URBANA, Ill. - Soil tests are one tool in your toolbox for managing landscape soil, said a University of Illinois Extension horticulture educator.
“Maintaining good soil structure and soil moisture are of first importance,” said Nancy Pollard. “You can improve or maintain soil structure by working the soil only when it is not wet and by incorporating organic matter into the soil on an annual basis.”
Pollard added that applying mulches, watering as needed, and improving drainage where feasible will help with moisture control in soil. Soil testing and applying fertilizers accordingly are additional steps in effective soil management.
A well-taken soil test will help in making management decisions. “It will help answer questions like, ‘Is there already enough phosphorus and potassium in the soil? Is it desirable to go to the expense to add more? Does the pH (acidity) of my soil match the requirements of the plants I want to grow?’” she said.
Commonly tested are pH, phosphorus (P), and potassium (K) levels, and sometimes magnesium (Mg) and Calcium (Ca). Usually estimated percent organic matter, and Cation Exchange Capacity (CEC) are shown in the results as well, Pollard explained. “Although high CEC soils can hold more nutrients, it doesn’t necessarily imply that they are more productive. Much depends on good soil management. Adding good organic matter always helps,” she said.
Labs do not test for nitrogen (N) because it is unstable in soil. If there is a recommendation for nitrogen, it is a standard one assumed for that particular crop.
“Labs only make recommendations if you include the name of the crop you are growing such as apples, blueberries, turf grass, perennials, tomatoes, or a general vegetable garden,” she explained. “Also, state that it is a home garden or your recommendations will be in tons per acre instead of pounds per 1,000 square feet.”
Soil labs are listed at http://urbanext.illinois.edu/soiltest/ or can be obtained by calling a U of I Extension office for a copy of those listed. Pollard said after obtaining the list growers should call for current fees and services. “Request an interpretation of the soil test results. Often labs will provide sample bags prior to you taking a soil sample if you request sampling information. Look for labs that give interpretations for home gardens,” she said.
“Recommendations can be no better than the sample tested,” Pollard said. “You will need to create a composite sample from the yard or garden area you want to know about so the results aren’t skewed to one spot.”
To create a sample, within the area selected, dig a hole to spade depth. With a shovel or trowel, cut a thin slice down one side of the hole. Place this slice in a clean pail. Do not include sod roots. Repeat this procedure in at least eight well-scattered spots within the chosen area. Place each slice in the pail with those previously taken. Break up clods and mix the slices of soil thoroughly, rotating the pail while mixing.
"In the end, you will only need to send about a representative cup or pint, the amount requested by the lab. Be ready to label the sample with your name and address and the crop,” she said. “If you are sending more than one, label each sample with a number, which will tell you where the sample was taken. Mark the sample flower garden, vegetable garden, shrub border, or lawn, etc. The more complete the information provided, the better the management recommendations will be.”
Heavy metal tests are additional tests that can be done. Pollard said to test for lead (Pb) if the food garden or children’s garden is within 1,500 feet of a highway that had busy traffic prior to 1970. “That is when gas contained lead. Also test for lead if the property was built before 1950 and paint chips may be contaminating the soil. Lead was banned from use in interior and exterior house paint in 1978,” she said.
“Other tests include testing for arsenic if an old orchard was on site. Arsenic was formerly used as an orchard pesticide. Knowing the history of your land can give you clues of possible other metals or compounds to test for,” she added.
Separate tests are required for each metal or compound.
“There is no one-size-fits-all test like it might appear on television. That is why knowing the history of your site is useful in determining if there are risks you want or need to evaluate. Soil tests are one tool in your toolbox for learning about and managing your soil,” Pollard said.