COLUMBIA CITY, Ind. — Whether you are a farmer growing crops or a homeowner growing vegetables, it’s always a good idea to do regular soil testing to gauge nutrient levels, pH, and other factors rather than guess about them.
Farmers tend to do regular soil tests. Rather than guessing on needed nutrients and pH levels, soil testing helps them determine a “prescription” for crop fields. As expensive as fertilizers are, one can see why a prescription, rather than a guess, can offer economic advantages.
Soil testing can also benefit homeowners who care for vegetables, flowers, or their lawn. A representative soil sample taken at least once every 3-5 years will tell you a lot, and may even save you money in the long run.
Absent of soil test results, landscapers and gardeners may apply fertilizer, lime, or other materials to soils without knowing whether the soils need these amendments or not. Some of these amendments may do more harm than good. In my years as an Extension Educator, I’ve heard many homeowners play this guessing game. Some of these guesses (especially in relation to amendments that adjust pH), may be exactly opposite of what is really needed.
Key information homeowners can learn from a soil test are soil pH level, organic matter content, cation exchange capacity (CEC), and phosphorus and potassium levels. Most labs don’t include a nitrogen test because it’s a moving target; soils don’t retain nitrogen, so this nutrient must generally be replenished every year for crops that need it.
Purdue experts Kyle Daniel and Rosie Lerner recently co-authored a publication entitled, “Collecting Soil Samples for Testing,” available at www.edustore.purdue.edu.
“Every soil test should provide you with your soil’s pH, which measures the acidity or alkalinity in your soil,” they said. “Soil pH affects how available most nutrients are for plant uptake.” They said most horticultural plants grow best when the soil pH is between 6.0 and 6.8 (slightly acidic). However, one should research the desired pH level for the plants you grow to see if amendments are needed. For example, potatoes and blueberries prefer an acid soil between 4.5 and 5.1 pH.
“If you need to raise the pH (and make the soil more alkaline), you add lime,” they said. “If you need to lower the pH (and make the soil more acidic), you add sulfur or acidifying nitrogen.”
Fall is generally accepted as a good time to take soil tests in the home landscape or garden. Whenever you decide to test, it’s a good idea to stay with that time to have more of an “apples to apples” comparison with subsequent soil tests.
“The first step of gathering a good soil sample is to draw a diagram of your property and indicate where you will take soil samples from,” they said. “It’s important for you to take samples from different parts of your property that have different characteristics.” For example, you should have different soil tests for your yard, your garden, your flower beds and your shrub beds.
“Since your sample will use only a small portion of the soil, it is very important the sample represents the area,” they said. “Usually, the best way to do this is to take several core samples (with a soil probe) or slices from different spots, evenly distributed, in the area.” They recommend taking 10-15 cores for a large area, like a yard, and 4-6 core samples for a smaller area, like a flower bed.
Gardens, shrub and landscape beds should be sampled to a depth of 6-8 inches. Turf can be sampled to about 3 inches. Tree root zones should be sampled to 8-12 inches.
After collecting core samples from an area, break up any lumps, remove rocks and debris, and allow the soil to air dry. Then, mix together for the composite sample you’ll send to the lab.
Soil testing laboratories will be happy to send you sampling bags and sample submission forms (which may also be available online).
Reports received back from labs are reasonably intuitive, but if you need assistance interpreting your results, bring your report to the county Purdue Extension office, and we’ll give you a hand.
A list of certified soil testing labs is available at: https://ag.purdue.edu/agry/soilfertility/Pages/soil_testing.aspx. Soil testing fees are very reasonable. So, don’t guess, soil test!
— Purdue University Extension, Whitley County
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