LimeR Protocols

LimeR SeriesAnalyzing 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Not for publication or reproduction in part or full without permission of authors.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

Fisher and Huang. LimeR Series

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.

Modeling Lime Reaction

Fisher and Huang. LimeR Series 1

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 718:461-468. Paul R. Fisher, Environmental Horticulture Dept., P.O. Box 110670, Gainesville FL 32611-0670, [email protected]. Jinsheng Huang, Dept. of Plant Biology, Univ. of New Hampshire, Durham, NH 03824, USA, [email protected] William R. Argo, Blackmore Co., 10800 Blackmore Ave, Belleville, MI 48111, USA, [email protected] 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.



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:



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.

FFt = ∑ (PFi x PSEi,t) [1] 6

i=1



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. meqrequired.L-1 = ∆pHrequired/pHB [4]

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



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.



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.

CaCO3 NLS OldCastle Mean of 24 horticultural lime samples (± s. dev.)

µm Screen size

U.S. mesh Screen size

Passing (%)

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 fraction (µm)

850-2000

250-850

150-250

150-250

75-150

75-150

45-75

45-75 <45 <45

Lime typez C,D C,D C D C D C D C D

K 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 1 1 1 1 1 1 1 1

S. err. of A 0.019 0.007 Days to 95%

reaction n/a n/a 13.7 19.7 5.8 8.9 2.9 4.3 2.0 3.0 Days to 50%

reaction 58.2 9.5 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.



Figures

Days after incorporating lime

0 7 14 21 28 35 42

Sub

stra

te-p

H

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

X

X

XX

X

Reagent grade CaCO3 NLS OldCastle X

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.

Days after incorporating lime0 7 14 21 28 35 42 49 56 63 70 77 84

Cha

nge

in s

ubst

rate

-pH

0.0

0.5

1.0

1.5

2.0

2.5

3.0

< 45 µm 75-45 µm 150-75 µm250-150 µm850-250 µm> 850 µm

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.



(A)

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

3.0 4.0 5.0 6.0 7.0

Predicted Substrate-pH

Obs

erve

d S

ubst

rate

-pH

day 7day 28

(B)

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

3.0 4.0 5.0 6.0 7.0

Predicted Substrate-pH

Obs

erve

d S

ubst

rate

-pH

day 7day 28

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

0 3 6 9 12 15 18Lime Application Rate (g lime/L of peat)

Sub

stra

te-p

H

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0R

esidual Lime

g CaC

O 3 equivalents /L of peat

CaCO3 pH NLS pH OldCastle pHCaCO3 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).

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.

LimeR Lime Reactivity Test


2.1 LimeR Lime Reactivity Test

Jinsheng Huang and Paul Fisher, University of Florida, [email protected], 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.



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 200-325 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



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:

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 passing a 325-mesh screen x 0.99 =_________

TOTAL Fineness Factor = _______

FFt = ∑ (PFi x PSEi,t) [1] 6



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



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.

LimeR Substrate Lime Requirement Test


2.2 LimeR Substrate Lime Requirement Test

Jinsheng Huang and Paul Fisher, University of Florida, [email protected], 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.



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



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) Chemicals Name Calcium Chloride Dihydrate Calcium Hydroxide Linear formula CaCl2.2H2O Ca(OH)2 CAS No. 10035-04-8 1305-62-0 Formula weight 147.02 74.09

EW-88222-54 (Cole-Parmer $89.80/kg) EW-88341-42 (Cole-Parmer $59.90/kg) Catalog No. (2009 pricing) S93162 (Fisher Scientific, $76.5/kg) EW-88234-31 (Cole-Parmer $77.40/kg) S75071 (Fisher Scientific, $16.1/kg)

MSDS sources http://www.coleparmer.com/catalog/Msds/95446.htm

http://www.coleparmer.com/catalog/Msds/95944.htm

http://www.coleparmer.com/catalog/Msds/00363.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.



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.

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, [email protected], 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 CO2-CaCO3 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



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. (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).

3. The general procedure involves dissolving the carbonate lime materials in a substrate sample and liberating CO2 gas using 6M HCl. A measured substrate sample (50-100 mL) is 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

A

B C

D

E

F

G

Fig.1 Apparatus for residual carbonates measurement.



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.



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.

LimeR Substrate pH Buffering Test


2.4 LimeR Substrate pH Buffering Test

Jinsheng Huang and Paul Fisher, University of Florida, [email protected], 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.



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 Range

∆pH after 40 meq HCl drench Residual Lime in CCE (g/L)*

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:



• 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.



Residual CCE (g/L) = 2.6 ∆pH + 5.75R2 = 0.77

0

1

2

4

5

-3.0 -2.0 -1.0 0.0

∆pH from an acid drench at 40 meq/L of substrate

Initi

al R

esid

ual C

CE

(g/L

of s

ubst

rate

)

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.

y = 1.2363x + 0.5784R2 = 0.9166

-3.5

-2.5

-1.5

-0.5

-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)

Del

ta p

H fr

om A

mm

oniu

m

Ferti

lizer

Comparison of HCl Drench and Ammonium Fertilizer Response

p = 0.005

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.



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).

y = 20.402x + 3.5645R2 = 0.9096

0

20

40

60

80

100

120

0 1 2 3 4 5 6Initial Residual CCE (g·L-1)

pH4.

5 B

uffe

ring

Cap

acity

(m

eq·L

- 1)

A. Meq of HCl to drop pH to 4.5

p <0.001

0

1

2

3

4

5

6

0 1 2 3 4 5 6

Initial Residual CCE (g·L-1)

pH4.

5 Buf

ferin

g C

apac

ity

(CC

E g·

L-1)

HCl (in CCE g/L) needed to drop pH to 4.5

p < 0.001y = 1.02x + 0.18R2 = 0.91

B

Materials for Conducting LimeR Series Tests


2.5 Materials for Conducting LimeR Series Tests

Jinsheng Huang and Paul Fisher, University of Florida, [email protected], 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. Thermometer for temperature 4. stop watch for time 5. lab stand 6. a magnetic stirrer & stir bar 7. 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-p-36021.html

3. acid dispensing burette (glass burette with stopcock) 4. titration burettes Please refer Appendix 2 for examples.



Appendix 2.5.1. Sources of chemicals

Chemicals Formula weight CAS No.

Catalog No. (Fisher Scientific)

Catalog No.(Cole-Parmer) MSDS

calcium carbonate (CaCO3) 100.09 471-34-1 S719222 WU-88341-39

http://fscimage.fishersci.com/msds/03880.htm

calcium hydroxide (Ca(OH)2) 74.09 1305-62-0 S75071 EW-88341-42


Hydrochloric acid (HCl) 36.46 7647-01-0 A142-212 WU-88011-72


sodium hydroxide (NaOH) 40.00 1310-73-2 S93369 WU-88137-38


sodium chloride (NaCl) 58.44 7647-14-5 S78449 WU-89100-67


calcium chloride dihydrate (CaCl2.2H2O) 147.02 10035-04-8 C79-3 EW-88222-54


sodium bicarbonate (NaHCO3) 84.01 144-55-8 S71986 WU-89100-63


methyl orange (C14H14N3NaO3S). 327.34 547-58-0 S71410 WU-88351-68


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.



“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.



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.



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.

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).

A

B C

D

E

F

G

Overall LimeR Model


2.6 Overall LimeR Model

Jinsheng Huang and Paul Fisher, University of Florida, [email protected], 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.

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.

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).

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 60-mesh 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": 0.6Critical value below which Fineness Factor is "coarse": 0.8Critical value above which Fineness Factor is fine": 0.95

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.

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.

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 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/

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