Farm Progress

Don't skip soil testing this fall! Knowing pH levels is just as important as clocking N, P and K, especially to make herbicides perform next year. Here's how to ensure the best sample.

Jill Loehr, Associate Editor, Prairie Farmer

October 18, 2016

3 Min Read

If your yields were solid this fall, it might be tempting to skip soil tests — especially to save dollars and time. But Russel Higgins, a University of Illinois Extension educator, says you’ve got to resist the temptation. Why? One word: pH.

Soil pH affects everything from nutrient availability to herbicide performance, he adds.

“[It] doesn’t get all the glory that N, P and K do,” Higgins says. “But pH is certainly important in our soils.”

5_keys_successful_soil_sample_1_636124004820179053.jpg

Knowing soil pH and nutrient levels starts with a good soil sample. Keep in mind, soil samples reflect soil conditions on that day and at that time. “It’s the best [information] we have, but there’s always some variability,” Higgins explains. “That’s why it’s so important to take a good sample.”

Higgins provides his tips for a successful soil test sample:

1. Be consistent. Pull at least five samples within a 10-foot radius of a sampling location; the composite sample will increase the accuracy of the soil tests. “The more [cores] you pull, the more likely you are to pull a representative sample,” Higgins adds. “GPS is a great asset in returning to sampling locations in successive sampling years.”

2. Watch your depth. Higgins suggests targeting a depth of 7 inches to match statewide fertilizer recommendations. This is especially important in no-till fields where nutrients may “stratify,” or layer, in the soil.  “Pull samples too shallow and you may overestimate nutrients,” Higgins explains. “Too deep, and you underestimate nutrients.”

3. Stay the course. Higgins recommends pulling soil samples in the fall when potassium numbers are more reliable, avoiding its “seasonal cyclical” pattern. However, if you typically pull soil samples in the spring, stick to the same timing. “You’re looking at a history of your soil tests, and we want you to be consistent,” he says. Pulling soil samples at the same moisture level, if possible, will also help provide consistent reports.

4. Don’t jump around. If you are happy with the reports you receive, pick a lab and stick with it. “Bouncing from one lab to another each time you have your fields tested may give you varied results,” says Higgins. If you need to find a reliable lab, the University of Illinois has a list of approved labs that are evaluated on their sampling prowess.

5. Ground-truth your report. If an individual soil test location seems off, Higgins says it’s important to go back and look at yield numbers or think about crop growth problems at that site that may confirm potential issues. If not, Higgins says the report could be considered an anomaly, but worth rechecking with the next soil test.

The ability to spot problem areas is a good reason to pull soil samples at least every four years, Higgins adds. More frequent soil tests may be warranted in fields where farmers have applied high levels of nutrients to correct low testing fields.

About the Author(s)

Jill Loehr

Associate Editor, Prairie Farmer, Loehr

Subscribe to receive top agriculture news
Be informed daily with these free e-newsletters

You May Also Like