New Research Shows Planting Cover Crops can Aid in the Destruction of Weed Seeds

I was aware of many benefits of cover crops but recent research has found one I did not know about.

Purdue University Entomologist Ian Kaplan and Carmen Blubaugh, who earned her doctorate at Purdue and is now a postdoctoral research associate at Washington State University discovered that cover crops provide habitat for beetles and rodents that feed on weed seed and prevent it from becoming part of a “seed bank” in the soil. They found that fields planted to cover crops had three to four times as many weed seeds eliminated due to feeding as those without cover crops.

Additional information may be found in this Morning Ag Clips news release: Cover crops increase destruction of weed seed.


Report – March 30 Cover Crops Workshop and Field Day

We had a great day March 30 for our Cover Crops Workshop and Field Day. We had 32 in attendance, 24 farmers and while we had to work around thunderstorms we did find a window where we could go out and look over the plots – unfortunately the soil pits had filled up with water from the rains.

Field Day Attendees

The morning program included a presentation from Corey Lacey. Corey is a Purdue University graduate student working with Dr, Shalamar Armstrong on whether nitrogen taken up and stored in cover crops is available the following crop year. Research is ongoing with this but the ultimate answer is, “some is available but it will take more research to determine exactly how much.” Hopefully at some point there will be enough research where this impact can be determined more precisely. We also discussed termination, herbicide carryover, and how this can impact cover crop selection.

As there was a morning window when it wasn’t raining, we took advantage of the situation to head out to the plots. NRCS Soil Scientist Mike Wigginton discussed what he found at the plots and in the soil pits with attendees.

NRSC Soil Scientist Mike Wigginton discussing the plots.

The pits had filled up with water from a combination of water infiltration (it’s been a wet spring here) and rain the night before so these pictures are from the day before when we dug the pits. I’m focusing on root depth because while top growth is nice to look at and offers some benefits, beneath the soil surface is where things are really happening. It may be difficult to see the roots themselves in the pictures so look for the golf tees. Keep in mind that cover crop roots:

  • Increase water holding capacity and infiltration by forming channels
  • Provide a pathway for crop roots to travel, allowing more access to water during dry periods
  • Provide habitat for soil microbes
  • Through decomposition improve soil organic matter and increase nutrient availability
  • Help break up soil compaction layers
  • In the case of legumes provide nitrogen fixation

The cereal rye plot had some good spring growth going on and there were very few weeds present. Mike found roots to 32 inches deep, down to the glacial till layer. As you can see from the picture, the pit started to fill with water running right above that dense till layer as soon as it was dug.

Roots in the Cereal Rye strip.

The second strip was planted to barley, rape and hairy vetch. The growth wasn’t quite as lush as the cereal rye strip but it was coming. Mike found living roots in the soil pit down to 26 inches, right above the glacial till layer.

Roots at 26″ in the barley/rape/vetch strip.

The final strip with spring growth was planted to annual ryegrass, hairy vetch, crimson clover and rape. The rape and vetch were just getting going, the clover was coming in well but was still fairly small and the annual ryegrass had a lot of growth. Mike found a lot of roots in this pit, down to 36″.

Quite a few roots here, down to 36″.

One of the interesting “finds” was that even though short, crimson clover had already started nodulation meaning it was starting to add nitrogen to the soil. I have no idea if this will be a significant amount for the corn we’ll be planting but it will be something to look for this fall during harvest (as I type this we are planning to terminate on April 17 if the weather holds).

If you look closely you can see the nodules forming in the roots of this crimson clover plant.

We always plant one strip to oats and tillage radish because this is a great mix for farmers just getting started with cover crops. Oats and radish both winter kill so it takes away any termination concerns. While you lose some benefit because of no spring growth, it still provides quite a bit. We did not dig deep pits for this or our “check” strip with no cover crops as we would not have found living roots. Keep in mind that last fall we planted the strips on October 18, well past the recommended September 15 date for both of these, based on the Midwest Cover Crops Council Selector Tool. The oats and radish did come up last fall but were pretty small. However even with this situation, the weed population was significantly less than in the straight no-till plots. The main weeds we found were dandelion, chickweed and purple deadnettle. Evidently, even though we planted later than recommended, the cover crops inhibited the germination of the winter annual weeds.

The left side is our strip without cover crops, on the right the oats/radish strip.

While we are not arguing that planting cover crops means you can do without weed control the next year (is anyone arguing this?) since purple deadnettle is a host for soybean cyst nematode (SCN), this mix, even planted late, may provide an advantage when planted ahead of soybeans.

While our plots are for demonstration and education, not research, I did find myself thinking it may be worth doing some weed counts in the future.

Following the plot tour we had a farmer panel featuring Zach Cain, a Montgomery County farmer, Clint Orr, a Clinton County farmers and Justin Mohler, who farms in Boone and Clinton counties. We had a good discussion. Much of it was on specifics such as planting equipment and setup, mixes that did and didn’t work, termination issues – really the nitty-gritty of cover crops.

For the final presentation of the day Brian Daggy shared information from Rulon Farms discussing the 321% return on investment they believe they have received through the use of cover crops.

This was a good day. I hope everyone learned a lot. On the evaluations several farmers said they intended to start planting cover crops and others mentioned new mixes they would try. Thank you to Boone County Farm Bureau for sponsoring lunch and, as always, to the many farmers, agribusinesses, lenders, etc., who have assisted with this project. I look forward to our next field day, sometime this fall.

SARE Cover Crops Innovators Series

Sustainable Agriculture Research and Education (SARE) has funded the development of a series of videos featuring 23 farmers around the country discussing their use of cover crops and the benefits they’ve seen. Two Indiana and several Midwestern farmers are among those included.

The videos were produced by Kurtis Harms of the University of Nebraska Cooperative Extension Service. You can find a link to the videos below.

Cover Crops Innovators Video Series

Field Day – Cover Crops 101

We had a very nice turnout for our March 24 Field Day. We had a total of 24 at the program, 19 farmers, which we were very happy with.

March 24 Attendees
March 24 Attendees

Unfortunately the weather didn’t allow us to be outside that day but we anticipated this might happen and had taken quite a few pictures the day before when we were digging pits and we also had a couple of soil cores taken from fields which had long-term cover crops plantings. As a fringe benefit, we may have gotten a few additional attendees as nobody could do field work.

Boone County SWCD Technician Brian Daggy discussing soil cores with farmers.
Boone County SWCD Conservation Technician Brian Daggy discussing soil cores with farmers.

Our main speaker for the day was NRCS Soil Scientist Mike Wigginton. Mike went through what he found at the pits and discussed the impact cover crops have on soil fertility and health. A substantial part of the morning involved group discussion, almost a round table where farmers shared their experiences and knowledge.

NRCS Soil Scientist Mike Wigginton in one of the pits.
NRCS Soil Scientist Mike Wigginton in one of the pits.

The Plots

We dug six soil pits and here’s a short summary of what was found. Keep in mind that last fall was the first time cover crops have been planted in this area.

Cereal Rye:
We had two different cereal rye plantings. One strip was planted on September 29 and the other was planted November 4. One of the farmers on our advisory committee suggested the late planting of rye to demonstrate how, even if conditions keep you out of the field until late, you can still get a good cover crop stand. The plots demonstrated this nicely. In the earlier planted cereal rye Mike found roots to 32″ deep in a pit with a dense till (glacial till) layer at 36″. He found roots to 33″ deep in the late-planted cereal rye strip.

Cereal Rye. The tee shows where Mike found roots. The water is from lateral movement above the dense till.
Cereal Rye. The tee shows where Mike found roots. The water is from lateral movement above the dense till.
Late-Planted cereal rye showing good early spring growth and root development.
Late-Planted cereal rye showing good early spring growth and root development.

Annual Ryegrass:
Mike found roots 36″ deep in the Annual Ryegrass strip. As expected, there was also a large amount of roots in the top few inches of the soil profile.

Annual Ryegrass.
Annual Ryegrass.

Oats-Annual Ryegrass-Crimson Clover:
This plot was one of our mixes. The oats winter-killed and the clover was just barely starting to come back so most of what was present was annual ryegrass. This was one of the shallower soils with a dense tillage layer at 27″. Mike found roots to 22″. This strip is one where it would be interesting to come back in a few weeks to see how things progress.

Oats-Oilseed Radish:
The oats and oilseed radish both winterkilled. We had a very dry month or so after planting last fall and didn’t have a lot of top growth though our germination was good. This was another shallow soil with glacial till starting at about 25″ deep. One of the interesting things Mike showed us was a permeable area indicated by soil color. This is a point where a cover crop root could penetrate and, over time (a long time) could begin to change the soil structure.

The grey color indicates a permeable area which will allow root penetration.
The grey color indicates a permeable area which will allow root penetration.

We dug a pit at our no-till “check” just to provide a visual contrast to the other plots. As you can see from the picture, there are no roots anywhere, not even in the top few inches. Even though weeds (and there were some) have root systems, they were very shallow and don’t provide much of a benefit.

No-till. You can see chickweed in the upper left of the photo but there are no visible roots, even near the surface.
No-till. You can see chickweed in the upper left of the photo but there are no visible roots, even near the surface.

The soil cores were very interesting as you could see roots 5 feet below the surface (which was the depth of the core).

You can't see the tape measure in this picture but the route identified by the golf tee is at about 60" depth.
You can’t see the tape measure in this picture but the root identified by the golf tee is at about 60″ depth.

This was a productive day with a lot of information shared. It will be interesting to compare these pictures with ones from future years to see if we can find any changes in soil structure, texture, color, etc., over time. It is unrealistic to expect significant changes in just a few months – the color and texture in the no-till strip did not vary significantly from the others – but in a few years we may see quite a bit.

March 24 Field Day Reminder

This is a reminder that we will be hosting a Cover Crops Field Day tomorrow, Thursday, March 24 from 9 a.m. to Noon (doors will open at 8:30 for coffee and donuts). The program will begin at the Boone County 4-H Fairgrounds Annex Building (the small building near the north entrance) in Lebanon, Indiana. If weather permits we will walk out and see soil pits in the County Education and Demonstration Area.

The forecast calls for rain and there is a chance that the weather will be bad enough that we’ll stay indoors. We dug the pits this morning and took a lot of pictures. We’ll also have some soil cores on hand. Even if it rains we’ll have a lot to talk about and will have the program as scheduled. We’ll just be talking about the pits from pictures rather than standing in the rain. If you are planning to attend please call the SWCD at 765-482-6355, ext. 134 or e-mail

You can find a flyer with additional information here.

The soil pits are dug!
The soil pits are dug!

The Nitrogen Scavenger

Curt Emanuel, Extension Educator, Purdue Extension – Boone County

In the page about Cover Crop Benefits one of the items discussed is the role of many of these as Nitrogen Scavengers. What is Nitrogen scavenging and how does it work?

The principle behind Nitrogen scavenging is pretty simple. Each growing season, some nutrients remain in the soil after the crop is harvested. In the case of most nutrients, we don’t worry much about them, so long as the soil stays in the field. They will be available for future growing seasons. Nitrogen (N) is different. It is not stable in soil so any excess N will usually be lost. This loss may occur in several ways. Some will be lost into the atmosphere through a process known as volatalization while some may be leached out of the soil or be carried off the soil surface as runoff by water.

Someone may look at the previous paragraph and say, “Shouldn’t farmers just use less nitrogen?” While there are certainly people who over-fertilize (but not many – fertilizer is expensive and farmers are no fonder than anyone else about spending money on something which does them no good), for the vast majority of farmers, the answer to that question is no. Farmers should plan to have a little nitrogen left over. It’s too fine a line to try to fertilize so the crop uses exactly the amount applied. All it takes is one rainfall event or some very hot, humid weather, and the crop runs out of N at the end of the growing season. The end of the growing season is when the plant sets its sights on reproducing – forming seed. By running out of N at this point, grain yields may be severely reduced. Corn ears may abort kernels, or they may add less starch to kernels, resulting in something known as low test weight, which will cause a dockage in the price farmers receive. Farmers should plan to have a little N left over; the financial risks of running short are too great.

When we plant cover crops, particularly those considered nitrogen scavengers – which all five fall, 2015 treatments are – those cover crops use the available N for their own growth. Instead of being lost, N remains in the field. Next spring as that cover crop is terminated, nitrogen remains available for the farmer to use in the next growing season.

In order to illustrate exactly how this works, we will need to do some math. The relevant information is that we applied 233.1 pounds of nitrogen per acre before planting the corn crop this May. That is enough N to grow 220 bushels of corn, which we were told is the yield potential of this field (our plot has very good, fertile soil). For those of you not in Central Indiana, this was a bad growing season. June and July had record amounts of rain. Waterlogged root systems are not efficient at transporting nutrients into the plant and producing high yielding corn. Our harvest for this plot was 150 bushels of corn per acre and we feel pretty good about that yield; many farm fields in this area did far worse.

In Indiana, the publication we use for making fertilizer calculations is Extension Bulletin E-2567, “Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat & Alfalfa.” If we go to page 9, we can see that 150 bushel corn should receive between 160 (for 140-bushel corn) and 190 (for 160-bushel corn) pounds of N per acre. We’ll split the difference and say that we should have applied 175 pounds of nitrogen per acre for 150-bushel corn.

When we subtract 175 from 233.1 we are left with 58.1 pounds of N remaining in the soil. The reality is that this year there probably isn’t quite that much. Due to the extreme wetness, some of this probably leached away. But much will remain. Instead of losing it either into the air or through future rainfall events this coming fall and winter, our remaining nitrogen will be taken up by our cover crops. This keeps it in the field where it will be available when we plant soybeans next spring. And while soybeans are a legume and produce their own nitrogen, they don’t start the nitrogen-fixation process until plants are several weeks old. Soybeans still use nitrogen to get started and what’s available will help in crop establishment.

There are many other cover crop benefits besides N-scavenging. However our crop situation this year, where yields are below expectations, provides a nice example of how cover crops can improve the environment by reducing the amount of nitrogen which finds its way into rivers and streams or the atmosphere. These cover crops may also help our financial situation by reducing the amount of fertilizer we need to use next spring. Double bonus!