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Secondary and Micronutrientsfor

VEGETABLES AND FIELD CROPS

By M.L. Vitosh, D.D. Warncke and R.E. LucasDepartment of Crop and Soil SciencesMichigan State University ExtensionE-486 Revised August 1994

MICHIGAN STATEU N I V E R S I T Y

EXTENSION

General Information . . . . . . . . . . . . . . . . . . . .1Extent of Secondary and Micronutrients . . . . . . . . .1Identifying Problem Areas . . . . . . . . . . . . . . . . . . . . .1Secondary and Micronutrient Fertilizers . . . . . . . . . .1Michigan Fertilizer Law . . . . . . . . . . . . . . . . . . . . . . .2

Calcium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2Calcium Deficiency Symptoms . . . . . . . . . . . . . . . . .3Correcting Calcium Deficiency . . . . . . . . . . . . . . . . .3Calcium Toxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Magnesium . . . . . . . . . . . . . . . . . . . . . . . . . . .3Magnesium Deficiency Symptoms . . . . . . . . . . . . . .3Correcting Magnesium Deficiency . . . . . . . . . . . . . .4Magnesium Toxicity . . . . . . . . . . . . . . . . . . . . . . . . . .4

Sulfur . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4Sulfur in Michigan Soils . . . . . . . . . . . . . . . . . . . . . . .4Sulfur Deficiency Symptoms . . . . . . . . . . . . . . . . . . .5Correcting Sulfur Deficiency . . . . . . . . . . . . . . . . . . .5Sulfur Toxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Manganese . . . . . . . . . . . . . . . . . . . . . . . . . . .6Manganese Deficiency Symptoms . . . . . . . . . . . . . .8Correcting Manganese Deficiency . . . . . . . . . . . . . .9Manganese Toxicity . . . . . . . . . . . . . . . . . . . . . . . . . .9

Zinc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10Zinc Deficiency Symptoms . . . . . . . . . . . . . . . . . . .10Zinc Fertilizer Carriers . . . . . . . . . . . . . . . . . . . . . . .11 Rates and Methods of Applying Zinc Fertilizer . . . .12Zinc Carryover . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12Soil and Plant Tissue Tests for Zinc . . . . . . . . . . . . .12Zinc Toxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Copper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13Copper Deficiency Symptoms . . . . . . . . . . . . . . . . .13 Correcting Copper Deficiency . . . . . . . . . . . . . . . . .13Copper Toxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14Iron Deficiency Symptoms . . . . . . . . . . . . . . . . . . .14Correcting Iron Deficiency . . . . . . . . . . . . . . . . . . . .14Iron Toxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Boron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

Boron Deficiency Symptoms . . . . . . . . . . . . . . . . . .15Correcting Boron Deficiency . . . . . . . . . . . . . . . . . .15Boron Toxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

Molybdenum . . . . . . . . . . . . . . . . . . . . . . . . .16Molybdenum Deficiency Symptoms . . . . . . . . . . . .17Correcting Molybdenum Deficiency . . . . . . . . . . . .17Molybdenum Toxicity . . . . . . . . . . . . . . . . . . . . . . .17

Foliar Application of Secondary and Micronutrients . . . . . . . . . . .18

*The authors gratefully acknowledge D.R. Christenson, J.F. Davis, B.D. Knezek and L.S. Robertson, Crop and SoilSciences Department, for their contribution of pictures andreview of this bulletin. We would also like to gratefullyacknowledge the following companies for their contribu-tions that offset the cost of color in this bulletin: Countrymark Cooperative, Inc., Crop Production Services,Inc., Traylor Chemical and Supply Co., Inc., and U.S. Borax, Inc.

COVER: Zinc response on dry edible beans. Four rowsbetween the two stakes received zinc in the starter fertilizer.The rest of the field received starter fertilizer without zinc.

Secondary and Micronutrientsfor

VEGETABLES AND FIELD CROPSBy M.L. Vitosh, D.D. Warncke and R.E. Lucas*

Department of Crop and Soil Sciences

Michigan State University is an Affirmative Action/Equal Oppor-tunity Institution. Extension programs and materials are opento all without regard to race, color, national origin, sex, disabil-ity, age or religion. ■ Issued in furtherance of MSU Extension

work in agriculture and home economics, acts of May 8 and June 30, 1914, in coopera-tion with the U.S. Department of Agriculture. Gail Imig, director of Extension, MichiganState University, East Lansing, MI 48824-1039. ■ All information in these materials is foreducational purposes only. Reference to commercial products or trade names does notimply endorsement by MSU Extension or any other unit of the university or bias againstthose not mentioned. This bulletin becomes public property upon publication with cred-it to MSU. Reprinting cannot be used to endorse or advertise a commercial product orcompany.Produced by Outreach Communications on recycled paper with vegetable-based inks.

Major Rev., destroy old, 8:94-3M-KMF, $2.50

Soils & Soils Mgmt-Fertilizer, File: 32.333

MICHIGAN STATEU N I V E R S I T Y

EXTENSION

GENERAL INFORMATIONPlant nutrients in fertilizers are classified as major

nutrients and micronutrients. The most importantmajor nutrients are nitrogen (N), phosphorus (P) andpotassium (K). Plants require these nutrients in rela-tively large amounts, and these are the nutrients mostlikely to be deficient for plant growth. The other majornutrients, also called secondary nutrients, are calcium(Ca), magnesium (Mg) and sulfur (S). They are alsorequired in relatively large amounts but are less likelyto be deficient. Micronutrients are essential for plantgrowth, but plants require relatively small amounts ofthem. They include boron (B), copper (Cu), iron (Fe),manganese (Mn), molybdenum (Mo) and zinc (Zn).These elements may also be referred to as minor ortrace elements, but “micronutrients” is preferred.

Extent of Secondary and Micronutrient Deficiencies

Secondary and micronutrient deficiencies in Michi-gan are not widespread, but a deficiency of any ofthese elements can cause plant abnormalities, reducedgrowth or reduced yield. Increased need for thesenutrients in crop production has drawn attention forthe following reasons:• More information on crop responses and availability

of nutrients in various soil types has been accumulat-ed.

• Today’s higher crop yields require larger amounts ofthese nutrients.

• Long-time cropping has removed measurableamounts of these nutrients.

• Today widespread use of animal manures hasdecreased and use of high-analysis fertilizers low innutrient impurities has increased.

• High potassium levels in the soil and greater use ofnitrogen fertilizer can cause a magnesium imbalancein some plants that creates the potential for hypo-magnesia (grass tetany) problems in livestock.

• High phosphorus levels in the soil may induce zincdeficiency in plants.

• Air pollution abatement practices have reduced sulfuremissions from industry and decreased the amount ofsulfur added to the soil by precipitation.

• More attention is being given to crop quality andnutritional value of today’s crops.

Identifying Problem AreasThe information used to help identify secondary and

micronutrient problems are soil tests, plant analyses,soil type, crop species and plant symptoms. A good

way to confirm a suspected nutrient deficiency is toobtain plant and soil samples from adjacent areas withnormal and abnormal plant growth and have themtested.

The MSU Soil Testing Laboratory will test soil sam-ples for pH, available phosphorus, exchangeable (avail-able) potassium, calcium, magnesium and extractable(available) zinc, manganese and copper. Some labora-tories may also offer soil tests for sulfur, boron andiron.

Many soil testing laboratories also offer plant tissueanalyses. Table 1 shows the acceptable or sufficiencynutrient concentrations required for production of sev-eral important Michigan crops. The values reported forvegetables are general and should be used only asguidelines. Nutrient values below the sufficiency con-centration may indicate a deficiency. Values above thesufficiency concentration may be excessive and possi-bly toxic.

When using tissue analysis to diagnose nutrient defi-ciencies, it is important to sample the specified planttissue at the proper time. It may also be helpful to notewhether deficiency symptoms existed on the plant ortissue sampled and any climatic conditions that mighthave caused the symptoms to occur.

Secondary and Micronutrient FertilizersThere are several ways to add secondary and micro-

nutrients to nitrogen, phosphorus and potassium(N-P-K) fertilizers. They may be incorporated into gran-ulated fertilizers during the granulation process so thateach granule of fertilizer contains an equal amount ofall nutrients. They may be blended with N-P-K fertiliz-ers at a bulk blending plant. If the particle size of sec-ondary and micronutrients is greatly different from thesize of particles containing the primary nutrients, asticker may be needed to prevent particle size separa-tion. Separation can lead to segregation of particle sizesand non-uniform application. These nutrients may alsobe added to liquid or suspension fertilizers. Chelatedsecondary and micronutrient formulations of thesenutrients are generally preferred to non-chelated mate-rials for mixing with liquid fertilizer because a largeramount of the nutrient can be added before precipita-tion occurs.

The amount of secondary or micronutrients requiredin mixed fertilizers depends on the application rate.Table 2 can be used to determine the appropriate per-centage of elements needed in mixed fertilizers basedon the amount of fertilizer to be applied and theamount of element required per acre. In this bulletin,

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MICHIGAN STATE UNIVERSITY EXTENSION

all secondary and micronutrient recommendations aregiven in pounds of element per acre.

Fertilizer LawsThe Michigan Fertilizer Law requires each fertilizer

manufacturer who claims secondary and micronutri-ents are present in fertilizer to guarantee the minimumcomposition of these nutrients in the fertilizer. Somestates have set minimums for claims at levels recom-mended by the Association of American Plant FoodControl Officials (AAPFCO). These levels are lowerthan those permitted by Michigan regulations. Webelieve that these low levels often do not supply suffi-cient quantities to correct a deficiency. For example,one application of 300 pounds of fertilizer containing0.05 percent manganese (minimum set by AAPFCO)per acre will supply 0.15 pounds of manganese. Indeficient soils, field trials have shown a need for atleast 5 pounds per acre—a 32-fold difference.

Some manufacturers claim that small amounts ofsecondary and micronutrients are needed to maintainsoil fertility. Such claims may have merit for somemicronutrient elements in very sandy soils. However,for most agricultural soils, the problem is not replacingthe nutrients at a maintenance level, but maintainingthe nutrients in an available form. Most soils have ade-quate total iron and manganese, but these nutrients arelargely in an unavailable form. The availability of cop-per and zinc is also governed by their adsorption tosoil particles. Boron is a highly mobile element thatdoes not accumulate to a great extent in sandy soils.

Therefore, it may be difficult to maintain boron inthese soils at sufficiently high levels for certain crops.In other soils, boron may be adsorbed and unavailablefor crop use.

CALCIUMCalcium, an essential part of plant cell wall struc-

ture, provides for normal transport and retention ofother elements and strength in the plant. It is thoughtto counteract the effect of alkali salts and organic acidswithin the plant. Calcium is absorbed as the Ca++ionand exists in a delicate balance with magnesium andpotassium in the plant. Too much of any one of thesethree elements may cause insufficiencies of the othertwo.

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Secondary and Micronutrients for Vegetables and Field Crops

TABLE 1. Nutrient sufficiency ranges for corn, soybeans, alfalfa, wheat, sugar beets, potatoes and vegetables.

Ear leaf sample ofinitial silk

Upper fullydeveloped leaf

sampled prior toinitial flowering

Top 6 inchessampled prior toinitial flowering

Upper leavessampled prior to

initial bloom

Center fullydeveloped leaf

sampled inmidseason

Top fully developedleaves

Petioles from mostrecently matured leaf sampled in

midseason

ELEMENT CORN SOYBEANS ALFALFA WHEAT SUGAR BEETS VEGETABLES POTATOES

Percent (%)Nitrogen 2.76-3.50 4.26-5.50 3.76-5.50 2.59-3.00 3.01-4.50 2.50-4.00 2.50-4.00Phosphorus 0.25-0.50 0.26-0.50 0.26-0.70 0.21-0.50 0.26-0.50 0.25-0.80 0.18-0.22Potassium 1.71-2.50 1.71-2.50 2.01-3.50 1.51-3.00 2.01-6.00 2.00-9.00 6.00-9.00Calcium 0.21-1.00 0.36-2.00 1.76-3.00 0.21-1.00 0.36-1.20 0.35-2.00 0.36-0.50Magnesium 0.16-0.60 0.26-1.00 0.31-1.00 0.16-1.00 0.36-1.00 0.25-1.00 0.17-0.22Sulfur 0.16-0.50 0.21-0.40 0.31-0.50 0.20-0.40 0.21-0.50 0.16-0.50 0.21-0.50

Parts per million (ppm)Manganese 20-150 21-100 31-100 16-200 21-150 30-200 30-200Iron 21-250 51-350 31-250 11-300 51-200 50-250 30-300Boron 4-25 21-55 31-80 6-40 26-80 30-60 15-40Copper 6-20 10-30 11-30 6-50 11-40 8-20 7-30Zinc 20-70 21-50 21-70 21-70 19-60 30-100 30-100Molybdenum 0.1-2.0 1.0-5.0 1.0-5.0 0.03-5.0 .15-5.0 0.5-5.0 0.5-4.0

0.5 1 2 4 6 10 20

Pounds of the element desired per acreLbs. offertilizerper acre

Percent in the fertilizer100 1⁄2 1 2 5 5 — —200 1⁄4 1⁄2 1 2 3 5 —300 1⁄4 1⁄2 1 1 2 3 —400 1⁄8 1⁄4 1⁄2 1 2 2 5600 1⁄4 1⁄2 1⁄2 1 2 3800 1⁄8 1⁄4 1⁄2 1 1 21000 1⁄4 1⁄2 1⁄2 1 21500 1⁄8 1⁄4 1⁄2 1⁄2 12000 1⁄8 1⁄4 1⁄4 1⁄2 1

TABLE 2. Percentage of the element needed in mixed

fertilizer, based on the amount of fertilizer applied.

Calcium Deficiency SymptomsCalcium deficiency is usually observed as a failure of

terminal buds and apical root tips to develop. In corn,new leaves fail to emerge from the whorl because of asticky, gelatinous material on the edges of the leaves.The tips of these leaves are also very chlorotic (yellow-ish). The young leaves of new plants are the first to beaffected. They are often distorted and small, the leafmargins are often irregular, and the leaves may showspotted or necrotic areas.

Disorders such as blossom end rot in peppers andtomatoes, blackheart in celery, internal tip burn in cab-bage and cavity spot in carrots are attributed to calci-um deficiency. These disorders are usually related tothe inability of the plant to translocate adequate calci-um to the affected plant part rather than to insufficientsoil calcium levels.

In Michigan, calcium deficiency occurs only on veryacid soil (< pH 5.0) or where excessive quantities ofpotassium or magnesium have been used. Soils thatare adequately limed are high in calcium. Even soilsthat are moderately acid (between pH 5.0 and 6.0) gen-erally contain sufficient calcium for plants. Poor plantgrowth on these soils is usually due to excess solublealuminum, manganese and/or iron rather than inade-quate calcium. In Michigan, calcium deficiency symp-toms sometimes occur when the root system has beenso damaged by nematodes, insects or diseases that theplant can not take up adequate calcium.

Correcting Calcium DeficiencyCalcium in plants is a relatively immobile element.

Where deficiencies exist and foliar sprays are used tocorrect the deficiency, it is very important to cover theyoung terminal growth with calcium. Applications onolder leaves will not benefit the plant. The suggestedrate for foliar application of calcium is 1 to 2 pounds ofcalcium in 30 gallons of water, using either calciumchloride or calcium nitrate. Agricultural lime should beused to correct calcium deficiency on acid soils. Cal-citic lime is suggested when the Ca/Mg equivalentratio is less than 1.

Calcium ToxicityExcessive levels of calcium are rarely detrimental to

plant growth, though excessive calcium carbonate inthe soil may result in other nutritional problems associ-ated with high pH. Band applications of acid-formingfertilizer may lower pH in the band and increase avail-ability of other nutrients. Spreading or spraying calci-um oxide over the top of plants may burn the foliage.

Excessive amounts of soluble calcium, such as calci-um chloride or calcium sulfate, have been known tocause problems in certain instances, but the problem isgenerally associated with the anions Cl– or SO4= ratherthan calcium per se.

MAGNESIUMMagnesium is a part of the chlorophyll molecule in

all green plants and is essential for photosynthesis. Italso helps activate many plant enzymes needed forgrowth. Magnesium, a relatively mobile element inplants, is absorbed as the Mg++ion and can be readilytranslocated from older to younger plant parts in caseof a deficiency.

Magnesium Deficiency SymptomsIn corn, magnesium deficiency symptoms first

appear as interveinal chlorosis in the older leaves(Figure 1). Symptoms often appear early in the seasonin cold, wet soils and may disappear as the soil warmsup and dries. Severe deficiency may cause stunting.

In oats and wheat, the older leaves show a distinc-tive chainlike yellow streaking. In potatoes, the loss ofgreen color begins at the tips and margins of the olderleaves and progresses between the veins toward thecenters of the leaves. The leaves become brown or red-dish and very brittle during the advanced stages of thedeficiency.

In celery, chlorosis begins on the tips of the olderleaves and progresses around the leaf margins (edges)and inward between the veins. The oldest leaves arealso the first to show symptoms of chlorosis in green-house tomatoes. The veins remain green while theinterveinal tissues become yellow and then brown, and

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Figure 1. Magnesium-deficient corn. Older leaves show interveinalchlorosis. Symptoms usually appear early but may later disappear.Severe deficiency causes stunting.

the leaves become very brittle.Other responsive crops in Michigan are cauliflower,

muskmelons, peas and rye. When deficiency occurs inthese crops, the oldest leaves are mottled or lightergreen than normal or new leaves.

Correcting Magnesium DeficiencyPresent soil test criteria used for recommending

magnesium in Michigan, Indiana, and Ohio are: (1) ifthe exchangeable magnesium level is less than 100pounds per acre for mineral soils (150 pounds per acrefor organic soils); (2) if the equivalents of potassiumexceed magnesium (on a weight basis, this is about 3parts of potassium to 1 part magnesium); (3) if the soilmagnesium (as a percent of total bases) is less than 3percent; or (4) if the equivalent ratio of calcium tomagnesium is greater than 10. Similar criteria havebeen adopted by other North Central states.

On acid soils where magnesium need is indicated, atleast 1,000 pounds of dolomitic limestone should beapplied per acre. On non-acid soils, a magnesium defi-ciency may be corrected with 50 to 100 pounds of solu-ble Mg per acre broadcast, or 10 to 20 pounds Mg peracre row applied. Magnesium sulfate, potassium mag-nesium sulfate, or finely ground magnesium oxide areall satisfactory sources of magnesium.

Magnesium can also be applied as a foliar spray.Suggested rates per acre are 10 to 20 pounds of magne-sium sulfate (Epsom salts) in 30 gallons of water.

Magnesium deficiency may be induced by high ratesof potassium. Inadequate liming and excessive potassi-um applications will depress magnesium uptake. Insome states, agronomists strive for at least 10 percentmagnesium in the total exchangeable bases (equivalentbasis). These rates are aimed at preventing grass tetanydisorders in livestock that feed on lush grass. Anyoneconcerned about grass tetany should avoid excessiverates of potassium fertilizer and feed legume hay,which is generally higher in magnesium than grasses.Some magnesium carriers can be mixed with grain orsalt rations. Contact your animal feed specialist foramounts and sources.

Magnesium uptake by celery may be related to itsgenetic makeup. Some celery varieties are unable totake up enough magnesium from the soil, resulting inmagnesium deficiency, while other varieties grow nor-mally. For those varieties that are inefficient users ofsoil-applied magnesium, foliar application of 5 to 10pounds of magnesium sulfate per acre sprayed at 10-day intervals may be necessary.

Magnesium ToxicityExcess magnesium has not been a problem in Michi-

gan. Studies in Ohio and Wisconsin have shown thatwidely different levels of exchangeable calcium andmagnesium can exist without causing a nutrient imbal-ance in the plant. Many farmers have used dolomiticlimestone for years and have not had any nutrientimbalance.

SULFURPlants take up sulfur primarily as sulfate ions

(SO4=). In the plant, it is reduced and assembled intoorganic compounds. Sulfur is a constituent of certainamino acids (cystine, cysteine, glutathione and methio-nine) and the proteins that contain these amino acids.It is found in vitamins, enzymes and co-enzymes. Sul-fur is present in glycosides, which give the characteris-tic odors and flavors to mustard, onion and garlicplants. It is also required for nodulation and nitrogenfixation of legumes. As the sulfate ion, it may beresponsible for activating some enzymes.

Sulfur in Michigan SoilsIn soil, sulfur is present primarily in the organic

form, which becomes available when organic matterdecomposes. The available sulfate ion (SO4=) remainsin soil solution, much like the nitrate ion (NO3

–), untilit is taken up by the plant. In this form, it is subject toleaching as well as microbial immobilization. In water-logged soils, it may be reduced to elemental sulfur (S)or other unavailable forms. Fertilizer impurities alsocontribute to the total supply of available sulfur insoils.

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Figure 2. Sulfur-deficient dark red kidney beans. Light–green colorand reduced growth, left. Resembles nitrogen deficiency. Plantsmature early. Normal plant, right.

Atmospheric deposition supplies a considerableamount of plant-available sulfur. For rural areas ofMichigan, the amount will generally vary from 8 to 15pounds per acre annually, depending on proximity toan industrial emission source. Precipitation within sev-eral miles of certain industrial sites may contain 10 to20 times as much sulfur as precipitation in more ruralareas. Sulfur dioxide in the atmosphere can also beabsorbed through the leaves of plants. Once absorbed,it is rapidly converted to the sulfate ion.

Because of the many light-colored sandy soils inMichigan, more intensive cropping systems andincreased use of fertilizers low in sulfur, one mightexpect sulfur deficiency to be widespread. Field trials,however, have shown little need for additional sulfurfertilizer. Soil mineral sources and sulfur fallout fromthe atmosphere currently provide adequate sulfur forcrop production in Michigan.

Sulfur Deficiency SymptomsSulfur-deficient plants are generally light green, simi-

lar to plants with nitrogen deficiency (Figures 2, 3).The most likely crops to show a sulfur deficiency arethose grown on sandy, low organic matter soils innorthern Michigan. Legumes, especially alfalfa and oth-ers with a high sulfur requirement, will normally bethe first crops to respond to sulfur fertilization. Dry edi-ble beans that were not adequately fertilized withnitrogen have been shown to respond to sulfur fertiliz-er. Corn, small grains and other grasses are less likelyto show sulfur deficiency.

Correcting Sulfur DeficiencySulfur research in other states has led to the devel-

opment of several methods for extracting available sul-fur from soils. The interpretation of these tests, howev-er, continues to be a problem. Consideration of avail-able sulfur from subsoil and atmospheric contributionsmay be necessary to accurately predict response toadded sulfur fertilizer.

Application rates of 20 to 40 pounds of sulfur peracre will correct a sulfur deficiency. Soluble sources ofsulfur—such as potassium sulfate, potassium magne-sium sulfate, Epsom salts, ammonium sulfate or gyp-sum—are usually preferred to elemental sulfur. Formost soils, one application is sufficient for 2 or 3 years.Very sandy soils, where leaching is a problem, mayrequire larger or more frequent applications.

Sulfur ToxicitySulfate/sulfur toxicity symptoms begin as an inter-

veinal chlorosis and scorching of the leaf margins,which gradually proceeds inward. Sulfur toxicity hasnot been observed in Michigan.

Irrigation water high in sulfate and/or soluble salt, apotential problem source normally occurring in aridand semi-arid regions, is often remedied by thoroughleaching. Excessive sulfur in some organic soils and so-called Kett clay soils can cause extreme acidity whensulfur is oxidized because of drainage.

Sulfur dioxide in the atmosphere is an air pollutantthat can injure plants. Plants relatively sensitive tosulfur dioxide injury are soybeans, dry edible beans,alfalfa, small grains and many vegetable crops. Thesymptoms of sulfur dioxide injury may resemble dam-age from frost, other air pollutants, chemical sprays orherbicide residues in soils. This often makes it very dif-ficult to identify the cause of injury. Positive identifica-tion can be made only after all foliar symptoms andrelated evidence have been considered.

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Figure 3. Sulfur-deficient corn. Light green plants growing onsandy soil low in organic matter. Plants usually grow out of thedeficiency as the roots penetrate the subsoil.

In general, symptoms are eitherchronic or acute, depending on therate of sulfur accumulation in theleaf tissues. Chronic injury is char-acterized by a slow accumulationcausing a general chlorotic appear-ance. Some plants may be ivory orwhite, while others show a strongreddish brown or black coloration.Later symptoms resemble normalsenescence.

Acute injury appears as marginalareas of dead tissue, which at firsthave a grayish green, water-soakedappearance. Later these areas takeon a bleached ivory color in mostplants. In small grains, tip diebackis a common symptom.

MANGANESEManganese deficiency in crops is

the most common micronutrientproblem in Michigan. The micronu-trient manganese should not beconfused with magnesium, a sec-ondary nutrient. Manganese ismainly absorbed by plants in theMn++ ionic form. Manganese maysubstitute for magnesium by acti-vating certain phosphate-transfer-ring enzymes, which in turn affectmany metabolic processes. A highmanganese concentration mayinduce iron deficiency in plants.

Manganese availability is closelyrelated to the degree of soil acidity.Deficient plants are usually foundon slightly acid (pH 6.6-7.0) oralkaline soils (pH >7.0), e.g., lakebeds, glacial outwashes, peats andmucks. Acid soils that have beenlimed are more likely to be man-ganese deficient than naturally neu-tral or alkaline soils.

Manganese-deficient organic soils and dark-coloredsandy loams usually have a pH greater than 5.8. ThepH of deficient mineral soils is usually above 6.5. Themineral soils are usually dark at the surface and have agray subsoil. Manganese deficiency is seldom found onglacial till or moraine soils.

Field and vegetable crops vary in their response tomanganese fertilizer. The degree of response to man-ganese fertilizer for several crops is given in Table 3.Dry edible beans, cucumbers, lettuce, oats, onions,peas, potatoes, radishes, sorghum, soybeans, snapbeans, spinach, Sudangrass, sweet corn, table beetsand wheat are the most responsive crops.

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Crop Mn B Cu Zn Mo Fe

Alfalfa low high high low mediumAsparagus low low low low low mediumBarley medium low medium low low mediumBlueberry low low mediumBroccoli medium high medium high highCabbage medium medium medium low medium mediumCarrot medium medium medium low lowCauliflower medium high medium high highCelery medium high medium lowClover medium medium medium low highCorn medium low medium high low mediumCucumber high low mediumDry edible bean high low low high medium highGrass medium low low low low highLettuce high medium high medium highOats high low high low low mediumOnion high low high high highParsnip medium medium medium lowPea high low low low mediumPepper medium low low mediumPeppermint medium low low low low lowPotato high low low medium lowRadish high medium medium medium mediumRye low low low low lowSnapbean high low low high medium highSorghum high low medium high low highSoybean high low low medium medium highSpearmint medium low low low lowSpinach high medium high high high highSudangrass high low high medium low highSugar beet high medium medium medium medium highSweet corn high medium medium high low mediumTable beet high high high medium high highTomato medium medium high medium medium highTurnip medium high medium mediumWheat high low high low low low

1Highly responsive crops will often respond to micronutrient fertilizer additionsif the micronutrient concentration in the soil is low. Medium responsive crops areless likely to respond, and low responsive crops do not usually respond to fertilizer additions even at the lowest soil micronutrient levels.

TABLE 3. Relative response of selected crops to micronutrient fertilizers.1

Response to micronutrient

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Figure 5. Manganese-deficient celery. Chlorosis of the leavesbetween the dark veins.

Figure 4. Manganese-deficient dark red kidney beans. Yellowingbetween the leaf veins. Veins remain green.

Figure 6. Manganese-deficient cabbage. Interveinal chlorosis ofthe leaves generally over the entire plant, center. Healthy plant infront.

Figure 7. Manganese-deficient onions. Olive green leaves mayappear wilted, right. Normal plants were treated with manganesestarter fertilizer, left.

Figure 8. Manganese-deficient corn grown on organic soil. Leavesare light green with yellowish stripes.

Manganese Deficiency SymptomsMost crops deficient in manganese become yellowish

to olive-green. Potatoes show reduced leaf size. Graincrops have a soft, limber growth, which often appearsdiseased. In oats, this may be described as “grayspecks.” Wheat and barley often show colorless spots.

Manganese-deficient corn plants grown on organic soilsshow light yellow-green pinstriping of the leaves, alsodescribed as interveinal chlorosis (Figure 8). Man-ganese deficiency in field corn has seldom beenobserved on mineral soils in Michigan.

Manganese deficiency in soybeans, dry edible beans,snap beans, sugar beets, celery, cucumbers and cab-bage often causes marked yellowing between the leafveins; the veins themselves remain dark green (Figures4-7). This pattern is similar to iron deficiency butoccurs more generally over the plant—iron deficiency is

8

Secondary and Micronutrients for Vegetabqles and Field Crops

Figure 9. Manganese-deficient sugar beets. Mottling between theveins, right. Chlorosis usually begins on the younger leaves.Severe deficiency causes gray and black specks along the veins.

Figure 10. Manganese-deficient wheat. Leaves are discolored andyellowish and may resemble diseased leaves. Found most oftenon high pH soils.

Figure 11. Manganese-deficient soybeans. Symptoms are yellow-ing between the leaf veins with the veins remaining dark green.Found most often on organic soils and high pH soils.

Figure 12. Manganese-deficient soybeans on organic muck soil, center. Caused by a manganese chelate that created iron-manganese imbalance in the plant. The manganese chelate wasconverted to an iron chelate in the soil after application.

most pronounced on new growth. In sugar beets andpotatoes, chlorosis begins in the younger leaves. Later,gray and black freckling may develop along the veins.

Manganese-deficient onions are olive-green and theleaves may appear wilted. Manganese deficiency issometimes confused with nitrogen deficiency. To sepa-rate the two, make a nitrogen tissue test. A tissue testfor nitrate N easily determines which nutrient is defi-cient. Manganese-deficient plants usually test higherthan normal in nitrate nitrogen because of the lack ofMn enzymes required to convert nitrate to protein N.

Correcting Manganese DeficiencyManganese deficiency in crops can be prevented by

band applying manganese fertilizer to the soil, sprayingit on the foliage or making the soil more acidic. Steamor chemical fumigation will also correct it temporarily.Generally, when manganese is deficient, manganesesulfate or manganous oxide is mixed with the fertilizerand applied in a band near the seed. Commercial man-ganese sulfate is 26 to 28 percent manganese (Mn);manganous oxide is usually 41 to 68 percent man-ganese.

Studies have shown that manganous oxide shouldbe finely ground to be effective. Granular manganousoxide (8 mesh) was largely ineffective. Manganousoxide powders (200 and 325 mesh) were less effectivethan manganese sulfate but were acceptable. Thesematerials do not blend well with other fertilizer materi-als—segregation problems occur because of differencesin particle sizes. However, the use of a sticker such asliquid fertilizer has made it possible to use these finelyground materials in the bulk blending process.

Manganic oxide (MnO4), which has been used inMichigan, is insoluble and ineffective as a manganesefertilizer regardless of mesh size. Chelated manganesematerials have not performed satisfactorily on organicsoils and have been less effective on mineral soils thanmanganese sulfate.

Broadcast application of manganese is not recom-mended because of high fixation in the soil. Residualcarryover of available manganese fertilizer is usuallylow. Therefore, manganese must be applied every yearon a deficient soil. Suggested rates of application basedon soil tests can be found in MSU Extension BulletinsE-550A and E-550B.

Foliar applications of manganese are recommendedwhen: (1) fertilizer is not applied in a band near theseed, (2) deficiency symptoms appear on the foliage, or(3) regular fungicide and insecticide sprays are applied.The recommended rate is 1 to 2 pounds of manganese

per acre in 30 gallons of water, using the 1-pound rateif plants are small and the 2-pound rate if plants aremedium to large. Spray grades of the manganese carri-ers are recommended to prevent nozzle plugging. Somefungicides contain manganese but generally notenough to correct a deficiency.

Acidifying the soil with materials such as sulfur andaluminum sulfate can correct manganese deficiency.These treatments cost more than manganese fertilizers.Acid-forming nitrogen and phosphorus fertilizers pro-mote the release of fixed soil manganese, especially ifbanded near the plant. Soil around the fertilizer bandmay be one pH unit more acid than soil farther fromthe fertilizer band. Some of the benefits accredited toband placement of fertilizer may be due to the releaseof fixed soil manganese.

Manganese ToxicityExcessive manganese is a problem in extremely acid

soils (<pH 5.0), especially if the soil is steamed orfumigated. A toxic manganese situation may alsodevelop in plants if excessive soil and/or foliar applica-tions are used. Liming soils to the desired pH range forthe crop will usually prevent any manganese toxicity.

In the early stages of plant growth, manganese toxic-ity symptoms may be similar to deficiency symptoms.The interveinal chlorosis caused by toxicity in soy-beans is more distinctive than that caused by deficien-cy. The typical spotting is followed by scorching on leafmargins and leaf cupping. In potatoes, the symptomsare chlorosis and black specks on the stems and under-sides of the leaves, followed by death of the lowerleaves.

The following crops are sensitive to excess man-ganese: alfalfa, cabbage, cauliflower, clover, dry ediblebeans, potatoes, small grains, sugar beets and toma-toes.

Plant tissue analysis is helpful in diagnosing man-ganese status. Values below 20 parts per million (ppm)are usually considered deficient. Readings of 30 to 200ppm are normal, and those over 300 ppm are consid-ered excessive or toxic.

Some growers have experienced plant damage fromcertain combination pesticide-manganese sulfatesprays. Soybeans and other crops have been damagedwhen 8 pounds of manganese sulfate per acre wasapplied by an air-blast sprayer. To prevent extensivedamage, growers should always try out a spray pro-gram on a limited acreage. Injury is evident within 48hours after application.

9


ZINCZinc is essential for plant growth because it controls

the synthesis of indoleacetic acid, which dramaticallyregulates plant growth. Zinc is also active in manyenzymatic reactions and is necessary for chlorophyllsynthesis and carbohydrate formation. Because zinc isnot readily translocated within the plant, deficiencysymptoms first appear on younger leaves. Researchshows a need for zinc in many areas where dry ediblebeans are grown. Corn, onions, soybeans and barleyhave also shown benefits from zinc applications atsome locations. Several other states report that Sudan-grass, sorghum, tomatoes and potatoes have beenresponsive.

Soils associated with zinc deficiency are usually neu-tral to alkaline in reaction. The more alkaline the soil,the greater the need for zinc. Deficiency is particularlynoticeable on crops growing where calcareous subsoilshave been exposed by land leveling or erosion, orwhere subsoil is mixed with topsoil, such as after tilingand spoil-bank leveling. Lake bed soils and organicpeats show the greatest zinc deficiencies in Michigan.

Observations and field tests show that dry ediblebeans following sugar beets often need zinc. The largequantities of phosphorus fertilizer used for sugar beetsand the high zinc requirement of dry edible beans arebelieved to cause the problem. A recent reduction inphosphorus use on sugar beets and the long-term useof zinc fertilizers have reduced the incidence of zincdeficiency.

Zinc deficiency varies from year to year. Wet, cool,cloudy weather during the early growth season increas-es the deficiency. Zinc deficiency in corn is occasional-ly noted in June, but the deficiency disappears after thesoils dry out and warm up. Crops on poorly drainedorganic soils show a deficiency probably because ofrestricted root growth. Field and vegetable crops oftenshow differences in response to zinc fertilizer. The rela-tive crop response to fertilizer zinc is given in Table 3.Dry edible beans, corn, onions, sorghum, snap beans,spinach and sweet corn are the most responsive crops.

High soil phosphorus levels have been known toinduce zinc deficiency, especially in responsive crops(see Figure 17). For years, the cause of this interactionwas suspected to be the formation of an insoluble zincphosphate, which reduced the concentration of zinc inthe soil solution to deficiency levels. Zinc phosphatehas since been shown to be soluble in soil and is anacceptable source of zinc when finely ground. Highlevels of phosphorus in plants have been shown to

restrict zinc movement within the plant, resulting inaccumulation in the roots and deficiency in the tops.Therefore, large applications of phosphorus fertilizermay contribute to zinc deficiency in zinc-responsivecrops.

Zinc Deficiency SymptomsZinc-deficient dry edible beans first become light

green. When the deficiency is severe, the area betweenthe leaf veins becomes pale green and then yellow nearthe tips and outer edges. In early stages of deficiency,the leaves are deformed, dwarfed and crumpled. Inlater stages, they look as if they have been killed by

10


Figure 13. Zinc-deficient corn. Yellow or white striping of theleaves usually developing near the stalk. Plants are often stuntedwith shortened internodes. Found most often on high pH soilsand organic soils.

Figure 14. Zinc-deficient corn. White to yellow striping of theleaves near the stalk. Shortened internodes with reddish discol-oration of the nodal tissues.

sunscald (Figures 15, 16 and 18). On zinc-deficientplants, the terminal blossoms set pods that drop off,delaying maturity.

Zinc deficiency in corn appears as a yellow stripingof the leaves. Areas of the leaf near the stalk maydevelop a general white to yellow discoloration. Insevere deficiency, the plants have shortened internodesand the lower leaves show a reddish or yellowishstreak about one-third of the way from the leaf margin(Figures 13, 14). Plants growing in dark sandy ororganic soils usually show brown or purple nodal

tissues when the stalk is split. This is particularlynoticeable in the lower nodes.

Deficiency in onions shows up as stunting, withmarked twisting and bending of yellow-striped tops(Figure 19). In potatoes, early symptoms are similar toleaf roll. The plants are generally more rigid than nor-mal, with smaller than normal leaves and shorterupper internodes.

Zinc Fertilizer CarriersSeveral zinc compounds can be used to correct a

deficiency. Zinc sulfate, zinc oxide, zinc chloride, zincsulfide and zinc carbonate are common inorganic salts.

11


Figure 15. Zinc-deficient dry edible beans, front. Beans in the backreceived zinc in the starter fertilizer.

Figure 16. Zinc-deficiency dry edible beans. Pale green leaves,yellow near the tips and outer edges at or soon after emergence.Leaves later become dwarfed or deformed and die. Plants are slowto mature.

Figure 17. Phosphorus-zinc interaction in dry edible beans. Brown-ish leaf discoloration, stunted plants and pods fail to develop.Beans above received increasing rates of phosphorus fertilizerwithout zinc.

Figure 18. Zinc-deficient dark red kidney beans. Yellow to whitishareas between the darker green veins. Similar to manganese defi-ciency but dark veins are not as prominent. Leave size may be dis-torted and irregular.

Organic compounds such as zinc chelates (zinc EDTAand zinc NTA) are about five times more effective thaninorganic salts with equivalent amounts of zinc. Organ-ic carriers, however, have a lower zinc concentration,ranging from 9 to 14 percent.

The zinc concentration of zinc sulfate ranges from25 to 36 percent, and that of zinc oxide, 70 to 80 per-cent. In field tests, granular zinc oxide was not aseffective as the powdered formulation. The test alsoshowed that mixing the zinc carrier with the fertilizerwas more effective than incorporating the carrier in thegranule.

Rates and Methods of Applying Zinc Fertilizer

To be effective, soil-applied zinc must be appliednear the seed at planting time. Mixing zinc with aphosphate fertilizer, such as 6-24-24, is acceptable.

Seed treatment with zinc oxide is not recommended.Tests have shown that 1 pound of zinc per acre fromzinc oxide applied on bean seed reduced emergenceand yields. Sidedress applications of zinc after the crophas emerged have not been very effective. If a zincdeficiency problem is diagnosed after emergence, spraythe foliage with 0.5 to 1 pound of zinc per acre. Thisamount can be found in 1.5 to 3 pounds of zinc sul-fate. The solution should not exceed 5 pounds of thesalt per 100 gallons of water. Response to spray appli-cations is usually obvious within 10 days. It may beapparent in five days if the treatment is applied whenthe plants are growing vigorously. For plants with waxyleaves, such as onions, a wetting agent in the watermay be needed to obtain good foliage cover.

Spraying crops such as corn, onions and potatoes

has had mixed results. The reason for poor results maybe inadequate zinc being translocated into the roots. Iffoliage sprays are used, they should be applied whenplants are small to obtain best results.

Some fungicides that contain zinc can be used asfoliar treatments. These fungicides may help correctzinc deficiency; however, they should not be relied onentirely because the amount of zinc applied in fungi-cides is very small.

Zinc CarryoverResidual carryover of available zinc varies from

slight to moderate, increasing as soils become less alka-line. On highly responsive soils, zinc broadcast at ratesabove 25 pounds per acre showed good carryover forseven years after application. When zinc is banded atthe rate of 3 to 4 pounds per acre, yearly applicationsare needed. After adding a total of 25 pounds of zincper acre through smaller annual applications, growerscan often reduce the rate of zinc application or elimi-nate application altogether. Growers should use thezinc soil test to decide if continued use of zinc fertilizeris necessary.

Soil and Plant Tissue Tests for ZincPlant tissue tests can help diagnose a need for zinc.

Tissues containing less than 20 ppm of zinc are oftendeficient. Values of 30 to 100 ppm are normal; valuesover 300 ppm may be considered excessive or toxic.Zinc response and suggested rates of banded zinc forsoil test levels can be found in MSU Extension BulletinsE-550A and E-550B. Recommendations are based onsoil pH and available zinc level.

Zinc Toxicity Excessive soil zinc levels may occur on extremely

acid soils (< pH 5.0) or in areas where zinc-enrichedmunicipal sewage sludge or industrial waste has beenadded to cropland as a soil amendment. Thoughinstances of plant zinc toxicity are rare in Michigan,the crop and variety being grown are critical.

High levels of available soil zinc that result in 100 to300 ppm zinc in crown leaf tissue seldom result in zinctoxicity in corn, which is very zinc tolerant. However,if the soil levels result in 40 to 50 ppm or more of zincin the leaf tissue of some varieties of dry edible beans,toxicity may occur because dry edible beans are a zinc-sensitive crop. Soybeans and most small grains fallsomewhere between corn and dry edible beans in zinctolerance. Vegetable crops are generally sensitive tohigh zinc levels, while grasses usually tolerate high lev-els of available soil zinc.

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Figure 19. Zinc-deficient onions. Yellow striping, twisting andbending of the tops.

A general guide for zinc concentration inmature leaf tissue is as follows: deficient—less than 20 ppm; sufficient—25 to 150ppm; excessive or toxic—300 ppm or more.Because plant tolerance to zinc toxicityvaries greatly, specific soil extractable levels,which might indicate toxicity, have not beenestablished.

COPPERCopper is essential for plant growth and

activation of many enzymes. A copper defi-ciency interferes with protein synthesis andcauses a buildup of soluble nitrogen com-pounds.

Normal plants contain 8 to 20 ppm cop-per; deficient plants usually contain lessthan 6 ppm. Each ton of dry hay containsabout 0.002 pounds of copper.

Without copper all crops fail to grow. For-tunately, most Michigan soils have sufficientcopper. Peaty soils, which have a low ashcontent, are generally the only soils defi-cient in copper. If the problem does appearon mineral soils, it will most likely be onacid soils that have been heavily cropped but well fer-tilized with N, P and K. Copper applied to soil is noteasily leached; nor is it extensively used by the crop.Consequently, no further copper fertilization is neededon organic soils if a total of 20 pounds per acre hasbeen applied for low responsive crops and 40 poundsper acre for highly responsive crops.

Copper Deficiency SymptomsCopper deficiency in many plants shows up as wilting

or lack of turgor and development of a bluish green tintbefore leaf tips become chlorotic and die (Figures 20-22).In grains, the leaves are yellowish and the leaf tips lookfrost damaged. Carrot roots, wheat grain and onionbulbs show poor pigmentation. Table 3 shows the rela-tive crop response to copper fertilizer. Alfalfa, lettuce,oats, onion, spinach, Sudangrass, table beet and wheatare the most responsive crops on organic soils.

Correcting Copper DeficiencyApplication rates for organic soils based on soil tests

are given in MSU Extension Bulletin E-550B. Rates ofcopper commonly used in highly responsive crops are3 to 6 pounds per acre, depending on the soil test level.These rates should be doubled on fields that havenever received copper.

Common carriers of copper are the sulfate and theoxide. Copper sulfate is blue and easily identified inmost fertilizers. It has a copper concentration of 22.5percent. Copper oxide, a brown material, has a copperconcentration of 60 to 80 percent. In field tests, thismaterial has been as effective as copper sulfate.

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Figure 20. Copper-deficient onion.Tip dieback of the tops. Poor pig-mentation of the bulb.

Figure 21. Copper-deficient Sudangrass.Wilting and eventual death of the leaf tips.Symptoms may resemble frost damage.

Figure 22. Copper–deficient corn. Development of bluish greenleaves and wilting or lack of turgor in the plant. Tips of theleaves later become chlorotic and die under conditions of severedeficiency.

Copper ToxicityExcessive soil copper levels have not been a problem

in crop production. However, the potential for coppertoxicity does exist because copper is applied annuallyfor some vegetables, either as a soil amendment or acomponent of some fungicides. Copper toxicity oftenresults in plant stunting, a bluish tint to leaf color, andleaf cupping followed by chlorosis or necrosis. Whenthe copper concentration exceeds 150 ppm in matureleaf tissue, toxicity may occur. Cumulative copperapplications of 100 pounds per acre have reducedcucumber and snap bean yields on sandy soils.

Copper is tightly adsorbed by most soils and will notleach. Therefore, once a copper toxicity problem devel-ops, it may be very difficult, if not impossible, to allevi-ate it.

IRONIron is a constituent of many organic compounds in

plants. It is essential for synthesizing chlorophyll,which gives plants their green color. Iron deficiencycan be induced by high levels of manganese. High ironlevels can also cause manganese deficiency.

Iron Deficiency SymptomsDeficiency symptoms are marked and show up first

in terminal leaves as a light yellowing. The symptomsare very similar to those of manganese deficiency (Fig-ure 23). A lack of iron in field and vegetable crops isnot common in soils with pH below 7.0.

Iron deficiency is common in the western states,where the soils contain considerable sodium and calci-um. In Michigan, woody plants such as pines, pinoaks, roses, certain ornamentals and acid-demandingplants such as blueberries, azaleas and rhododendronsmay need iron. Lawns, particularly putting greens ongolf courses, sometimes show a lack of iron because ofhigh pH and high levels of phosphorus.

Iron deficiency in many woody plants appears whenthey are grown in soils low in organic matter and highin pH. Mixing in organic materials such as manure oracid peat will help increase the availability of the iron.

Sphagnum peat moss in mixtures with sand, perliteor vermiculite intensifies the need for iron fertilizer inthe production of petunias, snapdragons, tomatoes andother bedding plants.

Correcting Iron DeficiencySoil treatments usually require applications of iron

chelates at a rate equivalent to 1⁄2 to 1 pound of iron

per acre. Often it is difficult to correct iron deficiencywith soil applications when soils are alkaline. Soilapplications are effective if soils are acid or neutral inreaction. Under alkaline soil conditions, foliage spraysare recommended. Use iron sulfate, iron chelates oriron citrate according to the supplier’s recommenda-tions. Wet foliage thoroughly. Iron chelates, thoughmore expensive than iron sulfate, persist longer.

Sometimes the best cure for Fe deficiency is to growvarieties that are not sensitive to Fe deficiency. Forinstance, some soybean varieties are more sensitive toFe deficiency than others. For bedding plant produc-tion, use 1 to 2 ounces of elemental iron per cubic yardof soil mix.

To help prevent an iron problem, avoid using exces-sive amounts of lime or phosphate. Apply chemicals orfertilizers to increase the soil acidity and add organicmatter.

Iron ToxicityInjury due to high soil iron concentrations is not

common under neutral or high pH soil conditions.Toxic situations occur primarily on acid soils (< pH5.0) and where excess soluble iron salts have beenapplied as foliar sprays or soil amendments. The firstsymptoms of iron toxicity are necrotic spots on theleaves.

An unusual form of iron toxicity has been observedin Michigan on organic soils and high organic sands.Some iron-rich, low pH, low manganese soils create anenvironment in which an interaction between the iron

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Figure 23. Iron–deficient corn. Light yellowing of the terminalleaves, with interveinal chlorosis of the leaves similar to thatcaused by manganese deficiency. Seldom found in Michigan fieldcrops. More commonly found in woody plants, ornamental andturf crops.

and manganese in the soil reduces manganese uptakeby plants. The symptoms observed on the plants are ofmanganese deficiency, but the low plant uptake ofmanganese is caused by excessive available iron in thesoil. The addition of iron chelates or manganesechelates, which rapidly convert to the iron form underthese soil conditions, aggravates the situation byincreasing the amount of available iron and withoutsolving the manganese deficiency problem.

BORONBoron primarily regulates the carbohydrate metabo-

lism in plants. It is essential for protein synthesis, seedand cell wall formation, germination of pollen grainsand growth of pollen tubes. Boron is also associatedwith sugar translocation.

Boron requirements vary greatly from crop to crop.Rates required for responsive crops such as alfalfa, cel-ery, sugar beets and table beets can cause serious dam-age to small grains, beans, peas and cucumbers. Borondeficiency may occur under a wide range of soil condi-tions. Alkaline soils have reduced uptake of boron dueto high pH. Leached soils may be boron deficientbecause of low boron reserves. The soil types most fre-quently deficient in boron are sandy soils, organic soilsand some fine-textured lake bed soils. Boron deficiencyfrequently develops during drought periods when soilmoisture is inadequate for maximum growth.

Boron Deficiency SymptomsBoron deficiency in crops causes a breakdown of the

growing tip tissue or a shortening of the terminalgrowth. This may appear as rosetting. Internal tissuesof beets, turnips and rutabagas show breakdown andcorky, dark discoloration.

Boron deficiency and leafhopper damage in alfalfaare often confused. Boron deficiency shows up as ayellowish to reddish yellow discoloration of the upperleaves, short nodes and few flowers (Figures 24, 25).Growing tips of alfalfa may die, with regrowth comingafter a new shoot is initiated at a lower axis. Leafhop-per damage shows up as a V-shaped yellowing of theaffected leaves and may appear on any or all parts ofthe plant; the growing tip is usually normal and theplant may support abundant flowers. When the soil isdry and plant growth is retarded, both boron deficiencyand leafhopper injury often occur in the same field.

Deficiency in cauliflower shows up as a darkening ofthe head and is associated with hollow and darkenedstems. Hollow stem can also be caused by adverseweather conditions. Boron deficiency usually appears

in small spots and may spread until the entire head isdiscolored.

In sugar beets, the first symptoms are white, nettedchapping of upper blade surfaces or wilting of tops.Later, if the deficiency becomes severe, transverse(crosswise) cracking of petioles develops, the growingpoint dies and the heart of the root rots (Figure 26).

In celery, the first symptoms are brownish mottlingalong the margins of the bud leaves and brittle stemswith brown stripes along the ribs. Later, crosswisecracks appear on the stems.

Acute deficiency in corn appears on the newlyformed leaves as elongated, watery or transparentstripes; later, the leaves turn white and die. Growingpoints also die and, in severe cases, sterility is com-mon. If ears develop, they may show corky brownbands at the bases of the kernels. Boron deficiency incorn has not been observed in Michigan.

Correcting Boron DeficiencyCrops grown in Michigan show a wide range of

response to boron fertilizer (see Table 3). The mostresponsive crops are alfalfa, cauliflower, celery, tablebeets and turnips. The boron recommendations for soilapplications are 1.5 to 3 pounds for highly responsivecrops and 0.5 to 1 pound per acre for medium respon-sive crops. Occasionally, certain deficient soils mayrequire up to 5 pounds of boron per acre for cauli-

15


Figure 24. Boron-deficient alfalfa. Yellow to reddish yellow discol-oration of the upper leaves. Often confused with leafhopper dam-age, which also causes yellowing of the tips of leaves.

flower and table beets. Thesuggested rate for foliage appli-cation is 0.3 pound of boronper acre in 30 gallons of waterfor highly responsive crops and0.1 pound for low to mediumresponsive crops.

The boron carrier most fre-quently used in fertilizer issodium borate, which rangesfrom 10 to 20 percent boron.“Solubor” is a trade name for asodium borate that is 20.5 per-cent boron. This compound iscommonly used in foliar spraysor in liquid fertilizers.

Because boron is fairlymobile in soils, several meth-ods of application can be used.Boron may be mixed with regu-lar N-P-K fertilizer, applied sep-arately on the soil, sprayed onthe plant, topdressed (for alfal-fa) or sidedressed (for rowcrops). Be sure to mix completely when boron is com-bined with other fertilizers. Segregation due to particlesize differences is often a problem. Boron should neverbe used in combination seedings containing legumesand grass or small grains because it will injure thegrass or small grains. Boron for the legume should be

topdressed after the grass hasbecome well established or thesmall grain companion crop hasbeen harvested. Be careful whenbanding fertilizers containing boronnear the seed or plants. Too muchboron near the seed or plant may betoxic to young plants or germinatingseeds.

Boron ToxicityBoron toxicity on Michigan crops

is usually limited to situationswhere boron-containing fertilizersare used at planting time on highlysensitive crops such as dry ediblebeans, corn, grass and small grains.Toxicity to crops has also occurredwhen sensitive crops were plantedwhere fertilizers containing boronhad been used earlier in the season.Similar problems may occur wheresensitive vegetable crops are plantedwith high rates of boron in thestarter fertilizer.

Unlike copper, zinc and manganese, boron is rapidlyleached out of the soil or fixed in the soil so there is lit-tle potential for toxic carryover from year to year. Somewastewaters used for irrigation may have high boronlevels, but irrigation waters are not a problem in Michi-gan.

Boron toxicity is characterized by yellowing of theleaf tips, interveinal chlorosis and progressive scorch-ing of the leaf margins (Figure 27). In soybeans, theleaves may have a rust-like appearance. High levels ofcalcium may increase the boron tolerance of plants.Average boron concentrations in mature leaf tissuescan be used to estimate plant boron status as follows:deficient—less than 15 ppm; sufficient—20 to 100 ppm;and excessive or toxic—over 200 ppm.

MOLYBDENUMMolybdenum functions largely in the enzyme sys-

tems of nitrogen fixation and nitrate reduction. Plantsthat cannot fix adequate N or incorporate nitrate intotheir metabolic system because of inadequate molybde-num may become nitrogen deficient. The usual carriersof molybdenum are sodium or ammonium molybdate.These salts contain about 40 percent of the element.

Molybdenum is required in very small amounts.Normal tissues usually contain between 0.8 and 5

16


Figure 25. Boron-deficient alfalfa. Shortening ofterminal growth and few flowers with yellow toreddish yellow leaves, left. Normal plant, right.

Figure 26. Boron-deficient sugar beets. Advance stage of severeboron deficiency. First symptoms are white, netted chapping ofthe upper leaves and wilting of tops. Plants later exhibit cross-wise cracking of petioles, death of the growing point and heartrot of the root.

ppm; some plants may contain up to 15 ppm. Deficientplants usually contain less than 0.5 ppm. Certain non-responsive crops such as grass and corn may containas little as 0.1 ppm. The responsive crops are clover,cauliflower, broccoli, lettuce, onions, spinach and tablebeets. Very few soils in Michigan show a need formolybdenum fertilizers. Those that do are fibrouspeats, acid sandy soils and organic soils that containlarge amounts of bog iron.

Molybdenum Deficiency SymptomsMolybdenum deficiency in clover shows up as a

general yellow to greenish yellow foliage color, stuntingand lack of vigor. The symptoms are similar to thosecaused by nitrogen starvation. Early stages of the defi-ciency in cauliflower and broccoli appear as a marginalscorching, rolling or curling upward, and withering andcrinkling of the leaves (Figure 28). In later growthstages, the deficiency shows up as “whiptail,” especial-ly in the younger leaves. The leaf blade is often verynarrow or non-existent. Older leaves show crinklingand marked yellow mottling between the veins. Inonions, molybdenum deficiency shows up as dying leaftips. Below the dead tip, the leaf shows 1 or 2 inchesof wilting and flabby formation. As the deficiency pro-gresses, the wilting and dying advance down theleaves. In severe cases, the plant dies.

Correcting Molybdenum DeficiencyMolybdenum deficiency can be corrected by seed

treatment and/or foliar applications. For seed treat-

ment, dissolve .5 ounce of the molybdenum compoundin 3 tablespoons of water and mix with sufficient seedto plant one acre. Using excess water can cause thechemical to penetrate and injure the seed embryo. Mixthe seed thoroughly and let dry. It is advisable to use asuitable fungicide dust to help dry the seed.

For foliar sprays, apply 2 to 3 ounces of the com-pound per acre. Use wetting agents in the spray whenapplying the solution to cauliflower or onions. Forsome cauliflower varieties, repeated applications attwo-week intervals are beneficial.

Soil acidity has a marked influence on the need formolybdenum—the greater the acidity, the greater theneed for molybdenum. Research plots on a Montcalmsandy soil showed that liming from pH 4.9 to pH 6.7increased the molybdenum concentration of cauli-flower fivefold. In a Houghton muck, raising the pHfrom 5.4 to 7.2 increased the concentration of molyb-denum more than threefold. Liming severely deficientsoils, however, will not completely correct the deficiency.

Molybdenum ToxicityPlants appear quite tolerant of high soil molybde-

num concentrations. There is no record of molybde-num toxicity under field conditions. In greenhousestudies, tomato leaves turned golden-yellow and cauli-flower seedlings turned purple. Animals fed foliagehigh in molybdenum may need supplemental copper tocounteract the molybdenum.

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Figure 27. Boron toxicity in navy beans. Yellowing of the leaf tipfollowed by interveinal chlorosis of the leaves and scorching ofthe margins.

Figure 28. Molybdenum-deficient cauliflower. Yellow mottlingbetween the leaf veins, rolling or curling upward and crinkling ofthe leaves.

FOLIAR APPLICATION OFSECONDARY ANDMICRONUTRIENTS

Nutrients can be absorbed through plant leaves. Insome situations, foliar-applied micronutrients are morereadily available to the plant than soil-applied micronu-trients, but foliar applications do not provide continu-ous nutrition as do soil applications. Foliar spray pro-grams may be used to supplement soil applications offertilizer or to correct deficiencies that develop in mid-season.

When spray equipment is available, secondary andmicronutrient needs of plants may be met with a goodspray program. Suggested secondary and micronutrientsources and spray rates per acre are given in Table 4.Use low rates for young plants and higher rates whenplants develop dense foliage.

Micronutrient chelates are generally no more effec-tive than water-soluble inorganic sources when foliarapplied. Chelates, however, are more compatible whenmixed with other spray materials.

For a preventive spray program, spray the crop aboutfour weeks after emergence or transplanting. Because

many micronutrients are not readily translocat-ed within the plant, a second spray will beneeded two weeks later to cover the newfoliage. When a known nutrient deficiencydevelops, spray the crop with the appropriatenutrient at the recommended rate every 10days until the deficiency is corrected. Completecoverage of the foliage is important, especiallyfor iron. Adding a wetting agent to the spraysolution will improve the coverage and mayincrease absorption, especially in crops withwaxy surfaces, such as cauliflower and onions.Micronutrients may be mixed with most fungi-cides and insecticides. However, some combi-nations are incompatible and may injure crops.When in doubt, spray only a limited acreageuntil compatibility is established. Any injurywill usually appear within 48 hours. Table 5provides a guide for obtaining the desired mix-ture of various secondary and micronutrientcarriers.In developing a spray program, remember thatsome fungicides and insecticides contain cop-per, manganese or zinc. The amounts of micro-nutrients present in these materials may ormay not be sufficient to correct a deficiencybut should be considered when determining aspray program.

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Element Lbs. element per acre Suggested sourceCalcium (Ca) 1-2 Calcium chloride or calcium nitrateMagnesium (Mg) 1-2 Magnesium sulfate (Epsom salts)Manganese (Mn) 1-2 Soluble manganese sulfate or finely

ground manganese oxideCopper (Cu) 0.5-1.0 Basic copper sulfate or copper oxideZinc (Zn) 0.3-0.7 Zinc sulfateBoron (B) 0.1-0.3 Soluble borateMolybdenum (Mo) 0.06 Sodium molybdate (2 ounces)Iron (Fe) 1-2 Ferrous sulfate2Use a minimum of 30 gallons of water per acre.

TABLE 4. Suggested rates and sources of secondary and

micronutrients for foliar application.2

TABLE 5. Pounds of secondary or micronutrient carrier needed to

obtain the desired amount of the element per acre.3

Pounds of element desired per acre.1 .2 .3 .4 .5 1.0 1.5 2.0

1 10.0 20.0 30.0 40.0 50.0 100.0 150.0 200.02 5.0 10.0 15.0 20.0 25.0 50.0 75.0 100.04 2.5 5.0 7.5 10.0 12.5 25.0 37.5 50.06 1.7 3.4 5.0 6.0 8.3 16.7 25.0 34.08 1.2 2.5 3.8 5.0 6.2 12.5 18.7 25.010 1.0 2.0 3.0 4.0 5.0 10.0 15.0 20.012 .8 1.7 2.5 3.4 4.2 8.4 12.6 17.014 .7 1.4 2.1 2.9 3.6 7.2 10.8 14.016 .6 1.3 1.9 2.5 3.2 6.3 9.5 13.018 .5 1.1 1.7 2.3 2.8 5.6 8.4 11.020 .5 1.0 1.5 2.0 2.5 5.0 7.5 10.025 .4 .8 1.2 1.6 2.0 4.0 6.0 8.030 .3 .7 1.0 1.4 1.7 3.4 5.1 7.035 .2 .6 .9 1.2 1.5 2.9 4.4 6.0

3 To convert from dry to liquid: 1 pint equals about 1 pound.

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secondary and micronutrients for vegetables …warncke/e0486.pdfsize of particles containing the...

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