CROP NUTRIENT DEFICIENCIES - TOXICITIES

CROP NUTRIENTDEFICIENCIES& TOXICITIES

Plant Protection ProgramsCollege of Agriculture, Food

and Natural Resources

IntegratedPestManagement

Published by MU Extension, University of Missouri-Columbia

$3.00 IPM1016

CONTENTS

How nutrient disorders develop . . . . . . . . . .3

Visual symptoms . . . . . . . . . . . . . . . . . . . . . . .4Sulfur-nitrogen . . . . . . . . . . . . . . . . . . . . . .5Zinc-magnesium-iron-manganese . . . . . . .5Others . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Nutrient deficiency in corn . . . . . . . . . . . . . . .6

Nutrient deficiency and toxicity in soybeans . . . . . . . . . . . . . . . . . .7

Nutrient deficiency in rice . . . . . . . . . . . . . . .8

Nutrient deficiency in cotton . . . . . . . . . . . . .9

Nutrient deficiency in wheat . . . . . . . . . . . .10

Nutrient deficiency in alfalfa . . . . . . . . . . . .11

Plant tissue testing . . . . . . . . . . . . . . . . . . . .12Five steps in plant tissue testing . . . . . . .12Sampling plant tissue . . . . . . . . . . . . . . . .12Submitting samples for testing . . . . . . . . .14Interpreting the test report . . . . . . . . . . . .14

Diagnosing nitrogen need from plant color .15Measuring greenness . . . . . . . . . . . . . . . . .15Radiometry . . . . . . . . . . . . . . . . . . . . . . . . .16Aerial imagery . . . . . . . . . . . . . . . . . . . . . . .16Other field quick tests . . . . . . . . . . . . . . . . .17

Table 1. Essential plant nutrients . . . . . . . . .3Table 2. Environmental conditions

associated with crop nutrient deficiency .12Table 3. Guide for plant sampling of

selected agronomic crops . . . . . . . . . . . .13Table 4. Guide for plant sampling of

selected vegetables, fruits and trees . . .13

Plant analysis submission form . . . . . . . . .18

Authors

Gene Stevens, Department of Agronomy,University of Missouri-Delta Center

Peter Motavalli, Soil Science Program, University of Missouri-Columbia

Peter Scharf, Department of Agronomy, University of Missouri-Columbia

Manjula Nathan, Department of Agronomy,University of Missouri-Columbia

David Dunn, Soil Test Laboratory, University of Missouri-Delta Center

Credits

Unless otherwise credited in the captions, thephotographs were provided by the authors. Manyof the symptom descriptions were taken from MUpublication G9132, Signs of Crop Hunger, byMarshall Christy.

On the World Wide Web

Updates to this publication will be posted on theWorld Wide Web at:http://muextension.missouri.edu/xplor/agguides/pests/ipm1016.htm

Production

MU Extension and Agricultural InfomationDale Langford, editorDennis Murphy, designer and illustrator

© 2002 University of Missouri

This publication is part of a series of IPMManuals prepared by the Plant ProtectionPrograms of the University of Missouri. Topicscovered in the series include an introduction toscouting, weed identification and management,plant diseases, and insects of field and horticul-tural crops. These IPM Manuals are availablefrom MU Extension at the following address:

Extension Publications2800 Maguire Blvd.

Columbia, MO 652111-800-292-0969

College ofAgricultureFood andNaturalResources

the largest amounts. Micronutrients (iron, copper,manganese, zinc, boron, molybdenum, chlorineand nickel) are required in relatively smalleramounts in plants. Other mineral elements thatare beneficial to some plants but are not consid-ered essential include sodium, cobalt, vanadium,selenium, aluminum and silicon.

A deficiency occurs when an essentialelement is not available in sufficient quantity tomeet the needs of the growing plant. Nutrienttoxicity occurs when an element is in excess ofplant needs and decreases plant growth or qual-ity. Nutrient deficiency or toxicity symptomsoften differ among species and varieties of plants.

HOW NUTRIENTDISORDERSDEVELOP

The occurrence of nutrient deficien-cies or toxicities is a result of soil,crop, climatic, and cultural factors.

These factors interact to influence the availabil-ity of nutrients to crop plants over the course ofa growing season.

Soil properties influence the form, amount,retention and movement of soil nutrients. Theeffects of soil properties on water availability alsoinfluence nutrient availability, because water isessential for chemical reactions, biological activ-ity, and the transport and absorption of nutrientsby roots. Among the critical soil chemical prop-erties affecting soil nutrient availability are soil pH(a measure of the acidity or alkalinity of a soil) andsoil cation exchange capacity (a measure of thecapacity of the soil to retain positively chargednutrient ions). Some important physical proper-ties affecting nutrient availability are soil texture(the proportion of sand, silt and clay-sized parti-cles in a soil), clay mineralogy (the type of soilclay), and soil structure (the physical arrange-ment of soil particles).

The soils of Missouri vary widely in theirinherent soil fertility and suitability for cropproduction. Information about the specific soilresources on your farm can be obtained byconsulting your regional extension specialist oryour county Farm Service Agency office or byusing the Center for Agricultural Resource and

Soil fertility is one of several factors,including light, moisture, weeds, insects,and diseases, that affect crop yield

(Figure 1). An important part of crop farming isbeing able to identify and prevent plant nutrientdeficiencies and toxicities. This publicationprovides background information on the natureand development of crop nutrient disorders underthe growing conditions commonly encountered inMissouri. It is a guide to identifying crop nutrientproblems through observable symptoms on cropplants. Information is provided on effects ofclimatic conditions on plant nutrient availability,and the results of soil and plant tissue testing.

Plants require 14 mineral elements fornormal growth and reproduction. Each of thesenutrients has a function in plants and is requiredin varying amounts in plant tissue (see Table 1).Macronutrients (nitrogen, phosphorus, potassium,calcium, magnesium and sulfur) are required in

CROP NUTRIENTDEFICIENCIESAND TOXICITIES

Table 1. Essential plant nutrients.

NameChemical symbol

Relative %in plant* Function in plant Nutrient category

Nitrogen N 100 Proteins, amino acidsPrimary macronutrientsPhosphorus P 6 Nucleic acids, ATP

Potassium K 25 Catalyst, ion transport

Calcium Ca 12.5 Cell wall componentSecondary macronutrientsMagnesium Mg 8 Part of chlorophyll

Sulfur S 3 Amino acids

Boron B 0.2 Cell wall component

Micronutrients

Chlorine Cl 0.3 Photosynthesis reactions

Copper Cu 0.01 Component of enzymes

Iron Fe 0.2 Chlorophyll synthesis

Manganese Mn 0.1 Activates enzymes

Molybdenum Mo 0.0001 Involved in N fixation

Nickel Ni 0.001 Component of enzymes

Zinc Zn 0.03 Activates enzymes

*Relative amounts of mineral elements compared to nitrogen in dry shoot tissue. May vary depending on plant species.

VISUALSYMPTOMS

Nutrient disorders may appear inmany ways in a plant, includingstunting or reduced growth, off-

colored leaves (often white, yellow or purple);abnormally shaped leaves, stems, and roots; anda breakdown of certain parts of the plant, includ-ing the root system. “Chlorosis” is a type of defi-ciency or toxicity symptom characterized byyellowing that can be generalized over the wholeplant, localized over individual leaves or isolatedbetween some leaf veins (interveinal chlorosis).“Necrosis” is a type of deficiency or toxicity symp-tom characterized by death of plant tissue some-times in spots. Yield and quality of grain or fibermay suffer when nutrition is inadequate.

When inspecting plants for symptoms ofnutrient disorders, compare plants displayingsymptoms with normal ones and examine newand older leaves. Nutrient deficiencies generallyappear first in the oldest leaves when nitrogen,phosphorus, potassium, and magnesium are limit-ing. These nutrients move from one part of theplant to another as needed.

Younger leaves and terminal buds show adeficiency when sulfur, iron, calcium, zinc copper,boron, manganese or chlorine are limiting. Thesenutrients do not readily move about in the plant.

As a deficiency becomes more severe, visualsymptoms may spread to the whole plant, leavesmay become more chlorotic or bleached in appear-ance, or stunting, deformity and death of plantparts may become more extensive. Deficiencies ofcertain nutrients, such as sulfur and phosphorus incorn, may also be visible only early in the growingseason because of immature root development orcold weather, and then become less apparent as theplant matures and the weather warms up.

Symptoms of nutrient toxicity vary, depend-ing on the element and the crop. Essential nutri-ents that can be toxic to plants include manganese,copper, boron and chlorine. Excessive quantitiesof other nutrients in the soil may cause nutrientimbalances in plants, resulting in poor growthand crop quality.

Visual symptoms of nutrient deficiency ortoxicity can be confusing because of problemswith more than one nutrient. Symptoms associ-

Environmental Systems (CARES) Web site(www.cares.missouri.edu).The parent material ofsome soils may contain a large amount of certainplant nutrients (e.g., potassium, calcium andmagnesium) and, therefore, the possibility of aplant response to additional fertilizer sources ofthose nutrients may be reduced. In addition,certain soils have natural soil physical and chem-ical restrictions that can limit potential cropproductivity. A prior knowledge of your soilresources will help you to develop a successfulnutrient management program.

Primary and secondary macronutrients areoften limiting factors for crop production inMissouri depending on soil conditions and priormanagement. Most soils in Missouri have suffi-cient amounts of micronutrients to supply plantneeds for crop production, but individual cropspecies may have special micronutrient require-ments, and soil properties may vary.

Factors such as soil pH and moisture canaffect the solubility of nutrients or interfere withthe ability of plant roots to absorb nutrients(Figure 2). Deficiencies of micronutrients occurmost often in soils with high pH (with the excep-tion of molybdenum). Phosphorus availability isreduced by soil acidity and alkalinity. Low soil pHincreases the availability of aluminum andmanganese, which can result in toxic levels ofthese elements.

Integrated Pest Management4

Potential yield

Insects and diseases

Weeds

Poor stand

Low

fertility

Lack of moisture

Poor soil structure

Improper crop variety

Figure 1. Low soil fertility is only one of several factors that can limit crop yields.

ears or grain. Split the stalks and study the inter-nal circulation system. If you observe potassiumdeficiency symptoms in cotton, always checkinside the stalks for discoloration from Verticilliumor Fusarium wilt. Likewise, check for soybeancyst nematodes on soybean plants with potas-sium deficiency symptoms. Do not overlookpossible contributing causes: disease, insects,herbicides, temperature, physical soil conditionsand moisture conditions. Plants stressed fromlack of nutrients are often more susceptible todiseases and some insects.

The following pages depict nutrient defi-ciency and toxicity symptoms in corn, soybeans,rice, cotton, wheat and alfalfa.

ated with different nutrients may resemble cropinjury caused by herbicide damage, insectdamage, or the effects of plant diseases. Listedbelow are nutrient deficiencies that may be diffi-cult to determine without laboratory tests.

Sulfur–NitrogenSymptoms of sulfur deficiency in crops are

similar to those of nitrogen deficiency. The maindifference is that sulfur deficiency may cause leafyellowing, beginning in the younger leaves,whereas nitrogen deficiency starts in the olderleaves and then spreads to the whole plant. Insome environments, sulfur and nitrogen deficien-cies can cause yellowing between the leaf veins.Without tissue testing, these similarities may causemisdiagnosis of the problem. Tissue testing effec-tively determines whether nitrogen or sulfur is inshort supply.

Zinc–Magnesium–Iron–ManganeseDeficiencies of zinc, magnesium, iron, and

manganese all typically cause yellowing of thetissue between leaf veins. Deficiencies of iron andmanganese usually occur in high-pH soils, butthese are rare in Missouri. Zinc deficiency is mostcommon in corn, and the bleached area canspread to include the veins, but the midrib and leafedges usually stay green. With magnesium defi-ciency, yellowing between veins will be seenmainly on older (lower) leaves, while zinc, ironand manganese deficiency symptoms will be seenmainly on younger (upper) leaves. Magnesiumdeficiency is best diagnosed with a soil test.

OthersUse care to distinguish among various under-

lying causes of crop deficiency symptoms. Insectdamage may look like a nutrient deficiency.Herbicides sometimes affect root, stem and leafdevelopment, thereby impairing nutrient uptake.Diseases also can impair nutrient uptake by rootsor the translocation of nutrients in the plant.Examine stems and stalks, root systems and the

Crop Nutrient Deficiencies and Toxicities 5

PotassiumIron

ManganeseZinc

CopperCobalt

Soil pH

Boron

Molybdenum

Sulfur

Phosphorus

Calcium, Magnesium

Nitrogen

4 5 6 7 8 9

Figure 2. The relative availability of nutrients to plant roots depends on the pH level ofthe soil.

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Figure 5. Corn with potassiumdeficiency is stunted andeasily lodged. Photo: GeraldBryan.

Figure 6. Potassiumdeficiency in corn causesbronzing and yellowingalong edes of lower leaves.

Figure 7. Phosphorus-deficient corn plants sometimeshave purple leaves.

Figure 4. Nitrogen-deficientcorn plants have pale greenor yellow leaves.

Figure 8. Zinc deficiency causes yellow stripes in theupper corn leaves.

Firing or drying at tips and along leaf edges (oldestleaves affected first); leaf edges ragged; iron accumu-lation in joints; weak stalks and excessive lodging; shortinternodes; poorly filled ear tips; chaffy nubbins(starchy, dull-colored kernels); roots weak (rot off);slow maturity (Figures 5 and 6).

Stunted, slow early growth; purplish stalks and leaftips of young plants (may be characteristics of somevarieties); weak stalks; shallow root system; delayedemergence of silks; imperfect pollination and barrenstalks; missing rows of kernels on ears: small twisted orcurved ears; retarded maturity (Figure 7).

Yellowing from leaf tip and along midrib while edgesremain green (oldest leaves affected first); spindly stalks;stunted growth; small ears (fail to fill at tip); ear tippinched off: kernels have glossy luster (low in protein,but high in fats); light brown stover at maturity; pooryields (Figures 3 and 4).

Narrow yellow or white stripes between veins of upperleaves (Figure 8). Stripes may join together to form ableached area between midrib and leaf margins, whichremain green.Potassium deficiency

Nitrogen deficiency

Zinc deficiency

White or yellowish streaking or bleaching betweenleaf veins; mainly on lower leaves. When rubbed, theaffected tissue may reveal a distinctive slickness(Figure 9).

Magnesium deficiency

Phosphorus deficiency

Figure 9. Magnesium-deficient corn will have white oryellow stripes on the lower leaves.

Figure 3.Yellow orbrown midribs indicatenitrogen deficiency.

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Figure 10. Leaves on right are from manganese-deficientplants. Manganese toxicity is common on low-pH soils.

Figure 11. Manganese deficiency causes yellowingbetween veins.

Irregular yellow mottling on leaflet edges, drying andcurling downward (older leaves affected first); deadleaf tissue falls away from leaf edges leaving raggedappearance; shriveled, poorly shaped seed; delayedmaturity and poor yields (Figure 13).

Potassium deficiency

Figure 13. Potassium deficiency in soybeans causesyellow areas along leaf margins between veins.

Seasonal changes in soil moisture affect salt tolerance;plants may be healthy in spring; as soil becomes dry, saltcauses plants to wilt and die; soil may have a white orlight gray-colored crust on the surface (Figures 14 and15).

Salt toxicity

Leaves have scorched appearance and eventually fall offthe plants (Figure 12).

Boron toxicity

Figure 12. Boron toxicity causes brown areas on soybeanleaves.

Leaves are mostly yellow, gradually becoming darkgreen next to veins; deficient plants are usually on darksandy soils that tie up manganese. Foliar or bandedapplications of manganese fertilizer are used to mini-mize fixation (Figures 10 and 11).

Manganese deficiency

Figure 15. White crystals onsoil surface usually indicatetoxic levels of sodium forsoybeans. Photo: Steve Hefner.

Figure 14. Dead areas inthis soybean field werecaused by sodiumtoxicity.

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Red or brown discoloration on tips and margins ofleaves; severity of condition varies by variety; leaf symp-toms usually develop after internode elongation (Figure16).


Figure 16. Potassium-deficient rice will have yellow orbrown areas on leaf tips and edges.

Slow, dwarfed growth; may not be noticeable until sickplants are compared with healthy plants of the sameage; abnormal bluish green color of foliage; slow matu-rity; poor yield and milling (Figure 21).


Figure 21. Rice plants on the right did not receivepreplant phosphorus fertilizer.

Poor tillering; leaves and stalks pale yellowish greenwith extreme yellowing of lower leaves on young plants;spindly stems and short heads; yellowing starts at leaftip of older leaves; plants do not form a completecanopy over water; poor yields (Figures 17 and 18).

Nitrogen deficiency

Figure 17. Nitrogen-deficient rice is pale green in colorand does not form a full canopy.

Figure 18. Tools such as the plant area board (above)and the cholorphyll meter can be used to monitor thenitrogen status of rice.

Leaves begin to turn brown after flooding fields; plantsfloat limply on the water surface instead of standingerect. If well water has calcium carbonate, the problemis most acute at the water inlet or other high pH loca-tions in fields; if the field is not drained quickly, riceplants will die (Figures 19 and 20).

Zinc deficiency

Figure 19. Zinc deficiency causes flooded rice seedlingsto starve for oxygen.

Figure 20. If the water is not drained from fields with zincdeficiency, rice plants will die.

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Magnesium deficiency causes purplish red leaves withgreen veins; symptoms late in season can be easily mistakenfor normal aging; appears first in lower leaves (Figure 23).

“Rust” starts with yellowish white mottling of leaves;tip and margin of leaves scorch and curl downward;whole leaves turn reddish brown, die and shed prema-turely; dwarfed immature bolls; plants are more suscep-tible to wilt diseases (Figures 26 and 27).


Magnesium deficiency

Figure 26. Cotton leaves with potassium deficiency haveyellow or bronze edges.

Figure 27. Potassium deficiency in cotton at midbloom.

Poor germination and emergence; death of seedlingplants; new leaves are “crinkled” as in thrips insectdamage; yellowish green foliage color; limited anddelayed fruiting; bending and collapse of leaf petioles;underdeveloped root system; delayed maturity (Figure24).

Low soil pH

Figure 24. Cotton grown on acid soil can have aluminumand manganese toxicity. The crinkle leaf symptom isoften mistaken for insect damage. Photo: Mike Milam.

First symptom is usually dark rings on leaf petioles; asthe season progresses, some leaves may becomedeformed (Figure 25).

Boron deficiency

Figure 25. Chronic boron deficiency on cotton terminal.Photo: Woody Miley, Arkansas Cooperative ExtensionService.

Yellowish green foliage; older leaves dry up and shedprematurely; stunted growth; fruiting branches fail todevelop (Figures 22 and 23).

Nitrogen deficiency

Figure 22. Light green strips in this cotton field indicatepoor distribution of nitrogen fertilizer.

Figure 23. Magnesium deficiency causes purplish leavesin cotton.

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Mild phosphorus deficiency in wheat can only be char-acterized by stunted growth with no distinct leaf symp-toms. In severe cases, phosphorus-deficient plantsbecome purple or brown (Figure 32).


Figure 32. Stunted wheat plants with purple leaves anddead leaf tips are signs of phosphorus deficiency.

Sulfur deficiency in wheat usually occurs on sandy soilswith low organic matter. Wheat plants with low sulfurhave pale green leaves and fail to “green-up” whenmore nitrogen fertilizer is applied. Tissue testing isusually needed to distinguish between nitrogen andsulfur deficiency (Figure 30).

Sulfur deficiency

Figure 30. Wheat leaves with pale green or yellow colorindicate sulfur deficiency.

Wheat plants with nitrogen deficiency have reducedplant height and produce fewer tillers than healthyplan. Leaf color in nitrogen-deficient plants is palegreen or yellow, resembling the symptoms of sulfurdeficiency (Figure 31).

Nitrogen deficiency

Figure 31. Nitrogen-deficient wheat is stunted with yellowleaves.

The leaves of wheat with potassium deficiency areyellow or brown along the tips (Figure 28). Potassiumdeficiency in wheat is difficult to diagnose withoutsupporting tissue test results. Symptoms from K defi-ciency are similar to symptoms caused by disease andinjury from blowing sand (Figure 29).


Figure 28. Leaves with yellow tips becoming scorchedalong the edges indicate potassium deficiency.

Figure 29. Blowing sand can cause scorched leaf tipsresembling potassium deficiency, but the rest of the plantwill usually be of normal size and color.

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Yellow leaf color in alfalfa may be caused by potassiumdeficiency. This deficiency begins at the bottom of theplants with small white spots on leaf edges. As potas-sium deficiency progresses, the tissue between the spotsturns yellow or brown and the leaves become ragged.Second and third cuttings are usually affected the mostby potassium deficiency (Figure 33).


Figure 33. White spots on edges of lower alfalfa leavesare caused by potassium deficiency; as plants get olderleaves turn yellow.

Alfalfa plants with phosphorus deficiency have retardedgrowth and small leaves (Figure 34).


Figure 34. Stunted alfalfa growth caused by phosphorusdeficiency.

The deficiency of boron is more common in alfalfa thanin other legumes. The upper leaves develop a reddishyellow rosette appearance (Figures 35 and 36). Injuryfrom potato leafhopper is often confused for boron orpotassium deficiency (Figure 37).

Boron deficiency

Figure 35. Boron deficiency causes yellow areas in alfalfafields.

Figure 36. Closeup of boron-deficient alfalfa.

Figure 37. Leafhopper injury can be confused with borondeficiency but causes a yellow “V” at the tip of a leaf.


Sampling plant tissueNutrient analysis of plant tissue at different

growth stages is a major tool for determiningwhich nutrients are limiting growth. Plant moni-toring with tissue testing is especially importantwith high value crops. Plant nutrient content willvary depending on the type of plant beingsampled, the specific plant part sampled, and thestage of growth of the plant.

Tables 3 and 4 provide guides for suggestedstages of growth and plant parts to sample for

Soil testing is the foundation of a soundnutrient management program and willhelp prevent the development of crop

nutrient deficiencies. Soil and plant testing arealso valuable diagnostic tools when possible nutri-ent deficiency symptoms are seen. Similar visualsymptoms may be caused by different nutrientdeficiencies or toxicities and by herbicide injury,diseases, insect damage or environmental condi-tions. As a result, diagnosis based on symptomsalone is much less reliable than diagnosis based onsymptoms plus additional evidence, which mayinclude soil test results, plant tissue test results orknowledge of other factors that are associatedwith deficiencies of particular nutrients (seeTable 2).

Plant tissue testing is the most accurate of alldiagnostic tools for nutrient deficiencies, partic-ularly when paired samples are taken. Plants withpossible deficiency symptoms should be comparedwith nearby plants that appear to be healthy.

Tissue testing is also the only way to detect"hidden hunger." Mild nutrient deficiencies maynot produce obvious visual symptoms, such asleaf yellowing or chlorosis. However, significantreductions in crop yields can occur with thesedeficiencies. Steps for successfully using tissuetests are shown in the box below.

PLANT TISSUE TESTING

Figure 38. “Hiddenhunger,” caused by mildnutrient deficiencies,can be detected only bysoil or tissue analysis.

Table 2. Environmental conditions associated with selected crop nutrient deficiencies.

Nutrient Conditions favoring deficiency

M a c r o n u t r i e n t s

Nitrogen • Wet currently, or wet since fertilizer application

• Surface application of urea• Broadcast N solution on high-residue

surface

Phosphorus • High or low soil pH• High soil clay content

Potassium • Dry or wet soil• Compacted soil

Sulfur • Sandy soil low in organic matter• Cool, wet weather

M i c r o n u t r i e n t s

Zinc • Very low soil organic matter (terrace channels, cut areas in leveled fields)

• Cool, wet weather• High soil pH

Iron • High soil pH

Manganese • High soil pH

Five steps in plant tissue testing

1. Determine correctplant part to sampleand how many plants tosample (see Table 3).Collect samples fromaffected plants and fromnearby healthy plants.

2. Handle samples prop-erly after collection toavoid contamination andpotential molding.

3. Clearly label all samplebags and maintainrecords of sampling date,field name or numberand any other identifyinginformation.

4. Complete plant sampleinformation forms forsubmission of samples toyour regional soil andplant testing laboratory.

5. Maintain records ofplant tissue test resultsand consult regional andlocal extension agents ifyou have questions aboutthe results and the testinterpretations.


Table 3. Guide for plant sampling of selected agronomic crops.

Plant Stage of growth Plant part Number of plants to sample

Corn

Seedling (<4 inches in height) Whole aboveground plant 20–30 Early growth (>4 inches in height to tasseling) Entire leaf fully developed below the whorl 15–25

Tasseling/bloom Earleaf 15–25 Maturity Earleaf 15–25

SoybeanSeedling Whole aboveground plant 20–30 Early growth and flowering Most recently matured trifoliate leaves 20–30

Small grainsSeedling to tillering Whole plant 50–60Before heading Upper 1/3rd of plant 50–60

AlfalfaBefore bloom (1/10th bloom) Top 6 inches or top 1/3 40–50Harvest Top 6 inches or top 1/3 40–50

Sorghum Head fully emerged but before pollination Most recently matured and fully expanded leaves 15–25

Cotton First square to midbloom Fourth petiole from the top of plant 30–40Rice First tiller (preflood) Whole aboveground plant 25–35Sources:Campbell, C.Ray (ed.) 2000. Reference sufficiency ranges for plant analysis in the Southern Region of the United States. Southern

Cooperative Series Bulletin #394, Raleigh, N.C.Mills, Harry A., and J. Benton Jones, Jr. 1996. Plant Analysis Handbook II, MicroMacro Publishing, Inc., Jefferson City, Mo.

Table 4. Guide for plant sampling of selected vegetables, fruits and trees.

Plant Stage of growth Plant part Number of plants

to sampleApples July 15 to August 15 Leaf from middle of current terminal shoot 60Asparagus Mature fern (August) Fern from 17 to 35 inches up 20Beans, snap Initial flowering Young mature trifoliate 50Beans, table Mature Young mature leaf 20Blueberries First week of harvest Young mature leaf 50Broccoli Heading Young mature leaf 15Cabbage Heads, 1/2 grown Young wrapper leaf 15Cantaloupe Early fruiting Fifth leaf from tip 25Carrots Midgrowth Young mature leaf 25Cauliflower Buttoning Young mature leaf 15Celery Half-grown Young mature leaf 20Cherry Summer Mature leaves from new growth 50Cucumbers Early fruiting Fifth leaf from tip 20Grapes Flowering Petiole from young mature leaf 75Lettuce Heads, 1/2 size Wrapper leaf 20Onions Midgrowth Top, no white portions 25Peaches/nectarines Spring at fruit set Midshoot leaf 20Peas First bloom Recently matured leaflet 50Pecan 56–84 days after terminal bud set Leaflet pairs from new growth 25Peppers Early fruiting Young mature leaf 20Plum Summer Whole leaf from midshoot growth 25Potatoes 40–50 days after emergence Young mature leaf 20Pumpkin/squash Early fruiting Young mature leaf 15Radishes Midgrowth to harvest Young mature leaf 40Raspberries First week in August Leaf 18 inches from tip 50Spinach 30–50 days old Young mature leaf 35Strawberries At flowering Young mature leaf 20Sweet corn Tasseling to silk Ear leaf 10Tomatoes First mature fruit Young mature leaf 20Walnut (black) Summer Mature leaf from new growth 5Walnut (English) Summer Center leaflet from mature leaf 25Watermelons Midgrowth Young mature leaf 15

growing well and from another area in which theplants are affected by a suspected nutrient disor-der. This comparison can assist in diagnosingspecific nutrient problems, especially when nutri-ent sufficiency ranges are not available for aspecific crop, growth stage or plant part. Planttissue samples from one plant may not be repre-sentative of all the plants in a field with a similarproblem. To obtain a representative sample, avoidcollecting plants that have insect damage, areinfested with disease, are covered with dust or soilor foliar-applied sprays, or are border row plants.If possible, take random plant samples fromseveral plants distributed throughout the affectedarea of the field.

Submitting samples for testingRemove any soil or foreign matter on the

collected plant material by wiping with a cleandamp cloth or rinsing directly with water whilethe material is still fresh. Place the collected planttissue samples in a clearly labeled paper bag. If theplant part is collected and stored in plastic bagsfor more than several hours, be sure to refriger-ate it to prevent the plant material from molding.Air dry the plant sample for 12 to 24 hours beforemailing it in an envelope or dropping it off at yourregional soil and plant testing laboratory or exten-sion office.

Maintain records of the sampling date, fieldlocation, submission date to the soil and planttesting laboratory and any prior results of tissueor soil testing. These records will help you tokeep track of your samples and assist you in moni-toring the effectiveness of your fertility manage-ment program over time.

Your regional soil and plant testing laboratorywill have forms for submission of samples forplant tissue testing (see the Plant AnalysisInformation Form for the University of MissouriSoil and Plant Testing Laboratory, page 18).Providing the requested information on the formsis crucial for interpreting analytical results fromplant tissue testing. You may wish to consult yourlocal or regional extension agent or the soil andplant testing laboratory as to the appropriateanalytical tests for your situation.

Interpreting the test reportYou will be sent your plant sample test results

within about five working days after the MU soiland plant testing laboratory receives your plantsamples (times may vary for other labs). An inter-

common agronomic and horticultural crops inMissouri. When the recommended plant part issampled at the designated stage of growth, the soiland plant testing laboratory can compare theresults of the tissue test with established nutrientsufficiency ranges for the crop.

If specific sampling instructions are not foundin the selected crops, the rule of thumb is tosample upper, recently matured leaves. Therecommended time to sample is just before thebeginning of the reproductive stage for manyplants. More specific information on plant tissuesampling procedures and available nutrient suffi-ciency ranges can be obtained by consulting yourregional soil and plant testing laboratory.

In sampling plants for tissue testing, it is crit-ical to obtain a representative sample. Take sepa-rate plant samples from an area in which plants are


Crop color can also be measured usinginstruments designed for this purpose. Thisapproach may allow greater sensitivity to smalldifferences in color, as well as making it easier tocollect enough color information to get a goodfield average. It can also be used to characterizethe spatial variability of crop color in support ofvariable-rate nitrogen applications. Several differ-

Nitrogen is one of the mostcommonly deficient plant nutrientsbecause large amounts of this

element are required to produce amino acids andproteins in the tissue and because nitrogen iseasily lost from the soil during wet conditions.Nitrogen-deficient crops are lighter green in colorthan healthy crops. The lighter the green, themore severe the deficiency and the more nitrogenfertilizer will be required to correct the deficiency.Crop color can be used as a guide to how muchfertilizer to apply to correct deficiencies.

There is also pressure, for environmentalreasons, to reduce overapplication of nitrogenfertilizer. Diagnosing nitrogen need from plantcolor has the potential to give accurate nitrogenrate recommendations that will ensure optimalcrop yield while reducing overapplication of N.

Measuring greennessThe simplest way to measure plant color is by

visual comparison to a color scale. The Universityof California has developed a leaf color chart tomeasure the “greenness” of crops (Figure 39),and has developed interpretations of the colorchart to guide midseason nitrogen applications forrice.


pretation of the results will also be included basedon crop and management information, availablenutrient sufficiency ranges, available soil testinformation, and (when paired samples aresubmitted) comparison of test results fromaffected and healthy areas (see the example of aplant tissue test report on page 14).

The sufficiency level for a particular nutrientmay depend on genetic and environmentalfactors. The sample from the healthy area of yourfield establishes the tissue nutrient levels neededfor healthy plants, given the genetics, soil type,and weather specific to your field.

Only nutrients with substantially differenttest levels between the affected and healthy areasshould be considered as possibly deficient andcontributing to the observed symptoms. If theobserved symptoms are typical for a particularnutrient deficiency, and if the tissue levels are

higher for that nutrient in the healthy area thanin the affected area, then deficiency of that nutri-ent is strongly indicated. For example, if brown-ing of the edges of older (lower) leaves is observed,and tissue potassium levels are higher in healthyplants than in affected plants, then potassiumdeficiency is a solid and convincing diagnosis.

If you do not submit healthy plants, theresults from your affected plants will instead becompared with a large database of tissue testresults for your crop to determine which nutrientsmay be deficient or excessive. Once a diagnosis ofnutrient deficiency is made, the appropriate nutri-ent may be applied immediately or for the nextgrowing season. Your local or regional extensionspecialist can assist you in understanding thereport and determining its significance for yourfuture management.

DIAGNOSING NITROGEN NEED FROM PLANT COLOR

Figure 39. Visual rating of "greenness" of corn plants with leaf color chart (scale 1 to 8).The row on the right did not receive nitrogen fertilizer. Preplant nitrogen fertilizer wasapplied in the left row.


Aerial imageryAerial images acquired with film or with digi-

tal image capture from satellites or airplanesprovide another way to measure crop color(Figure 43). This approach is particularly wellsuited for detecting for nitrogen deficiencies,because large areas can be examined quickly.Images are also well suited for detecting spatialpatterns of nitrogen deficiency and producingvariable-rate nitrogen recommendations.Experiments in Missouri have produced methodsfor interpreting images to produce nitrogen raterecommendations for corn, but capabilities for

ent types of instruments can be used in measur-ing crop color. One of the simplest is the MinoltaSPAD chlorophyll meter, a portable hand-helddevice that clamps over a leaf (Figures 40 and 41).This meter measures transmittance of red andinfrared light through the leaf and displays anumber that is proportional to the nitrogen andchlorophyll concentrations in the leaf. As with soilor tissue samples, numerous measurements spreadout evenly over the sample area must be taken toget a reliable average. Several states have devel-oped or are developing interpretations to convertmeter readings to nitrogen fertilizer recommen-dations.

RadiometryA spectral radiometer can also be used to

measure crop color. Most spectral radiometersmeasure light intensity over a range of visible andnear-infrared light wavelengths. One advantage ofspectral radiometers, relative to the chlorophyllmeter, is that they can be mounted on nitrogenapplicators (Figure 42). The color measurementsthen represent a much larger amount of planttissue, can capture spatial patterns in crop color,and can be used to guide variable-rate nitrogenapplications. Norsk Hydro manufactures a systembased on this concept for variable-rate nitrogenapplications to small grains.

The disadvantage of spectral radiometers isthat their readings are sensitive to sunlight inten-sity, sun angle, cloud cover and interaction of sunangle with plant geometry. A radiometer posi-tioned to measure the intensity of incoming light,as well as the light reflected from the crop, helpsto correct for these variations. Additionaladvances in these areas will improve the qualityof the nitrogen recommendations from spectralradiometers.

Figure 41. Hand-held devices such as a SPAD chlorophyllmeter can be used to monitor the nitrogen status of crops.

Figure 40. SPADchlorophyll meter.

Figure 42. A spectral radiometer mounted on a variable-rate applicator can reduce overapplication while deliver-ing nitrogen fertilizer where it is needed.

Figure 43.Aerial images can assist in detecting crop stresses,including nutrient deficiency. In Missouri, nitrogen deficiencyand waterlogging are the main causes of yellow-green corn.

Among the disadvantages of quick test kits istheir sensitivity to differences in types of plants,sample handling, and the time of day whensamples are taken. For example, time of day,temperature and cloudiness can affect the concen-tration of nitrate in plant sap and the calibrationof the instrument. For consistent results, samplesshould be collected at a standard time of day (10am to 2 pm) and taken indoors for analysis or ina shady area away from direct sunlight and wind.For woody plants, such as cotton, collecting suffi-cient sap to test can be a problem. Often it helpsto freeze the sample briefly because freezingbreaks down the cell walls and releases a largervolume of sap.

The usefulness of quick tests for plant nutri-ent management depends on the availability ofresearch-based information for interpretingnutrient concentrations in plant sap for specificcrops. In Misssouri, research is being conductedfor developing interpretation information fornitrogen and potassium readings from theCardy® meter for cotton. Interpretation tablesshould provide information that shows the rangesof deficient and sufficient nutrient concentra-tions for plant sap for the specific plant part andgrowth stage of the sampled crop.

Other disadvantages of many quick test kitsare a lack of quality control (e.g., use of standardsand blanks to ensure the test procedure is work-ing), dependence on a single supplier for newreagents and replacement parts for the kit, and theeffects of improper storage on the viability ofchemicals or strips used in the procedures.

acquiring and processing images and deliveringresults to producers in a timely manner remainlimited. It may be difficult to detect nitrogendeficiencies from aerial images before the crop hasa high percentage of ground cover.

Factors other than nitrogen deficiency cancause light-green or yellow-green coloration ofcrops. These factors include disease, insectdamage, herbicide damage, and deficiencies ofother nutrients. Automated sensors probablycannot detect the other features that allow thehuman eye to distinguish between these causes.Thus, these sensors are most suited to productionsystems in which nitrogen deficiency is by far themost common cause of light-green foliage. Thiswould be the case when a main part of the crop’snitrogen fertilizer requirement is to be appliedbased on color measurements. Humid regions,with greater potential for nitrogen loss and defi-ciencies, will be more suited to these tools thansemiarid regions. Soils with high pH may be lesssuited for these types of color measurementsbecause of relatively common micronutrient(iron, manganese, zinc) deficiencies that cause alight green or yellow-green color in the crop.

Other field quick testsNew technology and the need for rapid in-

field plant testing results have stimulated an inter-est in “quick test kits” for determining plant nutri-ent deficiencies. These kits often have theadvantages of being portable, less expensive thanstandard laboratory methods, and suitable for useby growers and consultants without extensivelaboratory training.

Extensive research has been conducted, espe-cially among horticultural crops, on several quicktest procedures, including the measurement ofnitrate and potassium in plant sap as indicators ofplant nitrogen and potassium nutrition.Concentrations of nitrate and potassium areusually measured with an ion-selective electrode(for example, the Horiba Cardy® nitrate or potas-sium meters, Figure 44) or by use of colorimet-ric test strips (for example, Merckoquant® nitratetest strips). With the ion-selective electrode,nitrate or potassium concentrations are deter-mined based on readings from standard solutionsof known concentrations. For test strips, a cali-brated color chart or a strip color reader can beused to estimate the color intensity, which is thenconverted to nutrient concentrations based oninformation supplied with the kit.


Figure 44. Using a Cardy® meter to test nitrate in cotton plants begins with extractingsap from cotton petioles with a garlic press.


Plant AnalysisSoil and Plant Testing Laboratory23 Mumford Hall, University of MissouriColumbia, MO 65211573-882-0623 Fax: 573-884-4288

(Please type or print) Lab # Lab Use Only

Date Sampled _______/_______/_______ Date ReceivedName Firm submitting Address Address (City) (State) (zip code) (City) (State) (zip code)Tel: Fax: Tel: Fax: e-mail address e-mail address County to be billed & Code___________________ Firm # Outlet #

Sample identification Crop Field I.D. Previous Crop Stage of Growth Accompanied by soil sample? Yes_______ No_____Moisture If Yes: Serial # When last limed Soil Test ResultsPosition on landscape N P K Ca Fertilizer applied Mg pH OM CEC Other:

Description of problem:

Check Tests Desired for this sample Analysis Cost Total Cost Regular Analysis: Nitrogen, phosphorus, potassium,

calcium and magnesium + drying and/or grinding $17.00

Micronutrients: (with regular analysis)Fe, Zn, Cu, Mn

$6.00($1.50 per micro-nutrient)

Analysis Package: (Regular+Micronutrients+Boron) N, P, K, Ca, Mg, Fe, Cu, Zn, Mn, B $25.00

Individual analyses (per nutrient)Nitrogen (TKN) $10.00Phosphorus (P) $5.00Potassium (K) $5.00Calcium (Ca) $4.00Magnesium (Mg) $4.00Iron (Fe) $4.00Copper (Cu) $4.00Manganese (Mn) $4.00Zinc (Zn) $4.00Sulfate-S $6.50Nitrate-N $8.00Boron (B) $5.00Chloride $6.50Sample Grinding $2.00

Total Due for this sample

We encourage a plant sample be taken from a poor growing area and compared to a sample from an adjacent normal area. Thetesting fee for a good sample accompanying an abnormal sample will be analyzed at one-half the regular price. Samples will bediscarded after 30 days unless other arrangements are made. November 2000

For further information

Available from Extension Publications 1-800-292-0969XPLOR [Extension Publications Library on Request] on the Web at http://muextension.missouri.edu/xplor/

EC929 – Micro and Secondary Nutrients in MissouriG9110 – How to Get a Good Soil SampleG9112 – Interpreting Missouri Sil Test ReportsG9174 – Nitrogen in Missouri SoilsG9175 – Nitrogen Management for Conservation Tillage in MissouriG9180 – Phosphorus in Missouri SoilsG9185 – Potassium in Missouri SoilsG9804 – Nitrate in Soils and PlantsMP729 – Use of a Portable Chlorophyll Meter to Manage Crop Nitrogen in RiceNCR326 – Management of Urea Fertilizers

Other publicationsAmerican Phytopathological Society. Nutrient Deficiencies and Toxicities of Plants

CD-ROM. Web address for ordering: http://www.scisoc.org/apspress/Bennett, William F. 1993. Nutrient Deficiencies and Toxicities in Crop Plants. American

Phytopathological Society (APS). Web address for ordering:http://www.scisoc.org/apspress/.

Mills, Harry A., and J. Benton Jones, Jr. 1996. Plant Analysis Handbook II. Micro-Macro Publishing, Inc. Phone number for ordering: 1-800-500-4635, email forordering: [email protected].

Potash and Phosphate Institute. 1999. Nutrient Deficiency Symptoms CD-ROM.Phone number for ordering: (770) 447-0335, e-mail for ordering:[email protected].

■ Issued in furtherance of Cooperative Extension Work Acts of May 8 and June 30, 1914, in cooperation with the United States Department ofAgriculture. Ronald J. Turner, Director, Cooperative Extension, University of Missouri and Lincoln University, Columbia, MO 65211. ■ UniversityOutreach and Extension does not discriminate on the basis of race, color, national origin, sex, religion, age, disability or status as a Vietnamera veteran in employment or programs. ■ If you have special needs as addressed by the Americans with Disabilities Act and need this publi-cation in an alternative format, write ADA Officer, Extension and Agricultural Information, 1-98 Agriculture Building, Columbia, MO 65211, orcall (573) 882-7216. Reasonable efforts will be made to accommodate your special needs.

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