1 CHLORINE DIOXIDE AS A SANITIZING AGENT IN RECIRCULATING IRRIGATION FOR GREENHOUSE HYDROPONIC BELL PEPPERS By LIBBY ROHRER RENS A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2011
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1
CHLORINE DIOXIDE AS A SANITIZING AGENT IN RECIRCULATING IRRIGATION FOR GREENHOUSE HYDROPONIC BELL PEPPERS
By
LIBBY ROHRER RENS
A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE
Closed-loop Production Systems for Greenhouse Vegetables ............................... 11 Sanitizing the Nutrient Solution ............................................................................... 12
Properties of Chlorine Dioxide ................................................................................ 14 In Summary ............................................................................................................ 16
2 CHLORINE DIOXIDE AS AN IRRIGATION SANITIZING AGENT REDUCES HYDROPONIC BELL PEPPER GROWTH ............................................................. 17
Materials and Methods............................................................................................ 17
Table page 2-1 Concentration of fertilizers in the nutrient solution used to produce
greenhouse bell peppers in Fall 2009 and Spring 2010 in Citra, FL. .................. 25
2-2 Fall 2009 comparison of greenhouse bell pepper growth in perlite and pine bark media in Citra, FL. ...................................................................................... 26
2-3 Pepper plant growth response to ClO2 concentration in perlite and pine bark media in Citra, FL. .............................................................................................. 27
3-1 Concentration of fertilizers in the nutrient solution used to produce greenhouse bell peppers Spring 2011 in Citra, FL. ............................................ 41
4-1 Concentration of fertilizers in the nutrient solution used to produce greenhouse bell peppers in Spring 2011 in Citra, FL. ......................................... 53
4-2 Pepper plant growth responses to two application strategies of ClO2 and two soilless medias in Citra, FL. ................................................................................ 54
8
LIST OF FIGURES
Figure page 2-1 Design of greenhouse bell pepper production system in Citra, FL showing a
single plot composed of ten plants. .................................................................... 28
2-2 Fall 2009 bell pepper whole-plant dry weight in response to increasing ClO2 concentration in Citra, FL. .................................................................................. 29
2-3 Fall 2009 bell pepper plant height in response to increasing ClO2 concentration in Citra, FL. .................................................................................. 30
2-4 Fall 2009 bell pepper leaf area in response to increasing ClO2 concentration in Citra, FL. ......................................................................................................... 31
2-5 Spring 2010 bell pepper whole-plant dry weight in response to increasing ClO2 concentration in Citra, FL. .......................................................................... 32
2-6 Spring 2010 bell pepper plant height in response to increasing ClO2 concentration in Citra, FL. .................................................................................. 33
2-7 Spring 2010 bell pepper leaf area in response to increasing ClO2 concentration in Citra, FL. .................................................................................. 34
4-1 Residual chlorine dioxide in the nutrient solution used to produce greenhouse bell peppers in Citra, FL. .................................................................................... 55
A-1 Fall 2009 root systems of pepper plants grown in perlite media irrigated with 0 to 40 mg L-1 chlorine dioxide. ........................................................................... 58
A-2 Fall 2009 root systems of pepper plants grown in pine bark media irrigated with 0 to 40 mg L-1 chlorine dioxide. ................................................................... 59
A-3 Spring 2010 root systems of pepper plants grown in perlite media irrigated with 0 to 10 mg L-1 chlorine dioxide. ................................................................... 60
A-4 Spring 2010 root systems of bell pepper plants grown in pine bark media irrigated with 0 to 10 mg L-1 chlorine dioxide. ..................................................... 61
A-5 Spring 2010 bell pepper plants. .......................................................................... 62
A-6 Water samples used in chlorine dioxide demand experiments. .......................... 63
9
Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science
CHLORINE DIOXIDE AS A SANITIZING AGENT IN RECIRCULATING IRRIGATION
FOR GREENHOUSE HYDROPONIC BELL PEPPERS
By
Libby Rohrer Rens
December 2011
Chair: Danielle D Treadwell Major: Horticultural Sciences
Sanitation of greenhouse irrigation systems with chlorine dioxide was investigated
for its use in hydroponic bell pepper (Capsicum annum, L. ‘Legionnaire’) production.
The goal of this project was to evaluate the plant response to chlorine dioxide
concentrations recommended for pathogen control in applied hydroponic systems and
was broken down into three objectives. The first objective was to determine the
response of bell pepper growth when exposed to a range of concentrations of chlorine
dioxide within the nutrient solution. The second objective was to determine the ClO2
demand of irrigation solutions used in recirculating hydroponic systems. The final
objective was to determine the impact of ClO2 application strategy and potting media on
greenhouse bell pepper growth. Together, these objectives help to optimize a
recommendation for chlorine dioxide application in commercial greenhouse systems.
In the first greenhouse experiments, plant growth, including plant height, fresh
weight and dry weight, decreased quadratically in response to increasing concentrations
of chlorine dioxide up to 40 mg L-1. Plants grown in pine bark media were less impacted
10
by chlorine dioxide than plants grown in perlite, likely due to the greater organic matter
content in the pine bark media leading to reduction of chlorine dioxide before coming
into contact with plant roots.
The chlorine dioxide demands of hydroponic nutrient solution, nutrient solution
leachate from pine bark media, and nutrient solution leachate from perlite media were
determined over a period of four hours in lab experiments. Chlorine dioxide demand
was dependant on both water source and initial application concentration over time. All
hydroponic solutions had a greater chlorine dioxide demand than deionized and well
water treatments, with pine bark leachate having the greatest demand. These results
indicate that higher concentrations of chlorine dioxide are needed to meet the demand
of irrigation water, and initial treatment doses should be tested at a range of
concentrations to determine the minimum treatment that will create an optimal
sanitizing residual.
In the final greenhouse experiment, bell pepper plants grown in pine bark media
were not impacted by 20 mg L-1 ClO2 application, whereas plants grown in perlite had a
significant growth reduction compared to the 0 mg L-1 control. Chlorine dioxide
application as a single-dose versus slow-release treatment was not as important as
media on plant growth.
Overall, pepper plants grown in pine bark media were less sensitive to chlorine
dioxide treatments as compared to perlite media, and this shows potential for use in
combination with concentrations of up to 20 mg L-1 chlorine dioxide.
11
CHAPTER 1 INTRODUCTION
Closed-loop Production Systems for Greenhouse Vegetables
Agricultural practices consume 128 billion gallons of water per day, accounting
for one third of the total freshwater withdrawn annually throughout the US (Kenny et al.
2009). The Federal Clean Water Act (FCWA), defined water quality load allocations to
reduce pollution of surface and ground waters. In 2005, Florida’s Department of
Agriculture and Consumer Services (FDACS) initiated a Best Management Practices
(BMPs) program for farmers and ranchers that includes a suite of recommended
practices designed to reduce risk to water quality and increase water efficiency (FDACS
2005;2006). Many of these practices are easily applied in greenhouse vegetable
production systems.
The United States produces 1,636 acres of greenhouse vegetables, with 622
acres in California, followed by Pennsylvania (68), New York (59), and Florida (47)
(USDA-NASS, 2009). Greenhouse vegetable production has added advantages over
field production including controlled atmosphere (carbon dioxide, humidity, temperature,
and light), exclusion of pests and inclusion of beneficial insects, controlled fertilization
and irrigation schedules, and higher planting densities which leads to its increase in
yield compared to field grown vegetables. While irrigation volume per acre can be
increased in greenhouse systems, the yield is often 3 to 10 times greater than field
production (Cantliffe and Vansickle 2009.; Cook et al. 2005; Jovicich et al. 2007;
Rouphael et al. 2004) meaning water use efficiency of greenhouse vegetable production
is higher than in field production. In previous studies, water use efficiency (grams of
water per kilogram of fruit) in the greenhouse was greater than in the field by 33% in
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cucumbers (Jovicich et al. 2007), and 54% in zucchini (Rouphael et al. 2005). To further
maximize greenhouse water use efficiency, irrigation can be conserved by utilizing a
closed-loop irrigation system where excess irrigation is collected and reapplied to the
crop. Recirculating irrigation solution has the immediate production benefits of reducing
greenhouse inputs of water up to 30% and fertilizer up to 50% (Ruijs and Van Os 1991;
Ruijs 1993; Van Os 1999; Van Os et al. 1991) thereby decreasing demand for fresh
water and reducing risk to water quality. In the Netherlands greenhouse crops are
required to be produced in closed loop systems (Van Os, 1999). As the salt content of
the nutrient solution (measured as electrical conductivity (EC) in mmol dm-3) increases
after leaching from the plants it must be dispensed out of the system once it reaches a
Table 2-3. Pepper plant growth response to ClO2 concentration in perlite and pine bark media in Citra, FL.
0 7.5 a 21.0 a 1213.3 a
10 4.3 b 18.7 a 631.3 b
20 3.0 b 17.2 ab 394.3 b
40 2.6 b 14.4 b 339.6 b
p-value
0 27.8 a 30.5 a 2793.5 a
2.5 21.7 b 27.8 ab 2262.5 b
5 19.9 b 27.3 ab 2210.4 b
10 18.7 b 24.9 b 1995.8 b
p-value
0 5.2 a 18.9 a 618.6 a
10 2.1 b 14.9 ab 203.2 b
20 1.5 b 11.2 bc 133.6 b
40 0.6 b 9.9 c 56.8 b
p-value
0 20.8 a 28.3 a 1868.4 a
2.5 11.8 b 22.7 b 915.6 b
5 8.0 bc 19.3 bc 553.1 c
10 5.2 c 18.4 c 372.7 c
p-value
-- Perlite Media --
0.0006
0.00180.00450.0054
0.0029
<0.00010.0002<0.0001
0.00050.00140.0023
0.0039
Dry
Weight (g)
Plant Height
(cm)
Leaf Area
(cm2)
ClO2
mg L-1
-- Pine Bark Media--
28
Figure 2-1. Design of greenhouse bell pepper production system in Citra, FL showing a single plot composed of ten plants.
29
Figure 2-2. Fall 2009 bell pepper whole-plant dry weight in response to increasing ClO2 concentration in Citra, FL. Main effects of media (p<0.0001) and mg L-1 (p<0.0001) were significant, however there was no significant interaction between the two (p=0.6950). y=dry mass and x=chlorine dioxide concentration. (R2=0.90).
0
1
2
3
4
5
6
7
8
9
0 10 20 30 40
Dry
We
igh
t (g
)
mg*L-1
Pine Bark y = 0.005x² - 0.31x + 7.3
Perlite y = 0.005x² - 0.31x + 5.1
30
Figure 2-3.Fall 2009 bell pepper plant height in response to increasing ClO2 concentration in Citra, FL. Main effects of media (p<0.0001) and mg L-1 (p<0.0001) were significant, however there was no significant interaction between the two (p=0.1928). y=plant height in cm and x=chlorine dioxide concentration. (R2=0.88).
0.0
5.0
10.0
15.0
20.0
25.0
0 10 20 30 40
Heig
ht
(cm
)
mg*L-1
Pine Bark y = 0.0043x² - 0.37x + 21.5
Perlite y = 0.0043x² - 0.37x + 18.5
31
Figure 2-4. Fall 2009 bell pepper leaf area in response to increasing ClO2 concentration in Citra, FL. Main effects of media (p<0.0001) and mg L-1 (p<0.0001) were significant, however there was no significant interaction between the two (p=0.1648). y=leaf area and x=chlorine dioxide concentration. (R2=0.87).
-200
0
200
400
600
800
1000
1200
1400
0 10 20 30 40
Lea
f A
rea
(cm
2)
mg*L-1
Pine Bark y = 0.904x²- 52.9x + 1150.4
Perlite y = 0.904x² - 52.9x + 648.6
32
Figure 2-5. Spring 2010 bell pepper whole-plant dry weight in response to increasing ClO2 concentration in Citra, FL. Main effects of media (p<0.0001) and mg L-1 (p<0.001) were significant, as well as the interaction between the two (p=0.0125). y = dry mass and x = chlorine dioxide concentration. (R2=0.95).
0
5
10
15
20
25
30
35
0 2.5 5 7.5 10
Dry
We
igh
t (g
)
mg*L-1
Pine Bark y = 0.186x² - 2.7x + 27.9 Perlite y = 0.186x² - 3.4x + 20.1
33
Figure 2-6. Spring 2010 bell pepper plant height in response to increasing ClO2 concentration in Citra, FL. Main effects of media (p<0.0001) and mg L-1 (p<0.001) were significant, as well as the interaction between the two (p=0.0264). y=plant height in cm and x=chlorine dioxide concentration. (R2=0.91).
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
0 2.5 5 7.5 10
Heig
ht
(cm
)
mg*L-1
Pine Bark y = 0.0968x² - 1.52x + 31.1
Perlite y = 0.0968x² - 1.94x + 27.5
34
Figure 2-7. Spring 2010 bell pepper leaf area in response to increasing ClO2 concentration in Citra, FL. Main effects of media (p<0.0001) and mg L-1 (p<0.001) were significant, as well as the interaction between the two (p=0.0001). y=leaf area and x=chlorine dioxide concentration. (R2=0.98).
0
500
1000
1500
2000
2500
3000
3500
0 2.5 5 7.5 10
Lea
f A
rea
(cm
2)
mg*L-1
Pine Bark y = 22.6x² - 285.2x + 2821 Perlite y = 22.6x² - 370.6x + 1806
35
CHAPTER 3 RESIDUAL CHLORINE DIOXIDE CONCENTRATION CHANGES OVER TIME IN
RECIRCULATING HYDROPONIC IRRIGATION SOLUTIONS
Materials and Methods
Objectives
Limited research has been performed on the ClO2 demand of greenhouse
hydroponic nutrient solutions intended for recirculation. The objective of this research is
to determine the ClO2 demand of water used in recirculating irrigation systems and to
further characterize the ClO2 sequestration of two common water sources and three
hydroponic irrigation solutions.
Experimental Design
Chlorine dioxide (Z-SeriesTM Sachets, ICA Trinova, Newnan, GA) was added to
two water sources and three hydroponic irrigation solutions and subsequently sampled
for residual ClO2 concentration over a period of four hours. Treatments included two
concentrations of ClO2 (10 mg L-1 and 20 mg L-1) and five water samples (deionized
water (DI), well water only, nutrient solution in well water, well water-nutrient solution
leachate from pine bark media, and well water-nutrient solution leachate from perlite
media), each measured at five time points (0.25, 0.5, 1, 2, and 4 hours). The experiment
was repeated four times over two days with two concurrent replications per day and was
conducted in the Plant Mineral Nutrition Laboratory at the University of Florida’s (UF)
main campus in Gainesville, FL.
Water Sources and Sampling
Water samples were collected from a hydroponic bell pepper production system
located at the UF Institute of Food and Agricultural Sciences (IFAS) Plant Sciences
Research and Education Unit (PSREU) greenhouses in Citra, FL. Hydroponic nutrient
36
solution was prepared using UF-IFAS recommendations for greenhouse bell pepper
production (Table 3-1) and prepared using PSREU well water. Well water was sampled
before the experiments were performed and tested low for chloride and other potential
contaminants. Leachate samples were collected from the bell pepper production system
and prepared as follows. Two benches were established with independent irrigation
systems and each supplied nutrient solution to ten pepper plants (Capsicum annum, L.
‘Legionnaire,’ Siegers Seed Co, Holland, MI). One soilless media type (perlite or pine
bark) was used at each bench and individual plants were potted into 12.1 L plastic pots
with drainage holes (Bato-buckets, General Hydroponics, Sebastopol, CA). At each
bench, nutrient solution was stored in a 55-gallon reservoir, injected by a pony pump
(Little Giant PP1-S, Oklahoma City, OK) through 0.75 inch polyethylene pipe set to 10
psi pressure, and supplied to plants through pressure compensating emitters (2L hr-1,
Netafim, Tel-Aviv, Israel). Irrigation events occurred between 7:00 am and 5:00 pm, and
were maintained at a frequency to produce 20% to 30% leachate, as recommended for
greenhouse vegetables with recirculating irrigation. Leachate from each bench
(composite of ten pots) was collected in a 5-gallon reservoir. Nutrient solution was not
recirculated for the purpose of data collection. Eight weeks after transplanting, leachate
from perlite and pine bark plots was accumulated for one week and used in laboratory
experiments.
Experimental Procedure
Water samples were pH adjusted to 6.0 with commercially available hydroponic
pH buffers (General Hydroponics, Sebastopol, CA). Chlorine dioxide was added to 300
mL of the sampled water at a concentration of 10 mg L-1 or 20 mg L-1 dependant on the
treatment and the solutions were tested for residual ClO2 at 0.25, 0.5, 1, 2, and 4 hours
37
after the ClO2 addition. The experiment was terminated four hours after ClO2 addition as
previous studies report suppression of many pathogens occurs well within this range
(Beardsell et al. 1996; 2010; Fisher et al. 2009; James et al. 1996; Mebalds et al. 1996).
Residual ClO2 concentration was measured using a titration procedure adapted from
Mahovic et al, 2009. Samples were combined with potassium iodide in pH 7.0
phosphate buffer and titrated using sodium thiosulfate to a colorless endpoint. Two-
normal sulfuric acid was then added to achieve a pH of 2.0 which produced a color
change, and a second titration with sodium thiosulfate was performed to a colorless
endpoint. The concentration of ClO2 was calculated from this procedure.
Statistical Analysis
The data were analyzed as ClO2 residual (the concentration remaining in the water
sample), and ClO2 demand (the treatment concentration minus the residual). Proc
Glimmix was used to perform repeated measures analysis (SAS V9.2, Cary, NC).
Chlorine dioxide concentrations were compared among all treatments to determine
differences between water samples and treatment concentration over four hours.
Averages were computed using the least squared means (LSMeans) option and
compared among treatments using Tukey’s Honestly Significant Difference Test (HSD).
Results and Discussion
Residual Chlorine Dioxide
In these experiments residual ClO2 concentrations were influenced by water
source, initial application concentration of ClO2 and time in significant three-way
interactions (p<0.0001; concentration-water-hour interaction p=0.0025). The residual
concentration of ClO2 throughout the four hour duration of the experiment was
38
significantly different between 10 and 20 mg L-1 treatment concentrations for each of the
water sources and time points tested (Table 3-2).
At the 15 minute time point the ClO2 residual in the DI and well water samples
remained relatively constant, whereas the residual in the leachates and nutrient solution
decreased by up to 80%. After four hours the residual concentration was reduced from
the treatment concentration in all water types (p<0.0001). Chlorine dioxide residuals in
DI water, well water, and nutrient solution treated with both initial concentrations, and
pine bark leachate treated with 20 mg L-1, gradually decreased throughout the four
hours. Only pine bark leachate receiving 10 mg L-1 ClO2 dropped to a minimum by 15
minutes and remained at approximately 2.5 mg L-1 throughout the 4 hours. In all other
treatments the residual ClO2 concentration changed considerably throughout the
treatment time. The response of ClO2 in perlite leachate observed in this experiment
was unexpected, as the residual concentration initially decreased by 65%, increased
over the next two hours, and then decreased again by the fourth hour. The researchers
believe that this response is an interference caused by the interaction between minerals
in the perlite media and chemicals used in the ClO2 titration method rather than a
generation of ClO2 within the leachate solution.
A ClO2 concentration of 3 mg L-1 for 8-12 minutes is one practice recommended to
greenhouse growers for control of waterborne pathogens (Fisher et al. 2009; Mebalds et
al. 1996). In this study, the use of 10 mg L-1 was more than a sufficient dose to attain
the recommended concentration-time in all water samples except for the pine bark
leachate where a higher initial dose is recommended.
39
Chlorine Dioxide Demand
Chlorine dioxide demand of the water samples was influenced by water source,
initial application concentration of ClO2 and time in significant three-way interactions
(p<0.0001; mg L-1-water-hour interaction p=0.0025) (Table 3-3). The magnitude of ClO2
demand would be same for both treatment concentrations if water quality a primary
factor in the determination of ClO2 demand, however not all water samples followed this
trend. Deionized water, well water and nutrient solution had similar demands of ClO2
while neither of the leachate samples had the same magnitude of loss between
treatment concentrations at any time point.
Chlorine dioxide demand of fresh well water was similar to the demand of DI water
over the 4 hour period at both the 10 and 20 mg L-1 initial concentrations and was less
than solutions containing fertilizers, root exudates, or leachate from pine bark. In the
nutrient solution, oxidizers such as ClO2 will oxidize ferrous iron (2+) ions to the ferric
iron (3+) and manganous manganese (2+) to (4+). These oxidized ions react with water
to form insoluble precipitates (US-EPA, 1999). These reactions may partially account
for the higher demand of ClO2 in the nutrient and leachate solutions. The precipitation of
iron and manganese will also impact the fertilizer concentrations needed to grow
greenhouse vegetables, however the use of chelated forms of these fertilizers will
maintain the concentration of iron and manganese in the desired form. The nutrient
solution accumulates more organic matter after flowing through the irrigation system,
the matrix of potting media and plant roots, and being dispensed as leachate. Leachate
from pine bark media also contains organic compounds such as amines, aldehydes,
and phenols which reduce ClO2 (Gagnon et al. 2005; Stevens, 1982; US-EPA, 1999).
These organic compounds account for the higher ClO2 demand of pine bark leachate as
40
compared to the nutrient solution. Other studies have found similar demands when
treating waste water samples including organic suspended solids with ClO2 (Narkis and
Kott 1992; Veschetti et al. 2005).
Concentrations of chlorine dioxide needed to adequately sanitize recirculated
greenhouse water will need to be high enough to meet the demand of the water as well
as to provide a sufficient residual to control pathogens over time. The demand will vary
by system, water quality, fertilizers used, and amount of recycled water in the solution.
These results indicate that ClO2 demand should be examined over a range of
concentrations to determine the minimum treatment dose that will create an optimal
ClO2 residual long enough to sanitize plant pathogens in hydroponic leachate intended
for recirculation without negatively impacting plant growth. In addition, as the ClO2
treated nutrient solution passes through the hydroponic system, it is anticipated that the
ClO2 concentration will decline further when ClO2 comes into contact with biofilm and
organic matter within the system (Gagnon et al. 2005). To compensate for this, a higher
treatment concentration is required in order to maintain a sufficient ClO2 residual while
the nutrient solution continues to recirculate throughout the irrigation system.
41
Table 3-1. Concentration of fertilizers in the nutrient solution used to produce greenhouse bell peppers Spring 2011 in Citra, FL.
Ca 160
N 102
Phosphoric acid H3PO4 P 51
Potassium chloride KCl K 157
Mg 48
S 67
Copper sulfate CuSO4 Cu 0.32
Iron EDTA* Fe 3.2
Manganese sulfate MnSO4 Mn 1.03
Sodium borate Na2B4O7 B 0.749
Sodium molybdate Na2MoO4 Mo 0.07
Zinc sulfate ZnSO4 Zn 0.34
Nutrient mg*L-1
Calcium nitrate
Magnesium sulfate
Ca(NO3)2
MgSO4
Molecular
FormulaChemical name
42
Table 3-2. Residual chlorine dioxide.
xMean separation in columns by Tukey's HSD test at α =0.05 (lowercase letters). yMean separation in rows by Tukey's HSD test at α =0.05 (uppercase letters).
PPM Water Sample
10 DI water 10.0 cx
Ay
9.7 b A 8.7 c B 7.6 c C 5.8 d D
Well Water 9.3 c A 9.3 b A 8.6 c A 7.4 c B 5.8 de C
Nutrient Solution 5.7 e A 4.8 c AB 4.3 de AB 3.8 d BC 2.6 f C
Pine Bark Leachate 2.2 f A 2.6 c A 2.9 e A 2.7 d A 3.1 ef A
Perlite Leachate 2.9 f C 4.0 c BC 7.1 cd A 7.9 c A 5.7 de AB
20 DI water 19.6 a A 18.6 a B 16.9 a C 15.0 a D 11.6 ab E
Well Water 18.9 a A 16.8 a AB 17.1 a AB 15.4 a BC 12.4 ab C
Nutrient Solution 16 a A 15.9 a A 14.9 ab AB 13.5 b B 9.9 bc C
Pine Bark Leachate 9.6 c A 8.8 b AB 8.8 c B 8.5 c B 7.5 cd C
Perlite Leachate 7.5 d C 9.7 b BC 13.5 b AB 14.9 a A 12.6 a AB
4 Hrs0.25 Hr 0.5 Hr 1 Hr 2 Hrs
mg*L-1
43
Table 3-3. Chlorine dioxide demand.
xMean separation in columns by Tukey's HSD test at α =0.05.
*Nonsignificant from zero at α=0.05.
Water Sample PPM
DI water 10 0.0* ex
0.3* g 1.4 d 2.3 e 4.2 e
20 0.4* e 1.4 efg 3.2 cd 5.0 d 8.4 bc
Well Water 10 0.8* e 0.8* fg 1.4 d 2.6 e 4.2 de
20 1.1* e 3.2 def 3.0 cd 4.6 d 7.6 bc
Nutrient Solution 10 4.3 d 5.1 bcd 5.7 bc 6.2 bc 7.4 c
20 3.9 d 4.1 cde 5.1 bc 6.5 b 10.1 ab
Pine Bark Leachate 10 8.8 c 7.4 bcd 7.1 b 7.3 b 6.9 cd
20 10.4 b 11.2 a 11.3 a 11.5 a 12.5 a
Perlite Leachate 10 7.1 c 6.0 bc 2.9 cd 2.1 e 4.3 de
20 12.5 a 10.3 a 6.5 b 5.1 cd 7.4 c
(mg*L-1
)
0.25 Hr 4 Hrs2 Hrs1 Hr0.5 Hr
44
Figure 3-1. Chlorine dioxide residual after10 mg L-1 treatment. Error bars represent standard error of the mean.
45
Figure 3-2. Chlorine dioxide residual after 20 mg L-1 treatment. Error bars represent standard error of the mean.
46
CHAPTER 4 HYDROPONIC BELL PEPPER GROWTH REDUCES DUE TO METHODS OF
CHLORINE DIOXIDE IRRIGATION APPLICATION
Materials and Methods
Objectives
Despite the apparent chemical and sanitizing benefits of ClO2 there are limited
studies optimizing the application strategies of ClO2 for sanitizing greenhouse irrigation
and the effects of those strategies on plant growth. The objective of this research is to
determine the impact of ClO2 application strategy and potting media on greenhouse bell
pepper growth.
Experimental Design
Treatments included two types of media (medium grade perlite and composted
pine bark), two concentrations of ClO2 (0 and 20 mg L-1) and two methods of ClO2
application (single-dose and slow-release). Treatments were arranged in a randomized
complete block design and replicated three times.
Transplant Production
Bell pepper [Capsicum annum, L. ‘Legionnaire’ (Siegers Seed Co, Holland, MI)]
transplants were seeded in 72-cell plastic trays using MetroMix 200 potting media (Sun
Gro, Vancouver, Canada) on 7 January, 2011 and were grown in a controlled
--- Growth response from ClO 2 concentration by media ---
Strategy
Root %
Water
Fruit
Weighty
(g)
Height
changez
(cm)
Plant
Fresh
Weight (g)
Plant Dry
Weight
(g)
Plant %
Water
Shoot %
Water
55
Figure 4-1 Residual chlorine dioxide in the nutrient solution used to produce greenhouse bell peppers in Citra, FL. Bars represent standard error of the mean. Both treatments were applied with the same amount of ClO2 by weight.
56
CHAPTER 5 CONCLUSIONS
Chlorine dioxide is well-documented to effectively eliminate many viral, bacterial,
and fungal pathogens that present issues in municipal and agricultural systems. Despite
the apparent chemical and sanitizing benefits of ClO2 there are limited studies reporting
potential phytotoxic effects of ClO2 when used as an irrigation sanitizing agent for
greenhouse plants. The few reports that are available indicate that plant damage may
occur, but the potential benefits of its use warrant further investigation. This research
was split into three objectives. First, to determine the response of bell pepper growth
when exposed to a range of concentrations of ClO2 within the nutrient solution, and to
identify the concentration associated with minimal negative effects on plant growth.
Secondly, to determine the ClO2 demand of water used in recirculating irrigation
systems, and to further characterize the ClO2 sequestration of two common water
sources and three hydroponic irrigation solutions. And finally, to determine the impact of
ClO2 application strategy and potting media on greenhouse bell pepper growth.
Pepper plants grown in pine bark were less impacted by ClO2 than plants grown in
perlite for all experiments. Chlorine dioxide reacts with organic compounds in pine bark
media such as amines, aldehydes, and phenols and is chemically reduced minimally
active byproducts before reaching the plant roots (Gagnon et al. 2005; Stevens, 1982;
US-EPA, 1999). Perlite is created from heated and expanded obsidian, and as an
inorganic media it does not contain chemicals that react with ClO2, allowing it to directly
contact plant roots. This inherent difference between the growing media is likely to be
57
responsible for the increased impact from ClO2 observed on plants growing in perlite
media.
As the sanitized solution flows through the hydroponic system it comes into
contact with biofilm, algae and pathogens harbored in irrigation lines and emitters.
Maintaining a high residual in the nutrient solution allows for disinfestation of irrigation
components in addition to the water itself (Coosemans 1995; Gagnon et al. 2005;
Huang et al. 1997). As control of a variety of pathogens has been reported at lower
residual concentrations than those used in this experiment, studies investigating the
effect of lower treatment doses and application methods of ClO2 on plants grown in
inorganic media, such as perlite, are warranted.
The initial concentration of chlorine dioxide initially dosed into the system needs to
be applied at a sufficiently high dose in order to meet the demand of irrigation water and
to attain the desired ClO2 residual to treat pathogens. The demand will vary by system,
water quality, fertilizers used, and amount of recycled water in the solution. In addition,
as the ClO2-treated nutrient solution passes through the hydroponic system, it is
anticipated that the ClO2 concentration will decline further when ClO2 comes into
contact with biofilm and organic matter within the system (Gagnon et al. 2005). To
compensate for this, a higher treatment concentration is required in order to maintain a
sufficient ClO2 residual while the nutrient solution continues to recirculate throughout the
irrigation system. ClO2 demand should be examined over a range of concentrations to
determine the minimum treatment dose that will create an optimal ClO2 residual long
enough to sanitize plant pathogens in hydroponic leachate intended for recirculation
without negatively impacting plant growth.
58
APPENDIX ADDITIONAL FIGURES
Figure A-1. Fall 2009 root systems of pepper plants grown in perlite media irrigated with 0 to 40 mg L-1 chlorine dioxide.
59
Figure A-2. Fall 2009 root systems of pepper plants grown in pine bark media irrigated
with 0 to 40 mg L-1 chlorine dioxide.
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Figure A-3. Spring 2010 root systems of pepper plants grown in perlite media irrigated
with 0 to 10 mg L-1 chlorine dioxide.
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Figure A-4. Spring 2010 root systems of bell pepper plants grown in pine bark media
irrigated with 0 to 10 mg L-1 chlorine dioxide.
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Figure A-5. Spring 2010 bell pepper plants. From left to right: Plants grown in perlite
media irrigated with 0, 2.5, 5, and 10 mg L-1 chlorine dioxide. Plants grown in pine bark media irrigated with 0, 2.5, 5, and 10 mg L-1 chlorine dioxide.
63
Figure A-6. Water samples used in chlorine dioxide demand experiments. From left to
right: deionized water, well water only, well water plus nutrient solution, well water- nutrient solution leachate from pine bark media, and well water-nutrient solution leachate from perlite media.
64
LIST OF REFERENCES
Amsing, J.J. 1995. Gnomonia radiicicola and a Phytophthora species as casual agents of root rot on roses in artificial substrates. Acta Hort. (382):203-211.
Atmatjidou, V.P., R.P. Fynn,and H.A. Hoitink.1991. Dissemination and transmission of Xanthomonas campestris pv. begoniae in an ebb and flow irrigation system. Plant Dis. 75(12):1261–1265.
Beardsell, D. and M. Bankier. 1996. Monitoring and treatment of recycled water for nursery and floriculture production: NY515, Sydney, NSW: Horticultural Australia Ltd.
Beardsell, D., K. Bodman, G. Cresswell, M. Mebalds, D. Nicholas, C. Rolfe, and B. Yiasoumi. 2010. Nursery Industry Water management best practice guidelines 3rd ed. A. Kachenko, ed., Epping NSW: Nursery and Garden Industry Australia.
Berkelmann, B., W. Wohanka, and G. Krczal. 1995. Transmission of pelargonium flower bread virus (PFBV) by recirculating nutrient solutions with and without slow sand filtration. Acta Hort. 382:256-262.
Buttner, C., K. Marquardt, and M. Fuhrling. 1995. Studies on transmission of plant viruses by recirculating nutrient solution such as ebb-flow. Acta Hort. 396:265–272.
Cantliffe, D.J. and J.J. Vansickle. 2009. Competitiveness of the Spanish and Dutch greenhouse industries with the Florida fresh vegetable industry. Florida Cooperative Extension’s Electronic Data Information Source (EDIS), Univ. of Florida, Gainesville, Fla. < http://edis.ifas.ufl.edu/cv284 >.
Carrillo, A., M.E. Puente, and Y. Bashan. 1996. Application of diluted chlorine dioxide to radish and lettuce nurseries insignificantly reduced plant development. Ecotoxicology and Environ. Safety 35(1):57-66.
Chastagner, G.A. 2004. Effectiveness of controlled release applications of chlorine dioxide gas in killing pathogen inodula. Amer. Phytopathol. Society, 94(6), p.150.
Chastagner, G.A. and K.L. Riley. 2002. Potential use of chlorine dioxide to prevent the spread of Fusarium basal rot during the hot water treatment of daffodil bulbs. Acta Hort. (570):267–273.
Chastagner, G.A. and K.L. Riley. 2005. Sensitivity of pathogen inocula to chlorine dioxide gas. Acta Hort. (673):355–359.
Chellemi, D.O., D.J. Mitchell, M.E. Kannwischer-Mitchell, P.A. Rayside, and E.N. Rosskoph. 2000. Pythium spp. associated with bell pepper production in Florida. Plant Dis. 84(12):1271–1274.
65
Cook, R.L. and L. Calvin. 2005. Greenhouse tomatoes change the dynamics of the North American fresh tomato industry, US Dept. of Agriculture, Economic Research Service.
Coosemans, J. 1995. Control of algae in hydroponic systems. Acta Hort. 382:263–268.
Copes, W.E., G.A. Chastaganer, and R.L. Hummel. 2004. Activity of chlorine dioxide in a solution of ions and pH against Thielaviopsis basicola and Fusarium oxysporum. Plant Dis. 88(2):188-194.
Copes, W.E., G.A. Chastagner, and R.L. Hummel. 2003. Toxicity responses of herbaceous and woody ornamental plants to chlorine and hydrogen dioxides. Plant Health Prog.
Davies, L.R.R., D.D. Treadwell, D.J. Cantliffe, J.A. Bartz, and M.R. Alligood. 2010. Vigor response of greenhouse bell pepper due to chlorine dioxide sanitized irrigation water. HortScience 45(8):S97-S98 (abstr.).
Davies, L.R.R., D.D. Treadwell, D,J, Cantliffe, J.A. Bartz, and M.R. Alligood.
2010.Chlorine dioxide as a sanitizer for closed loop irrigation systems in bell pepper. HortScience 45(4):515 (abstr.).
Ehret, D.L., B. Alsanius, W. Wohanka, J.G. Menzies, R. Utkhede. 2001. Disinfestation of recirculating nutrient solutions in greenhouse horticulture. Agronomie 21(4):323–339.
Fisher, P., B. Argo, J. Huang, P. Konjoian, J.M. Majka, L. Marohn, A. Miller, R. Wick, and R. Yates. 2009. Using chlorine dioxide for water treatment. <watereducationalliance.org.>
Florida Department of Agriculture and Consumer Services, 2006. Florida agricultural water conservation best management practices.
Florida Department of Agriculture and Consumer Services, 2005. Water quality/quantity best management practices for Florida vegetable and agronomic crops.
Gagnon, G.A., J.L. Rand, K.C. O’Leary, A.C. Rygel, C. Chauret, and R.C. Andrews. 2005. Disinfectant efficacy of chlorite and chlorine dioxide in drinking water biofilms. Water Res. 39(9):1809-17.
Gomez-Lopez, V.M., A. Rajkovic, P. Ragaert, N. Smigic, and F. Delieghere. 2009. Chlorine dioxide for minimally processed produce preservation: a review. Trends in Food Science and Technology, 20(1):17-26.
Hong, C.X. and G.W. Moorman. 2005. Plant pathogens in irrigation water: challenges and opportunities. Critical Rev. in Plant Sci. 24(3):189-208.
66
James, E., M. Mebalds, D. Beardsell, A. Van der Linden, and W. Trega. 1996. Development of recycled water systems for Australian nurseries: NY320, Gordon, NSW: Hort. Res. and Dev. Corp.
Jenkins Jr, S.F. and C.W. Averre. 1983. Root diseases of vegetables in hydroponic culture systems in North Carolina greenhouses. Plant Dis. 67(9):968–969.
Jovicich, E., D.J. Cantliffe, S.A. Sargent, and L.S. Osborne. 2009. Production of greenhouse-grown peppers in Florida. Florida Cooperative Extension’s Electronic Data Information Source (EDIS), Univ. of Florida, Gainesville, Fla. <
http://edis.ifas.ufl.edu/hs228>.
Jovicich, E., D.J. Cantliffe, and P.J. Stoffella. 2007. Bell pepper fruit yield and quality as influenced by solar radiation-based irrigation and container media in a passively ventilated greenhouse. HortScience 42(3):642-652.
Jovicich, E., D.J. Cantliffe, and P.J. Stoffella. 2004. Fruit yield and quality of greenhouse-grown bell pepper as influenced by density, container, and trellis system. HortTechnology 14(4):507-513.
Jovicich, E., D.J. Cantliffe, E.H. Simonne, and P.J. Stoffella. 2007. Comparative water and fertilizer use efficiencies of two production systems for cucumbers. Acta Hort. (731):235-241.
Junli, H., W. Li, R. Nenqi, L.X. Xue, S.R. Fun, and Y. Guanle. 1997. Disinfection effect of chlorine dioxide on viruses, algae and animal planktons in water. Water Res. 31(3):455-460.
Kenny, J.F., N.L. Barber, S.S. Hutson, K.S. Linsey, J.K. Lovelace, and M.A. Maupin. 2009. Estimated use of water in the United States in 2005, Washington DC: US Geological Survey, US Dept. of the Interior.
Mahovic, M., J. Bartz, K. Schneider, and J. Tenney. 2009. Chlorine dioxide gas from an aqueous solution: reduction of Salmonella in wounds on tomato fruit and movement to sinks in a treatment chamber. Journal of food protection, 72(5), pp.952-8.
McDonnell, G. and A.D. Russell. 1999. Antiseptics and disinfectants: activity, action, and resistance. Clinical Microbio. Reviews, 12(1): 147-79
Mebalds, M., A. van der Linden, M. Bankier, D. Beardsell. 1996. Using ultra violet radiation and chlorine dioxide to control fungal plant pathogens in water. The Nursery Papers, Australia.
Mebalds, M., D. Beardsell, A. Van der Linden, M. Bankier.1996. Current research into water disinfestation for the nursery and cut flower industries. In: Combined Proc.-Intl. Plant Prop. Soc.
67
Mebalds, M., W. Tregea, and A. Van der Linden. 1997. Disinfestation protocols for equipment used in the nursery industry, Hort. Res. and Dev. Corp.
Menzies, J.G., D.L. Ehret, and S. Stan. 1996. Effect of inoculum density of Pythium aphanidermatum on the growth and yield of cucumber plants grown in recirculating nutrient film culture. Can. J. of Plant Pathol. 18(1):50–54.
Narkis, N. and Y. Kott. 1992. Comparison between chlorine dioxide and chlorine for use as a disinfectant of wastewater effluents. Water Sci. and Technol. 26(7-8):1483–1492.
Nicola, S., J. Hoeberechts, and E. Fontana. 2004. Comparison between traditional and soilless culture systems to produce rocket (Eruca sativa) with low nitrate content. Acta Hort. (697):549–555.
Olsen, N.L., G.E. Kleinkopf, and L.K. Woodell. 2003. Efficacy of chlorine dioxide for disease control on stored potatoes. Amer. J. of Potato Res. 80(6):387–395.
Van Os, E.A. 1999. Closed soilless growing systems: A sustainable solution for Dutch greenhouse horticulture. Water Sci. and Technol. 39(5):105-112.
Van Os, E.A. 2000. General practices in Europe: disinfection of the recirculating nutrient solution. In Canadian greenhouse conference: workshop on recirculation and diseases in vegetable production, University of Guelph, Guelph:4–5.
Van Os, E.A., M.N.A. Ruijs, and P.A. Van Weel. 1991. Closed business systems for less pollution from greenhouses. Acta Hort. 294.
Premuzic, Z.. H.E. Palmucci, J. Tamborenea, and M. Nakama. 2007. Chlorination: phytotoxicity and effects on the production and quality of Lactuca sativa var. Mantecosa grown in a closed, soil-less system. Intl. J. of Exptl. Bot. 76:103–117.
Prieto, M., J. Penalosa, M.J. Sarro, P. Zomoza, and A. Garate. 2007. Seasonal effect on growth parameters and macronutrient use of sweet pepper. J. of Plant Nutr. 30(11):1803-1820.
Roberts, R.G. and S.T. Reymond. 1994. Chlorine dioxide for reduction of postharvest pathogen inoculum during handling of tree fruits. Appl. and Environ. Microbiol. 60(8):2864-8.
Rouphael, Y., G. Colla, A. Salerno, C.M. Rivera, and F. Karam. 2005. Water use efficiency of greenhouse summer squash in relation to the method of culture: soil vs. soilless. Acta Hort. (697):81–86.
Ruijs, M.N.A. 1993. Economic evaluation of closed production systems in glasshouse horticulture. Acta Hort. 340:87-94.
68
Ruijs, M.N.A. and E.A. Van Os. 1991. Economic evaluation of business systems with a lower degree of environmental pollution. Acta Hort. 295:79-84.
Saha, S.K. 2009. Utilization of chlorination and soilless media for management of Pythium Aphanidermatum (Edson) Fitzp. in greenhouse production of Capsicum annuum L. in a closed soilless system. Department of Horticultural Sciences, University of Florida, Gainesville, Fla, PhD dissertation.
Shannon, M. 1998. Tolerance of vegetable crops to salinity. Scientia Horticulturae 78(1-4):5-38.
Shin, J., B. Harte, S. Selke, and Y. Lee. 2011. Use of a controlled chlorine dioxide (ClO2) release system in combination with modified atmosphere packaging (MAP) to control the growth of pathogens. J. of Food Quality, 34(3):220-228.
Sorlini, S. and C. Collivignarelli. 2005. Trihalomethane formation during chemical oxidation with chlorine, chlorine dioxide and ozone of ten Italian natural waters. Desalination, 176(1-3):103-111.
Stanghellini, M.E. and S.L. Rasmussen. 1994. Hydroponics: a solution of zoosporic pathogens. Plant Dis. 78(12), p.1129.
Stevens, A.A. 1982. Reaction products of chlorine dioxide. Environ. Health Perspectives 46:101-10.
Stewart-Wade, S.M. 2011. Plant pathogens in recycled irrigation water in commercial plant nurseries and greenhouses: their detection and management. Irrig. Sci. 29(4):267-297.
United States. Environ. Protection Agency. 1999. Alternative disinfectants and oxidants guidance manual.
United States. Dept. of Ag. Natl. Ag. Stat. Serv. 2009a. 2007 Census of agriculture.
United States. Dept. of Ag. Natl. Ag. Stat. Serv. 2009b. 2009 Census of horticultural specialties.
Veschetti, E., B. Cittadini, D. Maresca, C. Citti, and M. Ottaviani. 2005. Inorganic by-products in waters disinfected with chlorine dioxide. Microchem. J. 79(1-2):165-170.
Werres, S., S. Wagner, T. Brand, K. Kaminski, and D. Seipp. 2007. Survival of Phytophthora ramorum in recirculating irrigation water and subsequent infection of Rhododendron and Viburnum. Plant Dis. 91(8):1034–1044.
69
Yao, K.S., Y.H. Hsieh, Y.J. Chang, C.Y. Chang, T.C. Cheng, and H.L. Liao. 2010. Inactivation effect of chlorine dioxide on phytopathogenic bacteria in irrigation water. J. Environ. Eng. Mgt. 20(3):157-160.
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BIOGRAPHICAL SKETCH
Libby Rohrer Rens was born in 1985 in Waupun, Wisconsin. She received her
Bachelor of Science degree in Horticultural Sciences and Plant Pathology from the
University of Wisconsin-Madison in December 2008. During pursuing her degree she
had the opportunity to work closely with orchard growers on the development of
Integrated Pest Management programs on their farms. In August 2009 she began her
graduate studies in the Department of Horticultural Sciences at the University of Florida
in Gainesville working on irrigation sanitation of greenhouse grown bell pepper.