By Nate Birt

Two hats qualify Corey Lacey, Ph.D., to vouch for the many benefits of regular soil testing on Illinois soybean farms.

As Environmental Policy Manager at Illinois Soybean Association, Lacey knows that when farmers are allowed to apply nutrients at agronomic rates, they can increase productivity and optimize environmental stewardship. And as President of Agricultural Laboratory Testing Association (ALTA), Lacey knows that farmers’ decisions improve with help from soil data provided by high-functioning soil-testing laboratories.

“Soil testing represents one of the most cost-effective investments on a farm, typically amounting to only $1 to $2 per acre in a standard testing cycle,” Lacey explains. “Despite its low cost, it yields one of the highest returns on investment. This is because it enables farmers to use precision agriculture technology (grid sampling, variable rate technology (VRT) maps, etc.) to make informed fertilizer and lime applications, which can amount to hundreds of dollars per acre in input costs.”

John Jones, the new soil fertility professor at University of Illinois who began his role in August, agrees that a strategic soil-testing framework adds real value for farmers. He grew up on a farm in south-central Wisconsin located on Saybrook and Plano soils—named after the northern and central Illinois communities where they were discovered.

“Each season provides the opportunity to collect information and make decisions that complete the picture of soil fertility management,” Jones explains.

Create Your Soil-Testing System

The best way to experience lasting value from soil tests is to implement a system that calls for regularly digging deep—literally.

“Farmers can monitor changes in soil health and nutrient levels over time, addressing nutrient deficiencies or imbalances before they cause problems,” Lacey says. Basic soil fertility packages include essential data on pH, to guide lime recommendations and macronutrients, as well as on phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) to inform fertilizer applications.

The question of when to schedule your soil sampling is important. The closer you can sample to the growing season, the better insights you’ll have to fine-tune the nutrients available to your crop. That often means, contrary to convention, that spring sampling provides superior insights compared to fall sampling.

“Spring sampling facilitates a smoother decision-making process,” Lacey points out. “Unlike in the fall, when farmers must rapidly make application decisions relatively soon after receiving sample results, spring sampling allows farmers to collect samples pre- or post-planting. They can then review the data over the summer and plan for fertilizer and lime applications in the fall.”

There’s also a financial incentive, in some cases.

“Since the majority of soil testing is conducted in the fall, some labs offer discounted pricing to incentivize a shift to spring testing,” Lacey says.

One caveat: Lacey notes potassium levels, in particular, can vary from fall to spring. Thus, if you choose to shift away from fall sampling and into spring sampling, be aware your lab data might reflect this reality.

Get Sound Advice On Soil Tests

Several types of experts can help you get the most from all soil samples you take.

First, Illinois farmers can work directly with soil-testing labs, which provide comprehensive services including soil sampling, data analysis and fertilizer recommendations, Lacey says. Some of those facilities are headquartered here, while others have multiple locations including Illinois.

Second, ag retailers often provide complementary services to labs. For example, Lacey notes, many ag retailers organize soil testing and provide data-interpretation support. Many even subsidize or fully cover the costs of soil testing for fertilizer customers. You can also access additional information on soil testing, nutrient management and sustainability via ag-retail industry organizations such as the Illinois Fertilizer and Chemical Association and the Illinois Nutrient Research and Education Council, funded by the fertilizer checkoff.

Third, your farm might benefit from working with the Illinois network of Certified Crop Advisors (CCAs), which offers customers local and independent advice on soil sampling and testing. “Additionally, they typically have strong relationships with local soil testing labs, which helps farmers gain access to the expert knowledge and insights from lab staff,” Lacey says.

Finally, Illinois farmers have the opportunity to learn from Jones, the new University of Illinois soil fertility professor. “Dr. Jones is an emerging expert in soil fertility highly respected for his research at Iowa State University and University of Wisconsin-Madison,” Lacey explains.

Jones has extensively studied phosphorus and potassium soil-test calibration for soybeans and corn, among other areas of specialty. He seeks to help Illinois farmers further synchronize soil supply of nutrients with time-sensitive crop demands while avoiding losses from the field. “I look forward to supporting and developing tools that farmers and agronomists can integrate into their process of making nutrient management decisions,” Jones says.

Illinois soybean farmers can implement a successful soil-testing strategy by taking specific actions at specific times during the year. John Jones, the new soil fertility professor at University of Illinois, shares some of the key checklist items that can be most helpful.

• Winter: Assemble a list of audibles that may need to be called, Jones advises. If soil testing has been conducted in a field before soybean planting, and results showed P or K values in the Very Low or Low categories, preparing for fertilizing at removal rates at a minimum could alleviate yield reductions. “It would be important to consider any P or K applied to soybeans going forward when planning soil sampling or fertilization in the following fall,” he says.
• Spring: Consider holistic soil fertility decisions beyond those tied to planting date and seeding rate. “The basics should still apply,” Jones says. “If soil-test levels for P or K are low prior to soybeans, yield reductions may occur.”
• Summer: Observe soybean responses to management decisions or environmental conditions, and adjust accordingly. “Hard data can be collected if nutrient limitations are suspected by tissue sampling paired with in-season soil sampling,” Jones says. “Locations in the field where plants or soil are sampled in-season can then suggest if post-harvest, routine soil sampling plans should be adjusted to account for zonal differences in a field.”
• Fall: After harvest, you or your trusted adviser should collect soil samples across uniform depths while ensuring an adequate number of cores per composite sample. Also, note soil conditions. “In recent years, different soil moisture conditions in the fall have been a good reminder that soil moisture may affect soil-test potassium values and soil pH, though this varies by soil and laboratory method,” Jones says. “If sampling conditions are extremely dry, or fields are too saturated, delaying sampling to spring is a viable option.”

Ask These Questions to Improve Your Soil Decisions

It’s a good idea to understand the basics of soil sampling and soil testing to ensure you’re asking the right questions to guide farm decisions.

One of the first questions to consider: Should I grid sample or zone sample?

Grid sampling is the simplest soil-testing approach to estimate fertility, Lacey says. In Illinois, this type of sampling is typically conducted on 1.1-, 2.5- and 5-acre grids. Those numbers indicate how many samples are collected per acre.

Zone sampling, alternatively, can help you simply differentiate fields based on soil type—or go very deep into your soil using a suite of precision ag tools including satellite data, sensors, software and yield data. “Farmers considering zone sampling should work with their trusted adviser to ensure they understand and agree with the zone sampling strategy being used,” Lacey recommends.

Next, ask: What soil-testing methods will my lab use? For example, while most labs serving Illinois farmers follow the University of Illinois Agronomy Handbook, different labs report data points such as phosphorus in different ways. You can work with a trusted adviser or directly with the lab to understand the data so fertilizer recommendations are accurate, Lacey says.

Finally, confirm: Does my lab have quality-assurance and quality-control processes in place? A simple way to do this is to verify that your lab is enrolled in the voluntary Soil Analysis Certification program available from ALTA. As part of this program, labs get a report card three times per year evaluating the quality of their soil tests, Lacey says. Additionally, confirm your lab participates in one of the two available proficiency testing programs—either the North American Proficiency Testing Program or the Agriculture Laboratory Proficiency Program.

Beyond trusted labs, exercise caution, Lacey advises. A variety of startup companies seek to improve soil-testing methods, and while some efforts appear promising, farmers should be aware of the risks.

“Most of these companies base their technologies on data from private soil testing labs, then apply corrections or correlations in the background to generate recommendations for farmers,” Lacey says. “I always encourage farmers looking at these options to consider if going to the original data source in the first place is a better approach.”

He anticipates continued innovation in VRT maps built from soil test data. And Lacey is watching Illinois-based Precision Planting and its Radical Agronomics as an interesting though unproven model for generating better soil insights.

Use the Data

Making use of all that soil-testing data might feel overwhelming, Lacey acknowledges. But Illinois farmers should seek out the support they need to use the data for decision-making.

“Many farmers get massive amounts of agronomic data that can help them make input decisions,” he says. “But they are not certain how to use the data, so they decide to ignore the data. Farmers can avoid this by making a plan for how to use the data before they collect it. Soil-test labs, trusted advisers and ag retailers can help farmers with this process.”

Illinois farmers have access to several experts who can provide actionable advice based on soil sample data, including soil-testing labs, CCAs, ag retailers and new University of Illinois soil fertility expert Dr. John Jones.