Benefits of Soil Testing

Soil testing can occur in the fall or spring and if the ground isn’t frozen, there’s still time to pull meaningful samples.

Why Soil Tests Matter

If you’re not testing soils, you’re working in the dark when it comes to fertility, says LG Seeds Agronomist Tim Beninga.

Beninga’s No. 1 piece of advice in terms of crop nutrient management is to make sure you’re working with up-to-date soil sample data. “This isn’t the time to be throwing things out there willy-nilly, but you also can’t shut off your fertility program. Sampling helps you determine what and how much fertility fields need.”

Right after harvest is a great time to sample soil because it allows for fall fertility and planning over the winter. Testing in late fall gives you more time to analyze results during the winter and build a data-driven fertility plan for the next growing season. But whether a grower pulls samples in the spring or in the fall, the important thing is to be consistent from year to year.

Timing: Why Cold Soil Matters

Testing closer to when the ground freezes, when soil temperatures dip below 7°C (45°F) — produces results that best represent spring planting soil conditions.

That’s because:

Microbial activity slows down, limiting nutrient mineralization or transformation.
Nutrient levels stabilize, reducing variability in test results.
Wet soils firm up, allowing for more accurate and consistent core sampling.

Essentially, it locks in a “snapshot” of nutrient availability similar to what you’ll see in early spring, helping you make more precise fertilizer decisions.

General Soil Sampling Methods

For best results, follow standard soil sampling practices. General recommendations include:

Use consistent sampling depth across all cores, typically 6–8 inches for most routine analyses.
Collect 10–15 cores per sampling area to create a representative composite sample.
Avoid unusual spots such as field edges, wet holes, burn sites, or old livestock areas.
Use a zig-zag or grid pattern to cover the area evenly and reduce bias.
Mix cores thoroughly in a clean container before sending them to the lab.

What Soil Tests Can Reveal

Crops perform best when nutrients are both sufficient and balanced. Soil tests help identify where that balance is strong and where it may be limiting next year’s yield potential.

“You’re only as good as your lowest nutrient,” Beninga says. Nitrogen, phosphorus, potassium and sulfur are important for corn, but micros like zinc and boron—along with what’s naturally available in the soil, also play a significant role.

“Micros affect many of the ways macros interact with the plant,” Beninga explains, citing phosphorus and zinc as an example. “If you’re putting on phosphate, you need to apply some zinc too. But if you put on too much zinc, you’ll tie up your phosphate. Balance is everything.”

Balance also matters for sulfur and nitrogen. “If you don’t have enough sulfur, then it doesn’t matter how much nitrogen you apply; it won’t be available to the plant,” he says.

Application timing is part of that equation. Nitrogen is often overapplied, making split applications a useful strategy to match nutrient supply with yield potential and in-season crop demand. Phosphorus, on the other hand, is the nutrient most often shorted—and one of the costliest to cut. “But it’s probably one of the worst nutrients to cut because it’s so important to plant growth and health,” Beninga says, encouraging growers to make the investment.

By understanding these nutrient interactions and your soil test results, growers can align fertilizer programs with actual field needs, supporting ROI and long-term soil health.

Using the Results: Plan Smarter Over Winter

The biggest advantage of testing late in the season is the lead time it provides.

With results in hand, you can:

Evaluate fertility trends across years
Budget and purchase fertilizers early
Adjust rates and blends for variable-rate application
Pair soil test data with yield maps or tissue tests for precision planning

Taking time this winter to study your soil results sets the stage for more efficient, cost-effective nutrient management next year.

Soil tests should guide cuts.
Beninga warns against pulling back on liquid starters. “Especially in North Dakota, starter pop-up fertilizer is crucial in our soils and can be a good ROI,” he says. “If you have to budget, look to your dry fertilizer.”

Fertility decisions should lean heavily on soil test values and whether a grower owns or rents their acres—both factors influence whether it makes sense to build fertility reserves.

High fertility range: Use some of the reserves.
Medium fertility range: Soil test crop removal rates are appropriate.
Low fertility range: A minimum of crop removal is still necessary.

“Farm operators will be faced with challenging decisions as they work to stay profitable,” Beninga says. “We want our growers to succeed and will support them any way we can, whether that’s helping them find the right seed for every acre or hashing out a fertility plan for the coming season.”