By MATTHEW D. ERNST

Missouri Correspondent

ST. LOUIS, Mo. — Tests measuring soil’s chemical properties, especially nutrients, micronutrients and pH, are a given for successful row crop production.

Growers are now evaluating whether investing in soil health tests – snapshots in time that include measures of its physical and biological properties – can pay off with greater profits, according to presentations at the Soil Health Summit, a gathering in St. Louis organized by the National Corn Growers Assoc.

Soil health, according to the USDA, is the “capacity of the soil to function as a vital, living ecosystem that sustains plants, soils and animals.” That means soil health tests, generally speaking, are aiming to measure biology rather than fertility. That makes soil health more difficult to assess than fertility, according to a June 2018 Purdue University guide to such tests.

“There are no standard tests or interpretations for soil biology that help field managers know what to do next,” said Purdue’s Stacy Zuber and Eileen Kladivko. “There are myriad organisms living in the soil that interact in complex food webs, respond to short-term changes in weather and crops and respond to longer-term changes in soil management systems. Soil biological tests are newer, and their practical implications are not yet clear.”

Getting a better handle on soil biology can benefit profitability, especially as more producers are adopting practices, such as cover crops, that have biological impacts that could affect crop economics.

Keep in mind that while many of the tests are well-documented and established, how they apply on individual farms can vary. Here is a look the soil health tests producers and researchers discussed at the Summit last month.

Measuring microbes

One of the more popular soil health protocols is the phospholipid fatty acid (PLFA) test.

“We have biological tests, like the PLFA, to look at the different microbial communities in the soil,” said Nick Ward, president of Ward Laboratories. The family-owned soil test lab in Kearney, Neb., is providing analytics for the Soil Health Partnership’s (SHP) research plots.

Measuring fatty acid levels can show the size of specific microbial groups, and researchers have used the PLFA test to evaluate soils since the 1990s, according to Kansas State University soil scientist DeAnn Presley. She and other soil scientists stress that microbial measures are snapshots of microbe populations at a certain time.

Another kind of microbial assessment is the Earthfort Soil Food Web Biology test. The Earthfort test measures similar microbes as PLFA, but uses a different technique that distinguishes between active and inactive bacteria.

Growers should stick with one type of microbial test and comparing fields over time. “The key for farmers and consultants is to be consistent and compare apples to apples by using the same lab, and making sure they have not changed their PLFA markers,” stated Purdue’s recent advice on soil health.

Cornell soil assessment

Understanding that different labs might use different techniques for measuring soil health is important, said Bob Schindelbeck, Soil Health Laboratory director at Cornell University. “Not only do we want to know what tests we should use, we want to have standardized test protocols.”

The Cornell Comprehensive Assessment of Soil Health was developed, in part, to meet demand from specialty crop growers in the Northeast. “A key is knowing what tests are most useful in your geography,” said Schindelbeck, speaking at the Summit.

Cornell’s assessment uses 12 soil health attributes to develop a soil quality score on a scale of 100. These include organic matter, active carbon, protein and respiration. The respiration test is conducted over a four-day period to measure how much microbial activity is taking place in the soil.

He said the Cornell test combines these measures of soil biology and microbial activity with four measures of the soil’s physical properties: wet aggregate stability, available water capacity, surface hardness interpretation and subsurface hardness interpretation. The last four measures are the traditional soil chemical properties: pH, phosphorous, potassium and micronutrients.

The Cornell test is $110, pricier than traditional soil tests and other soil health tests. But using a suite of health measures, combined with producer experience and observation, could pay off in the long run, say soil health proponents.

The current question researchers face is which suite of tests is most useful. “Everyone wants to come up with a standardized suite of soil health tests,” said Schindelbeck. “There are obviously a lot of different methods to take your soil samples on your farm, depending on what your end goal is.”

The Haney test

Row crop producers are also testing the Haney Soil Health Nutrient Tool, popularly called the Haney test. “A lot of the focus (on soil health testing) is around the Haney soil health assessment tool,” said Ward.

The unique thing about the Haney test – named for a Natural Resources Conservation Service researcher on the team that developed the test – is it measures water extractable organic carbon and nitrogen. That provides a measurement of the C and N available to microbes.

Like the Cornell test, the Haney test involves multiple assessments. “It’s more than just a single test; it’s a suite of tests. We’re looking at carbon to nitrogen, as well as the plant nutrients,” Ward explained.

Ward, whose lab advertises the Haney test at a cost of $49.50, said the potential benefit is in fine-tuning nitrogen applications. “We really want to be able to control inputs, from a financial sense.

“And one way that we stay ahead is controlling our input costs, managing our largest fertilizer, nitrogen. That’s the way that people get the return on investment on their Haney tests or other soil samples,” he said.

Producers agree that soil health is important, especially as end users and consumers want more information about how farms are stewarding their soils. But there remain many questions around precise production economics that can be attributed directly to soil health measures.

“It’s well-known that the science is evolving around a lot of the soil health indicators that we’ve been collecting,” said Maria Bowman, SHP lead scientist.

According to Purdue’s most recent guidance, the various soil health tests are unlikely to detect small changes in health. That means their payback may be best in monitoring fields where large changes are occurring – like a field that has always been conventionally tilled and is transitioning to conservation tillage and cover crop rotations.

Purdue also advises producers that soil health tests are snapshots in time; soil organisms cycle throughout the year. Soil organisms also vary across a field, and the means of evaluating soil biology are still in their infancy.

Still, soil health measures are important as researchers evaluate the economics of cover crop use and more widespread conservation tillage. Whether health tests will catch on for widespread adoption is yet to be determined.

“These tests show promise as important tools for gauging the improvements in soil health as you integrate conservation cropping practices into your system,” said Zuber. “However, these tests are expensive and there are many challenges to using and interpreting them.”