior undergraduates and graduate students by Co-PI Nick Hill at the University of Georgia. For instance, the carbon accumulation data we have generated has been incorporated into Forage and Pasture Management (course number CRSS4260/6260) and Sustainable Agriculture (course number CRSS 4010) courses at the University of Georgia. Emphasis in the Forage Management course is to view management intensive grazing dairy (MiGD) system is both an environmentally and economically sustainable system. Field trips to pasture-based dairies include pasture walks, soil assessment, livestock assessment, and interviews with farm managers and owners as to the environmental and quality of life aspects of the farms. The course compares conventional confinement dairies with the pasture-based system and explains why the pasture-based system is a more sustainable economic model as well. Field trips to typical beef cattle and equine farms were made to contrast soil quality and quality of life of these livestock enterprises with that of the MiGD. Student projects utilize land area and animal resources of these farms and match their added knowledge on forage/pasture management to develop management intensive pasture systems for the beef and equine farms to enhance the environment and quality of life with hopes of the farms becoming models for MiG. This data substantiates the context of the class that animal production systems, which utilize high quality forages provide both economically and environmentally sustainable agricultural enterprises. Scientific publications and presentations: Our research has been disseminated to the scientific community through conference presentation, scientific presentations, and student theses and dissertations. This compliments our educational efforts in extension and outreach. For instance, after publication of the rapid C gain in the MiGD system (Machmueller et al 2015) we followed up with a lay-public report of the work (Melancon et al 2015) as well as several extension-oriented publications (Hancock, 2016) with more in the pipeline as farmer interest has peaked in the last year on this topic. What do you plan to do during the next reporting period to accomplish the goals?Although this grant has ended, we are still engaged in several activities that are a direct result of this funding. We will be resampling the farms after 10 yrs (research funding Enriched Isotope work conducted. Re-sampling farms within the next 5 yrs to assess rate of soil C accumulation after the apparent plateau phase reported tin Machmuller et al 2015. We have several other publications from our laboratory experiments that are either in review or nearing submission and should be published within the next two years. In addition, we will expand our analysis of the samples collected from the enriched isotope experiments by analyzing them using nanoscale secondary ion Mass Spectroscopy (Nano-SIMS). Because we have samples with non-degradable organic matter derived from a high 13C and 15N enrichment source, we expect to be able to identify which mineral phases are associated with the enriched material. We are applying for Nano-SIMS instrument time through national user laboratory applications.

Impacts
What was accomplished under these goals? Goal 1: Farmers select forage type and re-growth age for maximum animal nutrition and these parameters also impact ruminal methane production. Using a custom system we fermented Bermuda and Annual Rye Grass forage samples across a maturity gradient ranging from 14 d to 42 d of regrowth. Forages were harvested at five maturity dates from plots at the University of Georgia, freeze-dried. and ground (2-mm sieve). Thirty grams of forage was fed daily to separate dual-flow continuous fermenters equipped with a gas sensor system to measure methane concentrations in headspace for three 7 d periods. We found forage lignin and starch content best-predicted methane. This was incorporated into numerical models for forage-intensive dairy systems. Methane production per unit digestible forage was higher for Bermudagrass than annual ryegrass and changes with forage regrowth age. Overall we found that longer re-growth ages of the forage yield lower methane production, but the data are not consistent until very long re-growth intervals (42-d). This is substantially longer than typical practice on the farms we worked at. Acetate/propionate concentrations were not affected by maturity. Goal 2: The ratio of fibrous materials to protein present in the animal's diet will impact the chemical composition in deposited manure. We defined the substrate quality of the forage or manure using the ratio of neutral detergent fiber (NDF) content (a measure of the structural components: cellulose, hemicellulose, and lignin) to crude protein (CP). The ratio of NDF/CP represents the relative proportion of structural plant cell components vs. more nitrogen rich components. Lower NDF/CP values indicate higher substrate quality. Forage maturity (or re-growth age) also impacts substrate quality as plant biochemical composition changes with age. Older forage tends to have lower protein content and higher lignin content. We found that for Bermudagrass increasing forage re-growth age (maturity) and digestion of that material into manure both decreased substrate quality. Using both un-digested and ruminal-digested forage we examined the influence of substrate quality on the potential for the formation of stabilized carbon. Carbon inputs to grazed pasture systems effectively span a range of substrate quality. Higher quality substrates are more efficiently utilized by microbes, yet the relationship between substrate quality and the formation of stable SOM associations is still unclear. We hypothesized that high substrate quality (low NDF/CP) would preferentially form stable SOM associations in silt and clay fractions despite higher initial mineralization rates. To test this we incubated (a) bermudagrass forage litter cut after 14d, 21d, 28d, 35d, and 42d of re-growth and (b) ruminal digestate from those litters in soil for 139 d and evaluated the carbon dynamics (CO2 production; carbon content in the bulk, silt, and clay fraction; bacterial and fungal colony forming unit-CFU counts). We found that undigested bermudagrass litter was respired at higher initial rates, had increased bacterial abundance and resulted in more clay-associated SOM. Likewise, silt and clay associated SOM increased more for younger maturity treatments. Overall, our results demonstrate that substrate lability promotes C and N stabilization within soil silt and clay fractions during decomposition. Goal 3: We evaluated soil C accumulation for 3 years across a 7-year chronosequence of three farms converted to management-intensive grazing. We showed that these farms rapidly accumulated C, increasing cation exchange and water holding capacity by 95% and 34%, respectively (Machmuller et al 2015). The three farms we sampled were within 40 km of each other on deep, well-drained, fine or fine-loamy Kandiudults. Forage species in the pasture systems include a hybrid of bermudagrass and stargrass (Cynodon dactylon (L.) Pers. X C. nlemfuensis Vanderyst; cv. 'Tifton 85') as a perennial forage base (grown May through October) that is over-seeded in the fall with annual ryegrass (Lolium multiflorum Lam.; cv. 'Big Boss', 'Marshall', and/or 'Feast'). Individual paddocks received stock densities ranging from 75-150 animal units per ha during any given 12-hr period. Dairy cattle were rotated among 45-60 paddocks (depending upon farm layout) twice daily, completing a cycle of grazing all paddocks within 15-45 d, depending upon time of year, growth rate and quality of the forage, and the nutritional needs of the herd. We found peak C accumulation occurs 2-6 years after pasture establishment with a gain of 8.0 ± 0.85 Mg C ha-1 yr-1 (r2=0.88, p<0.0001) in the upper 30 cm of soil. Following an apparent lag in the first two years, the most recently established farm (converted in 2009) accumulated C at 4.6 Mg C ha-1 yr-1 (r2=0.79, p=0.0184), the middle-established farm (converted in 2008) accumulated C at an average rate of 9.0 Mg C ha-1 yr-1 (r2=0.80, p=0.0395), while the earliest-established farm (converted in 2006) accumulated C at 2.9 Mg C ha-1 yr-1 (r2=0.97, p=0.1125) before an apparent decline in accumulation rate at 6.5 years following conversion. In all cases, detectable increases in C accumulation were limited to the upper 30 cm, with variability below 30 cm yielding an integrated C accumulation rate of 7.1 ± 2.7 Mg C ha-1 yr-1 in the top meter (Machmuller et al 2015). This suggests accumulation at depth may require a longer timeframe or a shift in management practices. Machmuller, B. M. et al. Emerging land use practices rapidly increase soil organic matter. Nat. Commun. 6:6995 doi: 10.1038/ncomms7995 (2015). Goal 4: The C-accumulation benefits of adopting management-intensive grazing practices are notable. We used a whole farm C-sequestration calculation based on updating values from Belflower et al 2012, who compared the whole-farm C-cycle balance between a Georgia conventional dairy farm and one of the intensively grazed dairies used in our study (Farm Site ID-2008 reported here) using the Integrated Farm System Model (IFSM). They reported an emission rate of approximately 2,350,700 kg CO2 equivalents yr-1 for this farm. By factoring in our estimates of soil C accumulation (8.0 Mg C ha-1 yr-1), we calculate a net soil sequestration rate of ~1.58 Mg C-CO2 equivalents ha-1 yr-1 or ~ 5805 kg CO2 equivalents ha-1 yr-1. Further, we estimate that a soil C accumulation rate of 6.4 Mg C ha-1 yr-1 or higher is required for these systems to serve as a net C sink. While such a high rate cannot be maintained indefinitely following conversion, intensively grazed pasture does meet this criterion for at least an initial 5-year period following land use change. Cautiously extrapolating these results regionally, we estimate that if just 10% of the 9 million hectares of cropland in the southeastern US (average C-stock: 10 Mg C ha-1) were converted to management-intensive grazing land, approximately 4.5 Tg of C would be accumulated per year. Assuming peak SOC stocks in the top 30 cm were reached at 40 Mg C ha-1, this accumulation would continue for a minimum of six years, reaching a regional accumulation of 27 Tg C. Based on a whole farm C-cycle analysis, C accumulation appears to offset methane emissions (Belflower et al 2012) during the rapid soil C accumulation phase yielding net C-sequestration rates of ~1.6 Mg C-CO2 equivalents ha-1 yr-1 or ~5805 kg CO2 equivalents ha-1 yr-1. As the C accumulation rate declines these farms will become net C-emitting--like all dairy production--due to ruminant methane emissions. However, the substantial soil quality benefits of higher organic matter remain and will likely increase the sustainability of dairy production using management-intensive grazing. Belflower, J. B. et al. A case study of the potential environmental impacts of different dairy production systems in Georgia. Agricultural Systems 108, 84-93 (2012).

Publications

• Type: Journal Articles Status: Published Year Published: 2015 Citation: Machmuller, M. B., Kramer, M. G., Cyle, T. K., Hill, N., Hancock, D., and Thompson, A., 2015. Emerging land use practices rapidly increase soil organic matter. Nat Commun 6. doi: 10.1038/ncomms7995
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Hancock, D.W. 2016. Soil Organic Matter: The Secret to Successful Farming. Progressive Forage Grower Magazine. 17(3):44-46.
• Type: Journal Articles Status: Published Year Published: 2013 Citation: Hancock, D.W. 2013. Extension expertise: Soil Organic Matter: Pastures Temperature Gauge. Hay and Forage Grower. 28(2): 32-33.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Hancock, D.W. 2015. New forage research for producing better pasture-fed beef and dairy. Presentation at the Arkansas Forage and Grassland Councils Annual Meeting. 4 November 2015. Conway, AR.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Hancock, D.W. 2015. Issues facing forage and livestock producers. Presentation at the South Carolina Cattlemens Association Annual Meeting. 7 March 2015. Columbia, SC.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Hancock, D.W. 2015. Forage systems for warm season dairying. Presentation at the World Dairy Expo. 10 October 2015. Madison, WI.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Hancock, D.W. 2016. Storing carbon and building soil organic matter through grazing management. 29 April 2016. National Grassfed Exchange. Perry, GA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Hancock, D.W. 2015. Bermudagrass production and emerging issues. Presentation at the American Forage and Grassland Councils Warm Season Grass Workshop. 18 August 2015. Lexington, KY.
• Type: Journal Articles Status: Submitted Year Published: 2016 Citation: Substrate quality influences organic matter accumulation in the soil silt and clay fraction by K. Taylor Cyle, Nick Hill, Kaylin Young, Thomas Jenkins, Dennis Hancock, Paul Schroeder, and Aaron Thompson.
• Type: Journal Articles Status: Under Review Year Published: 2016 Citation: "Methane prediction by nutrient profiles in ruminal continuous cultures fed an all forage diet of bermudagrass or annual ryegrass" by K.M Young, W.C Stringer, J.G Andrae,N.S Hill, D.W Hancock, A. Thompson, and T.C Jenkins

Progress 04/15/15 to 04/14/16

Outputs
Target Audience: Nothing Reported Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Graduate student Taylor Cyle defended his thesis based on this work and submitted one of his papers. How have the results been disseminated to communities of interest?Results from this project are continuing to be incorporated into our outreach/Extension activities. This includes routine in-service training for county Extension Agents by Dr. Dennis Hancock and communications with the GA/FL Grazing Dairy Network, a group of ~25 MiGD producers in Georgia and Florida who meet 2-3 times per year for educational trainings and peer-to-peer learning experiences on member farms. We published one manuscript on the MiGD chronosequence, noting what an extremely high rate of carbon accumulation during the first 6 years of MiGD conversion (Machmuller et al 2015). We submitted the first of several manuscripts on the stability of accumulated C in these soils. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? OUTPUTS: April 1, 2015 TO March 31, 2016 In our fifth year of this project we focused on writing manuscripts and outreach newsletters to disseminate our research findings to the scientific community and the agricultural producers, etc. IMPACT: April 1, 2015 TO March 31, 2016 We published one manuscript on the MiGD chronosequence, noting what an extremely high rate of carbon accumulation during the first 6 years of MiGD conversion (Machmuller et al 2015). We submitted the first of several manuscripts on the stability of accumulated C in these soils. Machmuller, M. B., Kramer, M. G., Cyle, T. K., Hill, N., Hancock, D., & Thompson, A. (2015). Emerging land use practices rapidly increase soil organic matter. NATURE COMMUNICATIONS, 6. doi:10.1038/ncomms7995

Publications

• Type: Journal Articles Status: Published Year Published: 2015 Citation: Machmuller, M. B., Kramer, M. G., Cyle, T. K., Hill, N., Hancock, D., & Thompson, A. (2015). Emerging land use practices rapidly increase soil organic matter. NATURE COMMUNICATIONS, 6. doi:10.1038/ncomms7995
• Type: Other Status: Published Year Published: 2015 Citation: Melancon, J., Machmuller, M., Hancock, D., Hill, N., Cyle, K. T., & Thompson, A. (2015). Farmland management changes can boost carbon sequestration rates. UGA News Service.
• Type: Book Chapters Status: Published Year Published: 2015 Citation: Perdrial, J. N., Thompson, A., & Chorover, J. (2015). Chapter 6: Soil Geochemistry in the Critical Zone: Influence on Atmosphere, Surface- and Groundwater Composition.. In Principles and Dynamics of the Critical Zone (pp. 173-201). Elsevier.
• Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Thompson, A. (2015). Critical zone research at the University of Georgia. In Seminar at the University of Padua, Italy. Padua, Italy.

Progress 04/15/14 to 04/14/15

Outputs
Target Audience: Nothing Reported Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest?OUTREACH: April 1, 2014 TO March 31, 2015 Results from this project are continuing to be incorporated into our outreach/Extension activities. This includes routine in-service training for county Extension Agents by Dr. Dennis Hancock and communications with the GA/FL Grazing Dairy Network, a group of ~25 MiGD producers in Georgia and Florida who meet 2-3 times per year for educational trainings and peer-to-peer learning experiences on member farms. Kramer presented research results from the MiGD project at more than 5 invited talks and scientific conferences in 2014 as part of a synthesis talk focused on understand global change through long-term experiments. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? OUTPUTS: April 1, 2014 TO March 31, 2015 In our fourth year of this project we continued to (a) write up data from our enteric methane and CO2 flux experiments and continuing to analyze changes in manure composition as a function of forage species and maturity (Obj. 1 and 2), (b) we completed our incubation experiments to understand the decomposition and longterm stabilization of carbon inputs (Obj. 3) and (c) we are continuing to quantify changes in carbon stocks across our Management Intensive Grazing Dairy (MiGD) chronosequence (Obj. 3). (a) Gas flux and manure composition as function of forage species and maturity We have processed and analyzed the remaining samples from our forage and manure characterization study, which quantifies methane flux as a function of Bermuda and Annual Rye Grass forage samples across a maturity gradient of ranging from 14 d to 42 d of regrowth. (b) Decomposition of carbon inputs as a function of forage species and maturity We conducted incubation experiments with the isotopically labeled forage and manure analogs, Our plan is to use these resulting materials to investigate the location of newly sequestered C via micro-scale methods (i.e., Nano-SIMS). Graduate student Brandon Snook at University of Florida completed soil column irrigation and incubation experiments to determine the rate of CO2 evasion and carbon loss from soils as a function of time since establishment across the chronosequence. He used simulated irrigation to match historical rainfall records and an IRGA C02 analyzer to track C loss. (c) Soil Carbon Stocks and fluxes across the MiGD Chronosequence We have focused on writing up publications related to the changes in C stocks and fluxes across the chronosequence. IMPACT: April 1, 2014 TO March 31, 2015 (a) Nothing significant to report this period. (b) Graduate student Brandon Snook found a higher rate of CO2 loss year-1 on the youngest chronosequence, which progressively declines a function of time since establishment. Mass balance calculations on the number of years it would take to lose all C inputs from MiGD. Snook also separated particulate organic matter (POM) from mineral associated as well performed particle size analysis on the various fractions. The results indicate that while most soil C accumulation can be attributed to POM, the form of POM appears to shift from root contributed C toward a more highly processed protein rich form (largely due to manure inputs). Mass balance calculations indicate while soil C accumulation takes six to eight years to reach an apparent plateau, it would take up to twenty years to lose all of the soil C that has accumulated if MiGD were discontinued. (c) Graduate student Megan Machmuller submitted a manuscript based on the group project data on soil properties and soil C to nature communications. The manuscript which hightlights key findings from the project will soon be published.

Publications

• Type: Other Status: Published Year Published: 2015 Citation: [Invited Seminar] Kramer MG. University of Florida. Soil Organic Matter Dynamics and Global Change: Evidence from Field Experiments. Howard T. Odum Center for Wetlands. February 2015.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Cyle, K., & Thompson, A. (2014). From grass to manure: How does digestion affect decomposition and SOM formation?. In Plant and Soil Graduate Symposium. Athens GA: CAES.
• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Cyle, K., Thompson, A., Hill, N., & Hancock, D. (2014). The effects of forage maturity and ruminal digestion on substrate decomposition and the formation of organomineral associations.. In 6th International Symposium on Soil Organic Matter. Kiawah Island, S.C..
• Type: Other Status: Published Year Published: 2015 Citation: Thompson, A. (2015). Management intensive grazing rapidly increases soil organic matter. In Sustainable Food Systems Initiative Symposium. Athens, GA.

Progress 04/15/13 to 04/14/14

Outputs
Target Audience: We communicated with the target audience of farmers at several on-farm field days conducted by Co-PI Dennis Hancock. In addition, the annual grazing school continues to feature the results of this research each year. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? At the University level we continue to disseminate information from our field measurements in a Forage Management class taught to senior undergraduates and graduate students by Co-PI Nick Hill at the University of Georgia. This project constituted the thesis research for three MS students, with one student Kaylin Young graduating during the reporting period. Kaylin has gone on to do work associated with MiG dairy opperations. In summer 2013, a high school student from Hull, Georgia was involved in this project in partnership with the Young Scholars Program of the University of Georgia. He aided in field sampling, processing, and data analysis throughout the month of June 2013. This outreach effort exposed data from the project to the student involved, as well as introducing him to routine soil analysis methods and experimental design and implementation. He organized a poster and presented to other students and parents involved in the program. This presentation included summary data from experiments he conducted on MiGD soil samples. His experiments evaluated proposed methods found in the soil science literature to assess biological soil quality. How have the results been disseminated to communities of interest? OUTREACH: April 1, 2013 TO March 31, 2014 Results from this project are continuing to be incorporated into our outreach/Extension activities. This includes routine in-service training for county Extension Agents by Dr. Dennis Hancock and communications with the GA/FL Grazing Dairy Network, a group of ~25 MiGD producers in Georgia and Florida who meet 2-3 times per year for educational trainings and peer-to-peer learning experiences on member farms. In Fall 2014, this research was also highlighted at the Mid-Atlantic Dairy Conference, which was held in Moltre, GA this year. Participants in the conference toured two MiG Dairies and associated cheese and yogurt production facilities. Drs. Hancock and Thompson both gave field demonstrations of carbon accumulation associated with this emerging agricultural systems. Dr. Hancock was responsible for the overall conference organization and planning. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? OUTPUTS: April 1, 2013 TO March 31, 2014 In our third year of this project we focused on (a) writing up data from our enteric methane and CO2 flux experiments and continuing to analyze changes in manure composition as a function of forage species and maturity (Obj. 1 and 2), (b) finalizing our first set of incubation experiments to understand the decomposition and longterm stabilization of carbon inputs (Obj. 3) and (c) continuing quantification of changes in carbon stocks across our Management Intensive Grazing Dairy (MiGD) chronosequence (Obj. 3). (a) Gas flux and manure composition as function of forage species and maturity Using data from our custom modified fermenters we have written a manuscript draft quantifying methane flux as a function of Bermuda and Annual Rye Grass forage samples across a maturity gradient of ranging from 14 d to 42 d of regrowth. This work constituted the MS thesis of Kaylin Young (Clemson). (b) Decomposition of carbon inputs as a function of forage species and maturity Ahead of conducting incubation experiments with the isotopically labeled forage and manure analogs, we conducted a experiments using non-labeled materials. These experiments were designed to answer questions regarding the influence of substrate quality on the potential for the formation of stabilized carbon. Carbon inputs to grazed pasture systems effectively span a range of substrate quality, which we assessed as the ratio of neutral detergent fiber (NDF-cellulose, hemicellulose, and lignin) to crude protein (CP). Higher quality substrates are more efficiently utilized by microbes, yet the relationship between substrate quality and the formation of stable SOM associations is still unclear. We hypothesized that high substrate quality (low NDF/CP) would preferentially form stable SOM associations in silt and clay fractions despite higher initial mineralization rates. To test this hypothesis, we incubated (a) bermudagrass forage litter cut after 14d, 21d, 28d, 35d, and 42d of re-growth and (b) ruminal digestate from those litters in soil for 139 d and evaluated the carbon dynamics (CO2 production; carbon content in the bulk, silt, and clay fraction; bacterial and fungal colony forming unit-CFU counts). (c) Soil Carbon Stocks and fluxes across the MiGD Chronosequence We have continued to resample the MiGD chronosequence farms throughout 2013 following similar protocols to previous sampling events. Carbon concentration, δ13C and δ15N were measured on all samples on both bulk and clay-particle size fractions, In addition to soil analyses, we continue to determined aboveground and belowground biomass and calculated estimates for aboveground and belowground productivity. Megan Machmuller (PhD, UGA) prepared a manuscript draft to report these findings. In addition, in July 2013 we sampled the farms to measure the potential for organic matter loss considering the scenario where these farm converted back to Row Crop agriculture. Brandon Snook (MS at University of Florida) used these samples to initiated soil column irrigation and incubation experiments. The goal of these experiments was to determine the rate of CO2 evasion and carbon loss from soils as a function of time since establishment across the chronosequence. We used simulated irrigation to match historical rainfall records, and an IRGA C02 analyzer to measure CO2 loss. We also performed mass balance calculations on the number of years it would take to lose all C accumulated during the MiGD activities. IMPACT: April 1, 2013 TO March 31, 2014 (a) Nothing significant to report this period. (b) From our unlabeled incubation experiments, we found that undigested bermudagrass litter was respired at higher initial rates, had increased bacterial abundance and resulted in more clay-associated SOM. Likewise, silt and clay associated SOM increased more for younger maturity treatments. Overall, our results demonstrate that substrate lability promotes C and N stabilization within soil silt and clay fractions during decomposition. (c) Our bi-annual chronosequence sampling campaign continues to find support for an extremely rapid soil C accumulation rate following the land-use change from row-crop to MiGD. We submitted a manuscript describing these results. For our soil column experiments determiner the rate of carbon loss from soils assuming a reverse conversion to row crop agriculture as a function of time since establishment across the chronosequence, we found a higher rate of CO2 loss year-1 on the youngest farm in the chronosequence, with progressively lower rates of as a function of time since establishment.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Cyle, K.T. and A. Thompson. (2014) The effects of forage maturity and ruminal digestion on substrate decomposition and the formation of organomineral associations .USDA-NIFA Project Directors Meeting, Gainesville, FL, 2014.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Snook, B., Kramer, M., Thompson, A. Soil Carbon Storage and Persistence Across a Chronosequence Of Management Intensive Grazing Dairies, An Emerging Land Use Practice In East Central Georgia. Annual meeting of the Soil Science Society of America. Tampa, FL. November 2013
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Cyle, K. T., Thompson, A., Kramer, M., Machmuller, M., Hill, N. Assessing the stabilization of rapidly accumulating carbon associated with management intensive grazing dairies in the southeastern United States. ZFM Summer School. Liebniz Universitat. Goslar, Germany. July 2013.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Thompson, A., Megan B Machmuller, Kevin Taylor Cyle, Marc Kramer, Nicholas S. Hill and Dennis W. Hancock. Rapid Carbon Accumulation Across a Chronosequence of Land Conversion to Grazing Dairies. Annual meeting of the Soil Science Society of America. Tampa, FL. November 2013
• Type: Other Status: Other Year Published: 2013 Citation: Kramer MG[Invited Seminar] Soil Organic Matter Dynamics and Global Change: Evidence from Field Experiments. University of Georgia. Department of Crop and Soil Science. October 2013.
• Type: Other Status: Other Year Published: 2013 Citation: Kramer MG [Invited Seminar] Soil Organic Matter Dynamics and Global Change: Evidence from Field Experiments.Tropical Research and Education Center, Homestead, FL Nov 2013.
• Type: Other Status: Other Year Published: 2013 Citation: Kramer MG [Invited Seminar] Soil Organic Matter Dynamics and Global Change: Evidence from Field Experiments. University of Florida, Soil and Water Science -Research Symposium. Sept 2013.
• Type: Other Status: Other Year Published: 2013 Citation: Kramer MG [Invited Seminar] Soil Organic Matter Dynamics and Global Change: Evidence from Field Experiments.Sonoma State University, Department of Geography. Dec 2013.

Progress 04/15/12 to 04/14/13

Outputs
Target Audience: Nothing Reported Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? At the University level two MS students and one PhD student received training on this project in the reporting period including attending and presenting research results at national conferences. In addition, we have disseminated information from our field measurements in a Forage Management class taught to senior undergraduates and graduate students by Co-PI Nick Hill at the University of Georgia. For instance, the carbon accumulation data we have generated has been incorporated into Forage and Pasture Management (course number CRSS4260/6260) and Sustainable Agriculture (course number CRSS 4010) courses at the University of Georgia. Emphasis in the Forage Management course is to view management intensive grazing dairy (MiGD) system is both an environmentally and economically sustainable system. Field trips to pasture-based dairies include pasture walks, soil assessment, livestock assessment, and interviews with farm managers and owners as to the environmental and quality of life aspects of the farms. The course compares conventional confinement dairies with the pasture-based system and explains why the pasture-based system is a more sustainable economic model as well. Field trips to typical beef cattle and equine farms were made to contrast soil quality and quality of life of these livestock enterprises with that of the MiGD. Student projects utilize land area and animal resources of these farms and match their added knowledge on forage/pasture management to develop management intensive pasture systems for the beef and equine farms to enhance the environment and quality of life with hopes of the farms becoming models for MiG. Two students have completed their degree programs and now are managing MiGD farms. Plans are to visit these farms in the future for assessment of the system by peers of similar age to the University students for added validation of the MiGD system. A lecture in the Sustainable Agriculture course was provided to illustrate how a change in land management impacts soil quality. How have the results been disseminated to communities of interest? Results from this project are continuing to be incorporated into our outreach/Extension activities. This includes routine in-service training for county Extension Agents by Dr. Dennis Hancock and communications with the GA/FL Grazing Dairy Network, a group of ~25 MiGD producers in Georgia and Florida who meet 2-3 times per year for educational trainings and peer-to-peer learning experiences on member farms. In spring 2013, this research was also highlighted at a conference and field day for agribusinesses that service pasture-based livestock industries in the Southeast U.S. Plans are also being advanced with both Burke and Jefferson Counties extension agents to incorporate this research into hands-on learning opportunities for local high school Earth Science classes. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? IMPACT: April 1, 2012 TO March 31, 2013 (a) We have found that feeding bermudagrass at 42 d decreased overall average methane production compared to the average of all other maturity treatments. Methane per g of dry mater or g of neutral detergent fiber fed had similar differences between maturities. Acetate/propionate concentrations were not affected by maturity. Our data suggest that forage maturity between 14 and 35 days has no effect on rumen methane production, but that feeding forages at maturities of 42 days does result in a decrease in methane production. (b) At the termination of all labeling periods, bermudagrass of 21-day and 42-day maturities had isotopic values of ~7 and 8 atom percent 13C and 1.4 and 1.3 atom percent 15N, respectively. Likewise composited annual ryegrass samples had isotopic values of 8 and 10 atom percent 13C and 2.4 and 1.2 atom percent 15N, respectively. This represents roughly 6 percent atom excess or greater 13C and 0.8 percent atom excess or greater 15N. (c) Our bi-annual chronosequence sampling campaign has found the land-use change from row-crop to MiGD is stimulating an extremely rapid soil C accumulation rate that persists for at least the first six years of conversion. Although many aggregating tropical forests accumulate C in aboveground biomass faster, the row-crop to MiGD land use change in the southeastern US accumulates C in the soil on par with the fastest rates yet reported. We suspect this high accumulation rate likely stems from a low initial C content due to till agriculture, a warm climate favorable to year round forage growth, management methods (irrigation and fertilization) to maximize forage production, and continuous return of manure to the grasslands.

Publications

• Type: Conference Papers and Presentations Status: Accepted Year Published: 2012 Citation: Cyle, K. T., Thompson, A., Kramer, M., Machmuller, M., Hill, N. Rapid Association of Clay Fraction Carbon in Soil from Grazing Dairy Pastures. ESA Annual Meeting, Portland, OR, poster presentation, August 2012
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2012 Citation: Machmuller, M.B., Taylor, K.T., Kramer, M., Hill, N. Thompson, A. Carbon accumulation across a chronosequence of land conversion to grazing dairies. ESA Annual Meeting, Portaland OR, oral presentation, August 2012.

Progress 04/15/11 to 04/14/12

Outputs
OUTPUTS: In our first year of this project we have focused on (a) designing and modifying equipment to quantify enteric methane and CO2 fluxes and determine changes in manure composition as a function of forage species and maturity (Obj. 1 and 2) and quantifying baseline carbon stocks and fluxes across our Management Intensive Grazing Dairy (MiGD) chronosequence (Obj. 3). (a) Gas flux and manure composition as function of forage species and maturity: Monitoring methane production from fermentation of forage in our simulated rumen reactors is a key objective of this project that required modification of our existing fermentors. After exploring commercially available biogas analyzers we designed a custom system to interface with our fermentors using component parts purchased from various vendors and in-house design expertise. Assembly of the system is underway to provide continuous monitoring of methane, carbon dioxide, and oxygen concentrations along with a central flow meter to calculate daily gas production from each of the 8 fermenters slated for this project. The system construction is expected to be complete by the end of April, 2012 and we will begin fermentation of forage samples in May, 2012. Toward this end we have harvested Bermuda grass across a maturity gradient of ranging from 7 d to 48 d of regrowth, and it is prepared for introduction to our fermentors. In addition, we have designed and purchased a growth chamber and gas flow system to produce 13C labeled forages for use in our fermentation experiments and subsequent soil incubations with labeled manure from these forages. (b) Soil Carbon Stocks and fluxes across the MiGD Chronosequence Total soil carbon and nitrogen concentrations, particle size and natural abundance stable isotopes (13C, 15N) have been measured in 1m deep representative soil pits and in composite cores of the top 5, 15 and 30cm at each of the sites across the MiGD chronosequence. The above ground biomass forage species and root biomass were sampled for stable isotope determination. Carbon concentration and composition measurements were separated into different depths and measured on bulk and clay-particle size fractions. A suite of carbon compositional methods have been developed and utilized including 13C-NMR, pyrolysis GC-MS, and a lignin extraction method. A subset of samples have been utilized to examine mineral assemblage using X-ray diffraction and selective extractions. We have begun a carbon lability experiment using 30% hydrogen peroxide and microbial incubations on both bulk and clay-particle size fractions. Total C and N as well as stable isotopes (13C, 15N) were measured throughout the experiment. Carbon compositional changes were also tracked at the beginning and end of the incubation using pyrolysis GC-MS. Field carbon dioxide flux measurements have been conducted monthly at each chronosequence site beginning in October 2011 using a Licor 6400XT and PVC collars placed in the field. Carbon compositional measurements described above will be utilized to determine the degree of soil organic matter decomposition at each depth and within each particle size fraction. PARTICIPANTS: Aaron Thompson (PI/PD) Nick Hill (PI) Dennis Hancock (PI) Tom Jenkins (PI) Marc Kramer (PI) Megan Machmueller (PhD student) K. Taylor Cyle (Undergraduate) Kaylin Young (MS student) Kelly Hughs (MS student) TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
Our carbon stock analysis has shown total and clay-associated soil carbon increased since time of conversion in the top 40 cm, with the greatest increase occurring from 3-5 years since land-use change. This resulted in a 63% increase in surface (0-5cm) bulk soil carbon and a 24% increase in clay-associated soil carbon. We observed root mass to increase from 1.9 g kg-1 to 45.9 g kg-1 soil from 2-5 years since conversion, an indication that long-term rotational grazing strategies increase belowground primary productivity. We also found that carbon in the top 40 cm of accumulation to trend towards isotopic enrichment (&#948;13C; -21.5) in bulk and clay fractions. Overall, the oldest site (5 years since conversion) exhibited the highest carbon dioxide flux (p<0.005) and was approximately 50% higher than the other two sites (2 and 3 years since conversion). Results from this project have already begun to be incorporated into our outreach/Extension activities. For example, preliminary data and materials from this effort have been included in a 2-day in-service training for county Extension Agents, USDA-NRCS personnel, and regulators from state departments of agriculture in the spring of 2011. Over 112 such persons came from 11 southeastern states to attend this training. These workshops provided in-depth information and hands-on activities on MiGD (see: http://www.caes.uga.edu/commodities/fieldcrops/forages/events/PBDSumm it/PBDSummit.html). The preliminary data and materials from this effort have also been communicated to the GA/FL Grazing Dairy Network, a group of ~25 MiGD producers in Georgia and Florida who meet 2-3 times per year for educational trainings and peer-to-peer learning experiences on member farms. In addition, we have disseminated information from our field measurements in a Forage Management class taught to senior undergraduates and graduate students by Co-PI Nick Hill at the University of Georgia. This data substantiates the context of the class that animal production systems, which utilize high quality forages provide both economically and environmentally sustainable agricultural enterprises.

Publications

• Thompson, A., Kramer, M., Hill, N., Hancock, D., and Jenkins, T. Carbon cycling in Management Intensive Grazing Dairy systems. Global Soil Change -- NSF/Duke University Calhoun Experimental Forest, S.C. & Cowetta Hydrologic Lab, NC, June 13-16, 2011. Invited Poster
• Thompson, A., Kramer, M., Machmuller, M., Cyle, K. T., Hill, N. Changes in soil carbon cycling accompanying conversion of row-crop to grazing dairy. American Geophysical Union. San Francisco, CA. December, 2011. Volunteered Poster