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1-1-2003 Nitrogen source and concentration affect growth and performance of bedding-plant impatiens Fredy Romero Orellana http://behost.lib.iastate.edu/DR/Romero-Orellana_ISU-2003-R667.pdf Iowa State University
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This Thesis is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Nitrogen source and concentration affect growth and performance of
bedding-plant impatiens
by
Fredy Rolando Romero Orellana
A thesis submitted to the graduate faculty
in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE
Major: Horticulture
Program of Study Committee: Richard J. Gladon, Major Professor Henry G. Taber David J. Hannapel Alfred M. Blackmer
Iowa State University
Ames, Iowa
2003 11
Graduate College
Iowa State University
This is to certify that the master's thesis of
Fredy Rolando Romero Orellana
has met the thesis requirements of Iowa State University
Signatures have been redacted for privacy 11l
TABLE OF CONTENTS
ABSTRACT v
Chapter 1. General Introduction and Literature Review 1
Introduction 1
Literature Review 2
Importance ofBedding-plant Impatiens 2
Nitrogen 2
Calcium 4
Thesis Organization 5
Literature Cited 6
Chapter 2. Nitrogen Source and Concentration Affect Growth and Performance of Bedding-plant Impatiens. 9
ABSTRACT 9
Introduction 10
Materials and Methods 11
Experimental Design 11
Plant culture 12
Treatment application 12
Growth evaluation 13
Substrate nitrate and ammonium analyses 13
Data analysis 14
Results 14 IV
Discussion 16
Literature Cited 21
Chapter 3. Increased Calcium Concentration does not Affect Growth and Postharvest
Performance of Bedding-plant Impatiens 38
ABSTRACT 38
Introduction 39
Materials and Methods 40
Experimental Design 40
Plant culture 40
Treatment application 41
Growth evaluation 41
Postharvest performance evaluation 42
Data analysis 42
Results 43
Discussion 44
Literature Cited 47
Chapter 4. General Conclusions 55
General Discussion 55
Recommendations for Future Research 56
ACKNOWLEDGMENTS 57 v
ABSTRACT
Impatiens (Impatiens wallerana Hook. f.) is the most important annual bedding plant in the U. S. based on wholesale dollar volume. Production of high-quality plants requires optimization of the nutrition regimen during growth, especially the total N concentration and the ratio ofN sources. Our objectives were to determine theN concentration and ratio ofN sources that optimize bedding-plant impatiens growth and development and to evaluate the effect of Ca concentration supplied during the production cycle on preharvest and postharvest
1 performance. We used four N concentrations (3.5, 7, 10.5, and 14 mmol N-L- ) in factorial combination with four ratios ofnitrate-N (N03--N) to ammonium-N (NH/-N) (4:0, 3:1, 1:1, and 1 :3). The postharvest experiment included five Ca concentrations (3, 5, 7, 9, and 11
1 mmol Ca·L- ) applied during the growing cycle at a uniform N concentration of 10.5 mmol·L-
1 with a 1:1 N03--N to NH/-N ratio. In both experiments, application oftreatments began at day 30 (22 dafter germination was complete), and applications were conducted until day 60.
From day 60 to day 70 only deionized water, as a leach, was applied. In the postharvest experiment, plants were held under shaded conditions for an additional 25 d, and tap water was used for irrigation. Nitrogen concentration and N source displayed an interaction. When
1 N was supplied at concentrations less than 7 mmol·L- , the N03--N to NH/-N ratio was not
1 important, but when N was supplied at concentrations greater than 10.5 mmol·L- , a 1:3 N03-
-N to NH/-N ratio yielded the greatest shoot dry weight, shoot fresh weight, and number of flower buds per plant. When the N03-- N to NH/-N ratio was elevated to 4:0, these growth parameters decreased. Substrate pH linearly increased from 4.9 to 5.8 as the concentration of nitrate increased in the nutrient solution, whereas substrate EC decreased linearly from 2.2 to
1 1.4 dS·L- • Substrate nitrate content was affected directly by theN concentration in the Vl nutrient solution, and it increased linearly from 0.08 to 9.6 mg·L-1 as theN concentration increased in the solution. In the postharvest experiment, Ca negatively affected shoot dry weight, shoot fresh weight, leaf number, substrate EC, and tissue potassium (K) concentration during the preharvest period and shoot dry weight, leaf number, and tissue K concentration during the postharvest period. To produce high-quality bedding-plant impatiens, N must be applied at N03--N to NH/-N ratios between 1:1 and 1:3 in combination with aN concentration of 10.5 mmol·L-1 at each fertigation for the first 30 days of the production cycle. Additional Ca during the production cycle does not increase preharvest growth or postharvest performance. 1
Chapter 1. General Introduction and Literature Review
Introduction
Most bedding plants are grown in greenhouses that provide optimum conditions to produce plants as rapidly as possible. Application of fertilizer is an important tool that growers use during production, and they can obtain high-quality plants only when the correct concentration and source of fertilizer are applied at the correct time. To obtain high-quality plants, it is necessary to optimize production factors during the period when flowering potential is determined. The management of plant growth and the quality that the grower builds into the plant is vital to the performance of the plant after production, where usually the conditions are adverse relative to the conditions where the plants were produced. The cultural and management practices that growers use during production impacts plant quality and longevity, and postproduction quality and performance of plants should be one of the most important issues that growers consider.
Nitrogen (N) and calcium (Ca) are important nutrients that exhibit an effect during the production cycle and during the postharvest period. The source ofN can affect substrate pH. When the root medium is too acidic, Ca is not available to the plant, and it is necessary to raise the pH to solubilize the Ca. In research conducted previously, it was found that Ca and ammonium (NH4+) application affected the longevity of rose flowers and the number of yellow leaves during postharvest rose life (Nielsen and Starkey, 1999). Nitrogen has a great impact on impatiens quality and growth especially during bedding-plant plug production
(Van Iersel et al., 1998ab). Total N concentration can affect the number of flowers produced
1 by the plant. Plants of Alstroemeria treated with high N concentrations (28.5 mmol-L- ) yielded more flowers with higher quality than plants treated with lower N concentrations 2
(Smith et al., 1998). In species such as cotoneaster (Cotoneaster dammeri Schneid.) and rudbeckia (Rudbeckia fulgida Ait. ), combinations of ammonium (NH4 +) and nitrate (N03 -) N often yield greater dry weight than either source alone (Kraus and Warren, 2002). In New
Guinea impatiens (Impatiens platypetala Lindl. ), fresh weight decreased as the percentage of ammonium increased (Weigle et al., 1982). However, little information is available on the effect ofN source and concentration on bedding-plant impatiens growth and development, and most of the research in this area has focused on pretransplant stages (Van Iersel et al.,
1998ab). Our objectives were to determine the optimum N concentration and N03--N to
NH4+-N ratio for growth ofbedding-plant impatiens and to determine whether increased Ca concentrations improve the postharvest life and quality ofbedding-plant impatiens.
Literature Review
Importance of Bedding-plants Impatiens
Over the last ten years, the wholesale volume of bedding plants has increased significantly. From 1990 to 1995, wholesale bedding plant production grew from $823 million to $1.158 billion (up 41 %), whereas flowering pot plants, foliage plants, and cut flowers showed decreased wholesale values of 6, 8, and 23%, respectively (Ball, 1998).
From 2000 to 2001, the total value of floriculture crops increased 3.5% (Miller, 2002). The bedding and garden plant segment accounted for $2.177 billion in 2001, up 3.9% from 2000
(Miller, 2002). Bedding plants essentially are the only growth area in the U.S. floriculture industry (Ball, 1998).
Nitrogen
Plant nutrients must be supplied to the developing plant in the form, amount, time, and place necessary to support absorption and prevent nutrient deficiencies from limiting 3 growth and quality (Van Iersel et al., 1998b). N plays an important role in plant metabolism, and hence, in determining growth (Gamiely et al., 1991; Broschat, 1998; Bar-Tal et al.,
2001), and fruit quality (Crisoto et al., 1997). Greater N concentrations may result in more rapid growth (Van Iersel et al., 1998a). Adequate levels ofN improve the quality of vegetables, generally by allowing for development of sufficient photosynthetic surface area
(Weston and Barth, 1997). In rice, N supply during vegetative growth is the most important restriction to gaining completion of yield potential (Kronzucker et al., 2000).
Nitrogen, absorbed as either nitrate-N (N03 --N) or ammonium-N (NH/-N), is the mineral that the plant needs in the largest quantity (Kronzucker et al., 1999). Nitrogen form limits plant growth in temperate zones due to of the low N concentration caused by leaching and microbial consumption (Tischner, 2000). Nitrate is theN form most commonly used by plants as a source ofN (Gamiely et al., 1991; Tischner, 2000). However, plants vary in their ability to adapt to the available source ofN (Kronzucker et al., 1999; Osorio et al., 2003).
Plant responses to NH4 +-N differ among plant species and are affected by temperature, light intensity, pH, and nutrient composition of the medium (Edwards and
Horton, 1982). Ammonium should be the preferred source ofN because its metabolism requires less energy than nitrate (Kronzucker et al., 1999). Ammonium produces superior growth in many plants like Calathea makoyana (Conover and Poole, 1986), rice ( Oryza sativa L.) and com (Zea Mays L.) (reviewed by Osorio et al., 2003). Ammonium N as the predominant N source in fertilization regimes can be harmful (Goyal et al., 1982; Lamb et al., 1993). Tomatoes do not grow well when ammonium is supplied as the onlyN source
(Pierpont and Minnoti, 1977). A 1:1 nitrate to ammonium ratio has been reported as optimal for tomato growth (Bar-Tal et al., 2001 ). In poinsettias, growth reduction and injury may 4 occur when ammonium constitutes 40 to 50% of the total N supply (Cox and Seeley, 1984).
Ammonium acidifies rhizospheric pH and decreases absorption of other important cations
(Lamb et al., 1993). Vegetative growth stimulated by excess N can cause stress in sensitive tissues by inducing a Ca requirement that cannot be met by root absorption. Root absorption of Ca is partly dependent on N form (Lawton et al., 1989), and the most common effect of
NH4 + is reduced Ca and Mg absorption (Edwards and Horton, 1982; Lawton et al., 1989).
Most of theN in complete fertilizer mixes is NH/-N, which is rapidly converted to nitrate by nitrification in mixes that contain some soil (Weigle et al., 1982). When N03--N and NH/-N are provided together, plant growth of purslane (Portulaca oleracea L.) is enhanced compared to growth when either of the sources is used alone (Palaniswamy et al.,
2002). The nitrate form has given the best responses for some crops (Edwards and Horton,
1982). Radish (Raphanus sativus L.) (Goyal et al., 1982), Vinca sp., wheat (Triticum aestivum), cucumber (Cucumus sativus L.), and bell pepper (Capsicum annuum L.) (Osorio et al., 2003) grew well when N03- was included in the nutrient solution.
Calcium
Calcium is important because it regulates ripening, activates enzymes, and affects the rates of respiration and ethylene production (Dris et al., 2001). Calcium is an essential macronutrient and frequently is supplied as a cation accompanying N03- in liquid fertilizers
(Smith et al., 1998). Calcium deficiencies cause many important physiological disorders that affect the quality of many vegetable crops (Weston and Barth, 1997). Increasing the calcium concentration in the nutrient solution reduced the amount of wilted flowers of rose
(Nielsen and Starkey, 1999). Calcium affects fruit senescence and quality by altering 5 intracellular processes, and at least 60% of the total Ca in the plant is associated with the cell wall fraction (Fallahi et al., 1997).
Torre et al. (1999) found that rose flowers produced under high ambient relative humidity (90%) contained a lesser amount of Ca in their tissues than plants grown under a lower ambient relative humidity. Petals had less Ca compared with those produced under low ambient relative humidity. Flowers that were produced under high ambient relative humidity and a low calcium concentration in their tissues had a shorter postharvest life. The authors also found that Ca increased postharvest life in either intact flowers or detached petals. Also, Ca promoted flower opening, and thus flower diameter was increased. Calcium enhanced the initial fresh weight increment and delayed the later reduction in relative fresh weight of intact flowers. Calcium status in the tissues affected the rate of senescence.
Nitrogen and Ca are more involved in various fruit quality factors than other elements and have been studied extensively in postharvest physiology of pome fruits (Fallahi et al.,
1997). Postharvest quality of fresh vegetables generally depends on the quality achieved at the time ofharvest (Weston and Barth, 1997). Calcium affects some membrane characteristics related to or associated with senescence. Apples with a high concentration of
Ca exhibit a lower rate of respiration and a longer storage life (Dris et al., 2001).
Thesis Organization
This thesis has four chapters. The first chapter gives general information about bedding plants, nitrogen, and calcium. Chapter 2 is a manuscript to be submitted to
HortScience reporting two independent runs of a greenhouse experiment. This experiment evaluated the effect of four nitrate to ammonium ratios and four nitrogen concentrations on the growth of bedding-plant impatiens. Chapter 3 is a manuscript to be submitted to 6
Hart Technology reporting an experiment where we evaluated the effect of five calcium concentrations on growth and shelf performance ofbedding-plant impatiens. Finally, chapter
4 is a brief discussion of my general conclusions based on the results ofboth experiments.
Literature Cited
1 Ball, V. 1998. Ball RedBook. 16 h Edition. Ball Publishing, Batavia, IL.
Bar-Tal, A., L. Kami, J. Oserovitz, A. Hazan, M. Itach, S. Gantz, A. Avidan, I. Posalski, N.
Tratkovski, and R. Rosenberg. 2001. Nitrogen nutrition of greenhouse pepper. II.
Effect of nitrogen concentration and N0 3 :~ ratio on growth, transpiration, and
nutrient uptake. HortScience 36:1252-1259.
Broschat, T.K. 1998. Nitrogen source affects growth and quality of Bougainvillea.
HortTechnology 8:346-348.
Conover, C.A. and R.T. Poole. 1986. Nitrogen source effects on growth and tissue content
of selected foliage plants. HortScience 21:1008-1009.
Cox, D.A. and J.G. Seeley. 1984. Ammonium injury to poinsettia: Effect ofNH4-N:N03-N
ratio and pH control in solution culture on growth, N absorption, and N utilization. J.
Amer. Soc. Hort. Sci. 109:57-62.
Crisoto, C.H., R.S. Johnson, T. DeJong, and K.R. Day. 1997. Orchard factors affecting
postharvest stone fruit quality. HortScience 32:820-823.
Dris, R., R. Niskanen, and S.M. Jain. 2001. Crop management and postharvest handling of
horticultural products. Science Publishers. Enfield, NH. p. 175-186.
Edwards, J.H. and B.D. Horton. 1982. Interaction of peach seedlings to N03:NH4 ratios in
nutrient solutions. J. Amer. Soc. Hort. Sci. 107:142-147.
Fallahi, E., W.S. Conway, K.D. Hickey, and C.E. Sams. 1997. The role of calcium and 7
nitrogen in postharvest quality and disease resistance of apples. HortScience 32:831-
835.
Gamiely, S., W.M. Randle, H.A. Mills, D.A. Smittle, and G.I. Banna. 1991. Onion plant
growth, bulb quality, and water uptake following ammonium and nitrate nutrition.
HortScience 26:1061-1063.
Goyal, S.S., O.A. Lorenz, and R.C. Hufaker. 1982. Inhibitory effect of ammoniacal nitrogen
on growth of radish plants. I. Characterization of toxic effects ofNH4 + on growth and
its alleviation byN03·. J. Amer. Soc. Hort. Sci. 107:125-129.
Kraus, H.T. and S.L. Warren. 2002. Nitrogen form affects growth, mineral nutrient content,
and root anatomy of cotoneaster and rudbeckia. HortScience 37:126-129.
Kronzucker, H.J., A.D. Glass, M.Y. Siddiqi, and G.J. Kirk. 2000. Comparative kinetic
analysis of ammonium and nitrate acquisition by tropical lowland rice: implication
for rice cultivation and yield potential. New Phytol. 145:471-476.
Kronzucker, H.J., M.Y. Siddiqi, A.D. Glass, and G.J. Kirk. 1999. Nitrate-ammonium
synergism in rice. A subcellular flux analysis. Plant Physiol. 119: 1041-1045.
Lamb, M.J., G.H. Clough, and D.D. Hemphill, Jr. 1993. Pretransplant watermelon nutrition
with various nitrate : ammonium ratios and supplemental calcium. HortScience
28:101-103.
Lawton, D.A., G.A. McDaniel, and E.T. Graham. 1989. Nitrogen source and calcium
supplement affect stem strength of poinsettia. HortScience 24:463-465.
Miller, M. N. 2002. Floriculture's changing face. GrowerTalks. 66(3):86-120.
Nielsen, B. and K.R. Starkey. 1999. Influence of production factors on postharvest life of
potted roses. Postharvest Biol. Tech. 16:157-167. 8
Osorio, N.W., X. Shuai, S. Miyasaka, B. Wang, R.L. Shirey, and W.J. Wigmore. 2003.
Nitrogen level and form affect taro growth and nutrition. HortScience 38:36-40.
Palaniswamy, U.R., B.B. Bible, and R.J. McAvoy. 2002. Effect ofnitrate:ammonium
nitrogen ratio on oxalate levels of purslane. Trends in new crops and new uses.
ASHS Press, Alexandria, VA. pp. 453-455.
Pierpont, R.A. and P .L. Minotti. 1977. Effects of calcium carbonate on ammonium
assimilation by tomato seedlings. J. Amer. Soc. Hort. Sci. 102:20-23.
Smith, M.A., G.C. Elliot, and M.P. Bridgen. 1998. Calcium and nitrogen fertilization of
Alstroemeria for cut flower production. HortScience 33:55-59.
Tischner, R. 2000. Nitrate uptake and reduction in higher and lower plants. Plant, Cell and
Environment 23:1005-1024.
Torre, S., A. Borochov, and A.H. Halevy. 1999. Calcium regulation of senescence in rose
petals. Physiol. Plant. 107:214-219
Van Iersel, M.W., R.B. Beverly, P.A. Thomas, J.G. Latimer, and H.A. Mills. 1998a.
Fertilizer effect on growth of impatiens, petunia, salvia, and vinca plug seedlings.
HortScience 33:678-682.
Van Iersel, M.W., P.A. Thomas, R.B. Beverly, J.G. Latimer, and H.A. Mills. 1998b.
Nutrition affects pre- and posttransplant growth of impatiens and petunia plugs.
HortScience 33:1014-1018.
Weston, L.A. and M.M. Barth. 1997. Preharvest factors affecting postharvest quality of
vegetables. HortScience 32:812-816.
Weigle, J.L., H.G. Taber, and S.K. Dunston. 1982. Ammonium toxicity of Impatiens
platypetala. HortScience 17:199-200. 9
Chapter 2. Nitrogen Source and Concentration Affect Growth and Performance
of Bedding-plant Impatiens
A paper to be submitted to HortScience
1 Fredy R. Romero , Richard J. Gladon, and Henry G. Taber.
ADDITIONAL INDEX WORDS. Nitrate, ammonium, fertigation, Impatiens wallerana
ABSTRACT. Impatiens (Impatiens wallerana Hook. f.) is the most important annual bedding plant in the U. S., based on wholesale dollar volume. Production of high-quality plants requires optimization of the nutrition regimen during growth, especially the total nitrogen (N) concentration and the ratio ofN sources. Our objective was to determine theN concentration and ratio ofN sources that optimize bedding-plant impatiens growth and
1 development. We used fourN concentrations (3.5, 7, 10.5, and 14 mmol N·L- ) in factorial combination with four ratios ofnitrate-N (N03--N) to ammonium-N (NH/-N) (4:0, 3:1, 1:1, and 1 :3). Application of treatments began at day 30 (22 d after germination was complete), and applications were conducted until day 60. From day 60 to day 70 only deionized water, as a leach, was applied. N concentration and N source displayed an interaction for most
1 growth parameters. When N was supplied at a concentration less than 7 mmol·L- , the N03--
N to NH4 +-N ratio was not important. When N was supplied at a concentration greater than
1 10.5 mmol·L- , a 1:3 N03--N to NH/-N ratio yielded the greatest shoot dry weight, shoot fresh weight, plant diameter, and number of flower buds per plant. But when the N03-- N to
Dept. ofHorticulture, Iowa State University, Ames, lA 50011 1 Graduate student, primary researcher, and author. 10
NH4 + -N ratio was elevated to 4:0, these growth parameters decreased. Substrate pH linearly increased from 4.9 to 5.8 as the concentration ofN03--N increased in the nutrient solution,
1 whereas substrate EC linearly decreased from 2.2 to 1.4 dS·L- • Substrate nitrate content was affected directly by theN concentration in the nutrient solution and linearly increased from
0.08 to 9.6 mg-L- 1 as theN concentration increased in the solution. To produce high-quality, bedding-plant impatiens, N must be applied at N03--N to NH/-N ratios between 1:1 and 1:3 in combination with anN concentration of 10.5 mmol-L- 1 at each fertigation for the first 30d of the production cycle.
Introduction
The floriculture sector of the greenhouse industry has grown tremendously during the last 50 years, and bedding plant production is a major segment of that industry (Miller,
2002). Impatiens has been the most important bedding plant during the last ten years (Miller,
2002). To obtain high-quality plants, it is necessary to optimize production factors during the period when flowering potential is determined (Nell et al., 1997). Postharvest longevity and quality of flowering potted plants are affected by mineral nutrition more than any other production factor (Nell et al., 1997). Nitrogen affects growth ofbedding plants, and most often, faster growth occurs with greater N concentrations (Van Iersel et al., 1998ab). In addition, form ofN and N concentration contribute greatly to the production of high-quality plants by affecting leaf chlorophyll content, plant size, transpiration rate, leaf weight, and leaf area (Bar-Tal et al., 2001).
In New Guinea impatiens (Impatiens platypetala Lindl.), fresh weight decreased as the percentage of ammonium increased (Weigle et al., 1982). In species such as cotoneaster 11
(Cotoneaster dammeri Schneid.) and rudbeckia (Rudbeckiafulgida Ait.), combinations of ammonium (NH4 +) and nitrate (N03-) N often yield greater dry weight than either source alone (Kraus and Warren, 2002). Some species are not affected either by theN source or N concentration (Conover and Poole, 1986; Stratton et al., 2001). Common N03--N to NH/-N ratios evaluated for various crops range from 4:0 to 0:4 (Scoggins and Mills, 1998; Stratton et al., 2001; Osorio et al., 2003). Nitrogen concentrations also have been evaluated at 10.5 mmol N·L-1 (Scoggins and Mills, 1998), 0 to 21 mmol N·L-1 (Stratton et al., 2001), and 0 to
32 mmol N·L-1 (Van Iersel et al., 1998b).
The balance between elements is important for plant growth, but it also is important for absorption of minerals from the soil and to improve postharvest quality. Mineral absorption can be affected by theN concentration and form (Lawton et al., 1989; Scoggins and Mills, 1998) and K concentration (Scoggins and Mills, 1998). In potted roses (Rosa hybrida L. ), the ratio between N and Ca influenced postharvest life because it affected Ca absorption (Nielsen and Starkey, 1999). However, little information is available on the effect ofN source and N concentration on bedding-plant impatiens growth and development, and most of the research in this area has focused on pretransplant stages (Van Iersel et al.,
1998ab). Our objective was to determine the optimum N concentration and N03--N to NH/-
N ratio for growth of bedding-plant impatiens.
Materials and Methods
Experimental Design. The experiment evaluated four N concentrations (3.5, 7, 10.5, and 14
1 mmol N-L- ) in factorial combination with four ratios ofnitrate-N (N03--N) to ammonium-N
(NH/-N) (4:0, 3:1, 1:1, and 1:3, respectively). The experiment was a completely 12 randomized block design and was repeated independently. The first run was conducted from
January to March 2003, and the second run was from March to May 2003. Before treatment began, the pots with plants were arranged in four blocks of 16 and were randomized
independently within each block.
Plant culture. Impatiens (Impatiens wallerana Hook. f. 'Super Elfin White') seeds were
sown in plug trays (288 cells/tray) filled with Fafard® Germination Mix root medium
(Conrad Fafard, Inc, Agawan, MA) on January 13 and on March 24 for the first and second
run, respectively. Trays were placed under tap-water mist at 23 oc for 8 d. After
germination, trays of seedlings were moved to a greenhouse and placed under high-pressure
sodium lamps (Model# HPS400, Sunlight Supply, Inc®, Vancouver, W A) that provided an
average of 54 ~mol·sec- 1 ·m- 2 of supplemental light from 0600 to 2200 hr daily and a constant
air temperature of 27 ± 1 °C. During days 8 through 22, seedlings in plug trays were
fertigated with constant liquid feed at a rate of7.0 mmol N·L-1 from a mixture of25% Excel®
All-purpose 21N-2.2P-16.6K and 75% Excel® CAL-MAG 15N-2.2P-12.45K fertilizers
(Scotts-Sierra Horticultural Products, Marysville, OH). This mixture provides 16.5% N
(2.52% NH/-N, 11.91% N03--N, and 2.06% urea). On day 23, the rate ofN applied from the
same source was increased to 10.5 mmol·L-1 until day 30 when plants were transplanted to
10-cm pots containing Sunshine LC-1 Mix© (Sun-Gro Horticulture®, Bellevue, WA).
Fertigation with the treatment solutions commenced after transplanting.
Treatment application. TheN concentrations and ratios were supplied by nutrient solutions
that were a modification of Hoagland's solution number 1 (Hoagland and Amon, 1950)
(Table 1). Nutrient solutions were made every 10 d by using deionized water, and their pH
was adjusted to 6.0 by using either 5M NaOH or 5M HCl. The growing substrate was 13 saturated with 200 mL of the respective nutrient solution before transplanting the seedlings.
One day later, plants with two pairs of true leaves completely developed were transplanted to the drained root medium. Each pot was fertigated every other day with 100 mL of nutrient solution, and the pH and EC of the substrate were measured every 10 d by using the
PourThru method (Whipker et al., 2000) starting the day of transplanting. Treatment applications ceased on day 60 after sowing and then only deionized water was applied every other day for 10 more days to avoid salt accumulation and regulate substrate pH during the last part of the production cycle.
Growth evaluation. Plant height was determined by measuring the distance from the bottom of the shoot, using the soil line as a reference point, to the top of the plant shoot.
Plant diameter was calculated by averaging two diameter measures taken perpendicular to one another. Chlorophyll content was determined in the four youngest, fully expanded leaves with a chlorophyll meter (Model SP AD-502, Spectrum Technologies, Plainfield, IL ), taking one measurement per leaf. At the end of each experiment, shoots, flower buds, and flowers were harvested and weighed (fresh weight), and then dried at 67 °C for 72 h (dry weight). At the end of each experiment, growth medium pH and EC were obtained by using the saturated medium extract (SME) method as established by the North Central Regional
Soil Testing Committee for Greenhouse Soils (Warnecke, 1998). Leachates were kept in plastic vials at 4 °C for future analyses.
Substrate nitrate and ammonium analyses. Leachates obtained from the SME were used for nitrate and ammonium analyses. Nitrate-N was determined by copperized Cd reduction
(Keeney and Nelson, 1982), and ammonium was determined by nitroprusside-salicylate
(Wallet al., 1975), both procedures by flow injection analysis (Smith and Scott, 1990). 14
Data analysis. Plant growth and media parameters were evaluated by using the general linear model procedure of the Statistical Analysis System® (SAS Institute, 1988). Regression analysis was used to identify significant treatment effects where appropiate.
Results
Our data are the results from two runs conducted in different seasons, and as expected, we found differences. Plants grew faster and became larger during the spring due to the greater temperature, irradiance, and day length in the second run. However, the trends were identical in both runs, and therefore, we combined the data from each run for the purpose of analysis and presentation.
The N concentration range was selected because preliminary experiments showed that
1 N concentrations less than 3.5 and greater than 14 mmol-L. at a 1:1 N03--N to NH/-N ratio negatively affected plant growth (data not presented). For almost all parameters, we found interactions between N concentration and N source. The 3.5 and 7.0 mmol N·L-1 concentrations were ineffective in promoting growth at any N source ratio (Fig. 1). Optimum shoot growth occurred at N concentrations equal to or greater than 10.5 mmol·L-1 with a 1:3
N03--N to NH/-N ratio. Increasing N03-- N resulted in a linear (P = 0.034) decline in growth from 3.7 to 2.6 g per plant in plants supplied with 10.5 mmol N·L-1 (Fig. 1). Fresh weight was 16 to 17 times greater than the dry weight for all treatments, and fresh weight showed the same pattern exhibited by dry weight (data not presented).
No interaction between N concentration and N source was found for plant diameter, and the greatest plant diameter was achieved when N was supplied at a N03--N to NH4 +-N ratio of 1:1. Plant diameter decreased quadratically (P = < 0.0001) from 18.6 to 15.8 em, as 15 the amount ofN in the nutrient solution deceased, and this effect is described by the equation
2 PD = 12.4 + 1.1 x [N] - 0.05 x [N] , where: PD =plant diameter in em and [N] =amount of
1 N in mmol· L- . But the source effect, although significant, was small because the reduction was only 9% of the plant diameter, compared with the 15% reduction due to the effect of the
N rate (Fig. 2). The optimum N rate occurred at 10.5 mmol·L-\ and it was not affected by the N source.
The optimum N rate for flower bud production depended on the N03--N to NH4 +-N ratio. The 3.5 and 7 mmol N· L- 1 treatments were ineffective in maximizing flower bud production (Fig. 3). Increasing the N03--N percentage of total N supplied reduced flower bud production, except at the 10.5 mmol N·L-1 (the most significant interaction). The greatest number of flower buds per plant was obtained when the ratio ofN03--N to NH4+_N was 1:1 at anN concentration of 10.5 mmol· L- 1 (Fig. 3). A similar trend was found with the leaf chlorophyll content, where the SP AD values decreased quadratically (P = < 0.001) as the
N03--N to NH4 +_N ratio increased from 1:3 to 4:0 (Fig. 4). However, the number of open flowers per plant at harvest was not affected by theN concentration or N source (data not presented).
The N concentration affected the number of leaves per plant, and the maximum number ofleaves per plant was obtained in plants treated with a 1:3 N03--N to NH/-N ratio and 14.0 mmol N-L- 1 (Fig. 5). The number ofleaves increased linearly (P = 0.02) from 118
1 to 154 as theN concentration increased from 3.5 to 14 mmol-L- .
Final substrate N03-- N content was affected only by the nutrient solution N concentration (Fig. 6). Substrate N03--N concentration increased linearly (P = < 0.0001) from 0.08 to 9.6 mg·L-1 as theN concentration in the nutrient solution increased from 3.5 to 16
1 14.0 mmo1·L- . Substrate NH/ -N content also was affected by theN rate, and it increased quadratically (P = 0. 0009) as the N concentration increased. However, the NH4 +-N concentrations found in the analyses were all less than 0.35 mg·L-1 (data not presented).
Final substrate pH and EC also were affected by N concentration and source. At low
N03 --N to NH/-N ratios, the greater theN concentration in the nutrient solution, the lower the substrate pH. Conversely, at greater N03--N to NH/-N ratios, the greater theN concentration in the nutrient solution, the greater the substrate pH (Fig. 7). The substrate pH increased linearly as the N03--N concentration increased in the nutrient solution (Fig. 7).
The greatest EC was obtained when the N03--N to NH/-N ratio was 1:3, and it linearly decreased as the amount ofN03--N increased in the nutrient solution without regard to theN concentration (Fig. 8). Substrate EC also was affected by theN concentration and the substrate EC increased as the N concentration increased in the nutrient solution. The differences in substrate EC were smaller as the N03--N to NH/-N ratio increased (Fig. 8).
Discussion
Production of high-quality bedding-plant impatiens requires optimization of the nutrition regimen during growth, especially the total N concentration and the ratio ofN sources. However, little information is available on the effect ofN source and N concentration on bedding-plant impatiens growth and development, and most of the research in this area has focused on the pretransplant stages (Van Iersel et al., 1998ab). We have found that a total N concentration of 10.5 mmol-L-1 is optimum for growth ofbedding-plant impatiens, but this rate depends on the N03--N to NH/-N ratio. 17
The best bedding-plant impatiens growth was obtained when plants were fertilized
1 with a 1:3 or 1:1 N03--N to NH/-N ratio and a total N concentration of 10.5 mmol·L- .
Nitrogen concentrations less than 10.5 mmol-L-1 were not sufficient to promote growth in this plant, whereas greater concentrations negatively affected it by decreasing shoot fresh and dry weight and plant diameter. These results agree with Osorio et al. (2003) who found small growth differences for taro when total N was supplied at low concentrations with ammonium or nitrate as theN source. Leaves from plants treated with lesser or greater N concentrations
1 than 10.5 mmol-L- and with N03--N to NH/-N ratios greater than 1:1 were smaller. Plant diameter also decreased quadratically (P = < 0.0001) at N concentrations greater and less
1 than 10.5 mmol·L- without regard to the N03--N to NH/-N ratio. According to our quadratic model, the best plant diameter would be obtained when plants were fertilized with
1 11 mmol N-L- .
The relatively high concentration ofNH4 +_N in the nutrient solution enhanced growth, which is consistent with previous research on other crops (Conover and Poole, 1986;
Bar-Tal et al., 2001; Kronzucker et al., 1999; Kraus and Warren, 2002; Palaniswamy et al.,
2002). However, our results were opposite those found for New Guinea impatiens, poinsettias, and tomato, where NH/-N reduced growth (Weigle et al., 1982; Cox and Seeley,
1984; Scoggins and Mills, 1998; Bar-Tal et al., 2001). Nitrogen is a critical nutrient in the
formation and development of the plant photosynthetic apparatus, and deficiencies or
excesses that retard photosynthesis also affect plant growth. An adequate amount ofN
improves plant growth and development, and this occurs via sufficient development of photosynthetic surface area, which is reflected in the shoot dry and fresh weight. 18
1 At low N concentrations (less than 10.5 mmol N-L- ), the ratio ofthe N sources was not important, but when the concentration increased to 10.5 mmol N·L-1 or greater, the ratio
became critical. Flower buds per plant decreased quadratically (P = < 0.001) as the N03--N
to NH/-N ratio increased from 1:3 to 4:0. The best flower bud production (110 per plant)
was obtained when plants were treated with a 1:1 N03--N to NH/-N ratio and 10.5 mmol
N·L-1 (Fig. 3). Nitrate-N to ammonium-N ratios greater than 1:1 and N concentrations lower
or greater than 10.5 mmol N-L-1 did not enhance flower bud production but reduced them to
60 buds per plant. Our results agree with previous research where increased N
concentrations (Smith et al., 1998; Broschat, 1998) and high N03--N reduced flower
production (Broschat, 1998).
Leaf chlorophyll content as measured by an SP AD meter was used as an indicator of
1 foliage greenness. The best SPAD value (58) was obtained at 10.5 mmol N·L- and at a N03--
N to NH4 +-N ratio of 1:1 (Fig. 4). Nitrogen concentrations less or greater than 10.5 mmol
1 N·L- and N03--N to NH4+_N ratios greater than 1:1 produced plants that looked chlorotic, and
therefore, less attractive. In bedding-plant impatiens, the leaf chlorophyll content (as
measured by the SP AD meter) was affected by the interaction ofN concentration and source.
However, leaf chlorophyll content in tomatoes was affected only by theN concentration and
not by theN source (Bar-Tal et al., 2001 ), whereas in Bougainvillea, chlorophyll was
affected only by theN source (Broschat, 1998). Leaf chlorosis caused by a high percentage
ofN03--N in the nutrient solution usually is associated with iron (Fe) deficiency and sodium
(Na) toxicity (Broschat, 1998). Although not enough information related to this problem is
available, in bedding-plant impatiens the Na toxicity seems to be more likely because of the 19
NaN03 that was used as source ofN03--N for the 4:0 N03--N to NH/-N ratio. The Na
1 concentration ranged from 0.5 mmol-L- for the 1:3 N03--N to NH/-N ratio to 7 mmol Na·L-
1 1 for the 4:0 ratio when the total N concentration was 14 mmol·L- . The leaf number increased linearly (P = 0.024) from 116 to 154 as theN concentration in the nutrient solution
1 increased from 3.5 to 14 mmol N-L- at a 1:3 N03--N to NH/-N ratio (Fig. 5). Our results were similar to those found for tomatoes (Bar-Tal et al., 2001) where greater N
concentrations improved leaf number. Plants with more leaves were able to conduct more
photosynthesis, and therefore, produced more fresh and dry weight (Weston and Barth,
1997).
Nitrogen source and concentration affected the substrate chemical composition where
the plants were grown. Substrate N03--N concentration was affected only by the nutrient
solution N concentration. As expected, the substrate N03--N content increased linearly (P =
< 0.0001) from 0.08 to 9.63 mg·L-1 as theN concentration in the nutrient solution increased
(Fig. 6). However, substrate N03--N concentration was low compared to the concentrations
supplied by the nutrient solutions. These low values are due to the fact that most of the N03-
-N in the substrate was leached during the ten days when only dionized water was applied.
Our results were similar to those in Bougainvillea, where the substrate N03--N content was
similar in treatments with different N sources (Broschat, 1998). Because the NH/-N
1 concentration was low (less than 1 mg·L- ), it is likely that all N supplied as NH4 +_N was
assimilated and/or converted to N03--N, and therefore, nitrification occurred in our growing
medium. Substrate pH and EC were affected by both the N concentration and source.
Substrate pH increased as the N03--N to NH/-N ratios increased from 1:3 to 4:0. However,
at low N03--N to NH/-N ratios, theN concentration affected pH directly, and the greater the 20
N concentration, the greater the substrate pH, whereas the opposite occurred at a high N03--
N to NH4 +-N ratio (Fig. 7). Our pH results are similar to those reported in previous research
(Cox and Seeley, 1984; Lamb et al., 1993; Osorio et al., 2003).
1 Low N concentrations (less than 7 mmol N-L- ) did not affect substrate EC, but the
1 substrate EC decreased linearly (P = < 0.008) from 2.2 to 1.4 dS·m- when N was supplied at
1 10.5 mmol N-L- and the N03--N to NH/-N ratio increased from 1:3 to 4:0. These substrate
EC values were directly related to the nutrient solution EC. The increment in the nutrient
solution EC, when the NH/-N increased on it, is related to the ammonium sulfate that was
used as the ammonium source. The difference in EC among the different N concentrations
was greater at a 1:3 N03--N to NH/-N ratio than at 4:0. Our EC results were different from
those found in privet (Stratton et al., 2001), where either N source or concentration, but not
their interaction, affected the substrate EC, as in our experiment. New Guinea impatiens
were intolerant of root medium EC greater than 2.0 dS·m-1 (Judd and Cox, 1992), and this
was reflected in its inability to grow in higher concentrations ofNH/-N (Weigle et al.,
1982). Although ammonium-rich solutions decreased substrate pH, this decline did not
affect bedding-plant impatiens growth and development. Our results suggest that bedding-
plant impatiens can tolerate some acidic growing conditions without adversely affecting their
growth and production of flower buds and leaves. However, ammonium nutrition must be
monitored carefully because of the acidifying effect on the root medium.
Not all plants respond similarly to N sources, and those responses differ among
species. Although some species can grow well on 100% N03--N, bedding-plant impatiens
did not grow well on 100% N03--N. No previous work has been published concerning theN
source preference of bedding-plant impatiens, but our data suggest they prefer a mixture of 21 ammonium-Nand nitrate-N. In our work, shoot dry weight and fresh weight were enhanced by the presence of ammonium-N, and plants fertigated with the 1:3 or 1:1 N03--N to NH/-N
1 ratios yielded the best plant growth when N was supplied at 10.5 mmol N·L- •
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Table 1. Composition of nutrient solutions that provided N concentrations and N03--N to NH/-N ratiosz to Impatiens wallerana 'Super Elfin White'. Solution pH was adjusted to 6.0 by using
5M NaOH or 5M HCL
Electrical 1 N concn Nutrient (mmol·L- ) conductivity
4:0 ratiox
3.5 1.50 0.50 3.50 2.1
7.0 3.00 1.00 2.00 2.1
10.5 3.50 3.50 1.50 2.3
14.0 3.50 7.00 1.50 2.7
3:1 ratio
3.5 1.25 0.44 0.13 3.75 2.2
7.0 2.50 0.88 0.25 2.50 2.2
10.5 3.50 1.31 0.88 1.50 2.4
14.0 3.50 1.75 3.50 1.50 2.7 26
Table 1 (cont.)
1:1 ratio
3.5 0.75 0.88 0.25 4.25 2.3
7.0 1.50 1.75 0.50 3.50 2.4
10.5 2.50 2.63 0.25 2.50 2.6
14.0 2.50 3.50 1.00 2.50 2.8
1:3 ratio
3.5 0.25 1.31 0.38 4.75 2.4
7.0 0.75 2.63 0.25 4.25 2.6
10.5 1.00 3.94 0.63 4.00 3.0
14.0 1.50 5.25 0.50 3.50 3.2
1 z All solutions contained, in mmol·L- : K2S04, 2.5; MgS04·7H20, 2.0; KH2P04, 1.0; and
1 micronutrients as follows, in JLmol·L- : H3B03,46.25; MnCh-4H20, 9.15; CuS04·5H20,
0.32; ZnS04·7H20, 0.77; H2Mo04·H20, 0.1; and FeEDTA, 13.43.
Y Calcium chloride was used to balance calcium in the solutions. x Expressed as N03--N to NH/-N ratio. 27
Figure Captions
Fig. 1. Effect ofN concentration and source ratio on shoot dry weight (SDW) of Impatiens wallerana 'Super Elfin White'. Treatments were applied for 30 d, followed by 10 d of irrigation with deionized water, and dry weight was obtained when plants were 70 d old. SDW for 14
1 1 mmol N·L- ( +): Y = 4.02-0.016 X (P = 0.0067) (~= 0.22) (--). SDW for 10.5 mmol N-L-
(•): Y = 4.05-0.015 X (P = 0.034) (~ = 0.14) (-).
Fig. 2. Effect ofN concentration on plant diameter of Impatiens wallerana 'Super Elfin White'.
Treatments were applied for 30 d, followed by 10 d of irrigation with deionized water, and measurements were obtained when plants were 70 d old. Nitrogen source did not affect plant diameter. The line indicates significant (P = < 0.0001) quadratic effects(~= 0.15) (-).
Fig. 3. Effect ofN concentration and source ratio on number of flower buds (FB) per plant of
Impatiens wallerana 'Super Elfin White'. Treatments were applied for 30 d, followed by 10 d of irrigation with deionized water, and flower buds were counted when plants were 70 d old. FB for
1 2 14 mmol N·L- (+): Y = 90.69 + 0.63X- 0.009 X (P= < 0.0001) (~= 0.48) (--). FB for 10.5
1 2 mmol N-L- (•): Y = 74.78 + 1.51X- 0.016 X (P = < 0.0001) (~= 0.58) (-).
Fig. 4. Effect ofN concentration and source ratio on the leaf chlorophyll content (LCC) of
Impatiens wallerana 'Super Elfin White'. Treatments were applied for 30 d, followed by 10 d of irrigation with deionized water, and LCC was obtained when plants were 70 d old. LCC for 14
1 2 mmol N· L- ( +): Y = 43.13 + 0.64X- 0.007 X (P = < 0.0001) (~ = 0.62) (--). LCC for 10.5
1 2 2 mmol N·L- (•): Y = 35.95 + 0.8X- 0.007 X (P = < 0.0001) (r = 0.54) (-). 28
Fig. 5. Effect ofN concentration and source ratio on number ofleaves (NL) per plant of
Impatiens wallerana 'Super Elfin White'. Treatments were applied for 30 d, followed by 10 d of irrigation with deionized water, and leaves per plant were counted when plants were 70
2 d old. NL for 1:3 N03--N to NH/-N ratio (•): Y = 104.75 + 3.5X (P = 0.024) (r = 0.16)
(-).
Fig. 6. Effect ofN concentration on substrate N03--N content (SNC) of Impatiens wallerana
'Super Elfin White'. Treatments were applied for 30 d, followed by 10 d of irrigation with deionized water, and leachates from the growing media were obtained when plants were 70 d old.
Leachates for nitrate analyses were obtained by using saturated medium extract methodology.
TheN concentration line indicates a linear effect (P = < 0.0001) (~ = 0.32).
Fig. 7. Effect ofN concentration and source ratio on substrate pH (SPH) of Impatiens wallerana
'Super Elfin White'. Treatments were applied for 30 d, followed by 10 d of irrigation with deionized water, and leachates from the growing media were obtained when plants were 70 d old.
Leachates for nitrate analyses were obtained by using saturated medium extract methodology.
1 SPH for 14 mmol N·L· ( +): Y = 4.35 + 0.016X (P = < 0.0001) (~= 0.63) (--). SPH for 10.5
1 1 mmol N-L' (•): Y = 4.69 + 0.013X (P = < 0.0001) (~= 0.64) (-). SPH for 7.0 mmol N-L'
1 (.._): Y = 4.89 + 0.008X (P = < 0.0001) (~ = 0.51) (----). SPH for 3.5 mmol N-L- ( •): Y = 5.24
+ 0.004X (P = < 0.018) (~ = 0.17) (" .... ).
Fig. 8. Effect ofN concentration and source ratio on substrate EC (SEC) of Impatiens wallerana
'Super Elfin White'. Treatments were applied for 30 d, followed by 10 d of irrigation with 29 deionized water, and leachates from the growing media were obtained when plants were 70 d old.
Leachates for nitrate analyses were obtained by using saturated medium extract methodology.
1 SEC for 14 mmol N-L- ( +): Y = 2.79- 0.01X (P = < 0.0001) (r= 0.45) (--). SEC for 10.5
1 1 mmol N-L- (•): Y = 2.43- 0.01X (P = < 0.008)(r= 0.214)(-). SEC for 7.0 mmol N-L- ("'):
Y = 2.05- 0.005X (P = < 0.02) (r2 = 0.16) (----). 30
4.0 -I N concn, mmoi·L
• 14.0 • 10.5 ... 7.0 3.5 • 3.5
OJ) '-" ...... 3.0 ~ -~ ~ ...... 2.5 0 ...c:0 • • 1/J. • • SE(0.05) = 0.42 2.0 • 2 r = 0.82 0.0 ...______,______...______,______...______I :3 I : I 3 : I 4:0
N03--N: NH/-N ratio
g. 1 31
19.0 • 18.5
18.0 r--, 17.5 s(.) 2 '--' PD = 12.4 + 1.1 [N]- 0.05 [N] ;...... Q) 17.0 Q) § ...... 16.5 '"0 § -p.., 16.0 15.5 SE(O.OS) = 1.47 l=o.n 15.0 0.0~ 0.0 3.5 7.0 10.5 14.0
1 N concentration (rnrnol·L- ) 32
120 -I N concn, mmol· L
• 14.0 110 • 10.5 ...• 7.0 ... • 3.5 100 --. § ~ 0... -1-< ()) • • 0... 90 r:/l ... "'0 ... ""' ;::j ""'. ..0 ... 1-< ()) 80 • • • ~ ""' '\ 0 '\ • -~ 70 \ SE(0.05) = 14 ~ 2 60 r = 0.54 • 0 1 : 3 1 : 1 3 : 1 4:0 33
-1 60 N concn, mmo1· L __.---+-- • 14.0 / • 10.5 57 ... 7.0 ,--_ 3.5 N / 0 • l/1 / 0 54 0...< r/) "-' 1:::v 51 1::: 0 C) -E 48 0.. • 0 l-; 0 • ..0 -u 45 SE(O.OS) = 3.8 •
?=075
0 1 : 3 1 : 1 3 : 1 4:0
N0-3 -N: NH+4 -N ratio
.4 34 35
12
,..-...... I ....:l 10 6n • SNC = -3.11 + 0.91[N] '-..../s ~ (P = < 0.0001) 0 8 ~ ·-!-<
1::(!) C) ~ 0 6 C)
zI <"') 0 4 z SE(o.05) = 4.57 (!) 2 ~ r = 0.57 ...... !-< "-l .g 2 r/1 • • 0 0.0 3.5 7.0 10.5 14.0
1 N concentration (mmol· L- )
Fig. 6 36
6.3 • 6.0
5.7
•
-1 N concn, mmol· L
4.8 • 14.0 10.5 • 7.0 • 3.5 4.5
0.0 L..._____ ..,.l______~, _____..______.______1:3 1 : 1 3: 1 4:0 37
2.4 -I • N concn, mmol ·L 2.2 • • 14.0 • 10.5 ::::--..._ .. 7.0 ~ • 3.5 ,_...__ 2.0 '-;' ~· 8 ~"'-~ ~ ifJ...... ~ '\:I 1.8 '--' ...... u ...._ ...... ""' ""-• (.Ll (!) -~ 1.6 ~ ~- ...... 1-< r:n ~----- "§ • ifJ. 1.4 • • • • 1.2 SE = 0.41 • 2 r =0.53
0.0 1 : 3 1 : 1 3:1 4:0
.8 38
Chapter 3. Increased Calcium Concentration does not Affect Growth and
Postharvest Performance of Bedding-plant Impatiens
A paper to be submitted to HortTechonology
Fredy R. Romero, Richard J. Gladon, and Henry G. Taber
ABSTRACT. Impatiens (Impatiens wallerana Hook. f.) is the most important annual bedding plant in the U. S. based on wholesale dollar volume. It has been shown that calcium
(Ca) improves the postharvest life and quality of some crops like roses. Our objective was to evaluate the effect of Ca concentration supplied during the production cycle on preharvest growth and development and postharVest performance of bedding-plant impatiens. The
1 experiment included five Ca concentrations (3, 5, 7, 9, and 11 mrnol Ca-L- ) applied during
1 the growing cycle at a uniform N concentration of 10.5 mmol·L- with a 1:1 N03--N to NH/-
N ratio. Application of treatments began at day 30 (22 dafter germination was complete), and applications were conducted until day 60. From day 60 to day 70 only deionized water, as a leach, was applied. After day 70, plants were held under shaded conditions for an additional 25 d, and tap water was used for irrigation. Increased Ca negatively affected shoot dry weight, shoot fresh weight, leaf number, substrate EC, and tissue potassium (K) concentration at the end of the preharvest period and shoot dry weight, leaf number, and tissue K concentration at the end of the postharvest period. Therefore, additional Ca applied during the production cycle did not increase preharvest growth and postharvest performance. 39
Introduction
Postharvest longevity and quality of flowering potted plants are affected by mineral nutrition more than any other production factor (Nell et al., 1997). Calcium is an essential macronutrient and is frequently supplied as a cation accompanying N03- in liquid fertilizers
(Smith et al., 1998). Calcium also is important because it regulates ripening, activates enzymes, and affects the rates of respiration and ethylene production (Dris et al., 2001).
Calcium deficiencies cause many important physiological disorders that affect the quality of many vegetable crops (Weston and Barth, 1997). Increasing theCa concentration in the nutrient solution reduced the amount ofwilted flowers ofrose (Nielsen and Starkey, 1999).
Calcium affects fruit senescence and quality by altering intracellular processes. At least 60% of the total Ca in the plant is associated with the cell wall fraction (Fallahi et al., 1997).
Torre et al. (1999) found that rose flowers produced under a high ambient relative humidity (90% RH) contained less Ca than plants grown under a lower ambient relative humidity. Petals had less Ca compared with those produced under low ambient relative humidity. In addition, those flowers had a shorter postharvest life. The authors also found that an increased Ca concentration decreased flower drop and decreased the rate of senescence. Also, Ca promoted flower opening, and thus flower diameter was increased.
Calcium enhanced the initial fresh weight and delayed the later reduction in fresh weight of intact flowers.
Nitrogen and Ca are more involved in various fruit quality factors than other elements, and these elements have been studied extensively in postharvest physiology of pome fruits (Fallahi et al., 1997). Calcium affects some membrane characteristics related to or associated with senescence, and apples with a high concentration of Ca exhibit a low rate 40 of respiration and a longer storage life (Dris et al., 2001). Our objective was to evaluate the effect of calcium (Ca) concentration supplied during the production cycle on the preharvest growth and postharvest performance of bedding-plant impatiens.
Materials and Methods
Experimental Design. This experiment included five Ca concentrations (3, 5, 7, 9, and 11
1 mmol-L- ). The nutrient solutions for this experiment were made by using the solution of
1 10.5 mmol N·L- at a ratio of 1:1 N03--N to NH/-N, varying theCa concentration only.
Each experiment was a completely randomized block design with four replicates and was repeated independently. The first run of the experiment was conducted from March to June
2003, and the second run from April to July 2003. Before treatments began, the pots with plants were arranged in four blocks of 10, and were randomized independently within each block. There were two pots per treatment in each replicate.
Plant culture. Impatiens (Impatiens wallerana Hook. f. 'Super Elfin White') seeds were sown in plug trays (288 cells/tray) filled with Fafard® Germination Mix root medium
(Conrad Fafard, Inc., Agawan, MA) on 24 March and 25 April2003. Trays were placed under tap-water mist at 23 °C for 8 d. After germination, seedlings were moved to a greenhouse and placed under high-pressure sodium lamps (Model # HPS400, Sunlight
Supply, Inc®, Vancouver, W A) that provided an average of 54 J..tmol·sec-1·m-2 of supplemental light from 0600 to 2200 daily and a constant air temperature of 27 ± 1 °C.
During days 8 through 22, seedlings were fertigated with a constant liquid feed at a rate of 7 mmol N·L-1 from a mixture of25% Excel® All-purpose 21N-2.2P-16.6K and 75% Excel®
CAL-MAG 15N-2.2P-12.45K fertilizers (Scotts-Sierra Horticultural Products, Marysville, 41
OH). On day 23, the rate ofN applied from the same source was increased to 10.5 mmol
N·L-1 until day 30 when plants were transplanted to 10-cm pots containing Sunshine LC-1
Mix© (Sun-Gro Horticulture®, Bellevue, WA). Fertigation with the treatment solutions commenced after transplanting.
Treatment application. The Ca concentrations were supplied by nutrient solutions that were a modification ofHoagland's solution number 1 (Hoagland and Arnon, 1950). TheN
1 concentration used as the basis for this experiment was the 10.5 mmol N-L- and a 1:1 N03--N to NH4 + -N ratio (Table 1 of Chapter 2), varying only theCa concentration. Nutrient solutions were made every 10 d by using deionized water, and their pH was adjusted to 6.0 by using either 5M NaOH or 5M HCl. The substrate was saturated with 200 mL of the respective nutrient solution before transplanting the seedlings. One day later, plants with two pairs of true leaves completely developed were transplanted to the drained root medium.
Each pot was fertigated every other day with 100 mL of nutrient solution, and the pH and EC of the substrate were measured every 10 d by using the PourThru method (Whipker et al.,
2000) starting the day of transplanting. Treatment applications ceased after 30 d, and then only deionized water was applied for 10 more days to avoid salt accumulation and regulate substrate pH during the last part of the production cycle.
Growth evaluation. At the end of the production cycle, one plant per treatment per block was harvested to evaluate growth parameters. Plant height was determined by measuring the distance from the bottom of the shoot, using the soil line as a reference point, to the top of the plant shoot. Plant diameter was calculated by averaging two diameter measures taken perpendicular to one another. Chlorophyll content was determined in the four youngest, fully expanded leaves with a chlorophyll meter (Model SP AD-502, Spectrum Technologies, 42
Plainfield, IL). At the end of each harvest period, flower buds and flowers were counted, and shoots were harvested and weighed (fresh weight), and then dried in a forced-air over at 67 oc for 72 h (dry weight) and ground through a 20 mesh screen in a Wiley mill. Tissue K, Ca, and Mg concentration was measured by using inductively coupled argon plasma emission techniques (Munter and Grande, 1981; Jones, 1977) following dry ashing at 490 oc and digesting in 1N aqua-regia. At the end of each experiment, growth medium pH and EC were obtained by using the saturated medium extract (SME) method as established by the North
Central Regional Soil Testing Committee for Greenhouse Soils (Warnecke, 1998).
Leachates were kept in plastic vials at 4 oc for future analyses.
Postharvest performance evaluation. The second plant of each treatment was moved to a different greenhouse where the conditions of a retail establishment were simulated. Those plants were held under shade for 25 d and watered only with tap water. The light intensity during the postharvest period was kept between 43 and 120 ~-tmol·sec- 1 ·m- 2 • Temperature was not controlled so that retail conditions would be simulated. At the end of the 25-d postharvest period, all plants were harvested, and the data collected were the same as at the end of the production cycle.
Data analysis. Plant growth, root medium parameters, and shelf-life performance were evaluated by using the general linear model procedure of the Statistical Analysis System®
(SAS Institute, 1988). Regression analysis was used to identify significant treatment effects. 43
Results
Our data are the results from two runs and we found differences. Plants grew faster and became larger during the second run due to the greater temperature, irradiance, and day length. However, the trends were identical in both runs, and therefore, we combined the data from each run for the purpose of analysis and presentation.
For plants harvested at the end of the production cycle, the greatest dry weight and fresh weight were obtained with Ca concentrations equal or less than 7 mmol·L-1 (Table 1).
The number of leaves per plant also decreased as the Ca concentration in the nutrient solution increased (Table 1). The leaf chlorophyll content also decreased from 54 to 46 as the Ca concentration in the nutrient solution increased. No differences were observed for any of the other parameters (Table 1). Substrate EC increased as the Ca concentration increased in the nutrient solution, whereas substrate pH was not affected by Carate (Table 2). The amount of
Ca found in the substrate at the end of the production cycle increased linearly (P = < 0.0001) as theCa concentration of the nutrient solutions increased. However, theCa in the substrate at the end of the postharvest period was less than that found at the end of the production cycle (Fig. 1).
Extra Ca supplied during the production cycle affected only shoot dry weight and number of leaves per plant during the postharvest period (Table 3). Shoot dry weight decreased linearly (P = 0.048) from 5.58 to 4.98 gas the preharvest Ca solution rates increased. Leaf number also decreased linearly (P = 0.06) from 225 to 186 as the preharvest
Ca solution rates increased. All other parameters evaluated after the Postharvest period were not affected by preharvest Ca rates. The Ca concentration in both preharvest and postharvest shoots increased linearly (P = < 0.001) as theCa concentration increased in the nutrient 44 solution (Table 4). The values after both periods of time were similar. On the other hand, shoot K concentration decreased as the amount of applied Ca increased during both periods.
The shoot concentrations of K found during the preharvest period were greater than the concentrations found at the end of the postarvest period (Table 4).
Discussion
Increased Ca greater than 7 mmol-L-1 supplied during the production cycle did not improve growth and postharvest shelflife, quality and performance of bedding-plant impatiens in a retail simulation. The best shoot dry and fresh weights were obtained when
1 plants received less than 7 mmol Ca·L- • Our results agree with those found in watermelon
(Citrullus lanatus (Thunb.) Matrum and Nakai.), where Ca at 8 mmol-L-1 or greater suppressed transplant growth (Lamb et al., 1993) and Alstroemeria where dry weight decreased with increasing Ca concentrations (Smith et al., 1998). Other parameters of postharvest quality such as plant diameter, number of flower buds, and leaf number were not affected by the concentration of theCa applied during the production cycle.
Most crops do not respond to increased root zone Ca concentrations (McLaughin et al., 1998), and based on our results, bedding-plant impatiens are not an exception. Based on previous experiments (Chapter 2), we supplied the optimum N source ratio and N concentration for growth to our plants. Our results are consistent with those found in
Alstroemeria where Ca had no effect on the number of flowers per plant, number of florets, or number of flower buds per stem (Smith et al., 1998). However, our results were inconsistent with Torre et al. (1999), who found that increased Ca concentrations promoted 45 open flowering and enhanced shoot dry weight and reduced the number of wilted flowers of fresh-cut rose.
Increasing theCa concentration in the nutrient solution from 3 to 11 mmol·L-1
1 directly affected the substrate EC, which linearly increased from 2.7 to 3.78 dS·m- • This might be related directly to the calcium chloride used to provide the different Ca concentrations in the nutrient solutions. Although we did not find specific recommendations about the substrate EC for bedding plant impatiens, it is commonly accepted that the substrate EC should not be greater than 1.0 dS -m- 1 (Ball, 1998). However, our results showed that bedding-plant impatiens could tolerate up to 3.0 dS -m- 1 without affecting plant growth. The increased substrate EC seemed to have affected the absorption of other nutrients such as N, which was reflected in the decline in the leaf chlorophyll content, and therefore, plants treated with Ca concentrations greater than 7 mmol-L-1 looked chlorotic. This low content of leaf chlorophyll affected the rate of photosynthesis and the source of energy for the plants to grow. This result also differed from previous research where Ca reduced the number of yellow leaves (Nielsen and Starkey, 1999).
The Ca concentrations applied during the growing season were reflected in the tissue
Ca concentration not only during the preharvest period, but also during the posthavest period.
Concentrations in both periods were similar and had the same linear trend (P = < 0.0001 for both periods). Shoot Ca concentration increased linearly from 1.7 to 3.01% as theCa concentration increased from 3 to 11 mmol-L-1 in the nutrient solution. These values remained almost identical during the postharvest period, and this shows that Ca in the plant is immobile and that most of theCa absorbed by the plant is used for cell structure (Fallahi et al., 1997). Conversely, shoot K concentration during the preharvest period decreased linearly 46 from 3.38 to 2.8% as the Ca concentration in the nutrient solution increased from 3 to 11
1 mmol-L- . This decrement was associated with a cation competition between Ca and Kin the root zone. The same trend was observed during the postharvest period, but the values decreased by about 35%. These changes are understandable because the plants continued to
grow during the postharvest period, even though no K had been added to the irrigation water used during the posthaverst period. However, the K concentration in the tissue was within
the sufficiency range (1.3 7 to 2.35%) for bedding-plant impatiens production (Mills and
Jones, 1996).
In the shelf-life experiment, only dry weight and number of leaves per plant were
affected negatively by the increased Ca concentrations. The plants treated with theCa rates
1 commonly used for bedding-plant production (3 to 5 mmol-L- ) showed the greatest shoot dry
weight (3.24 and 3.06 g) and the largest number ofleaves per plant (168 and 145,
respectively). During this phase of the experiment the chlorophyll content was similar in all
the treatments, as was the substrate EC. The reduction of the substrate EC was due to the tap
water applied during the 25 d of the postharvest experiment. The other parameters were not
affected by the Ca concentrations evaluated in this experiment.
It is important to point out that Ca concentrations in the nutrient solution greater
than 7 mmol·L-1 yielded lower dry weight and leafnumber, as well as greater substrate EC
1 and tissue Ca concentrations than those fertilized with concentrations less than 7 mmol·L- •
This clearly showed the negative effects of increased Ca concentrations on growth and
performance ofbedding-plant impatiens. Therefore, no beneficial effect either in the
production cycle or in the postharvest performance was obtained by adding more Ca to the
nutrient solution than what is used under commonly accepted commercial practices. The 47 postharvest performance of these plants depends on the quality achieved during the production cycle (Weston and Barth, 1997).
Literature Cited
Ball, V. 1998. Ball RedBook. 1ih Edition. Ball Publishing, Batavia, IL.
Dris, R., R. Niskanen, and S.M. Jain. 2001. Crop management and postharvest handling of
horticultural products. Science Publishers. Enfield, NH. p. 175-186.
Fallahi, E., W.S. Conway, K.D. Hickey, and C.E. Sams. 1997. The role of calcium and
nitrogen in postharvest quality and disease resistance of apples. HortScience 32:831-
835.
Jones, J.B., Jr. 1977. Elemental analysis of soil extracts and plant tissue ash by plasma
emission spectroscopy. Commun. Soil Sci. Plant Anal. 8:345-365.
Hoagland, D.R. and D.I. Amon. 1950. The water culture method for growing plants without
soil. Calif. Agr. Expt. Sta. Circ. 347.
Lamb, M.J., G.H. Clough, and D.D. Hemphill, Jr. 1993. Pretransplant watermelon nutrition
with various nitrate : ammonium ratios and supplemental calcium. HortScience
28:101-103.
McLaughin, M.J., S.J. Andrew, M.K. Smart, and E. Smolder. 1998. Effects of sulfate on
cadmium uptake by Swiss chard: I. Effect of complexation and calcium competition
in nutrient solutions. Plant and Soil202:211-216.
Mills, H.A., and J.B. Jones, Jr. 1993. Plant analysis handbook II. MicroMacro Publishing,
Inc. Athens, GA. 422 p.
Munter, R.C. and R.A. Grande. 1981. Plant tissue and soil extract analysis by ICP-atomic 48
emission spectrometry, p. 653-672. In: R.M. Barnes (ed.). Developments in atomic
plasma spectrochemical analysis. Heyden and Sons, London.
Nell, T.A., J.E. Barrett, and R.T. Leonard. 1997. Production factors affecting
postproduction quality of flowering plants. HortScience 32:817-819.
Nielsen, B. and K.R. Starkey. 1999. Influence of production factors on postharvest life of
potted roses. Postharvest Biol. Techno!. 16:157-167.
SAS Institute. 1988. SAS/STAT user guide, release 6.03 ed. SAS Inst., Cary, NC.
Smith, M.A., G.C. Elliot, and M.P. Bridgen. 1998. Calcium and nitrogen fertilization of
Alstroemeria for cut flower production. HortScience 33:55-59.
Torre, S., A. Borochov, and A.H. Halevy. 1999. Calcium regulation of senescence in rose
petals. Physiol. Plant. 107:214-219.
Warnecke, D. 1998. Greenhouse root media, p. 61-64. In: Recommended chemical soil test
procedure for the North Central Region. NCR Publ. No. 221 (Revised), Missouri
Extension and Ag. Inf., 1-98 Ag Bldg., Columbia, MO.
Weston, L.A. and M.M. Barth. 1997. Preharvest factors affecting postharvest quality of
vegetables. HortScience 32:812-816.
Whipker, B.E., W.C. Fonteno, T.J. Cavins, and D.A. Bailey. 2000. PourThru nutritional
monitoring manual. N.C. Commercial Flower Growers' Assoc. 49
Table 1. Effect of calcium concentration during the production cycle on growth of Impatiens wallerana 'Super Elfin White'. Plants were harvested 35 dafter treatments began.
Shoot weight (g) Number per plant Ca concn Plant Plant
Dry Fresh diameter (em) Flower buds Leaves height (em)
3 3.24x 51.8 20.0 82 168 6.3
5 3.06 50.9 20.2 72 145 5.7
7 3.09 52.4 19.6 82 155 6.2
9 2.78 45.4 19.8 69 138 6.1
11 2.66 43.3 19.6 69 145 6.2
Significance 0.004 0.004 NS NS 0.05 NS
x Each treatment mean represents two experiments each with four replicates run independently.
NS Nonsignificant at P > 0.05, P value stated otherwise. 50
Table 2. Effect of solution Ca concentration on substrate pH and EC of Impatiens wallerana
'Super Elfin White' at the end of the production cycle and posharvest period.
pH Ca concn
Preharvestz Postharvese Preharvest Postharvest
3 5.6 2.70 0.96
5 4.9 5.7 2.96 1.00
7 4.7 5.6 2.98 0.97
9 4.7 5.7 3.27 0.91
11 4.7 5.7 3.78 0.91
Significance NS NS 0.021 NS
z The preharvest samples were taken after 30 d oftreatment application and 5 d of irrigation
with deionized water.
Y The postharvest samples were taken 25 d later than the preharvest samples, after the plants
were held in the simulated retail environment for 25 d.
x Each mean represents two experiments each with four replicates run at different times.
NS Nonsignificant at P > 0.05, P value stated otherwise. 51
Table 3. Effect of calcium concentration applied during the production cycle on postharvest shelf-life performance of Impatiens wallerana 'Super Elfin White'.
Plants were held for 25 d under conditions similar to those provided by a retailer.
Shoot weight (g) Number per plant Ca concn Plant Plant
Dry Fresh diameter (em) Flower buds Leaves height (em)
3 5.58x 87.6 29.7 68 225 11.9
5 5.48 88.3 30.5 74 215 12.0
7 5.64 91.5 29.2 82 238 11.0
9 5.14 83.0 28.0 59 207 12.0
11 4.98 82.5 29.2 61 186 11.1
Significance 0.03 NS NS NS 0.0008 NS
Trend L (P = 0.048) NS NS NS L,Q (P = 0.06) NS x Each mean represents two experiments each with four replicates run at different times.
Ns Nonsignificant at P > 0.05, P value stated otherwise. 52
Table 4. Effect of solutions Ca concentration applied during the production cycle on the amount of shoot Ca and K of Impatiens wallerana 'Super Elfin White' at the end of the preharvest and postharvest period.
Ca K Ca concn
Preharvest2 Postharvese Preharvest Postharvest
%
3 1.70x 1.88 3.38 2.21
5 2.07 2.23 3.12 2.13
7 2.44 2.37 3.03 2.04
9 2.65 2.66 2.96 1.82
11 3.01 2.85 2.8 1.78
Significance < 0.0001 < 0.0001 0.0002 < 0.0001
Trend L (P = < 0.0001) L (P = < 0.0001) L (P = 0.002) L (P = < 0.0001) z The preharvest samples were taken after 30 d of treatment application and 5 d of irrigation with deionized water.
Y The postharvest samples were taken 25 d later than the preharvest samples. x Each mean represents two experiments each with four replicates run at different times.
Ns Nonsignificant at P > 0.05, P value stated otherwise. 53
Figure Captions
Fig. 1. Effect of different amounts of Ca applied in the nutrient solution on substrate Ca concentration (SCC) of Impatiens wallerana 'Super Elfin White'. The preharvest SME samples were taken after 30 d oftreatment application and 5 d of irrigation with deionized water. The postharvest SME samples were taken 25 d later than the preharvest samples.
Local tap water used for the Postharvest portion of this experiment routinely contains about
1 2 90 mg Ca-L- • SCC for the preharvest period (A): Y = 134.17 + 12.36 X (P = 0.0035) (r =
0.23) (-). 54
300 Ca concentration at & Preharvest Postharvest ~ 250 • ~ 6o '--'8 ~ ...... 0 200 'Fj !-<
1:1(]) (.) ~ 0 150 (.) ro u (]) 'Fj ~ 100 (/) • • • .g • • r:/1
50 0~~--~--~----~--~--~ 3 5 7 9 11
1 Ca concentration applied (mmol·L- ) 55
Chapter 4. General Conclusions
General Discussion
Production of high-quality bedding-plant impatiens requires optimization of the nutrition regimen during growth, especially the total N concentration and the ratio ofN sources. N is a critical nutrient in the formation and development of the plant photosynthetic apparatus. Deficiencies or excesses that retard photosynthesis also affect plant growth.
Bedding-plant impatiens need 10.5 mmol N-L- 1 to develop all of their growth potential, and concentrations above or below 10.5 mmol N·L-1 reduced growth.
An interaction ofN concentration and N03--N to NH/-N ratio affected plant growth.
Although ammonium-rich solutions decreased substrate pH, this decrement did not affect bedding-plant impatiens growth and development. Therefore, bedding-plant impatiens could tolerate some acidic growing conditions without affecting their growth and production of flower buds and leaves per plant.
Although some species grow well on 100% N03--N, bedding-plant impatiens did not grow well on 100% N03 --N. Our data suggest bedding-plant impatiens prefer a 1:3 or 1:1
1 N03--N to NH/-N ratio at 10.5 mmol N·L- for best growth in terms of plant diameter, flower buds per plant, and leaves per plant. Therefore, to produce high-quality bedding-plant
1 impatiens, concentrations of 10.5 mmol N-L- at a ratio of 1:3 or 1:1 N03--N to NH/-N should be used.
No beneficial effect either in the production cycle or in postharvest performance was obtained by adding more Ca to the nutrient solution. Increased Ca greater than 7 mmol-L-1 56 did not improve growth and did not improve postharvest quality or performance of bedding- plant impatiens in a retail simulation.
Recommendations for Future Research
We propose continuing with these evaluations, focusing more attention on how absorption of minerals is affected by the N source and N concentration and if the size of the container and type of substrate affect theN preference of bedding-plant impatiens. We also suggest evaluating whether or not increased Ca concentrations have any effect on the shelf- life performance of bedding-plant impatiens when they are exposed to different types of stresses. Finally, we recommend extending these experiments to more crops for which limited information about their preferences for the amount and form ofN is available. 57
ACKNOWLEDGMENTS
I give thanks to the Fulbright program for giving me the opportunity to further my education and to the Horticulture Department for all the resources provided to help me accomplish this task. I especially thank my major professor, Dr. Richard J. Gladon, for his support, suggestions, and positive critique of my work during the course of my M.S. program. I feel privileged to have worked under his guidance and appreciate the time of assistance in developing and correcting my work.
I thank Dr. Henry Taber, Dr. David Hannapel, and Dr. Alfred Blackmer for their suggestions and for serving as members of my program of study committee. Also to Dr.
Henry Taber, for helping me with the soil and tissue analyses and for his suggestions to improve this document. I am grateful to Dr. Philip Dixon for helping me to deal with numerous statistical analyses of my research. I am also thankful to Dr. Delate for her advice and encouragement. I have so many people that I want to express my gratitude for their help and support in making my carreer at ISU so special.
I express my deep appreciation and thankfulness to my family, for giving me love, and a strong motivation and ability to deal with the challenges of everyday life. To my wife and daughter, for being there for me every time that I needed a shoulder to lean on during the most difficult times.
This work is dedicated to the memory of my father who always will be present in my life no matter the circumstances. I know you are still watching over us. I will love you forever!