How to Create the Most Effective Soil Sampling Program

An Oregon wetland resource manager examines a soil core sample. Proper soil sampling should accurately capture the variability of a field and provide useful data for input and management decisions. Photo by Jack Dykinga, USDA ARS.

Choose Your Lab

In his Soil Sampling Guidelines paper, Ackerson advises farmers to use the same lab for analysis every time they take soil samples because labs can use different methods, which may lead to different results. Using the same lab every time will ensure any changes you see are because of changes in the soil, rather than the testing.

Determine Where You’re Going to Collect Samples

Whole-Field vs. Spatially Explicit Sampling

There are two primary strategies for choosing your sampling locations: whole field and spatially explicit. With the whole-field approach, you’ll collect several samples across the field, known as subsamples, which will then be mixed to create one composite sample. As Ackerson explains in “Soil Sampling Guidelines,” composite samples reduce the effects of soil variability and are less sensitive to unusually high or low soil test values that might occur due to concentrated fertilizer applications or natural soil variation.

Grids vs. Zones

If you want to make any precision applications, you’ll need to choose between grid and zone sampling.

Keep Your Data Consistent

While zone sampling is the better strategy if you’re making precision applications, Ackerson doesn’t recommend changing your practice if it’s going to conflict with the data you already have.

But What if You Haven’t Been Sampling Properly?

If you learn your soil sampling program hasn’t been following best practices, should you scrap the data you already have and move to something different?

Focus on Capturing pH

If you’ve been doing whole-field sampling and you’re not happy with the results or looking to improve your spatially explicit sampling program, consider precision sampling for pH. Ackerson has heard ag retailers say this is often the №1 thing growers can do to improve their soil sampling because it provides a great return-on-investment. The reason for this is two-fold:

Best Practices for Pulling Samples

Once you’ve picked your lab and your soil sampling strategy, you’re ready to pull soil samples. Now you must decide who is going to collect them.

Pull Different Depths Under Conservation Tillage

Nutrients tend to stratify in no-till and reduced-tillage fields, which can lead to overapplication of inputs if we don’t sample at different depths, Ackerson explains. It’s not uncommon to see very low pHs in the soil’s surface layer because of continuous anhydrous ammonia applications that aren’t incorporated, while underneath the pH is fine.

Avoid Small Areas That Misrepresent the Soil

While you want to tease out the differences in soil between the zones or any areas you’re managing separately, you don’t want to pull samples from small spots that may be inconsistent with that zone or area.



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