Demonstrating the Economic and Environmental Advantages of Legume Cover Crops to New England Growers

Final Report for LNE92-031

Project Type: Research and Education
Funds awarded in 1992: $100,000.00
Projected End Date: 12/31/1994
Matching Non-Federal Funds: $6,290.00
Region: Northeast
State: Massachusetts
Project Leader:
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Project Information


[Note to online version: The report for this project includes tables and figures that could not be included here. The regional SARE office will mail a hard copy of the entire report at your request. Just contact Northeast SARE at (802)-656-0471 or [email protected].]

Winter rye (Secale cereale) is the predominant cover crop species seeded in the northeastern United States. This winter-annual species is used widely in this area because it is inexpensive, can survive the harsh winters of this region and it protects the soil from wind and water erosion. However, this commonly used cover crop will not add much nitrogen to the soil.

Legumes are nitrogen-rich plants due to a symbiotic association with bacteria in the soil. One legume in particular, hairy vetch, has several characteristics that are advantageous for New England. The most important characteristic is that it is very efficient in fixing nitrogen from the atmosphere. This legume can add tremendous amounts of nitrogen to the soil if allowed to grow long enough. A second important characteristic is that this cover crop is winter-hardy and can survive the cold winters here in New England.

The emphasis in this project was to deliver this legume and the necessary technology to use it effectively to growers. To this end, trials were set up on approximately 80 farms in Massachusetts, Vermont and Maine in 1993 and 1994. Results from these trials have supported research findings that hairy vetch can significantly reduce the addition of other synthetic sources of nitrogen. The majority of growers that allowed this legume to grow long enough were able to significantly reduce the amount of nitrogen fertilizer applied. Some growers were able to eliminate nitrogen fertilizer all together.

In order to support the extension aspect of this work, replicated experiments were carried out at the research stations of the University of Massachusetts and Maine. These studies continue to show the advantages that hairy vetch has for growers in this region. However, these studies also emphasis that special attention has to be paid to several management practices with the use of these cover cropping systems.

The economics of using hairy vetch depend on several factors: how much nitrogen the cover crop can add to the system; the cost of nitrogen fertilizer; and the comparison of hairy vetch management to the standard cover crop management on a particular farm. Comparison of many different options show that using a vetch seeding rate of 30 lbs/acre and allowing the cover crop to grow long enough to accumulate sufficient nitrogen is economically more viable than winter rye alone.

Cover cropping with hairy vetch appears to offer New England farmers opportunities to reduce dependence on fertilizer and manure as sources of nitrogen for vegetable crop production. However, as shown in the work described in this report, results of using vetch in vegetable production systems are variable. Many aspects of management remain to be worked out. Greater attention needs to be focused on (i) control of insect pests, such as seed corn maggot, whose abundance and damage may be increased by use of vetch; (ii) identification of vetch genotypes that survive Maine winters consistently; (iii) comparison of winter and summer cover cropping strategies; and (iv) development of management strategies that effectively balance the need to plow vetch early, to allow timely planting of subsequent cash crops, against the need to delay plowing, in order to maximize biomass and nitrogen production.

Project Objectives:

1. Conduct farm-scale demonstrations of hairy vetch/rye cover crops and determine regional variability of hairy vetch nitrogen supplying capacity at varying seeding rates.

2. Evaluate (and demonstrate to vegetable growers) hairy vetch/rye and hairy vetch/oat cover crop systems for weed suppression and nitrogen contribution with conventional and reduced tillage systems, and evaluate nitrogen movement toward ground water.

3. Demonstrate the economic advantage of legume/grass cover crops over no cover and grass cover crops.


Research results and discussion:

On-Farm Component

Massachusetts and Vermont

Enough cover crop seed to cover 1/2 acres was given to interested growers for the 1993 and 1994 seasons. Each grower was asked to maintain normal cover cropping and fertility management on a similar sized piece of land adjacent to the legume/cereal mixture. This would provide a good comparison of the new system, both for the grower and extension personnel.

Cover crops and technical information were delivered to growers who had expressed interest in using these cover crop species in the late summer and fall of 1992 and 1993. A major focus of the project was to have the growers seed the cover crops in the fall and manage the cover crops the following spring and summer so that they would have hands-on knowledge of the system. Much of the earlier on-farm work with these alternative cover cropping systems had been managed by extension personnel. It became apparent that this approach left the grower unaware of many of the management practices needed to ensure success of this system.

Cover crops were sent to 75 growers in Massachusetts and Vermont in the late summer and fall of 1992 and 1993. In addition, several growers that participated in the program bought their own vetch, but received technical advice from the project. Figure 1 shows the location of the 35 growers in Massachusetts that were given cover crop seed in 1993.

Not all of the 75 growers that received the cover crops seed were able to complete the project. Some were not able to establish the seed in the fall for various reasons. Some that did seed the cover crops in the fall did it so late that it was not able to survive the winter. Some growers did not allow the cover crops to grow long enough in the spring to get sufficient nitrogen accumulation. These growers are not included in the information presented in Tables MA-1, MA-2 and MA-3.

The trials were monitored over the course of the season by the growers and project staff. Growers were visited early in the year, before incorporation of the cover crops, to review management options. A soil sample was taken and analyzed in time to estimate phosphorous and potassium requirements. Copies of the soil tests were sent to the growers along with recommendations for their cash crop.

Growers were encouraged to reduce, if not completely eliminate, the amount of nitrogen broadcast on land that had hairy vetch. For many growers this was difficult because of the analysis of fertilizer that they had in stock. In most cases the soil tests would call for certain amounts of phosphorous and potassium to be applied to the field. When the growers used their fertilizer to meet the P and K requirements, they would also be applying nitrogen to their fields.

We would try to visit the farm again before the cover crops were incorporated so that we could take a cover crop sample that would allow us to estimate the amount of nitrogen that the above-ground portion of the cover crops were providing. In some cases this was not possible to arrange.

Growers were visited one or two times more during the growing season, if possible. For sweet corn, and a few other select cash crops, we tried to take a soil sample a week before a nitrogen sidedress would be applied (pre-sidedress nitrate test). The soil test was analyzed by the soil lab at the University of Massachusetts and the results were phoned to us in one day. I would then call the farmer with the results and would consult with him as to the amount of nitrogen fertilizer that should be used.

Farmers were asked to keep records of the amount of fertilizer applied to the cash crops in addition to all other aspects of crop growth. Growers were contacted at the end of the season and were asked to evaluate the project. This information is summarized in Tables 1, 2 and 3.

Demonstration plots were established at the Brattleboro office of Vermont Cooperative Extension in 1993/1994. One quarter acre each of vetch plus rye, vetch plus oat and rye alone were seeded. Results from these trials were disseminated through twilight and grower meetings.


On-farm cover crop trials evaluating vetch as a winter annual green manure were conducted at two locations in Maine. This year's variable results are consistent with past performance of vetch in Maine. At the Piecemeal Farm, operated by Tom Roberts and Ben Wilcox, Dixmont, Maine, hairy vetch planted with rye in mid August 1993 performed well. Measured on 20 May 1994, two fields contained 1247 and 349 kg /ha above ground vetch dry mass (DM) which contributed 37 and 8 kg N /ha, respectively. Roberts and Wilcox also had success establishing vetch through planting a mixture of oats/peas/vetch. The three species mixture was planted early June 1993, mowed in late July 1993 and on the 20 May 1994 sampling date contained 1239 kg DM /ha vetch (54 kg N /ha). Alternatively, Paul and Karen Volckhausen at Happytown Farm, North Orland, Maine, planted rye/vetch in mid September 1993 - at this location essentially all of the vetch winter killed.

Although there is a niche for using hairy vetch as a full season cover crop in Maine, variable performance limits its use as a winter annual green manure. A function of location, establishment method, and vetch genotype (see Research Results), additional research is necessary to understand the causes of this variability. Growers such as Tom Roberts and Ben Wilcox who can take a field out of production for a season are generally pleased with a three species, spring-sowed green manure. The mixture of oats/peas/vetch, referenced in early farming literature as a soil building green manure, produces much biomass and is quite weed suppressive. At the Maine Agricultural Experiment Station, Presque Ile, Maine, oat/pea/vetch is typically planted at 54, 168, and 34 kg /ha, respectively. In 1992 and 1993 this mixture produced 6343 and 6513 kg DM /ha (208 and 178 kg N /ha), respectively. Although the extent of oat/pea/vetch spring green manuring in Maine is not known, in 1994 the mixture was sold by both Johnny's Selected Seeds (Albion, Maine) and Fedco Seeds (Waterville, Maine) (Figure ME-1) suggesting a somewhat recent market demand for this mixture.

Constraints to Adoption

There are three major points that are viewed as potential constraints to the adoption of these alternative cover cropping strategies by growers. They are summarized as follows:

1. Considerations unique to the use of hairy vetch as a cover crop.

A. Timely establishment of hairy vetch. As stated above, many growers were given hairy vetch who were not able to establish it early enough in the fall, if at all. Many growers are accustomed to seeding their cover cops very late in the fall, too late for successful establishment of hairy vetch. We are recommending the vetch be seeded no later than mid-September (however growers on the coast can easily seed vetch later than this). Growers seeding their fields with rye in October is not uncommon. Most growers that did not seed it said it was just a question of not having enough time.

B. Cost and availability of hairy vetch. Seventy-seven percent of the growers that participated in the project in 1993 said that they are willing to plant hairy vetch again. However, many growers expressed concern about the cost of this cover crop. The price varies greatly depending on where it is purchased. This project has been buying hairy vetch from a company in Nebraska where the seed costs $. .75/lb. With shipping costs it comes to about $1.00/lb.

Local seed companies are now carrying this seed in stock whereas previously they would have to make special orders. However, the prices at these companies are well over $1.00/lb. There are some local growers that are beginning to raise this seed and combine it themselves. A grower in Great Barrington, Massachusetts offered hairy vetch that he had raised for well under $1.00/lb.

C. Proportion of hard seeds in commercially available hairy vetch seed. A common concern regarding the use of hairy vetch as a cover crop is that hard seeds will result in weedy vetch for years to follow. Studies in Maine indicated that hard seed ranged from 0 to 18% in six vetch accessions studied over two years (Jean-Luc Jannink, unpublished results). Hard seeds will likely continue to be a problem until varietal improvement eliminates this trait from commercial seed sources.

D. Overwintering of vetch in Maine. While somewhat consistent in more southern states, vetch overwintering in Maine is variable. Research conducted in Maine suggests that site, method of vetch establishment, and vetch genotype influence overwintering (Jean-Luc Jannink, unpublished results; see "RESEARCH RESULTS").

2. Considerations regarding soil fertility

A. Applying blended fertilizer at planting. Soil samples were taken on all fields in time to estimate the amount of phosphorous (P) and potassium (K) needed on each field. In most cases growers had already purchased the blended fertilizer to be broadcast or applied through the planter. This occasionally led to excessive amounts of nitrogen being applied at planting in order to add sufficient amounts of either P or K. For example, if the soil test indicated that 80 kg/ha of P2O5 was needed and the grower had a blended fertilizer with an analysis of 10-10-10, this would mean that they would have to add 80 kg/ha of nitrogen in order to satisfy the phosphorous requirements. We have recommended with this program that little or no nitrogen be applied at planting.

In some cases the growers were willing to purchase fertilizer with an analysis that would better fit their needs on that particular field. However, many growers prefer to buy fertilizer in bulk, in order to get cheaper rates, which will then be used on all fields for multiple years.

B. Reluctance to reduce nitrogen fertilizer. There were some growers who were very hesitant to dramatically reduce the amount of nitrogen applied. It was difficult for them to realize the amount of nitrogen that the cover crops were supplying. For some of these growers it was also a question of ignorance as to the amount of nitrogen that they were applying. When asked the amount of fertilizer that they normally apply at planting, some growers would give the total weight of the fertilizer and did not know the analysis.

Some growers were also concerned that the cover crops would 'run out a gas' and that the cash crop would need some nitrogen after the window of application had passed.

3. Interval between cover crop incorporation and planting.

Freshly incorporated plant material acts as an oviposition cue to seed corn maggot (Delia platura) adults. The larvae attack soybean, dry bean, corn, and a wide variety of vegetable crops including peas, numerous brassicas, spinach as well as potato and onion. Planting prior to the emergence of the larvae can result in severe infestation. Although degree day models have been used to specifically predict larval development and safe planting dates, a conservative measure is to delay planting until three weeks after green manure incorporation. The requisite planting delay may require incorporation of the green manure at an earlier date thus reducing the period of spring regrowth.

Economic Aspects of Hairy Vetch Mixtures

Hairy vetch mixtures are economically profitable as long as the farmer accounts for nitrogen saved and keeps seeding rates relatively low. Vetch mixtures become less cost effective when nitrogen prices are very low, when the farmer doesn't include the full amount of the nitrogen credit, and when vetch seed prices are high.

For most crop farmers in the Northeast, the major consideration is which fall cover crop to apply. There are relatively few options following a cash crop. Oats are inexpensive, provide quick growth if applied early enough, but are not winter hardy. Their major benefit is their ability to minimize soil erosion. Winter rye alone is also relatively inexpensive, provides quick growth and continues to grow late into the fall. It also provides growth in the spring, and acts to tie up nutrients in the soil. The use of hairy vetch mixed with either oats or winter rye can provide a significant amount of nitrogen production on top of the benefits of any winter cover crop.

Farmers making a decision on whether to use hairy vetch, or any other cover corp, need to assess a variety of factors, including: how the crop(s) fit into the crop rotation planned for the field; vulnerability of the field to erosion; and, costs of the various cover crop options.

Results of research conducted throughout New England has shown that the use of hairy vetch in mixtures with rye and oats can provide significant winter cover while supplying nitrogen to the crop which follows. Because hairy vetch seed is relatively expensive, the benefits from the use of hairy vetch depend a good deal on the seed price and on the length of time that the cover crop grows.

Most farmers who choose to grow a fall cover crop are already incurring some basic costs. Current recommended seeding rates of rye (2 bushes/acre), plus the cost of incorporating the rye in the Spring through plowing and disking, are estimated to cost about $38.00 per acre. Oats alone would be less expensive because most farms would not need to dow plow, and could prepare a seed bed by disking alone.

The hairy vetch/rye mixtures are very similar to rye alone in terms of cropping activities. The seed is planted in the fall, either spun on or drilled. In the spring, the vetch and rye resume growth until plowed under, with subsequent disking to prepare a seed bed. As a result, the extra costs associated with including hairy vetch in the cover crop mix are related primarily to the cost of the vetch seed.

Seed prices for vetch might present a major barrier to adoption of the crop, especially at higher seeding rates. At low seeding rates, any cropping strategy which can let the vetch grow until mid-season is cost effective, even at vetch seed prices up to $1.40 per pound (assuming nitrogen at $.30 per pound). At the higher seeding rates (40#/acre), vetch mixes are cost effective only when the cover crop grows for a long season and seed prices are below $1.00 per pound (assuming nitrogen at $.30 per pound). (See Figure 2 for comparisons).

The final decision is ultimately the farmer's. The key issues are determining the seeding rate and whether the cover crop can be maintained long enough in the Spring for the nitrogen credit to offset the cost of the vetch seed.


University of Maine

On-station experiments examined winter hardiness of hairy vetch genotypes, sweet corn yield following vetch, and weed-crop competition when fertility is supplied by a legume green manure.

1. Winter hardiness of vetch from six commercial sources.

Experiments to address the problem of inconsistent vetch over wintering in Maine were conducted by Jean-Luc Jannink, a M.S. student working with Drs. Liebman and Merrick at the University of Maine, Orono. Previous research had examined effects of planting date (mid-August vs. early September), soil drainage (well vs. somewhat poorly drained) and companion crop (none vs. rye vs. oat) on vetch over wintering. Vetch overwintered successfully only in 1990, and only on the well drained soil. Sole cropped vetch planted in mid-August, 1990 produced 96 g m 2 by May 1991, vs. 16 g m 2 when intercropped with rye and 32 g m 2 when Sole cropped in early September. Although vetch biomass in the vetch-rye mixture was low relative to sole cropped vetch, the consistent growth of rye reduced the coefficient of variation (CV) of aboveground N from 52% to 23% and weed dry weight from 57 to 19 g m 2. The multiple functions required of a winter annual green manure may therefore be fulfilled more effectively by a vetch-rye mixture than by Sole cropped vetch.

Subsequent experiments, planted in 1992 and 1993, evaluated the effects of location (central vs. northern Maine) and a rye companion crop on winter hardiness of vetch from six commercial sources. The degree of hairiness of hairy vetch varied among accessions. Interestingly, the more hairy genotypes (accessions 5 & 6) were more winter hardy than the less hairy genotypes (Table ME-1). Rye increased vetch winter survival; without rye average survival was 42.1% compared to 50.8% for vetch grown with the rye companion crop. Improvement in vetch winter hardiness and more information on the vetch-rye interaction are needed to make vetch a reliable winter annual green manure for Maine and areas with similar winter conditions.

2. Nitrogen fertilizer replacement value of cover crops preceding sweet corn

During 1993-1994, an experiment was continued at the MAFES Sustainable Agriculture Research Farm to quantify the nitrogen (N) contribution from alfalfa, winter rye, and rye plus hairy vetch cover crops to a subsequent sweet corn crop. The first rotation cycle (1992-1993) was described in the 1993 progress report.

Although there were no significant differences in cover crop biomass in May, 1994, weed biomass in the alfalfa cover crop (601 kg /ha) was greater than either rye or rye plus vetch. Nitrogen content of alfalfa, rye, and rye plus vetch at destruction were 85, 53, and 61 kg /ha, respectively. The similar nitrogen contribution from rye and rye plus vetch was due to a poor stand of vetch in the mixture; the mixture was 90% (w/w) rye.

Response of sweet corn to cover crop and fertilizer N is summarized in Table ME-3. Cover crops affected leaf chlorophyll at the 6-leaf and silk stage; however, no cover crop effect was observed in relation to sweet corn yield. The number of marketable ears /ha increased with N fertilizer rate in all cover crop systems, but the response was more pronounced in the system containing rye alone. This differential response depended on whether a legume is included (see contrast Table ME-3). The same contrast was significant when looking at marketable yield, indicated that the response to supplemental N depends on whether a legume cover crop is used.

In the first cycle of this experiment (1992-93) the legume green manures contributed significantly to sweet corn yield. The lack of this response in the second cycle (1993-94) may be explained by several factors. First, cover crop biomass at incorporation was 60% lower in the spring of 1994 than in the spring of 1993. This reduction is attributed to later seeding date (14 d) and earlier destruction date (10 d) in 1993-94 compared to 1992-93 which limited cover crop growth. There was a large difference (84 kg /ha) in the biomass of the rye-vetch mixture between the rotation cycles due to the much less successful establishment of vetch in 1993-94. For the rye-vetch mixture, spring biomass was 62% vetch in 1993, but only 10% vetch in 1994.

3. Cover crop and N fertilizer effects on Marafax bean grown alone or with mustard.

In addition to their role in building soil quality and supplying subsequent crops with nitrogen, legume green manures may also affect weed population dynamics and weed-crop competition.

In 1993 an experiment was initiated to determine if wild mustard (Brassica kaber) interference with dry bean (Phaseolus vulgaris cv. Marafax) can be reduced through fertilization with green manure instead of synthetic N fertilizer. In the spring of 1994 bean and mustard monocultures and bean-mustard mixtures were planted on plots treated with a factorial combination of crop residue (wheat stubble vs. red clover) and N fertilizer (applied or not applied). Incorporation of wheat stubble resulted in the addition of 11 kg N /ha compared to 100 kg N /ha from 239 g m-2 of above ground red clover dry biomass. Synthetic N fertilizer was side dressed to appropriate plots immediately after planting. At 24, 51, 72, and 96 days after planting (DAP) plants were harvested to determine root, stem, leaf and reproductive biomass, and leaf area. Mustard caused the greatest reduction in bean seed yield (96DAP) when N was side dressed and plants were grown following incorporation of wheat stubble. Bean seed yield was higher and mustard was less competitive following clover than following wheat stubble. In contrast, clover residue caused a decrease in mustard pod biomass in the bean-mustard mixtures. These results demonstrate the potential for the incorporation of legume green manure fertility management to influence weed population dynamics.

University of Massachusetts

Three experiments were initiated at the UMass Research Station in South Deerfield, Mass. Two were undertaken in both 1993 and 1994. One was only initiated in 1993. The results from this third experiment were not put in the 1993 report.

1. Comparison of Conventional and Alternative Cover Crop and Nitrogen Management in Sweet Corn

This experiment was initiated at the UMass Research Station in South Deerfield, Mass. by three members of the Vegetable IPM Program. The goal was to integrate fertility, weed and insect management into one experiment. Only the fertility management parts of this experiment are presented here.

The goal of this experiment was to compare conventional cover crop and nitrogen management practices with alternative systems featuring the use of hairy vetch. The treatments here are very similar to those found on many of the cooperators farms. This experiment was implemented in 1993.

The experiment was set up as a replicated complete block with four replications. The 'conventional' treatment was seeded to winter rye and in the spring had the majority of its nitrogen applied as ammonium nitrate (see Table 4). The 'biointensive' treatment was seeded to hairy vetch, with either rye or oat, and had no nitrogen fertilizer applied at planting.

Only 35 lbs/acre of fertilizer nitrogen was added to the corn in the early biointensive experiment and no nitrogen fertilizer was added to the late planting. In both plantings there was no statistical difference between the yield in the biointensive and the conventional.

In the late planting, soil nitrate levels were 25 ppm after corn harvest compared to 4 ppm in the biointensive. This supports the premise that alternative nitrogen sources can be used to get good yields while lessening the potential environmental contamination.

2. Nitrogen Fertilizer Effects on Legume and non-Legume cover crops

There are situations in which no nitrogen fertilizer has to be added when a legume-based fertility management system is employed. However, there are occasions when nitrogen fertilizer has to be added to ensure that there is no reduction in yield of the cash crop. These experiments gives us more information on the effects of nitrogen fertilizer on sweet corn following different cover cropping systems.

Figure 3 gives the results for an experiment that had three cover crop treatments as main effects. Each cover crop treatment had four rates of nitrogen fertilizer added to the sweet corn in split applications.

The results from this past year were similar to those in 1993. Hairy vetch without the synthetic fertilizer gave very good yields, similar to those achieved with high rates of synthetic fertilizer when winter rye or no cover crop were used.

The yield of the sweet corn in the hairy vetch treatment rose dramatically with the addition of synthetic fertilizer. This was not observed in the 1993 trial. The variety used ('Sweet Sal') will produce two marketable ears per plant under optimal conditions. Many of the plants in the vetch treatments had two marketable ears with the addition of synthetic nitrogen.

3. Comparing different rates of hairy vetch with conventional cover cropping and nitrogen management systems.

Concern has been expressed about the cost of the cover crop hairy vetch. An experiment was implemented in 1993 and 1994 to compare lower rates of vetch to the standard rate of 40 lbs/acre. In both years the reduction of the hairy vetch seeding rate from 40 lbs brought a concomitant reduction in sweet corn yield (Figure 4). However, no nitrogen fertilizer was applied to any of the hairy vetch treatments. Figure 3 from the previously described experiment demonstrates that a small amount of nitrogen fertilizer will make the use of lower seeding rates of hairy vetch very attractive.

Participation Summary
No milestones
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.