By John C. Fech and Brad Jakubowski
Of the many maladies that a field manager has to stay on top of, nutrient deficiencies are difficult to deal with for many reasons. First, you don’t see them every day. A manager may ask him/herself, just what does deficiency look like anyway? I know that we had it a few years back, but I don’t remember exactly. Second, unlike a turf plot at a university or manufacturer trial, this is a real game field with players and daily/weekly damage from cleats and compaction. Third, other than odd looking leaves, the easy to see signs and symptoms—bugs, spots and rots—are often missing. As we dig into the potential for nutrient deficiency a little deeper, maintain a “wide funnel” of thinking about possible influencers and symptoms.
Before jumping to conclusions
When working with the possibility of a nutrient deficiency, it’s best to take a reasoned and steady course of action steps. The scenario where a good chunk of the soccer field is looking kinda rough….yellow, not green…you may be asking yourself, Should I be worrying? Should I run out and buy a bag of fertilizer and dump it on quick? The answer is maybe; or maybe not. It’s wise to avoid the accomplishment of Tom Smykowski and create a “Jump to Conclusions mat”, (think Office Space) where there would be a set of nutrient deficiencies that you could assume are responsible.
In the case of maybe not, fully consider that there could be lots of other causes of the look of the turf. A process of triage to eliminate other causes is very helpful. Asking questions of other turf managers, considering recent weather events, thinking about diseases that have been a problem in the past are all good initial actions at the outset of diagnosis.
Appearance categories
In the overall context of trying to figure out the cause of the yellowish appearance, a basic set of appearance categories to work through can be useful.
Category 1. Turf is dry, bluish green, wilts, brown on leaf blade edges; possibilities include drought, wilt, uneven watering
Category 2. Turf is pale, yellow, thin or grows slowly; possibilities include nutrient deficiency, over-application of growth regulators
Category 3. Turf suddenly appears scorched; possibilities include fertilizer burn, pesticide burning, mower injury
Category 4. Turf is bare and/or thinned, often in trafficked areas and shade; possibilities include algae, moss, compaction
Category 5. Regular or irregular patches of dead and dying turf; possibilities include thick thatch or buried debris, sod webworms, anthracnose
In the case of maybe, where there aren’t obvious other causes, the best place to start is with a soil test.
Soil test
The best way to get a handle on the current level of various nutrients is by conducting a soil test. However, even though a soil test can provide great insights, a report is best thought of as a snapshot of results, not a solid guarantee of what is in the soil. This is especially true for nitrogen, which is a mobile nutrient, one that can leave the rootzone quickly or change from unavailable to available in a relatively short period of time.
The best soil test is a representative one. The key word in the last sentence is representative. The soil sample must mirror the entire affected area as closely as possible. In order for that to be the case, many subsamples must be taken. On a given area that is suspected of nutrient deficiency, an average of 10 soil cores should be taken and mixed together before submission. In order to gain better insights as to the cause of the decline, a set of samples should be taken from the non-affected areas and then compared to the ones from the area of concern. Consider making a soil test when your turf is growing at its optimum, this may give you a baseline to compare against when conditions aren’t so good.
When sampling, keep in mind the rootzone for the turf plants; this is generally the upper 8 inches of soil profile. Use a soil probe to extract a sufficient number of cores, then cut off the upper 2 inches of the extracted soil plug. The reason for the removal of the upper portion is that it usually contains a fair amount of thatch and old turf crowns, which can skew the results of the soil test.
Soil testing can be greatly affected by the nature of the soil substrate, namely a native soil vs. a sand based field. Generally, deficiencies are more likely to occur on sand based fields, in that the particles have fewer attachment sites due to the greater glazing of the surfaces. The Cation Exchange Capacity (CEC) is a good measure of this, and will be noted on the soil test report. As such, sand-based fields often lend themselves to the application of light and frequent doses of nutrients as opposed to native soil fields, which are usually best maintained with three or four applications of moderately concentrated fertilizer applications.
Also keep an eye on pH. Since nutrient availability is closely related to soil pH, make sure you know the optimum availability ranges for your turfgrass areas. Interestingly, plant nutrient availability normally decreases when a soil’s pH starts to exceed 7.5; however, Molybdenum’s availability starts to reach its maximum at that point.
Classic symptoms of deficiency
Visual clues are useful for determining if the lack of nutrients is the cause of a turfgrass malady as well as the amount(s) indicated in a soil test report. Another consideration to keep in mind is nutrient mobility within the plant. Under deficient conditions, the more mobile nutrients will be moved to the younger, upper leaves, causing the older, lower leaves to exhibit nutrient deficiencies. Immobile nutrients will exhibit deficiencies on the younger leaves because the plant was unable to move them to the new growth.
Nitrogen (mobile nutrient). Slowing of vertical growth, general yellowing appears first on the lower leaves. This leads to loss of shoot density, leaf dieback at leaf tips and eventually an overall loss of color with older leaf death and lack of tillering. Ask yourself: Do I have sandy soils? Have I experienced high rainfall or irrigation? Do I have low organic matter? Have I been removing clippings? Or do I have compacted or waterlogged soils?
Phosphorous (mobile nutrient). Reddish-purple cast appears from the tip of the lower leaf blades, especially in cool weather, dull blue-green color, poor overall growth, slow root growth, often new sod is slow to knit. Ask yourself: Have I experienced cold temperatures? Do I have sandy, low CEC irrigated soils? Is my soil pH high (7.5-8.5)? Am I growing my turf on infertile or marginal subsoils? Are my soils high in clay?
Potassium (mobile nutrient). Yellow-streaking of the lower (older) leaves followed by browning and death of tips and margins, eventually will become completely yellow. Wilts sooner than normal during a drought, poor resistance to disease and cold injury, reduction in turf density. Ask yourself: Have I experienced high rainfall or leaching conditions? Do I have low CEC or acidic (pH<5.5) soils? Have I been removing my clippings?
Iron (immobile nutrient). Chlorotic between the upper (younger) leaf veins, eventual loss of most chlorophyll. Entire plant may turn white or spindly. Turfgrass stand may appear mottled with some grass exhibiting the symptoms, while others not. Ask yourself: Do I have high soil pH (>7.5)? Do I have excessive thatch or cold, wet soils? Did my soil test high in P? Are we irrigating with reclaimed municipal water that may be high in heavy metals?
Magnesium (mobile nutrient). Green or yellow-green stripes in the lower (older), changing to cherry red, older leaves affected first, increased winter injury. Ask yourself: Do I have low pH (<5.5) sandy soils, with high leaching potential?
Sulfur (immobile nutrient). General yellowing of younger (upper) leaves, gradual firing starting at leaf tip. Ask yourself: Do I have low CEC soils with low organic matter? Have I received high rainfall? Do I remove clippings?
Manganese (immobile nutrient). Chlorosis of younger leaves, yellow green spots on older leaves, withering at tips. Ask yourself: Do I have higher pH soils (>7.0) and have experienced warm, dry weather?
Calcium (immobile nutrient). Reddish-brown between veins along younger leaf margins, tips die and curl. Ask yourself: Do I have sandy soils, low in pH (<5.5)? Have I had leaching problems?
Boron (immobile nutrient). Slow growth, pale green younger blade tips, bronze tint. Leaves may curl. Ask yourself: Do I have leached, calcareous and sandy soils? Are my soils high in Ca and K?
Molybdenum (mobile nutrient). Pale yellow foliage, bleaching and withering of the lower (older) leaves. Ask yourself: Do I have acidic and sandy soils? Did my soil test indicate high concentrations of other micronutrients?
Zinc (immobile nutrient). Younger leaves yellow, smaller, grouped together. Some curling on the leaf edges. Ask yourself: Do I have shady conditions and high pH? Do I have high levels of micronutrients? Has it been wet and cool outside?
Toxicity, not deficiency?
If not too little, could it be too much? Again, this is where the soil test helps, as well as the overall pattern of appearance of the turf. If it looks burnt, stunted, etc., at least consider that too much of a particular element has been applied.
One way to find out would be the plywood test. Cover a portion of the area to be treated with a sheet of plywood, apply your particular nutrient, remove the plywood and wait to see if there is a plant response over the next few days to a week.
John C. Fech is a horticulturist and certified arborist with University of Nebraska-Lincoln Extension; Brad Jakubowski is an instructor in the Environmental and Earth Sciences Department at Doane College, Lincoln, NE.