Content ID


Is There a Soil Health Payback?

Poor Potter Stewart. The late Supreme Court justice ruled on landmark legal cases during his 1958-1981 tenure on the nation’s highest court. Yet, Stewart is just a footnote in history, except for one comment he made regarding a 1964 obscenity case. 

“I can’t define it (pornography), but I know it when I see it,” he said. 

Stewart’s synopsis is akin to defining soil health. Some farmers just know they have healthy soils. You know the stuff – rich, black soil brimming with earthworms and invisible microbes that slowly crumbles in your hands. 

“Maybe I’m old-fashioned, but I still go by how soil structure looks,” says Jodi DeJong-Hughes, a University of Minnesota (U of M) Extension educator. A well-structured soil contains a crumbly mix of fine and coarse aggregates, she adds. It provides excellent housing for soil microbes that help transfer nutrients and water to cash crops. The aggregation mix spawns good infiltration that helps ensure crop roots can access soil profile water. 

“Soil structure is a great indicator of a healthy soil,” she says. 

Soil Health Tests 

These days, though, soil scientists have developed new tests to evaluate soil health on a physical, chemical, and biological basis. 

“Farmers can use them to assess what their management is doing to their (soil) investment and productivity,” says Jane Johnson, a USDA-ARS soil scientist based in Morris, Minnesota. 

Older metrics like soil structure combined with new ones like active carbon could eventually help boost farmland value just as drainage now does, says Mark Thompson, a farm manager with Sunderman Farm Management, Fort Dodge, Iowa. 

“A farm that is pattern-tiled every 100 feet commands a premium in north-central Iowa,” he says. That’s because drainage helps ensure timely planting and a good seedbed environment.

Soil health isn’t quite yet to that point. “We have not seen anyone willing to pay an extra $500 (per acre) for 6% organic matter,” says Thompson. 

That will change, he believes. 

“We think soil health is going to become one of the major factors in future land markets,” he says. 

How Soil Health Tests Differ

Farmers have used soil tests to assess nitrogen (N), phosphorus (P), potassium (K), and organic matter levels for decades, says Dan Davidson, an independent agronomist and consultant for Woods End Laboratories. 

“Those tests are well calibrated,” he says. “Agronomists know how to use those numbers.”

Soil health? The metrics are more nuanced, particularly the biological ones. Underneath the soil surface lies a labyrinth of soil life, as microbes that benefit soil and crops savagely battle for food and survival.  Measuring their activity gives soil scientists insights into the health of a soil. 

Yet, sampling the numbers of these subterranean critters is akin to hand-catching a salmon slithering through a rapid stream. 

Assessing soil health also entails gauging physical and chemical properties. If any of these factors is limiting, soil health may suffer, says Johnson.

Soils oozing with high soil organic matter can mineralize N. This lessens dependence on commercial fertilizer, which saves farmers money. Meanwhile, the water a high-organic matter soil retains can help a crop withstand drought.

Still, a physical malady like compaction can nix these benefits.  

“A good analogy is a doctor’s exam, where a patient’s blood pressure and sugar levels are good, but cholesterol is high,” says Johnson. 

Soil health tests cast a wide net, measuring factors ranging from soil respiration to active carbon to heavy metal content. Prices may range from a basic $60 sample package to an extended one that costs $170, according to a U of M analysis. 

Farmers, though, can start assessing soil health through existing metrics, says Johnson. Although organic matter content has been a soil test staple for decades, it remains an excellent soil health indicator, says Johnson. 

“When you overlay a U.S. map to where the most productive soils are, it is no accident that those soils are high in organic matter,” Johnson says.    

A downside of monitoring soil organic matter is that it takes years to obtain meaningful measurements. One new measurement from soil health tests – active carbon – reveals results much quicker.  

“Active carbon shows what is there for microbes to eat and respire on,” says DeJong-Hughes. The more carbon, the more microbes that theoretically exist, she points out. 

Soil health respiration is another new soil health measurement, says Davidson.

“It measures the activity of microbiome creatures like bacteria and fungi,” he says. “A healthy soil has a healthy microbiome, and respiration is a good indicator of those levels.” 

Several types of soil health tests exist. The Solvita test measures the amount of carbon dioxide that soil releases, says Will Brinton, founder of Woods End Soil Laboratories. Another Solvita test called SLAN (Solvita Labile Amino-Nitrogen) measures not-yet-available organic N that’s stored by soil.

“I wanted to enable farmers to see what life was going on in the soil by indirectly capturing the carbon,” says Brinton. “Soil organisms breathe just like we do. They take in oxygen and give off carbon dioxide. It is the carbon dioxide coming off the soil that indicates soil life.” 

The Cornell (University) Soil Health Testing Laboratory has developed its Comprehensive Assessment of Soil Health (CASH). It measures 15 physical, biological, and chemical characteristics that identify soil health.

CASH, though, may be simplified to gauge soil health. Active carbon can predict 60% of a soil’s health, says Harold van Es, a Cornell University soil scientist. Add soil respiration, organic matter, and aggregate stability measurements to those of active carbon, and soil health predictability rises to 73%, he adds. 


Before shelling out cash for these tests, though, farmers should first ask where they are in building their soils, says DeJong-Hughes. 

“If they are just beginning, I don’t think they need them (soil health tests),” she says. A more pressing matter for many farms is soil erosion. 

“If that’s the case, it doesn’t matter what their soil microbiology tests say. If their soils are eroding, they have a much bigger issue. If we can slow down erosion, we can show huge benefits to farmers. By the way, it also protects our waterways downstream.”

Soil health tests have some other hurdles that include the following. 

Sampling technique. Sampling a field to determine microbial numbers with a soil respiration test could provide a beginning baseline number, says DeJong-Hughes. Subsequent samples, though, would have to be taken in the same area – nearly down to the inch – to assess microbial progress.

“So many microbes live around the roots that where you sample can make a big difference,” says DeJong-Hughes. “Just a few inches’ difference can be worlds apart when it comes to the number of microbes present.”

Soil fertility recommendations. Soil health tests may be used to monitor factors like microbial numbers, says Liz Stahl, a U of M Extension educator. She doesn’t advise using them for fertilizer recommendations.

“So far, none of them been calibrated and correlated for state-specific conditions,” she says. 

A soil test is considered correlated when it can predict lower yields at lower soil test values, she says. Conversely, higher yield and plant growth can be predicted at higher soil test values. Calibration determines how much fertilizer is needed to meet nutrient needs of a crop at different soil test levels. 

Both factors are key components of time-tested land-grant university fertilizer recommendations, Stahl says. Not so with current soil health tests. Relying on uncalibrated and uncorrelated soil tests can result in erroneous fertilizer applications, she says. 

Soil health scores can also differ between locations, says Abbey Wick, North Dakota State University Extension soil health specialist. 

“A field with high organic matter levels in a two-crop rotation could come back with a nice soil health score,” Wick says. However, it would not accurately reflect areas with high clay soils, such as in states like North Dakota, she adds. 

Monitoring Benefits 

Eventually, though, old and new ways to assess soil health will help farmers understand how proper management can improve the land and ultimately the land investment, says Thompson.

“We are taking it very seriously on our own farming operations,” he says.

Johnson concurs. 

“Since soil is a nonrenewable resource, we had better take care of what we have,” she says.

Soil Health Payback?

So will healthy soils help farmers make more money?

“My gut feeling is that healthier soils should be more productive in the long term, but at this point, it is hard to quantify,” says Liz Stahl, a  University of Minnesota Extension educator. “We are just scratching the surface. There is a lot we don’t know yet about soil health.”   

Abbey Wick’s goal  is to be financially net neutral when it comes to soil health.  

“This include maintaining yields or cutting costs while  using soil health tools like no-till and cover crops,” says the North Dakota State University Extension soil health specialist. 

Mark Thompson admits there’s a transition time when switching from tillage to no-till. “The first couple years are tough, and it’s worse if you throw a wet year on top of that,” says Thompson, who’s a farm manager for Sunderman Farm Management, Fort Dodge, Iowa. 

Cover crops help. “We have cut our transition time in half using them, as opposed to just no-tilling,” says Thompson, who also farms near Badger, Iowa. 

This spring was a good example of how soil health tools can pay, Thompson says. 

“You had planting windows that lasted just hours,” he says. On long-term no-till punctuated with cover crops, Thompson planted corn due to improved water infiltration, while nearby tilled fields sat idle . 

A 2014-2016 Iowa State University trial at seven locations showed yields of corn planted at 35,000 plants per acre declined 30% when planted during a May 25-June 5 window compared with April 20-May 5. 

“People are going to see this as a benefit for the future, especially with all the crazy weather cycles and how healthy soils handle them,” says Thompson.

Thompson is also experimenting with small grains to diversify the corn and soybean rotation. Adding them can trigger more microbes that transfer nutrients and water to crops. 

It’s not easy, though. Small grain infrastructure  in north-central Iowa is scant. Ditto for markets. 

Conversely, small grains open up other opportunities.

Thompson planted  Piper Sudan grass after small grains that he will harvest this fall for a livestock feeder. He will then plant the field to corn in  2020. 

Landlords willing to commit to a multi-year contract are key, Thompson says.  

“They see the future,” he says.  “By working with us in those early years, they now can reap the benefits."

Read more about

Crop Talk