Biogeosciences News

Cover Crops, Sensors, and Food Security

Forward-Thinking Ideas for the USDA’s Agriculture Innovation Agenda

By DJ McCauley

Marty McFly and Doc Brown stand at the end of an unfinished bridge, dangling out over a ravine. The two had planned to use the bridge as a runway for a time-traveling DeLorean, accelerating them back to the future.

“Oh well, guess we’ll have to wait a year until it’s finished,” Marty says.

“Marty, you’re just not thinking fourth dimensionally!” Doc Brown says.

“Right, right, I have a real problem with that,” Marty replies.

Of course, in the future, the DeLorean won’t jet off the end of the bridge—the bridge will be finished!

It was “fourth-dimensional” ideas that Elizabeth Stulberg sought when leading a task force of 12 agricultural stakeholders to think about the biggest problems confronting farmers in the United States.

Stulberg is the science policy manager for the American Society of Agronomy (ASA), Crop Science Society of America (CSSA), and Soil Science Society of America (SSSA). From the Science Policy Office where she works in Washington, D.C., Stulberg put together a group of experts, guiding them through brainstorming sessions and compiling their comments. The task force formally submitted comments in August 2020.

The mission of the Agriculture Innovation Agenda (AIA) of the U.S. Department of Agriculture (USDA) is to “align USDA’s resources, programs, and research to provide farmers with the tools they need.” By using measurable outcomes, the USDA’s goal is to increase agricultural production by 40% while halving its environmental impact by 2050.

Dig Deeper
Interested in food security? The podcast of ASA, CSSA, and SSSA—Field, Lab, Earth—recently released a series of episodes relating to this topic. You can find the podcast online or through your favorite podcast provider.

These are lofty goals. In 2019, the National Academies of Sciences, Engineering, and Medicine published Science Breakthroughs 2030: A Strategy for Food and Agricultural Research, which outlines the immediate “how” of increasing production and decreasing the environmental impacts of agriculture. But the AIA will serve as a mission statement and vision for those goals—the “fourth-dimensional” view of agriculture.

Here we take a deep dive into two of the technologies put forward by the AIA task force: cover crops and biodegradable, ubiquitous sensors. In both cases, the advances researchers can make in the next 30 years—by 2050—will help us maintain our food supply, grow food more efficiently, and care for our climate and environment. All of which contributes to greater food security.

Cover Crops

“It’s not debatable, at this point: Cover crops provide a whole range of agroecosystem services,” Steven Mirsky says. “But there are lots of things we don’t know. To what degree do they provide those services? How do we enhance them? How do services change based on your climate, your soil, your management?”

Mirsky is a research ecologist at the Sustainable Agricultural Systems Laboratory, a USDA Agricultural Research Service (ARS) site in Maryland. Mirsky coleads a Coordinated Agricultural Project that includes over 100 researchers in more than 29 states, all focused on documenting cover crop use, management, and breeding.

By definition, cover crops cover soil during gaps in the crop rotation where the field might otherwise lie fallow. They’re often worked into rotations in the winter (between cash crops) in high-yielding systems.

Aside from the aesthetic benefit of keeping the landscape green for a larger chunk of the year, cover crops are a boon to soil health and water conservation. They help capture nitrogen, preventing it from leaching into waterways. They increase soil organic matter, recycle nutrients, and suppress pesky weeds. They prevent erosion, increase soil aggregation, build soil biology, and increase water infiltration.

“Cover crops don’t take land out of production, but they reduce our environmental footprint,” says ASA Fellow Rob Malone, a task force member and USDA-ARS agricultural engineer. “It’s exactly the kind of thing the AIA is looking for.”

Typical cover crops fall into four broad categories: grasses, brassicas, legumes, and mixes.

Farmers use grasses like winter rye, oats, annual ryegrass, and sudangrass to prevent erosion, build soil aggregation, and retain nutrients, which reduces leaching. Many grass cover crops can also be used as forage for livestock—an immediate economic benefit. Some grass species die off over the winter, making it easier for farmers to manage them before planting their cash crops in the spring.

Legumes, with their nitrogen-fixing capabilities, are suited for summer, winter, or even perennial or biennial cover. However, farmers must remember to inoculate legumes with nitrogen-fixing bacteria, and bacterial species are crop specific.

Producers are increasingly incorporating brassicas like mustard, rapeseed, forage radish, and canola into their rotations, particularly in specialty crop production.

Finally, there are the mixtures, in which farmers combine two or more cover crop species for specific outcomes. A mixture provides much the same advantage as a diverse ecosystem: If one species struggles, there are others present to fill the gap. Each species in a mix brings different benefits to the soil, but mixtures can be difficult to seed and manage.

Those are just some of the choices a farmer faces in selecting a species of cover crop. There are unique management questions for each, too. But with these challenges comes great opportunity.

Benefits and Breeding

As Mirsky pointed out, researchers don’t have a complete grasp on the degree of benefits provided by cover crops. Often, cover crops are tested in two- or three-year-long studies, and information is swayed by the weather.

“You could have one year that’s wet, and one that’s dry, and you just won’t be able to detect any differences even if you have a bunch of treatments,” Mirsky says.

Mirsky’s team, coled by Chris Reberg-Horton at North Carolina State University, is piloting collection methodologies and wrangling data from longer-term, on-farm studies across the United States. They’re trying to quantify the benefits cover crops can offer, learning from farmers versed in their management. The team was awarded a five-year grant from USDA National Institute of Food and Agriculture in 2019.

At the same time, researchers are confronting gaps in knowledge about cover crop breeding. From locally adapting certain varieties to designing blends of seeds for a farmer’s specific needs, the field is wide open for further research.

“Cover crops are messy—they don’t always behave like you want them to,” Mirsky admits. “They’re very responsive to their environment, and there’s been little improvement to their genetics. We can make big strides in very little time, just because there’s been so little focus on them.”

Cover Crop Adoption

The National Cover Crop Survey has been collecting data about cover crop use and management since 2012. The number of acres planted with cover crops of all kinds increased 50% between 2012 and 2017.

Even with that year-over-year increase, it’s still only a tiny fraction of America’s farmland. In 2017, cover crops were planted on only 15.4 million of the 395 million acres farmed in the United States—a mere 3.9%.

What’s keeping farmers from using them?

“You don’t just wake up one day and say, ‘I’m going to grow cover crops!’” says Eileen Kladivko, an ASA and SSSA Fellow. Kladivko, a professor of agronomy at Purdue University, is a founding member of the Midwest Cover Crops Council. “There’s site-specific selection, there’s getting the right crop, there’s managing it, and there’s the economic aspect, too.”

Economic benefits to farmers aren’t immediate, and they aren’t always found in increased yield. After a farmer shells out for seeds, spends time and energy planting in the fall, and either terminates or plants into the crop in the spring, the costs can be daunting.

But Kladivko cites potential benefits in reduced herbicide use and decreased inputs as ways to offset those initial costs.

“Cutting back on inputs isn’t something that happens in a single year, either,” Kladivko says. “I remind farmers that for every 10 or 20 pounds of nitrate they keep from going into a tile drain, that’s building organic matter.”

Like a certificate of deposit, farmers can’t cash in on soil nutrient benefits right away. Over time, the inputs begin to recycle as soil microorganisms release them in forms that plants can use.

The reason a farmer turns to cover crops is usually not the same reason a farmer keeps planting them. At first, a farmer might be looking for an immediate fix for soil erosion or a solution for earlier cash crop planting in the spring, but long-term benefits have surprised early adopters.

“I’ve heard a lot of farmers talking about how cover crops have added to their enjoyment of farming,” says Rob Myers. “They like figuring out how to use them in different fields; they like keeping their farms greener.”

Myers, the director of USDA’s North Central Sustainable Agriculture Research and Education (SARE) program, says that farmers are innovating faster than some researchers can keep up. Myers encourages researchers to keep track of the latest innovations farmers are using—something SARE keeps abreast of by asking questions about management in their National Cover Crop Survey.

All this to say that the key to unlocking the benefits that cover crops offer is communication and coordination across stakeholder groups.

Biodegradable Sensors

Illustration of biodegrading crop sensors
This schematic displays a biodegradable sensor network (left) and a sensor node (right). The node degrades over time as is shown clockwise in the four blocks on the right. Credit: Raj Khosla

Picture an object about the size of a dollar coin. It’s made of beeswax or wood or biodegradable plastic—it’s not built to last. You have a pile of these little gadgets, and you’re going to scatter them across your field.

Over the course of a growing season, these sensors will send you data every 30 minutes, hour, or day. They’ll document soil moisture and nutrient levels like nitrate and record if pests or weeds threaten your plants. You can precisely manage inputs, applying them just to parts of the field you know need them.

You check your sensor data, looking at a map that visualizes moisture levels across your fields. You start watering, and as your center pivot irrigation makes its way across the field, the map changes. Over a day or so, you see soil moisture increasing and pivot, applying a little less water to the areas of your fields that retain more water. You do the same for nitrogen inputs as the data integrate with technology already installed on your precision-input tractor.

At the end of the season, there’s no need to go on a scavenger hunt for sensors—they degrade in the soil. With the money you save on fertilizer, herbicide, pesticides, and water, you buy another set for the next year.

This is the vision of Raj Khosla, a task force member and professor of precision agriculture at Colorado State University in Fort Collins. His team is developing sensor technology specifically aimed at measuring moisture and nutrient levels in the soil.

“You can’t manage what you can’t measure,” Khosla says. “We have the tractors, the applicators, and the sprinklers to apply the right inputs at the right time, in the right place, in the right amount, in the right manner, down to a square foot level. But we have to collect data in high density from the field to take advantage of what precision technology offers.”

Like Back to the Future’s Doc Brown, Khosla sees past the unfinished business of the present. The sensors of today are expensive, bulky, metal-made, and battery-operated machines.

“It’s a major limitation,” admits Subash Dahal, a postdoctoral researcher in Khosla’s lab. “We can’t put them at a spatially dependent scale to capture all the variability in the field.”

Other means of monitoring, from GPS technology to drone-based images, do not give direct measures of in-field variables.

“It’s an indicator, not a measurement,” Khosla explains. “If you go to the doctor, they don’t take a blood test and say, ‘Maybe you’re diabetic.’ No! They diagnose you, given their measurements of your blood. Right now, we can’t measure nitrogen, phosphorus, or potassium with sensors. We’re always using surrogate measures.”

With only indicators to go on, farmers cannot manage fields in real time, and they definitely can’t catch signs that sensors could. For example, precision technology of the future could measure pest infection before physical indicators of infection appear and spread. With this kind of forewarning, farmers could prevent yield losses or disease spread long before they could even see it happening.

If cover crops get at the heart of environmental challenges facing agricultural systems in the United States, precision technology addresses issues of efficiency.

“We have to use our resources efficiently because those resources are limited,” Dahal says.

Challenges for Sensor Technology

There’s one drawback: Sensor technology is a high-risk, high-reward area of research.

A student holds a pot of maize to check damage to biodegradable sensors
Wub Yilma assesses the damage to the biodegradable sensor candidate after 90 days of maize growth as Huma Tariq looks on. Yilma and Tariq are Ph.D. students in the Khosla Lab at Colorado State University. Credit: Raj Khosla

“I’ve been involved with smart agriculture since its inception,” Khosla says. “The first 20, 25 years were an uphill battle. It created challenges and issues and conundrums for farmers because we didn’t have the answers. It’s slowly but surely gaining attention because we’ve advanced the technology, and we have the data to show it can make a difference.”

For example, a farmer applying fertilizer at an average rate for a given field may over- or underapply nutrients more than 90% of the time, according to Khosla. With a net of sensors scattered in a field, farmers can apply fertilizer more precisely—just the right amount to meet the needs of an individual section of a field.

For now, the team is trying to find ways to create biodegradable sensors that supply accurate measurements for the course of one growing season but still break down.

“They’re not encased in metal—they go in the soil where there are microbes and herbicides and fertilizers; they can be trampled by tractors or penetrated by roots,” Dahal says. “There are so many things that can go wrong, and we have to control for so many factors to get this to work.”

Regardless, we could be nearing a breakthrough. Dahal estimates that biodegradable soil moisture sensors could be manufactured at scale within two or three years. Nitrate sensors will take a little longer.

The other major challenge?

“The talent pool,” Khosla says without hesitation.

Finding researchers with the right combination of agricultural savvy and computer science acumen is difficult. And with the sheer amount of data generated by a whole interconnected web of sensors, managing those data becomes a difficult task.

The next frontier for much of agricultural research is finding ways to create clever, efficient means of managing data. Whether it’s using artificial intelligence to generate prescriptions for water or nutrient application or creating neural networks that help farmers predict what’s going to happen in their fields tomorrow based on data from today, we need researchers with an agricultural education and knowledge of programming and statistics.

Dahal, who was just hired in Khosla’s lab this year, offers advice for young researchers.

“Don’t just focus on the field you’re working on—try to gain some knowledge and expertise of the fundamentals of statistics and computer science,” Dahal says. “Big data is everywhere, no matter which field you’re in.”

Thinking Fourth-Dimensionally

“These are wicked problems,” Khosla says. “We can’t keep doing the same thing and expect different results.…We need to harness the intelligence and expertise of different disciplines. We need to be willing to invest dollars that bring, and continue to bring, different disciplines together to look at the same problems.”

Undergirding the AIA is the idea that collaboration is the way forward, but to collaborate, researchers need funding.

According to the Farm Bureau, public funding for agricultural research and development has decreased by 30% in the last 10 years—not to mention, the USDA receives less funding earmarked for research than the Department of Defense, Department of Health and Human Services, Department of Energy, NASA, and the National Science Foundation.

Karl Anderson, director of government relations at the ASA, CSSA, and SSSA Science Policy Office, advocates for agricultural research interests on Capitol Hill. He likens the federal budget to personal finance.

“You’ve got to pay the mortgage, the utilities, buy food,” Anderson says. “Then you’re left with a little bit of cash, and you have to decide: How do I invest for the future? It’s that last little bit that’s like discretionary funding, and Congress has to decide how to spend it.”

The timing is right to position agriculture as part of the solution for the issues facing our environment and a changing climate.

“There’s a lot of interest in things like soil health, water quality, and the environmental footprint of food production,” Anderson says. “That’s the biggest opportunity for us to show what our members are doing to help solve those issues.”

With investment—in time, talent, and research budgets—we can look out over the unfinished bridge and see where we’ll be in 30 years.

— DJ McCauley (@DarrynJayne), CSA News

This article originally appeared as part of a series on food security in CSA News magazine.

Text © 2021. The authors. CC BY-NC-ND 3.0
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