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.

2016 Harvest

We harvested the plot on Tuesday, October 11. Total yield was 60 bushels per acre, not bad considering it was planted on June 1.

SWCD Supervisor Chris Branaman volunteered to harvest the plot for us.
SWCD Supervisor Chris Branaman volunteered to harvest the plot for us.

Even though harvested acreage was only a little over 7 acres, there were a couple of interesting items. First, as can be seen from the table at the bottom of the page, the presence of cover crops made little difference in yield. As this was the first year for cover crops, this was not a surprise. Check back in a few years to see if this changes.

We had weed issues on the southern side of the field. We don’t know why but the two southern strips, planted to cereal rye and annual ryegrass last fall, had significantly more weeds. However the northern strips using those two cover crops did not. We’re not sure if there was a problem spraying or what however yields for those two strips were lower.

The weeds – mostly grass – on the right covered two strip treatments. The rest of the field was relatively weed-free.

We had volunteer oilseed radish. The two oats/radish strips had some very lush plants. This also appears to have affected yields though not as severely as the weeds did. We don’t know why this happened. We planted last fall about two weeks after the recommended time but radish did germinate and emerge. This may have been from seeds which did not germinate last fall. It may also have been plants that did not winter kill. Last winter was extremely warm and even though oilseed radish typically winter kills, some may have survived. 1 Whatever the cause, it shows how a cover crop can become a weed.

Oilseed radish
Oilseed radish “infestation.”
Our Purdue Extension intern holding a radish we “harvested” before cutting soybeans.









Most of the field looked good. We harvested by running a combine with a 20′ bean head down the center of each 40′ strip and stopped to measure from the yield monitor. This is not terribly scientific but we were looking for differences between strips, not absolute yield numbers.

Harvest in progress. We ran the combine down the center of each cover crop
Harvest in progress. We ran the combine down the center of each cover crop “treatment” to measure yield.

The following table shows the yields for the cover crop strips.

Click for a larger image to see yields.
Click for a larger image to see yields.
Map showing the cover crop strips planted in fall, 2016.
Map showing the cover crop strips planted in fall, 2016.

Our next step is to plant our 2016 cover crops. We also plan on soil testing the field. We do not expect to see much change in soil characteristics after just one year but plan to monitor this on a regular basis going forward.

1 Between December 1, 2015 and April 1, 2016 the lowest temperature in Whitestown, about 2 miles south of this field, was 19.7 degrees according to the National Weather Service. In fact, temperatures fell below freezing only in January and February. This is extremely warm for this area.