Learning from farmer innovation in nitrogen fixation for improved nutrient management on organic farms

Final Report for LNE07-252

Project Type: Research and Education
Funds awarded in 2007: $99,108.00
Projected End Date: 12/31/2011
Region: Northeast
State: New York
Project Leader:
Julie Grossman
Cornell University
Laurie Drinkwater
Cornell University
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Project Information


The crux of this project was to combine on-farm research with outreach activities in order to measure nitrogen fixation in working vegetable farms and promote farmer-farmer and farmer-researcher knowledge exchange. Detailed measurements of soil properties, cover crop biomass and biological nitrogen fixation rates were conducted in 27 fields located on 11 farms. We learned that nitrogen fixation rates are generally greater in hairy vetch cover crops compared to peas and that overall nitrogen fixation is highly variable across farms and fields. Nearly all of our farmer collaborators sought our advice on management options related to legume cover crops and all of them modified their cover crop management practices in some way during the three years of this project. We reached 259 stakeholders through a series of intensive workshops and shorter presentations at meetings and field days. On average, about half of the participants in the intensive workshops could identify a specific change or new management practice that they planned to test within six months. We also provided information on legume management to nearly 30,000 stakeholders through Q and A columns published in newsletters and other publications targeting farmers in the northeast. Lastly, we produced a new legume management resource which was published in The Natural Farmer (readership of 5500) and will also be made available on line.


Over the past ten years, in-depth discussions with organic growers involved in our long-term research projects have shown the extreme need for studies on nitrogen fixation in green manure cover crops. Biological nitrogen fixation (BNF) is the major source of new nitrogen in organic agriculture and conventional growers are also becoming increasingly interested in using N fixing cover crops due to the increasing costs of purchased fertilizers. With the exception of soybeans and major forage species such as alfalfa, measurements documenting how much N is being fixed by legumes are extremely rare and, even for these common legumes, there is little research documenting how management practices impact this process on working farms. In addition, few widely used, temperate green manures have been characterized at all in terms of their nitrogen fixing traits. Furthermore, BNF is a complex biological process resulting from bacterial-plant collaboration and the level of farmer knowledge about how to optimize management of this process is highly variable. This project aimed to benefit vegetable growers who either rely on BNF to manage soil N fertility or who are interested in incorporating legumes into their rotations in two main ways: 1) We measured BNF and documented management practices on working farms to provide farmers with rates of N-fixation in their fields; and 2) we provided farmers with access to information on BNF through workshops and field days, a series of newsletter columns, an extensive special issue published in The Natural Farmer and provision of educational materials on managing legume cover crops for educators who are training beginning farmers.

Literature Review

Although our atmosphere is 78% N2 gas, N is often the most limiting nutrient for plant growth because plants lack enzymes that can convert it into a usable form. As a result, plants in natural ecosystems rely on the N released via microbial decomposition of SOM. Leguminous plants are unique in that they have evolved a symbiosis with specialized bacteria that produce enzymes to “fix” N2 gas into amino acids, a biologically active form of nitrogen. In exchange for fixed N2, the plant provides energy in the form of carbon (hereafter, C) substrates and protection to the bacteria in specialized root structures called nodules. This mutualistic relationship allows N-fixing plants to grow in very poor soils where other non-N-fixing plants cannot grow (Vitousek et al., 2002).

Biological nitrogen fixation: The foundation of organic soil fertility

Soil management is the cornerstone of organic production, especially BNF, which is used to provide the cash crop with N to meet its growth and production needs. Most organic farms combine BNF with varying levels of composts or animal manures to provide the remaining complement of major and minor nutrients (Drinkwater et al. 1995; Watson et al. 2002). While some farms do rely on composts and animal manures as major nitrogen sources, this is more common during the transition phase and is not sustainable in the long run. A major challenge faced by farmers who rely on BNF as the chief source of N additions is determining how to best optimize BNF so that cash crop N requirements are met. All growers with whom we spoke include legumes in their rotations at some point and assume that N-fixation is contributing to soil N fertility. These farmers said that they would ultimately like to ‘grow their own fertility’ by having legumes provide a majority of the N for their cash crop, but lack of information on specific management practices is a major constraint (Lou Johns, Blue Heron Farm, personal comm.).

Leguminous cover crops serve multiple functions in organic cropping systems. The functions we hear mentioned most often by organic growers are: 1) nitrogen source, 2) build SOM, 3) weed suppression, 4) provide habitat for beneficials, 5) disease suppression, 6) build soil tilth and 7) reduce nitrate leaching and 8) reduce soil erosion. Other cover crops fulfill the functions that are not related to N-fixation and in some cases non-N-fixing plants are more effective at achieving these other outcomes. For example, grasses are usually more effective for weed suppression and reducing soil erosion (Gallandt et al. 1999) and brassicas excel at capturing nitrate to reduce leaching losses (Kristensen & Thorup-Kristensen 2004). To increase the probability that a cover crop can achieve these multiple functions, organic farmers often plant mixtures that combine legumes with non-N-fixing plant species. Therefore, the choice of using legumes in cover crops is usually based on the expectation of improved N fertility. However, farmers and scientists do not know how much N is actually being fixed by leguminous cover crops.

The soil environment exerts influence on BNF through direct and indirect effects on the plants and microorganisms involved in N-fixation. This complexity is reflected in the high variability found in BNF rates in natural and agroecosystems (Carlsson & Huss-Danell 2003). Although we know that these interactions involved in governing BNF are operating in agricultural systems, most work aimed at gaining a holistic understanding of BNF as an ecological process has been conducted in natural ecosystems (Clay 2001, Vitousek et al. 2002). Soil N availability is a primary factor governing N-fixation rates (Vitousek et al. 2002) and plants decrease their investment in nodule formation if sufficient soil N is available (Waterer & Vessey 1993).

Surprisingly, the relationship between organic soil N reserves and BNF has rarely been studied in agricultural systems even though there is extensive indirect evidence suggesting that N-fixation rates are extremely variable across farmer’s fields (Russelle & Birr 2004). Based on our current knowledge, we expect that in organic farming systems, BNF will be influenced by management practices such as compost additions and rotation which tend to gradually build SOM and increase soil N fertility. In 2004 we initiated research on BNF in organic and conventional grain systems in New York. We had been conducting research on the relationship between soil management strategies, nutrient balances, C and N cycling in these sites since 2002, so they were well characterized. We found that N-fixation varies tremendously across organic grain farms. For example, N fixation rates by soybean varied from 40-90% corresponding to 44 to 209 kg ha-1 in these fields. Nitrogen fixation rates declined with increasing soil fertility as indicated by total soil N and the greatest amounts of N-fixation occurred in transitional organic grain fields. To our knowledge, our investigation is the first to measure N-fixation in working organic farms. This research provides the foundation for the work we propose to do in vegetable systems where a more diverse array of legumes are commonly used as green manures.

Farmer learning and information sharing about Nitrogen Fixation

Extension of agroecological information requires an alternative form of pedagogy that relies more on social learning than traditional top-down training. Organic vegetable farmers in the NE have told us in informal interviews that they best learn about cover crop management primarily by reading technical bulletins and grower newsletters and then discussing options face-to-face with farmer peers. One of the most successful pedagogical strategies in alternative agriculture has been shown to be the development of multi-year agro-environmental partnerships that include growers, a growers organization, and one or more scientists to extend agroecological knowledge and field scale demonstrations (Warner, 1999). This kind of partnership demands that members collectively analyze a situation from different perspectives and carefully monitor one another’s work. Well-functioning groups can bring about powerful change and results. Our project seeks to work closely with innovative farmers to learn about nitrogen fixation in a collaborative relationship, and in this way improve farming practices throughout the NE region.

Performance Target:

Our project had two main objectives:

1. Survey of BNF on Working Farms: We will provide farmers with rates of N-fixation in their fields by conducting an extensive on-farm survey on 25-30 vegetable farms.

2. Farmer Learning Opportunities: We will design and offer two opportunities for farmers to learn more about green manures and BNF (workshops and newsletter column).

Three performance targets supported these objectives:

1. Over 2000 growers and those working as grower educators will read answers to farmer questions on green manure management for BNF in our newsletter column.

2. Of the 50-60 farmers involved as workshop attendees or collaborators, 25 will plan to adjust their management of green manures within 6 months of workshop and survey completion.

3. Overall, the 60 farmers trained in green manure management for BNF will act as informal educators to another 60 farmers who were not directly trained.

Evaluation of performance targets

There were two key events that occurred during the first 18 months of the project which required some modifications in how we actually carried out the work. First, Sarah Johnston, the Director of NOFA-NY, left her position and as a result the organization withdrew from the project in order to evaluate priorities and focus on re-staffing and building the organization. We collaborated extensively with NOFA-NY, through using their venues for workshops and writing columns for their newsletters, however we did not have their assistance in linking with growers for collaborative on-farm research or for workshops and evaluations of impact. Secondly, Dr. Julie Grossman accepted a faculty position at NC State and was not able to serve as the lead educator for the project. Julie was highly skilled and had extensive experience in conducting farmer education on nitrogen fixation and legume management so she could not be easily replaced. Her departure meant that the PI (LED) had to carry out some of the work Dr. Grossman originally planned to do. While I enjoyed the opportunity for greater first-hand involvement, it was extremely difficult to add this work to my packed schedule since I am only 10% extension and teaching often interferes with grower workshops in the winter. Despite these two setbacks, we accomplished more outreach and were able to provide learning opportunities to a broader audience of growers and educators than we originally planned. We also collected a tremendous amount of on-farm data on cover crop management and performance. Nevertheless, without the active involvement of NOFA-NY to assist us in recruiting farmers, we did not engage quite as many active collaborators for the on-farm sampling as would have liked and the duration of the project was lengthened by 18 months.

Over 2000 growers and those working as grower educators will read answers to farmer questions on green manure management for BNF in our newsletter column.

We greatly exceeded our expectations in this area of delivering information about legume cover crops to growers and educators through written resources. The Vicki Vetch columns are still running and NOFA NY has just requested that we expand the column to answer other grower questions. We published 8 columns in 2 newsletters, and the Small Farms Quarterly magazine reaching a total readership of nearly 30,000 stakeholders. Furthermore, during the final year of the project we co-produced a special issue for The Natural Farmer (circulation 5,500) with the editor, Jack Kittredge. This special issue will be posted on the web and will serve as a resource for growers and educators for the next several years.

Of the 50-60 farmers involved as workshop attendees or collaborators, 25 will plan to adjust their management of green manures within 6 months of workshop and survey completion.

For a variety of reasons including changes in project personnel, increased interest in leguminous cover crops among both organic and conventional growers and interest in the unique, on-farm measurements of cover crop performance from working farms, we surpassed this performance target. We reached 259 growers/educators through eight workshops and field days. We conducted before and after assessments in the three intensive workshops (two conducted at the NOFA-NY winter meetings and the more recent workshop for new farmers held in Ithaca). Feedback from participants indicates significant learning on a practical level and a high frequency of plans for adjusting management regimes. In the introductory workshop held in 2008, more than half of those who filled out the evaluations gave examples of plans to modify cover crop management as a result of the workshop. In our second, more advanced workshop, the evaluations indicated 80% agreed/strongly agreed that the workshop was beneficial to their work and described an adjustment/new practice they planned to try based on what they learned at the workshop. Follow-up on actual changes in practices 6-months prior to the end of the project proved to be more challenging. Farmers were very difficult to reach and despite considerable effort devoted to calling participants for follow-up conversations, we were not as successful at gathering quantitative information in this way, particularly from farmers that we knew only through their participating in workshops. We do have several examples of innovation and management adjustments among collaborating farmers with whom we have more regular contact. Within this group, we see a trend for increased efforts to expand the use of cover crop mixtures in rotations. From our conversations with these 18 farmers, it is clear that our project has provided support for these management adjustments; however we also know that there are several other factors driving this increased motivation. We discuss this in more detail in the Impacts/Outcomes section.

Overall, the 60 farmers trained in green manure management for BNF will act as informal educators to another 60 farmers who were not directly trained.

This performance target was significantly adjusted to reflect staffing changes in the project. Instead of emphasizing knowledge transfer through informal networking, we instead focused on actively promoting farmers who had developed successful legume management schemes and innovations on their farms in formal venues as workshop presenters and by highlighting their practices in The Natural Farmer special issue on biological nitrogen fixation and managing legume cover crops. In addition to the stories documenting these successful farmer-developed examples, six growers who collaborated with the on-farm research presented information on how they manage legume cover crops to 108 peers and farmer educators in three workshops that we organized. Two of these growers had very little experience in sharing their innovations previously. Our non-quantitative assessment of farmer educators who attended the workshops indicates that at least five are using the information from our workshops and we have received unsolicited communication from educators who are using The Natural Farmer special issue their education efforts. In summary, our performance target of training the trainers was achieved through a different means than originally planned and we achieved significant transfer of farmer knowledge through more formalized farmer-to-farmer channels.


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  • Carol MacNeil
  • Greg Swartz


Materials and methods:

On-farm measurements of N-fixation

Beginning in Fall 2007 through Fall 2009 we established plots on a total of 11 working farms and one long-term cropping system experiment for assessment of nitrogen fixation rates. Preliminary contact was made with 40 vegetable farms from the NOFA list, followed up with a personal phone-call. A total of 20 farms planting winter legumes intercropped with a non-legume were identified. Most farms were planting hairy vetch intercropped with rye, oats, or winter wheat. Data of fall or spring pea/oats mixtures is the second most prevalent. On each farm, four replicate sets of plots were established in one or more fields. Within two weeks of farmer seeding, each plot was weeded accordingly to create three sub-plot treatments including a) legume only, b) non-legume reference plant only (rye, oats or wheat), and c) farmer practice (both legume + non-legume). On each of the farms on which we established plots, we described the experiment to the grower and answered any questions he/she had. A total of 28 fields from 11 farms were sampled during Spring 2008 through Spring 2010.

Cover crops in the plots were allowed to grow and were be sampled for 15N abundance before cover crop incorporation. Cover crop biomass was sorted from weeds, dried at 60oC, weighed and analyzed for total N and 15N natural abundance. Soil samples were also collected and analyzed for soil texture; soil nutrients, pH, CEC and soil organic C and N were also measured. Soil organic matter was characterized using particulate organic matter density separation. Information on seeding date and rates, date of incorporation/mowing and other soil fertility management practices was collected for each of these fields.

Detailed overview of the method: This method was developed for measuring N-fixation from legume cover crops on a farm/field scale in fields where a mixed (legume and non-legume) or legume-only cover crop has been planted. It involves setting up plots just after the cover crop is established. The goal is to estimate total cover crop N and N fixation for the entire field or the area planted to a cover crop with four samples. We divided the field (bed or group of beds) into 4 equal parts and then randomly placed one set of small plots in each of these sections after the cover crop had germinated and the plants are established. The precise method used to plan the location of the plots depended on how the fields were managed and whether cover crops were planted into whole fields or permanent beds. The small plots (1.5 x 1.5 meters) were arranged in groups of either three or two depending on whether a mixture or monoculture cover crop was planted in the field. Flags and stakes were used to mark the corners. Groups of 3 sub-plots (mixed field) or 2 sub-plots (legume only field) were arranged in farmer’s fields as shown in Figures 1 and 2.

About 2-4 weeks after the establishment of the plots, we checked to make sure that no legumes were growing in the non-legume (reference) plots. With hard seeded cover crops like vetch, or slow germinating covers like clover, new plants tended to spring up. Also, if the legumes were not removed thoroughly enough, some were occasionally re-growing from the roots. We collected biomass samples from an area of 0.5 m2 from each plots before the cover crop in the field were mowed or incorporated.

Farmer Learning Opportunities

The second focus of our project was to develop a strong outreach program that involved stakeholders in dissemination of farmer knowledge about legume management as well as information produced in the course of the on-farm research. The social nature of sustainable agriculture education demands that we place an educational emphasis on flexible learning processes necessary to initiate and facilitate learning through participatory approaches (Röling and Wagemakers, 1998). As part of this grant we provided teaching and learning opportunities for NE organic farmers who are enthusiastic about increasing their knowledge about BNF in cover crops, while at the same time extending our knowledge about how cover crop management influences BNF in vegetable cropping systems.

Workshops on BNF in cover crops

We developed three intensive workshops for growers to learn about BNF from both basic and advanced perspectives. The first workshop was designed to convey the basics of N-fixation in green manures commonly used in our Northeast region to farmers. We covered much of the accepted knowledge about cover crop management, as well as newly developed knowledge from our lab and others working in this area. Three experienced growers presented overviews of their farms and explained how legumes were integrated into their rotations. We also developed a second workshop which was held the following year, addressing more advanced topics of cover crop management for BNF. In this workshop, results from the on-farm measurements of BNF were presented and four growers presented detailed information on successful legume management regimes. In this workshop the grower presentations were more specific and were sufficiently detailed to enable participants to adapt these practices for their own cropping systems. We conducted a 3-hour session covering the basics of BNF, cover crop functions and management and specific information about how to manage legumes effectively. This was our only in-depth workshop that did not feature farmer presenters since the class routinely heard from experienced farmers in the other sessions. However, in this workshop we piloted an experiential activity using a cover crop quick assessment tool we have been developing. In planning the curriculum for all of these workshops, we solicited input from stakeholders and farmer educators associated with the project. The second tier of workshops/field days includes several shorter presentations and field day talks which we were invited to give in various venues. For these workshops, we targeted the material to cover topics related to legume cover crop management as requested by the organizers. In addition to these in-depth workshops we participated in several other outreach opportunities. We presented a two-hour symposium at the NY State Fruit and Vegetable Expo to an audience consisting mainly of conventional vegetable growers. This program also featured three farmers with complementary descriptions of cover crop management within their intensive vegetable systems. Our final in-depth workshop was part of a 10-week course aimed at new farmers.

Linking Growers to Farmer-Experts and Researchers: newsletter column

Alternative forms of grower outreach were greatly appreciated by farmers with whom we spoke, who often cannot take the time out of busy schedules to attend educational events of interest. We designed and piloted a quarterly/bi-annual newsletter column in which we “fielded” farmer questions related to nutrient management and cover crops. Our column was published in the NOFA-NY quarterly newsletter (1,700 subscribers), Small Farms Quarterly (27,000 subscribers) and the extension monthly Veg Edge (circulation 350 organic, transitioning and conventional growers). Our final publication was developed jointly with Jack Kittredge who solicited input from several growers who he relies on for feedback on content. To produce this publication we hired Sharon Tregaskis, a local organic farmer who also works as a free-lance journalist to assist with editing and writing articles.

Research results and discussion:

Milestone 1: Over 2000 farmers learn about the first workshop through NOFA-NY website, newsletters and our www.organic.cornell.edu website.

We reached a wide audience of at least 1,700 with publicity about the anticipated workshop. We learned that workshop attendance at the Winter NOFA-NY meetings really draws from those who decide to attend the NOFA conference.

Milestone 2: Over 1,700 farmers subscribing to NOFA newsletter expand knowledge of cover crop management by reading newsletter columns.

We launched the “Dear Vicki Vetch” newsletter column in January 2008 with an announcement soliciting grower questions on cover crops in the NOFA-NY newsletter. Vicki Vetch was carried by three newsletters: 1) The Small Farms Quarterly is mailed to 27,000 small farms in several states and is also available on-line. 2) The NOFA-NY newsletter ‘Organic Farms, Folks, and Foods’ which is distributed to all NOFA-NY members (distribution 1,700). 3) The Cornell Cooperative Extension newsletter VegEdge is distributed to farmers in Western NY, including Ontario, Yates, and Monroe counties (mailed to 350 growers). We have continued the column at the request of the NOFA editor. The most recent question we received was asking how to bring a degraded, fallow field back into production. The NOFA staff are receiving positive feedback on the column from their stakeholders.

This spring we produced a special issue on nitrogen fixing cover crops in The Natural Farmer, a regionally-targeted publication with an audience of farmers and educators (distribution 5,500). This extraordinary opportunity enabled us to capitalize on our access to scientific information and farmer knowledge. We were able to highlight farmers we worked with during the project who have developed innovative legume cover crop regimes. The in-depth supplement included six articles by our group, complemented by two articles by the editor Jack Kittredge who interviewed two of our farmer collaborators for in-depth feature articles. There were also several articles written by Sharon Tregaskis, a journalist we hired to assist with this effort. Sharon also served as editor for the other pieces written by LED. We are using this resource already in workshops, classes at Cornell, and have even shared it with urban farmers and community garden coordinators at the American Community Gardeners’ Conference in New York City. Most of the feedback we have received in response has been from farmer educators who intend to use the supplement in their educational efforts. We have also received farmer questions via email.

Milestone 3: 25-30 collaborating farmers find out about BNF on their farm through ongoing sampling by the Cornell team.

On-farm research: measuring legume performance
While we made farm visits and conducted phone as well as in-person interviews with 48 growers, we found that only about 50% of those contacted through organic certification lists were routinely planting winter legumes intercropped with a non-legumes, the central practice we were attempting to characterize. Of these 48 farmers, we visited 18 farms, collected soil samples and made established cover crop plots on 14 farms, and successfully sampled these cover cropped plots on 27 fields located on 11 farms. We also measured legume cover crop BNF in one long-term experiment. The majority of these farms were using hairy vetch intercropped with rye, oats, or winter wheat. Fall or spring pea/oats mixtures were also fairly common.

The main difficulty in making measurements on a larger number of farms was related to the requirements for quantifying nitrogen fixation rates. The 15N natural abundance method is really the only approach that is compatible with on-farm measurements of BNF. Since this requires establishing a reference plot (a plot of non-legumes growing in close proximity to the legumes) we must either visit the farm several times to establish, maintain and then sample the plots or, we must enlist the assistance of growers. Multiple visits to fields within 2.5 hours drive or less was not a problem, however, we did not have adequate resources to manage and sample plots at distances beyond a day’s drive. This posed a problem because there were several excellent collaborators who were very interested in the project and wanted to work with us to measure BNF rates on their farms.

In order to accommodate this interest of stakeholders who were not in the Ithaca area, we tested two different strategies. First, we developed a simple method for establishing small plots for measuring BNF, provided farmers with training and kits which contained everything needed to set up these plots and offered compensation for labor expended in setting up plots. We found that growers were eager to collaborate with us and contribute to these measurements of nitrogen fixation in their cover crops as long as we could provide compensation for labor. However, this approach had a very low success rate of full implementation, mainly due to the multiple steps involved, some of which coincided with times when the demands for crop production were greatest. About 30% of the farmers who were trained and provided with kits followed through and established cover crop plots. Of these, a smaller proportion was successfully sampled for various reasons including flooding of fields where plots had been established, cover crop failure and scheduling problems. Another 30% changed their plans and did not plant a legume cover crop in the field we had soil sampled, and the remaining farmers simply missed setting up plots altogether for various reasons. A second approach we tried was to provide more support to farmers by helping with plot establishment. We thought this would be manageable with groups of farms clustered in distant locations such as the Hudson Valley. We thought that by coordinating with a group of growers we could establish and/or sample cover crop plots on multiple farms at the same time. This improved the rate of plot establishment, but was very difficult to continue this approach at sampling time because the plans for cover crop incorporation were highly variable across farms. After trying these approaches in 2008, we focused on collecting more data from farms within about a 2.5 hour radius of Ithaca in 2009. We coordinated with growers to identify fields, and then we took care of all the steps involved by setting up, maintaining and sampling the plots. This was our most successful strategy and yielded the greatest amount of information. While we successfully measured BNF in 28 fields, these were distributed on 11 farms, not 25 as we had originally planned.

One of our long-term goals is to develop quick, visual assessment tools that can be used by farmers to estimate the amount of nitrogen in their fields of cover crops. To that end we have combined our rigorous research data collection methods with quick measurements of cover crop stand height and density and digital documentation. We’ve used photographs of fields, as well as close ups that illustrate height and density, paired with data on nitrogen content and fixation rates in our workshops. These illustrations have been very effective for showing the relationship between cover crop stand and nitrogen content (Figures 3-6). We have tested the ability of workshop participants to estimate ground coverage and cover crop composition using visual keys (Figure 7) and found that most people can improve their ability to make these estimates with practice. We plan to continue this work and expect to have keys for three commonly grown legumes developed as part of our next cover crop project. The precise timeline depends on funding availability.

Milestone 4: 25 farmers develop basic knowledge about leguminous cover crop management during the first NOFA workshop on BNF.

The first workshop, "What Can Legumes do for YOU? Understanding Biological Nitrogen Fixation from the Ground Up" as held at The 26th Annual NOFA-NY Winter Organic Farming & Gardening Conference, Northeast Organic Farming Association, New York, Saratoga, NY, January 2008. We had 20 participants plus the farmer instructors. After participating in the workshop, more than half of those who filled out the evaluations gave examples of plans to modify cover crop management as a result of the workshop. The agenda is posted in PDF form as Document 1: Participants version and Document 2: Instructors version. Overall this workshop ran smoothly and participants asked lots of questions. The farmer facilitated discussions went very well and provided an opportunity for the participating farmers to discuss details of specific management improvements with feedback from other farmers, including the “expert farmers” who served as facilitators for each group. We believe that this opportunity accounts for the very high percentage of respondents who gave examples actions they planned to take as a result of what they learned. The main drawback was that we ran out of time so many participants did not take the time to complete evaluations. We did not reach our target of 25 participants for this specific workshop; however we more than compensated for this through outreach activities conducted later in the project.

Milestone 5: 25-30 collaborating farmers expand their knowledge about N-fixation on their farms by participating in the second (and third) year of the on-farm BNF survey.

A summary of our findings from the on farm measurements and discussion of the larger literature follows here.

Summary of our research findings
Legumes can provide as much as 300 pounds/acre of nitrogen, although 80–150 pounds/acre is more common. Our measurements of nitrogen fixation rates in organic vegetable farms showed that the amount of nitrogen fixed is highly variable and ranged from 10-120 pounds/acre in these fields. Compared to grain systems, vegetable farmers tend to rely more heavily on compost and other additions for nitrogen. In an earlier study we conducted, we found that of inputs on twelve organic grain and vegetable farms in the Northeast, organic grain farms relied on legumes for an average of 80 percent of all nitrogen inputs. In contrast, organic vegetable farms relied on legumes for an average of less than 20 percent of nitrogen inputs; the majority of their nitrogen inputs were from compost additions.

The soil environmental conditions resulting from a farmer’s management practices—such as the use of compost additions, tillage regimen, and rotational sequence—interact with the biological processes governing nitrogen fixation and influence how much nitrogen legumes will fix. In addition to practices that directly affect the soil environment, other deci¬sions such as choice of legume species and plant¬ing methods—including seeding rates, timing, and whether or not the legume is planted with non-nitro¬gen fixing plants—will determine how much nitro¬gen is fixed.

Environmental factors and their impact on nitrogen fixation
Factors affecting the growth of nitrogen-fixing le¬gumes can be divided into two main categories: 1) the environmental, management and biological con¬ditions that affect plant growth in general and which also apply to legumes and 2) a more limited set of factors that specifically affect the nitrogen fixation processes that determine how much of the element legumes will “fix” from the atmosphere.
All plants, including legumes, need fertile soil, suf¬ficient light and water, appropriate temperatures, and day length suitable for their particular eco¬logical niche. Biological conditions that influence growth include competition from weeds and damage from pests such as insects and pathogens. As with non-fixing plants, the specific requirements for op¬timal growth vary with legume species, ecological adaptations, and life history. Some legumes are bet¬ter adapted to withstand very cold temperatures (i.e. hairy vetch), whereas others are well adapted to hot, dry conditions (i.e. cowpea). The excellent SARE cover-cropping manual, Managing Cover Crops Profitably, covers basic information on species traits and requirements for optimal growth.

Factors that specifically affect nitrogen fixation rates reflect the unique requirements associated with the process of biological nitrogen fixation. Legumes tend to have greater requirements for phosphorus, which is important for nodule formation and for the process of nitrogen fixation. Phosphorus is a constituent of the molecules that transfer energy from photosynthesis and catalyze the reactions that actually break the dinitrogen bond, a crucial step in nitrogen fixation.

Nitrogenase—the enzyme that mediates the ni¬trogen fixing reaction—and leghemoglobin—the protein necessary for maintaining favorable oxygen levels—incorporate particular micronutrients in their structures. Micronutrients such as iron (Fe), molybdenum (Mo), and cobalt (Co), are particu-larly important for legumes. Soils with deficiencies in these micronutrients will not support high rates of nitrogen fixation. Soil pH and tilth also have a significant influence on nitrogen fixation. Most ag-ricultural legume species prefer soil pH in the range of 5.5–7.0. In soils with lower pH, nitrogen fixation is suppressed. Because nitrogen fixation is an energy intensive process, root respiration rates can be very high in legumes; soil conditions that limit the avail¬ability of oxygen are not conducive to high nitrogen fixation rates. Maintaining good soil tilth to opti¬mize soil drainage and aeration is very important for promoting nitrogen fixation in legumes.

Background soil nitrogen levels also influence fixation rates (Figure 8). Nitrogen fixation is energy inten¬sive, compared to uptake of nitrogen from the soil. Soils with high nitrogen fertility suppress fixation, because most legumes preferentially take up soil nitrogen rather than carrying out biological nitro¬gen fixation. In our measurements on organic farms we’ve found that nitrogen fixation rates are reduced in fields with higher levels of available soil nitrogen. While the legumes showed good growth, when we analyzed what sources had supplied nitrogen in the system we found more had been pulled from the soil and less had been acquired through fixation (Table 1).

Our measurements suggest that as soil nitrogen fertility increases, the impact on legumes and nitrogen fixation is generally more pro¬nounced when legumes are grown in mixtures with non-legumes. In monocultures, legumes respond to greater soil nitrogen fertility by reducing nitrogen fixation in favor of soil nitrogen uptake. In mixtures with non-legumes, the other plants can draw down soil nitrogen and encourage the legume to fix more nitrogen than if it were alone, an ideal outcome. However, in situations where soil nitrogen fertil¬ity is high enough to allow the non-legume to grow very rapidly it can end up reducing nitrogen fixation by suppressing legume growth. While this outcome is not ideal in terms of nitrogen fixation, the sensi¬tivity of mixtures to soil fertility provides an internal mechanism for balancing nutrients. Soils with high nitrogen fertility do not need as much new nitrogen and the rapid growth of the non-legume is crucial for weed suppression in highly fertile soils. Also, the greater capacity of the non-legume to efficiently scavenge and recycle soil nitrogen ensures that ni¬trogen losses to the environment are minimized as is the case in most natural ecosystems.

Differences among legume species
The amount of nitrogen fixed by different legume species varies with total plant biomass, life history, and each species’ rate of nitrogen fixation and soil nitrogen assimilation. As a starting point, it is help¬ful to recognize that since the concentration of nitro¬gen in legume shoot tissues is fairly similar across species, usually ranging from 3 to 4 percent, the amount of total nitrogen is directly related to size: Greater biomass corresponds with more nitrogen. In general, the legumes that grow for longer periods of time produce more biomass and fix more nitrogen. Perennial legumes such as red clover tend to ac¬cumulate more aboveground biomass and fix more nitrogen than annuals; however some annual legumes such as hairy vetch that can produce a very large biomass and fix substantial amounts of nitrogen. Because it takes about six weeks for the process of nodule formation and nitrogen fixation to fully ramp up, short-lived annuals which grow quickly and have shorter life cycles generally fix less nitrogen than longer-lived annuals or biennials that overwinter or are allowed to grow for the entire growing season. In the vegetable farms we samples, we found that hairy vetch generally fixed greater amounts of nitrogen compared to peas (55 and 30 lbs/acre, respectively).

Even after accounting for life cycle and plant bio¬mass, different legumes and their associated rhizo¬bia fix nitrogen at different rates. Hairy vetch and alfalfa, for example, fix more nitrogen than clover or field peas. In some cases, including that of grain soybean, breeding has altered a seed variety’s reli¬ance on fixed nitrogen. Even within a particular variety of legume, nitrogen fixation rates will vary field-by-field and season-by-season due to the soil environment, which has both direct and indirect ef¬fects on the plants and bacteria involved. If plants can absorb enough nitrogen directly through the soil—from compost, for example—they will reduce their investment in the nodules that support nitro¬gen-fixing bacteria.

One reason for this variation in nitrogen fixation among legume species is differences in the ability to access soil nitrogen and to compete with non-legumes for soil nitrogen. Legumes that are able to take up more soil nitrogen generally fix less nitrogen. The basis for these differences is not fully understood; how¬ever, they are most likely due to species adaptations to their habitat of origin. We found that most legumes used as cover crops are pretty efficient nitrogen fix¬ers and fix at least 60 percent of their nitrogen or more; rates as high as 80 percent are not uncommon. Cowpea is an example of a legume that stands out as a “lazy” nitrogen fixer, hovering at rates closer to 30 percent. On the other hand, cowpea is more competitive in mixtures, compared to many legume species, and can fix greater amounts of nitrogen in a mixture than when grown as a monoculture.

Species mixtures as cover crops: Legumes and grasses
Farmers managing organic vegetable systems of¬ten employed mixed plantings of two or more species in their cover crop rotation. Since each plant species has unique characteristics, increasing species diver¬sity in cover crop plantings increases the chances of successful germination and growth and also allows growers to choose species with ecological traits that meet their objectives. For this reason farmers typically planted legumes with non-legumes such as grasses—oats, wheat, and rye—or buckwheat. In some cases, growers planted mixtures incorporating multiple legume species.

In thinking about how soil conditions affect bio¬logical nitrogen fixation, remember that legumes are uniquely adapted “pioneer species.” Their sym¬biotic relationships with mycorrhizal fungi—for phosphorus uptake—and rhizobial bacteria—to facilitate nitrogen fixation—allow them to grow in very young soil with low nutrient contents. As a result, legumes grow in low fertility soils where other plants cannot. The downside of this ability is that since supporting these symbionts—with carbon substrates from photosynthesis—is energetically expensive, legumes are less competitive in fertile environments where their symbionts are not needed. Thus, in the more fertile soils commonly found on organic farms in our region, legumes can be smoth¬ered by non-legume species, particularly those such as grasses and weedy species that take up soil nitro¬gen very quickly. These differences in the ability to take up soil nitrogen, however, can be harnessed to inspire legumes to fix more nitrogen by using crop mixtures that provide some competition for soil ni¬trogen without overwhelming the legumes. The trick is to combine plants with complementary attributes.

There are many benefits to pairing legumes with non-legumes. Two among them are vital. First, many legumes are small seeded, so they germinate as tiny plants and grow slowly at first. Planting these legumes with a grass that can act as a nurse crop and help with weed suppression while the legumes are becoming established usually results in a cover crop stand with fewer weeds. Second, grasses also provide a structure that can support viney legumes like vetch, allowing them to grow taller and gain ac¬cess to more light. Getting the seeding rates right for each species in the mix—so that neither plant spe¬cies dominates the mixture—is tricky. The goal is to have plants seeded with sufficient density so that there is enough competition to help suppress weeds and stimulate nitrogen fixation by the legumes, without having so much competition that the faster growing species completely out-competes the slow¬er growing species (which is usually the legume).

Using species that differ in the timing of their growth can help. For example, in buckwheat/clover combinations, the buckwheat grows very quickly and shades out the weeds. It also inhibits the clover growth; however, since it flowers after six to eight weeks, it is mowed and competition is removed, which allows the clover to take off at just the right time—at six weeks, when its nitrogen fixing sys¬tem is fully functional. Likewise, when red clover is frost-seeded into winter grains, it grows slowly while the grains are in the field, due to shading and competition for other resources. Once the grain is harvested, however, the clover takes off and produc¬es lots of growth and fixed nitrogen. Seeding grasses such as rye and wheat with vetch can be more challenging; if the ratio of grass to legume is too high, the grass will dominate and instead of provid¬ing structure to support the vetch, it will suppress the vetch. In some cases, nitrogen fixation can be severely reduced (Figure 9).

Because many mixtures consist of species that are growing simultaneously, it is difficult to predict how much nitrogen they will fix. We found that the growth of legumes in mixtures is highly variable across farms (Figure 10). Legumes in mixtures interact with the other species growing in the mixtures. The soil environment, especially the level of soil fertility, influences these interactions. As a result, there are trade-offs in the functions that mixtures perform well. Since non-legumes scavenge more effectively for soil nitrogen than legumes, the competition for soil nitrogen in mixtures is expected to increase the legumes’ reliance on nitrogen fixation. The absolute amount of nitrogen fixed, however, depends on the nitrogen fixation rates and biomass production of the legume in the mixture. In mixtures where le¬gume biomass is suppressed due to severe competi¬tion, nitrogen fixation is reduced compared to the legume monoculture. Non-legumes tend to be better at suppressing weeds than legumes; therefore, mix¬tures dominated by non-legumes are generally better able to suppress weeds than legume-dominated mix¬tures. However, non-legume dominated mixtures often suppress both weeds and legume biomass. As a result, mixtures that effectively suppress weeds may have reduced nitrogen fixation rates. In situa¬tions where weed control is equally as important as nitrogen fixation, these mixtures are a nice solution because they respond to the specific environmen¬tal conditions in any given field. In higher fertility soils, weeds tend to grow faster and might out-com¬pete a legume monoculture. Adding non-legumes serves as a kind of insurance against weeds. In soils with more limited fertility, both the weeds and the non-legumes will grow more slowly, giving the le¬gume the opportunity to grow and fix nitrogen. As research continues, we are finding additional com¬binations that are promising in terms of balancing weed control and nitrogen fixation.

Milestone 6: July 2008: At least 1,700 growers throughout the Northeast learn about Workshop II through NOFA-NY email, newsletters and websites.
Yes, we had good publicity for this workshop. NOFA-NY helped in publicizing the second workshop.

Milestone 7: 25 farmers trained in advanced cover crop management for soil fertility during NOFA-NY second workshop on Advanced Cover Crop Management.

The second, more advanced workshop had 24 participants and incorporated the most effective strategies used in the first workshop combined with the presentation of results from our on-farm measurements of BNF (Document #3). Four growers presented specific examples of how legume cover crops can be managed in vegetable production systems. The final hour of the workshop was dedicated to small group discussions on problem solving. The evaluations indicated 80% agreed/strongly agreed that the workshop was beneficial to their work and described an adjustment/new practice they planned to try based on what they learned at the workshop. We had other opportunities to present findings from our on-farm sampling. These are listed in Section 8.

Our final, intensive workshop targeted new farmers and was part of a 10 week course on farming conducted by a local organization (Groundswell) which is dedicated to training beginning farmers. We viewed this workshop as an opportunity to learn about the needs of beginning farmers. We’ve noticed that over the years, a larger proportion of our audience at NOFA and other meetings consists of new farmers. Before the workshop, we surveyed the group with a written questionnaire of ten questions to assess their prior knowledge on nutrient cycling and cover crops. The group’s answers varied widely, and ranged from a few who were able to describe the nitrogen cycle while many were starting with minimal background knowledge. For example, about half could provide an accurate one sentence description of the process of biological nitrogen fixation while the majority did not identify leaching or denitrification as important mechanisms contributing to nitrogen losses from agricultural fields. Because the participants in the new farmer training are for the most part not yet farming, it was not possible to gauge the adoption of cover crop practices. However, their enthusiastic participation and positive evaluations indicate that the majority found the workshop provided useful information they planned to use in the future. A large majority (84%) of participants replied that the workshop “covered useful material” and 77% agreed that the material was “Practical to my needs and interests.”

Lastly, another venue for outreach for our project is the development of on-line resources for trainers. In Spring 2011, as an additional outcome of the workshop we conducted for the beginning farmer course, we developed and tested materials that comprise a cover crop workshop module for educators who are engaged in training new farmers. The Northeast Beginning Farmers Project staff is working with us to make these educational materials available to a network of 100 organizations that are targeting new farmers in the Northeast region. These materials are in the final stages of being edited/ formatted to be posted on-line. The Beginning Farmers Project has a “Trainer Toolbox” that can be accessed by extension educators and beginning farmer trainers everywhere through: http://nebeginningfarmers.org/trainers/

Participation Summary


Educational approach:

Overview of publications

Our publications fall into two categories—a column called “Dear Vicki Vetch” that was published in three publications and circulated to approximately 30,000 farmers, and a special issue of The Natural Farmer comprised of eight articles addressing the science behind, and application of, legumes as cover crops.

We launched the “Dear Vicki Vetch” newsletter column in January 2008 with an announcement soliciting grower questions on cover crops in the NOFA-NY newsletter. Vicki Vetch was carried by three newsletters: 1) The Small Farms Quarterly is mailed to 27,000 small farms in several states and is also available on-line. 2) The NOFA-NY newsletter ‘Organic Farms, Folks, and Foods’ which is distributed to all NOFA-NY members (distribution 1,700). 3) The Cornell Cooperative Extension newsletter VegEdge is distributed to farmers in Western NY, including Ontario, Yates, and Monroe counties (mailed to 350 growers).

We published a special issue on nitrogen fixing cover crops in The Natural Farmer, a regionally-targeted publication with an audience of farmers and educators (distribution 5,500). This extraordinary opportunity enabled us to capitalize on a winning combination of scientific information and farmer knowledge. We were able to highlight farmers we worked with during the project who have developed innovative legume cover crop regimes. The in-depth supplement included six articles by our group, complemented by two articles by Jack Kittredge of NOFA-NY and several written by Sharon Tregaskis, a journalist we hired to assist with this effort. We are using this resource already in workshops, classes at Cornell, and have even shared it with urban farmers and community garden coordinators at the American Community Gardeners’ Conference in New York City.


Drinkwater, L.E. (Summer 2011) It’s Elemental—How Legumes Bridge the Nitrogen Gap. The Natural Farmer Special Issue, p B-1-6. Barre, MA: NOFA Education Fund.

Drinkwater, L.E. (Summer 2011) A Holistic View: Leguminous cover crop management in organic farming systems. The Natural Farmer Special Issue, p B-20-24. Barre, MA: NOFA Education Fund.

Tregaskis, S. (Summer 2011) In the Mix: Effective inoculation pairs active rhizobia with symbiotic legumes. The Natural Farmer Special Issue, p B-7. Barre, MA: NOFA Education Fund.

Tregaskis, S. (Summer 2011) Perennial Favorite: Legumes boost fertility and smother weeds in asparagus. . The Natural Farmer Special Issue, p B-9. Barre, MA: NOFA Education Fund.

Tregaskis, S. (Summer 2011) An Interview with Eric Nordell: Cover crops to suppress weeds, boost biomass, and fix nitrogen. The Natural Farmer Special Issue, p B-30. Barre, MA: NOFA Education Fund.

Drinkwater, L.E. (Summer 2011) The Word: key terms for understanding the science of cover cropping to boost nitrogen. The Natural Farmer Special Issue, p B-7. Barre, MA: NOFA Education Fund.

Drinkwater, L.E. (Summer 2011). Dear Vicki Vetch: Reviving a Depleted Field. (Vol summer,p.26-27) Cobleskill, NY: The Northeast Organic Farming Association of New York.

Drinkwater, L. E., and M. Gregory. (Winter 2010). Dear Vicki Vetch: The Why and How of Compost Analysis. Organic Farms, Folks, and Foods (vol. Winter 2010). Cobleskill, NY: The Northeast Organic Farming Association of New York.

Drinkwater, L. E. (2010). Dear Vicki Vetch: Clover Grass Combinations for Cover Cropping. Organic Farms, Folks, and Foods (vol. Spring 2010). Cobleskill, NY: The Northeast Organic Farming Association of New York.

Drinkwater, L. E., Schipanski, M., Piombino, A. (2009). Dear Vicki Vetch: Nutrient Budgeting and Cover Crops. Organic Farms, Folks, and Foods (vol. Spring, pp.1). Cobleskill, NY: The Northeast Organic Farming Association of New York.

Drinkwater, L. E. (2009). The Ins and Outs of Nutrient Budgeting. Organic Farms, Folks, and Foods (vol. Spring, pp. 20-22). Cobleskill, NY: The Northeast Organic Farming Association of New York.

Drinkwater, L. E., Piombino, A. (2009). Dear Vicki Vetch: New Varieties of Hairy Vetch. Small Farms Quarterly (vol. Winter, pp. Page 17). Ithaca, NY: Cornell Small Farms Program.

Drinkwater, L. E. (2009). Dear Vicki Vetch: Nutrient Budgeting and Cover Crops. Small Farms Quarterly (vol. Spring). Ithaca, NY: Cornell Small Farms Program.

Drinkwater, L. E., Schipanski, M. (2009). Dear Vicki Vetch: Red clover vs clover-grass mix for a cover crop in winter grains. Small Farms Quarterly (vol. Summer, pp. Page 17). Ithaca, NY: Cornell Small Farms Program.

Drinkwater, L. E., Gregory, M. (2008). Dear Vicki Vetch: Interseeding Cover Crops. Organic Farms, Folks, and Foods (vol. Summer, pp. Page 15). Cobleskill, NY: The Northeast Organic Farming Association of New York.

Drinkwater, L. E., Piombino, A. (2008). Dear Vicki Vetch: New Varieties of Hairy Vetch. Organic Farms, Folks, and Foods (vol. Fall). Cobleskill, NY: The Northeast Organic Farming Association of New York.

Drinkwater, L. E., Gregory, M. (2008). Dear Vicki Vetch: Interseeding Cover Crops. Veg Edge (vol. 4, issue 9). Ithaca, NY: Cornell Cooperative Extension Vegetable Program.

Drinkwater, L. E., Piombino, A. (2008). Dear Vicki Vetch: New Varieties of Hairy Vetch. Veg Edge (vol.4 issue 12). Ithaca, NY: Cornell Cooperative Extension Vegetable Program.

Overview of workshops and related outreach activities

We conducted outreach through eight events—three in-depth workshops and five shorter presentations or field days ranging from 30 minutes to 2 hours in length. We followed our original plan of holding an introductory workshop during the first winter of the project that provided basic information about the biology of nitrogen fixation and included a panel of experienced growers who had successfully integrated legume cover crops into their farming systems. In the second, more advanced workshop held in January 2010 we presented our findings on nitrogen fixation rates in farmer fields and a panel of four growers who collaborated with our on-farm assessments. The third in-depth workshop targeted beginning farmers and also served as a pilot test for educational materials we were developing to be used by farmer educators. We conducted before and after assessments in all three of these intensive workshops. After the first, introductory workshop held in 2008, more than half of those who filled out the evaluations gave examples of plans to modify cover crop management as a result of the workshop. In our second workshop, the evaluations indicated 80% agreed/strongly agreed that the workshop was beneficial to their work and described an adjustment/new practice they planned to try based on what they learned at the workshop.


Drinkwater, L.E., Scott, H.A. Groundswell New Farmer Training, “Cover Crops: How they work, how to choose them effectively, and how to assess them in the field,” Northeast Beginning Farmers Program, West Haven Farm, Ithaca, NY. (June 2011), 2 hrs (20 attendees)

Drinkwater, L. E., Van Zyl, B., The Empire State Fruit and Vegetable Expo, "Supplying Nitrogen With Warm Season Legumes", Cornell Cooperative Extension, Syracuse, NY. (January 2010), 30 minutes,( 60 attendees)

Drinkwater, L. E., Organic Farming and Gardening Conference: Circles of Caring, "Getting the Most Out of Legume Cover Crops", The Northeast Organic Farming Association of New York, Saratoga Springs, NY. (January 2010), 3.5 hrs (24 attendees)

Drinkwater, L. E., Cornell Organic Cropping Systems Field Day, “Evaluating cover crop performance in the field.” Freeville Organic Research Farm. (August 2009), 1 hr., (20 attendees)

Van Zyl, B. (Presenter & Author), Drinkwater, L. E. (Author Only), Cornell Organic Cropping Systems Field Day, “Warm season cover crops: field demonstration”, Freeville Organic Research Farm. (August 2009), 1 hr. (20 attendees)

Drinkwater, L. E., Empire State Fruit and Vegetable Expo Farmers' Direct Marketing Conference, “ What can legumes do for you? Understanding biological nitrogen fixation from the ground up!” New York State Vegetable Growers Association, Rochester, NY. (January 2009), 2 hrs. (65 attendees)

Drinkwater, L. E., Twilight meeting: Farmer's Research Circle, "Managing legumes to optimize biological N fixation", Invited, Farmscape Ecology Program, Ghent, NY. (July 2008); 1.5 hrs, (30 attendees).

Grossman, J. and Drinkwater, L. E. and , The 26th Annual NOFA-NY Winter Organic Farming & Gardening Conference, "What Can Legumes do for YOU? Understanding Biological Nitrogen Fixation from the Ground Up", Northeast Organic Farming Association, New York, Saratoga, NY. (January 2008), 3.5 hrs. (20 participants)

No milestones

Additional Project Outcomes

Project outcomes:

Impacts of Results/Outcomes

Overall, the verification process which mainly depended on follow-up phone calls was not very effective. As a result of reaching nearly 260 growers/educators through eight workshops/field days we could not follow up with all of these participants to document actual numbers who modified cover crop practices as a result of workshop participation. We targeted a smaller subset of these participants; however, despite significant efforts we did not capture enough data to permit quantitative analysis of uptake of practices from these workshops. In contrast, we did see evolution of practices on the farms we sampled for BNF. However, it is difficult to attribute these changes to our project since many of these growers are innovators in cover crop management. Furthermore, we were not promoting a single clear practice since we did not begin this project with a solution in mind. Rather, the aim of our work was to collaboratively investigate legume cover crops usage among vegetable producers to determine how effectively BNF was being managed. On that front, we learned a great deal from the collaborating farmers and the detailed measurements we made on their farms. We found that BNF rates in these vegetable farms are extremely variable across farms and fields compared to grain farms. The amount of nitrogen fixed is particularly variable in legume grass mixtures and is highly dependent on whether or not the non-legume out-competes the legume. We are working to develop rules of thumb that can be used by growers to adjust their seeding rates for mixtures so that they are better matched to the soil fertility conditions on their farms. While we need additional measurements in order to sort out the relative importance of soil fertility, planting dates and seeding rates, our preliminary analyses indicate that farmers can use systematic observations to adjust seeding rates so that a more optimal balance of grass and legume biomass is produced. Additional key outcomes are summarized below. • One farmer collaborator conducted evaluations comparing different cover crop species and mixtures on his farm with the aim of expanding the choices for legumes that could fit into his rotations. • One grower in the Hudson Valley who was very interested in expanding summer N-fixing cover crops tried to purchase seeds to test one of the mixtures we have evaluated and found that forage soybeans are difficult to find. • Another farm near Ithaca is expanding their acreage so that they can grow more cover crops. We are working with them to fine-tune a pea mixture to precede their fall brassicas. • Two younger farmers who have had less experience in presenting their management techniques spoke on farmer panels for our workshops and expanded their roles as farmer educators. • Effective management of cover crops is particularly difficult for beginning farmers. We consistently found that experienced growers were able to include more N-fixing cover crops in their rotations and reduce their reliance on compost. The exception to this was farms in farms that were land limited where even experienced growers were not able to meet their goals for inclusion of cover crops in rotations. • Nearly all of the farmers which we contacted and conducted some on farm sampling (18) had questions for us on how to better manage legumes. From these conversations, we learned about barriers and additional needs for optimizing legume management as well as innovations that farmers were experimenting with in the course of refining their management systems. • We learned a great deal about successful systems that farmers are using. These farmer-developed systems for managing legumes were disseminated through workshops and are also documented in the Special Issue published by The Natural Farmer. Four different examples of successful grower management systems for legume cover crops were captured in this special issue. • We have heard from four farmer educators who are using materials and information resulting from our project. • In addition to the issues related to managing intensive vegetable rotations so that cover crops can fit into the rotations, we learned about other barriers. Difficulty with finding cover crop seed for purchase is also a barrier that farmers mentioned frequently. Future outcomes: NOFA –NY has decided to expand the Ask Vicki Vetch column to cover a broader range of topics continuing with the Q & A style so that farmers can submit questions on any aspect of organic farming. We are in the process of working out the specifics of this opportunity. Luckily, the PI has funding from another source which is supporting an education specialist who can assist with this on-going opportunity.

Economic Analysis

We did not propose to carry out any economic analysis in our project.

Farmer Adoption

Farmer adoption issues have been discussed in Section 6. Impact of results/outcomes. Feedback on publications: “The summer 2011 issue of The Natural Farmer is the best issue I have read in the last few years. It was very in depth and a great combination of the science and the practical. Keep up the good work.” “I just read your excellent introductory article in the Natural Farmer… I am a part-time farmer, part-time teacher, and will be teaching an Ecological Agriculture seminar here on my farmstead this summer – for “non-traditional” students - i.e. older students returning to school for their undergraduate degrees. I think this article will work very well to help them understand and be inspired by the complexities of soil/plant interactions. I really appreciated the accessible language you used, which at the same time did not over-simplify these wondrous relationships between plants and rhizobia.” ON Vicki Vetch from the NOFA farmer educators: “… we nominated several newsletter contributors for the “CAP” Creal Journalism Awards for this year, and you are among them. We submitted your (Ask Vicki Vetch) piece on reviving a neglected field with cover crops. We’ve never done this before (that I know of), and we’re not sure exactly what types of articles the program is looking for, so we picked out several different types of articles by a range of contributors.” Feedback from workshop participants We collected detailed feedback from our two workshops held at the NOFA-NY meeting. We ran out of time so only 8 participants filled out the evaluation questionnaire; seven out of eight provided examples of how they would use the information from the workshop on their farms and in farmer education. We had a much better return rate of evaluations for the second workshop (15/24) due to better time management. Of the fifteen participants who filled out the questionnaires after the second workshop, 100% agreed or strongly agreed that the organization and presentation of material was effective, 80% agreed/strongly agreed that the workshop was beneficial to their work. Eleven out of the fifteen respondents listed a management change they planned to try. A sampling of responses to evaluation questions are included below. What were the most useful features of the workshop? • Advice from experienced cover-cropping farmers who have already walked where I'm trying to get to; the knowledgeable lead organizer/presenter; the attention to using time efficiently • Discussion about cover crops and weed suppression • Learning what legume cover crops are used for • Some of the farmer presentations that discussed specific mixes and specific planting times; presentation on environmental factors affecting N fixation • Specifics on cover crop application successes • Verification of two theories: that legumes fix less nitrogen in the presence of greater levels of soil nitrogen, and that grasses can be used to soak up nitrogen, but that the relationship b/w grass and legume needs to be managed so the legume isn't competitively suppressed to the point where it can't fix N. Combined responses for both workshops: “Will the information you learned today change your management of soil fertility and use of nitrogen-fixing green manures? If so, list one specific change you will consider using, at least on a trial basis, in the next year?” • Bell bean and clover seedings • Yes; mixed legume-non legume cover crop; fava beans; buckwheat/clover mix • Possibly experimenting with Bell Beans, planting oats with my spring peas • Trying bare fallow periods targeting specific needs • Yes, next year I’ll not hesitate to use green manures on newly plowed land, hope to use green manure for last year’s potato area• Possibly experimenting with Bell Beans, planting oats with my spring peas • Yes, very helpful, will try peas • Mixing N and C cover crops • Yes, keeping fertility curve in mind so legumes aren’t necessarily going into the most fertile beds. • Bell beans, using mixes • Just expanding timing and successions of covers • Yes, nurse crop change from typical rye/vetch combo • “I will encourage people in NYC to plant winter legumes, and try using living mulches between crops. Also, I will work to bring workshops on cover cropping with legumes to NYC gardeners”
Assessment of Project Approach and Areas of Further Study:

Areas needing additional study

Cover crops are a key element of multifunctional agricultural systems that aim to increase ecological performance while also supporting production outcomes. While there has been a fair amount of research on specific cover crop management regimes, there are still some major knowledge gaps. There are two key areas where we believe additional work would be extremely beneficial. First, there is a wealth of farmer knowledge about cover crop management systems which is extremely detailed and sophisticated and is continuing to evolve. Currently, this knowledge is disseminated through informal and formal farmer networks, which largely bypass the research community. There is a need to improve the exchange of information from farmers to agricultural researchers so that scientists can complement state-of-the-art farmer innovations with research. Efforts to document farmer practices in the area of cover crop management are needed so that information on actual practices and their success rates are more widely available. Second, additional research on nitrogen fixation in legume species used as cover crops in the northeast is needed. We were surprised by the extreme variability in nitrogen fixation rates across these farms. Farmers need more information about how these legume species respond to environmental conditions and soil fertility. In addition, interactions between specific cover crop management options such as planting dates and seeding rates with soil environmental conditions are needed so that farmers can fine-tune cover crop mixtures and obtain more consistent rates of nitrogen fixation. This is particularly important for mixtures of legumes and non-legumes, where nitrogen fixation rates varied nearly ten-fold across farms. Lastly, there is also a need for additional measurements of nitrogen fixation rates in legume cover crops on working farms.

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.