Should you soil test this year?

Farm Forum

As the number of harvested fields climb and the soil sampling season ushers in, I’d like to cover a few Frequently Asked Questions (FAQs) on how to get the most from your soil test.

1. How often should I soil test?

Most likely you are not testing every field every year. Here are a few tips on how often you should:

• In general, test every 2-4 years.

• Consider testing more often if you have introduced a new crop rotation.

• Test new fields more often to gain an understanding of the soil variability.

2. What time of year should I be soil sampling?

In general, the rule is after harvest but before any new fertilizer applications. The important thing to remember is to be consistent from one year to the next. If you choose to pull samples in the fall, sample again in the fall the next time you test that field.

3. How deep should I pull samples?

Like timing, how you pull samples should be consistent from year to year. Consult with your local agronomist, but industry standards are 6-8 inches for conventional-tillage fields and 4 inches for no-till fields.

4. What should I soil test for?

Most soil test labs routinely share results for the major nutrients (NPK), soil organic matter and pH. Be sure to request micronutrient levels from the soil test lab, too. Even if you have not previously tested for them, micronutrients can drag yield if they are deficient. Don’t let a micronutrient like zinc or boron determine whether you get the most from your seed and fertilizer investments.

5. What should I look for on my report from the soil test lab?

The most important thing to correct before fertilizer rates is soil pH. High or low soil pH can affect how nutrients will react and behave in your soil. A video from Ag PhD ( is a helpful guide on how to turn soil test results, including soil pH, into fertilizer decisions.

Also, work with your retailer or agronomist to decide which micronutrients you may need to apply. Here are some tips on which micronutrients to pay attention to:

• Any micronutrients you know have been issues in that field’s past.

• Zinc – it’s the most important for many regions and crops – and today’s high-yielding corn hybrids tend to remove more zinc per bushel than traditional corn genetics.

• If you’re planning a rotation into soybeans, pay attention to manganese.

• For a rotation into wheat, look at copper. Up to 30% of soils spanning from central Texas north to Alberta, Canada have tested low to moderate for copper.

• More and more soils, especially in lightly textured ground, are showing boron deficiency. A&L Great Lakes Laboratories reports that of all the soil samples they tested from the Midwest in 2013, 72% were rated low to very low in boron.

In the past, a medium or low level result for boron may have been overlooked because of toxicity concerns. But some crops have critical needs for boron. Alfalfa fields may need boron applications as often as 1-2 times each year! Visit to learn how Boron DDP makes boron applications safe for crops.

As a territory manager for Compass Minerals plant nutrition products, Steven Tillman provides technical support to retailers and farmers from Indiana to New Jersey.