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Taking a Soil Sample

Ken Olson

The most critical step in the soil testing procedure is obtaining representative samples. A spade or trowel and a clean plastic or stainless steel container are the tools you need. These prevent the sample from being contaminated with zinc from a metal container. You also need to identify the sample by a letter or numbering system on a paper or plastic sample bag and also on a field sketch for future reference.

Divide the field into uniform areas. Each area should have the same soil color and texture and the same past cropping, fertilizing and liming treatment. Sample each area separately. For farmland, get equal-sized slices from fifteen or more places with the spade. For yards and gardens sample six areas. Do not mix light and dark colored soils together. To take samples:

• Take soil from the surface to the plow depth of 6-8 inches in cropping situations, or two to three inches in permanent pastures and in lawns.
• Place the slices in a clean plastic pail. Mix them thoroughly, breaking up the cores or slices. If the soil is muddy, dry it at room temperature before mixing. If the soil crumbles easily, dry after mixing.
• Spread the mixture out on clean paper to dry. Do not heat it in an oven, microwave, or stove. Do not place the sample where fertilizer or manure may get into the sample and contaminate it.
• Fill the sample bag with the air-dry mixture of soil. Discard the rest.

When obtaining samples: stay away from farm lanes; field borders; fertilizer bands in row crops and small grains; areas within one hundred and fifty feet of gravel roads; and any other areas which are distinctly different, such as pot holes, sandy ridges and eroded spots.

The lab recommendations will be as good as the information you send in. Include field history; fertilizer, lime and manure added; crop to be planted, and yield level desired; or lawn maintenance practices. Indicating crops grown during the past two growing seasons also provides the laboratory with essential information. They will then provide the most accurate nitrogen recommendations.

You determine desired yield for the crop that best fits your soil and management situation. You can obtain this information from your local Extension Office along with the soil sample information sheets, sample bags, where to send the samples and the cost of each desired analysis. If your county doesn't have an Extension Office, call the Farm Information Line at 1-800-232-9077. FIL is staffed from 8:30 a.m. - 1:30 p.m., Monday through Friday.

Reviewed by Brad Carlson 2009.