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Home  > Conversations from the Field > Dave Wilson

Conversations from the Field

ATTRA talks to movers and shakers in the sustainable ag movement

Conversations from the Field Archives

Conversations from the Field features interviews with sustainable agriculture leaders. It is designed to highlight successful practices, creative programs, and progressive ideas, and to encourage readers to develop a more comprehensive understanding of the sustainable ag movement. We welcome your feedback on Conversations from the Field.

The Rodale Institute, Part 2 of 2
Dave Wilson — Research Agronomist

Dave Wilson

Our latest feature interview with a sustainable agriculture leader is the second installment of a two-part series on cover crop and reduced-tillage research at The Rodale Institute.

Dave Wilson is The Rodale Institute's (TRI) Research Agronomist in Kutztown, Pennsylvania. Dave conducts research on organic farming systems at the 300-acre Rodale Institute farm. For this installment, NCAT agriculture specialist Andy Pressman talked with Wilson, last September, about the organic farming and organic no-till system research at the TRI.


Q. How has your research in organic no-till corn and soybeans contributed to the success of the roller crimper as an appropriate technology?


For the latest results from the 2007 field trails, please visit The New Farm.

A. As an agronomist, I look at this system as two agronomically sound practices that are tied together by the roller crimper. The first is growing cover crops. In the case of growing no-till corn, we're growing hairy vetch (Vicia villosa), a legume. In the case of soybeans, we're growing winter rye (Secale cereale). Then we come along with this piece of equipment, in the late spring, and we mechanically roll the cover crop into a weed-suppressing mat. This is the second agronomically sound practice because we are organically suppressing weeds and, in the case of hairy vetch, fixing nitrogen.


Q. The major consideration in using these winter annual cover crops is timing the mechanical rolling to the bloom stage. Why is this important for no-till plantings?

A. Waiting for the cover crops to reach the full-bloom stage before rolling provides the highest amount of kill. For no-till, this ensures that the cover crop is mature enough to supply enough biomass for both weed suppression and nitrogen for the corn.


Q. Does this imply that plant nitrogen levels are highest as they reach the end of their life cycle?

A. We are looking for a 90-100% bloom. This is important for hairy vetch because we want to maximize our nitrogen percentage. If we're talking about hay, farmers time their cuttings of alfalfa or clover to maximize protein, which is referring to nitrogen. In the case of green manures, we are talking about the same thing, but we refer to this as nitrogen tissue level. At this level of bloom, the amount of biomass, as well as the percentage of nitrogen in the tissue, is greatest.


Q. How does the nitrogen from the biomass become available to the plants?

A. Nitrogen from the mat gets into the soil through weathering and leaching. That is why we measure the above-ground biomass, which can be anywhere from 4,000 to 9,000 pounds per acre of dry matter. We multiply that by the tissue analysis which, if it's earlier in the season, can give us anywhere from 100 to over 200 pounds of nitrogen per acre. This is available slowly as it decomposes and is leached down, but not all of it is available. Some nitrogen is released from being stored in organic matter. The roots of hairy vetch also house the rhizobium nodules that fix nitrogen that is not only used by the plant, but is also exuded out into the soil.


Q. You mentioned green manures, which are crops grown to improve the soil by incorporating them into the soil while they are green or soon after flowering. How do the nitrogen levels from cover crops differ from those of green manures?

A. In organic systems, we depend on green manures as a direct source of nitrogen. Rolling cover crops makes less nitrogen available because some of it volatilizes back into the atmosphere; perhaps up to 50%. This is why stewardship and soil fertility are so important. Building soil organic matter drives organic cropping systems. The hairy vetch is the only source of nitrogen in our system.


Corn with cover crop

Q. Is there ever too much nitrogen resulting in free nitrates?

A. My research includes incorporating "catch crops" of small grains to reduce the amount of free nitrates. I have found that when planting the hairy vetch with small grains, the amount of biomass gained from the small grains reduces the amount of legume nitrogen. We plant corn with spring oats rather than barley, wheat, or rye because oats gives us early cover since the hairy vetch establishes more slowly. The oats die when the ground freezes, at which point the hairy vetch grows and maximizes the amount of biomass. Oats will also help soak up some of the free nitrates in the fall because they are a grass. This is important because if a legume has free nitrates, it doesn't send the signal to the rhizobium to fix nitrogen. It is more energy efficient to take the free nitrates than to feed the rhizobium. Therefore, we have more legume biomass in the spring, than legume/grain biomass. For organic corn growers, it is critical to get nitrogen for the corn. A conventional grower can use the legume/grain mix and add nitrogen to make up the difference.


Q. Does planting small grains allow for a reduction in seeding rates?

A. In looking at our drill, it says to plant 22-30 lbs/acre for hairy vetch. We find that we can cut that rate in half by planting every other drill row with oats. So with hairy vetch, you can get away with a little less seeding rate. This is important because the cost of hairy vetch seed keeps increasing in response to the demand for nitrogen. For rolling and not harvesting small grains, we tend to increase the seeding rates to get more uniform biomass. There is one exception; planting rye with vetch. We look for 2 ½ -3 bushels per acre of rye. That's 3 to 3 ½ million plants per acre. Typically, it can be less when combined with vetch. Many farmers are combining these for plow-down green manures.


Q. Do you consider germination rates into the seeding equation?

A. Being cautious about germination rates is very important. Hairy vetch should have a germination rate of about 85%. I've seen some seed packs that have a 70 to 75% germination rate. This difference of 10% impacts the seeding rate. We also have to be cautious about the fact that about 10% of the 85% is hard seed. This is especially true with legumes. They can stay dormant for several years before becoming prolific.


Q. Should farmers be concerned about the variety of cover crop used in this system?

A. Variety is also very important. In looking at varieties of rye, we are interested in those that produce more biomass. For hairy vetch, we are interested in winter survivability. We need a cover crop in the spring and some varieties don't make it through the winter. Most hairy vetches are sold VNS (Variety Not Stated). Therefore, we look at the origin of the seed. This will affect bloom dates and plant viability. We like to use varieties from the south because they bloom earlier, in which case we can roll and no-till corn earlier.


Q. Would this at all affect crop rotations?

A. If they have the same life cycle. For instance, hairy vetch has the same life cycle as winter wheat and spelt. If you plant hairy vetch now, it may germinate when your rotation is for winter wheat, in which case you can't combine. One the other hand, spelt growers can separate the hairy vetch from the spelt. Keep in mind that a conventional farmer can spray herbicides to control the hairy vetch.


Q. How does TRI organically control the hairy vetch in the corn rotation?

A. For us, we have hairy vetch growing back in every field. This is OK because we typically have a longer rotation with a three-year hay crop. Then we go into corn, followed by soybeans.


Fields at TRI

Q. At what point do you decide to give up the practice of no-till in the rotation?

A. Conventionally speaking, no-till means "park-the-plow." This is a continuous system that relies heavily on chemicals and genetically modified seeds. Organic no-till is not continuous no-till. We are interested in establishing a cover crop in a cleanly tilled, weed-free seed bed in the fall. I prefer to call organic no-till "rotational no-till," because we are rotating the practice of no-till in the system. If you have enough biomass, you can roll and plant that year, but that doesn't mean it will work the following year. This gets the benefits of the cover crops and the agronomic practice of no-till. We are trying to take our systems out of tillage, but we are not saying, "plow, plow, plow!" Organic farmers have to keep in mind plowing if the cover crop doesn't make it.


Q. Many farmers think of planting into crop stubble when they hear the term no-till. Can you clarify what you mean when you refer to no-till?

For TRI's new DVD No-Till Roller Crimper, please contact Paula Hunker at TRI at 610-683-1400 ext.1427

A. In this system, no-till refers to rolling and crimping followed by no-till planting. We are not planting into crop stubble. We are no-tilling into a two- to four-inch mat of cover crop. We are riding two to four inches above the soil surface. That means we have to adjust our equipment so that the planter can aggressively get through the mat, and with good seed placement. It is so important that farmers start down the row; stop and get off of the tractor; walk around to the back and look to see if the seeds are in the furrow and are covered.


Q. Why are weeds suppressed and not the cash crop?

A. It has to do with the size of the seed. The corn and soybeans are large seeds that have a lot of stored energy in the starch. That energy allows them to be planted deep and grow through the residue. Typically, the majority of agronomic weeds are summer annuals with small seeds (ie. ragweed, foxtail, lambs quarter). These small seeds are buried during tillage so they can't come up. In conventional no-till, they are at the surface and are controlled with herbicides. In organic no-till, the mat blocks the small seeds from coming up, so they burn up their energy and can't get light for photosynthesis.


Q. How effective is the mat in suppressing these weeds?

A. This is not a perfect system and we do have challenges. Some of our fields are weedier than others. And we are finding that weeds can and do break through the rolled mat. In our no-till soybeans, many of the weeds, particularly ragweed and foxtail, are germinated and growing in between the rows of rye before it is rolled. When we roll the rye down, these weeds tend to continue growing and are somewhat resilient to the roller.


Q. Do you have problems with other types of weeds, such as perennials?

A. Some of the other weed problems that do occur involve deep-seeded weeds, such as Giant Ragweed, which are bigger seeds. There is lots of energy to push up through the mat. Perennial weeds, like Canada thistle and hemp dogbane, have root reserves of carbohydrates, allowing them to be quite noxious and challenging for us. Typically, we take care of these weeds through tillage with the moldboard plow.


Q. Does your research address these challenges?

A. One interesting observation I have made and measured is that in the clean till system (plowing, disking, cultivating) there are weeds right in the row with the crop. In between the rows is cultivated, so we have crop rows and weed rows. The weeds are in close association with the roots of the cash crop. They are more competitive for resources of water and nutrients growing right in the row than the weeds in the middle of the row. But there aren't any there because we till them up. In contrast, in the no-till system, what you'll find is that there are very few weeds right there with the crop, but many weeds in between the rows. It's the complete opposite. This is more of a problem with soybeans than corn, because corn grows tall and its canopy out-competes many of the weeds in any type of system. The only weeds that will win are those than grow taller than the corn and can access light. Most of the summer annuals are lower-growing and don't really compete.


Q. Are there other challenges you have experienced that other farmers should be aware of before implementing this type of practice?

A. One challenge with the no-till hairy vetch/corn system we are faced with in the Northeast is that the earlier planted corn gets hit by black cutworms (Agrotis ipsilon). The cutworms are on the hairy vetch before the corn germinates. In 2006, we performed a cutworm evaluation that showed we had about 32,000 cutworms per acre, which is equal to the amount of plants per acre. If the population peaks when corn is most vulnerable, you are at a loss.


Q. Have you found any preventative measures to control the cutworms?

A. Conventionally, there is transgenic Bt corn that prevents cutworm damage. But since we are organic, we have found that biologically timing the plantings seems to provide damage control . This is evident in our field trials. For example, one year we had 90% bloom of hairy vetch and planted something like 36,000 plants at four different planting dates. The early planting had only 7,000 plants survive. The second planting had 14,000 plants survive. Around 27,000 plants made it through the third planting and the fourth date had 29,000 survive the cutworms.


Q. What do you feel is your take-home message to both organic and conventional farmers?

A. Ideally, conventional farmers who use this system can really optimize well because they can get the benefits of using cover crops and still put down nitrogen, herbicides, and pesticides. Studies at Penn State University show that farmers can cut herbicide amounts by 1/16-1/32. That's working towards sustainability. What makes the organic farmer, in a sense, different than the conventional farmer, is that they have to know the biology of when to plant cover crop, the variety of cover crop, timing of kill date, and how to adapt to control pests. All of this information needs to be shared with sustainable, organic, and conventional farmers.


Conversations from the Field Archives


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This page was last updated on: February 9, 2015