The Importance of Soil Testing for Agriculture

You don’t assume your truck is “fine” just because it’s running; you routinely check its fluids and parts to make sure they’re performing optimally. The same logic applies to soil testing for agriculture. Routine soil testing is a key step to assess changes in soil nutrient levels that require maintenance. 

Learn about the importance of soil testing in agriculture, and how timing impacts your decision-making. 

📷 BASF Employee | BASF Employee using soil probe to take an SCN soil sample

Advantages of ag soil testing

A soil test is a diagnostic tool for your field that can: 

1. Guide fertilizer prescriptions 
2. Boost yields 
3. Improve efficiency of fertilizer applications 

In other words, soil testing for agriculture helps growers gauge timing and need for plant macro nutrients including phosphorus, potassium, nitrogen, sulfur, calcium, and magnesium. Agricultural lime contains calcium and magnesium used to raise soil pH. It is also good to test for micro nutrients as levels of boron, manganese, and zinc often need to be adjusted to obtain maximum yields.

When requesting a soil analysis from a soil testing lab, reports will commonly provide the suggested additional amount of each nutrient needed to provide a healthy crop and meet your yield goal.

Ideal timing for ag soil testing

Ideally, you should conduct ag soil testing at least every 2 to 3 years to guide decisions like fertilizer recommendations and how much liming material to use. To produce accurate results, compare results from fields where soil management practices remain consistent. If tillage and fertilization practices have varied, test more frequently.  

However, even where management practices have remained the same, nutrient levels fluctuate throughout the season and over the years due to recent fertilizer applications, nutrient plant uptake and leaching. Keep your soil test timing and processes consistent to avoid introducing new variables that could influence outcomes and result in misguided decisions. 

Soil testing is typically conducted in spring or fall depending on time constraints and what insights you are looking for:

1. Spring pre-plant ag soil testing: Testing in spring gives the soil time to recover from the previous season and may provide a more neutral representation of your soil. You should also test pre-plant for a clearer picture of which nutrients your upcoming crops will need. 
2. Fall post-harvest ag soil testing: Due to recent nutrient uptake from the harvested crop, fall testing will likely provide different results from spring pre-plant testing. Post-harvest soil testing has the advantage of occurring when there are fewer demands on time and equipment, and it provides additional time to review the results and weight management decisions before next spring. 

Which variables dictate when to conduct soil testing for agriculture? 

Changes in the field

It is recommended to sample or resample the soil if any major change in the field has occurred, such as: 

1. Establishing a new crop, including before a standard crop rotation 
2. A new tillage method 
3. Large compost or manure applications
4. Irrigation water quality changes 

Moisture conditions that can affect measurement

Soil moisture — or lack thereof — can affect the measurement of the nutrient balance itself. If soils are dry for several weeks to months, soil pH and/or potassium levels may be lower than expected¹. Additionally, if soil is extremely wet at the time of sampling, this can make sampling depth hard to control and cores hard to remove from the soil probe. 

When it comes to soil pH, salts can accumulate near the soil surface, causing lower pH readings in the lab. Usually, these salts are moved down in the soil profile by rainfall. 

For potassium, dry soil may “trap” potassium and a routine soil test may not be able to detect it². Once rainfall is received, the pH and potassium levels usually stabilize within a couple of weeks. 

Learn more at Grow Smart® Live:

Discover more about how to get your soil ready for the next season: 

1. Soil Properties You Can Change
2. How to Prepare a Field for Planting Corn
3. Soybean Soil Requirements: How to Prepare for Planting

Experts are available to help you make your decisions. Reach out to your seed retailer, a nearby extension office agent, or a seed company professional like your regional BASF representative.

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Endnotes

1. Camberato, Jim. "Keep In Mind Soil Test K And PH Are Affected By Low Soil Moisture." Pest&Crop Newsletter, 13 Oct. 2022, extension.entm.purdue.edu/newsletters/pestandcrop/article/keep-in-mind-soil-test-k-and-ph-are-affected-by-low-soil-moisture/. Accessed 22 Sept. 2024.
2. Mallarino, Antonio. "Beware of Dry Conditions When Soil Sampling and Interpreting Test Results." Integrated Crop Management, 5 Oct. 2022, crops.extension.iastate.edu/cropnews/2022/10/beware-dry-conditions-when-soil-sampling-and-interpreting-test-results. Accessed 22 Sept. 2024.