Analyzing the results to improve turf health
While your customers may not want to think about the soil beneath the grass, lawn care professionals need to pay close attention to it. That starts by taking soil samples, sending them off to a reputable lab and then interpreting the facts and figures that are returned.
Tim Vanini, president of New Dimensions Turf (www.ndturf.com), is a consultant for home lawns, sports fields and golf courses. He says soil pH is the best place to start when reviewing the results of a soil test. “The pH is going to dictate so much of an impact on everything else you do,” he says.
Soil pH is an indicator of what is available to the grass, says Vanini. “At a pH of 5, for example, nutrients such as copper, zinc and iron are more available in soil solution, while phosphorus and calcium are not as available. If your pH drops below 5, then the efficiency of your fertilizer starts to become an issue because of [limited] microbial activity. Nitrogen needs to be broken down by the bugs.”
In such a scenario, the natural inclination to increase fertilizer applications isn’t going to help compensate, he points out. “When you start getting into a pH of 4 or 5, using limestone or Dolomite is going to make a difference in getting that soil into an acceptable range,” says Vanini. “That’s a battle you want to take on, because it can make a big difference.”
If you have a basic soil, say it’s above 8, it can be a significant challenge to drop the soil down to a neutral range. “It’s not impossible, but it’s really tough,” Vanini says.
One reason that it can be difficult to change soil pH is that the scale we’re familiar with (0 to 14, with 7 being neutral) doesn’t fully show how dramatic even a single point difference can be. “First, pH is on a log scale, and I think there are some people who don’t understand that. Whether the soil is too acidic or too basic, they think they just have to move it by a factor of one,” says Vanini. “But, really, it’s a factor of one times 10.” For example, he points out that the difference in the concentration of hydrogen ions in solution between a soil with a pH of 5 and that with a pH of 7 isn’t 2, but rather 990,000.
Another common misperception that can come from interpreting soil test results has to do with nitrogen, says Vanini. “Many people see the N value on the results and think that the lab is telling you what the nitrogen content is in the soil, but basic soil tests usually don’t test for nitrogen.” This is somewhat ironic because many soil tests are submitted specifically with a hope of finding out how much more nitrogen the grass needs. Really, the nitrogen recommendations given on the soil test are based on scientific data showing the typical needs of the particular turfgrass species on that lawn.
For example, Kentucky bluegrass or perennial ryegrass is likely to have a different recommendation than fine fescue. It’s important to properly identify the turfgrass species to the lab when submitting soil samples to receive back relevant nitrogen recommendations. “Look at the basic recommendations that are made and then plan out how you want to do it,” says Vanini. If the recommendations call for 3 pounds of nitrogen for the whole year, it might be best to break that into spring, summer and late fall applications, he says. Using a slow-release product is another option.
It’s not just established lawns that can benefit from soil test results. It’s a common misperception that phosphorus needs to be applied when seeding, and taking a soil test before establishing a new lawn is helpful to determine if a phosphorus application is necessary. “A lot of companies are starting to eliminate phosphorus from fertilizer. Just because you’re seeding does not mean you have to go out and put phosphorus down; that’s where a soil test is very handy,” he explains. “In our area [Buffalo, N.Y.], the soil tests I’ve seen have shown phosphorus to be quite plentiful in the soil, so there’s no need to put down more phosphorus or a starter fertilizer.”
Jim Thomas with Thomas Turf Services (www.thomasturf.com), a Texas firm specializing in soil analysis and turf management, says different labs use different testing and reporting methods, making it difficult to offer a blanket explanation of every soil test. “Some use what’s called the ‘sufficiency method’ for testing and might use a graph, others might have arrows or say ‘High’ or ‘Low’ for each nutrient,” he explains.
Another method is called the base saturation technique. Thomas says, “It compares ratios of things: How much is out there compared to how much can the soil hold. It also gives you a feel for balance: Do you have too much of one thing and not enough of another in the soil?” He cautions that this method only works for major nutrients rather than micronutrients. This method also uses ranges, which provides information about whether the soil in question is above, below or within the prescribed range.
Thomas says choosing the soil testing method is a matter of customer preference. “Some people like to see both,” he adds. For basic soil testing in lawn applications, he advises that the sufficiency method offers perhaps the simpler results to interpret. “You can look at the results and see, ‘OK, I’ve got this much, and I can see if I need to add more or I can see that I don’t need to add more.’ It’s pretty intuitive, and people and can wrap their minds around it.”
Thomas recommends taking eight to 10 subsamples from a lawn at random locations and combining those together to send in one sample to the lab. “That way you have something that’s representative of the entire lawn,” he explains. Using a clean soil probe, trowel or shovel and a clean mixing bucket will help ensure the sample isn’t contaminated by dry soil from another property. Thomas encourages focusing on the upper 4 inches of soil, where turf plant roots exist.
“When you submit a sample, the lab typically has a form to fill out asking which crop, in this case which grass, you’re growing, along with what it’s being used for [is it a soccer field or a home lawn, etc.] and when it was last fertilized,” says Thomas. “That lets the lab select the correct sufficiency level for what you have. For example, you won’t get a nitrogen recommendation for bermudagrass, which requires a lot of nitrogen, when you actually have zoysiagrass, which needs much less.”
There are limits to the information you can learn from a basic soil test, Thomas says. “For example, it will not tell you if you have problems due to poor irrigation water quality. That’s a salt issue, and if they don’t measure that you won’t get that information. If you think you have poor irrigation quality, you might want to ask the lab to test for salts,” he explains. “A soil test also won’t tell you about any diseases or nematodes or any other microorganism that’s attacking the plant root or leaf. A soil test won’t tell you that; it’s solely designed to tell you fertility. It’s one management tool to tell you if there’s enough ‘food’ out there for the plant.”
Mike Murray, owner of Organic Soil Solutions (www.organicsoilsolutions.com) in Needham, Mass., says that because of the organic approach his company follows, soil tests are especially important. “Soil is so important to us; we’re not putting down water-soluble products, they have to be broken down by the biology in the soil,” says Murray. “We like to do a soil test as soon as possible when we get a new client,” he says.
Most of the soil in his area tends to be acidic. “If the pH is down to 5.2, for example, it’s hard for the grass to obtain nutrients,” Murray explains. Based on the results of the initial soil test, he may apply limestone, and he keeps testing until the pH is up over 6. After that, soil tests are conducted on each property every three years.
Murray takes samples using a soil probe. “We usually take six samples from around a yard and mix those together to get a good idea of what we’re looking at,” he explains. He uses Spectrum Analytic (www.spectrumanalytic.com), a laboratory in Ohio. “They provide us [with] a fact sheet and guidelines to explain the results and why things like the cation exchange capacity and the amount of organic matter in the soil are important,” says Murray. He adds that different labs might conduct portions of the soil test in different ways, so it’s important to understand how they work and helpful to stick with one lab to ensure that results are comparable over time.
Murray says that soil tests also provide an added professional element to his company’s work. “I think it’s a marketing tool. I write our customers a nice letter explaining the results of the soil test, so they know we’re keeping an eye on the soil,” he explains. “And, if the pH is low and we need to put down limestone, for example, I can write them a letter the following year to show them how much things have improved.”
Patrick White is a freelance writer and editor who has covered every aspect of the green industry in the past 13 years. He is based in Middlesex, Vt., and is always on the lookout for unusual stories.