Soil testing takes center stage

Soil testing is a tool used to assess the status of soil fertility and the potential for nutrient imbalances in turfgrass. While soil testing has been around for decades, it’s becoming more important because of mandatory nutrient management programs.

Various soil-testing methods provide information about soil nutrient availability.

Mandatory soil-testing programs have been established in some states for certain agriculture production and land application of organic wastes. They also are being applied to golf courses. These programs were prompted by excess levels of phosphorus, nitrogen and pesticides found in soils that have shown to be detrimental to the environment, particularly rivers and lakes. These environmental soil-testing issues will receive even more attention as public awareness and research data increase.

Healthy turf is key
The key to producing healthy turfgrass is to reduce stress on the plant. Physical stress includes soil layering, wet soil, compaction, poor aeration, poor drainage, or soils with high clay or stone content. Chemical stress might include low fertility, excess nutrients (imbalance/toxicity), salts, high or low pH levels and pesticides. Biological stress includes insects, viruses, wilts and blights, nematodes, diseases, susceptible varieties, grass types and animals. Finally, there are weather issues such as temperature extremes, precipitation and light.

Weather and physical factors are always at the top of the plant stress list. Fortunately, superintendents can control nutrient fertility more easily than many of the other stress types. A superintendent’s goal should always be to focus on the stresses within his control and be aware of those he can’t control. Soil testing alone can be risky when assessing turf nutrient efficiency. Plant tissue analysis used in conjunction with soil testing is one way to verify efficient nutrient management.

Soil tests differ
University researchers have developed various soil-testing methods to provide information about soil nutrient availability. Some soil-testing methods are developed and calibrated to be used on soils with certain properties. For example, there are about six phosphorus soil tests (Mehlich III, Bray I, Olsen, Mehlich I, Morgan and AB-DTPA) performed by laboratories in the United States.

Each of these phosphorus tests has its own unique chemistry, strengths and weaknesses. The strong acid Mehlich I test is used mainly in the Southeast because of the more acid soils in the region. Labs mainly in the Northeast perform the acid Morgan test because that’s where it was developed. The Olsen and AB-DTPA tests are recommended in higher pH soils in which their unique chemistry makes them more accurate. The Olsen and AB-DTPA tests also are used extensively for soils in the central and western United States where more alkaline soils are found.

When testing soil of a green or fairway (Orchard Park Country Club in N.Y. pictured), chemist Jake Alaniz suggests taking random samples and mixing them together for a more representative result.

Mark Flock, a laboratory director and agronomist for Brookside Laboratory in New Knoxville, Ohio, is president of the North American Soil and Plant Testing Council and is a member of the USGA Putting Greens Materials Testing Technical Advisory Committee. Flock says the acid Bray I phosphorus test has been a favorite test for many areas.

“It has been shown to be accurate on soils with pH levels below 7.2,” he says. “In alkaline soils, this test falls apart and might produce erroneous low phosphorus levels.”

The acid Mehlich III test is performed on more soils than any other phosphorus test. Like the Bray I test, it’s accurate on all acid soils and on soils with higher pH levels.

“If you perform each of these six tests on one sample, you would get six distinctly different levels of available phosphorus in the plant,” Flock says. “Which one is right? Actually, all six could be right. It’s important to understand each of these methods has different chemistries. But each has been calibrated, and the calibration scale is different for each test. It’s like comparing Fahrenheit and Celsius scales. Both are good, accurate measurements of temperature, but the levels are different for equivalent temperatures. This is why it’s critical superintendents work with a laboratory, consultant, field representative or extension agent that understands the testing methods.”

Soil samples give direction

Superintendent Bob Kelly of Orchard Park (N.Y.) Country Club uses several tools to ensure his soil has the right chemistry levels and the turf is healthy. He takes soil samples in spring and fall and tests the quality of his irrigation water annually. “We’ve been trying to change some of the levels in the soil, and analyzing soil samples lets us know if our programs are working,” he says. “It takes time to make changes, but some of our numbers are off, and we need to do something. I use fertilizer with a lot of calcium and drag in other amendments when we aerify. As we get closer to our goals, we can fine-tune the program and concentrate on specific areas.” Kelly also uses the services of a turfgrass consultant who visits the course at specified intervals to check for disease and other issues. “If we have something we don’t recognize or want to confirm a problem we suspect, he takes samples and gets back to us within 24 hours,” Kelly says. “This is especially important on greens because a lot of things look the same when we’re mowing at 1/8 inch. We’re on the lookout for issues every day, but he sees so many courses. The most valuable thing to me is that he knows what’s coming. For example, he will know that a particular insect might be two weeks early. I don’t have to spend as much of my day tracking down potential problems. And disease control programs are so specialized that it’s possible for us to spray the wrong chemical. It might not damage the turf, but it will certainly waste money.” .

Proper interpretation of results can’t be made unless the superintendent knows which test was performed and has the calibration data to follow.

“Stick with a good laboratory that is active in proficiency programs and stays active with regional testing meetings,” Flock says. “Consistency in sampling, testing methods and reporting of results will make your job much easier. Sending samples to different labs that might be performing different test methods can be confusing. Some laboratories get blamed for poor testing when, in fact, the testing is good, but because the superintendent might be comparing results of different methods, he’s comparing apples and oranges.”

Most laboratories use tests developed in their region. Universities publish bulletins listing the recommended chemical soil test procedures for different regions of the country. This works fine for agriculture soil testing, but for turf testing, even using local soil testing methods can be challenging because constructed soils on golf courses could be considerably different than natural native soils. Many times golf course tees and greens are constructed with materials such as calcareous sands that might require special testing. Whether a USGA-specified or California green is constructed, if calcareous sand is used, there will be a soil with a pH near 8.0. The local soil test method calibrated for acid soils might not be appropriate for these soils.

“Performing a Bray I phosphorus test on soils like this will likely result in erroneously low results, too,” Flock says. “Most standard soil tests work best when testing acid (pH < 7.0) soils. Plant nutrient uptake can be more difficult to predict with high pH soils. Also, more greens are constructed with inorganic amendments such as porous ceramics, zeolites and calcined clays. These materials can affect soil test levels for nutrients like potassium, and test results can be deceiving.”

Some researchers are looking at less aggressive soil extractants that use weak salts. Many consultants are using water solubility tests to better predict nutrient excesses and deficiencies with low exchange capacity sands. These might prove to be better soil tests for low exchange capacity sands like those found on USGA spec greens. Until extensive field calibration data is collected on these newer extractants, the existing methods will need to be used.
Sam Ferro, president of Turf Diagnostics & Design in Linwood, Kan., says different extractants will have greater or lesser ability to draw chemicals from the soil.

“One lab might have drastically different results on the same soil sample than another lab depending on the extractant used,” Ferro says. “While these results might be quite different, hopefully the fertilizer recommendations will be similar. This is because fertilizer recommendations are developed for each extractant.”

More calibration data
Extensive field calibration data exists for soil tests for agriculture production, but there’s less available field calibration data for turf. Some universities have developed calibration data for certain turf types grown in a particular region of the country. Laboratory tests are useless without the field calibration research establishing the critical scale for that turf with those soil conditions.

Orchard Park superintendent Bob Kelly takes soil samples in the spring and fall.

“Soil test calibration requires years of plot research measuring different soil test levels for turf health,” Flock says. “Thus, you establish the scale (responsive/nonresponsive level) to follow for that nutrient.”

Soil testing for turf can be valuable if done properly and consistently. One of the challenges testing turf is that soil chemistry levels can change considerably faster than levels monitored in typical agriculture production. This is because most soils built for turf are sandy and need more micromanagement.

“These are sandy soils with a very low cation exchange capacity that can’t hold nutrients well,” Flock says. “Many times they’re irrigated with water that has a highly variable chemistry. Nutrients are applied throughout the year, and some might be slow-release materials that hopefully will supply the grass efficiently.
“A superintendent is trying to monitor a system that can always be changing,” he adds. “He tests the soil to monitor nutrient levels and develops a fertility program that will maintain nutrient levels needed for healthy turf. Because the levels can change faster in sandy soils, he needs to establish a fertility program that works best to provide steady, long-term fertility. For some courses, the program might come down to maintaining minimum levels of N, P, K, Ca and Mg.”

Working with nutrient percentages can be deceptive in low CEC soils because small changes in nutrient concentration might represent much larger changes in percentages. This might be different for individual courses based on the fertilizers used, the quality of irrigation water, frequency of irrigation, rainfall, soil texture, grass type and internal drainage. When some nutrients are high, they can create imbalances with other nutrients. Then plant analysis is needed to verify the deficiencies.

“While nitrogen is one of the most important nutrients for turfgrass growth and health, nitrogen recommendations usually aren’t based on nitrogen test results,” Ferro says. “They’re based on soil organic matter content, soil texture, turf type and maintenance levels. This is because nitrogen moves through the soil quickly, and test results for nitrogen are highly variable.”

It’s not uncommon to see irrigation water quality dictate the fertility program. More and more, effluent water, which contains various levels of nutrients, is mandated for use on golf courses. This water’s chemistry can dominate the soil chemical properties.

“Simple soil test data like pH and organic matter can be useful to monitor changes in turf soils over time,” Flock says. “Is there a thatch layer building up? Is irrigation water dramatically affecting soil pH?”

Combined analysis
Soil testing in conjunction with plant and irrigation water analysis is necessary if good fertility programs are to be established. Including less aggressive soil tests such as saturation paste testing to monitor soluble nutrient levels and salts could be valuable, too. In areas where little field calibration exists, superintendents need to work with someone who will gather this data and establish levels that provide healthy turf. Working with a lab or consultant that exclusively works in turf and gathers a lot of good laboratory and field data can be invaluable to a superintendent’s agronomic success.

Jim Thomas, president of Thomas Turf Service in College Station, Texas, says chemical analysis of soil also protects the environment.

“Using too much fertilizer not only wastes money, but adds chemicals to the environment,” he says. “Our goal is to feed the turf only what it needs with no excess amount. We determine how much of each nutrient is in the soil and then calculate how much to put on. We want to keep nutrient levels in a range where there are no deficiencies and no excesses.”

Testing low CEC soils found in most golf courses poses challenges because maintaining steady levels of nutrients might be difficult.

“Superintendents should work with people who have extensive experience gathering data and establishing ideal nutrient levels in turf,” Flock says. “Ask them what their approach is in developing recommendations. Whose calibration data do they use? Contact laboratories you test with and find out what soil methods are being used. Ask the laboratory what proficiency and certification programs they’re involved with. Do they have a quality control officer and a quality control manual? Good laboratories will gladly provide this information. Gathering good soil test data should help you establish a more efficient fertility program. It will also put you in a better position when mandatory testing is required in the future.”

Jake Alaniz, a chemist for Thomas Turf, says it’s important to make sure the soil sample is representative of the area tested because a bad sample will give the wrong answer.

“On a 4,000-square-foot green, a sample from one spot isn’t representative,” he says. “It would be better to get 10 to 15 random samples. Put them in a bag and mix them up. This will be representative of the entire area. Similarly, on a two-acre fairway, don’t just take a single sample from the middle. Go to both sides and back to front, again mixing the sample.” GCN

David Wolff is a freelance writer based in Watertown, Wis. He can be reached at dgwolff@charter.net.