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/