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What lies beneath the turf is ultimately responsible for whether a lawn will thrive or struggle. Soil tests help lawn care operators determine what nutrients are necessary to include in a program.
Kristen Hampshire
A soil sample is the only way to take the guesswork out of lawn care. “It gives you an understanding of what’s there from a plant nutrition standpoint so you know what you’ll need to add in your nutrient management and fertilization program,” says Charles Peacock, professor and turfgrass extension specialist at North Carolina State University.
A soil sample is important for every lawn, and especially properties that a lawn care operator has just acquired. (Long-time accounts may go every two or three years between soil samples.) Also, if there are areas of lawn that are not responding to a program, a soil sample should be collected and sent to a laboratory to get answers.
“If you see some variations in the soil texture and color, you ought to isolate those spots and only sample from those particular areas,” Peacock says. “If the soil looks fairly uniform, you can take samples from throughout the property and send a composite sample to the lab.”
The number of samples drawn from a lawn will depend on what an LCO sees in terms of variations in color and texture, Peacock says. What’s critical is to let the lab know that the sample should be interpreted from a fertilization viewpoint.
That way, specialists will know the purpose of the soil test and provide relevant recommendations. “You can get different recommendations based on the same soil test results depending on the lab interpretation,” Peacock says.
Here are four soil test components Peacock emphasizes, though a soil test report from their local extension will provide exact recommendations based on their geography.
pH: Perhaps the important information you’ll glean from a soil test is pH level. The optimum pH range for plant-available nutrients is between 6.2 and 6.5, Peacock says. If a soil is too acidic, those nutrients can be “too available” and toxic to roots systems (especially in the case of aluminum). When soil is too alkaline, not enough nutrients are freely available, so plants are basically not getting a proper meal from the soil.
The fix: Acidic soil benefits from additional magnesium. Alkaline soil requires a fertilizer nitrogen source that is acid-forming and will react with soil to reduce its alkalinity, such as ammonium nitrate or ammonium sulphate.
Phosphorus: You might have seen advertisements for phosphorus-free fertilizers, particularly from box stores promoting what is seemingly a healthier product for lawns. But if your soil is phosphorus deficient, this type of fertilizer won’t deliver results. Phosphorus and potassium are critical for establishing stress and drought tolerance, and cold hardiness.
The fix: Research shows that fertilizers with a 2:1 nitrogen potassium level are effective in soils with a deficit, Peacock says. Phosphorus-deficient soils should be treated with fertilizers that do contain phosphorus.
Calcium and magnesium: Magnesium stokes chlorophyll production, which is essential for photosynthesis. Some soils have an imbalance of calcium and magnesium. When calcium is highly concentrated in the soil and magnesium is lacking, more magnesium is necessary to compete with calcium, Peacock says.
The fix: Products such as Sulfa-Mag will increase magnesium and potassium levels without affecting soil pH. (When soil pH is on the high end, adding straight magnesium can increase it further.)
Micronutrients: “In coastal areas and the deep south, their sandy soils have very poor inherent nutrient content,” says Peacock, adding that micronutrients are not widely available in these types of soils.
“A soil test will give you an index value (of micronutrients), so you can determine what range the soil is in and whether you need to add back micronutrients.”
“An effective lawn care program is truly about creating a nutrient management program, not just fertilizing.” – Charles Peacock, professor and turfgrass extension specialist, North Carolina State University
The fix: Iron and manganese are some common micronutrients that are added back into sandy soils that show deficiencies, though a soil test is the only way to identify exactly what soil needs.
Achieving a balance.
Soil tests demystify what lies beneath the turf and help LCOs understand exactly how they can supplement the lawn with nutrients to achieve clients’ goals.
“It’s a real balancing act,” Peacock says of making sure the nutrients in a lawn care program interact appropriately and benefit the soil pH.
“An effective lawn care program is truly about creating a nutrient management program, not just fertilizing,” he says.
“You have to manage nutrients based on what the soil analysis tells you and what a particular turfgrass needs, and this can vary year to year.”