MICRO-MANAGINGDo not underestimatethe importance of...rmcronutrlents Inintensively managedturfgrass.BY JIM SKORULSKI

Micronutrient nutrition is probably theleast understood facet in turfgrassfertilizer management programs. This is

understandable, considering acute deficiency andtoxicity symptoms are rare and only recently havescientists begun to understand the complexfunctions micronutrients play in turfgrass plantsand the field situations that enhance deficienciesor excesses. Analytical tests for micronutrients insoils and plant tissues are also becoming morerefined for turfgrass systems. The knowledge baseis not complete by any means, but the mysteriesof micronutrients are slowly disappearing.

So who should be concerned with micro-nutrient nutrition? Every turf manager should atleast be able to identify the plant essential micro-nutrients and understand the situations or condi-tions where deficiencies or excesses may exist andthe potential impacts they can have on a turfgrasssystem. Golf course superintendents irrigatingwith effiuent or salt-affected water, growing-in anew golf course, working with low-CEC andheavily leached soils, or managing highly acidic,calcareous or organic soils are more apt to dealwith deficiency or micronutrient imbalances andshould have a greater knowledge of the role ofmicronutrient availability and nutrition.

THE ROLE OF MICRONUTRIENTSThe essential macronutrients - nitrogen (N),phosphorus (P), potassium (K), calcium (Ca),magnesium (Mg), and sulfur (S) - are used inlarge quantities by plants as building blocks foramino acids, proteins, sugars, and starches. Iron(Fe), manganese (Mn), zinc (Z), copper (Cu),molybdenum (Mo), boron (B), chlorine (Cl), andnickel (Ni) are also considered essential nutrientsfor plant growth but are found in much lower

Manganese-deficient bentgrass plants are more susceptible to take-all patch disease.Themanganese (Mn) is critical in the production of the lignin found in cell walls and makes theplant more resistant to disease. Soil acidification programs or supplemental applications ofMn can be used to maintain adequate levels of Mn in the rootzone.

concentrations in the plant and thus are termedmicronutrients. Their role is equally important,serving as catalysts in a wide array of metabolicfunctions. Table 1 provides a list of functions forvarious micronutrients.

SOIL AND TISSUE TESTINGMicronutrients are monitored with soil and tissuenutrient tests. Laboratories most often utilizeweak acids or chelating agents such as DTPA(diethylene triaminepentaacetic acid) or theuniversal extracting agent Mehlich- III combinedwith the chelating agent EDTA (ethylenediamine tetraacetic acid) to extract plant-available

SEPTEMBER-OCTOBER 2003 13

Table IMicronutrient functions and soil, management, and climatic conditions associated with deficiencies and excesses/toxicity.

Functions

Fe • Chlorophyll synthesis• Electron transfer in Pn• Activator for enzyme in

respiration• Constituent of antioxidant

enzymes• Lignin synthesis

Mn ' • Oxygen evolution in Pn• Chlorophyll synthesis• N utilization and assimilation• Lignin synthesis• P and Mg uptake• Enzyme activation

Cu. Electron transfer in Pn andrespiration

• Synthesize antioxidant enzyme• Lignin synthesis

Zn • Structural component of manyenzymes

• Constituent of antioxidant enzyme• Carbohydrate metabolism• Protein synthesis

B • Cell wall, plasma membranestructure

• Synthesize antioxidant enzyme• Root cell elongation

Deficiencies

• Soil pH > 7• Weak root system• Excess thatch• Cold soil temperatures• High [Cu], [Mn], [Zn]• Calcareous, arid soils

• High pH soils• Highly leached, low pH or

calcareous sands• Peat, muck soils pH > 7• High [Cu], [Zn], [Fe], [Na] in

low CEC soils• Dry, warm weather

• High pH soils• Peat and muck soils• Highly leached calcareous soils• Rarely deficient in turfgrasses

• Rarely deficient in turfgrasses• High soil pH• Peat and muck soils• High [Fe], [Cu], [Mn], [Na]• Cool, wet weather• High soil moisture

• Most grasses insensitive to Bdeficiency

• pH> 6.5• High [Ca]• Dry soils• High [K] in B deficient soils• Peat or muck soils

Excesses/Toxicity

• Can induce Mn deficiency• Leaf blackening• Centipedegrass sensitive• Acidic, poorly drained soils can

produce toxic levels of soluble Fe

• Soil pH < 4.8• Anaerobic soils with low pH• Induce Fe, Ca, or Mg deficiencies

• Acidic soils• Heavy applications of copper-

based fungicides• Reduced shoot and root

production• Suppress uptake of Fe, Mn, Zn,

and Mo

• Toxic levels may inhibit root andrhizome development

• High levels may induce Fe andMg deficiencies

• Some mine spoils and municipalwastes may contain high levels ofzinc

• Irrigation water with high [B]• Soils naturally high in B (arid and

semi-arid soils)• Some composts• Overapplication of B fertilizer.Toxic levels in tissue range

100 - 1,000 ppm

Fe, Cu, Mn, and Zn from soils. Hot water or awater-saturated paste extract is used for B. Micro-nutrient concentrations are reported in parts permillion in the soil test report. Sufficiency rangesfor micronutrients in soils are listed in Table 2.The sufficiency ranges are guidelines used to helpinterpret a test and make recommendations.

Soil test recommendations for micro nutrientsinvolve a ranking system that is based on expectedplant response. The rankings are often titleddeficient, low, optimum, excessive, etc. A deficientor low ranking indicates that a positive plantresponse is likely to occur as a result of an appli-

14 GREEN SECTION RECORD

cation of that nutrient. A low ranking does notnecessarily mean that a deficiency symptom willbe evident in the field. This is especially true withZn and Cu. Rankings for Fe and Mn aregenerally more consistent. A low ranking shouldbe used as a red flag, indicating the need toinvestigate fertility and management programsmore closely. Similarly, a high or excessive rankingfor a particular nutrient does not mean thatsymptoms of toxicity will appear, but that a closerlook should be taken at fertility practices.

Micronutrient analysis is not always a standardpart of a soil nutrient test, and it may have to be

'After Tisdale et al. and Mortvedt.bExtractable micronutrient levels are preferred to be within the High range for high-maintenance,recreational turfgrass sites but within the Medium range for non-recreational grasses.

eRankings for micronutrients are more accurate for plants sensitive to a particular micronutrient,such as vegetable crops, than for turfgrasses, which are not sensitive to micronutrients.Reference: R. N. Carrow et al. 2001. p. 251.

• Is there anything in the water quality tests thatmay influence micronutrient status?• Have tissue tests been completed for affectedand non-affected areas?• Are you managing grass species or cultivars thathave special requirements?• Have smaller-scale test applications of micro-nutrients been completed to confirm a suspecteddeficiency?

Micronutrient deficiencies may occur becauseof certain weather conditions or interactions withother micro nutrients. Examples of deficienciescan sometimes be seen with iron, when soiltemperatures remain cool, wet, or when rootsbecome dysfunctional because of high soiltemperatures or disease. Excessive concentrationsof one micronutrient may induce a deficiency ofanother. The heavy leaching requirements of salt-affected soils can also cause deficiencies of Fe,Mn, Cu, and Zn.

Soil pH probably has the largest impact onmicronutrient availability. Micronutrientdeficiencies occur more commonly in calcareoussands or soils, or where water pH is high .Excessive liming can have the same impact. Fe,Mn, Zn, and Cu are more soluble in acidic soils,and deficiencies are not anticipated unless thesoils are heavily leached. Excessive levels of Fe,

Micronutrient

requested. Ask the laboratory to include theranking scale and to list the extractant used forthe test. The frequency of testing will dependupon your site conditions. A micronutrient testshould always be included as part of the generalsoil nutrient test for any new golf course site,during grow-in programs, or where micro-nutrient problems are expected. Periodic test-ing is recommended even where there are noproblems to monitor changes and evaluateongoing fertility practices.

A soil analysis is an important tool to helppredict potential micronutrient deficienciesand imbalances. A tissue test may be morehelpful to confirm suspected deficiencies andtoxicity problems. The tissue test is only asgood as the sample collected, so care shouldbe taken to keep samples clean and free ofsoil and limited to the site you wish to betested. Clipping samples can be collectedfrom both problem and non-problem areasfor comparison purposes. A more repre-sentative sample should be used if the test is formonitoring purposes. The clippings can becollected from mowing baskets on greens orclipped manually from other golf course areas .Root tissue samples can be obtained using a soilprobe. Avoid sampling soon after a fertilizerapplication has been made. The laboratory youwill use to complete the test can also providemore information on specific sampling techniquesand packaging of the tissue samples .

Commercial and university laboratories areequipped to complete an analytical tissue test. Theclipping Qr root samples received in the laboratoryare first washed and then dried or ashed andtreated with strong acids to dissolve the nutrients.The concentrations are calculated and the resultsprovided along with a ranking that compares thevalues with normal ranges. Table 3 providessufficiency ranges for micronuttients in turf grasstissues.

SITE ANALYSISThe following considerations are helpful whenevaluating the status of micro nutrients at yoursite:• Are site conditions conducive to a particulardeficiency?• Are there visual symptoms present onindividual plants that may indicate a deficiency?• Are there any "red flags" indicated in the soilnutrient tests?

DTPAeFeMnZnCu

Mehlich lIIeFeMn

ZnCu

Table 2DTPA and Mehlich III extractable Fe,Zn, Cu, and Mn levels

used by many laboratories for micronutrient availability.'

Low High(Deficient) Medium (Sufficient)b

------------------------------------ ppm ------------------------------------< 2.5 2.6 - 5.0 > 5.0< 1.0 1.0 - 2.0 > 2.0< 0.5 0.6 - 1.0 > 1.0< 0.2 0.2 - 0.4 > 0.4

<50.0 50 - 100 >100.0< 4.0 4.0 - 6.0 > 6.0 (pH 6.0)< 8.0 8.0 - 12.0 > 12.0 (pH 7.0)< 1.0 1.1 - 2.0 > 2.0< 0.3 0.3 - 2.5 > 2.5

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Table 3Sufficiency ranges for nutrient concentrations in clippings from turfgrass.

Generalb

2.75 - 3.500.30 - 0.551.00 - 2.500.50 - 1.250.20 - 0.600.20 - 0045

35 - 10025 - 1505 - 20

20 - 5510 - 60no data

St.Augustinegrassa1.90 - 3.000.20 - 0.502.50 - 4.000.30 - 0.500.15 - 0.25

no data50 - 30040 - 25010 - 2020 - 100

5 - 10no data

Sufficiency Ranges forPerennialRyegrassa

3.34 - 5.100.35 - 0.552.00 - 30420.25 - 0.510.16 - 0.320.27 - 0.56

97 - 93430 - 73

6 - 3814 - 645 - 17

0.5 - 1.00

CreepingBentgrassa

4.50 - 6.000.30 - 0.602.20 - 2.600.50 - 0.750.25 - 0.30

no data100 - 30050 - 1008 - 30

25 - 758 - 20

no data

Bermudagrassa

4.00 - 6.000.25 - 0.601.50 - 4.000.50 - 1.000.13 - 00400.20 - 0.50

50 - 50025 - 3005 - 50

20 - 2506 - 30

0.10 - 1.20

NutrientN,%P,%K,%Ca,%Mg,%S,%Fe,ppmMn,ppmCu,ppmZn,ppmB,ppmMo,ppm

rt

aMillsand Jones, 1996.bJones, 1980.Reference: R.N. Carrow et al.2001.p. 172.

concern.Foliar application of any fertilizer

requires time for absorption into theplant, so delaying mowing practices willensure that higher concentrations ofnutrients are absorbed. Foliar applica-tions of both Fe and Mn must be madefrequently, as the nutrients are not

deficiencies are the most common among themicronutrients. Foliar applications of Fe arecommon to correct the deficiencies and to main-tain desirable color. Mn deficiencies are less com-mon, but supplemental applications may berequired in high-pH soils, heavily leached low-pH sands, or where patch diseases are a concern.Calcareous soils, salt-affected sites, or heavilyleached sandy soils (CEC<2-3 meq per 100 gmsoil) may require more frequent and light appli-cations of micronutrient-based fertilizer packagesor supplemental applications of Fe or Mn.

Micronutrient fertilizers are available in solubleformulations for foliar or soil applications. Foliarapplications of micronutrients may be desirablewhere a rapid response is required or if there areconcerns about soil availability (see Table 1).

Chelated formulations of micro-nutrients are available for foliar and soilapplications as well. The chelates aremore expensive but will remain avail-able to plants longer in high-pH soils orother instances where availability is a

Mn, Cu, and Zn are more likely to be available toplants in higWy acidic soils (PH <5). Borontoxicity is also more prevalent in low-pH soilswhere B levels in the native soils or irrigationwater are high. High levels of a micronutrientmay also accumulate in soils and plant tissuefollowing repeated use of certain composts,sludge-based fertilizers, and plant fugicides.

FERTILIZER STRATEGIESMicronutrients can often be managed proactivelywith an application or two of a fertilizer contain-ing a complete micronutrient package and bymanaging soil pH. Seldom will applications ofCu, Zn, or B alone be necessary, and adequateconcentrations of those nutrients can be main-tained by using one of the fertilizer packages. Fe

Table 4Application rates of various micronutrients for test plots

to determine the need for wider-scale applications.

Lbs.per Fluid oz. per FertilizerMicronutrient I,000 sq. ft. 1,000sq. it.* SourcesIron .0250 2.000 Ferrous sulfate (20% Fe)Manganese .0125 .800 Manganese sulfate (26-28% Mn)Zinc .0 I00 0460 Zinc sulfate (35% Zn)Copper .0030 .140 Copper sulfate (25% Cu)Boron .0020 .190 Boric acid (17% B)Molybdenum .00 I0 .036 Sodium molybdate (47% Mo)

*Fluid oz. of product applied in 1-3gallons of water per I,000 sq. ft.

16 GREEN SECTION RECORD

mobile inside the plant. Zn, Cu, B, and Mo aremore mobile, and deficiencies can be correctedmore easily with foliar applications. Soil applica-tions of Mn are most effective to increase Mnconcentrations in the roots.

Soil and tissue tests help chart micronutrientstatus in soils and the plant. However, a suspecteddeficiency of a micronutrient can also be con-firmed by completing a field application of thatnutrient over a small test plot. A plant responsefollowing the application confirms the deficiencyand perhaps the need for wider-scale applications.Table 4 provides application rates of the variousmicronutrients for such tests.

Managing micronutrients is not an exactscience. Those managing sandy or high-pH soils,salt-affected sites, or who are growing-in a golfcourse should be familiar with the interactionsamong micronutrients, the factors that can causeimbalances, and what fertilizer strategies can beused successfully. So take the time to learn moreabout the role of micronutrients in turf grasssystems and how site conditions, managementpractices, and weather conditions can impacttheir availability. This is one time when micro-

managing is not just acceptable, but is downrightnecessary.

ACKNOWLEDGEMENTA very special thank-you goes to Dr. Bob Carrow,University of Georgia, for his helpful guidance during thewriting of this article.

REFERENCESCarro\\!, R. N., D.V Waddington, and P. E. Rieke. 2001. Turf-grass Soil Fertility and Chemical Problerns:Assessment andManagement, John Wiley & Sons, Inc. 375pp.

Hill,W J.,J. R. Heckman, B. B. Clarke, and J. A. Murphy.1999.Take-All Patch Suppression in Creeping Bentgrass withManganese and Copper. HortScience 34(5):891-892.Hull, R.J. 1999. Iron Usage byTurfgrasses. TUljgrassIrends8(2):1-10.

Hull, R. J. 2001. Zinc Usage by Turfgrasses. TUljgrassIrends10(7):7 -11.

Hull, R.J. 2001. Manganese Usage by Turfgrasses. TuifgrassIrends 10(9):6-13.Hull, R. J. 2002. Copper is Essential Bridge for Many PlantFunctions. Tuifgrass Irends 11(9):14-16.

JIM SKORULSKI is the Green Section agronomist whovisits golf courses throughout New England and easternCanada.

Cold soil temperaturesand an already weakroot system can impactnutrient absorptionand result in nutrientdeficiencies in theplant.

SEPTEMBER-OCTOBER 2003 17