By Kris Gallagher
After researching soil for the articles in the spring 2018 issue of DePaul Magazine, I cast a wary eye on the yard surrounding my 110-year-old home in Oak Park, Ill. Was I perched on top of a smelter? Was I poisoning my kids with my kale? Jim Montgomery, associate professor of environmental science and studies in the College of Science and Health, and his student team ran soil samples from my yard and raised-bed garden through their testing process. Here’s what I found out.
Lead: 251-386 parts per million (ppm)
My front yard has about 251 ppm of lead and my back yard 386 ppm, while my raised-bed garden has 157 ppm. All of these are well below the EPA’s threshold of 1200 ppm for non-play areas, although Montgomery notes that there is no “safe” level of lead. I filled my raised-bed garden with purchased topsoil and compost from my kitchen and yard, which likely introduced some lead from grass clippings, leaves and branches. Montgomery recommends I further dilute lead concentrations by adding purchased compost and mixing it in thoroughly.
Soil salinity/electrical conductivity: 0.0003
Salts are essential for plant growth, but too much salt restricts the type of plants that can grow in soil. Scientists determine how salty soil is by testing its electrical conductivity. The best soils have conductivity below 0.98, like mine.
Acidity (pH): 8.01-8.16 pH
Soil pH measures how acidic or alkaline the soil is, which impacts the availability of nutrients and minerals and how active organisms are. The optimal pH range for vegetables is 5.5-7.0. My soil is a bit alkaline. Montgomery recommends that I add sulfur about three months before planting, which I did in February.
Microbial respiration: 20.9-31.4 lbs. C02/acre/day
Soil doesn’t breathe, but the microorganisms and roots that live in it do. Soil respiration is a measure of the amount of carbon dioxide they expel daily. The ideal range is 32-64 pounds per acre per day, so my soil is good but not optimal. Montgomery suggests I add manure or compost.
Nitrate (NO3): 78.73-138.23 ppm
Plants require nitrates, a form of nitrogen, to grow. The ideal range is 25-30 ppm. Too much nitrogen means plants produce too many leaves and few flowers or vegetables. My raised bed garden had five to six times too much nitrogen, which explains my spotty yields. Montgomery suggested I add mulch in the fall and avoid nitrogen-based fertilizers.
Potassium (K): 85.89-97.92 ppm
Plants require this nutrient and absorb large amounts through their roots. Gardens should range between 110-510 ppm. My yard and garden are below optimum, so I should add potassium.
Soluble reactive phosphorus (PO42): 85.75-117.21 ppm
Plants require phosphorus to grow, but too much leads to discolored leaves and damaged flowers. Lack of phosphorus stunts growth and reduces flowering. The ideal range for gardens is 30-50 ppm. My garden is above optimum, so I should avoid phosphorus-rich fertilizers.
How to get your soil tested
It’s free and easy for Chicagoans to request a soil analysis from DePaul’s Department of Environmental Science and Studies in the College of Science and Health. Just follow these easy steps or watch the video from the Centers for Disease Control and Prevention.
• Imagine a giant X on your front or back yard, with two points next to your house, two next to your sidewalk and one in the middle of the yard.
• Using a trowel, take a vertical sample about 6 inches deep from each location. Combine all five samples and mix.
• Label a gallon-sized closable plastic bag with your home address, the area you sampled (“front yard”) and, if you know it, the age of your home.
• Scoop the mixture into the plastic bag and seal it. You don’t need to dry the soil first.
• If you want to sample another location, such as your garden or sandbox, repeat the process with a second bag, including the full label.
• Include a note with your preferred telephone number and email address.
Box and ship the note and bag(s) to DePaul University, Attn: James Montgomery, Department of Environmental Science and Studies, McGowan South, Suite 203, 1110 West Belden Ave., Chicago, IL 60614. If you are near the Lincoln Park Campus, you may drop the samples off during business hours. You’ll receive a formal report on your soil’s health after students complete the analysis. Turn-around time is limited by department funding, so you may have to wait a while for the result.
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