ort cience container substrate-ph response to differing...

HORTSCIENCE 42(5):1268–1273. 2007.

Container Substrate-pH Responseto Differing Limestone Typeand Particle SizeJinsheng HuangDepartment of Plant Biology, University of New Hampshire, Durham,NH 03824

Paul R. Fisher1

Environmental Horticulture Department, University of Florida, Gainesville,FL 32611

William R. ArgoBlackmore Co., 10800 Blackmore Ave., Belleville, MI 48111

Additional index words. calcium carbonate, calcite, dolomite, fineness factor, hydrated lime,substrate pH, pH management, particle size distribution, neutralizing value

Abstract. The objective of this study was to develop reactivity indices to describe the pHresponse for liming materials incorporated into container substrates. Three reactivityindices [particle size efficiency (PSE), fineness factor (FF), and effective calciumcarbonate equivalence (ECC)] were developed based on lime particle size distributionand lime neutralizing value (NV) in CaCO3 equivalent. Six lime particle size fractions(2000 to 850, 850 to 250, 250 to 150, 150 to 75, 75 to 45, and <45 mm) separated from eachof three calcitic limes and seven dolomitic limes were used to calibrate PSE, and werebased on the increase in substrate pH (DpH) incited by the particle size fraction relativeto reagent grade CaCO3 when mixed in a sphagnum peat substrate at 5 g CaCO3

equivalents per liter of peat. PSE for calcitic carbonate limes at day 7 (short-term pHresponse) were 0.13, 0.40, 0.78, 0.97, 1.00, and 1.00 for 2000 to 850, 850 to 250, 250 to 150,150 to 75, 75 to 45, and <45 mm particle fractions, respectively. Other PSE values weredescribed for dolomitic carbonate limestones and for long-term pH response, and PSEwas modeled with a function over time. FF was calculated for a liming material bysumming the percentages by weight in each of the six size fractions multiplied by theappropriate PSE. ECC rating of a limestone was the product of its NV and FF. ECCmultiplied by the applied lime incorporation rate could be used to predict substrate-pHresponse. Estimated PSE values were validated in two experiments that comparedexpected and observed substrate pH using 29 unscreened carbonate and hydrated limesources blended with peat. Validation trials resulted in a close correlation and no biasbetween expected and observed pH values. Revised PSE values are useful to evaluate thereactivity of different limestone sources for container substrates given the fine particlesize, short crop duration, and pH sensitivity of many container-grown crops.

The effectiveness of a lime material forneutralizing acidity of substrates depends onits neutralizing capacity, fineness of grinding,chemical composition, and mineralogy (Barber,1984). Because the dissolution of limestoneoccurs as a surface reaction, the particle sizedistribution of a liming material directlyinfluences the dissolution rate and its effec-

tiveness in neutralizing soil acidity. A parti-cle size efficiency (PSE) factor can beassigned to each particle size fraction of anagricultural limestone (Meyer and Volk,1952; Motto and Melsted, 1960; Murphyand Follett, 1978). A single limestone sourceincludes a range in particle sizes, and thepercent by weight of each particle sizefraction (PF) describes the distribution. Theoverall PSE (ranging from 0 to 1) of a limesource can be described by its fineness factor(FF), calculated for time t as the sum of PFand PSE for each of i = 1 to n particle sizefractions:

FFt =Xn

i=1

PFi 3 PSEi;t

� �[1]

The term ‘‘effective calcium carbonateequivalence’’ (ECC), calculated as a ratio ofneutralizing value compared with CaCO3,quantifies the combined effects of particlesize distribution and acid neutralizing value

(NV) of a limestone on pH response, calcu-lated as:

ECC = FF 3 NV [2]

PSE values have been defined for agriculturallimestone in field soils. Liming particlescoarser than 2000 mm (retained on a U.S.10-mesh screen) had no effect on soil pH(Meyer and Volk, 1952; Motto and Melsted,1960; Murphy and Follett, 1978; Tisdaleet al., 1993). A lime particle size finerthan 250 mm (passed through a 60-mesh)had 100% effectiveness for agronomy crops(Barber, 1984; Tisdale et al., 1993). For limeparticle fraction 250–2000 mm, there is someinconsistency between sources on the relativeeffectiveness for agronomic lime use. How-ever, it is generally agreed that the PSE ofthree particle fractions of >850 mm (retainedon a 20-mesh screen), 850 to 250 mm (passinga 20-mesh but retained on 60-mesh screen),and <250 mm (passing a 60-mesh screen)could be assigned as �20%, 60%, and100%, respectively, on the basis of a reviewof published research (Meyer and Volk,1952; Motto and Melsted, 1960; Murphyand Follett, 1978), lime material review andtexts (Barber, 1984; Tisdale et al., 1993), andstate extension sources (Little and Watson,2002; Peters et al., 1996).

PSE could also be used as a reactivityindex to characterize lime materials for con-tainer substrates, but existing PSE valuesbased on long-term response from coarselime grades applied in field soils requirerecalibration. Many limestones used in con-tainer substrates are classified as pulverized,superfine (Schollenberger and Salter, 1943),with the majority of particles <250 mm.Agronomic PSE values would therefore pro-vide no distinction between these very finegrades of limestone. Furthermore, nurseryand greenhouse crop duration (and thereforerequired lime reaction times) is often onlyseveral weeks in length, rather than monthsor years for field crops and pasture.

In this study, we evaluated the PSE ofsix particle size fractions ranging from>850 mm (retained on U.S. standard 20-mesh screen) to <45 mm (passed through325-mesh screen) based on a survey ofhorticultural lime samples. We then quanti-fied FF, NV, and ECC based on the PSE ofeach limestone. The specific objectives ofthis project were:

(a) To develop PSE appropriate for horti-cultural substrates that can quantifythe reactivity of fine particles withshort-term substrate-pH responses.

(b) To quantify the ECC of a surveyof lime sources and validate the re-lationship between particle size andsubstrate-pH change.

Materials and Methods

Description of limestone samples. Reagent-grade CaCO3, and 29 commercial liming

Received for publication 14 Dec. 2006. Acceptedfor publication 13 Mar. 2007.Use of trade names in this publication does notimply endorsement of the products named orcriticism of similar ones not mentioned.We thank the American Floral Endowment, Black-more Co., Center Greenhouses, D.S. Cole Growers,Ellegaard, Greencare Fertilizers, Kube-Pak Corp.,Lucas Greenhouses, Pleasant View Gardens, Pre-mier Horticulture, Quality Analytical Laboratories,Sun Gro Horticulture, and the UNH AgriculturalExperiment Station.1To whom reprint requests should be addressed;e-mail [email protected]

1268 HORTSCIENCE VOL. 42(5) AUGUST 2007

samples that are used horticulturally in con-tainer substrates were used in this study (Table1). The limestone materials represented awide range of physical and chemical proper-ties, and came from 14 sources of green-house, fertilizer, and substrate companies.The sample included 25 carbonate and fourhydrated limes. Moisture content for thetested limestone samples varied from 0.05%to 1.2% (data not shown), which is importantbecause increasing moisture decreases effec-tive NV per gram of limestone. Moisturelevel for our data set was low compared withup to 10% moisture measured in some agri-cultural limestones (Barber, 1984).

Based on the Ca/(Ca + Mg) ratio, carbon-ate limestones were categorized into twodistinct groups: calcitic limestones and dolo-mitic limestones (Table 1). The Ca/(Ca +Mg) ratio for calcitic lime samples rangedfrom 0.84 to 0.99, with an average of 0.94.For dolomitic lime samples, the Ca/(Ca +Mg) ratio ranged from 0.62 to 0.67, with anaverage of 0.64. The overall average Ca andMg content for calcitic lime samples were34.5% and 2.2%, respectively, comparedwith 19.8% Ca and 11.3% Mg for dolomiticlime samples. Hydrated lime materialsincluded both calcitic and dolomitic sources,with up to 46.7% Ca content in calcitichydrated lime and 19.8% Mg in dolomitichydrated lime (Table 1). In comparison, purecalcite contains 40% Ca with no magnesiumcontamination, while pure dolomite contains21% Ca and 13% Mg.

Tested lime samples contained othernutrient elements and Al, which affects bothfertilizer value and lime reactivity. Increas-ing metal oxide content directly decreasesacid neutralizing value, and metal oxidecoatings of limestone particles can inhibitlimestone dissolution reaction (Warfvingeand Sverdrup, 1989). Fe content varied from0.03% to 0.4%, with an average of 0.11%.Mn content varied from 0.004% to 0.04%,with an average of 0.012%. The averagecontents of B, Al, P, and K were 0.008%,0.04%, 0.05%, and 1.03%, respectively.Micronutrients Cu, Zn, and Mo were not atdetectable levels. Previous research showedthat, at a normal application rate (10 t per ha),many agricultural limestones contain impor-tant amounts of Fe and Mn for field crops(Chichilo and Whittaker, 1958, 1961). At therecommended incorporation rate of 6 g�L–1 ofsoilless container substrates (Nelson, 2003),the tested carbonate lime samples would supply1.05–2.37 g Ca, 0.02–0.76 g Mg, 1.8–24.2 mgFe, and 0.24–2.46 mg Mn in 1 L of substrate.

The NV of calcitic limes ranged from94% to 101% (Table 1), with an average of99%. In contrast, the NV of dolomitic lime-stones varied from 95% to 108.7%, with anaverage of 103.4%. Dolomitic lime samplestended to have higher neutralizing capacitiesthan calcitic sample because of the lowermolecular weight of MgCO3 compared withCaCO3, although inert impurities decreasedNV in several dolomitic limestones (D1,D3, D4, D8, and D15). The hydrated limingmaterials, with lower molecular weights

than calcium carbonate, had the highestaverage NV (137.8%), ranging from 117%to 163%. The dolomitic hydrates (H1 andH3) had higher NV than calcitic hydrates(H2 and H4).

Dry sieving was performed in a sieveshaker for the first 30 min, and each individ-ual sieve was then manually shaken to ensureall fine particles passed through the sieve.The sample was passed through a series of sixstandard sieves and the results are expressedas percentage passing through or remainingon each sieve: >850 mm (retained on a U.S.standard 20-mesh sieve), 850 to 250 mm(retained on a 60-mesh sieve), 250 to 150 mm(retained on a 100-mesh sieve), 150 to 75 mm(retained a 200-mesh sieve), 75 to 45 mm(retained on a 325-mesh sieve), and <45 mm(passed through a 325-mesh sieve). Eachfraction was dried and weighed to obtain itspercentage in the sample (Table 1).

Trial 1. The pH response from the sixparticle size fractions for the calibrationsamples and from all unscreened 29 limesamples and reagent CaCO3, was quantifiedby incorporating the lime samples at 5 g CCEper liter of peat substrate. The substrate was aCanadian sphagnum peat (Professional BlackBale Peat, SunGro Horticulture, Bellevue,WA) with long fibers and little dust (VonPost scale 2–3; Puustjarvi and Robertson,1975). The initial pH of the raw peat was3.5. Substrate moisture was brought to con-tainer capacity (near saturation point at 500mL water per liter of substrate) in a partiallyopen plastic bag and was incubated at roomtemperature (22 �C) for 11 weeks. SubstratepH was measured at days 0, 1, 7, 14, 21, 28,35, 42, 49, and 77 with three replicates usingan Orion 620 pH meter (Thermo ElectronCo., Waltham, MA). On each pH measure-ment date, the solution was squeezed fromthe substrate into a corner of the bag, withoutremoving the solution or substrate from thebag. Substrate pH was then measured directlyin the solution, and the solution was thenmixed back in with the substrate (minimalevaporation occurred).

Trial 2. The 29 unscreened limestonesamples and reagent CaCO3 were incorpo-rated into a different peat sample (unlimedpH 3.7) but from the same commercial sourceas in Trial 1, at a rate of 5 g per liter of peat(equivalent to 5 kg�m–3 or 8.3 lb/cubic yard,not corrected for equal NV). Sample prepa-ration and data collection were consistentwith Trial 1, and substrate pH was measuredon days 0, 1, 7, 14, 21, 28, 35, and 44 withthree replicates.

Quantifying lime reactivity parameters.Three calcitic and seven dolomitic limestonesamples were randomly selected from amongall 29 commercial limestone samples for thecalibration of PSE values (Table 1), includingthree calcitic and seven dolomitic limestones(Table 1). Because not all limestone samplescontained particles >850 mm, only five sam-ples were analyzed (C2, D5, D7, D9, andD12) for this particle fraction (Fig. 1A andB). The six particle fractions separated fromeach of the ten limestone samples were mixed

at 5 g CaCO3 equivalents (CCE) per liter ofpeat substrate as described below for Trial 1.Substrate pH was measured over time, andthe PSEt on day t of a particle size fractionwas determined as:

PSEt = ðpH increase on day tÞ=ðcorresponding pH increase on

day t for reagent CaCO3Þ [3]

ANOVA was used to evaluate substrate pHfor Trial 1 separately for each measurementdate and particle fraction, with chemical type(calcitic or dolomitic) as the main effect, andlimestone source as a nested effect withinchemical type. PSE values were then calcu-lated based on the screened calibration sam-ples in Trial 1 using Eq. [3]. PSE data foreach lime source were analyzed separately bydate using PROC GLM of SAS (SAS Insti-tute, 1999) to test effects of lime chemistry(calcitic or dolomitic), particle size fraction,and their interaction. Means for each limechemistry and particle size fraction wereseparated by Tukey’s HSD (P # 0.05). PSEvalues based on pH response at day 7 wereused to calculate the FF and ECC for all 29unscreened limestone samples. The relation-ship between the ECC and pH from Trials 1and 2 for the unscreened limestones wasanalyzed using SAS PROC REG, separatelyby measurement date and trial.

PSE data were also plotted over time foreach chemistry and particle size fraction, anda monomolecular curve was fitted for eachparticle size fraction. The equation of themonomolecular function was

PSE = A ð1� e�ktÞ [4]

where A represents the maximum effective-ness between 0 and 1, k is a rate parameter,and t represents the days after incorporatingthe lime into peat. The monomolecular func-tion is a symmetrical function that is deriv-able, separates the magnitude of pH response(A) from the reaction rate (k), and may thereforebe useful for simulating pH change over time.

Using PSE to estimate pH response. Sub-strate pH response following lime incorpora-tion in a peat substrate depends on the initialsubstrate pH, the buffering of the substrate tochange in pH, and the effective applied limeincorporation rate. Substrate buffering (pHB)can be quantified with units of DpH permilliequivalent of base per liter of substrate[DpH/(meq CaCO3�L–1)]. Titration of peatwith Ca(OH)2 shows a nearly linear pHresponse with increasing application rate ofbase up to a pH near 7.0 (Rippy and Nelson,2005). Because of this linearity, few datapoints are needed to quantify pHB for a givensubstrate. In our study, we used the final pH(day 77 in Trial 1, and day 44 in Trial 2)following incorporation of 5 g reagentCaCO3 per liter of peat to quantify pHB.

One gram of pure CaCO3 equals 1000/50.045 = 19.98 meq of base. The ECC of aparticular lime source at a given number ofdays t after incorporating lime can be calculated

HORTSCIENCE VOL. 42(5) AUGUST 2007 1269

SOIL MANAGEMENT, FERTILIZATION, AND IRRIGATION

Tab

le1

.T

este

dli

min

gm

ater

ials

,th

eir

acid

neu

tral

izin

gv

alu

e(N

V)

in%

CaC

O3

equ

ival

ents

,p

arti

cle

size

dis

trib

uti

on

,ch

emic

alco

mp

osi

tio

n,

fin

enes

sfa

cto

r(F

F),

and

effe

ctiv

eca

lciu

mca

rbo

nat

eeq

uiv

alen

ce(E

CC

)in

%C

aCO

3eq

uiv

alen

ts.

Lim

eco

dez

NV

(%)

Par

ticl

esre

tain

ed(%

)L

ime

gra

dey

Ca

(%)

Mg

(%)

Ca/

(Ca

+M

g)

FF

(%)x

EC

C(%

)[=

FF

·N

V]

Lim

ety

pe

85

0–

20

00mm

25

0–8

50

mm1

50

–2

50

mm7

5–

150

mm4

5–

75

mm<

45

mmC

alib

rati

on

sam

ples

Rea

gen

tC

aCO

3R

99

.90

.00

.00

.00

.00

.01

00

.0S

up

erfi

ne

40

.00

0.0

01

.000

10

0.0

99

.9C

alci

tic

(hig

hC

a)C

29

8.9

88

.51

0.7

0.0

0.1

0.0

0.7

Co

arse

39

.54

0.3

30

.992

16

.61

6.4

C3

10

1.0

0.0

0.4

3.7

19

.22

5.1

51

.7S

up

erfi

ne

38

.38

1.1

70

.972

98

.59

9.5

C6

10

0.2

0.0

0.7

7.9

22

.91

3.2

55

.3S

up

erfi

ne

29

.29

4.7

70

.860

97

.29

7.3

Do

lom

itic

D2

10

1.8

0.0

0.6

6.4

26

.82

4.1

42

.1S

up

erfi

ne

21

.65

12

.62

0.6

329

4.8

96

.5D

51

03

.64

.15

.93

.21

5.7

21

.94

9.1

Su

per

fin

e1

9.4

61

1.3

70

.631

90

.19

3.4

D6

10

6.9

0.0

0.6

5.2

24

.01

8.6

51

.5S

up

erfi

ne

19

.83

11

.70

0.6

299

5.4

10

2.0

D7

10

6.7

0.5

25

.62

1.3

25

.01

0.8

16

.9G

rou

nd

20

.67

11

.96

0.6

337

4.6

79

.6D

91

07

.90

.48

1.9

15

.21

.50

.40

.5C

oar

se1

9.7

61

1.6

70

.629

45

.14

8.7

D1

21

08

.60

.21

.35

.11

9.3

20

.05

4.1

Su

per

fin

e1

9.5

31

1.5

40

.629

95

.41

03

.6D

16

10

7.1

0.0

15

.81

1.9

11

.31

1.6

49

.4P

ulv

eriz

ed1

8.8

41

0.8

80

.634

85

.39

1.4

Rem

ain

ing

lim

esa

mp

les

Cal

citi

c(h

igh

Ca)

C1

94

.20

.00

.00

.00

.10

.29

9.7

Su

per

fin

e3

2.4

44

.15

0.8

871

00

.09

4.2

C4

10

0.8

0.0

0.2

4.5

17

.82

7.6

49

.9S

up

erfi

ne

38

.92

0.7

80

.982

98

.49

9.1

C5

10

0.8

0.0

0.1

1.0

19

.42

8.1

51

.4S

up

erfi

ne

29

.24

5.5

30

.841

99

.19

9.9

C7

97

.50

.00

.53

.91

1.2

9.2

75

.1S

up

erfi

ne

34

.32

0.2

70

.992

98

.49

5.9

C8

10

0.3

0.0

0.9

4.5

19

.81

3.1

61

.7S

up

erfi

ne

34

.04

0.4

10

.988

97

.99

8.2

Do

lom

itic

D1

95

.70

.00

.22

.62

8.0

26

.24

3.0

Su

per

fin

e2

1.2

71

2.4

40

.631

96

.29

2.1

D3

95

.72

.21

6.4

16

.63

6.2

14

.11

4.5

Gro

un

d2

2.1

61

1.0

40

.667

79

.07

5.6

D4

98

.10

.03

.54

.01

5.1

25

.05

2.4

Su

per

fin

e1

9.7

81

1.3

40

.636

95

.09

3.2

D8

95

.80

.00

.11

.01

5.1

22

.36

1.4

Su

per

fin

e1

9.8

21

0.1

20

.662

98

.09

3.9

D1

01

06

.80

.10

.72

.61

3.8

21

.16

1.7

Su

per

fin

e2

0.2

51

1.8

60

.631

97

.21

03

.8D

11

10

8.7

0.1

6.8

13

.92

1.5

14

.24

3.4

Pu

lver

ized

19

.39

11

.52

0.6

278

8.9

96

.6D

13

10

8.0

0.0

0.6

6.9

25

.62

3.6

43

.4S

up

erfi

ne

19

.00

11

.30

0.6

279

4.8

10

2.4

D1

41

05

.50

.00

.13

.12

1.7

23

.85

1.3

Su

per

fin

e1

8.6

81

1.3

30

.623

96

.71

02

.0D

15

95

.00

.00

.00

.01

.62

0.9

77

.5S

up

erfi

ne

17

.54

9.1

70

.657

99

.89

4.8

D1

71

06

.80

.00

.20

.71

.50

.99

6.8

Su

per

fin

e1

9.3

71

0.7

80

.643

99

.61

06

.4H

ydra

ted

H1

162.6

0.0

0.0

0.1

2.4

5.5

91.9

Super

fine

33.7

119.7

80.6

30100.0

162.6

H2

11

7.2

0.0

0.0

0.0

0.2

1.1

98

.6S

up

erfi

ne

46

.23

0.7

30

.984

10

0.0

11

7.2

H3

13

8.1

0.0

0.7

2.7

16

.41

1.5

68

.7S

up

erfi

ne

28

.96

16

.76

0.6

331

00

.01

38

.1H

41

33

.50

.00

.00

.00

.50

.79

8.8

Su

per

fin

e4

6.6

80

.41

0.9

911

00

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33

.5zL

ime

cod

esR

,C

,an

dD

repr

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tre

agen

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aCO

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calc

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(C),

and

dolo

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y.

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ime

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des

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atio

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(Sch

olle

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reen

,at

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t6

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of

pu

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lim

esto

new

illp

ass

thro

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a1

50

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(#1

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)sc

reen

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dat

leas

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(#2

00)

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or

the

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,<6

0%

of

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gh

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(#6

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for

C2

and

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for

D9

,re

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ely

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ased

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.


from Eq. [2] using PSE values estimated attime t from Eq. [4], multiplied by 19.98 togive the effective meq of base per gram. ThepH response (pHt) at time t for a givennumber of grams of applied lime�L–1 (C)can be calculated from

pHt = pHinit + CðECCt 3 19:98Þ3 pHB [5]

where pHinit is the initial unlimed substratepH. We used Eq. [5] to validate our PSEestimates. The substrate pH for eachunscreened limestone was predicted usingEq. [5] for Trial 1 and Trial 2 and was thencompared against the observed substrate pH.

Results and Discussion

Peat pH responses for different particlesize fractions. Reagent CaCO3 had only oneparticle size fraction, with 100% passedthrough a 325-mesh sieve (<45 mm) (Table1). After 77 d, final substrate pH from reagentCaCO3 increased by 2.18 pH units (Fig. 1K),which equaled the mean final DpH for thefour finest particle fractions. In contrast, thetwo coarsest particle fractions had a lowerfinal DpH (1.18 and 2.03 on day 77 for the>850 mm and 850 to 250 mm fractions forboth calcite and dolomite, respectively) com-pared with either finer particles or reagentCaCO3 (Fig. 1). Substrate pH on day 77 wassimilar between calcitic and dolomitic chem-ical types. The mean DpH on day 77 was 2.14and 2.19 for calcitic and dolomitic chemicaltypes, respectively (within 0.05 pH unit, P =0.36).

Within a given mesh size, there weredifferences in pH response between limesources, indicating that factors other thanparticle diameter and Ca/Mg balance alsocontributed to pH change. For example,variation from the mean pH on day 77 for agiven particle fraction was within ±0.3 pHunit for a particular lime source. On earliermeasurement dates, differences from a givenlime source and the mean pH was also within±0.4 pH unit. Lime reactivity is affected bytotal surface area including internal porespace (Barber, 1984; Haby and Leonard,2002; Love and Whittaker, 1954, Parfitt andEllis, 1966), crystal structure (Rippy, 2005),and iron contamination (Parfitt and Ellis,1966; Warfvinge and Sverdrup, 1989), whichwere not evaluated in our study. The moder-ate level of variation between lime sources ata given particle fraction found in this exper-iment increases confidence that different lime

Fig. 1. Changes in the substrate pH of a peat substrate over time for peat amended with 5 g CCE�L–1

for the six particle size fractions of the ten different lime sources in the calibration sam-ples plus reagent grade CaCO3 (calcitic materials—C2, C3, and C6; dolomitic materials—D2,D5, D6, D7, D9, D12, and D16). The confidence interval (95% CI) in parentheses represents thepooled value within the same particle size fraction. Legends for calcitic and dolomitic mate-rials are enclosed in K and L, respectively. Reagent CaCO3 had only one particle size fraction(<45 mm) and was only plotted in K. For the coarsest particle size fraction (2000 to 850 mm)had only one calcitic limestone sample (C2) and four dolomitic limestone samples (D5, D7, D9,and D12).

Table 2. Particle size efficiency (PSE) estimates based on six screened particle fractions from 10 calibration lime samples on different days after mixing limestoneinto the substrate in Trial 1.z

Particle size (mm)

Day 1 Day 7 Day 14 Day 28 Day 77

Calcitic Dolomitic Calcitic Dolomitic Calcitic Dolomitic Calcitic Dolomitic Calcitic Dolomitic

850–2000 mm (10–20 mesh) 0.013 h 0.028 h 0.103 f 0.181 f 0.213 e 0.263 e 0.357 d 0.365 d 0.530 c 0.551 c250–850 mm (20–60 mesh) 0.107 g 0.106 g 0.447 e 0.442 e 0.652 d 0.620 d 0.826 c 0.803 c 0.909 b 0.933 b150–250 mm (60–100 mesh) 0.229 f 0.213 f 0.794 c 0.662 d 0.908 bc 0.866 c 0.986 ab 0.976 b 0.973 ab 0.980 a75–150 mm (100–200 mesh) 0.421 d 0.356 e 0.913 abc 0.831 c 0.966 ab 0.978 ab 0.986 ab 0.997 a 0.970 ab 0.991 a45–75 mm (200–325 mesh) 0.642 b 0.506 c 0.981 ab 0.935 ab 0.993 ab 0.987 ab 0.983 ab 0.993 ab 0.979 ab 0.986 a<45 mm (>325 mesh) 0.778 a 0.636 b 0.987 a 0.957 ab 0.986 ab 0.997 a 0.990 ab 0.994 Ab 0.974 ab 0.990 azMeasured PSE = (DpH from the lime fraction)/(DpH from reagent-grade CaCO3) for each measurement day. Data were analyzed separately by measurement day,and means were compared with Tukey’s HSD at the P # 0.05 level.


sources had a culturally similar (althoughstatistically different) pH response at a givenparticle fraction and that the mean pHresponse across lime sources may be areasonable approximation for estimatingPSE. It may also be possible to improveprediction of pH response by incorporatingfactors such as total surface area.

The greatest DpH (3.26) for the reagentCaCO3 occurred 1 d after incorporation,decreased by day 7 to DpH 2.52, and declinedgradually to a final DpH 2.18 (Fig. 1K). Theinitial rapid pH increase and subsequentdecline were probably incited by an initialdisequilibrium with respect to both CO2 and

exchange of protons at substrate exchangesites, as discussed by Rippy and Nelson(2005). The finest particle fraction (<45 mm)had a similar reaction pattern to CaCO3, withthe highest DpH occurring on day 1 or 7, witha particularly high initial pH increase forcalcitic lime sources. In contrast, DpH for thetwo coarsest lime fractions was still increas-ing slightly by day 77. Duration required toincrease mean DpH by at least 2.18 units was1, 7, 7, or 28 d for the <45, 75 to 45, 150 to 75,and 250 to 150 mm fractions, respectively.

Relative PSE, FF, and ECC. PSE of eachparticle fraction differed on day 1 such thatPSE ranged from 0.013 to 0.778 for calcitic

and from 0.028 to 0.636 for dolomitic limesamples (Table 2). By day 77, there wereonly two statistically separate PSE groups forcalcitic limestones (>850 mm and all otherparticle sizes), and three statistically separatePSE groups for dolomitic limestones (>850mm, 250–850 mm, and all finer particle sizes),with no difference between chemical types.No differences in PSE occurred betweenchemical types (calcitic vs. dolomitic limes)for the two most coarse particles fractions of>850 mm and 250–850 mm on any measure-ment day, although there were only fivelimestone sources with >850 mm-sized par-ticles, which reduced the statistical power ofthe analysis to identify differences. For thefiner particle fractions, calcitic limestoneshad a slightly higher PSE than the dolomiticlimestones on days 1 and 7. Differencesbetween the two chemical types diminishedas time progressed, limestones reacted morecompletely, and PSE approached 1.

As each particle fraction graduallyreacted with the peat acidity, PSE increasedover time to a maximum of 1 with a pattern ofdiminishing returns (Fig. 1). A monomolec-ular function, Eq. [4], was used to quantifyPSE increases over time (Table 3, Fig. 2).Estimates of A, the maximum PSE parameterin Eq. [4], were not significantly differentfrom 1 for the four particle fractions finerthan 250 mm, and A was therefore set to avalue of 1 in the nonlinear regression forthese fractions. In contrast, A equaled 0.563for the >850 mm and 0.900 for the 850 to 250mm fractions. The largest particle sizes maynever completely react in peat, at least duringthe short time frame for seasonal greenhousecrops. Coarse particles have low exposedexterior surface area in general and may alsohave greater internal surfaces (or internalpores) than fine particles (Rippy, 2005), bothof which would reduce reactivity comparedwith fine particles. In addition, the surface oflimestone particles can become coated byprecipitates of Fe and organic C from soil

Table 3. Parameter estimates for the monomolecular function to estimate the particle size effectiveness (PSE) for six lime particle size fractions over time, wherePSE = A(1 – e–kt).z

Particle size fraction (mm)

850–2000 250–850 150–250 150–250 75–150 75–150 45–75 45–75 <45 <45U.S. mesh size 10–20 20–60 60–100 60–100 100–200 100–200 200–325 200–325 Pass 325 Pass 325Lime typey C, D C, D C D C D C D C DK 0.038 0.085 0.219 0.152 0.513 0.335 1.027 0.693 1.504 1.009SE of k 0.003 0.003 0.009 0.003 0.027 0.011 0.003 0.016 0.059 0.016A 0.563 0.900 1 1 1 1 1 1 1 1SE of A 0.019 0.007Days to 95% reaction N/A N/A 13.7 19.7 5.8 8.9 2.9 4.3 2.0 3.0Days to 50% reaction 58.2 9.5 3.2 4.5 1.4 2.1 0.7 1.0 0.5 0.7r2 x 0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.98 0.99

Calculated PSE values (suggested for horticultural description of lime sources)w

Short-term (7 d) 0.13 0.40 0.78 0.66 0.97 0.90 1.00 1.00 1.00 1.00Long-term (77 d) 0.53 0.90 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00zA represents the maximum effectiveness between 0 and 1, k is a rate parameter, and t represents the days after incorporating the lime into peat. Days to 95%reaction, days to 50% reaction, and short- and long-term PSE values were calculated using the monomolecular function.yC = calcitic, and D = dolomitic carbonate limes. For the two most coarse particle size fractions, there was no significant difference between PSE for calcitic anddolomitic limes.xThe r2 was determined for a simple linear regression between the estimated PSE using the monomolecular function vs. the measured PSE. Measured PSE = (DpHfrom the lime fraction)/(DpH from reagent-grade CaCO3).wThese PSE values are calculated from the monomolecular function in this table based on day 7 (‘‘Short-term’’) or day 77 (‘‘Long-term’’). For highly reactivehydrated lime, PSE can be assumed to equal 1.00 for all particle sizes over both short and long terms.

Fig. 2. Reaction curves (shown as lines) estimated with the monomolecular function to estimate the PSEfor six lime particle size fractions over time for calcitic (C) and dolomitic (D) carbonate limes, wherePSE = A(1 – e–kt) and parameter estimates for A and k are described in Table 3. Symbols represent thecalculated mean PSE with 95% CIs.


solutions (Warfvinge and Sverdrup, 1989).These coatings, formed from the oxidation ofamorphous iron carbonate readily precipitat-ing on the mineral surfaces, inhibit limestonedissolution reaction.

The ECC is a measure of expected basestrength of a limestone (considering bothacid- neutralizing capacity and particle size)and therefore substrate-pH response. Fordynamic simulation of pH over time, themonomolecular function could be used (addi-tional model parameters for substrate buffer-ing capacity, temperature and moisture levelwould also be part of a substrate-pH model).However, to compare and classify limestonesources, discrete PSE values are needed. Allparticles smaller than 75 mm (passing througha 200-mesh screen) were estimated to reactby day 7, and all particles smaller than 250mm (passing a 60-mesh screen) were esti-mated to react by day 77, as indicated by aPSE of 1.00 in Table 3. Because pH (and PSE)changes over time, the question arises ofwhich measurement day is most appropriatefor selecting a PSE value and resulting ECC.

Our suggested PSE values for short- andlong-term reaction of limestones in containersubstrates are shown in the bottom of Table 3.In Trials 1 and 2, conditions were close tooptimum for pH reaction, with the substratemaintained near saturation and at 22 �C.However, in commercial situations, thesereaction conditions can vary widely. Forexample, the moisture level of compressedbales may start out to be <25% while loose-filled bags may be >40% saturated. If thebales or bags are exposed to precipitation,then the moisture levels can go much higher.The storage temperature of the substrate canrange from <0 to >30 �C. Storage durationcan range from <30 min to >4 months. Oncethe substrate is placed into a pot, variablemoisture levels and temperatures can alsooccur.

It is our conclusion that a PSE based onday 7 may be most appropriate for short-termcrops (4–8 weeks) and as a measure of limereaction rate, because rapid pH rise is neededin short-term crops and there is insufficienttime for complete lime reaction for coarseparticles (Table 3, see ‘‘Short-term’’ PSEvalues). For long-term crops (2-month durationor more) and as a measure of potentialequilibrium-pH, a PSE based on day 77 maybe more appropriate (Table 3, see ‘‘Long-term’’PSE values).

The estimated FF for each lime sourcewas calculated based on the short-term (day7) and long-term (day 77) PSE values. Short-term FF (Table 1) for carbonate limes rangedfrom 16.6% (coarse: C2) to 100% (fine: C1)and averaged 89.7%. Long-term FF (data notshown) ranged from 57.3% to 100%. Multi-plying FF by NV, the ECC at day 7 rangedfrom 16.4 (C2) to 162.6 (H1), indicating thatH1 had 10 times the initial acid neutralizingcapacity of C2.

Validation of pH response. Expected sub-strate pH for day 7 and 28 for the unscreenedlimestones in Trials 1 and 2 was calculatedusing Eq. [5], where the PSE values wereestimated using the monomolecular functionfor t = 7 or 28 d (Table 3). Substrate buffering(pHB, Eq. [5]) was calculated from pHresponse with CaCO3 from day 77 (Trial 1)or day 44 (Trial 2) and equaled 0.0225 or0.0246 pH unit/meq CaCO3, respectively.For Trial 1, the lime concentration (C inEq. [5]) varied between lime sources to equal5 g CaCO3 per liter of substrate, whereasC equaled 5 g for each limestone in Trial 2(not corrected for NV). Expected andobserved substrate pH are compared inFig. 3. For all comparisons (day 7 and day28 in both trials), the intercept did not differsignificantly from 0 and the slope did notdiffer from 1, indicating that the estimateswere not biased. Adjusted r2 for the compar-

isons ranged from 0.83 to 0.88, indicatingthat the majority of variation in substratepH was accounted for by Eq. [5] and pro-viding validation of the monomolecularfunction parameters (see Table 3) for calcu-lating PSE.

Literature Cited

Barber, S.A. 1984. Liming materials and practices,p. 171–209. In: F. Adams (ed.). Soil acidity andliming. 2nd ed. Agron. Monogr. 12. ASA,CSSA, Madison, WI.

Chichilo, P. and C.W. Whittaker. 1958. Traceelements in agricultural limestones of AtlanticCoast regions. Agron. J. 50:131–135.

Chichilo, P. and C.W. Whittaker. 1961. Traceelements in agricultural limestones of theUnited States. Agron. J. 53:139–144.

Haby, V.A. and A.T. Leonard. 2002. Limestonequality and effectiveness for neutralizing soilacidity. Comm. Soil Sci. Plant. Anal. 33:2935–2948.

Little, C. and M. Watson. 2002. Understandingvalue in lime. The Ohio State UniversityExtension Fact Sheet ANR-9-02.

Love, K.S. and C.W. Whittaker. 1954. Surface areaand reactivity of limestones. J. Agr. FoodChem. 2:1268–1272.

Meyer, T.A. and G.W. Volk. 1952. Effect ofparticle size of limestone on soil reaction,exchangeable cations, and plant growth. SoilSci. 73:37–52.

Motto, H. and S.W. Melsted. 1960. The eff-iciency of various particle size fractions oflimestone. Soil Sci. Soc. Amer. Proc. 24:488–490.

Murphy, L.S. and H. Follett. 1978. Liming—takinganother look at the basics. Agrichem. Age(Omaha) 22:22–26.

Nelson, P.V. 2003. Greenhouse operation andmanagement. 6th ed. Prentice-Hall, EnglewoodCliffs, NJ.

Parfitt, R.L. and B.G. Ellis. 1966. Studies onMichigan agricultural limestones. MichiganAgr. Expt. Sta. Qrtly. Bul. 49(2):12–23.

Peters, J.B., K.A. Kelling, and E.E. Schulte. 1996.Choosing between liming materials. Univ. ofWisconsin—Extension Publication A3671.

Puustjarvi, V. and R.A. Robertson. 1975. Physicaland chemical properties, p. 23–28. In: D.W.Robinson and J.G.D. Lamb (eds.). Peat inhorticulture. Academic Press, New York.

Rippy, J. 2005. Factors affecting pH establishmentand maintenance in peat moss-based substrates.North Carolina State Univ., Raleigh, PhD Diss.

Rippy, J.F.M. and P.V. Nelson. 2005. Soilless rootsubstrate pH measurement technique for titra-tion. HortScience 40(1):201–204.

SAS Institute, Inc. 1999. SAS/STAT user’s guide,version 8. SAS Institute, Inc., Cary, NC.

Schollenberger, C.J. and R.M. Salter. 1943. A chartfor evaluating agricultural limestone. J. Amer.Soc. Agron. 35:955–966.

Tisdale, S.L., W.L. Nelson, J.D. Beaton, and J.L.Havlin. 1993. Soil fertility and fertilizers. 5thed. Macmillan Publishing Co., Inc., New York.

Warfvinge, P. and H. Sverdrup. 1989. Modelinglimestone dissolution in soils. Soil Sci. Soc.Amer. J. 53:44–51.

Fig. 3. Comparison between expected and observedsubstrate pH at 7 or 28 d after mixing lime intothe substrate, from two trials. Expected pH wascalculated using pH = pHinit + C(ECC · 19.98)· pHB, where pHinit is the initial unlimedsubstrate pH, C is the lime rate (g�L–1), ECCis the effective calcium carbonate equivalence,and pHB represents substrate pH buffering[DpH/(meq CaCO3�L–1)]. PSE was estimatedwith the monomolecular function from Table 3for days 7 and 28. The solid line represents a1:1 relationship.


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