Interpretation of leaf nutrient analysis results

Brassica crops are noted for their susceptibility to deficiencies of nitrogen, boron and molybdenum and,increasingly, sulphur. Both yield and marketable quality can be affected by these and other nutrient deficiencies.If the nutritional status is below the ‘critical level’, visual symptoms will be present in the field. In the absence ofvisual symptoms, ‘subclinical’ deficiencies or toxicities may be present which will reduce growth andsubsequently yield.

This factsheet aims to:• Assist with the diagnosis of the most common visual deficiency symptoms • Provide guidance on sampling plants so that meaningful results are obtained• Provide guidance on interpreting leaf tissue analysis results• Provide information on managing nutrient deficiencies

Don Tiffin, ADAS Boxworth

Factsheet 21/05

Brassicas (cabbage, Brussels sprouts, cauliflower, broccoli, turnip and swede)

HorticulturalDevelopmentCouncil

Bradbourne House

East Malling

Kent ME19 6DZ

T: 01732 848383

F: 01732 848498

E: hdc@hdc.org.uk

disorders. There are, however, severaldifficulties in relying solely on visualsymptoms:

• Severe deficiencies are rare

• Crop disorders induced by non-nutritional factors such asdrought, low temperatures,

herbicides, pests and diseases or even air pollutants may result in symptoms that can be mistaken for nutrient disorders

• More than one nutrient may be deficient causing differentsymptoms from those caused by a single nutrient

Visual symptomsVisual diagnosis of nutrient disorderscan be made where specificsymptoms of deficiency and toxicityhave been accurately described anddocumented. It is the quickestmethod for diagnosing the cause ofpoor crop performance due to nutrient

Nutrient deficiencysymptoms The diagnosis of a nutrient disorder in the field should follow clearlydefinable steps:1 Realisation that something is wrong

with the crop2 Observation of abnormalities,

noting if these are worse on older or younger leaves; chlorosis orinterveinal yellowing; marginalscorch around leaf edges, necrosisof leaf tissue; pattern of distribution;deformities such as cupping,twisting and thickening

3 Relate a particular disorder to thefield circumstances e.g. soil type or pH

4 Knowledge of susceptibility of a brassica crop to that disorder

5 Consider the possibility ofsymptoms having arisen from other causes such as drought,waterlogging, etc

6 Identification of possible causes by use of photographs illustratingnutrition deficiency

7 If doubt still remains, checkdiagnosis by means of leaf analysis

Photographs of nutrientdeficiencies in brassicasNote: Not all deficiencies produceclear field symptoms. Photographsare helpful in providing a visualdiagnosis, but may be slightlyambiguous. ‘A colour illustrated guide to pests, diseases anddisorders of vegetables’, a CD-ROMthat contains further images andinformation on vegetable nutrientdeficiencies is available from HDC. If in doubt, confirm diagnosis with leaf analysis.

Nitrogen (N)Deficiency symptoms:Marked reduction in growth with erectand thin stems. Leaves turn palegreen, becoming yellow, bronzed,pink or purple as the leaf ages, withleaf abscission in extreme cases. Inturnip, cauliflower and young swedesthe predominant colour change is toyellow-orange. In cabbage, broccoli,Brussels sprouts and older swedes,

this also occurs but is often precededby a muddy-purple flush on the olderleaves. In broccoli, cabbage, Brusselssprouts and cauliflower the newleaves can have a particularly grey,stiff, waxy appearance.

Occurrence:Very common whenever insufficientN available especially on sandy soilsfollowing heavy rainfall, where

excessive leaching or waterlogginghas occurred.

Similar symptoms:May also be induced by other factorssuch as cold weather, drought stress,root damage from nematodes andwater logging. Sudden cold and Pdeficiency can produce purple tints.

Phosphorus (P)

Nitrogen – deficient cabbage showing overall

pale colour and purple tinge on old leaves*

Nitrogen – Brussels sprout seedling showing

grey–green waxy new leaf and bronzed

cotyledons*

Nitrogen – turnip showing yellowing of older

leaves and pink petioles*

Deficiency symptoms: Reduction in growth but with scarcelynoticeable foliage symptoms. Possibilityof abnormally stiff and erect plants inbroccoli and cauliflowers. Older leavesbluish green with dull purple tints, similarto nitrogen deficiency but withoutyellow-orange colours. Cauliflower mayhave reddish curds.

Occurrence: On acid soils, calcareous soils or peatswhere levels of plant available

Phosphorus – dull purple flush on swede leaf*Phosphorus – red curd and stiff, pointed,

purple edged leaves in cauliflower*

Magnesium (Mg)

Potassium (K)Deficiency symptoms:Leaves bluish green. Marginal andinterveinal scorch and some blotchychlorosis of older leaves. Tissuecollapse can occur, with scorchededges of leaves curling forwards.

Occurrence: On sandy soils inherently low in K andprone to leaching where insufficient Kapplied in the base dressing.

Similar symptoms: Marginal scorch of lower leaves canbe confused with chloride toxicity andwind damage.

Potassium – scorched leaves from deficient

cabbage*

Potassium – turnip showing tissue collapse

and scorch confined to top half of leaf*

Deficiency symptoms: A chlorotic marbling, which maybecome very striking, occurs on olderleaves whilst main veins remain green.The chlorosis may be accompaniedby a blotchy purple colour, especiallybetween veins, near margins and onthe underside of the leaf. Towardsmaturity other brilliant orange and redtints may occur particularly incauliflowers. In turnip the leaf marginsmay initially remain green whereassome swede varieties show a blotchyreddening moving in from the olderleaf margins. Older leaves of plantsmay wither and die.

Occurrence: On acid soils, on soils with very highextractable potassium/magnesiumratios particularly if soil compaction ispresent, or on very sandy soilssubject to leaching after heavy rainfall.

Similar symptoms: Easily confused with N deficiency andmanganese deficiency. Symptoms ofMg deficiency can occur as a result ofrestricted root growth, commonly dueto soil compaction or prolongedwetness. Also frequently associatedwith low spring temperatures. Some resemblance to cauliflowermosaic virus symptoms and in turnipsbeet western yellows virus.

Magnesium – deficiency in swede showing

blotchy reddening moving in from leaf edge*

Magnesium – deficiency in cauliflower, older

leaves chlorotic marbling followed by strong

orange, red & purple tints

Magnesium – turnip with leaf margin initially

remaining green*

Magnesium – field view at harvest of

deficient crop

phosphate are low. Temporary deficien-cies can occur on cold, wet soil.However occurrence is rare becausemost vegetable growing soils containgood levels of plant available phosphate.

Similar symptoms: Low temperatures and drought cancause similar symptoms. N deficiencymay also produce purple tinting whichmay give leaves a very dull appearance.

Deficiency symptoms:Deficient plants are typically small and spindly characterised byinterveinal chlorosis of the young and middle leaves that cup bothconcavely (mainly while emerging) and convexly, and may become brittleand eventually may fail to grow. Thechlorosis is very characteristic in thatthe veins stand out as a ratherblurred, blue-green pattern against a pale green background. On theunderside of the leaf these dark areasare purple, and this purple or bronzecoloration may later affect whole

leaves. Symptoms tend to developslowly. In Brussels sproutscharacteristic symptoms are yellowingtops and restricted rooting.

Occurrence: S deficiency can occur on all soiltypes, but is more likely to be aproblem on light textured soils whereleaching occurs or on thin soilsoverlying chalk and low in organicmatter. Heavier textured soils such asclays and clay loams are unlikely tosuffer from S deficiency, as is any fieldhigh in organic matter or receivingfrequent applications of animal

manures. Areas away from heavyindustry or centres of population arelikely to be at risk from deficiency andinclude East Anglia and Lincolnshire,the south-west, Lancashire, theScottish borders and eastern Scotland.

Similar symptoms: Distinguished from magnesiumdeficiency in that chlorosis is on youngleaves, and accompanied by cuppingand distortion of these leaves.Symptoms can be distinguished fromnitrogen deficiency by the fact thatthey occur on younger leaves.

Sulphur (S)

Sulphur – four week old sprouting broccoli

with fourth leaf (bottom right) showing

characteristic chlorosis*

Sulphur – turnip showing chlorosis and

necrosis moving in from leaf tip*

Sulphur – deficiency in Brussels sprouts

showing yellowing of top of plant

Deficiency symptoms: Cupping, distortion and tipburn ofyoung leaves, which may lead to deathof growing point. Frequently it appearsas though a string had been threadedaround the leaf edge and drawn tight,causing the leaf to crinkle and cupdeeply (as in Brussels sprouts) orbuckle upwards, so that the ‘cup’begins to turn itself inside out. Anothercommon symptom is tissue collapsethat occurs in bands across leaves, sothat the distal part of the leaf hangsdown and eventually shrivels up. Thecollapsed zone may also occur at theleaf edge. In turnips, the collapsebegins with yellowing. In Brusselssprouts, a commercially importantphysiological disorder known as

Calcium (Ca)

Calcium – buckling and cupping of leaves*

Calcium – tissue collapse in five week old

cabbage*

Calcium – ‘internal browning’ in Brussels

sprouts*

‘internal browning’ has been attributedto calcium deficiency and similarly,internal tipburn of stored cabbage.

Occurrence: Not related to soil type but can beassociated with rapid growth in hot,humid weather, excessive soluble saltsand soil compaction. This deficiency israrely due to an absolute lack ofcalcium, problems occur when calciummovement in the transpiration streamtowards susceptible tissue is low.

Similar symptoms:Frost damage

Deficiency symptoms: An interveinal chlorotic yellow oryellow-white marbling (‘freckled’ or‘speckled’ appearance) of the olderleaves is the first symptom to appear.This can be confused with magnesiumdeficiency but manganese deficiencyusually produces a finer moreintensely yellow mottle. In severecases the whole of the leaf maybecome almost bleached and somenecrosis may develop. Severelyaffected plants are stunted in growth.

Occurrence: Frequently induced by overliming.Most severe problems occur onorganic and peaty soils with a pHabove 6.0. Deficiency is generallyless severe on sands and loamysands. Symptoms are often transientand may disappear following rain.

Similar symptoms: Symptoms may be masked by anadditional stress factor such asdisease, herbicide damage, and other

Manganese (Mn)

Manganese – sprouting broccoli showing

bleaching of young leaves, pink tinges on

petioles, veins & leaf edge*

Manganese – severe interveinal chlorotic

marbling and necrosis

plant nutrient deficiencies or frostdamage. Can be confused withmagnesium deficiency. May beconfused with cauliflower mosaic virus.

Deficiency symptoms: Brassica crops are sensitive to borondeficiency and exhibit numerous verycharacteristic symptoms, but not alloccur on all species. For all crops thefirst symptoms may be rolling andcurling of the leaves that becomebrittle and are mottled round themargins. Cracked and corky stems,petioles and midribs can occur on allbrassica species.

Cabbage: Small blister-like swellings appear onthe stem and lower surface of the leafstalks. The stem is frequently hollowand discoloured internally with brownwatery areas in the pith. Premature fall

of older leaves may occur and headsare often yellow and small whendeficiency is severe.

Brussels sprouts: Interveinal chlorosis, worst on oldleaves. Hollows also found in thestems. Brussels sprout plants willproduce few sprouts if the deficiencysets in before they are formed: ifdeficiency occurs later, the sproutswill be small and loose.

Cauliflower: Cotyledons may grow very large withsubsequent very thick, brittle, finger-like new leaves. The stem is frequentlyhollow and discoloured internally nearthe curd. If the deficiency appears

before curd formation the stem stopsgrowing, causing a flat-topped plantwith many side shoots and the curdfails to develop. In contrast if the curdis already present the curd turns brown giving a discoloured productunsuitable for marketing.

Broccoli: First symptoms similar to those forcabbage but chlorosis is marginal, withbrilliant red and yellow colours.Premature fall of older leaves may occur.

Turnip and swede: If the deficiency occurs at the seedlingstage, the new leaves show convexcupping, marginal chlorosis withbrilliant red and orange colours. Later

Boron (B)

outside may take on a rough, corky,leathery appearance. This conditionis commonly known as ‘brown heart’or ‘raan’.

Occurrence: Boron deficiency is more likely to occuron sands, loamy sands and sandyloams that have been limed recentlyrather than those which are naturallyalkaline, and particularly when the soilpH is raised above pH 6.5 and moreusually over pH 7.0. Since boron iswater soluble and readily leached fromsandy soils, deficiency is more commonfollowing a wet winter and spring, andparticularly in dry summers.

Similar symptoms: Most incidences of hollow stems inbrassicas are associated with irregularwater supply resulting in unevengrowth. Excessive nitrogen maysometimes be involved in thissymptom. Likewise cracking may bephysiological in origin and occur inwet seasons or when dry weather isfollowed by wet weather thus causinga spurge of vegetative growth. Alsocracking and corkiness on stems andpetioles can result from the action ofgrowth regulator type herbicides.Growing point injury can be due toinsect attack e.g. swede midge.

on yellow and purple areas on theleaves of turnips are often associatedwith the deficiency. The growing pointdoes not normally die in field crops,but some of the consequences of itsmoribund condition may appear e.g.multiple crowns. Boron deficiencycan exist without any externalsymptoms. It is often only noticedwhen roots are cut open and brownwater-soaked areas are found atirregular intervals, normally in theouter regions of the root. In thesecircumstances the central tissue maybreak down and the root becomesincreasingly hollow, fibrous, bitter andinvaded by rotting organisms. The

Deficiency symptoms: Almost unknown though cabbagemay show faint diffuse interveinalchlorosis of expanding and matureleaves with withering. In turnipsdeficiency can cause severe yellowingof the foliage which also developsyellowish-white spots. There isconsiderable stunting of roots.

Occurrence: Copper deficiency has only beendiagnosed in a few specific soilsituations. It could occur on peats andoccasionally on loamy peats, mainly inthe Fens and also on leached sandysoils, particularly reclaimed heathlandand thin organic soils over chalk.

Zinc (Zn)Deficiency symptoms: Extremely rare in the UK. Expandingcabbage leaves cupped with out-curvedmargins and interveinal bronzing ofolder leaves.

Occurrence: Associated with coarse sandy soilsthat are high in pH. Excessivephosphate applications may inducethis deficiency.

Boron – rosetting of cabbage* Boron – convex cupping at the seedling stage*

Boron – 14 week old Brussels sprout showing

misshapen leaves with several forms of

interveinal chlorosis

Boron – left and centre swede roots showing

‘brown heart’. Note discoloration and hollow

below crown of centre root. Healthy root

on right*

Boron – cauliflower longitudinal section

showing browning of curd and lesions in pith

(not specific for boron; may be due to other

causes in the field)

Copper (Cu)

Iron (Fe)Deficiency symptoms: Very rare in brassica crops. Youngleaves turn yellow and later virtuallywhite, with some green colourremaining along midrib and mainveins. In turnip and swede chloroticmottling of all foliage. Disorder veryunlikely except as a result of heavymetal toxicity.

Occurrence: Can occur on soils containing freecalcium carbonate particularly ifpoorly drained.

Similar symptoms: Manganese deficiency may resembleiron deficiency but would be on older leaves.

Molybdenum (Mo)Deficiency symptoms:Of the brassica crops, cauliflower(both summer and winter) is the mostsensitive to molybdenum deficiency.Other brassica species are notnormally affected. The characteristicsymptoms in cauliflower are known as‘Whiptail’. Growth of the leaf laminaris severely restricted giving narrowstrap-like inward cupping of theleaves. The remaining lamina isirregular in outline, puckered, greatlyreduced in area and brittle. Growingpoint becomes blind or stub-like andnew shoots may appear fromhypocotyl.

Occurrence: Molybdenum deficiency only occurson acid soils as this nutrient is moreavailable at higher pHs. If soil pH is6.5 or higher it will not be a problem.

Why analyse leafsamples?There are two reasons forrecommending the use of leaf analysisin brassica crops:

• To confirm a diagnosis based on theappearance of symptoms: in suchcases the leaf nutrient concentrationswill usually be well below the ‘criticallevel’ and there should therefore belittle doubt about the diagnosis.

• To test for ‘subclinical’ deficienciesor toxicities which may be alreadylimiting growth but which are notyet resulting in visible symptoms.

Guidance on methods ofcrop foliage sampling fornutrient analysis

It is essential to collect leaf samplesthat accurately reflect the nutritionalstatus of the crop submitted foranalysis. Therefore to adequately

represent any field or smaller area of crop, the following samplingprocedure should be followed:

• sample at the crop stage indicated in table 1 (unless thesample is for the confirmation of a deficiency)

• for each plant take the youngestmature leaf

• if there is a clear differentiationbetween ‘good’ and ‘poor’ crop,

Similar symptoms:Blindness of the growing point, withsome swelling of the surroundingpetiole bases, can also be caused bypreceding sub-zero temperatures, orby swede midge attack. In the lattercase very small white larvae should

Iron – deficiency in Savoy cabbage showing

severe chlorosis of leaves beginning as a

chlorotic mottling

Iron – deficiency in turnips showing chlorotic

mottling of leaves

be present on the petioles. Bothdisorders are distinct from whiptail inthat leaf shape is unaffected. Cuppingof leaves with mottled margins can beconfused with manganese toxicitywhich is the main symptom of soilacidity.

Molybdenum – ‘whiptail’ in cauliflower* Molybdenum – plant showing signs of

recovery of new growth*

* of limited use as even the smallest amount of soil contamination invalidates the analysis and the deficiency may not be related to actual content.

collect a second sample of leavesfrom the ‘good’ crop

• sample 20–30 plants to provide aminimum of 250 g of fresh material

• sample the crop following a ‘W’pattern,collecting leaves at regular intervals

Do not sample• diseased or dead plant material

• plant tissue damaged by insectsand mechanical equipment

• plant tissue which has beenstressed by excesses of cold, heat or moisture

• plant tissue within 10 days of foliar application of nutrients or fungicides

When sending samples to ananalytical laboratory:• ensure there is sufficient plant

material, a minimum of 250g offresh material

• avoid soil contamination

• ensure that the sample isrepresentative of the crop/area

Crop

Cabbage

Brussels sprouts

Cauliflower

Broccoli

Turnip and swede

Growth Stage

mid growth – as the plant is beginning to heart

mid growth – as the plant initiates the first buttons

first indication of buttoning

mid growth – when first spears are starting to form

first indication of root swelling

• include all relevant documentationand background information(sowing/planting date, variety, fieldname, growers details, etc)

• pack the sample, typically in a JiffyBag, so it arrives in the bestpossible condition

• do not post fresh material in anairtight container

• label each sample clearly

• avoid sending samples beforeweekends and bank holidays

• send by overnight courier or deliverdirectly to the analytical laboratory

Precise and meaningful analyticalresults are only possible whencarefully selected plant materialis submitted for analysis.

Element

Nitrogen

Phosphorus

Potassium

Magnesium

Sulphur

Calcium

Manganese

Boron

Copper

Zinc

Iron*

Unit

%

%

%

%

%

%

mg/kg

mg/kg

mg/kg

mg/kg

mg/kg

Cabbage

3.0–5.0

0.3–0.5

3.0–4.5

0.2–0.7

0.3–0.8

1.5–3.0

25–200

25–60

5–20

20–200

50–200

B Sprout

3.0–5.0

0.26–0.6

2.5–4.0

0.2–0.7

0.3–0.8

0.5–2.0

25–200

25–60

5–20

20–200

50–200

Cauliflower

3.0–5.0

0.3–0.7

3.0–4.0

0.2–0.7

0.3–0.8

1.0–2.0

25–200

25–60

5–20

20–200

50–200

Broccoli

3.5–5.5

0.3–0.7

2.0–4.0

0.2–0.7

0.3–0.8

1.2–2.5

25–200

25–60

5–20

20–200

50–200

Turnip

3.5–5.0

0.3–0.7

2.5–5.0

0.3–0.6

0.35–0.8

1.8–4.0

30–300

30–150

5–25

20–100

50–150

Table 1

Table 2

Interpretation of leaftissue analysis results

Interpretation of laboratory results ispossible by comparison with normallevels expected for the crop. Theinterpretations given here are basedon the best information available.

Soil Nutrition

Though soil nutrition is outside thescope of this factsheet, growers are

advised to consult and act upon thenutrition requirements and fertilisermanagement for brassicas crops in‘Fertiliser Recommendations forAgricultural and Horticultural Crops(RB209)’, PLANET NutrientManagement software or theappropriate crop protocols.

All brassicas, and in particularcauliflower, have a high fertilityrequirement though Brussels sproutsare less likely to develop deficienciesthan other brassica crops. Turnipsand swedes have a lower fertilityrequirement than other brassica

crops. Brassicas are noted for theirdeficiencies of nitrogen and boron (orpseudo boron deficiency caused bygrowing conditions), and theincreasing possibility of sulphurdeficiency. Cabbages are also fairlysusceptible to deficiencies of calciumand magnesium. Turnips and swedesmay be prone to deficiencies ofphosphorus and potassium becausethey are often grown on less fertilesoils, also to boron as they have in thepast been grown on more acid soils.

Strategy andspecific actionto rectify nutrientdeficiencies

As deficiencies normally occurindividually, specific treatmentsshould be applied to the soil or cropfoliage as appropriate to remedy aproblem in a particular field.

All trace elements, except ironwhich is never a problem, can beapplied as simple salts, usually asfoliar sprays, though soil treatmentsare preferable for boron andmolybdenum These treatments arecost effective, although more than onespray may be needed for manganese.

Multi-element sprays may notcontain enough of a particularelement to correct a deficiency, andwhere no deficiency exists,application can be wasteful.‘Insurance’ treatments are notrecommended where no deficiencyhas been identified, but wheredeficiencies are known to occurprophylactic sprays may be used.

Nitrogen (N)Leaf analysis is valuable for theconfirmation of plant N status.Treatment is usually by addition of Nfertiliser at the appropriate rate andtime to the soil and plant response tonitrate is very rapid except when thesurface soil is very dry. Foliarapplications of N are sometimes usedas a ‘fire brigade’ treatment; foliarsprays of ammonium and nitrate saltscan cause leaf damage except at very

low concentrations. Urea may beused but there is still a risk of scorch.

Phosphorus (P)Most soils have adequate P suppliesand there should never be a need toapply a foliar spray of P if notice istaken of soil analyses results. Foliarfeeding is not recommended becausethere is a high risk of leaf scorch.

Potassium (K)Soil applications of potassium fertiliseraccording to crop requirement, basedon soil analysis, should mean that Kdeficiency is not seen in brassicacrops. Foliar feeding is notrecommended because there is a highrisk of leaf scorch.

Magnesium (Mg)The application of magnesium fertiliserto the soil is a more effective long-term method for controlling thedeficiency than the foliar application ofa magnesium salt. The latter methodhowever is useful when crops developsymptoms during the growing season,as a spray containing Mg can oftengreatly improve the appearance andmarket value of the crop though theremay be little affect on yield. Symptomsof Mg deficiency can occur as a resultof restricted root growth, commonlydue to soil compaction or wetness andfrequently associated with lowtemperatures in the spring. Foliarsprays of 20 kg/ha magnesiumsulphate (Epsom salts) plus wetter in500 l water may accelerate recovery.

Sulphur (S)All brassica crops are increasingly atrisk due to lower S inputs. S

deficiency symptoms are more likelyto be seen in soils low in organicmatter (sulphur is mineralised fromorganic matter) and light textured soilsas sulphur can be leached. Plantanalysis is generally considered amore reliable tool for diagnosis of Sdeficiency than soil testing. Wherereserves of sulphur are low and cannotbe maintained, fertilisers containingsulphur should be used. Sulphur canbe absorbed through leaves so foliarapplications may be useful, but cannotbe guaranteed to cure a problem. Todate, sulphur deficiency has beendetermined by using tests based ontotal S, sulphate – S or a N:S ratio. Forexample, plant material samples withan N:S ratio of >16:1 are deficient andhighly likely to respond to a sulphurapplication. Plant material with an N:Sratio of between16:1–13:1 may benefitfrom an insurance dressing, and aratio of <13:1 is satisfactory andunlikely to suffer sulphur deficiency.Recently a new test based onmalate:sulphate ratio has beendeveloped and experience in cerealsand oil seed rate shows it to be abetter indicator of S deficiency. It isrecommended that N:S ratios shouldbe monitored as applications ofsulphur to growing crops onceproblems have been seen is notguaranteed to solve the problem.

The sulphur containing compounds‘glucosinolates’ are an importantcomponent of flavour in brassicas andsome have beneficial health effectsfor humans, these compounds arealso part of the plant’s own protectionsystem against some pests.

Calcium (Ca)Ca is a major nutrient and providedsoil pH is satisfactory there should bealways be a good supply to brassicas.If Ca problems occur it is generallynot an absolute deficiency but ratherthe lack of movement of the elementwithin the plant, due to water stress,so it is the youngest tissues which willsuffer. Foliar sprays of Ca have notbeen found to be useful but irrigationmay be helpful.

Boron (B)Soil analysis should be used toassess the boron need for susceptiblecrops such as swedes grown onsandy soils. Plant analysis can beused to complement visual diagnosisbut often by the time symptoms ofdeficiency are seen it is too late toapply a remedial treatment. If foliarsprays are required, apply 5–10 kg/haSolubor in at least 250 l water at anearly crop stage, the amountdepending on the severity of thedeficiency as measured by analysisand the crop requirement.

Copper (Cu)As there is often only a slightdifference in the copper content ofhealthy and deficient plants, plantanalysis has been of much less valuein diagnosis than soil analysis. Thedisorder can be treated by application

of Cu compounds to soil using coppersulphate or by foliar sprays of copperoxychloride or cuprous oxide at 2 kg/ha.

Manganese (Mn)Diagnosis is often possible by visualsymptoms and leaf analysis is a usefulaid when in doubt. Soil analysis is ofno practical use. Response to a foliarspray of manganese sulphate is rapidand reliable and the spray should beapplied as soon as symptoms areseen. The normal application rate is4.5 to 9 kg/ha of manganese sulphateplus wetter in at least 250 l water. Therate of application used should matchthe severity of deficiency, the risk ofleaf scorch which may occur if cropsunder moisture stress are sprayed inbright sunshine, and field conditions.More than one spray may benecessary. Avoid over limingparticularly on organic or peaty soils,for example where lime is applied forclubroot control.

Zinc (Zn)Leaf analysis is the most useful aid todiagnosis, but commercial incidencein brassica crops is extremely rare.

Iron (Fe)Very unlikely in brassica crops in theUK. Soil and plant analysis offers littlehelp in diagnosing deficiency, asresults are difficult to interpret due to

the presence of physiologicallyinactive forms of iron within the tissue.Also, soil contamination of leavesgrowing close to the ground mayelevate total iron results.

Molybdenum (Mo)Soil and plant analysis are difficult andnot usually necessary, since thedeficiency can be identified by plantsymptoms. Adequate and even limingto pH 6.5 will generally prevent thedeficiency occurring on a field scale.Soil treatment with sodium orammonium molybdate at 300 g/ha isrecommended or a foliar drench at0.25 g/l if deficiency occurs in theplant raising stage, though all modulecomposts should contain sufficientMo for good growth.

Always check compatibility ifmixing nutrients withagrochemicals

Toxicities Leaf analysis can be used to confirmtoxicities of boron and manganese,but is of less use for heavy metals. Manganese toxicity can occur in acidsoils especially those low in organicmatter. Symptoms are concavecupping of leaves, particularly middleto old leaves, and a pale ‘rim’ roundleaf edges, followed by marginalspotting and scorching.

Boron toxicity is occasionally foundas a result of application of too muchB. Symptoms are marginal chloroticband on old leaves.

Copper should not be applied tosoils without a demonstrated need bymeans of soil and plant analysis. Toxiceffects from over-application can lastmany years.

Chloride toxicity causes marginalleaf scorch, abscission and chlorosis

and is usually associated withirrigating with saline water.

Analytical laboratoriesIt is not possible within this factsheetto list all the laboratories that offera leaf tissue analysis service. Growersshould discuss the options with theiragronomist or crop protectionconsultant.

AcknowledgementPhotographs marked * are courtesy ofand copyright of Warwick HRI.

Manganese toxicity showing restricted lateral

growth of leaf laminae and incurling and

brown spotting of margins

Additional information:

August 2005

Whilst publications issued under the auspices

of the HDC are prepared from the best available

information, neither the authors or the HDC can

accept any responsibility for inaccuracy or

liability for loss, damage or injury from the appli-

cation of any concept or procedure discussed.

© 2005 Horticultural Development Council.

No part of this publication may be reproduced in

any form or by any means without prior permis-

sion of the Horticultural Development Council.

Design and production: HDR Visual Communication