Our new report, Turning Soils into Sponges: How Farmers Can Fight Floods and Droughts, is a serious scientific analysis that documents how soil-covering farm practices can help farmers and communities better withstand rainfall variability. It took me the better part of two years to complete. But—lucky you!—we also made a quirky little movie about it that you can watch in less than three minutes:
Okay, yes, the video has an element of silliness, but as I said, this is a serious topic with a lot of research behind it. So I thought I’d use the blog as an opportunity to write more about the science and science communication behind our masterpiece.
The star of the show—the soil—comes from a real live research site
The soil used in the side-by-side demonstration comes from a long-term research site maintained by US Department of Agriculture (USDA) scientists in Ames, Iowa, where I collected the primary data for my dissertation research. It’s a site that grows corn one year and soybeans the next, varying practices like tillage (plowing), use of cover crops between crops, and addition of nitrogen fertilizer to measure their impacts on soil and water quality.
In the video, we call them “healthy soil” and “unhealthy soil,” and these descriptors are quite accurate in relative terms: the healthier soil came from some of the first plots established at this site back in 2000, the first year a winter rye cover crop was planted, and there has been no plowing on that plot since 2002. The unhealthy soil in the video comes from a nearby plot that does not include a cover crop (so the soil is bare from roughly October until April or May), and it has been plowed repeatedly within the last six years. Although soil properties can vary from one spot on a field to the next, these two samples were taken from very close to each other (just about 40 feet away); so we can assume that they are not very different, beyond the plowing and cover crop practices.
In the video, you can see how differently the two soil samples respond to a heavy “rain.”
How do soils on real farms measure up?
In the video, I say that “much of the nation’s farmland” is treated like our unhealthy soil sample. That’s because data from the USDA tells us that very little farmland across the country uses practices that protect it with living plants year-round.
Let’s start with the data on cover crops. The 2012 agricultural census estimated that approximately 2% of the major corn-producing states in the country were using a cover crop, although that number could be as high as 3% across the United States (approximately 10 million acres of the 300 million cropped acres).
Cover crops are not the only way to avoid bare soil on farmland. Perennial crops (crops that have deep living roots in the soil all year long), agroforestry (integrating trees into croplands) and even double cropping (growing two crops during one year) are other options. However, these things are also not the norm.
It isn’t easy to get a solid number on the total land planted to perennial crops in the US, but the value for hay grasses is one indicator. These perennial grasses, which include crops such as alfalfa, comprised less than 18% of total harvested cropland in the United States last year.
Estimates from the Economic Research Service from 1999-2012 find that just 2% of farms are double cropping. Limited numbers for agroforestry acres exist, although USDA has estimates for the acres its programs support, and while those numbers are incomplete, they would equal well less than 1% of harvested crop acres. It’s good news that some researchers and non-profits are working to quantify and map agroforestry and other perennial practices.
If we add those numbers up, we’re talking about less than one-quarter of all agricultural land in the United States, so it seems fair to say that much of the nation’s farmland is farmed “naked” for extended periods of time during the year.
Our data show soil can be a solution
If you’re curious about the numbers from the new report that we included in the video, here is the Cliff Notes version.
In 70% of the 150 field experiments we examined, the soil’s “spongy” properties were improved by farming methods such as no-till practices, crop rotations, cover crops, perennial crops, and better grazing management. The properties we analyzed included infiltration rates, pore space and water available to plants. In our examples of how to get healthier soils on farms, we focused on those practices that we found to offer the largest and most consistent improvements: cover crops, perennials and improved grazing management.
The flood frequency number was calculated from the number of months reaching flood stage with current land use, and how many fewer months amounted when there was a shift to more ground covering crops and healthier soils. The 1/5 value came from our calculation for one specific watershed in Eastern Iowa impacted by flooding during the last several decades.
We also found there to be a 20% reduction in runoff when we evaluated specific areas impacted by historic flood events, and this number comes from a watershed in western Iowa hit by heavy flooding in 2011.
These are not insignificant numbers when you think about how much damage these events can do (on the order of billions of dollars, as we detail in the report), and the human impact they have. In fact, Iowa state senator Rob Hogg, an ardent champion for climate change solutions, whose Cedar Rapids region was devastated by flooding in 2008, reminded us that “Floods not only cause preventable damage—they create long-lasting trauma and heartbreak.”
The science communication behind the scenes
This infiltration rate demonstration is something I first gathered supplies for and worked up when I was a student just starting my Ph.D. program at Iowa State University. In fact the whole thing started with a test run with soda bottle “beakers” in a friend’s backyard. The idea came from Ray Archuleta of the USDA, who is known for performing this demonstration. At the time, I was curious if the soil from Iowa would produce such a strong contrast. It did then, and it has every time I’ve tried it since.
And in case you think this is only the case with Iowa soil, it’s not. We were also fortunate to have additional soil from a long-term research site maintained by USDA scientists in Maryland that included a comparison of no-till soil to conventional tillage. I did an informal test in my office and found that this soil indeed worked the same way.
In the end, we only needed to use the soil from our Iowa experiment for the demo, but I share this in part because experts who study soil health suggest infiltration tests as an important indicator. So, do try this at home with your own soil, if you are so inclined!
Are you more curious about soil? We hope so!
I’m super proud of the finished product. We aimed to be accurate in our descriptions and there is research and evidence to back up everything. I am thinking all the time about how to make some of these agricultural concepts more broadly applicable, and I hope the video does just that.
AND, because making a video never goes 100% perfectly, we thought you might enjoy two of our favorite outtakes.