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Nutrient solution growth ofsorghum and corn in mineralnutrition studiesRalph B. Clark aa U.S. Department of Agriculture, AgriculturalResearch Service , University of Nebraska,Department of Agronomy , Lincoln, NE, 68583Published online: 21 Nov 2008.

To cite this article: Ralph B. Clark (1982) Nutrient solution growth of sorghumand corn in mineral nutrition studies, Journal of Plant Nutrition, 5:8, 1039-1057

To link to this article: http://dx.doi.org/10.1080/01904168209363037

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JOURNAL OF PLANT NUTRITION, 5(8), 1039-1057 (1982)

NUTRIENT SOLUTION GROWTH OF SORGHUM ANDCORN IN MINERAL NUTRITION STUDIES

KEY WORDS: Sorghum bicolor (L.) Moench, Zea mays L., Water c u l t u r e ,Solution c u l t u r e , Hydroponics, Nutrient solution pH, NO3/NH4 in so l u t i o n s , P t o x i c i t y .

Ralph B. Clark

U.S. Department of AgricultureAgricultural Research Service

Department of AgronomyUniversity of Nebraska

Lincoln, NE 68583

ABSTRACT

The growth of plants in n u t r i e n t solutions i s an invaluable toolfor mineral n u t r i t i o n s t u d i e s . Successful growth of plants in n u t r i e n tsolutions require special attention and consideration. Details andhelpful ideas for the growth of plants in nutrient solutions are oftenomitted in publications where techniques like these are used. Theobjective of this report is to focus on some of the concerns, succes-ses, experiences, and problems noted for the growth of sorghum and cornin nutrient solutions. Topics discussed are nutrient solution compo-s i t i o n , pH of nutrient solutions, phosphorus concentrations, sourcesof Fe in solutions, plus several suggestions and comments for success-ful growth of sorghum and corn in nutrient solutions.

INTRODUCTION

Plants have been grown in nutrient solutions for many years. Ahi s t o r i c a l background of many of the early experiments using thesemethods and many of the advances made with time are discussed by Hewitt(1966). Many of the problems and experiences, as well as d e t a i l s , ofgrowing many plants by nutrient solution are described in this volume.

Published as Paper No. 6754, Journal Series, Nebraska Agricultural Ex-periment Station.

1039

Copyright © 1982 by Marcel Dekker, Inc.

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1040 CLARK

Growing plants in nutrient solutions has both advantages anddisadvantages. One major advantage is that the composition of thegrowth medium can be carefully defined and controlled compared toso i l s . Another advantage is that roots can easily be studied andincluded in analyses. Disadvantages of nutrient solutions are thatplants require more care, frequent replenishment of the medium may berequired, and the system may be somewhat a r t i f i c i a l compared to fieldconditions where plants are normally grown. Since some researchrequires that specific factors be controlled more carefully and theeffects of other factors eliminated as much as possible, plants arecommonly grown in nutrient solutions. This is of special importance inmineral nutritional studies• Without nutrient solutions, much of theinformation on individual mineral element effects on plant growth andmetabolism would be unavailable. Nutrient solution culture of plantshas been and will continue to be invaluable in mineral nutritionstudies.

The objective of this a r i t c l e is to relate some of the approachesand experiences noted for growing sorghum [Sorghum bicolor (L.) Hoench]and corn (Zea mays L.) in nutrient solutions in mineral nutritionstudies.

NUTRIENT SOLUTION COMPOSITION

Within reason, plants can tolerate relatively wide ranges ofmineral elements in nutrient solutions. Some macronutrients may bevaried fairly extensively without severe consequences to plant growth.Limits to these elements occur, however, and caution must be used. Agood example of this is P which is discussed l a t e r . The balance ofelements and their osmotic concentration can be important. Someelements interact with other elements more than with others. Plantspecies differ in their requirements of: mineral elements for optimumplant growth, especially dicotyledonous and monocotyledonous plants.Young seedlings normally do not withstand solutions as concentrated asolder plants, thus young plants are often grown i n i t i a l l y in solutionsthat are diluted from the full-strength.

Many recipes for nutrient solution composition have been used togrow plants by water culture. Recipes used are usually referred to inthe l i t e r a t u r e by the name of the s c i e n t i s t ( s ) who originally composedor reported the solution. Examples of this are solutions of Sachs,Knop, Maze, Hoagland, Hoagland and Aronon, Steinberg, Shive, Crone,Trealease and Trealease, Piper, Robbins, and numerous others. Thecomposition of the many solutions attributed to the various scientistshave been compiled and given in Hewitt (1966). The names of thesesolutions are ambiguous to most persons unless that person has know-ledge of the specific composition of each solution. Of greaterambiguity is the use of "a modified solution". It is important to knowand l i s t the concentration of each essential mineral element for plantgrowth in the solution, and in some cases the chemical compounds of

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MINERAL NUTRITION STUDIES 1041

some of the reagents used. The units used to report these concentra-tions (moles, parts per million, equivalents, mg/liter, etc.) are amatter of preference, orientation, or desire of journal editors.

The composition of full-strength nutrient solutions that has beenused successfully in our laboratory for the growth of sorghum is givenin Table 1. The i n i t i a l solution used for the growth of seedlings is0.2- to 0.4-strength dependent on the number of plants to be grown andthe desired age of seedlings when treatments are to be administered orplants are to be transferred to new solutions.

With the growth of some plants, i t is important to define thesource or type of compound used in the solution. This information mayoften explain some of the problems or concerns that arise when growingplants in nutrient solutions. For example, the pH of the nutrientsolution may be assessed by the r a t i o of NO, to NH, . The prevalenceor frequency of Fe or Zn deficiency may be predicted from the type ofFe chelate, Fe compound, or the amount of P used. I n i t i a l nutrientsolution pH values may be altered by the type of P compound used.These are discussed l a t e r .

Because of some of the above problems and concerns, the concentra-tion of the nutrient solution should be given or reference made to thespecific solution used. This reduces much of the ambiguity andconfusion that can arise when other s c i e n t i s t s want to use the samesolution composition.

CONTAINERS, WATER, AERATION, AND PLANT SUPPORT

Containers. Containers used to grow sorghum and corn (or anyother plant), depends on the experimenter and his objectives. Almostany size container made of various materials may be used. Somecontainers made from polyvinyl chloride (PVC) materials have beenfound to contain toxic substances for some time after i n i t i a l use, butwith continued use this problem often disappears. In mineral nutritionstudies, plastic or glass containers are used exclusively. In many ofthe recent studies with sorghum, growth of numerous plants in the samecontainer has been desired for screening purposes. Plates prepared tof i t inside p l a s t i c household dish pans hold sorghum and corn plantsthat are grown in nutrient solutions (Fig. 1). When smaller plants aredesired, smaller containers are used, and when larger plants aredesired, larger containers are used. Individual or multiple sorghum orcorn plants have been successfully grown to maturity using containersof relatively small volumes (Fig. 2). Common household buckets orsoil containers lined with p l a s t i c have been used successfully.

Water. Distilled or deionized water is used in mineral nutritionexperiments. Tap water is often used for growing plants in nutrientsolutions when the composition of solution is not c r i t i c a l . The pH ofnutrient solutions with tap water are usually higher than solutionswith d i s t i l l e d water and this higher pH often causes Fe deficiency

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Table 1. Composition of nutrient solution used for the growth of aorghum plants.

Solutionnumber +

1

2

3

4

5

6

Stock solution

Salt

Ca(NO ) -4H,0NH NO

4

KC1K SO.

KRO-

Mg(N0,),-6H,02

KH.PO,

Fe(NO,)-9H.OHEDTA

MnCl,'4H,0H,BOjZKSO^7H,0CuSO7'5H,0Na Mo04-2Hj0

Concn.

g/Hter

270.033.8

18.644.024.6

142.4

17.6

13.318.68

2.342.040.880.200.26

Stocksoln.used

ml/liter

6.6

7.2

2.8

0.5

1.5

1.5

CaNH.

KKK

Mg

K

FeNa

Mn

ZnCuNa

Full-strength

Cation

nutrient

Anion

. mg element/liter -

- 302.4-N - 39.0

- 70.2- 142.2- 68.5

- 37.8

- 2.5

2.76- 4.48§

0.974

» 0.3000.0760.074

NO,-N -NO.-N -

J

ClSNO.-N -

NO,-N -

P -

NO -N -HEDTA -

ClB *S

s «Mo «

211.439.0

63.758.324.5

43.6

2.00

2.1

13.0

1.3

0.5360.1470.0380.155

solution

- - - -Final composition - - -

element

CaKMgNO.-Nmr-NCl 5

spFeMnBZnCuMoNa iHEDTA

mg/liter

30228337.8

321

39.065.058.52.002.760.9740.5350.3000.0760.1554.5613.0

pM

754072401550

22900278019401820

654918504.61.21.6

20047

oto

t In each solution the respective salts were dissolved together in the same volume. Some of the salts in solutions1 to 4 nay be combined to make fewer stock solutions if desired, but keep Ca salts separate from SO. and PO, aalts.Combinations of the salts noted are for convenience.

| This solution was prepared by (a) dissolving the HEDTA [N-2-(hydroxyethyl)-ethylenediarainetriacetaic acid] in 200 mldis t i l l e d water • 80 ml IN NaOH; (b) adding solid Fe(HO,)3-9H,O to the HEDTA solution and completely dissolving the Fesal t ; (c) adjusting the pH to 4.0 with small additions of IN NaOH (approx. 50 ml); and (d) bringing the solution tovolume. Care should be taken not to add NaOH in step (c) too rapidly to allow Fe to precipitate. The HEDTA was ob-tained from Aldrich Chemical Co., Milwaukee, WI (catalog No. H2650-2). This source of HEDTA is not the only sourceavailable and mention of this company or product does not constitute a guarantee or warranty of the company or productby the U.S. Department of Agriculture and does not imply the product approval to the exclusion of others that may besuitable.

i Assumes 130 ml IN NaOH used to adjust pH of FeHEDTA to 4.0 and no pH adjustment of nutrient solution.

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MINERAL NUTRITION STUDIES 1043

Fig. 1. Twenty-four (top) and 125 (bottom) sorghum plants (variousgenotypes) grown in the same container of nutrient solution.

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CLARK 1044

Fig. 2. Sorghum ( l e f t ) and corn (right) grown to maturity in nutrientsolutions.

problems. High pH nutrient solutions (above 7) are particular problemsfor the growth of young plants. Water held in galvanized tanks orpassed through metal pipes often have elements or substances that aretoxic to plant growth. Successful growth of sorghum has been achievedwith bulk solutions prepared in galvanized tanks lined with plastic orcoated with epoxy paints.

Aeration. Corn growth is inhibited more extensively with noaeration than sorghum growth. Optimum growth of corn was obtained onlywhen solutions were aerated. Under some conditions, sorghum growth isinhibited without aeration, but relatively short-term experiments havebeen conducted without aeration and no apparent detrimental effectswere noted. Some culture solution systems have been used withoutaeration when a portion of the upper roots of sorghum have been abovethe level of the growth solution. Successful aeration has been

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MINERAL NUTRITION STUDIES 1045

obtained using aquarium aerator bubblers suspended in nutrient solu-tions. The bubblers are connected by tubing to a central hose byhyperderraic needles. Small a i r or vaccuum pumps have been usedsuccessfully to provide a i r .

Plant Support. Seedlings wrapped with narrow s t r i p s of spongerubber and inserted into holes in container lids have been sufficientsupport for the growth of plants (Fig. 1 and 2). The holes in the lidare s u f f i c i e n t l y large that plant stalks can expand without r e s t r i c -tion. Styrofoam lids (usually 2 to 5 cm thick, Fig. 2, l e f t ) havegiven sufficient support to sorghum plants grown to maturity, althoughverti c a l rods supported by the lid may be needed to help support theplants until some auxiliary brace roots develop. Corn plants grownthis way may require additional support if grown to maturity (see Fig.2, right)

ELEMENT DEFICIENCIES AND SALT PURIFICATION

Mineral Element Deficiencies. Reagent grade chemical compoundsare used to prepare nutrient solutions in our laboratory. Macronutri-ent deficiencies have been obtained readily in young sorghum and cornplants by omitting the desired element from solution. Some of theseelement deficiencies are so severe by the omission of the desiredelement that small amounts of the appropriate element are added toobtain sufficient plant material for analysis. Of the micronutrients,Mn and Fe deficiencies have been readily obtained in young plants byomission of these elements from the solution, but Zn, Cu, B, and Modeficiencies have not. Good Zn deficiencies have not been obtained inyoung sorghum or corn plants without macronutrient salt purificationto reduce heavy metal contamination. Zinc deficiencies have been mored i f f i c u l t to obtain in young sorghum plants than in young corn plants.Regardless of the precautions taken I have not been able to obtain Cu,B, and Mo deficiencies in young sorghum or corn plants grown innutrient solutions. Reduced concentrations of B and Cu have been notedin plants grown by nutrient solutions without these elements, butreductions in growth have not been noted. Copper and Mo deficienciesin corn (Brown, 1954; Brown and Clark, 1974) and Cu deficiencies insorghum (Brown et a l . , 1977) have been obtained when plants were grownin s o i l s . Boron and Cu deficiencies have been obtained in youngsorghum and corn plants grown in purified sand (Agarwala and Sharma,1979). Descriptions of mineral element deficiencies in sorghum andcorn, as well as element t o x i c i t i e s in sorghum, have been givenelsewhere (Clark, 1970; Clark, 1981; Clark et a l . , 1981).

Purification of Salts. Many methods have been and are used topurify s a l t s to reduce contamination of the heavy metals (Hewitt,1966). Whenever purified s a l t s have been needed in our laboratory,macronutrient s a l t s have been purified with 0.25% 8-hydroxyquinolinein chloroform and subsequently washed with chloroform. Any chloroformremaining in the stock solution is evaporated by heating beforesolutions are brought to volume.

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1046 CLARK

GERMINATION OF SEED

Seeds may be germinated by many methods to prepare s e e d l i n g s fortransfer to nutrient solutions. Washed sand, glass beads, vermicu-l i t e , wire mesh, paper towels, petri dishes, and many other methodshave been used. Sorghum seeds have been germinated successfullybetween rolled paper towels (Fig. 3). Corn seed is usually germinatedon wire mesh under cheesecloth if no contact with external materials isdesired or in a solid medium (vermiculite or sand) if contact with asold medium is unimportant.

Unless seeds have been treated, microorganism growth (particu-larly fungi) are common problems with germinating seeds. Captan [N-trichloromethylthio)-cyclohex-4-ene-l, 2-dicarboximide ] treated seedhas successfully reduced growth of fungi on germinating sorghum andcorn seed. Too much Captan may reduce germination.

pH OF NUTRIENT SOLUTIONS

Good plant growth can be achieved by plants grown in nutrientsolutions over a relatively wide pH range (from about 4 to 8) ifsufficient mineral elements can be obtained by the plants. As solutionpH changes, the solubility and availability of many elements change andabsorption may be enhanced or inhibited. In general, maximum uptake ofboth cations and anions occur between pH 5 and 7 (Clark, 1982). At pHvalues below 5, cation uptake is usually inhibited more than anionuptake and at pH values above 7, anion uptake is inhibited more thancation uptake. These responses can be explained, in part, by Hcompetition for cations and OH competition for anions (Hiatt andLeggett, 1974).

Fig. 3. Germination of sorghum seeds in wrapped paper towels.

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MINERAL NUTRITION STUDIES 1047

The i n i t i a l pH of nutrient solutions may be altered or adjusted bythe use of different P compounds. This is noted when compounds likeK3PO , K5HPO,, KH PO,, or H-PO, are used. The i n i t i a l pH ofsolutionsis higher when higher amounts of K are attached to PO, . Othersources of P can also affect the i n i t i a l pH of nutrient solutions. Theamount of P needed in nutrient solutions is considerably lower than theother macronutrients. Most other essential mineral elements havel i t t l e effect on the i n i t i a l nutrient solution pH unless they arecompounds with high amounts of soluble H or OH . Using the composi-tion of elements common in our studies (P is 2 to 4 mg/liter), thein t i a l pH of the nutrient solutions is near 5.5 with KH.PO, and near6.5 with K2HPO4.

As plants grow, they absorb ions from the solution and oftenrelease other ions (like H and HCO, ) to the solution. These changesin ions cause pH changes in the nutrient solution. These pH changesgenerally occur rapidly dependant on the size of roots and the volumeand concentration of the solutions. Maintaining a constant pH innutrient solutions is d i f f i c u l t . Methods used to maintain constant pHin nutrient solutions entail continual adjustment of pH with acid orbase, continual replenishment or replacement of solution, use of largevolumes of solution in proportion to the volume of roots, use of short-term (often hourly) experiments, and use of buffered solutions. Buf-fered solutions often induce more complications than original solu-tions.

Monitoring the solution pH as plants grow is a relatively easy andconvenient means for noting some of the changes that occur in solu-tions.

The type of N in solution is one method for controlling, to somedegree, the pH of nutrient solutions. When only NO, is used as asource of N, the solution pH rises and remains near or above 7. Whenonly NH, is used as a source of N, the solution pH decreases andremains near or below 4. When a mixture of NO. and NH, is used, thepH usually remains somewhere between the extremes noted for either NO,or NH,+ only as a source of N. Examples of these are noted in Fig. 4.

Ten-day-old sorghum plants (RS671) grown in nutrient solutions (2plants/1.9 l i t e r s ) containing different NO~/NH, ratios showed thatas long as some NH, remained in solution, the pH decreased from ani n i t i a l pH of about 5.2 to a low of about 3.5 and remained at that levelthroughout the experiment (Fig. 5). Once NH, was depleted fromsolution, the pH rose fairly rapidly to that of*solutions where onlyNO, was added as a source of N. The longer NH remained in solution,

e longer the solution pH remained low. Rise in solution pH wasthe longer the solution pH remained low. Rise in solution pHrelated to NH, levels of 1 mg/liter or lower in solution. "" *became Fe deficient as the solution pH rose above 6.5 to 7.

With most of the experiments conducted in our laboratory, NO,/NH, ratios of 8:1 with solution N levels of about 300 mg N/liter a r |used (Table 1). Good plant growth has been obtained at this NO. /NHratio and the pH remains relatively low throughout the experiment.

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1048 CLARK

PH

7.0

6.0

5.0

4.0

3.0

?O

\ N .

\

1 1

No3" + rJH

^ ^ - - — •

1 1 1 1 1

I 2 3 4 5 6 7DAYS AFTER TREATMENTS WERE ADDED

Fig. 4. The pH of nutrient solutions with time when only NO- , onlyNH, , and 8 NO.~/1 NH, were used as the sources of N for

1 sorghum growth. Seventy plants of various genotypes weregrown in 7.0 lite r s of solution using the method shown inFig. 1.

Solution pH measurements are used as a n o n i t o r of normal, healthy p l a n tgrowth. Once solution pH values begin to ri s e , nutrient solutionsbecome depleted of NH, and possibly other mineral elements. Abnormalplant growth appears when pH values do not remain low. The mostserious problem is Fe deficiency. With Fe added to alleviate the Fedeficiency, other mineral interactions arise which bring about furthercomplications.

Sorghum usually reduces and maintains slightly lower pH values innutrient solutions than corn. It is not uncommon to note nutrientsolution pH values of 3.5 to 4.0 for sorghum and 4.0 to 4.5 for corn.Deleterious growth effects on sorghum and corn have not been noted atthese relatively low pH values, even though deleterious growth effectshave been noted for many other plant species at pH values below 4(Hewitt, 1966).

On occasion, reviewers have criticized the growth of plants atsuch Tow pH values and suggest that plants should be grown in the pH 5to 7 range; the pH common for most so i l s . As mentioned above, i t isdi f f i c u l t to maintain a constant pH in nutrient solutions with activelygrowing plants. I t would be of interest to know actual pH values atroot surfaces of plants grown in soil s . The buffered pH of soilssurrounding roots may not reflect the actual pH at root surfaces. The

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MINERAL NUTRITION STUDIES 1049

CM

00

CO

10

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. -H

•a B0) T3

•H CO

> 2o> 3

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ca a)o El

•H 4J

o

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4JCO

u01}_)

4-1

ffi (11

c*O!5

X!S

•gICO

4-1

C

CD

a•a

oCOCO

Of-l

lut:

oCO

01XI4 J

iH

t o o

9 i w4J CO T3T3 01

XI I T3•U O T3•H H (j

CO &C U Mq 0

•H -au c «3 CD M

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bo &

01 O 60•H CM1-1 O>•U T3 XI3 CO 4J

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60

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1050 CLARK

use of buffered nutrient solutions usually cause complications notencountered in normal growth solutions. Plants should be allowed toperform their normal function(s) when grown in nutrient solutions andchanges that occur should be monitored.

PHOSPHORUS CONCENTRATION IN NUTRIENT SOLUTIONS

Phosphorus concentrations in nutrient solutic is vary extensivelywith investigator. Some plant species t o l e r a t e considerably more P insolution than others. Experience with sorghum and corn grown innutrient solutions indicates that most reported nutrient solutionscontain considerably more P than is needed for optimum plant growth.In some cases, higher than needed P levels may be detrimental to plantgrowth, particularly root development.

In many reports where P levels in nutrient solutions are near thatof the Hoagland solutions (31 mg P / l i t e r ) , the amount of Fe added isusually high to avoid Fe deficiency in the plants. This might beexpected since P interac t s extensively with Fe. Phosphorus is oftenadded to nutrient solutions to induce Fe deficiency in plants (Brown,and Jones, 1976; Clark et a l . , 1982). The amount of P needed to inducesevere Fe deficiencies in sorghum within four to five days was 12mg/liter (Clark et a l . , 1982). In early experiments with corn (Clark,1970), Fe had to be added to nutrient solutions every other day to keepFe deficiency from occuring. The P level in these nutrient solutionswas 22 mg/liter. Nutrient solutions had lower P in la t e r experiments(Clark 1975, 1978a, 1978b; Clark and Brown, 1974) and considerably lessFe was required. Decreases in plant growth did not occur, and plantsappeared to grow b e t t e r . In the l a t t e r studies, Fe was added only tothe i n i t i a l solutions unless nutrient solutions were changed.

Phosphorus added above r e l a t i v e l y low levels has not enhancedsorghum and corn root growth (Table 2). In some cases, higher P levelsinhibited root growth. In these experiments, nutrient solution compo-si t i o n was that given in Table 1, except that P in solution was varied.In the sorghum experiment (Experiment 1), 16-fold increases in Pincreased root dry matter by only about 252 compared to top dry matterincreases of over 100%. In the corn experiments (Experiments 2, 3, and4), root dry matter yields were inhibited at rel a t i v e l y low levels ofP. On the other hand, top dry matter yields were inhibited only when Plevels were high (60 mg P / l i t e r ) .

In other experiments using similar composition of nutrients givenin Table 1, large numbers of sorghum plants (70 to 125) were grown for10 to 14 days in the same container of nutrient solution with 2 mgP/ l i t e r (7 l i t e r s ) without developing P deficiency symptoms (Clark eta l . , 1982; Furlani and Clark, 1981; Williams et a l . , 1982). Eventhough differences in sorghum genotypes were noted, plants were grownfor as long as three to four weeks with 2 mg P before P deficiencysymptoms appeared (Clark et a l . , 1978). In most experiments, sorghumplants are grown in nutrient solutions with 2 to 4 mg P / l i t e r .

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MINERAL NUTRITION STUDIES 1051

Table 2. Top and root dry matter yields of sorghum (Experiment 1)and corn (Experiments 2, 3, and 4) grown at varied levelsof P in nutrient solutions, t

Experiment

Dry matter yield

P levelin solution

mg/liter

0.51.02.04.08.0

0.0670.20.652.0

0.10.31.04.0

0.22.0

2060

Tops

62 E83 D107 C132 A123 B

0.34 D0.64 C1.28 B1.89 A

0.74 C0.91 B1.12 A1.10 A

0.48 C1.28 B1.62 A1.38 B

Roots

mg/plant

g/plant

4550586152

175307470369

464471382318

231460401

CCABABC

DCAB

AABC

CAB

.276 C

+ Conditions were-70 7-day-old sorghum plants (various genotypes)grown in the same dishpan (Fig. 1) with 7.0 l i t e r s of solutionfor 14 days and five 7-day-old corn plants (four genotypes inseparate containers) grown in 3.8-liter containers for 10 days.

f Numbers in each column of each experiment followed by the samele t t e r were not significantly different (P = 0.05) according tothe Duncan's Multiple Range Test.

In some of the init i a l experiments with sorghum grown in nutrientsolutions, a red-purple speckling or necrosis appeared on the lowerleaves of many genotypes. Later studies indicated that the severity ofthis speckling could be induced by P (Furlani et al. , 1978). This"red-speckling" could be induced on leaves of older plants when P wasadded, but the amount added had to be at concentrations higher than foryounger plants. A study was conducted to determine the level of Pneeded to induce the "red-speckling" on leaves of young sorghum plants.Even though sorghum genotypes differed in the severity of "red-speckling" symptoms, the speckling could be induced in a fairlysusceptible genotype at P levels as low as 0.2 mg/liter. Both "red-speckling" and P deficiency symptoms could be imposed on the same plant

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Fig. 6. LEFT: The e f f e c t of varied P l e v e l s on "red-speckling" on thet h i r d l e a f of KS35 sorghum. Seven-day-old p l a n t s were grown( l e f t t o r i g h t ) with 0.5, 1.0, 2.0, 4.0, and 8.0 mg P / l i t e rfor 14 days. RIGHT; "Red-speckling" on the lower leaves andFe deficiency on the upper leaves of RS671 sorghum. Five 7-day-old p l a n t s were grown 10 days with 5.0 mg P / l i t e r (3.8-l i t e r container) during which time the "red-speckling" ap-peared on the lower leaves. At 17 days of age, an additional120 mg P/liter was added to the container and plants allowedto grow another 7 days during which time Fe deficiencydeveloped.

within four to five days. The "red-speckling" symptoms became moresevere as P in solution increased (Fig. 6, l e f t ) . If sufficiently highP was added, Fe deficiency could be induced in the upper leaves of thesame plant that had "red-speckling" on the lower leaves (Fig. 6,right). This "red-speckling" was also induced in sorghum plants grownat relatively low levels of P in soils. Regardless of P level used,some genotypes did not exhibit this "red-speckling" on their leaves.However, most genotypes studied are susceptible to this "red-speck-ling". If the "red-speckling" can be classed as a P-toxicity symptom,

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'MINERAL NUTRITION STUDIES 1053

then P toxicity appears at low levels of P in sorghum. To reduce theamount of "red-speckling" on sorghum leaves, sorghum is grown atrelatively low levels of P in nutrient solutions. If sorghum plantsare to be grown for extended periods of time, P is added at frequentintervals to reduce as much "red-speckling" as possible.

SOURCES OF IRON IN NUTRIENT SOLUTIONS

The "source of Fe supplied to plants grown in nutrient solutionsvaries with nutrient solution recipe. The effectiveness of many Fecompounds is discussed by Hewitt (1966). The pK of nutrient solutionsoften determines the amount of Fe available to plants. In general, foreach unit increase in pH, Fe solubility decreases about 1000-fold.Higher amounts of Fe are usually added to nutrient solutions wheninorganic sources are used compared to organic sources.

Within the past two to three decades, synthetic Fe chelates havebeen shown to be effective sources of Fe in nutrient solutions.Differences have been noted among synthetic Fe chelates for effec t i v e -ness in providing Fe to plants. In addition, solution pi! oftendetermines chelate effectiveness for providing Fe to plants (Halvorsonand Lindsay, 1977; Lindsay, 1972). For an understanding of thes t a b i l i t y of many Fe chelates in nutrient solutions and their chelationwith various other cations, the a r t i c l e by Halvorson and Lindsay (1972)should be consulted. The-effectiveness of Fe chelatec is often plantor genotype specific. The Fe chelate FeEDTA ( f e r r i c ethylenediamine-t e t r a c e t a t e ) has been a good source of Fe for many plants grown innutrient solutions (Halvorson and Lindsay, 1977; Lindsay, 1972).However, Brown and collegues (Brown and Bell, 1969; unpublished/showed that FeHEDTA ( f e r r i c hydroxyethylonediaminetriacetate) was abetter source of Fe chelate than FeEDTA, FeDTPA ( f e r r i c diethylene-triaminepentaacetate), and FeEDDHA ( f e r r i c ethylenediamine d i ( o -hydroxyphenylacetate) over the pH range for which most plants are grownin nutrient solutions.

For the past several years, FeHEDTA has been used as a source ofFe in our laboratory for sorghum and corn grown in nutrient solutions.I t has been superior to other compounds used. Iron is added to thei n i t i a l nutrient solution at about 5 mg/liter and no Fe deficiencyproblems have been encountered throughout the growth period in thatsolution. From our i n i t i a l methods for growing corn in nutrientsolutions, the amount of Fe in solution has been reduced extensively.Unless Fe deficiencies are induced purposely, problems of Fe d e f i c i -ency have been nil with sorghum and corn grown in nutrient solutionswith FeHEDTA. A source of commercial FeHEDTA has not been found sosolutions are prepared in our laboratory using FeCl_ or Fe(N0_), as theFe source with equivalent amounts of the chelate 11EDTA (see Tanle 1).

CHARGE OF SOLUTIONS WITH PLANT AGE

Some s c i e n t i s t s do not want growth solutions to decrease in

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element concentration more than a few percent of the original concen-t r a t i o n vihile other s c i e n t i s t s prefer plants to u t i l i z e as much of eachelement as possible before adding more nut r i e n t s or changing solu-t i o n s . Some plants take up certain elements or sources of an element,namely NO or "H, , nsore readily during early stages of growth than atlflter stages of growth. Dependent on the experimental objectives,plants "lay be <:rown by various means and for various lengths of time.Because of these f a c t o r s , as well as many others, the concentrations ofthe mineral elements in solution change and solutions may need to bereplaced or replenished.

For many sorghum genotypes grown to maturity in several green-house experiments using 7 - l i t e r containers (1 plant/container), solu-tions were changed at 30-day intervals a f t e r the i n i t i a l f ull-strengthnutrient solution was given. The composition of the nutrient solutionis given in Table 1. That i s , solutions were changed twice a f t e r thei n i t i a l solution for plants grown to maturity. Because many sorghumgenotypes are susceptible to "red-speckling" on the leaves from high P,P was added at weekly intervals to reduce th i s problem. About 125 mgP/ l i t e r was added throughout the l i f e of the plant. Otherwise, onlywater and P were added frequently to the solutions to grow sorghumplants to maturity. Plants grown in these experiments appeared normaland produced grain.

In other experiments with sorghum, plants have been grown tomaturity without changes in nutrient solution. Additional nutrientshave been added frequently. Whenever water was added, i t was added asa nutrient solution. The amount of nutrients added to the solutionswere unknown in these experiments. No concern was given for "red-speckling", since the newer leaves did not have such, and at maturity,most of the lower "red-speckled" leaves had senesced.

For the corn plants grown to maturity (Fig. 2), nutrient solutionswere changed biweekly the f i r s t six weeks of growth, every 10 days forthree changes, and weekly t h e r e a f t e r . From calculations of thenutrient contents in the plants, solutions would not have required asfrequent changes to provide the nutrients taken into the plants.

In the usual procedure where plants are four weeks of age or lessat the time experiments are terminated (1 plant/2 l i t e r s or moresolution), nutrient solutions are not changed unless additional solu-tion treatments are administered. Except for P, mineral deficiencieshave not been observed and plants appeared normal. Phosphorus i susually added two to three times during th i s time to avoid P d e f i c i -ency.

CONCLUSIONS

The growth of plants in nutrient solutions has been an invaluabletool for mineral n u t r i t i o n studies. The key to successful growth of

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plants in nutrient solutions cannot always be defined. Many of thesuccessful conditions and details involved for successful growth ofplants in nutrient solutions are not explained in publications wherethese methods haye been used. Much of the information about nutrientsolution growth °£ plants is taken for granted and l e f t to theingenuity and experience of investigators. Many helpful ideas andpractices come only from experience. Some of the concerns, problems,and successes that have occurred when sorghum and corn plants have beengrown in nutrient solutions have been discussed. While many otherconsiderations and helpful ideas and practices could have been includ-ed, i t is hoped that the comments and ideas given will be helpful toothers who grow plants in nutrient solutions.

ACKNOWLEDGEMENT

The contributions, discussions, and experiences of L. Bernando,J. C. Brown, R. L. Chaney, J. D. Eastin, G. E. deFranca, A. M. C.Furlani, P. R. Furlani, J. W. Maranville, P. A. Pier, C. Y. Sullivan,E. P. Williams, and Y. Yusuf are greatly appreciated. These personshave provided data, information, and comments that have been helpful inthe preparation of this a r t i c l e .

REFERENCES

1. Agarwala, S. C., and C. P. Sharma. 1979. Recognizing micronutri-ent disorders of crop plants on the basis of visible symptomsand plant analysis. Prem Printing Press, Lucknow, India.

2. Brown, J. C. 1954. Some observations on the reduction of 2, 3, 5-triphenyltetrazolium chloride in plant tissue as influenced bymineral nu t r i t i o n . Plant Physiol. 29:104-107.

3. Brown, J. C., and W. D. Bell. 1969. Iron uptake dependent upongenotype of corn. Soil Sci. Soc. Am. Proc. 33:99-101.

4. Brown, J. C., and R. B. Clark. 1974. Differential response to twomaize inbreds to molybdenum s t r e s s . Soil Sci. Soc. Am Proc.38:331-333.

5. Brown, J. C., R. B. Clark, and W. E. Jones. 1977. Efficient andinefficient use of phosphorus by sorghum. Soil Sci. Soc. Am.J. 41:747-750

6. Brown, J. C. and W. E. Jones. 1976. A technique to determine ironefficiency in plants. Soil Sci. Soc. Am. J. 40:398-405.

7. Clark, R. B. 1970. Effects of mineral nutrient levels on theinorganic composition and growth of corn (Zea mays L.). OhioAgr. Res. Dev. Center Res.Cir. No. 181.

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8. Clark, R. B. 1975. D i f f e r e n t i a l nagnesium e f f i c i e n c y in maizeinbreds. 1. Dry-matter yields and mineral element composi-t i o n . Soil Sci. Soc. Am. Proc. 39:488-491.

9. Clark, R. B. 1978a. D i f f e r e n t i a l response of corn inbreds tocalcium. Commun. Soil Sci. Plant: Anal. 9:729-744.

10. Clark, R. B. 1978b. D i f f e r e n t i a l response of corn inbreds to Zn.Agron. J. 70:1057-1060.

11. Clark, R. B. 1981. Plant response to mineral element t o x i c i t yand deficiency. In: C. F. Lewis and M. N. Christiansen (ed.)Breeding plants for marginal environments. John Wiley & Sons,New York, NY. (in p r e s s ) .

12. Clark, R. B. 1982. Effect of various f a c t o r s on n u t r i e n tcomposition of p l a n t s . In: M. Recheigl, J r . (ed.) Handbook ofNutrition and Food. CRC Press, Boca Raton, FL. (in p r e s s ) .

13. Clark, R. B., and J. C. Brown. 1974. D i f f e r e n t i a l phoshorousuptake by phosphorus-stressed corn inbreds. Crop Sci. 14:505-508.

14. Clark, R. B., J. W. Maranville, and H. J. Gorz. 1978. Phosphoruse f f i c i e n c y of sorghum grown with limited phosphorus. p. 93-99. In A. R. Ferguson, R. L. B i e l e s k i , and I . B. Ferguson(e d . ) . Plant Nutrition - 1978. Proc. 8th I n t . Colloq. PlantAnal. F e r t . Prob., Auckland, New Zealand.

15. Clark, R. B., P. A. P i e r , D. Knudsen, and J. V). Maranville. 1981.Effect of tra c e element d e f i c i e n c i e s and excesses on mineraln u t r i e n t s in sorghum. J. Plant n u t r i t i o n 3:357-373.

16. Clark, R. B., Y. Yusuf, R. M. Ross, and J. W. Maranville. 1982.Screening for sorghum genotypic differences to iron d e f i c i -ency. J. Plant Nutr. (in p r e s s ) .

17. F u r l a n i , Angela M., R. B. Clark, and C. Y. Sullivan. 1978.Properties of a phosphorus-induced 'red-speckling' on sorghumleaves. Agron. Abstr. 1978:153.

18. F u r l a n i , P. R., and R. B. Clark. 1981. Screening sorghum foraluminum tolerance in n u t r i e n t s o l u t i o n s . Agron. J. 73:587-594.

19. Halvorson, A. D., and W. L. Lindsay. 1972. Equilibriumr e l a t i o n s h i p s of metal chelates in hydroponic s o l u t i o n s . SoilSci. Soc. Am. Proc. 36:755-761.

2+20. Halvorson, A. D., and W. L. Lindsay. 1977. The c r i t i c a l Zn

concentration for corn and the nonabsorption of chelated zinc.Soil Sci. Soc. Am. J. 41:531-534.

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21. Hewitt, E. J. 1966. Sand and water culture methods used in thestudy of plant n u t r i t i o n . Tech. Commun. No. 22 (2nd ed.)Commonwealth Agricultural Bureaux, Farnham Royal, Bucks, Eng-land.

22. H i a t t , A. J., and J. E. Leggett. 1974. Ionic i n t e r a c t i o n s andantagonisms in p l a n t s , p. 101-134. In: E. W. Carson (ed.) Theplant root and i t s environment. Univ. Press Virginia, Char-l o t t e s v i l l e , VA.

23. Lindsay, W. L. 1974. Role of chelation in micronutrienta v a i l a b i l i t y , p. 507-524. In: E. W. Carson (ed.) The plantroot and i t s environment. Univ. Press Virginia, C h a r l o t t e s -v i l l e , VA.

24. Williams, E. P., R. B. Clark, Y. Yusuf, W. M. Ross, and J. W.Maranville. 1982. V a r i a b i l i t y of sorghum genotypes to t o l e -r a t e iron deficiency. J. Plant Nutr. (in p r e s s ) .

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