PHOTO: CAFNR/Flickr
Lisa Kivirist
November 29, 2016

Q:

I recently purchased a farm I want to rehabilitate for crop production. What is a soil test, and how can I use it for this purpose?

A

A soil test determines the content and characteristics of your soil. It analyzes the levels of nutrients, contaminants and, depending on the type of test, a variety of other characteristics, such as pH. Think of a soil test as a checkup for your garden. It helps determine what your soil might need more or less of and serves as a tool to help you better manage soil health, thereby growing the healthiest plants possible. Follow these four key steps when soil testing.

1. Research your area.

“Find out as much as you can through existing information about the soil in your area first,” advises Jean Eells, Hamilton Soil and Water District Commissioner in Webster City, Iowa. “The Natural Resources and Conservation Service has a Web Soil Survey that provides soil data and information specific to your location and helps identify what the area soil is capable of growing.”

2. Acquire a soil test.

While garden centers and farm-supply stores often sell basic, do-it-yourself soil test kits, your best bet is to contact your local extension office to see what university-affiliated test options are available in your area. Such tests are often quite economical (less than $20 for a basic test in my area of Wisconsin) and connect you to local resources more familiar with soil management in your area. Additionally, such tests will be analyzed by a commercial lab, often university run, yielding more accurate results.

3. Take a soil sample.

Follow the directions on your soil test to gather the sample. Typically, tests require a composite sample, combining soils from several different locations in the area you want to analyze. While a soil probe or auger is the best tool for taking a soil sample because it collects a continuous core while not disturbing the surrounding soil, a garden shovel or trowel will also work. Generally, you’ll need to dig 5 to 7 inches deep for a sample in order to look down through the top layers of soil into the root zone, or where roots grow most actively.

A good way to take soil samples is to walk through the field in a W pattern, taking samples of soil without plant residue at each point of the W. Follow the test instructions carefully if you’re sending the soil to a lab; the sample needs to be returned and analyzed quickly for accuracy—ideally within 24 hours.

While you can technically sample soil anytime the ground is not frozen, it is best to sample in early spring or late fall so you have time to develop and act on a nutrient-management plan before the growing season.

4. Understand your results.

After you receive your soil report, the soil-management process begins. Soil tests typically check for three major nutrients—nitrogen (N), phosphorus (P) and potassium (K)—as well as soil pH level. Look at each element and understand what it means and at what level it should be in relation to your garden—extension and other agency resources can be very helpful in making these determinations. For example, pH levels range from 0 to 14; a 7 is considered neutral while 0 is totally acidic. While most plants bearing edibles need a pH level of around 6.5, some plants, such as blueberries, need a higher acidity of 4.5 to 5 to thrive. There are many reasons why soil pH levels might be out of balance, such as application of chemical fertilizer or disturbance of the surface. Depending on your needs and where your numbers come out, you might need to increase alkaline levels by adding lime or decrease soil acidity with sulfur.

Soil tests generally can be repeated every three to four years as a barometer and planning tool for long-term soil health. Remember, healthy soil reflects the fundamental principle of organic gardening: Feed your soil well with natural inputs and let that nutrient-dense soil feed your plants. While larger, commercial growers might apply chemical fertilizers as a quick fix to achieve soil balance, taking the time to understand your soil as the living, natural organism it is and continually adding healthy inputs, such as compost, enables your soil and, subsequently, your crops to thrive naturally and consistently.

A soil test is typically not a contingency for buying a farm, but it’s not a bad idea to know the basic nutrient content, especially the deficiencies of your soil’s nutrient profile, before buying the land. Depending on what you want to grow and how quickly you want to harvest and sell your first crop, a soil test can help you decide if the soil’s current condition meets your needs. That said, remember that soil can slowly be improved over time on most properties. If everything is perfect about a potential property, from the house to the outbuildings to a great view, only terribly problematic soil tests should impact a purchase decision. Learn more at the NRCS Soils website.


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