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Field evaluation of inorganicand chelated iron fertilizersas foliar sprays and soilapplicationDavid Wm. Reed a , Calvin G. Lyons Jr. a &George Ray McEachern aa Department of Horticultural Sciences, TexasA&M University, College Station, TX, 77843Published online: 21 Nov 2008.

To cite this article: David Wm. Reed , Calvin G. Lyons Jr. & George RayMcEachern (1988) Field evaluation of inorganic and chelated iron fertilizers asfoliar sprays and soil application, Journal of Plant Nutrition, 11:6-11, 1369-1378,DOI: 10.1080/01904168809363894

To link to this article: http://dx.doi.org/10.1080/01904168809363894

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JOURNAL OF PLANT NUTRITION, 11(6-11), 1369-1378 (1988)

FIELD EVALUATION OF INORGANIC AND CHELATED IRONFERTILIZERS AS FOLIAR SPRAYS AND SOIL APPLICATION

KEY WORDS: Iron, iron deficiency, iron chlorosis, plant nutrition, grape, peach

David Wm. Reed, Calvin G. Lyons, Jr. and George Ray McEachern

Department of Horticultural SciencesTexas A&M University

College Station, TX 77843

ABSTRACT

A series of inorganic and chelated ferric and ferrous fertilizers were testedfor their ability to alleviate Fe chlorosis as foliar and soil application on peachand grape under field conditions. Limited re-greening was obtained with foliarapplication of ferric citrate/ammonium nitrate, ferrous sulfate and DTPA onpeaches, and with foliar application of ferric citrate/ammonium nitrate and fer-rous sulfate and soil application of ferric citrate/ammonium sulfate and ferriccitrate/urea/ammonium nitrate on grapes. The only treatments that resulted incomplete elimination of iron deficiency, as indicated by complete re-greeningand plant rating, was soil application of EDDHA on both peach and grape. Soilapplication of methyl-EDDHA was almost as effective as EDDHA, resulting inslightly less intense re-greening and chlorophyll content.

INTRODUCTION

Iron deficiency is one of the major problems of growing plants in areas ofalkaline soil or irrigation water (Lindsay and Schwab, 1982). Many of our mostimportant horticultural and agronomic crops are susceptible to iron deficiency.The currently available iron containing fertilizers for correction of iron defi-ciency either are ineffective or, if effective, are very expensive (Hagstrom,1984). Therefore, there is the need for an effective yet economical iron ferti-lizer.

The objective of this study was to test the effectiveness of ferrous sulfate, acommercial ferric citrate/ammonium nitrate mixture, a commercial ferriccitrate/urea/ammonium nitrate mixture, and ferric DTPA, EDDHA and methyl-EDDHA, as both a foliar spray and soil application under field conditions.

1369

Copyright © 1988 by Marcel Dekker, Inc.

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1370 REED, LYONS AND MC EACHERN

TABLE 1

Soil test of peach orchard and grape vineyard used in iron studies.

Peach Orchard Grape Vineyard

Parameter

nitrogenphosphoruspotassiumcalciummagnesiumsodiumzincmanganeseironbicarbonatepHsoil type

ppm

12150632

35214264551.7108.2

-7.6silty clay

Interpretation

moderatevery highvery highvery high

highmoderate

highhighhigh

-mildly alkalineloam

ppm

1471752

35212861751.66.910.23987.9Burleson

Interpretation

moderatevery highvery highvery high

highlow

highhighhigh

-mildly alkalineclay

MATERIALS AND METHODS

Site Selection and Location

Peach and grape were chosen as the model test plant because large blocks ofuniformly chlorotic plants were available. The peach orchard was located at SanMarcos, TX on a silty clay loam soil. First year 'Bicentennial' peach on 'Nema-gard' rootstock was treated. The plants averaged 1 1/2 to 2 inches trunk caliper.The grape vineyard was located at the Texas A&M University Stiles Farm atThrall, TX. on a Burleson clay. Two-year old own-rooted 'Champanel' grapeswere treated All plants were on drip irrigation as needed. The soils at bothsites have a high pH and phosphorus content, which renders the high iron con-tent unavailable to the plants (Table 1).

Treatment

Eight foliar and 5 soil treatments were applied at the rates given in Table 2.The experimental ferric citrate/ammonium sulfate (Arcadian Corp.) was appliedat two rates; one equal to the label rate of NFe (ATcadian Corp.) and one equalto the label rate of Sequestrene 138 (EDDHA, Geigy Corp.). All commercialproducts were applied at the highest recommended label rate in order to assurethat any ineffectiveness observed was due to the inadequacy of the compoundand not to a less than optimum rate of application. Fall and spring applicationswere made. On grapes, the same plants were treated in the fall and the spring,due to a limited number of available plants. On peaches, separate gToups of

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INORGANIC AND CHELATED IRON FERTILIZERS 1371

TABLE 2

Iron compounds and application rates used in the peach and grape study.

Rate Fe Applied

Treatment2

1) ControlFoliar Applied2) Ferrous sulfate''3) Ferrous sulfate* + 1% PEG"4) Fe cit/AmSuir5) Fe cit/AmSuir6) NFev

7) EDDHA (Seq. 138)u

8) DTPA (Seq. 330)1

9) DTPA (Miller 330)s

Soil Applied10) Ferrous sulfate''11) Fe cit/AmSuir12) NFev

13) EDDHA (Seq. 138)u

14) methyl-EDDHAr

(Miller Ferric Plus)

Label Rate

2 lb/100 gal2 lb/100 gal

--

3 qt/100gal3 lb/100 gal1 lb/100 gal1 lb/100 gal

0.25 lb/ 1" trunk-

4 qt/10,000 ft2

2 oz/1" trunk2 oz/1" trunk

Foliarmg Fe/liter

500500225

12001200225120120

_---

Soilg F e / 1 " trunk

-------

22.75.85.83.43.4

zFoliar treatments applied to run-off; soil treatments applied in a 18-inch ringat base; fall treatment based on 1 1/2-inch diameter trunk, spring treatmentbased on 2-inch diameter trunk.

yRates taken from Welch and Gray (1976); foliar fall treatment at recommended5 lb/100 gal.however, foliar rate changed to 2 lb/100 gal for spring treatmentdue to foliar burn.

XPEG, polyethylene glycol, molecular weight 1000."Experimental product of ferric citrate and ammonium sulfate, 7-0-0-6Fe,

Arcadian Corp.vNFe, mixture of ferric citrate, urea and ammonium nitrate, 16-0-0-4Fe, Arca-

dian Corp."Sequestrene 138, 6% Fe from ferric ethylenediamine di-10-hydroxyphenylacetic

acid, Geigy Corp.'Sequestrene 330, 10% Fe from ferric diethylenetriamine pentaacetic acid, Geigy

Corp."Miller 330, 10% Fe from ferric diethylenetriamine pentaacetic acid, Miller

Chemical and Fertilizer Corp.'Miller Ferric Plus, 6% Fe from ferric methyl-ethylenediamine

di-10-hydroxyphenylacetic acid, Miller Chemical and Fertilizer Corp.

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1372 REED, LYONS AND MC EACHERN

plants were treated in the fall and in the spring. The Miller Chemical and Fer-tilizer Corp. products Miller 330 (DTPA) and MilleT Ferric Plus (methyl-ED-DHA) were applied only in the spring application to peaches. For soil applica-tion, the fertilizers were uniformly spread in an 18-inch diameter ring aroundthe base of the trees, then lightly raked-in. For the fall application, a 1-1/2inch trunk diameter was assumed for both peach and grape; and for the springapplication, a 2 inch trunk diameter was assumed for both peach and grape. Forthe foliar spray treatments, freshly prepared solutions in distilled water wereapplied to run-off with a back-pack Solo sprayer.

Sample Collection and Washing

The individual treatments weTe evaluated for effectiveness by rating eachplant for overall response and leaf samples were taken to determine chlorophyll,extractable Fe and total Fe. Overall plant rating was on a scale of 1 to 5 asfollows: 1 = severe chlorosis and older leaves defoliated, 2 = severe chlorosiswith no defoliation, 3 = very pale green with slight chlorosis, 4 = pale greenwith slight chlorosis, and 5 = deep green leaves.

For laboratory analysis, twenty randomly selected leaves were taken, immedi-ately placed in sealed plastic bags, and placed in a light excluded ice chest oveTice. For grape, the first fully expanded leaf from the tip of the stem was sam-pled. For peach, samples were taken from the 4-6th expanded leaf from theterminal portion of the shoot Leaves were washed to remove any surface con-tamination and spray residue according to the method of Smith and Storey(1976). The individual groups of 20 leaves were loosely held and dipped repeat-edly for about 5 seconds successively in 1% Liquinox detergent, tap water, 1%HCI, 3 rinses in distilled water, then the leaves were blotted dry. For thoseassays that used fresh tissue (chlorophyll and extractable Fe), leaf disks werepunched immediately and placed in the respective extracting solutions. For totaliron analysis, the leaves were dried for 24-48 hours at 70 C C

Total Iron Analysis

Dried leaf samples were ground in a stainless steel Wiley mill to pass a40-mesh screen. A uniform sample of the ground tissue was wet digested by theselenium-lithium-sulfuric acid-hydrogen peroxide digestion procedure in a blockdigesteT. The samples were assayed for total iron content by an InductivelyCoupled Plasma Emission Spectrophotometer (ICP). The iron content is expressedas ug Fe/g dry leaf tissue.

HCI andOPH Extractable Ferrous Iron

For HCI extraction, ten disks, 0.31 cm2 each, from each of 20 leaves pertreatment were added to 4 ml of 0.1N HCI and allowed to extract while shakingfor 24 hours at 21 °C. The extract was filtered through a 10 itm filter and 1ml of 1.5% o-phenhydroxylamine (OPH) was added and allowed to develop colorfor 30 minutes. Absorbance was read at 510 nm and the readings compared to astandard CUTVC The procedure was modified from Takkar and Kaur (1984). ForOPH extraction, ten disks, 0.31 cm2 each, from each of 20 leaves per treatmentwere added to 3 ml of 1.5% o-phenhydroxylamine (OPH) and allowed to extract

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INORGANIC AND CHELATED IRON FERTILIZERS 1373

while shaking for 24 hours at 21 CC. The extract was filtered through a 10 wnfilter and the absorbance of the extract was read at 510 nm and compared to astandard curve. The procedure was modified from Katyl and Sharma (1980) andPierson and Clark (1984). Both procedures attempt to measure the "active" fer-rous (Fe*2) Fe content of leaves.

Chlorophyll Analysis

Ten disks, 0.31 cm2 each, from each of 20 leaves per treatment were addedto 20 ml of N,N-dimethylformamide (DMF) and allowed to extract at 5 °C for24 hours. The extract was warmed to room temperature and absorbance meas-ured at 664 and 647 nm. Chlorophyll was determined by the sum of 7.04A664

and 20.27AM7 (Moran, 1982; Moran and Porath, 1980).

RESULTS AND DISCUSSION

Crape Study

When treated in the fall, the 'Champanel' grapes were very chlorotic withmany leaves being completely yellow and some almost white with stunted termi-nal growth. Soil analysis (Table 1) revealed a high soil content of iron, whichmay have been made unavailable to the plants due to the high pH (Lindsay andSchwab, 1982) and/or phosphorus content (Elliot and Lauchli, 1985). This iscompounded by the soil being a Burleson clay, which can tie up large quantitiesof nutrients. The 'Champanel' were planted from cuttings, hence, were growingon their own roots. 'Champanel', therefore, appears to be iron inefficient. Some'Champanel' in the same vineyard had been grafted onto 'Dogridge' rootstock,and were exhibiting very little to no iron chlorosis, indicating that 'Dogridge' isan iron efficient rootstock and has the ability to modify the rhizosphere (acidi-fication, reduction and/or chelation) and make iron available for absorption.

The grape plants were first treated in the fall 1985 and new growth wassampled in the spring 1986 in order to determine which of the treatments car-ry-over through the winter for spring growth (Table 3). The control plantsexhibited severe chlorosis. The only treatments that significantly increased thechlorophyll content, and hence re-greening, was the ferrous sulfate foliar sprayand the EDDHA (Sequestrene 138) soil application. The increased re-greeningwith the ferrous sulfate foliar spray was not due to residual spray on the leaves,because the leaves that were sprayed in the fall had defoliated and new springgrowth was sampled. This is unusual because foliar sprays usually do not carry-over to new growth. The EDDHA soil treated plants were deep green andappeared normal without exhibiting any deficiency symptoms. The vines werevigorously growing and the leaves were large. The ferrous sulfate sprayed plantswere a paler green and were not exhibiting as much growth nor did they haveas large a leaf size as the EDDHA soil treated plants.

Foliar applied DTP A, and soil applied Fe citrate/ammonium sulfate andEDDHA significantly increased both HC1 or OPH extractable Fe, however, onlythe EDDHA treatment increased chlorophyll and re-greening. This indicates that

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1374 REED, LYONS AND MC EACHERN

TABLE 3

Response of grapes to iron treatments applied in the fall (9/19/85) and growthsampled in the spring (5/14/86) to determine the degree of winter carry-over.

Chlorophyll HC1 Fe OPH FeTreatment ug cm'2 ng cm"2 ng cm*2

1) Control 11.1 cz 0.28 b 0.17 cFoliar Applied2) Ferrous sulfate 21.9 ab 0.39 ab 0.26 be3) Ferrous sulfate 12.0 be 0.51 ab 0.27 be

+ 1% PEG4) Fe cit/AmSulf 7.5 c 0.44 ab 0.24 c5) Fe cit/AmSulf 12.5 be 0.29 b 0.16 c6) NFe 10.9 c 0.32 ab 0.26 be7)EDDHA 8.8 c 0.43 b 0.14 c8) DTPA (Giegy) 9.1 c 0.79 a 0.15 cSoil Applied10) Ferrous sulfate 10.9 c 0.31 ab 0.15 c11) Fe cit/AmSulf 11.7 be 0.32 ab 0.35 a12) NFe 13.3 be 0.24 b 0.19 c13) EDDHA (Geigy) 24.2 a 0.44 ab 0.32 b

zMeans within columns followed by the same letter are not significanly differentat p=0.05 by Duncan's Multiple Range Test.

the HC1 and OPH extraction procedures were not accurately diagnosing the ironstatus of the plants.

The same gTape plants were re-treated in the spring immediately after sam-pling, then Tesampled 15 days later. The control plants were still chlorotic withlow chlorophyll content (Table 4). Both the foliar (at the higher rate) and soilapplied experimental ferric citrate/ammonium sulfate, the foliar applied ferroussulfate + PEG, and the soil applied EDDHA (Sequestrene 138) significantlyincreased the chlorophyll content, hence re-greening, over the control plants.However, only the soil applied EDDHA treatment caused complete re-greeningof the plants, normal growth and leaf size, and high plant rating. In this study,many of the treatments significantly increased the extractable ferrous iron overthe control values, with the higher rate of foliar applied experimental ferriccitrate/ammonium sulfate being the highest.

Peach Study

Before the fall treatment the peach trees exhibited classical iron deficiencysymptoms of interveinal chlorosis of the young leaves with the older leavesbeing darker gTeen. The plants were treated in the fall 1985 and the new growth

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INORGANIC AND CHELATED IRON FERTILIZERS 1375

TABLE 4

Response to grapes to iron treatments applied in the fall (9/19/86), re-treatedin the spring (5/14/86) and sampled 15 days later (5/29/86).

Treatment

1) ControlFoliar Applied2) Ferrous sulfate3) Ferrous sulfate

+ 1% PEG4) Fe cit/AmSulf5) Fe cit/AmSulf6)NFe7) EDDHA8) DTPA (Giegy)Soil Applied10) Ferrous sulfate11) Fe cit/AmSulf12) NFe13) EDDHA (Geigy)

Chlorophyllug cm"2

12.9 bcz

13.3 be21.6 a

14.0 be18.7 ab13.3 be14.7 be11.8 c

14.2 be19.0 ab14.3 be25.0 a

HClFeug cm"2

0.17 d

0.46 c0.72 b

0.44 c1.00 a0.56 be0.43 cd0.38 cd

0.34 cd0.35 cd0.32 cd0.41 cd

OPH Feug cm"2

0.05

0.150.25

0.140.34 a0.190.140.12

0.100.110.100.13

d

cb

ci

bccdcd

cdcdcdcd

zMeans within columns followed by the same letter are not significant differentat p=0.05 by Duncan's Multiple Range Test.

was sampled in the spring 1986. Only the soil applied EDDHA (Sequestrene 138)treatment significantly increased chlorophyll content over the controls, whichresulted in complete re-greening as indicated by the significantly highest plantrating (Table 5). None of the treatments increased the HC1 extractable ferrousiron over the controls, however, many of the treatments significantly increasedthe OPH extractable ferrous iron.

A separate block of peach trees was treated in the spring and sampled 43days later. In the spring treatment, methyl-EDDHA (Miller Ferric Plus) wasadded as an additional treatment. The results were basically the same as the falltreatment. Both the soil applied EDDHA and soil applied methyl-EDDHA sig-nificantly increased the chlorophyll content over the controls, which resulted incomplete re-greening and significantly higher plant rating (Table 6). In addition,the foliar applied experimental ferric citrate/ammonium sulfate, ferrous sulfateand DTPA (Sequestrene 330) resulted in higher plant ratings. None of the treat-ments significant increased the HC1 extractable ferrous iron over the control,but many treatments significantly increased the OPH extractable ferrous ironover the controls. These samples also were assayed for total iron. The experi-mental ferric citrate/ammonium sulfate, EDDHA and methyl-EDDHA resulted

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1376 REED, LYONS AND MC EACHERN

TABLE 5

Response of peach to iron treatments applied in the fall (9/19/85) and newgrowth sampled in the spring (4/3/86) to test for fall treatment carry-overthrough the winter for spring growth.

Treatment

1) ControlFoliar Applied2) Ferrous sulfate3) Ferrous sulfate

+ 1% PEG4) Fe cit/AmSulf5) Fe cit/AmSulf6)NFe7) EDDHA8) DTPA (Giegy)Soil Applied10) Ferrous sulfate11) Fe cit/AmSulf12) NFe13) EDDHA (Geigy)

Chlorophyllugcm"2

18.4 V

11.1 b13.1 b

12.3 b15.8 b15.3 b10.5 b14.3 b

15.9 b11.7 b12.3 b38.5 a

HCIFeug cm"2

17.5 a

31.6 a20.5 a

26.0 a17.9 a27.1 a18.8 a18.1 a

23.5 a25.6 a25.2 a24.5 a

OPHFeug cm"2

18.9 b

22.6 ab21.8 ab

20.4 ab20.4 ab19.6 b18.1 b20.4 ab

18.1 b19.6 b22.8 ab28.0 a

PlantRating2

2.7 b

2.3 b2.3 b

1.7 b2.7 b2.7 b2.0 b3.0 b

2.3 b2.7 b2.0 b5.0 a

zOverall plant rating scale: I = severely chlorosis with partial lower leaf defolia-tion, 3 = overall very pale with slight interveinal chlorosis with no defoliation,5 = all leaves deep green.

yMeans within columns followed by the same letter are not significant differentat p=0.05 by Duncan's Multiple Range Test

in the highest total iron contents, but none were significantly greater than thecontrol (Table 6).

In general, none of the foliar spray treatments were very effective in cor-recting the iron deficiency problem. DTPA (Sequestrene 330, Miller 330) was noteffective, even though it commonly is used and recommended as a foliar spray.Both ferrous sulfate and the experimental ferric citrate/ammonium sulfateyielded some positive response, but the results were not satisfactory from acommercial standpoint. Ammonium ferric citrate was shown to be effective asboth a foliar spray and soil application on wheat (Sheikh, 1986). These resultsdramatically demonstrate the lack of knowledge we have on the mechanism andfactors controling the foliar absorption of iron. Additional research is needed inthis area in order to improve the preformance of foliar application.

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INORGANIC AND CHELATED IRON FERTILIZERS

TABLE 6

1377

Response of peach to iron treatments applied to the new growth in the spring(4/3/86) and sampled 43 days later (5/16/86).

Treatment

1) ControlFoliar Applied2) Ferrous sulfate3) Ferrous sulfate

+ 1% PEG4) Fe cit/AmSulf5) Fe cit/AmSulf6) NFe7) EDDHA8) DTPA (Giegy)9) DTPA (Miller)Soil Applied10) Ferrous sulfate11) Fe cit/AmSulf12) NFe13) EDDHA (Geigy)14) methyl-EDDHA

(Miller)

Chlorophyllug cm"2

12.0

11.4-

9.59.1

15.27.2

14.715.5

11.37.3

10.334.8 a30.3 a

b

bbbbbb

bbb

HC1 Feug cm'2

0.31 b

0.20 b-

0.22 b0.28 b0.99 a0.23 b0.24 b0.25 b

0.23 b0.22 b0.22 b0.26 b0.24 b

OPHFeug cm'2

0.11 c

0.14 c-

0.13 c0.18 be0.19 be0.14 c0.22 abc0.21 be

0.19 be0.18 be0.25 abc0.35 a0.31 ab

Total Feug gdw"1

58 abc

52 be-

67 ab46 c42 c49 be50 be59 abc

60 abc51 be43 c75 a65 ab

PlantRating2

2.3 b

3.7 ab-

2.7 ab3.7 ab3.3 ab2.3 b4.2 ab2.8 ab

2.5 ab2.3 b2.7 ab5.0 a5.0 a

zOverall plant rating scale: I = severely chlorotic with partial lower leaf defoli-ation, 3 = overall very pale with slight interveinal chlorosis, 5 = all leaves deepgreen.

yMeans within columns followed by the same letter are not significant differentat p=0.05 by Duncan's Multiple Range Test.

For the soil applications, EDDHA (Sequestrene 138) and a similar productmethyl-EDDHA (Miller Ferric Plus) were the only treatments that effectivelyre-greened the plants. EDDHA is one of the few chelates known to maintainiron available in very alkaline soil (Chen and Barak, 1982). EDDHA generallyhas been shown to be the most effective Fe fertilizer for the correction of Fechlorosis under alkaline conditions on peach (Rogers, 1978; Rozeto,1982) andother species (Hagstrom, 1984). However, EDDHA often is not economical touse because of its extremely high price (Hagstrom, 1984). Methyl-EDDHA hasbeen marketed as low as one-half the price of EDDHA, but even this is veryexpensive from a field production standpoint. The very high pH (7.6 and 7.9,respectively) and phosphorus content (150 ppm and 71 ppm, respectively) in thepeach orchard and grape vineyard probably were too high for the citrate and

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1378 REED, LYONS AND MC EACHERN

DTPA chelates to remain stable (Chen and Barak, 1982; Elliot and Lauchli, 1985;Lindsay and Schwab, 1982). However, citrate and DTPA may prove effectiveunder less alkaline conditions.

ACKNOWLEDGEMENTS

Texas Agricultural Experiment Station Article No. 22760. Mention of tradenamesdoes not imply endorsement of the product.

References

Chen, Y. and P. Barak. 1982. Iron nutrition of plants in calcareous soil. Adv.Agron. 35:217-420.

Elliot, G.C. and A. Lauchli. 1985. Phosphorus efficiency and phosphate-ironinteraction in maize. Agron. J. 77:399-403.

Hagstrom, G.R. 1984. Current management practices for correcting iron defi-ciency in plants with emphasis on soil management J. Plant Nutr. 7:23-46.

Katyal, J.C. and B.D. Sharma. 1980. A new technique of plant analysis toresolve iron chlorosis. Plant Soil 55:105-119.

Lindsay, W.L. and A.P. Schwab. 1982. The chemistry of iron in soils and itsavailability to plants. J. Plant Nutr. 5:821-840.

MoTan, R. 1982. Formulae for determination of chlorophyllous pigmentsextracted with N,N-dimethyformamide. Plant Physiol. 69:1376-1381.

Moran, R. and D. Porath. 1980. Chlorophyll determination in intact tissues usingN,N-dimethylformamide. Plant Phyiol. 65:478-479.

Pierson, E.E. and R.B. Clark. 1984. Chelating agent differences in ferrous irondeterminations. J. Plant Nutr. 7:91-106.

Rogers, E. Iron chlorosis and mineral content of 'Fay Alberta', 'Shippers LateRed' and 'Redhaven' peach trees as affected by iron chelates. J. Amer.Soc. Hort. Sci. 103:608-612.

Rozeto, B. 1982. Treatments for iron chlorosis in peach trees. J. Plant Nutr.5:917-922.

Sheikh, S. 1986. Effect of ammonium iron (III) citrate as liquid-fertilizer onwheat. J. Plant Nutr. 9:975-979.

Smith, M.W. and J.B. Storey. 1976. The influence of washing procedures on sur-face removal and leaching of certain elements from pecan leaflets. HortS-cience 11:50-52.

Takkar, P.N. and N.P. Kaur. 1984. HC1 method for Fe2+ estimation to resolveiron chlorosis in plants. J. Plant Nutr. 7:81-90.

Welch, C.D. and C. Gray. 1976. Iron chlorosis of turf grasses, ornamentals andvegetables, Texas Agricultural Extension Service Bulletin L-435.

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