Fields of Green: Fall Cover Crop Biomass Sampling

An unseasonably warm fall has made an excellent year for cover crop growth! The ILF team has been traveling across the state and has seen some beautiful, green cover crop fields. With more growing degree days this fall, it has been a good year for radishes in the southern portions of the state. Check out this growth on radishes at Crawfordsville!

If you have cover crops and are interested in measuring the amount of biomass growing in your fields, follow along with our methodology in this blog. Check out the end of the blog for a summary of how you can apply this research to your own farm.

As part of our National Conservation Innovation Grant/Cover Crop Mixtures demonstration project, we are interested in learning if more biomass can be generated by seeding a single species of cover crop in a plot versus a mixture of cover crop species. To see which treatment yields more biomass (pounds per acre), we collected biomass in the fall and spring from six research sites throughout the state.

To sample biomass, we start with a frame that we constructed out of PVC piping. Our frame measures 19.2 inches x 30 inches (about four square feet). We toss the frame randomly into our test plots. Wherever the frame lands, we sample the cover crop biomass to the soil surface within the frame. We use clippers to cut the cover crop biomass, and we do not include soil, cash crop residues, or weeds in the sample. We try to only capture cover crop biomass and then place it in a labeled paper bag that tells us which test plots the sample came from.

We walk to a different portion of the plot and repeat the process. We always use a different paper bag for each sample and make sure to close the bag after sampling so that sampled biomass cannot escape. We go through the same process in all of our cover crop plots.

We take our biomass samples back to a lab on campus at Iowa State University within the Department of Agricultural and Biosystems Engineering and immediately open the bags the allow them to start air drying. This can prevent sample degradation, like molding on wet samples, from occurring.


We then sort our samples from each plot by species. For the mixture plots, sorting helps us separate the biomass generated by each cover crop species. For all plots, it ensures that crop residue and other items can be separated from the sample before it is dried and then weighed.

Sorted samples are then placed into their own paper bag and dried in a drying oven at low heat (104 degrees) for at least 48 hours to remove any remaining water. We weigh the samples to get the dry measurement of the biomass. For our demonstration project, the last stop for our samples is the ISU Soil Processing Lab in the Agronomy Department. The samples are analyzed for Total Carbon and Total Nitrogen of the plant.

On-farm Research: If you’re interested in measuring the biomass growing on your own farm, here’s a summary of steps you can follow to make it happen.

Step 1: Create your frame (as long as you know how many square feet are within your frame, the math will work).

Step 2: Take samples in your field and place the samples in separate paper bags. We recommend taking at least eight square feet of samples to get a representative average for the field.

Step 3: Dry the biomass (about 104 degrees for 48 hours). Regional ISU Research Farms may have facilities for you to dry your samples.

Step 4: Calculate total biomass. Weigh the sampled biomass with a scale with two decimal precision (ounce or gram). Also weigh the paper bag by itself.



Average the total biomass from all of your samples to get an average biomass for the field. Convert results to appropriate lbs/acre using unit conversions.  1lb = 16 ounces = 453.592 grams, 1 acre = 43,560 sq. ft.

And finally, always expect surprises! We found a few purple top turnips mixed into our mix of oats, radish, and hairy vetch.


Julie Whitson


Cover Crops: Taking a Closer Look at Legumes

In the previous weeks, we’ve showcased grasses and brassicas as great options for cover crops that can be readily integrated into corn and soybean cropping systems across Iowa. Now it’s time to show some love to the legumes!

Last month, Liz shared the Top 10 Cover Crops for Iowa in 2016 identified by plant scientists, agronomists, and other researchers focused on cover crops, as well as you, our blog readers. Two of the top ten cover crops from this poll are legumes: red clover and hairy vetch.


What makes the legumes special, and why consider them as potential winter cover crops in your farming operation? The biggest difference between legumes and the other (non-leguminous) cover crops is their ability to fix nitrogen. Particular bacteria in the soil (rhizobium species) form nodules on the roots of the legume plant. It’s a natural symbiotic relationship that allows for the capture of nitrogen from the atmosphere (N2 gas) and conversion of this nitrogen to forms that are plant usable. This process is referred to as biological nitrogen fixation.


A very common example of this nitrogen fixation process happens in our soybean fields. The reason nitrogen fertilizer historically has not been added to soybean crops is because they are able to pull the nitrogen they need from the atmosphere as well as from mineralized nitrogen in the soil.

LegumesKnowing that legumes have the potential to add nitrogen back into the soil, this offers another “tool in the toolbox” when it comes to cover crops!  Hairy vetch and red clover were mentioned above, but there are a number of other legume cover crops to consider as well, including common vetch, crimson clover, white clover, kura clover, sweet clover, cow peas, winter lentils, and alfalfa.

When it comes to getting your cover crop planted in the fall, legumes and brassicas need more heat units than small grains to be effective. Thus, timely planting is of the essence!  In the Cover Crops: A Guide for Iowa Producers recommendations from USDA-NRCS, legumes should optimally be seeded between August 1 – September 15.

Seeding rates vary based on the specific legume you’re using – check out Practical Farmers of Iowa’s Cover Crop Recommendations and the Midwest Cover Crops Council webpage, which includes information on a variety of cover crop research trials as well a robust cover crop selector tool.


Do legume cover crops survive over the winter? It depends – it depends on the intensity of the winter, when the legume cover crop was planted, fall weather conditions (how much fall cover crop growth was attained?), and where geographically you are located in the state! From the Iowa Learning Farms’ perspective, the only experience we’ve had with legumes overwintering in Iowa came from one of our farmer-partners in the southern part of the state, and that was only described as being moderately successful.

Legumes on their own can offer many benefits, including fixing atmospheric nitrogen, providing a nitrogen source for the soil to be used by future crops, as well as protection from soil erosion along with building soil structure and organic matter. However, this is ultimately dependent upon how much growth is achieved, which can be a big challenge – weed control abilities are less, and legumes do not increase soil organic matter as much as other cover crops.

However, legumes can be used in a cover crop mixture with grasses or brassicas, which offers the ability to harness some of the benefits of different types of cover crops. From SARE’s Managing Cover Crops Profitably: Third Edition, “Mixtures of legume and grass cover crops combine the benefits of both, including biomass production, N scavenging and additions to the system, as well as weed and erosion control.”


We are using one legume, hairy vetch, as part of our USDA-NRCS Conservation Innovation Grant investigating cover crop mixtures. It is being utilized in a three species grass-brassica-legume mixture, including oats, radish, and hairy vetch (this specific mixture is seeded in the fall following soybeans). All three species can be seen distinctly in the above photograph from November 2015; the hairy vetch is the small plant with fern-like leaves in the foreground.

Fall 2015 offered fantastic conditions for cover crop growth, including hairy vetch, so it will be interesting to see what impact that has as we carry out soil testing as well as look at the nitrate-nitrogen data in the spring. Will there be observable differences between the single species plots (containing oats only) compared to those with a mixture of oats, radish, and hairy vetch? Stay tuned…

Additional Cover Crop Resources:
Cover Crops in Iowa: A Quick Guide (Iowa Learning Farms)
Cover Crops: A Guide for Iowa Producers (USDA-NRCS)
Cover Crop Recommendations (Practical Farmers of Iowa)
Cover Crop Business Directory (Practical Farmers of Iowa)
Overview of Legume Cover Crops (SARE)
Managing Cover Crops Profitably: Third Edition

Ann Staudt

What happens to all of that cover crop biomass?

This has been an amazing fall (and winter) for cover crops! Driving around the state, it makes my day to see those lush fields of green. In an earlier blog post titled The weather outside is frightful, but the cover crops are oh SO delightful!, we showed you some of the beautiful cover crop growth that was achieved at the ISU Armstrong Research Farm near Lewis in southwest Iowa, as documented when we were there collecting fall biomass samples in late November.

Once the biomass is collected, what happens next? Let’s go on a bit of a behind-the-scenes tour documenting the next steps in the processing and analysis of the cover crop biomass.

When sampling the cover crop biomass in the field, all of the above-ground biomass from each PVC frame is harvested and transferred to a brown paper bag.

Once we’re back to campus, the bags are transported to the porous media lab in Sukup Hall, part of the brand new Biorenewables Complex that houses Iowa Learning Farms and ISU’s Department of Agricultural and Biosystems Engineering. Each individual bag is opened up immediately and allowed to start air drying; it is important to start the drying process right away to prevent wet samples from molding or any other sample degradation.

With 6 research farm sites and 10 on-farm demonstration sites (each with multiple replicated treatment strips) where cover crop biomass was collected, you can imagine that we have collected quite a few bags of cover crop biomass by the end of the season!


SORTING of the biomass comes next. The goal is to collect just the above ground cover crop biomass, so the first step is sorting out any non-cover crop material from the bag – including soil, corn stalks, soybean residue, and trimming off any cover crop roots that may have been collected.

Since many of our demonstration projects involve cover crop mixtures, then we begin sorting the biomass by species in order to determine how much growth was achieved by each of the species in the mixture. This sorting is done visually, using photographs of the individual cover crops to identify and sort the cover crop biomass on a species basis.

Here, intern Kayla Hasper sorts a cover crop mixture that includes radish, hairy vetch, and oats. The biomass from each species is put on its own pile, and once fully sorted, each individual species is transferred into its own brown paper bag.


Samples are dried at low heat (60C) for 48 hours to remove any remaining water. Each individual species sample is then weighed. Knowing this dry weight measurement as well as the size of the PVC frame used for sampling, we can calculate the amount of biomass grown in the field on a lb/acre basis… per species, as well as the total lb/acre for the mixture. We’ll do the same thing in the spring to see what kind of growth is achieved then.

Finally, the biomass samples are submitted to ISU’s Soil Processing Lab in the Agronomy Department to determine the Total Carbon and Total Nitrogen makeup of the plant biomass. These numbers can then be related to the Total Carbon and Total Nitrogen in the soil, the nitrate concentrations found in the water samples collected from each plot, and the crop yields in each plot… each individual piece of data helps us gain a better understanding of the big picture in terms of the numerous benefits of cover crops integrated into corn and soybean cropping systems!

Ann Staudt

The weather outside is frightful… but the cover crops are oh SO delightful!



If there was ever a picture perfect fall season for cover crops, 2015 would absolutely be it! Rainfall was timely – there was sufficient precipitation in August and September – to help the freshly seeded cover crops germinate and kick start their fall growth. Beyond that, we’ve had beautifully mild temperatures for the majority of October and November.

While many parts of the state experienced freezing conditions back in October, cover crops are quite hardy – just one cold night that drops below the freezing point is not enough to knock them out! So as the fall marched on, the cover crops grew and grew…


However, winter-like weather has arrived this week, which meant it was high time for the Iowa Learning Farms team to get out there and take care of our fall field work responsibilities. As part of our National Conservation Innovation Grant/Cover Crop Mixtures demonstration project, we were collecting fall cover crop biomass at each of our demonstration sites across the state. In order to obtain the most accurate cover crop growth data, the collection of cover crop biomass is ideally done as close as possible to the time of an extended hard freeze – which is now looming very near. So Iowa Learning Farms team members have been “on the clock” this week trying to complete all of our fall field work and sampling before the cold is here to stay!



Included below are a number of photographs from our cover crop mixture plots at the ISU Armstrong Research Farm near Lewis in southwest Iowa. These photographs were all taken on Wednesday, November 18. We hadn’t been back to the Armstrong Farm since the cover crops were seeded in early September, so it was thrilling to see the beautiful growth that has been achieved!

In the plots that had soybeans in ‘15 (going to corn in ’16), the cover crop treatments included:

Single species cover crop (oats)

Cover crop mixture (oats, hairy vetch, and radish)


Now in the third year of this project, this is the first time that we really definitively saw strong growth of all species in the mixture!

While there is no denying the amount of intrigue in using radishes as a cover crop, we typically have not seen as much success with it in Iowa when compared to other states, due to our shorter window of opportunity for fall growth. This year is turning out to be a good year for the radish, as well. Healthy radish growth was found throughout our mixture plots, with many radishes forming tubers around 1/2” in diameter. However, there were a few big boys that just went crazy…


Moving across the farm to our corn plots (going to beans in ’16), the cover crop treatments included:

Single species cover crop (cereal rye)


Cover crop mixture (rye, rapeseed, and radish)


While the dates of cover crop planting and growing conditions (temperature, precipitation, sunlight – as related to leaf drop/canopy opening with the cash crop) certainly vary across the state, it is exciting to see such vibrant cover crop growth this fall.

How are the cover crops looking in your area? We’d love to see any photographs that you may have. Send them to us at, or share with Iowa Learning Farms on social media (we’re on Facebook and Twitter).

Ann Staudt

Another month of growth…

Over the last two weeks, Iowa Learning Farms team members (with help from our friends at Practical Farmers of Iowa) have been visiting ISU Research and Demonstration Farms statewide, checking up on our cover crop mixture plots planted as part of the National Conservation Innovation Grant.   Our visits to the six sites include collecting fall above-ground biomass from each of the cover crop plots, the final water sampling of the season, and winterizing the suction lysimeters until sampling resumes in spring.

In a previous blog post, I shared photos from the Armstrong Research and Demonstrations Farm in Southwest Iowa from our trip there at the end of September.   After another month-plus of growth, the cover crops are flourishing!  So for comparison purposes, let’s take a look post-harvest:

Treatment #1: Single Species Cover Crop (rye pictured here in corn plots)

Treatment #1: Single Species Cover Crop (Rye in corn plots, 9/26/2014)

Treatment #1: Single Species Cover Crop (Rye in corn plots, 11/5/2014)

And how about those mixtures?

Treatment #2: Cover Crop Mixture (Blend of rye, radish, and rapeseed shown here in corn plots)

Treatment #2: Cover Crop Mixture (Blend of rye, radish, and rapeseed in corn plots, 9/26/2014)

Treatment #2: Cover Crop Mixture (Blend of rye, radish, and rapeseed in corn plots, 11/5/2014)

And a few views from the soybean plots:

Cover Crop Mixture used in Soybeans (Blend of oats, radish, and hairy vetch)

Cover Crop Mixture used in Soybeans (Blend of oats, radish, and hairy vetch, 9/26/2014)

Cover Crop Mixture used in Soybeans (Blend of oats, radish, and hairy vetch, 9/26/2014)

Collecting water samples from suction lysimeter in Cover Crop Mixture plots (Blend of oats, radish, and hairy vetch, 11/5/2014 – All species present, but definite frost damage observed here)

Two sets of biomass samples are collected in each plot:


Biomass Sampling in Progress: All cover crops within the quadrant are cut at ground level, collected in bags, and brought back to ISU for analysis to determine the amount of cover crop growth (# biomass/acre) and well as total carbon/total nitrogen content of the cover crop biomass collected. Biomass is collected in the fall (as close to hard freeze as possible) and in the spring (as close to termination as possible).


Want to learn more?   Join us for one of our upcoming November field days!   Detailed information for each is available on the Iowa Learning Farms website.

Nov. 12, 10:30 am-12:30 pm
Wallace Learning Center at Armstrong Research Farm

Nov. 18, 10:30 am-12:30 pm
Borlaug Center at Northeastern Research Farm

Nov. 19, 10:30 am-12:30 pm
Fire Department building

Nov. 20, 10:30 am-12:30 pm
Rob Stout farm, Washington Co.

Nov. 25, 11 am-1 pm
Truro Lions Club, Madison Co.

Ann Staudt

Friday Photos: Cover Crops Thriving!

ILF staff visited the Armstrong Research and Demonstration Farm in Southwest Iowa earlier today, and we were pleased to find some good growth in our recently-seeded cover crop plots.   As part of a National Conservation Innovation Grant looking at cover crop mixtures, these plots involve an investigation of three different cover crop treatments:

Treatment #1: Single Species Cover Crop (rye pictured here in corn plots)

Treatment #1: Single Species Cover Crop (Rye in corn plots, 9/26/2014)

Treatment #2: Cover Crop Mixture (Blend of rye, radish, and rapeseed shown here in corn plots)

Treatment #2: Cover Crop Mixture (Blend of rye, radish, and rapeseed in corn plots, 9/26/2014)

Treatment #3: No Cover Crop (in some very nice looking no-till!)

Treatment #3: No Cover Crop (in some very nice looking no-till, 9/26/2014)


The crops are looking great in SW Iowa, as are the cover crops.  However, when walking through the plots, beware of badger holes!


One very ambitious badger makes its home in our corn plots at the Armstrong (SW) Research and Demonstration Farm.

The cover crop species in our plots are different based on whether they are planted into standing corn or soybeans.  The above images all come from standing corn.   Here’s a view from the soybean plots, as well:

Cover Crop Mixture used in Soybeans (Blend of oats, radish, and hairy vetch)

Cover Crop Mixture used in Soybeans (Blend of oats, radish, and hairy vetch, 9/26/2014)

How are your cover crops looking this fall?  We’d love to see any photographs you may have, and will share them in future blog posts. Send them to us at

Ann Staudt

Newly Posted: Cover Crop Anthem

Get ready to ROCK your Tuesday morning with the much-anticipated “Cover Crop Anthem” music video!  Prepare to be amazed…

Cover Crop Anthem was produced by our sister program Water Rocks!.  Visit to watch more videos and learn about this exciting youth education program, combining STEM (science, technology, engineering and mathematics) and the arts.

– Ann Staudt