This photo shows the effects of iron deficiency.

You walk out to one of the most important fields at your facility and see blotches of off-color turf. As you examine the symptoms more closely, your mind starts to consider all the possible causes – foliar disease, root disease, surface feeders, subsurface feeders, compaction, uneven irrigation, fertilizer misapplication, vandalism – the list of possibilities seems endless. One more to add to the list is nutrient deficiency.

Diagnosis in general

There are several methods of diagnosis. Some sports turf managers prefer looking through textbooks for color photos, while others simply run through a list of previous maintenance activities. Both of these have merit as well as consulting with other sports turf managers, university researchers and extension faculty. Regardless of the approach, success is all about paying attention to the signs and symptoms and going through a process to narrow the list of choices. All approaches have some element of “process of elimination” in them.

Whether you realize it or not, each approach is embedded with several factors. One of the most important is the influence of season of the year on the likelihood that a particular causal agent is responsible. Of course, it’s rare that turf declines from only one cause. In almost all cases, factors such as thatch, soil drainage, traffic and pH will work together with a disease or insect to cause the problem.

In the overall context of diagnosis, consider the following set of choices, maladies that occur regardless of season or weather conditions:

Choice A. Turf gradually becomes pale green to yellow, grows slowly, often thinned.

Possibilities: 1. Iron chlorosis – interveinal yellowing of younger leaves, chlorosis of older, lower leaves.

2. Nitrogen deficiency – stunting of growth, older leaves lose green color, resulting in a thin stand.

Choice B. Turf suddenly appears scorched.

Possibilities: 1. Chemical or mower burn – brown leaves and stems, usually in patches, streaks or bands.

2. Fertilizer burn – bands, streaks or irregular patterns; grass is stimulated at margins of injury.

3. Dog injury – ring of dark green grass at margin; patches are up to 1 foot across.

4. Scalping injury – entire turf area or patches over slight elevations or mowing corners are yellow to brown.

5. Dull mower injury – leaf tips are shredded; appear gray, then tan.

Choice C. Regular to irregular patches of dead and dying turf.

Possibilities: 1. Thick thatch or buried debris – thatch in excess of 5/8 inch or construction remnants present.

2. Sod webworms – thinned turf; presence of tunnels, silken webs and webworms.

Choice D. Turf bare or thinned; often in traffic areas, dense shade or waterlogged soils.

Possibilities: 1. Algae – greenish to brown scum that later forms a black crust.

2. Moss – small green plants that grow on soil in slight mounds.

3. Compaction – soil hard in heavily trafficked areas; on paths, under playground equipment.

Choice E. Turf dry, bluish green, wilts, may later turn brown.

Possibilities: 1. Drought, wilt or improper watering – plants with slow growth, withered stems that respond favorably to proper irrigation practices.

Soil testing

After working through the diagnostic key and considering other possible causes for the expressed symptoms, the next step in determining if lack of nutrients is plausible is to conduct a thorough soil test. An important first step is to target the proper layer of soil for extracting samples. Since the active rootzone for most turfgrass species grown in a sports turf setting is the upper 8 inches, sampling deeper is not likely to produce usable results. As well, the upper 2 inches or so is not desirable as thatch/mat influences are likely to distort the findings.

In the affected areas, begin by removing the turf and upper 2 inches of soil with a golf cup cutter or sod spade. Next, use a trowel or similar hand tool to extract a small amount of soil and put the soil in a plastic (nonmetal) bucket. Repeat this process for about eight to 10 subsamples. Most soil laboratories request about a pint of soil for a sample. Mix the soil together from an area with similar visual symptoms. Finally, take a series of subsamples from an adjacent but nonsymptomatic area. This will be helpful for comparison purposes when the report returns from the lab.

Interpreting soil test results

Lucky for those of us who are numerically challenged, most reputable soil testing labs make it easy to visualize the levels or relative amounts of the various nutrients that may be lacking, as well as other important issues such as pH, soluble salts and cation exchange capacity. This is usually provided in the form of bar charts or pie graphs.

Each nutrient has a desirable range that will vary based on soil texture, pH and usage. Table 1 outlines general nutrient sufficiency levels for phosphorus and potassium.

For most soils above a pH of 6.0, calcium and magnesium are rarely deficient. However, sandy soils with a soil test of 0-50 PPM may be deficient in magnesium if high amounts of potassium have been used. In most circumstances, an 8-to-1 calcium to magnesium ratio is considered sufficient.

Phosphorous deficiency usually shows up in the spring.

Visual symptoms

Combining specific visual symptoms with soil test results is a good way to be certain of the correct nutrient deficiency and assist in taking the best possible corrective action.

  • Nitrogen deficiency

    Yellowing of the plant and slowing of vertical growth most often is the result of a nitrogen deficiency. Another indicator may be the emergence of clover due to its ability to fix its own nitrogen and outcompete the turfgrass.

  • Phosphorus deficiency

    Purpling is usually characteristic of phosphorus deficiencies and will often occur in spring while the soils are still cold and root uptake is relatively low.

  • Sulfur deficiency

    Yellow on the youngest newest tissues is usually characteristic of sulfur deficiencies and can be easily confused with symptoms produced by iron, nitrogen and potassium deficiencies.

Now what?

After working through the diagnostic key and soil test, the easiest way to determine if you need a particular nutrient is to set up a small test area where you can compare the application of a nutrient with the adjacent untreated area. For example, if you suspect a magnesium deficiency, mix 1 teaspoon of Epsom salts with a pint of water and apply it to a 1-by-1-foot area of turf using a spray bottle. Within 24 hours an obvious color response would confirm your suspicion.

As you modify your fertility program, you can monitor your adjustments on the field by conducting a “plywood test” by covering a small portion of your turf with a 3-by-3-foot sheet of plywood prior to your application. After the application is complete, remove the plywood and compare the turfgrass’ response in the treated and nontreated areas. This can either confirm that your modifications are benefiting the turf or that additional adjustments are necessary.

When making modifications to your fertility program, applying lower rates more frequently or spoon-feeding may be the preferred method. This enables you to make applications, monitor the results and make adjustments when necessary. Fortunately, spoon-feeding can be accomplished through spraying, fertigation and applying granular carriers.

As with all fertilization strategies, many factors influence the appearance and performance of the turf, so be sure to keep as detailed records as possible of weather conditions, field use, pests, changes in management practices and anything else that affects your location on a regular basis. By doing this, you will give yourself the best chance possible to provide the best field possible.

John Fech is an extension educator specializing in turf and ornamentals at the University of Nebraska-Lincoln. Bradley Jakubowski is a professor of environmental science with Doane College in Nebraska and a diagnostic consultant in the sports turf industry.