LimeR Series
Analyzing Lime in Container Substrates
Not for publication or reproduction in part or full without permission of authors.
Copyright, March 30 2009.
By Dr. Paul R. Fisher and Dr. Jinsheng Huang, University of Florida
In collaboration with other authors including Dr. William R. Argo, Blackmore Co.
Table of Contents
LimeR Series
Analyzing Lime in Container Substrates
Table of Contents
1. Modeling Lime Reaction in Peat-Based Substrates......................................................................1
2. Laboratory Protocols.......................................................................................................................9
2.1
LimeR Lime reactivity test (tests the pH effect of a particular lime source).............................9
2.2
Lime R Substrate lime requirement test (tests how much lime is needed for a particular batch
of substrate to achieve a target pH)..........................................................................................14
2.3
A gasometric procedure to measure residual carbonate in container substrates (used to
measure residual lime level) ....................................................................................................18
2.4
LimeR Substrate pH Buffering Test (evaluates pH buffering of a horticultural substrate using
a mineral HCl acid drench) .....................................................................................................22
2.5
Materials for conducting LimeR series tests............................................................................27
3. Overall LimeR Model ....................................................................................................................32
Thanks to our sponsoring companies...............................................................................................38
We thank the American Floral Endowment, and Young Plant
Research Center partners including U.S. greenhouse firms and
Blackmore Co., Ellegaard, Fafard, Greencare Fertilizers,
Pindstrup, Premier Horticulture, Quality Analytical Laboratories,
and Sun Gro Horticulture for financial support of this project.
This research was conducted at the University of Florida and
University of New Hampshire.
We also thank Dr. Paul Nelson and Dr. Janet Rippy from North Carolina State University for their
research and technical input.
Fisher and Huang. LimeR Series
Modeling Lime Reaction
1. Modeling lime reaction in peat-based substrates
This overview of lime reactions was originally published as: Fisher, P.R., J. Huang, and W.R.
Argo. 2006. Modeling lime reaction in peat-based substrates. Acta Horticulturae 718:461468.
Paul R. Fisher, Environmental Horticulture Dept., P.O. Box 110670, Gainesville FL 32611-0670,
pfisher@ufl.edu.
Jinsheng Huang, Dept. of Plant Biology, Univ. of New Hampshire, Durham, NH 03824, USA,
huang@unh.edu
William R. Argo, Blackmore Co., 10800 Blackmore Ave, Belleville, MI 48111, USA,
bargo@blackmoreco.com
Keywords: residual lime, peat, greenhouse, pH, gasometric, growing media, substrate-pH
Abstract
Limestone is incorporated into peat-based substrates to neutralize substrate acidity, increase pH
buffering capacity, and provide calcium and magnesium. Limestones differ in their rate of pH
change, equilibrium pH, and proportion of unreacted “residual” lime. In horticulture, lime reactivity
is currently measured empirically in batch tests whereby limestone is incorporated into a batch of
substrate and pH change is measured over time. Our objective was to develop a quantitative model
to describe reaction of lime over time. The lime reaction model predicts the substrate-pH based on
lime acid neutralizing capacity, lime type (calcitic, dolomitic, or hydrated), lime particle size
distribution, application concentration, and the non-limed pH and neutralizing requirement
(buffering) of the substrate. Residual lime is calculated as the proportion of lime remaining
following gradual neutralization of the substrate acidity (by subtraction of reacted lime from total
applied lime).
INTRODUCTION
The amount of lime required to neutralize acidity of a soilless container growing medium is
currently measured empirically in batch tests, whereby limestone is incorporated into substrates and
pH change is measured over time (Argo and Fisher, 2002). In order to develop a quantitative model
of lime reaction in horticultural substrates, three “R’s” need to be considered: Reactivity, Residual,
and Requirement. Reactivity, which describes the magnitude of pH change (∆pH) over time, is
primarily a function of lime particle size, lime chemistry (calcitic (CaCO3) versus dolomitic
(CaMg(CO3)2) versus hydrated (Ca(OH)2), acid neutralizing value (NV)), and initial substrate-pH.
Residual lime is the proportion of unreacted lime remaining following neutralization of substrate
acidity. Residual lime is the major source of buffering to pH change over time in soilless substrates,
which have low cation exchange capacity per unit volume (Argo and Biernbaum, 1996). Lime
Requirement (g of lime/L of substrate) depends on the amount of acidity that needs to be
neutralized in order to raise the substrate pH to a specific level (pH buffering), and is measured in
units of ∆pH per milliequivalent of base per unit volume (liters) of substrate.
Our objective was to develop a quantitative model to describe reaction of lime over time.
The model predicts the substrate-pH based on lime acid neutralizing capacity, lime type (calcitic,
dolomitic, or hydrated), lime particle size distribution, application concentration, and the non-limed
pH and neutralizing requirement (pH buffering) of the substrate.
Fisher and Huang. LimeR Series
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Modeling Lime Reaction
MATERIALS AND METHODS
Reactivity
Figure 1.1 illustrates how substrate-pH response can differ between liming sources. Rate of
pH change decreased in the order from reagent grade calcium carbonate (CaCO3) to NLS limestone
to OldCastle limestone. Substrate-pH was measured in all experiments using the squeeze solution
displacement method where moisture level was maintained at 95% container capacity (Rippy and
Nelson, 2005). The difference in reaction rate resulted primarily from differences in particle size
distribution, and secondarily in NV (Table 1.1, where NV was determined using the AOAC Official
Method 955.01 (Horwitz, 2003)). Reagent grade calcium carbonate was composed entirely of
particles that passed a 45 µm (U.S. 325 mesh) screen. In contrast, NLS had a particle size
distribution similar to the mean of our survey of limes used in horticultural substrates in the U.S. and
Canada, and OldCastle was coarser than the mean particle size distribution of horticultural limes
(Table 1.1). Differences between limes in NV occur because of the low molecular weight of
magnesium compared with calcium carbonates – compared with pure CaCO3 as a standard,
dolomitic (CaMg(CO3)2) carbonate limes have a higher NV per gram of lime. In addition, hydrated
lime (calcium or magnesium hydroxide), which is commonly used in container media has a lower
molecular weight, faster reaction rate, and higher NV than carbonate limes. For four hydrated limes
we tested that are used in horticultural substrates in the U.S. and Canada, NV ranged from 117.2% to
162.6% CaCO3 equivalents. Hydrated limes are chemically manufactured, with very fine particle
size.
Because the dissolution of limestone occurs as a surface reaction, the particle size
distribution of a liming material directly influences dissolution rate. To evaluate the effect of
particle size on soil pH changes in agronomy, a particle size efficiency (PSE) factor can be assigned
to each particle size fraction of an agricultural limestone ranging from 0 (unreactive) to 1 (highly
reactive) (Barber, 1984; Tisdale and Nelson, 1975). However, because lime sources used in
horticulture tend to be finer and faster-reacting than limes used on field soils, PSE from the
agronomy literature are too imprecise for a horticultural model.
We quantified new PSE parameters for six lime particle size fractions (>850 (retained on 20
U.S. standard mesh), 850 to 250 (retained on 60 mesh), 250 to 150 (retained on 100 mesh), 150 to 75
(retained 200 mesh), 75 to 45 (retained on 325 mesh), and < 45 µm (passed through 325 mesh)).
PSE was calculated from pH responses for separated lime fractions from ten calcitic and dolomitic
limes, based on their increase in substrate pH (∆pH) relative to reagent grade CaCO3 when mixed in
a Canadian sphagnum peat substrate (SunGro Horticulture Inc., Bellevue, Wash.) with long fibers
and little dust (Von Post scale 2-3; Puustjarvi and Robertson, 1975) at 22oC and maintained at a
moisture level near container capacity, at 5 g CaCO3 equivalents/L of peat.
PSE increases over time to a maximum of 1, as the lime fraction gradually reacts with the
peat acidity. We were interested in simulating pH response, and the response in pH over time shows
diminishing returns (Figure 1.2). We therefore empirically quantified the change in PSE over time
using an exponential decay (monomolecular) function (Table 1.2), where A represents the maximum
PSE (equal to 1) and k is a rate parameter. The monomolecular function closely fit the measured
PSE data, with a p-value less than 0.001 for all curve fittings, and r2 greater than 0.98.
Lime sources normally include a range in particle sizes, and the percent by weight of each
particle size fraction (PF) describes the distribution. The overall particle size efficiency of a lime
source was described by its fineness factor (FF), calculated for time t as the sum of PF and PSE for
each of the six particle size fractions described in Table 1.2:
Fisher and Huang. LimeR Series
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Modeling Lime Reaction
6
FFt = ∑ (PFi x PSEi,t)
i=1
[1]
The term calcium carbonate equivalence (ECC), calculated as a ratio of neutralizing value
compared with CaCO3, quantifies the combined effects of particle size distribution and acid
neutralizing value (NV) of a limestone on pH response, calculated as:
ECC = FF x NV
[2]
Factors other than acid neutralizing value and particle size may affect lime reaction rate. For
example, Rippy et al. (2004) found large differences in surface area between limes within a given
particle size fraction. When we evaluated pH response over time for each of six particle size
fractions using three calcitic and seven dolomitic limes, pH varied by less than 0.3 pH units between
lime sources of a given type (calcitic or dolomitic) for almost all data points, particularly for the fine
particle sizes that predominate in horticultural limes. We consider that error level acceptable, and
both particle size distribution and lime chemistry are factors that are easily measured and are
standard reported technical specifications for lime sources.
Residual
When a lime is incorporated into a growing medium, a proportion of the lime may remain
unreacted. This residual lime fraction is very important because most of the buffering to pH change
in container media comes from this unreacted pool of lime (Argo and Biernbaum, 1996). Residual
lime arises both because the solubility of limestone decreases as pH increases, and because coarse
particles may become coated with organic and mineral precipitates over time, thereby reducing
surface reactivity (Warfvinge and Sverdrup, 1989). For example, for the most coarse lime particles
(>850 µm), the asymptote for the pH reaction was only 56.3% of the chemically-potential pH
response (Table 1.2), even though the curve was fitted using pH data from up to 77 days after mixing
at near ideal conditions. Therefore, coarse lime particles contribute little to initial neutralization of
substrate acidity, but contribute more to the residual lime pool compared with fine lime particles.
Figure 1.3 shows that as lime application rate increased, pH increased to a plateau level around 7.5
for CaCO3 – additional lime remained as unreacted residual. pH response (and therefore the
proportion of lime reacted) was less for the NLS and Oldcastle lime sources than CaCO3, and
consequently the quantity of unreacted residual lime was greater for these two limestones.
It is possible to analytically measure total alkalinity in the substrate (including carbonates,
hydroxides, and other molecules such as phosphate, and ammonia/ammonium that contribute to pH
buffering) through acid titration (Richards, 1954; Loeppert et al., 1984). Carbonate sources of
alkalinity can also be quantified using a gasometric Chittick apparatus (Dreimanis, 1962). In
addition, if the pH buffering of a particular substrate is calculated, residual lime can be calculated by
subtracting the proportion of reacted lime from the total lime applied.
Fisher and Huang. LimeR Series
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Modeling Lime Reaction
Requirement
Lime requirement for a substrate depends on the initial substrate pH, and the buffering of the
substrate to changes in substrate-pH. Substrate buffering (pHB) can be quantified with units of ∆pH
per milliequivalent of base per L of substrate (∆pH.meq.L-1). Titration of peat with Ca(OH)2 shows
an approximately linear pH response with increasing application rate of base up to a pH near 7.0
(Rippy and Nelson, 2005). Because of this linearity, few data points are needed to quantify pHB for
any given substrate.
The target pH (pHtarget), often around 6.0 for horticulture, can be calculated from the initial
substrate pH (pHinit), resulting in a required ∆pHrequired:
∆pHrequired = pHtarget – pHinit
[3]
The milliequivalents of base (meqrequired) required to achieve a target substrate-pH can be
calculated from the substrate buffering and initial substrate pH.
[4]
meqrequired.L-1 = ∆pHrequired/pHB
The effective milliequivalents of a particular lime source at a given number of days t after
incorporating lime can be calculated from equation 2 in order to convert meq.L-1 to g lime.L-1. In
addition, the pH response at time t for a given number of grams of applied lime. L-1 (C) can be
calculated from
pHt = pHinit + C.(ECCt.meq CaCO3/g lime).pHB
[5]
where ECC on day t is calculated using the monomolecular function parameters in Table 1.2.
The parameters for equations [1] and Table 1.2 were calibrated using screened particle size
fractions of three calcitic limes, and seven dolomitic limes. We then validated the model in two
experiments using 29 unscreened calcitic and dolomitic carbonate and hydrated lime sources,
including the 10 calibration limes. In one experiment, 1L of peat was blended at 5g of lime (i.e. not
corrected for differences in NV between limes). In the second experiment, 5 g/L of CaCO3
equivalents for each lime, i.e. corrected for NV, was blended with a different peat source, using the
same 29 lime sources. The predicted pH on days 7 and 28 are compared with measured media-pH in
Fig. 1.4. The model described the overall pH trend for different lime types, with improved
prediction of pH at day 28 compared with day 7.
MODEL APPLICATION AND CONCLUSIONS
We developed a prototype application based on the model for predicting lime requirement for
a given lime source and substrate. The inputs are data from a Ca(OH)2 titration to quantify pH
buffering of the substrate, the particle size distribution and chemical characteristics of the lime, and
the target pH (assumed to occur at t=14 days). Outputs of the model are the contribution of each
particle size to pH change, residual, or reactivity; proportion of the lime that is expected to be
residual or reacted, and a sensitivity analysis of pH, which includes a monomolecular curve to
represent the solubility of CaCO3 with increasing pH. Further research is needed to validate and
expand the scope of the model. Environmental conditions could certainly affect reactivity and need
to be incorporated into the model, particularly media temperature and moisture level.
The majority of published lime research has been conducted with field soils over long time
periods, typically with limestones that are coarser than those used in peat-based substrates. A
Fisher and Huang. LimeR Series
4
Modeling Lime Reaction
quantitative model has potential to improve lime selection, lime incorporation rate, and management
of residual buffering. The model provides a framework to incorporate other factors that influence
substrate-pH over time, for example fertilizer and water alkalinity in simulation of substrate-pH.
ACKNOWLEDGEMENTS
Funding support was provided by the American Floral Endowment, University of New Hampshire
Agricultural Experiment Station, Blackmore Co., Center Greenhouses, D.S. Cole Growers,
Ellegaard, Greencare Fertilizers, Kube-Pak Corp., Lucas Greenhouses, Pleasant View Gardens,
Premier Horticulture, Quality Analytical Laboratories, and Sun Gro Horticulture. We thank Dr. Paul
V. Nelson and Dr. Janet Rippy from North Carolina State University for information about lime
surface area and reactivity.
Literature Cited
Argo, W.R. and J.A. Biernbaum. 1996. The effect of lime, irrigation-water source, and water-soluble
fertilizer on the pH and macronutrient management of container root-media with impatiens. J.
Amer. Soc. Hort. Sci. 121(3):442-452.
Argo, W.R. and P. R. Fisher. 2002. Understanding pH management of container grown crops.
Meister Publishing, Willoughby, Ohio.
Barber, S.A. 1984. Liming materials and practices. In F. Adams (ed.) Soil acidity and liming. 2nd
ed. Agron. Monogr. 12. ASA, CSSA, Madison, WI. Pp171-209.
Horwitz, W. 2003. Official Methods of Analysis of AOAC International, 17th Edition. AOAC
International, Gaithersburg, Maryland 20877 USA.
Dreimanis, A. 1962. Quantitative gasometric determination of calcite and dolomite by using Chittick
apparatus. J. Sedimentary Petrology, 32: 520-529.
Loeppert, R.H., C. T. Hallmark and M. M. Koshy. 1984. Routine procedure for rapid determination
of soil carbonates. Soil Sci. Soc. Am. J. 48: 1030-1033.
Puustjarvi, V., and R.A. Robertson. 1975. Physical and chemical properties. p. 23–28. In: D.W.
Robinson and J.G.D. Lamb (ed.) Peat in horticulture. Academic Press, New York.
Richards, L.A. 1954. Diagnosis and improvement of saline and alkali soils. USDA Handbook No.
60. U.S. Government Printing Office, Washington D.C.
Rippy, J. and P. V. Nelson. D.L. Hesterberg, and E.J.Kamprath 2004. Specific surface versus
particle diameter of limestones. HortScience. 39(4): p877.
Rippy, J. F.M. and P. V. Nelson. 2005. Soilless root substrate pH measurement technique for
titration. HortScience. 40(1): 201-204.
Tisdale, S.L., and Nelson, W.L. 1975. Liming. In Soil Fertility and Fertilisers. Macmillan
Publishing Co., Inc. New York. Pp. 412-24.
Sparks, D.L. 2003. Kinetics of Soil Chemical Processes. In: C.R. Crumly (ed.) Environmental Soil
Chemistry, 2nd edition. Academic Press, pp 207-244.
Warfvinge, P., and H. Sverdrup. 1989. Modeling limestone dissolution in soils. Soil Sci. Soc. Am. J.
53: 44-51.
Warncke, D.D. 1995. Recommended Test Procedures for Greenhouse Growth Media. In
Recommended Soil Testing Procedures for the Northeastern United States, 2nd Edn.; Univ. of
Delaware Agricultural Experiment Station, Bulletin #493, Dec. 1995; 76-83.
Fisher and Huang. LimeR Series
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Modeling Lime Reaction
Tables
Table 1.1. Physical and chemical characteristics of the three lime materials (CaCO3, and two
limestones – NLS and OldCastle) tested in Figure 1.1, along with the mean and standard deviation
for 24 calcitic and dolomitic carbonate lime sources used in horticultural substrates in the U.S. and
Canada.
NLS
OldCastle
Mean of 24 horticultural
CaCO3
lime samples (± s. dev.)
µm
U.S. mesh
Passing (%)
Screen size
Screen size
850
20
100
100
98
99.7±0.9
250
60
100
98
73
92.9±17.4
150
100
100
93
55
86.8±21.5
75
200
100
65
23
69.6±22.7
45
325
100
50
< 23
52.2±22.3
Chemical analysis
Ca (%)
40
21
22
24.5±7.4
Mg (%)
0
12
11.5
8.4±4.6
NV (%)
100
105
104
102.1±4.9
Table 1.2. The monomolecular function used to empirically quantify the particle size effectiveness
(PSE) for six lime particle size fractions over time, with the exponential decay curve PSE = A(1-ekt).
A represents the maximum effectiveness between 0 and 1, k is a rate parameter, and t represents the
days after incorporating the lime into peat. A was not significantly different from 1 for particles
sizes greater than 250 µm.
Particle size 850- 250- 150- 15075754545fraction (µm) 2000 850
250
250
150
150
75
75
<45
<45
Lime typez
K
C,D
C,D
C
D
C
D
C
D
C
D
0.038 0.085 0.219 0.152 0.513 0.335 1.027 0.693 1.504 1.009
S. err. of K 0.003 0.003 0.009 0.003 0.027 0.011 0.003 0.016 0.059 0.016
A
0.563 0.900
S. err. of A 0.019 0.007
Days to 95%
reaction
n/a
n/a
Days to 50%
reaction
58.2
9.5
1
1
1
1
1
1
1
1
13.7
19.7
5.8
8.9
2.9
4.3
2.0
3.0
3.2
4.5
1.4
2.1
0.7
1.0
0.5
0.7
r2 y
0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.98 0.99
z
C = calcitic, and D = dolomitic carbonate limes. For the two most coarse particle size fractions,
there was no significant difference between PSE for calcitic and dolomitic limes.
y
The r2 is based on correlation between the PSE estimated using the monomolecular function versus
the measured PSE. Measured PSE was calculated as ∆pH from the lime fraction/ ∆pH from reagent
grade CaCO3.
Fisher and Huang. LimeR Series
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Modeling Lime Reaction
Figures
7.5
7.0
Substrate-pH
6.5
6.0
X
5.5
X
X
5.0
X
4.5
Reagent grade CaCO3
4.0
3.5
X
NLS
OldCastle
X
3.0
0
7
14
21
28
35
42
Days after incorporating lime
Figure 1.1. pH response for three liming sources blended into peat at 6 grams of lime per liter of
substrate. NLS and OldCastle are two lime sources used in horticultural substrates. The substrate
temperature was maintained at 22oC, and substrate moisture was 0.3L deionized water/L of
substrate. Symbols represent the average response for 3 media-samples ± one standard error.
3.0
Change in substrate-pH
2.5
2.0
1.5
1.0
< 45 µm
75-45 µm
150-75 µm
250-150 µm
850-250 µm
> 850 µm
0.5
0.0
0
7
14
21
28
35
42
49
56
63
70
77
84
Days after incorporating lime
Figure 1.2. Mean change in substrate-pH for six particle size fractions averaged over ten calcitic
and dolomitic limes. Symbols represent the average response for 30 media samples ± 95%
confidence error.
Fisher and Huang. LimeR Series
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Modeling Lime Reaction
8.0
14.0
7.5
10.0
Substrate-pH
6.5
6.0
8.0
5.5
6.0
5.0
4.5
4.0
4.0
2.0
3.5
3.0
Residual Lime
g CaCO 3equivalents /L of peat
12.0
7.0
0.0
0
3
6
9
12
15
18
Lime Application Rate (g lime/L of peat)
CaCO3 pH
NLS pH
OldCastle pH
CaCO3 Residual (g/L)
NLS Residual (g/L)
OldCastle Residual (g/L)
Figure 1.3. pH response (left vertical axis) and residual lime (right axis) for three lime types with
increasing lime application rates, 14 days after incorporating the lime into a peat substrate. Residual
lime (g CaCO3 equivalents per liter of substrate) was measured using gasometric analysis
(Dreimanis, 1962).
7.0
(A)
6.5
Observed Substrate-pH
Observed Substrate-pH
7.0
6.0
5.5
5.0
4.5
4.0
day 7
day 28
3.5
3.0
(B)
6.5
6.0
5.5
5.0
4.5
4.0
day 7
day 28
3.5
3.0
3.0
4.0
5.0
6.0
Predicted Substrate-pH
7.0
3.0
4.0
5.0
6.0
7.0
Predicted Substrate-pH
Figure 1.4. Validation of the pH model, with two experiments and 29 unscreened lime sources
applied to peat, with different peat sources in each experiment. In experiment 1 (A), 1L of peat was
blended at 5g of lime. In the second experiment (B), 1L of peat was blended at 5 g CaCO3
equivalents for each lime.
Fisher and Huang. LimeR Series
8
LimeR Lime Reactivity Test
2.1 LimeR Lime Reactivity Test
Jinsheng Huang and Paul Fisher, University of Florida,
pfisher@ufl.edu, 352 392 1831 ext 375. Copyright, 2009.
March 30, 2009.
Description: A protocol to test the reactivity of a liming material in horticultural substrates
Goal:
To calculate reactivity indices of a horticultural lime material, so that the reactivity of the lime
source can be characterized, and to allow prediction of pH changes over time when the lime is
incorporated into container substrates, specifically:
1. To calculate the overall particle size efficiency of a lime source (i.e. its fineness factor, FF)
based on its particle size distribution and its particle size efficiency factor (PSE) of each of
six particle size fractions [>0.85 (retained on 20 U.S. standard mesh), 0.85 to 0.25 (retained
on 60 mesh), 0.25 to 0.15 (retained on 100 mesh), 0.15 to 0.075 (retained 200 mesh), 0.075
to 0.045 (retained on 325 mesh), and < 0.045 mm (passed through 325 mesh)];
2. To calculate the effective calcium carbonate equivalence (ECC) of a horticultural lime based
on its FF and neutralizing value (NV).
Principle:
Limestones are used to raise and buffer pH and supplement Ca and Mg nutrients in container
substrates. The effectiveness of limestone for neutralizing acidity of media components such as peat
or bark varies depending on mineralogy, morphology, particle-size distribution, and chemical
composition. Since the dissolution of limestone occurs as a surface reaction, the particle size
distribution of a liming material directly influences the dissolution rate and its effectiveness in
neutralizing soil acidity. A particle size efficiency factor (PSE) can be assigned to each particle size
fraction of a horticultural grade limestone. In our research, we estimated the PSE for six particle
size fractions [>0.85 (retained on 20 U.S. standard mesh), 0.85 to 0.25 (retained on 60 mesh), 0.25 to
0.15 (retained on 100 mesh), 0.15 to 0.075 (retained 200 mesh), 0.075 to 0.045 (retained on 325
mesh), and < 0.045 mm (passed through 325 mesh)] of a horticultural grade limestone. Although
substrate-pH (and therefore PSE) changes over time, lime suppliers use a single PSE value for each
lime fraction to describe reactivity (pH response) of a particular liming source. Based on our
research, we consider that using a PSE based on pH response on day 7 (Table 2.1.1) is appropriate
for container media.
Fisher and Huang. LimeR Series
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LimeR Lime Reactivity Test
Table 2.1.1. Particle Size Efficiency factors(PSE) for calcitic and dolomitic limestones.
Particle size (µm)
Calcitic limestone
Dolomitic limestone
850-2000 µm (10-20 mesh)
0.18
0.18
250-850 µm (20-60 mesh)
0.45
0.44
150-250 µm (60-100 mesh)
0.79
0.66
75-150 µm (100-200 mesh)
0.91
0.83
45-75 µm (200-325 mesh)
0.98
0.93
<45 µm (passes 325 mesh)
0.99
0.96
To interpret Table 2.1.1 using an example, if a calcitic limestone had all of its particles in the 200325 mesh size range, the effectiveness would be 0.98, which is more than twice as effective at
raising pH compared with coarse 20-60 mesh limestone (0.45).
Procedures:
For a lime sample, the following parameters should be measured to appropriately address its
reactivity:
1. Moisture content of a lime sample (M%)
Moisture content can be measured by drying the limestones at 110oC to constant weight,
based on AOAC Method 924.02. Moisture content is calculated as (lime weight before dry –
lime weight after dry)/lime weight before dry. Moisture content is reported as a percentage
of the total weight.
2. Neutralizing value (NV)
Neutralizing value (NV) of the liming materials can be determined based on the AOAC
Official Method 955.01. A lime sample (1g for carbonates and 0.5 g for hydrated) is
digested with standardized 0.5M HCl. After the reaction progresses to completion, the
unreacted HCl in the solution is back-titrated using standardized 0.25M NaOH, and the NV
can be calculated from the acid initially consumed by the lime. NV is reported as a
percentage and is a measure of the chemical effectiveness of limestones compared with pure
CaCO3. For examples of typical NV of liming materials, see Appendix 2.1.1.
3. Chemical composition (Ca and Mg content)
The Ca and Mg content can be measured by taking a 5 g of each lime sample and digesting it
with strong acid (6M HCl) based on AOAC 962.01 procedure, and the resulting solution can
be analyzed using inductively-coupled plasma (ICP) atomic emission spectrophotometry.
Chemical composition can be reported for each nutrient as a percentage of the total weight.
4. Particle size distribution (PF)
Lime sources normally include a range in particle sizes, and the percent by weight of each
particle size fraction (PF) describes the distribution. Particle size distribution can be
measured using the dry sieving method for carbonate materials, and wet sieving based on
Fisher and Huang. LimeR Series
10
LimeR Lime Reactivity Test
AOAC 924.02 for the hydrated liming materials. Dry sieving can be carefully performed in a
sieve shaker for the first 30 min., and each individual sieve should be then manually shaked
to make sure the entire fine particles pass through the sieve. For analysis, weigh about 150g
(to the nearest 0.1g) and place in the top sieve of six stacked sieves (in the order of # 20 to #
325 as the # 20 on top, and a pan on the bottom). The sample needs to be passed through the
previously mentioned six standard sieves and the results can be expressed as percentage
remaining on the variously sized sieves. More specifically, a limestone sample should be
separated into six fractions: >850 µm (retained on a U.S. standard no. #20 sieve), 850 to 250
(retained on a #60-mesh sieve), 250 to 150 µm (retained on a #100-mesh sieve), 150 to 75
µm (retained a #200-mesh sieve), 75 to 45 µm (retained on a 325- mesh sieve), and < 45 µm
(passed through a #325-mesh sieve). For wet sieving procedure, each fraction should be
dried and weighed to obtain its percentage in a sample.
The results can be calculated as:
% retaining sieve size = weight remaining a size fraction * 100/sample weight.
5. Fineness factor (FF)
The overall particle size efficiency of a lime source is described by its fineness factor (FF),
which can be calculated for time t as the sum of PF and PSE for each of the six particle size
fractions:
6
FFt = ∑ (PFi x PSEi,t)
[1]
The FF value of a lime sample can be as high as 1 and as low as 0.18.
For calcitic liming material, Fineness Factor is calculated from:
_______ % material remaining a 20-mesh screen x 0.18
= _________
+ _______ % material remaining a 60-mesh screen
x 0.45
= _________
+ _______ % material remaining a 100-mesh screen
x 0.79
= _________
+ _______ % material remaining a 200-mesh screen
x 0.91
= _________
+ _______ % material remaining a 325-mesh screen
x 0.98
= _________
+ _______ % material passing a 325-mesh screen
x 0.99
=_________
TOTAL Fineness Factor
Fisher and Huang. LimeR Series
= _______
11
LimeR Lime Reactivity Test
For dolomitic liming material, Fineness Factor is calculated from:
_______ % material remaining a 20-mesh screen x 0.18
+ _______ % material remaining a 60-mesh screen x 0.44
+ _______ % material remaining a 100-mesh screen x 0.66
+ _______ % material remaining a 200-mesh screen x 0.83
+ _______ % material remaining a 325-mesh screen x 0.93
+ _______ % material passing a 325-mesh screen
x 0.96
TOTAL Fineness Factor
= _________
= _________
= _________
= _________
= _________
=_________
= _______
6. Effective calcium carbonate equivalence (ECC)
The term effective calcium carbonate equivalence (ECC), calculated as a ratio of neutralizing
value compared with CaCO3, quantifies the combined effects of particle size distribution and
acid neutralizing value (NV) of a limestone on pH response, calculated as:
ECC = FF x NV
[2]
7. Lime reactivity can be calculate using LimeR Lime Reactivity Test (Appendix 2.1.2).
References
Huang, J., P. R. Fisher and W.R. Argo. 2007. Container substrate-pH response to differing limestone
type and particle size. HortScience. 42: 1268-1273.
Appendix 2.1.1. The following table presents typical CCE values of horticultural liming materials
and the kilograms of each material needed to produce the same neutralizing power as one kilogram
of pure CaCO3.
Liming Material
Range of CCE (%) Kg Required to be Equivalent
to 1.0 Kg of CaCO3
Calcite (pure)
100
1.0
Calcitic (High Ca) limestone
94 to 101
1.06 to 0.99
Dolomitic limestone
95 to 108
1.05 to 0.93
Quick lime (Hydrated and burned)
117 to 163
0.85 to 0.61
MgCO3
119
0.84
Ca(OH)2
136
0.74
(CaMg)CO3
109
0.92
CaO
179
0.56
Fisher and Huang. LimeR Series
12
LimeR Lime Reactivity Test
Appendix 2.1.2. The “Lime reactivity test” worksheet in the “LimeR tests 1h.xls” Excel spreadsheet can be used to enter information
on lime particle size distribution, chemistry, and moisture level. This report can be printed. The laboratory logo can be added to the
report, but the UF-IFAS and Young Plant Research Center logos should remain.
Enter information into the gray boxes on the left side of the screen. Any white area shows calculated values. Information on the right
side of the screen explains how to interpret the information.
Fisher and Huang. LimeR Series
13
LimeR Substrate Lime Requirement Test
2.2 LimeR Substrate Lime Requirement Test
Jinsheng Huang and Paul Fisher, University of Florida,
pfisher@ufl.edu, 352 392 1831 ext 375. Copyright, 2009.
March 30, 2009.
Description: A protocol to determine the lime requirement of a
horticultural substrate using a calcium hydroxide:pH-titration curve.
Principle:
Titration of peat-based substrate with Ca(OH)2 shows an approximately linear pH response with
increasing application rate of base up to a pH near 7.0 (Rippy and Nelson, 2005). We also observed
a linear trend using both the reagent Ca(OH)2 and reagent microfine CaCO3 (100% passed a 325
mesh), however the pH response begins from CaCO3 can begin the plateau phase below pH 6.5.
Substrates vary in their buffering capacity, which can be quantified using a linear relationship [Eq.
1]
pH = m + n * b
[1]
where m represents the offset (non-limed substrate-pH), n is the gradient [buffering capacity, in units
of ∆pH/(meq of CaCO3·L-1 of substrate)], and b is the applied lime in units of meq of CaCO3·L-1 of
substrate.
At any given substrate-pH value, the milliequivalents of CaCO3 (CCE) (b) required to neutralize
that amount of substrate acidity can be calculated from the titration curve [Eq. 2].
b = (pH – m)/n
[2]
If a known weight of limestone (a) in meq of CaCO3·L-1 were applied to the substrate and pH is
measured, the meq of residual (unreacted) CaCO3·L-1 is represented by a minus b. Because the pH
response for substrate-pH is approximately linear below 7.0, few data points (tested lime rates) are
required to develop a pH titration curve for a specific batch of substrate.
Fisher and Huang. LimeR Series
14
LimeR Substrate Lime Requirement Test
Procedure
Development of a pH titration curve for a batch of substrate
1. To develop a pH titration curve, weigh reagent grade Ca(OH)2 samples to the nearest 1 mg
and mix at 0, 1, 2, or 4 grams of Ca(OH)2 with 1 L samples of the substrate (which should
have been pre-amended with pre-plant nutrients and wetting agent, but without liming
materials). 1 g reagent Ca(OH)2 is equivalent to1.35g CaCO3, or equivalent to 27 meq. of
CaCO3. The substrate density should be lightly packed (as close as possible to its density in
a loose bag of commercial growing medium). Place 1 L samples into 1-gallon Ziploc or
similar bags.
For research purposes, we recommend 3 replicates per lime rate, but for media production
lines only one replicate may be feasible. In addition, to streamline this protocol you could
choose to apply only one lime rate that is approximately equivalent to the CCE you normally
apply for this commercial mix.
2. Add distilled water to the substrate in each bag to raise moisture level to appropriately 90%
container capacity (appropriately 450 mL water per liter of substrate for a 70% peat + 30%
perlite substrate).
If there is no pre-plant fertilizer charge in the substrate sample, consider using 0.01M CaCl2
rather than distilled water in step 2. A dilute salt solution (0.01M CaCl2) is sometimes used to
provide a measurement of potential acidity because it takes into account effects of fertilizer
salt concentration and substrate cation exchange capacity on pH trends that are likely to
occur during crop production. For sources of Ca(OH)2 and CaCl2, and instructions for
preparing a 0.01M CaCl2 solution, see Appendices 2.2.1 and 2.2.2.
3. Put the substrate mixture in an open plastic bag to allow for gas exchange at room
temperature.
4. After three days, measure substrate pH (1 to 3 replicates per lime rate), by which time a
stable substrate-pH should be observed. The pH can be measured directly in the bag by
squeezing the solution to one side of the plastic bag.
5. Plot the average pH at each lime rate versus the corresponding reagent Ca(OH)2 rate as
CaCO3 equivalent (CCE) by multiplying grams Ca(OH)2 times 27.
6. Select two lime rates (0, 1, 2, or 4 g Ca(OH)2) that are above (first reading) and below
(second reading) the target pH. For example, a typical target pH would be 6.0. If the 0, 1, 2,
and 4 g Ca(OH)2 show pH readings of 3.5, 4.1, 5.5 and 7.0, select the 7.0 reading (4 g/L), and
either the 3.5 (0 g/L) or 4.1 (2 g/L) reading. Avoid any pH readings above 7.0 because
Ca(OH)2 solubility may decline at high pH.
7. From the two readings you select, determine the pH buffer capacity (n) using Eq. 1. Note
Appendix 2.2.3, which shows a spreadsheet for entering in the pH values
Fisher and Huang. LimeR Series
15
LimeR Substrate Lime Requirement Test
8. The milliequivalents of CCE (b) required to reach a target pH can be calculated from the
titration curve using Eq. 2.
9. (b) can be converted into (c) grams of CaCO3 per liter of substrate by multiplying 50 and
dividing by 1000.
10. (c) can be converted into grams of a limestone source per liter of substrate by dividing (c) by
the effective calcium carbonate of the limestone (based on the LimeR lime reactivity test).
Reference
Rippy, J. F.M. and P. V. Nelson. 2005. Soilless root substrate pH measurement technique for
titration. HortScience. 40(1): 201-204.
Appendix 2.2.1. Sources of Ca(OH)2 and CaCl2 (March 2009 information)
Name
Linear formula
CAS No.
Formula weight
Catalog No. (2009
pricing)
MSDS sources
Calcium Chloride Dihydrate
CaCl2.2H2O
10035-04-8
147.02
EW-88222-54 (Cole-Parmer $89.80/kg)
S93162 (Fisher Scientific, $76.5/kg)
Chemicals
Calcium Hydroxide
Ca(OH)2
1305-62-0
74.09
EW-88341-42 (Cole-Parmer $59.90/kg)
EW-88234-31 (Cole-Parmer $77.40/kg)
S75071 (Fisher Scientific, $16.1/kg)
http://www.coleparmer.com/catalog/Msds
/95446.htm
http://www.coleparmer.com/catalog/Msds/9594
4.htm
http://www.coleparmer.com/catalog/Msds/0036
3.htm
Cole-Parmer 1-800-323-4340, http://www.coleparmer.com/
Fisher Scientific 1-800-766-7000, http://www.fishersci.com/
CAS No. refers to Chemical Abstracts Service Registry Number
Appendix 2.2.2 Instructions for making a 0.01M solution of CaCl2.
To make a 0.01M CaCl2 solution:
• Dissolve 1.47 g calcium chloride dihydrate (CaCl2.2H20) and dilute to 1 L with deionized
water.
OR another option is to make 1M CaCl2 solution first ( dissolve 147.02g CaCl2.2H2O in 1L
deionized water). Then add 10 mL 1M CaCl2 solution to 990 mL of deionized water. This gives
one liter of a 0.01M CaCl2 solution. Shake well by hand.
Fisher and Huang. LimeR Series
16
LimeR Substrate Lime Requirement Test
Appendix 2.2.3. The “Substrate lime requirement test” worksheet in the “LimeR tests 1h.xls” Excel spreadsheet can be used to
enter information on lime particle size distribution, chemistry, and moisture level. This report can be printed. The laboratory logo can
be added to the report, but the UF-IFAS and Young Plant Research Center logos should remain.
Enter information into the gray boxes on the left side of the screen.
Fisher and Huang. LimeR Series
17
Gasometric Procedure to Measure Residual Lime
2.3 A Gasometric Procedure to Measure
Residual Carbonate in Container
Substrates
Jinsheng Huang and Paul Fisher, University of Florida,
pfisher@ufl.edu, 352 392 1831 ext 375. Copyright, 2009. March 30, 2009.
Goal
A substrate test protocol to measure residual carbonate in substrates in units of CaCO3 equivalent
(CCE), by applying a strong mineral acid (HCl) to a substrate sample, and measuring the evolved CO2
gas with a gasometric method.
Principle
The most common liming materials used in greenhouse substrates are carbonate-based limestones:
calcite (CaCO3 with 40% Ca), calcitic [CaMg(CO3)2 with >30% Ca and <5% Mg], dolomitic
[CaMg(CO3)2 with <30% Ca, and > 5% Mg], and dolomite [CaMg(CO3)2 with 22% Ca and 13% Mg].
When carbonate-based limestones react with acid from proton sources, such as acidic peat, then calcium
(Ca2+) and/or magnesium (Mg2+), water (H2O), and carbon dioxide (CO2) gas result:
CaCO3 (calcite) + 2H+ ↔ Ca2+ + H2O + CO2 (gas) [1]
CaMg(CO3)2 (dolomite) + 4H+ ↔ Ca2+ + Mg2++ 2H2O + 2CO2 (gas) [2]
The principle of this test, based on research measuring CCE in agronomic soils (Dreimanis 1962;
Hülsemann, 1966), is that the unreacted lime concentration (on the left side of Equations 1 and 2) can be
determined in a peat-perlite substrate by addition of a strong acid, and subsequent measurement of
released CO2 gas through volume displacement. The volume of CO2 gas evolved by the chemical
reaction can be determined with a Chittick apparatus (or variants thereof), which is easily constructed
from basic laboratory glassware and tubing (Dreimanis, 1962). Once the device is calibrated by use of
prepared CaCO3 standards, (1) media samples are introduced and reacted with HCl, (2) the volume of
CO2 released is measured; and (3) the amount of residual carbonate is calculated with either a CO2CaCO3 standard curve or the Ideal Gas Law with a known air temperature and air pressure.
Unreacted residual limestone in the container substrate is known to play a key role in pH management
and resistance to pH changes (i.e. pH buffering). Residual CCE in a substrate is an important property
which should be considered for pH control and management in greenhouse crops production. Our results
indicated that the gasometric system could be useful for optimizing lime application rate, lime source, or
management of residual CCE during crop production. For different lime sources, it would be possible to
quantify the reacted and residual CCE at a given lime incorporation rate to a particular substrate. It may
be possible to identify a desirable minimum residual CCE for adequate pH buffering to avoid a rapid pH
Fisher and Huang. LimeR Series
18
Gasometric Procedure to Measure Residual Lime
drop during production. If residual CCE is found to be close to zero, corrective actions such as a basic
drench may be useful for crops sensitive to iron/manganese toxicity at low pH.
Procedures
1. Reagents (based on AOAC method 923.02)
(1). Displacement solution- dissolve 100g NaCl or
Na2SO4.10H2O in 350 ml H2O. Then add 1g NaHCO3 and 2
mL methyl orange (0.5% aqueous solution), and then enough
H2SO4 (1+5) or HCl (1+2) to make the acid solution a
decidedly pink color. Stir until all CO2 is removed. This
solution is used for measuring burette and leveling burette
and seldom needs replacement.
C
E
B
D
F
(2). 6M HCl (1 volume of HCl + 1 volume of H2O)
2. Apparatus
The gasometric system (adapted from the Chittick apparatus,
AOAC method 923.02) consists of 1 L decomposition flask
(A), rubber tube (B), stopcock (C), a gas measuring burette
(D), level burette(E) and an acid dispensing burette (F), and
a magnetic stirrer (G) (Fig. 1).
A
G
3. The general procedure involves dissolving the carbonate
lime materials in a substrate sample and liberating CO2 gas
Fig.1 Apparatus for residual
using 6M HCl. A measured substrate sample (50-100 mL) is
carbonates measurement.
placed in the bottom of the decomposition flask (A in Fig.
1). Deionized water (CO2 free) is added to the substrate at 1.5 times the sample volume (i.e., 0.075
and 0.15 L for the substrate sample of 0.05 and 0.1L, respectively). The flask is then attached to the
gasometric system. Open stopcock C, and burette E is used to bring the displacement solution to the
zero mark. The acid dispensing burette F is added to the reaction flask, A. The apparatus is left to
stand for two min. for temperature and pressure within the apparatus to come to room conditions.
The stopcock C is then closed, and the leveling burette E is lowered below the surface level of the
gas-measuring burette D to reduce the pressure within the apparatus. 6M HCl is slowly introduced
into the decomposition flask at 0.5 times the sample volume (0.025 and 0.05L aliquot of 6M HCl
for 0.05 and 0.1L substrate samples, respectively) from the acid dispensing burette F. During
reaction, the surface of the displacement solution in the leveling burette E should be kept lower than
that in gas measuring burette D. The sample in the flask (A) needs to be constantly stirred using a
magnetic stirrer (G). A heat isolation pad (such as polyfoam) should be put in between the top
surface of stirrer and the bottom of decomposition flask to isolate the possible heat from the running
magnetic stirrer. The pressure is equalized in the measuring burette D, using the leveling burette E,
and the volume of gas is read in the measuring burette D. The reaction time is 10 min for reagent
CaCO3, and 30 min (Dreimanis, 1962) for the horticultural limestone. Record air pressure and
Fisher and Huang. LimeR Series
19
Gasometric Procedure to Measure Residual Lime
temperature. The CCE can be calculated based on the volume of CO2 produced using the Ideal Gas
Law:
NCO2 = PCO2VCO2/RT. [3]
Where NCO2 represents the moles of CO2 liberated, PCO2 represents CO2 partial pressure (atm), VCO2
represents the volume of CO2 (L) liberated, R is the universal gas constant (0.0821 L atm/mol K ),
and T is temperature (K) (oC + 273.2). NCO2 equals the moles of carbonate material decomposed
according to the stochiometry of equations [1] and [2] (1 mole CO2 = 1 mole CaCO3 = 100 g
CaCO3).
4. System calibration and standard curve development:
System should be calibrated using reagent CaCO3. A standard CO2(mL)-CaCO3 (g) curve is
recommended for CCE determination if the air temperature and air pressure are stable, or
alternatively the Ideal Gas Law should be used for each experimental run following measurement of
the air temperature, air pressure and volume of evolved CO2 in the gas-measuring burette. To
prepare a standard CO2 (mL)-CaCO3 (g) curve, weigh reagent grade CaCO3 samples to the nearest
0.1 mg and place in 1L decomposition flasks. Sample weights of 0.05, 0.10, 0.20, 0.30 and 0.40 g
are suggested if the total solution is 0.1 L in the flask, and sample weights of 0.05, 0.10, 0.20, 0.40
and 0.60 g are suggested if the total volume of the liquid solution is 0.2 L in the flask. Using the
same procedure for measuring the volume of CO2 released in the substrate samples; the suggested
reaction time is 10 min. After 10 min of reaction time, the volume of released CO2 is recorded and
regression linear curve can be plotted as a function of corresponding standard CaCO3 weight.
5. Substrate sample size: measure 0.050 or 0.1 L to the nearest 1 mL substrate samples and transfer
into 1 L decomposition flasks. The recommended substrate sample is 0.1 L if the residual CCE is
less than 0.5 g/L, and 0.05 L substrate if CCE is larger than 0.5 g/L. The substrate sample should
contain at least 0.05 g CCE for accuracy.
6. Volume of deionized water and volume of 6M HCl: Add 0.075 L of deionized water into the 1L
decomposition flask that contains the 0.05 L substrate sample, place a magnetic stir bar in the flask,
then attach the flask to the gasometric system. After the system is closed, add 0.025 L of 6M HCl
into the decomposition flask through the acid dispensing burette. The final initial acid concentration
in the soil solution is 1.5M with 0.1 L of solution in total. For a 0.1 L substrate sample, the volumes
of deionized water and 6M HCl are 0.15 and 0.05 L, respectively, which will result in the same 1.5
M HCl for the total 0.2 L of solution.
7. Reaction time: the recommended average time for general grade of dolomite and calcite is 30 min.
The guideline on when to finish the experimental run is when the CO2 volume reading is stable for
at least 5 min.
8. Input data (such as CO2 volume (mL), air temperature (OC) and air pressure (atm)) in Residual
Lime Calculator (Appendix 2.3.1) for residual lime calculation.
Fisher and Huang. LimeR Series
20
Gasometric Procedure to Measure Residual Lime
References
Dreimanis, A. 1962. Quantitative gasometric determination of calcite and dolomite by using Chittick
apparatus. J. Sedimentary Petrology, 32: 520-529.
Huang, J.S., P.R. Fisher, and W.R. Argo. 2007. A gasometric procedure to measure residual lime in
container substrates. HortScience. 42:1685-1689.
Hülsemann, J. 1966. On the routine analysis of carbonates in unconsolidated sediments. Journal of
Sedimentary Petrology. 36: 622-625.
Appendix 2.3.1. The “Residual Lime Calculator” worksheet in the “Residual Lime Calculator.xls”
Excel spreadsheet can be used to enter information on substrate sample volume, HCl volume, CO2
readings, air pressure, air temperature and reaction time. This report can be printed. The laboratory
logo can be added to the report, but the UF-IFAS and Young Plant Research Center logos should
remain. Please refer the details regarding system calibration and standard curve development in “System
Calibration” and “Standard Curve” worksheets.
Enter information into the gray boxes on the left side of the screen.
Fisher and Huang. LimeR Series
21
LimeR Substrate pH Buffering Test
2.4 LimeR Substrate pH Buffering Test
Jinsheng Huang and Paul Fisher, University of Florida,
pfisher@ufl.edu, 352 392 1831 ext 375. Copyright, 2009.
March 30, 2009
Description: A protocol to quickly determine pH buffering of a horticultural substrate by measuring
pH change following an application of mineral acid (HCl).
Principle:
Substrate pH buffering capacity is an important chemical property for successful nutritional
management in crop production. pH buffering capacity refers to the ability of a substrate to maintain
a stable pH following addition of acid or base. The main factor that contributes to the buffering
capacity of a soilless substrate is residual lime concentration.
Substrate-pH buffering can be quantified by measuring the pH change following mineral acid
drenches without plants. Our previous research showed that dosage with either 40 meq acid from
HCl per liter of substrate or a titration with different concentrations of HCl acid to substrate-pH of
4.5 in the lab were well-correlated with pH buffering in greenhouse trials using acidic fertilizers
(Fig. 2.41) and should be useful laboratory protocols to compare pH buffering of substrates.
Substrate-pH buffering capacity was significantly correlated with the initial substrate residual lime
concentration (Fig. 2.4.2). The relationship between substrate-pH changes (∆pH; final pH – initial
pH ) after one dose drench of 40 meq·L-1 of substrate and the initial residual lime concentration (R;
CCE g/L of substrate) could be described as:
R(CCE g/L) = 2.60*∆pH + 5.75
r2 = 0.7695
[1]
(Note: 20 meq = 1g CCE)
The amount of acid required to decrease substrate-pH from the initial pH to pH 4.5 was quantified as
the “pH4.5 Buffering Capacity” (in either meq·L-1, or CCE g·L-1), and is approximately equal to
residual lime concentration (R; g CCE/L, Fig. 2.4.3). To calculate the “pH4.5 Buffering Capacity”,
however, requires multiple applications of acid, and fitting of an acid pH response curve, or can be
approximated from:
pH4.5 Buffering Capacity (meq·L-1) = 20.40 * R + 3.57
r2 =0.91
[2]
Using Equation (1), the residual lime concentration can be estimated by the ∆pH value using the
application of 40 meq·L-1 of acid drench. The pH4.5 Buffering Capacity can also be predicted using
Equation (2). Table 2.4.1 summarized a survey of pH buffering of ten commercial substrates that
are currently used in container production, using HCl acid drenches.
Fisher and Huang. LimeR Series
22
LimeR Substrate pH Buffering Test
Table 2.4.1. Survey of pH buffering for ten commercial media that are currently used in horticultural
industry, using acid drench method.
pH Buffering
∆pH after 40 meq HCl drench
Residual Lime in CCE (g/L)*
Range
Low
<-1.9
<1.0
Medium
-1.9 to -1.0
1.0 – 3.0
High
-1.0 - 0
>3.0
*CCE: CaCO3 equivalent.
Procedures
1. Reagent: 0.5N HCl: dilute 42 mL from concentrated 36% (12M) hydrochloric acid to 958
mL deionized water, then standardize using standard 0.25N NaOH. [alternatively, 1N HCl
standard solution can be purchased, then dilute it to 0.5N using distilled water. For example,
today’s price for 4L 1N HCl from Fisher Scientific (http://www.fishersci.com/) is $50.00
with Catalog No. S748561].
2. Measure 200 mL substrate sample and place in an open plastic bag. Measure 6 bags for each
medium sample and divide into two sets, with 3 bags per set.
3. For the 1st set of 3 bags (Set I), add enough deionized water to raise moisture level to
appropriately 95% container capacity (appropriately 450 mL water per liter of substrate for a
70% peat + 30% perlite substrate). Leave the plastic bag open at room temperature (20 oC)
for gas exchange. (Samples can be placed in warm temperature around 30 oC for fast lime
reaction).
4. For the 2nd set of 3 bags (Set II), add one dosage of 40 meq HCl per liter of substrate to the
substrate samples. For 0.5N HCl, it will be equivalent to 16 mL HCl for a 200 mL substrate
sample. Then use deionized water to bring moisture level to appropriately 95% container
capacity. Mix the acid with the substrate thoroughly, and leave in the original open plastic
bag at room temperature (20 oC). (Samples can be placed in warm temperature around 30 oC
for fast lime reaction).
5. After 7 days (in room temperature) or 3 days (in warm temperature), measure substrate-pH
(for Set I and Set II). The pH can be measured directly in the bag by squeezing the solution to
one side of the plastic bag. By this time, a stable substrate-pH should be observed.
6. Estimate substrate pH buffering capacity based on pH changes after 40 meq HCl acid drench.
(1). Calculate substrate delta pH (∆pH):
∆pH = average substrate-pH for Set II – average substrate-pH for Set I
(2). Using Equation (1) to calculate residual lime concentration (R) in the medium.
(3). Estimate substrate pH4.5 Buffering Capacity using Equation (2).
(4). Using Table 1 to find out the pH buffering range:
Fisher and Huang. LimeR Series
23
LimeR Substrate pH Buffering Test
•
If ∆pH <-1.9, substrate pH buffering capacity is rated as “low”, the residual lime
concentration is <1.0 g CCE/L of substrate.
•
If ∆pH is in the range of -1.0 to -1.9, substrate buffering capacity is rated as
“medium”, the residual lime concentration ranges from 1.0 to 3.0 CCE/L of substrate.
•
If -1.0< ∆pH <0, substrate pH buffering capacity is rated as “high”, the residual lime
concentration is > 3.0 g CCE/L of substrate.
(5). Recommendations can be made accordingly.
Limitations and other usage:
1. This procedure is applicable only if residual lime is present in the growing media (the initial
substrate-pH should be larger than >4.5). If the initial substrate-pH (for Set I) is less than
4.5, there is little residual lime in the media. No acid drench is necessary.
2. Equation (1) could be used for predicting residual lime concentration (R) up to 3.0 g CCE per
liter of substrate in a growing medium. If the residual lime concentration is larger than 3.0 g
CCE/L, then 60 or 80 meq acid drench is recommended for accuracy.
a. For 60 meq acid drench (if residual lime concentration > 3 g CCE/L):
R(CCE g/L) = 2.18*∆pH + 6.30
r2 = 0.62
[3]
b. For 80 meq acid drench (if residual lime concentration > 4 g CCE/L):
R(CCE g/L) = 2.03*∆pH + 7.10
r2 = 0.65
[4]
3. If either 60 or 80 meq acid drench is applied, use Equation (2) to estimate pH4.5 Buffering
Capacity.
Fisher and Huang. LimeR Series
24
LimeR Substrate pH Buffering Test
Figure 2.4.1. Substrate-pH buffering evaluated using dosage with 40 meq acid from HCl per liter of
substrate in the lab was well-correlated with pH buffering in the greenhouse trial using acidic
fertilizer.
Delta pH from Ammonium
Fertilizer
Comparison of HCl Drench and Ammonium
Fertilizer Response
-0.5
-1.5
p = 0.005
y = 1.2363x + 0.5784
R2 = 0.9166
-2.5
-3.5
-3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5
0.0
Delta pH from HCl Drench (40 meq/L of
substrate)
Figure 2.4.2. The relationship between substrate-pH changes (∆pH; final pH – initial pH) after one
dose 0.5N HCl drench of 40 meq·L-1 of substrate and the initial residual lime concentration.
Initial Residual CCE
(g/L of substrate)
5
Residual CCE (g/L) = 2.6 ∆pH + 5.75
R2 = 0.77
4
2
1
0
-3.0
-2.0
-1.0
0.0
∆pH
from an acid drench at 40 meq/L of substrate
Fisher and Huang. LimeR Series
25
LimeR Substrate pH Buffering Test
Figure 2.4.3. The relationship between initial residual lime concentration and pH4.5 Buffering
Capacity ( in either meq/L (A) or g CCE/L of substrate(B)). A close one to one relationship was
observed as shown in (B).
A. Meq of HCl to drop pH to 4.5
pH4.5 Buffering Capacity
(meq·L- 1)
120
100
80
60
p <0.001
40
y = 20.402x + 3.5645
20
R2 = 0.9096
0
0
1
2
3
4
5
6
-1
Initial Residual CCE (g·L )
6
B
5
(CCE g·L -1)
pH4.5 Buffering Capacity
HCl (in CCE g/L) needed to drop pH to 4.5
4
3
2
p < 0.001
1
y = 1.02x + 0.18
R2 = 0.91
0
0
1
2
3
4
5
6
Initial Residual CCE (g·L-1)
Fisher and Huang. LimeR Series
26
Materials for Conducting LimeR Series Tests
2.5 Materials for Conducting LimeR Series Tests
Jinsheng Huang and Paul Fisher, University of Florida,
pfisher@ufl.edu, 352 392 1831 ext 375. Copyright, 2009.
March 26, 2009.
Chemical reagents
1. calcium carbonate (CaCO3)
2. calcium hydroxide (Ca(OH)2)
3. Hydrochloric acid (HCl)
4. sodium hydroxide (NaOH)
5. sodium chloride (NaCl)
6. calcium chloride dihydrate (CaCl2.2H2O)
7. sodium bicarbonate (NaHCO3)
8. methyl orange (a pH color indictor for replacement solution in the gasometric system, in an
acid it is reddish and in alkali it is yellow).
Please refer Appendix 1 for these chemical sources.
Apparatus
1. pH meter
2. Barometer for air pressure
examples: http://www2.oregonscientific.com/shop/product.asp?cid=20&scid=78&pid=777
http://www.thealtimeterstore.com/hh2b.html
3.
4.
5.
6.
7.
Thermometer for temperature
stop watch for time
lab stand
a magnetic stirrer & stir bar
screen sieves for lime particle size distribution analysis
Glassware
1. Filtering flasks (1000 mL capacity, #8 stopper size, such as Pyrex No. 5340, or Kimax No.
27060)
2. "Salvarsan" tubes (large and wide capacity for leveling, and small and accurate for CO2
measuring)
An example http://www.expressmedicalsupplies.com/profex-kalon-salvarsan-tube-p36021.html
3. acid dispensing burette (glass burette with stopcock)
4. titration burettes
Please refer Appendix 2 for examples.
Fisher and Huang. LimeR Series
27
Materials for Conducting LimeR Series Tests
Appendix 2.5.1. Sources of chemicals
Chemicals
Formula
weight CAS No.
Catalog
No.
Catalog
(Fisher
No.(ColeScientific) Parmer)
MSDS
calcium carbonate
100.09
(CaCO3)
471-34-1
S719222
WU-88341-39
http://fscimage.fishersci.com/ms
ds/03880.htm
calcium hydroxide
74.09
(Ca(OH)2)
1305-62-0
S75071
EW-88341-42
http://fscimage.fishersci.com/ms
ds/03980.htm
Hydrochloric acid
36.46
(HCl)
7647-01-0
A142-212
WU-88011-72
http://fscimage.fishersci.com/ms
ds/11155.htm
sodium hydroxide
40.00
(NaOH)
1310-73-2
S93369
WU-88137-38
http://fscimage.fishersci.com/ms
ds/21300.htm
58.44
7647-14-5
S78449
WU-89100-67
http://fscimage.fishersci.com/ms
ds/21105.htm
147.02
10035-04-8
C79-3
EW-88222-54
http://fscimage.fishersci.com/ms
ds/03901.htm
sodium bicarbonate
84.01
(NaHCO3)
144-55-8
S71986
WU-89100-63
http://fscimage.fishersci.com/ms
ds/20970.htm
methyl orange
(C14H14N3NaO3S). 327.34
547-58-0
S71410
WU-88351-68
http://fscimage.fishersci.com/ms
ds/60355.htm
sodium chloride
(NaCl)
calcium chloride
dihydrate
(CaCl2.2H2O)
Cole-Parmer 1-800-323-4340, http://www.coleparmer.com/
Fisher Scientific 1-800-766-7000, http://www.fishersci.com/
Appendix 2.5.2: Examples of laboratory apparatus and glassware
A Hand Held Altimeter w/ Barometer can be used for recording both air
pressure and temperature.
Fisher and Huang. LimeR Series
28
Materials for Conducting LimeR Series Tests
“Salvarsan” tubes for measuring CO2 (250 ml capacity, with 1 mm increments, left) and leveling
burette (large capacity, 300 ml, right) for the gasometric system.
A glass burette with stopcock can be used as an acid dispensing burette, a funnel can be attached to
the top for easily pouring the acid into the burette.
Fisher and Huang. LimeR Series
29
Materials for Conducting LimeR Series Tests
1000 mL filtering flask with 8# rubber stopper as decomposition flask in the gasometric system.
(such as Pyrex No. 5340, or Kimax No. 27060)
Classic burettes and a lab stand (left) for lime neutralizing value measurement and pH titration. A
digital burette (right) can also be used.
Fisher and Huang. LimeR Series
30
Materials for Conducting LimeR Series Tests
To analyze the particle size distribution of a lime sample, 6 series of screen sieves are needed (No.
20, 60, 100, 200 and 325 mesh size). A sieve shaker is recommended.
C
E
B
D
F
A
G
A gasometric system for residual carbonate measurement. The apparatus consists of 1 L
decomposition flask (A), rubber tube (B), stopcock (C), a gas measuring burette (D), level
burette(E), an acid dispensing burette (F), and a magnetic stirrer (G).
Fisher and Huang. LimeR Series
31
Overall LimeR Model
2.6 Overall LimeR Model
Jinsheng Huang and Paul Fisher, University of Florida,
pfisher@ufl.edu, 352 392 1831 ext 375. Copyright, 2009.
March 30, 2009.
Description: A research model that combines different aspects of lime reactivity, requirement, and
residual to predict pH response and lime buffering.
The LimeR protocols and their underlying research and chemistry were combined into a prototype
Excel spreadsheet model called “Overall LimeR Model”. This model is part of our ongoing research
in collaboration with Young Plant Research Center partners, and is therefore a tool intended to
integrate our current state of knowledge, and to allow R&D departments of media and fertilizer
companies to explore the likely combined effects of different lime types, lime rates, and substrates.
This section describes how to use the spreadsheet tool.
Open the file “Overall LimeR Model Mar 2009.xls” and you will see the above screen on the LimeR
model sheet.
The following provides information about each component on the screen.
Fisher and Huang. LimeR Series
32
Overall LimeR Model
Substrate Titration:
For this section, you need to enter data from the lime requirement test (Section 2.2 LimeR Substrate
Lime Requirement Test) used to calculate buffering of the substrate to pH change.
Input the data from lime requirement test into the gray cells. Initial pH refers to the pH of the
substrate after mixing in the preplant nutrient charge, but without mixing in any lime.
In this test, at least two rates of calcium hydroxide are added to the unlimed substrate, the substrate
is moistened, and pH is measured after 3 days.
In the “Low rate” column, enter the number of grams of hydrated lime for the LOWEST of two rates
of calcitic hydrated lime (for example 1 gram per liter of substrate) used to calculate the slope for
lime requirement, and the corresponding substrate-pH (for example, 4).
In “High rate” column, enter the pH after 3 days into this cell for the HIGHEST of two rates of
calcitic hydrated lime (for example 4.14 gram per liter of substrate) used to calculate the slope for
lime requirement, and the corresponding substrate-pH (for example, 6.5).
The slope of this line is used to measure pH buffering, and therefore to calculate how many
milliequivalents of lime will be needed.
Lime Characteristics:
For this section, you need to enter data from the lime reactivity test (Section 2.1 LimeR Lime
Reactivity Test) used to test the reactivity of a liming material in horticultural substrates.
Fisher and Huang. LimeR Series
33
Overall LimeR Model
Input the data from the lime reactivity test into the gray cells. The “Descriptive name for this lime”
label is just used for record keeping, and does not affect calculations.
In the “Particle size distribution” rows, enter the data from the particle size distribution analysis,
with 6 mesh size ranges.
The acid neutralizing value (NV) of lime is needed to help calculate lime requirement of this lime
source.
The Ca and Mg content helps calculate lime reactivity (calcitic versus dolomitic) for this lime
source.
The moisture level is needed to accurately calculate the amount of lime needed to achieve a target
pH. Low moisture (2% or below) means that there is more neutralizing power for this lime per lb or
kg than higher moisture levels.
Lime type influences lime reactivity and solubility.
Management objective
In this section, enter the information in the gray cells for the target pH and the number of days to
achieve this target pH. Substrate-pH is a moving target - it changes dynamically over time. Enter
the days after mixing when the target pH should be reached. This assumes warm temperature
(around 20C/68F) and high moisture level (near container capacity). The standard value is 7 days,
which is the duration used for the particle size efficiency calculations in Section 2.1. However, if
you change the duration specified in the “Days to achieve target pH” cell, it will change the
predicted amount of lime required, and proportions of reacted and residual lime in the charts (try
changing this to understand those effects).
Model output:
In this section, the model calculates substrate pH buffering capacity, lime fineness factor, ECC and
required lime rate to achieve a target pH. Substrate buffering is quantified with units of ∆pH per
milliequivalent of base per L of substrate (∆pH/meq.L-1).
Fisher and Huang. LimeR Series
34
Overall LimeR Model
The fineness factor (reactivity of this lime source in peat compared with reactivity of reagent CaCO3
based on particle size distribution) in this table is dependent on the "days to achieve target pH"
above. For example, if you want to achieve the target pH after 7 days, the fineness factor will be
lower than after 14 days because coarse particles will have had more time to react by 14 days.
The term “Effective calcium carbonate equivalence (ECC)” quantifies the combined effects of
particle size distribution and acid neutralizing value (NV) of a limestone on pH response. Most
horticultural carbonate limes are above 90%.
High magnesium indicates a dolomitic lime. Low calcium indicates a calcitic lime. Calcitic limes
tend to react more quickly than dolomitic limes. We use a threshold where %Mg less than 6% is
defined as a "calcitic" lime, otherwise it is a dolomitic lime.
Lime particle size distributions are separated into coarse, ground, pulverized, and superfine grades
which are terms commonly used in agriculture. Note that states vary in their exact definition of
those terms.
In our spreadsheet, we compare this lime source with research on 29 other limes used in horticultural
container media in the U.S. and Canada. Very coarse limes (most of the lime does not pass a 60mesh screen) are unlikely to react quickly enough for container use. Coarse to moderate limes
provide some buffering to pH change during crop growth, but may take a week or two longer to raise
pH than fine limes at the start of the crop. Fine or very fine limes provide little buffering, but react
quickly to raise pH. Specifically, we compare the fineness factor in the following ways (note this
comparison is only valid if the duration to the target pH is set at 7 days, as described in the previous
page):
Critical value below which Fineness Factor is "extremely coarse":
Critical value below which Fineness Factor is "coarse":
Critical value above which Fineness Factor is fine":
Fisher and Huang. LimeR Series
0.6
0.8
0.95
35
Overall LimeR Model
Reacted and “unreacted”residual lime concentration as influenced by particle size distribution
The above chart shows the expected reactivity of different particle sizes of lime, as illustrated by the
reacted lime (“Contribution to pH change”) and unreacted residual lime (“Contribution to residual”)
portions for each of the six screened particle sizes. This prediction is at the duration specified in the
“Days to achieve target pH” cell (typically 7 days).
Based on our research, the intermediate limestone particle size fractions (20 to 60 or 60 to 100 US
mesh) provided the greatest pH-buffering, contributed to most of the residual lime. Particle fractions
finer than 100 mesh reacts quickly over time, whereas buffering by particles coarser than 20 mesh is
limited because of the excessively slow reaction rate.
Residual lime and reacted lime:
The chart below shows the expected proportions of
residual lime and reacted lime in the medium. Reacted
lime neutralizes acidity of substrate components such as
peat, and is important for target pH, whereas the
unreacted residual lime plays an important role in
buffering substrate-pH changes over time.
Fisher and Huang. LimeR Series
36
Overall LimeR Model
Lime requirement:
This chart below shows an expected pH at the duration specified in the number of “Days to achieve
target pH” cell (typically 7 days) with different rates of limestone, with the effective calcium
carbonate equivalents entered.
Fisher and Huang. LimeR Series
37
Thanks to Our Sponsoring Companies
Thanks to these leading companies and
organizations for sponsoring our research
This research is a product of the University of Florida
Institute of Food and Agricultural Sciences
http://ifas.ufl.edu
The American Floral Endowment provided a grant on pH
management for this project www.endowment.org
The Young Plant Research Center is a university/industry
consortium, with leading media, fertilizer, and grower
companies http://hort.ifas.ufl.edu/yprc/
Blackmore Co. is a founding member of the Young Plant
Research Center www.blackmoreco.com
Ellegaard is a founding member of the Young Plant
Research Center http://www.ellepot.dk/
Fafard is a member of the Young Plant Research Center
http://www.fafard.com/
Greencare Fertilizers is a founding member of the Young
Plant Research Center www.blackmoreco.com
PINDSTRUP MOSEBRUG A/S
Pindstrup is a member of the Young Plant Research Center
http://www.pindstrup.com/
Premier Horticulture is a founding member of the Young
Plant Research Center http://www.premierhort.com/
Quality Analytical Laboratories is a founding member of
the Young Plant Research Center http://www.qal.us/
Sun Gro Horticulture is a member of the Young Plant
Research Center http://www.sungro.com/
Fisher and Huang. LimeR Series
38