Lighting up the black box: Improving legume performance on organic farms by optimizing microbially-mediated plant and soil nitrogen cycling processes.

Final Report for LS10-227

Project Type: Research and Education
Funds awarded in 2010: $192,000.00
Projected End Date: 12/31/2014
Region: Southern
State: North Carolina
Principal Investigator:
Dr. Julie Grossman
University of Minnesota
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Project Information


We evaluated four cover crop termination treatments (organic herbicide, flail mowing, rolling, incorporation) with three cover crop species (hairy vetch, crimson clover, Austrian winter pea) to determine decomposition rate and nitrogen delivery. Hairy vetch had the greatest overall average nitrogen contribution. Disking was found to release hairy vetch N most rapidly, contributing the most N at 6-10 weeks after termination. An evaluation of nodule rhizobia occupants found native rhizobia to be out-competing the inoculant for nodule occupancy, as most nodules evaluated were found to contain native soil rhizobia rather than inoculant rhizobia.

Project Objectives:

Objective 1: Randomly survey 200 organic growers from North and South Carolina, in order to determine current rhizobia inoculant handling procedures, and production challenges and perceived benefits of legume cover crop use.


Objective 2: Establish three demonstration plots on working organic farms to learn about the impact of inoculation on nodulation and legume production.


Objective 3: Determine how various methods of legume cover crop termination common in organic farming systems (rolling, disking, and flail mowing) impact indicators of microbial activity and N supply to crop plants.


Objective 4: Disseminate results to agronomic organic growers and jointly educate organic growers and students nationwide about soil microbial N-cycling processes in sustainable agriculture.



The purpose of this project is to improve legume cover crop management by examining key soil microbial processes that regulate nitrogen (N) cycling in organic agriculture. In parallel, we seek to improve stakeholder knowledge of soil microbial processes by developing an integrated educational and outreach program involving farmers and soil ecology students. Organic grain production is an emerging market in the Southern region of the U.S. and many questions exist about how to increase efficiency of N delivery to crops from organic residues. This project will strengthen organic production in the long term by providing growers with information about how to best manage legumes to encourage beneficial microbial interactions, and how to manage cover crop residue for optimal N release in Southern climates. Short-term project impacts include improved farmer decision making about legume management, and improved student understanding of nutrient management challenges facing organic growers.

All farming systems, organic and conventional, require nutrients to be made available to crop plants at critical points in the plants lifecycle. Soluble inorganic fertilizers used by conventional growers are made available immedi­ately to plant roots, so nutrient application is timed to coincide with crop uptake need. In contrast, organic farmers rely on cover crops and other organic nutrient sources that require microbial activity to make them available to crop plants. It is critical that we know how to design agroecosystems where nutrient availability from certified organic sources is maximized, yet we are only just beginning to understand how organic management practices influence soil nutrient cycling and availability. 

Organic growers cite nutrient management as one of their most serious and intractable problems. Nitrogen management in particular is a critical, and often a costly, practice for organic growers. Long term USDA organic cropping experiments have shown that supplying adequate N for corn is the biggest challenge to achieving equivalent yields between organic and conventional cropping systems (Cavagelli et al., 2008). Nitrogen is often the most limiting nutrient in organic systems (Gaskell and Smith, 2007), while at the same time inefficient N management can lead to water body contamination and widespread environmental degradation (Mitsch, et al., 2002). As legume based systems have reduced carbon and N losses (Drinkwater et. al, 1998), efforts to maximize the efficiency of legume N delivery in organic systems at the time of greatest crop need (Crews et al., 2005) is in desperate need of study.

Growers with whom we work would appreciate additional information about two key microbially-driven processes they utilize on their farms, biological nitrogen fixation (BNF) and mineralization of legume residues. One common management practice in organic farms, as well as on increasing numbers of conventional farms due to costly synthetic N fertilizers, includes the use of legume cover crops. Legume cover crops can increase plant-available nitrogen through their symbiotic association with specific nodule forming, di-nitrogen fixing bacteria, or rhizobia, housed in legume root nodules.  Through the process of BNF, legumes associated with the appropriate root nodule bacteria can improve the nitrogen economy of an agricultural system and in some cases eliminate or reduce the need for supplemental N fertilization from manures or other organic sources. Biological nitrogen fixation is a major source of new nitrogen entering organic farming systems. Growers are eager to understand the functioning of the belowground soil community responsible for making nitrogen available to crops through cover crop management, including rhizobia ecological interactions, mycorrhizal fungi associations, and microbial mineralization of legume residue. Understanding these processes will help farmers better manage their legume cover crops for improved N cycling and availability.

Highly efficient strains (types) of rhizobia are often added with legume seeds at planting, a process called inoculation. While most organic growers inoculate their cover crop legumes with a recommended rhizobia inoculant, little is known about the ecology and the efficiency of rhizobia in fields under organic management. In many places where legumes are cultivated, indigenous or native populations of rhizobia are also plentiful in the soil. In some regions these native rhizobia can be beneficial as they may allow for improved legume production without inoculation. In contrast, soils containing an abundance of native rhizobia can be problematic if they are competitive with the strain introduced through inoculation and prove to be less efficient in fixing nitrogen than the inoculant strain (Obaton et al., 2002; McDermott and Graham, 1990)

Recent research results indicate that rhizobia ecology of legume cover crops is quite complex. Previous work conducted by Dr. Grossman at Cornell University found greater diversity in nodule occupancy among organic farm-grown legumes than conventional, even across sites where legumes received the same inoculant strain formulation. This calls into question the origin of the rhizobia diversity observed in the nodules; were the bacteria from the inoculant or resident soil populations? Here at NC State we have made some headway in answering this question with regards to cover crop nodules. Our preliminary results are indicating nodules of hairy vetch are more likely to contain native rhizobia strains rather than the applied inoculants, leading us to question the competitive ability of background rhizobia already present in soils where legumes have been planted for many years. Often organic growers have been using various legume species for many growing seasons, possibly increasing the number of background rhizobia able to compete with the introduced inoculant. Nodule formation by competitive resident soil rhizobia may result in reduced overall legume N contribution to the organic system if that strain is shown to be less efficient in N-fixation. As part of this project we will investigate rhizobia ecology and assess diversity of rhizobia within and among organic farm soils. Since organic farmers often use a variety of legumes in rotation, we hypothesize that native populations of rhizobia present at planting will affect nodulation and nodule occupancy in desired legume crops.

 Along with the ecological interactions of rhizobia in farm soils, the efficacy of the inoculants themselves is also of critical importance. There appears to be great variation in how farmers are handling and using inoculants, including practices that damage rhizobia and possibly render them useless. In conversations with organic grain growers at workshops in North Carolina we were told that some growers inoculate at planting, others do not, and most have a wide range of inoculant application and storage techniques. As inoculant contains live rhizobia, its effectiveness is based on the number of viable organisms present in the product at legume planting. Recent research carried out in the Grossman laboratory demonstrated that numbers of viable rhizobia in a random sample of commercial cover crop inoculants ranged from 4-68% of the commercially guaranteed minimum levels (Ballard and Grossman, 2008). These low numbers will limit the numbers of viable rhizobia entering the soil and reduce overall nodulation and nitrogen fixation from the inoculant strain. We would like to understand how farmers are handling inoculants so that we can improve the viability and success of rhizobia inoculation.

Further, organic growers have a wide range of legume cover crop choices to include in their farming system. As researchers at NC State, we are contacted on a regular basis by growers questioning which legume species might be their best options to provide plenty of plant biomass and fixed N to their cropping systems. We suspect that farmer decision-making regarding cover crop choice is based on a combination of economic and production data, as well as experience and information-sharing between growers. Using a rigorous survey of organic growers in North and South Carolina, we will assess current inoculation use and handling techniques, as well as perceived challenges to and benefits of using different species of winter annual legume cover crops.

In order for organic growers to fully benefit from legumes in their organic systems, it is critical that we understand many distinct pieces of the ‘N-input puzzle’, including the nodule occupants and their efficiency and the timing of N availability under various cover crop management practices. Growers are ultimately concerned with the total N that is made available for crop growth, either from soil organic matter or cover crop decomposition, so that N availability is synchronous with crop demand. There is a wealth of previous research demonstrating the utility of winter legume cover crop in increasing N availability to crops in the Southeast (i.e. Wagger, 1989; Rannels and Wagger, 1997a; 1997b). However, recent advances in cover crop breeding (Devine, 2008) have raised important questions about the performance of early-flowering cover crop populations, especially in the context of organic agriculture.  

Legume termination (kill) methods vary by farmer objectives and implement availability, but widely used practices include various combinations of mowing the cover crop, soil incorporation, and rolling/crimping using a large water-filled drum. Rolling and mowing leave residues on the soil surface where they are in less contact with decomposing soil organisms, while incorporation increases the decomposer-residue contact. Mowing and tillage intensity have been shown to increase N mineralization rate in hairy vetch (Snapp and Borden, 2005; Drinkwater et al., 2000), however we have found no studies comparing the 3 common termination practices mentioned above, especially in the absence of glyphosate treatment. Further, we predict that the warmer climes in the Southeast will impact both cover crop production and mineralization rates as microbes are known to ‘speed up’ their metabolic activities in warmer conditions and likely decompose residues at a much faster rate.  We will investigate how non-chemical legume kill method (rolling-crimping, flail mowing, and incorporation) impact N availability from decomposing legume residues. Since methods of legume termination place the killed cover crop at different points of contact with soil microorganisms (surface vs. in soil), we hypothesize that mineralization rates will be influenced. 


Click linked name(s) to expand/collapse or show everyone's info
  • Dr. Sarah Bowen
  • Dr. Amy Germuth
  • Dr. Michelle Schroeder-Moreno
  • Dr. Wei Shi


Materials and methods:

Objective 1 Methods: In 2010 a survey containing questions related to legume inoculant use was administered to over 500 farmers, resulting in 82 responses, falling short of our initial goal of 200 even after follow-up with survey recipients and an incentive prize drawing for those who responded. The survey focused on cover crop choice, inoculation approaches, inoculant care and maintenance, information sources, and farm demographics. The growers' responses were compared with the most recommended practices by extension, manufacturers and the literature.


Objective 2 Methods:Commercial rhizobia inoculant is often added at planting to increase legume biological nitrogen fixation (BNF) and is of particular importance in organic farming systems where cover crop BNF is a leading fertility source.  To maximize nitrogen contribution, a better understanding of inoculation effectiveness in the presence of established soil rhizobia populations is needed. This objective attempted to respond to these needs.  Fall of 2010 we established three demonstration plots on organic land in North Carolina, located on 3 organic farms, each planted with 4 legume cover crop varieties:  crimson clover (Trifolium incarnatum L) cultivar Dixie, hairy vetch (Vicia villosa Roth) cultivar Auburn Early, Austrian winter pea (Pisum sativum subsp. Arvense), and woolypod vetch (Vicia villosa Roth) cultivar lana.   Cover crop root nodules from all farms and cover crop varieties were harvested to analyze nodule occupancy.  Five-hundred-fifty nodules were used total - half from inoculated treatments, and half from nodules only exposed to native soil populations. ??


Objective 3 Methods: The goal of this objective is to identify leguminous winter cover crops and methods for incorporation that achieve the optimal synchrony of plant-available nitrogen for a crop. With fertilizer prices increasing sharply and nitrogen from runoff being one of the biggest problems in streams and open waterways, one of the key goals of this study is to assess N contribution from cover crop legumes that have been terminated using different approaches. In October 2010 (Y1) and 2011 (Y2), 144 experimental plots were established at the Caswell Research Station in Kinston, N.C, grown throughout the winter, and terminated in Spring 2011/2012 to investigate impact of termination method on N mineralization. Then again in October 2011 (Y2), experimental plots were established at a second site at the Center for Environmental Farming Systems (CEFS) in Goldsboro, NC, grown throughout the winter, and terminated in Spring 2012 to investigate impact of termination method on N mineralization. In this study, four leguminous winter cover crop species, Austrian winter pea, hairy vetch, and balansa and crimson clovers, were terminated using a roller-crimper, flail mower, disk, or an herbicide.  Bi-weekly inorganic soil tests and Plant Root Simulator ion resin probes were used to measure plant available NO3- and NH4+. Cover crop biomass, total carbon, and total nitrogen were measured for each species prior to termination. Second year field plots (2012) were assessed for the following arbuscular mycorrhizal fungi (AMF) responses: 1) AMF species diversity in spring, prior to cover crop termination;  2) AMF root colonization of each cover crop prior to cover crop termination;  and 3) AMF root colonization of corn, 3 weeks after cover crop termination.  ??


Objective 4 Methods: On April 19, 2011 (Y1) we held a SE SARE funded workshop to describe advantages of cover crops, how to estimate fertility impact on cash crops, as well as offer a visual example of legume growth immediately prior to spring termination.  The workshop, entitled “Growing Your Own N: Improving Legume Cover Crop Management” was held at the certified organic Abundant Life Farms in Clayton, NC. It was a hands-on workshop experience in that farmers were able to sample biomass and determine N contribution through common and easy to use “rules of thumb” related to biomass N content of typical cover crop legumes.  Growers were also able to see and compare cover crop varieties at full maturity.  In Y3 we held two workshops at the Southern Sustainable Agriculture Working Group meetings in Little Rock, AK describing advantages of cover crops, how to estimate fertility impact on cash crops, and presenting data from our two-years of cover crop termination method trials. Students were also trained in cover crop benefits, and those students in Dr. Julie Grossman’s Service-Learning for Urban Food Production course designed three lesson plans for low-income youth and taught them in conjunction with the Inter-Faith Food Shuttle’s Farm and Community Garden project over an 8-week period. The sites where the units were taught included 1) a manufactured home community in Raleigh (i.e. trailer park) with predominantly African American and Hispanic/Latino residents and 2) Young Farmer Training Program, supported by our community partner, designed for lower income participants Lessons were transferred to the Inter-Faith Food Shuttle at the end of the semester for use in their community outreach activities.

Research results and discussion:

Objective 1 Results: Final survey results were analyzed in 2012 and suggested that 41% of growers choose inoculants based on recommendations from the seed vendor, but obtain information about what practices to follow equally from the seed vendor (25%), inoculant vendor (22%), organic online information (18%), and the seed package (23%).  Only 55% of growers surveyed follow recommendations of storage temperature practices of 40 F and 26% follow the most recommended application practices of using a sticky agent other than water with solid inoculant. Unexpectedly, new growers (less than three years of experience) who likely have the greatest need for inoculation, inoculate the least. From these observations it was concluded that in a majority of cases growers do not follow recommended practices for inoculation success. Although our study represents only those who participated in the survey, results indicated a lack of proper handling procedures and care for rhizobia inoculants that contained live cultures. This could possibly result in decreased nitrogen fixation resulting from active symbiosis in crops were improperly handled inoculants are applied to legume seeds at planting. 


Objective 2 Results: Cover crop production on our three demonstration organic farms ranged from 2,300 - 5,800 lbs of biomass per acre, with lbs of N ranging from 72-183 lbs N per acre. There was no correlation between soil characteristics, including organic matter, soil pH, or naturalized soil rhizobia population size, and the effect of inoculation on plant biomass.   At three field sites, legume inoculation did not result in an increase in plant biomass, biomass nitrogen, nodule number, or mass. Molecular analysis of nodule occupants was striking, showing that when the DNA of nodules of inoculated and un-inoculated plants were analyzed, as few as 8.5% of strains isolated from inoculated nodules had DNA fingerprints closely related to the commercial inoculant. This suggests that native rhizobia may be out-competing the inoculant for nodule occupancy.  A majority of rhizobia isolates belong to 13 DNA fingerprint clusters whose occupants were over 70% similar, typically not correlated to cover crop host, farm location, or inoculation treatment.. Fingerprinted strains similar to inoculants had genetically distinct nodC sequences from inoculants, suggesting that applied inoculant strains are not present in host nodules.  Results indicate that complex rhizobia ecology may be present in organic farm soils resulting from high levels of competitive native rhizobia populations established through diverse cultivation histories. 


Objective 3 Results: Over the two years of our study, mineralized nitrogen was most available from Austrian winter pea and hairy vetch across all termination treatments at six to ten weeks after kill. Disked hairy vetch contributed the greatest plant available nitrogen amongst all 16 combinations.  Biomass contributions of cover crops ranged from 2.4 Mg ha-1 to 9.7 Mg ha-1 in balansa clover and crimson clover, respectively. Hairy vetch had the greatest overall average biomass nitrogen contribution of 226.4 mg kg-1, while Austrian winter pea grew 188.71 kg ha-1 and crimson clover averaged 181.1 kg ha-1. Corn yield was not correlated with plant-available N, determined with soil inorganic N tests and PRS probe measurements.  Results show that termination technique in combination with cover crop species can result in as much as double the amount of plant available forms of nitrogen in the soil. Results from the mycorrhizae portion of this objective show that 1)  Fifteen AMF species were found in the second year field plots:  Acaulospora laevis, A. scrobiculata, Glomus clarum, Gl. etunicatum, Gl. intraradices, Gl. mosseae, Gl.sinuosum, Gigaspora gigantea, Gi. roseae, Gi. margarita, Scutellospora fulgida, Sc. heterogama, Sc. gregaria, Sc. pellucida and Sc. reticulata, 2)  Austrian winter pea, hairy vetch and crimson clover all supported higher AMF colonization than balansa clover.  3) The same trend was evident in 3-week corn colonization, with enhanced AMF colonization following hairy vetch and suppressed AMF colonization following balansa clover.   Lastly, AMF colonization of 3-week corn was significantly lower in the Disk/ Till treatment than in the other cover crop termination treatments.


Objective 4 Results: One on-farm grower workshop was conducted, and two larger indoor lecture-style workshops presented at Southern SAWG (2013) to over 200 producers.  A total of 16 local youth participated in the lessons developed through this grant in Y2 and three lesson plans were developed and returned to the IFFS for use in their gardening education program in low-income neighborhoods. In Fall 2012, evaluation efforts were expanded to collect data on community youth’s learning gains, as well to learn how the lessons conducted by NCSU students are helping to increase community youth interest in agriculture and soil science.

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

M.S. Theses produced using support from this grant:

Matthew Brown M.S. Thesis title: “Decomposition and nitrogen release of legume cover crops in organic agriculture using varied cover crop destruction techniques”??

Sarah Seehaver M.S. Thesis title:  “Improving nitrogen contribution to organic farming systems through improved understanding of rhizobia diversity”


Scholarly manuscripts either under review or published based in-part on results of this SARE grant:

  1. Brown, M., Grossman, J., Israel, D., Shi, W. Evaluating termination methods of four winter annual leguminous cover crops for optimizing nitrogen synchronyUnder Review, Agronomy Journal. 
  2. Smith, S. Grossman, J.M., Bradley, L., Hesterberg, D. Preparing students for a diverse future: Using service-learning to train students for careers in agricultural community outreach, Accepted, National Association of College Teachers of Agriculture (NACTA) journal.
  3. Niewolny, K.L., Grossman, J.M., Byker, C., Helms, J. Clark, S.F., Cotton, J., Jacobson, K.L. 2012. Sustainable Agriculture Education and Civic Engagement: The Significance of Community-University Partnerships in the New Agricultural Paradigm.  Journal of Agriculture, Food Systems and Community Development, May, 2012, pp. 27–42.
  4. Grossman, J. Sherard, M., Prohn, S., Bradley, L., Goodell, S., Andrew, K.  2012. An Exploratory Analysis of Student-Community Interactions in Urban Agriculture, Journal of Higher Education Outreach and Engagement, 16(2):179-196.

Honors presented for work related to this grant:

2013   Ernest A. Lynton Award for the Scholarship of Engagement for Early Career Faculty Nomine?
2011   Appointed as a “Community-Engaged Faculty Fellow” by the Office of the Provost, NCSU for excellence in community engagement through teaching and service-learning.?
2011   Opal Mann Green Engagement Award winner, NCSU, Office of Extension and Engagement.?
2014    Sarah Seehaver, Awarded 4th Place in Graduate Student Poster Competition, Soil Science Society of North Carolina?2012    Suzanne Fleishman, undergraduate researcher working with inoculation survey; Golden Opportunity Scholar, ASA-CSSA-SSSA National Meetings?
2012    Matt Brown, 1st Place Graduate Student Category, NC Soil Science Society Annual Meetings


Presentations reporting on data gathered through support of this grant:

Grossman, J., Sooksa-nguan, J., Seehaver, S., Parr, M. Carbon and nitrogen contributions of legume cover crops to organic farms in North Carolina. 57th Annual Meeting of the Soil Science Society of North Carolina, January 21-22, 2104, Raleigh, NC.

Seehaver, S., Grossman, J., Israel, D., Louws, F. Effect of inoculation on nodule occupation and rhizobia diversity of cover crop legumes. 57th Annual Meeting of the Soil Science Society of North Carolina, January 21-22, 2104, Raleigh, NC.

Sooksa-nguan, T., Grossman, J., Seehaver, S. Mothapo, N. Exploring Rhizobia Diversity of Legume Cover Crops in Organic Systems. 57th Annual Meeting of the Soil Science Society of North Carolina, January 21-22, 2104, Raleigh, NC.??

Grossman, J. Putting Legumes to Work on Organic Farms. Annual Sustainable Agriculture Seminar Series, The Pennsylvania State University, January 17, 2013, State College, PA??

Grossman, J. Managing Plant-Soil-Microbe Relationships for Better Soil Fertility. Southern Sustainable Agriculture Working Group (SAWG), January 25 and January 26, 2013, Little Rock, AK.

Grossman, J. Schroeder-Moreno, M., Jayaratne, K. S. U., Smith, S. Application of service-learning in two courses for a hands-on, minds-in, and hearts-felt educational experience. National Association for College Teachers of Agriculture (NACTA) Conference, July 25-29, 2013.??

Grossman, J., Smith, S., Schroeder-Moreno, M. Laying the groundwork for soil science education through urban agriculture service-learning. Ecological Society of America Conference, 97th Annual, August 5-10, 2012, Portland, OR.??

Fleishman, S., Grossman, J., Larsen, E. and Bowen, S. Grower adherence to legume cover crop rhizobia inoculant maintenance and use recommendations in the Southeast. ASA-CSSA-SSSA International Annual Meetings, October 22-24th 2012, Cincinnati, OH.

Brown, M., Grossman, J. Horton, S.C. and Shi, W. The influence of termination techniques on plant available nitrogen mineralized from winter annual leguminous cover crops. ASA-CSSA-SSSA International Annual Meetings, 22-24th 2012, Cincinnati, OH.??

Brown, M., Grossman, J. Shi, W., Reberg-Horton, S.C. Evaluating termination methods of leguminous cover crops for optimizing nitrogen synchrony, Ecological Society of America Conference, 97th Annual, August 5th-10th, 2012, Portla

Schroeder-Moreno, M. and Grossman, J. Diverse strategies to develop and assess student impacts from community garden service learning experiences, Sustainable Agriculture Education Association National Conference, Aug 4-5, 2011, Lexington, KY.

Smith, S. and Grossman, J. Impact of cultural competence training on student success in urban agriculture community education. Sustainable Agriculture Education Association National Conference, Aug 4-5, 2011, Lexington, KY.

Project Outcomes

Project outcomes:

Impacts of this research and education project emphasize farmer's willingness to try 'something new', based on our detailed evaluation following our workshops, and the interest in low-income youth and college students in pursuing careers related to agriculture. Future impacts are expected to come through publication of the scientific findings to advance our understanding of cover crop N. Using our external evaluator, we gained information regarding specific knowledge workshop attendees gained through observation of our research plots and workshop activities, including these verbatim comments from growers about what they learned: Crop choice – plant and kill time plant and kill methods; Better understanding of legume crop N cycle; N being tied in the plant material not leached in soil; N yield per species; most N being found in the above ground portion of the cover crop; availability of the nitrogen; how much; biomass; how to measure N in cover crop; seed sources, prices; and one statement that Hairy vetch one to use for best bang for N. Regarding which practices participants stated they would use on their farm or their job, farmers mentioned: Waiting until plants are mostly flowering before tilling under; Inoculate my legumes; feel more confident about using cover crops; mowing the cc versus incorporating into soil; planting timing for cover crops, and restrictions on manure use due to high zinc, etc. levels. 


Preliminary results from the development of our service-learning teaching modules on cover cropping and nutrient cycling show that 75-100% of the participating community youth now know more about the important functions of soils in our daily lives; and 75% of participant youth feel they have greater knowledge about career paths related to agricultural fields. All but one of the participating youth described an interest in teaching others what they had learned through the lessons. One youth stated that he is excited about taking further courses in agriculture because of what he learned from NC State students regarding environmental problems, pushing him to “become more aware of the environment.” Former NCSU students in the service-learning course also chose career paths related to teaching within under-served and low-income communities. At least two former students are now teaching science in rural areas with the Teach for America program, and several more have indicated interest in working with low-income youth and agricultural education in their future. In a letter to Dr. Grossman, one student stated “I have been labeled as the token ‘Ag Kid’ in my Teach for America cohort among my humanity-urbanite colleagues. I have you to thank for that and so much more. My college career and life trajectory changed so much because of the relationship I had with your [community engagement program].” 

Economic Analysis


Farmer Adoption

Six months after the field workshop follow up phone calls were made to participants to determine how they were using knowledge gained in the workshops on their farms or in their jobs, gathering information from a total of eight farmers and seven extension and Natural Resources Conservation Service (NRCS) personnel. Out of the eight growers who responded to our call, seven were using information learned in the workshop to help them make decisions on the farm, including planting new species of cover crops, new mixes, and calculating N contribution from cover crops. Although we were only able to contact 8 individuals, we hope that most participants used the information learned at the workshop. Extension and NRCS personnel were asked which aspects of the workshop they found particularly useful. The most important concepts these participants learned included termination time, amount of N contributed through cover crop biomass, visualizing species differences, and the process of biomass mineralization after termination. Almost 80% of Southern SAWG workshop participants stated said they learned something useful, and almost 67% said they would ‘absolutely’ use the information they learned in the next year. Specific comments included appreciation for calculations on how to determine N contribution from cover crops, as well as for the scientific results from SARE-funded field trials.


Areas needing additional study

Results from our inoculation survey suggest that awareness of effective inoculant use and handling procedures among Southeast organic growers may need to be increased. Results stimulated drafting of an eOrganic (online web portal) publication on ‘Inoculation practices for organic farms’ in order to help farmers navigate inoculation of legume cover crops, now available online. 

Since legume root nodules were shown to have primarily native soil-dwelling rhizobia and not inoculation strains, determination of native rhizobia effectiveness in BNF is needed.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.