Cover Crop Impact on Crop Yield and Water Quality: Single Species vs. Mixtures


Emily Waring

How do single species cover crops compare to mixtures when considering impacts to water quality and crop yield? On Wednesday, Emily Waring, Graduate Research Assistant at Iowa State University, presented results from a research project that has been carried out at six Iowa State University research farms from 2013 – 2018.

The research project compared oats and a mixture of oats, hairy vetch and radish before corn to a control site where no cover crops were used before corn. Before soybeans, the cover crops used were cereal rye and a mixture of cereal rye, rapeseed and radish, which were again compared to a site where no cover crops were used before soybeans.

Waring’s take home messages were:

  • Corn and soybeans are fundamentally “leaky” – cover crops can fill the void in the brown months (before cash crop planting and after cash crop harvest)
  • Nitrate concentrations were significantly reduced with the use of cover crops – with the highest reductions seen when using rye and oats
  • Corn and soybean yields were unaffected by the use of the cover crops
  • Rye and oats provide the best biomass return on seed investment

The research project results show that single species perform well, when when looking at water quality improvement and crop yield. The cover crop species mixtures were more expensive and did not perform better than the single species at reducing nitrate and improving water quality, however Waring stated that there are likely more benefits to diversifying mixtures that aren’t reflected in this study. Future research will look at the soil health benefits of using cover crops and will compare the use of single species vs. mixtures when improving soil health is the goal.

To learn more about the research results, watch the full webinar here.

Join us next month, on Wednesday, June 19 at noon, when Chris Hay, Senior Environmental Scientist at the Iowa Soybean Association, will present an Iowa Learning Farms webinar titled “Drainage Water Recycling: An Emerging Conservation Drainage Practice”.

Hilary Pierce

May 15 Webinar: Cover Crop Impact on Crop Yield and Water Quality: Single Species vs. Mixtures


Join us on Wednesday, May 15 at noon, when Iowa Learning Farms will host a webinar about cover crops and their impacts on water quality and crop yields.

Emily Waring

This webinar will discuss the impact of different cover crop species on water quality, measured via lysimeters, and cash crop yield at six Iowa State University research farms. Emily Waring, Graduate Research Assistant at Iowa State University, will present the current results from the research project.

“This research investigates which cover crop species are the most effective across the state of Iowa, and takes into consideration environmental quality and economic viability,” said Waring. Waring is a PhD student working with the Agricultural Water Management group; her research promotes environmental quality within agriculture through cover crops by measuring soil physical properties and subsurface drainage water quality.

A Cover Crop Adviser board approved continuing education unit (CEU) is available for those who are able to watch the live webinar. Information for submitting your CCA/CPAg/CPSS/CPSC number to earn credit will be provided at the end of the presentation.

Don’t miss this webinar!
DATE: Wednesday, May 15, 2019
TIME: 12:00 p.m.
HOW TO PARTICIPATE: and click the link to join the webinar

More information about this webinar is available at our website. If you can’t watch the webinar live, an archived version will be available on our website:

Hilary Pierce

Have we reached a tipping point for phosphorus saturation?

CLG-BannerImages-180213-04Phosphorus is one of the main nutrients of focus in the Iowa Nutrient Reduction Strategy. It is essential to the growth of plants, but when phosphorus enters our water bodies it leads to excessive plant growth and increases in toxic algae that are harmful to human and animal health.

A recent study from the University of Montreal quantified, for the first time, the maximum amount of phosphorus that can accumulate within the watershed before additional pollution is released into the water.

Their results indicate a relatively low threshold compared to current application rates and notes that tipping points could be reached in less than a decade.

Research supervisor, Roxane Maranger, aquatic ecosystem ecologist at University of Montreal, compared the relationship of the land and phosphorus accumulation like this:

“Think of the land as a sponge,” Maranger said. “After a while, sponges that absorb too much water will leak. In the case of phosphorus, the landscape absorbs it year after year after year, and after a while, its retention capacity is reduced. At that point historical phosphorus inputs contribute more to what reaches our water.”

Be sure to read the full article to learn how they conducted the study and further implications of the results.

Locally, the implementation of nutrient reduction strategy practices like no-till, cover crops, phosphorus application management, perennial vegetation, buffers and more are imperative to the long-term sustainability on our water resources.

Liz Juchems

Who Knew? Cover Crops, Corn and Water Molds Webinar Recap

Cover crops have numerous benefits, but not everyone is using them. Decreased yield is a major barrier but terminating at the right time can minimize risk. What are the factors that may impact yield and why does timing matter?

Dr. Alison Robertson, professor of plant pathology and microbiology and extension field crops pathologist at Iowa State University, wondered if corn seedling disease could be the culprit.

“As a pathologist, when I look at reduced stands, more barren plants, and slower emergence, I automatically think of seedling disease.”

In this month’s podcast, Robertson details the research her team is doing to determine what management practices could reduce yield drag.

They first had to determine if winter rye can even host pathogens that infect corn seedlings. They discovered that rye can host Fusarium graminearum and Pythium sylvaticum.

Next, they set up a field trial experiment seeding winter rye ahead of planting corn. They terminated five plots at different times, anywhere from 25 days before planting to two days after planting.


Cover crop test fields in Boone, Iowa.

They found that when conditions are favorable, winter rye acts as a ‘green bridge’ for Pythium to infect the corn. Fusarium was present whether cover crops were used or not and Rhizoctonia did not appear at all.

Watch Dr. Robertson’s webinar here to learn the optimal time for termination and what additional factors may change it.

Brianne Osborn

Meet Conservation Learning Labs Farmer Brian Sampson

CLL Brian.jpg

Brian Sampson and his wife Deb raise corn and soybeans as well as operate a cattle feedlot in rural Story County. In 2016, Iowa Learning Farms approached Brian to be a part of a new Conservation Learning Labs (CLL)* project that is studying changes in nitrogen and phosphorus loss at the delivery scale.

Brian lives near an existing Conservation Reserve Enhancement Program (CREP) wetland in Story County that has measured water quality for about three years. Using the CREP wetland monitoring system, the project will be able to measure changes in water quality after the implementation of conservation practices like cover crops and strip-tillage in the project area over the next three years.


CREP Wetland near Roland in Story County

Brian tried cover crops on some of his fields in the past, but his results were mixed. In the fall of 2012, Brian says, “I flew cover crops onto my corn. I wanted to grow them to boot stage for my cattle. In the spring, it got wet and my bean planting was delayed . . . but it was a beautiful stand. I ended up baling it.” Brian tried cover crops again in 2013, but a dry fall hindered germination. The start of the CLL project was the assistance he was looking for to give cover crops another try.

“I flew cover crops onto my corn. I wanted to grow them to boot stage for my cattle. In the spring, it got wet and my bean planting was delayed . . . but it was a beautiful stand. I ended up baling it.”

In 2017, through the NRCS conservation planning process, Brian seeded a cereal rye cover crop and started strip-tillage on his fields, treating 42% of the project watershed. With technical support from CLL project partners and Key Coop, Brian hopes to be successful as he makes changes to his operation.

“I’m not an island. I need help,” Brian commented. “I have felt very supported through the project help I have received from ISU Extension, NRCS and Iowa Learning Farms.”

Brian and Deb have two children, Alex and Brice. In addition to farming, Brian is a member of the Story County Cattlemen’s Association and the Story County Farm Bureau.

Julie Winter

*The Conservation Learning Labs project is funded by the Iowa Department of Agriculture and Land Stewardship (IDALS) and the United States Department of Agriculture – Natural Resources Conservation Services (USDA-NRCS) of Iowa.

ILF Steering Committee Helping Make A Difference

Jake Hansen | Water Resources Bureau Chief at the Iowa Department of Agriculture and Land Stewardship (IDALS)

ILF_Badge_Multi_SMFor nearly 14 years, Iowa Learning Farms has established and maintained a presence as a respected and trusted source of conservation outreach and education in the state of Iowa and beyond. While many similar programs have come and gone over the years in shorter cycles, ILF has managed to remain at the forefront of the public dialogue around great things happening in conservation and opportunities that lie ahead.

The lion’s share of the credit for this should be given to the staff and the cooperators that have worked tirelessly to advocate for good land stewardship by farmers and urban dwellers alike. However, there is another group of key stakeholders that have worked with Iowa Learning Farms over the years to identify emerging education needs. That group is the Iowa Learning Farms Steering Committee.

Led by Iowa State University Extension and Outreach, the ILF Steering Committee includes representatives of six organizations that provide financial and technical support to the program. In addition to ISU Extension and Outreach, other agencies and organizations on the committee include the Iowa Department of Agriculture and Land Stewardship (IDALS), USDA- Natural Resources Conservation Service (NRCS), Iowa Department of Natural Resources (DNR), Iowa Farm Bureau, and Conservation Districts of Iowa (CDI).


Bioreactor: an edge-of-field conservation practice designed to reduce nitrate loss from the field scale

These organizations contribute decades of knowledge on conservation practices and outreach efforts along with access to statewide networks of farmers, agricultural decision makers, and local leaders. Our job is to identify emerging challenges faced by our farming community, as well as opportunities to use demonstrations by local conservation champions. In addition, we want to find means of scaling up implementation of key conservation activities.

The ILF Steering Committee typically meets 3-4 times per year and reviews program activities completed by staff while helping to identify future programming needs. The committee also provides insight and support on outreach funding sources and advises ILF leadership on potential funding opportunities. Perhaps most importantly, committee members are constantly in touch with a broad range of constituents and can provide real-time input on challenges to conservation adoption, ranging from management of cover crops to the economics of land use decisions and much more.

DSCN9848Even if you don’t interact regularly with the Iowa Learning Farms staff, don’t hesitate to reach out to one of these partners if you have a suggestion for a field day or a conservation issue that might merit some attention. ILF and the Steering Committee are always looking for input from our audiences on how to help decision makers balance conservation ethics with the economic realities of modern farming. Additionally, if you have recently attended an ILF field day, consider attending others, as the topics and the network of people you will meet continue to evolve!

Jake Hansen

Nurturing the Seeds of Conservation

In 2009, the Soil and Water Conservation District commissioners challenged us to teach Iowa’s youth about soil and water. The Conservation Station and Water Rocks! program were our answers. Since that time, we have been to every county in Iowa at least twice, reaching over 100,000 people, inspiring the next generation to be thinking about and talking about conservation issues.

Starting this year, we are reaching out to the next generation in a new way, by getting college students out to our field days and talking to college students who want to farm about water quality and conservation issues.

On August 30th, we held a field day at the Gilmore City Research and Demonstration Site. If you want to learn about conservation and water quality practices that work, this research site is the place to be. A few days before the field day, we sent an email out to all the Agricultural and Biosystems Engineering undergraduates to invite them to attend. Nine students enthusiastically took us up on the offer and joined us for this excellent event (read more about it in Ann’s blog Cover Cropping on the Lobe).

During the actual field day presentations, the college students quietly listened and didn’t say much. However, the faculty and staff who accompanied them said that when they got back into the van, they were filled with so many questions and were nonstop talk about what they were seeing and learning.

It is very likely that each of these students will either farm someday or work in the agricultural industry. We are doing our part to whet their curiosity about conservation practices such as cover crops and wetlands. We are also fertilizing the seeds that will grow into a lifelong conservation ethic. We plan to offer more of these field days with college students – in partnership with both ISU and our many other outstanding colleges/community colleges around the state —  in the months and years to come.

In addition, with the help of a new grant from the Natural Resources Conservation Service and the Iowa Department of Agriculture and Land Stewardship, we are developing and launching an “Emerging Farmers” program. This program takes a proactive approach to address the need for new programming that reaches out to limited resource farmers, emerging farmers and future landowners. We define emerging farmer as someone with ties to agricultural land, not currently farming but would like to return to the farm or have a voice in its management.

In collaboration with ILF farmer partners, Iowa Beef Center, Beginning Farmer Center and Practical Farmers of Iowa, we will produce a series of emerging farmers conservation publications. Partners will collaborate to create a sustainable business plan template for the emerging farmers. We will host workshops across the state, as well as a two-day intensive emerging farmer workshop. In the years to come, we will present emerging farmer seminars to ISU agricultural student groups, as well as to community colleges and colleges across Iowa to reach those individuals with ties to agricultural land, infusing the traditional agricultural curriculum with a strong conservation focus.

The SWCD commissioners challenged us in 2009 and we continue to listen to that challenge as the Iowa Learning Farms adapts to meet the needs in Iowa for conservation education. We cannot succeed if we are not engaging and inspiring our young people. Send me an email if you would like to get involved in these efforts.

Jacqueline Comito