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Effect of Nitrogen Rates and Mowing Heights on Nitrogen Leaching, Turf Quality and Spectral Reflectance in Floratam St. ...

Permanent Link: http://ufdc.ufl.edu/UFE0024544/00001

Material Information

Title: Effect of Nitrogen Rates and Mowing Heights on Nitrogen Leaching, Turf Quality and Spectral Reflectance in Floratam St. Augustinegrass
Physical Description: 1 online resource (67 p.)
Language: english
Creator: Sharma, Shweta
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: augustinegrass, leaching, multispectral, nitrogen, radiometry, saint, st
Environmental Horticulture -- Dissertations, Academic -- UF
Genre: Horticultural Science thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Increasing urbanization throughout Florida is causing concerns about potential pollution of water resources from fertilization of home lawns. Best Management Practices have been developed for the commercial lawn care service in Florida to minimize any potential adverse impacts from the fertilization and lawn care activities. The objectives of this study were to evaluate the effect of nitrogen rates and mowing heights on nitrate (NO3-N) leaching of St. Augustinegrass (Stenotaphrum secundatum Walt. Kuntze.), and to evaluate the response of N rates and mowing heights on St. Augustinegrass turf quality and physiological responses. The experiment was conducted in a greenhouse at the Turfgrass Research Envirotron Laboratory at the University of Florida in Gainesville. The grass was grown in 42.5 L poly vinyl chloride tubs in sandy loam soil (Hyperthermic, uncoated, Quartzipsamments in the Candler series). Nitrogen was applied as urea (46-0-0) at the rate of 2.5, 4.9, 7.4 and 9.8 g N m-2 every two month. Each interval between fertilizer applications was considered a fertilizer cycle (FC), of which there were three. Turfgrass mowing height treatments were 7.6 and 10.2 cm. Turf that was maintained at 7.6 cm was mowed once every week and turf that was maintained at 10.2 cm mowing height was mowed once every two weeks. Irrigation was applied twice a week throughout the experimental period at 1.27cm of water per application. Leachate was collected every 15 days. Turf visual quality ratings were taken every 15 days. Multispectral reflectance, chlorophyll measurements and canopy temperature readings were taken every month. Experimental design was a randomized complete block with four replications. In FC1 and 2, there were no differences in nitrate-N leaching due to N rate; however, due to insect damage in FC3, there was greater leaching at the higher N rates. Percent of applied N leached was less than 1% throughout the study at all N rates. There were no differences in nitrate-N leaching due to mowing height in the FCs, but when data were averaged over the course of the study, greater leaching occurred at the lower mowing height. Turf visual quality and color scores increased with N rate, but were at acceptable levels at all N rates. Spectral reflectance showed some differences to N rate, but responses were not characteristic of turf responses to N rate. Where there were differences in reflectance in response to mowing height, optimal responses occurred at the higher mowing height. From results of this research, it does not appear that application of high rates of N to St. Augustinegrass will result in nitrate leaching, particularly when the grass is maintained in a healthy condition.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Shweta Sharma.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: Trenholm, Laurie E.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0024544:00001

Permanent Link: http://ufdc.ufl.edu/UFE0024544/00001

Material Information

Title: Effect of Nitrogen Rates and Mowing Heights on Nitrogen Leaching, Turf Quality and Spectral Reflectance in Floratam St. Augustinegrass
Physical Description: 1 online resource (67 p.)
Language: english
Creator: Sharma, Shweta
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: augustinegrass, leaching, multispectral, nitrogen, radiometry, saint, st
Environmental Horticulture -- Dissertations, Academic -- UF
Genre: Horticultural Science thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Increasing urbanization throughout Florida is causing concerns about potential pollution of water resources from fertilization of home lawns. Best Management Practices have been developed for the commercial lawn care service in Florida to minimize any potential adverse impacts from the fertilization and lawn care activities. The objectives of this study were to evaluate the effect of nitrogen rates and mowing heights on nitrate (NO3-N) leaching of St. Augustinegrass (Stenotaphrum secundatum Walt. Kuntze.), and to evaluate the response of N rates and mowing heights on St. Augustinegrass turf quality and physiological responses. The experiment was conducted in a greenhouse at the Turfgrass Research Envirotron Laboratory at the University of Florida in Gainesville. The grass was grown in 42.5 L poly vinyl chloride tubs in sandy loam soil (Hyperthermic, uncoated, Quartzipsamments in the Candler series). Nitrogen was applied as urea (46-0-0) at the rate of 2.5, 4.9, 7.4 and 9.8 g N m-2 every two month. Each interval between fertilizer applications was considered a fertilizer cycle (FC), of which there were three. Turfgrass mowing height treatments were 7.6 and 10.2 cm. Turf that was maintained at 7.6 cm was mowed once every week and turf that was maintained at 10.2 cm mowing height was mowed once every two weeks. Irrigation was applied twice a week throughout the experimental period at 1.27cm of water per application. Leachate was collected every 15 days. Turf visual quality ratings were taken every 15 days. Multispectral reflectance, chlorophyll measurements and canopy temperature readings were taken every month. Experimental design was a randomized complete block with four replications. In FC1 and 2, there were no differences in nitrate-N leaching due to N rate; however, due to insect damage in FC3, there was greater leaching at the higher N rates. Percent of applied N leached was less than 1% throughout the study at all N rates. There were no differences in nitrate-N leaching due to mowing height in the FCs, but when data were averaged over the course of the study, greater leaching occurred at the lower mowing height. Turf visual quality and color scores increased with N rate, but were at acceptable levels at all N rates. Spectral reflectance showed some differences to N rate, but responses were not characteristic of turf responses to N rate. Where there were differences in reflectance in response to mowing height, optimal responses occurred at the higher mowing height. From results of this research, it does not appear that application of high rates of N to St. Augustinegrass will result in nitrate leaching, particularly when the grass is maintained in a healthy condition.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Shweta Sharma.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: Trenholm, Laurie E.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0024544:00001


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EFFECT OF NITROGEN RATES AND MOWI NG HEIGHTS ON NITROGEN LEACHING, TURF QUALITY AND SPECTRAL RE FLECTANCE IN FLORATAM ST. AUGUSTINEGRASS By SHWETA SHARMA A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2009

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2 2009 Shweta Sharma

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3 To my beloved husband, parents and brothers

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4 ACKNOWLEDGMENTS I express m y gratitude to Dr. Laurie E. Tre nholm (chair of my supervisory committee) for her excellent guidance, time and support. Her assistance during the course of my graduate work gave me the opportunity to reach my goal. I would like to thank my committee members Dr. Jerry Sartain and Dr. J. Bryan Unruh for their advice, support, and insp iration. I would like to acknowledge Florida Department of Environmental Protection (FDEP) for funding of this research. I would like to thank Basil Wetheringt on for technical support of my study and for his valuable suggestions. I am grateful to To mmy Deberry, Brian Owens, Jason Haugh Ronald Castillo, Amy Cai and Jinyong Bae for their help in my research. I am deeply grateful to my parents (M r. Madhu Sudan Sharma and Mrs. Ram Pyari Sharma) and my brothers (Shwadhin Sharma and Swapnil Sharma) for their love and moral support. Finally, I thank my husband Subodh Achary a for his love, encouragement and patience.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ............................................................................................................... 4TABLE OF CONTENTS ............................................................................................................. ....5LIST OF TABLES ...........................................................................................................................7LIST OF FIGURES .........................................................................................................................9ABSTRACT ...................................................................................................................... .............10INTRODUCTION .................................................................................................................. .......12Environmental Concerns with Nitrogen Use .......................................................................... 12Mowing Heights and Nitrogen Leaching ............................................................................... 16MATERIALS AND METHODS ...................................................................................................19EFFECT OF FERTILIZER RATES AND MOWING HEIGHTS ON Nitrate leaching FROM ST. AUGUSTINEGRASS .......................................................................................... 22Introduction .................................................................................................................. ...........22Materials and Methods ...........................................................................................................26Results and Discussion ........................................................................................................ ...28Nitrate Leaching (mg m-2) ............................................................................................... 28Nitrate Leaching by Concentration (mg L-1) ................................................................... 29Visual Color and Quality .................................................................................................30Shoot and Root Growth ...................................................................................................31Conclusions .............................................................................................................................33EFFECT OF FERTILIZER RATES AND MOWING HEIGHTS ON SPECTRAL REFLECTANCE OF ST. AUGUSTINEGRASS ................................................................... 42Introduction .................................................................................................................. ...........42Materials and Methods ...........................................................................................................45Results and Discussion ........................................................................................................ ...48Multispectral Reflectance ................................................................................................48Canopy Temperature .......................................................................................................49Chlorophyll Index ............................................................................................................ 49Correlation .......................................................................................................................50Conclusions .............................................................................................................................51CONCLUSIONS.................................................................................................................... ........60REFERENCES .................................................................................................................... ..........62

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6 BIOGRAPHICAL SKETCH .........................................................................................................67

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7 LIST OF TABLES Table page 3-1 Nitrate leaching (mg m-2) from Floratam St. Augustineg rass in response to N rates and mowing heights in a greenhouse experiment .............................................................. 343-2 Percentage Nitrate leached from Floratam St. Augustinegrass in response to N rates and mowing heights in a greenhouse experiment .............................................................. 343-3 Nitrate leaching (mg L-1) from Floratam St. Augustinegrass in response to N rates and mowing heights in a greenhouse experiment .............................................................. 353-4 Visual color score of Floratam St. Augus tinegrass in response to N rates and mowing heights in a greenhouse experiment ...................................................................................353-5 Visual quality score of Floratam St. Augustinegrass in response to N rates and mowing heights in a greenhouse experiment ..................................................................... 363-6 Total Kjeldahl Nitrogen percentage Floratam St. Augustinegrass in response to N rates and mowing heights in a greenhouse experiment ..................................................... 363-7 Turf shoot weight (g m-2) Floratam St. Augustinegrass in response to N rates and mowing heights in a greenhouse experiment ..................................................................... 373-8 Turf root weight (g m-2) Floratam St. Augustinegrass in response to N rates and mowing heights in a greenhouse experiment ..................................................................... 373-9 Correlation matrix of average color, aver age quality and average nitrate leached from Floratam St. Augustinegrass in response to N rates in a greenhouse experiment ............. 384-1 Multispectral reflectance values of Floratam St. Augustinegrass in a greenhouse experiment in response to N ra tes and mowing heights in FC1. ....................................... 524-2 Multispectral reflectance values of Floratam St. Augustinegrass in a greenhouse experiment in response to N ra tes and mowing heights in FC2 ........................................ 524-3 Multispectral reflectance values of Floratam St. Augustinegrass in a greenhouse experiment in response to N ra tes and mowing heights in FC3 ........................................ 534-4 Canopy temperature reading (C) of Fl oratam St. Augustinegrass in a greenhouse experiment in response to N rates and mowing heights .................................................... 534-5 Chlorophyll reading Floratam St. Augustin egrass in a greenhouse experiment in response to N rates and mowing heights ............................................................................ 544-6 Correlation matrix of visual color and quality (from chapter 3) with reflectance values of Floratam St. Augustinegra ss in a greenhouse experiment ................................. 54

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8 4-7 Correlation matrix of canopy temperature (CT) and chlorophyll index (CI) with reflectance values of Floratam St. A ugustinegrass in a grass experim ent ......................... 54

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9 LIST OF FIGURES Figure page 3-1 Average NO3-N leached from the turf at differe nt fertilization cycles. Means are averaged for fertilizer cycles ..............................................................................................393-2 Observations NO3-N (mg m-2) leaching with respect to th e three fertilization dates. Black arrows indicate fert ilizer application dates .............................................................. 393-3 Interaction between mowing height and N rate with respect to NO3-N leaching from Floratam St. Augustinegrass in FC3 .................................................................................. 403-4 Interaction between mowing height and N rate with respect ot shoot growth of Floratam St. Augustinegrass .............................................................................................. 403-5 Interaction between mowing height and N ra te with respect to visual color (a) and quality (b) ratings at FC1. .................................................................................................. 414-1 Interaction between N rate and mowing height of Floratam St Augustinegrass in a greenhouse experiment with respect to (a) NFVI (b) Stress1 (c) Stress2 during FC1 ...... 554-2 Interaction between N rate and mowing height of Floratam St Augustinegrass in a greenhouse experiment with respect to MS R at different wave lengths in FC2. (a) 450nm (b) 660nm (c) 694nm (d) 710nm ........................................................................... 564-3 Interaction between N rate and mowing height of Floratam St Augustinegrass in a greenhouse experiment with respect to canopy temperature during FC3 ..........................564-4 Average canopy temperature (oF) of Floratam St. Augustinegrass in a greenhouse experiment with different N tr eatments during the study period ....................................... 574-5 Average chlorophyll readings of Flor atam St. Augustinegrass in a greenhouse experiment with different N tr eatments during the study period ....................................... 574-6 Relationships between visual color and quality of Floratam St. Augustinegrass in a greenhouse experiment with different refl ectance ratios. (a)NDVI and color (b) NDVI and quality (c) Stress2 and color (d) Stress2 and quality........................................ 584-7 Relationship of canopy temperature and ch lorophyll index with reflectance ratios of Floratam St. Augustinegrass in a greenhous e experiment (a) NDVI and chlorophyll (b) NDVI and canopy tempertature (c) Stre ss2 and chlorophyll (d) Stress2 and canopy temperature ............................................................................................................59

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10 Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science EFFECT OF NITROGEN RATES AND MOWING HEIGHTS ON NITROGEN LEACHING, TURF QUALITY AND SPECTRAL RE FLECTANCE IN FLORATAM ST. AUGUSTINEGRASS By Shweta Sharma May 2009 Chair: Laurie E. Trenholm Major: Horticultural Science Increasing urbanization throughout Florida is causing concerns about potential pollution of water resources from fertiliz ation of home lawns. Best Ma nagement Practices have been developed for the commercial lawn care service in Florida to minimize any potential adverse impacts from the fertilization a nd lawn care activities. The obj ectives of this study were to evaluate the effect of nitrogen ra tes and mowing hei ghts on nitrate (NO3-N) leaching of St. Augustinegrass (Stenotaphrum secundatum [Walt.] Kuntze.), and to evaluate the response of N rates and mowing heights on St. Augustinegrass turf quality and physiological responses. The experiment was conducted in a greenhouse at the Turfgrass Research Envirotron Laboratory at the University of Florida in Gainesville. The grass was grown in 42.5 L pol y vinyl chloride tubs in sandy loam soil (Hyperthermic, uncoated, Quartzipsamments in the Candler series). Nitrogen was applied as urea (46-0-0) at the rate of 2.5, 4.9, 7.4 and 9.8 g N m-2 every two month. Each interval between fertilizer applications was cons idered a fertilizer cycle (FC), of which there were three. Turfgrass mowing height treatments were 7.6 and 10.2 cm. Turf that was maintained at 7.6 cm was mowed once every week and turf that was maintained at 10.2 cm mowing height was mowed once every two weeks. Irrigation was applied twice a week throughout the experimental period at 1.27cm of water per appl ication. Leachate was co llected every 15 days.

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11 Turf visual quality ratings we re taken every 15 days. Multispectral reflectance, chlorophyll measurements and canopy temperature readings were taken every month. Experimental design was a randomized complete block with four repli cations. In FC1 and 2, there were no differences in nitrate-N leaching due to N rate; however, due to insect damage in FC3, there was greater leaching at the higher N rates. Percent of app lied N leached was less than 1% throughout the study at all N rates. There were no differences in nitrate-N leaching due to mowing height in the FCs, but when data were averaged over the cour se of the study, greater leaching occurred at the lower mowing height. Turf visual quality and colo r scores increased with N rate, but were at acceptable levels at all N rates. Spectral reflectance showed some differences to N rate, but responses were not characteristic of turf responses to N rate. Wh ere there were differences in reflectance in response to mowing height, optim al responses occurred at the higher mowing height. From results of this rese arch, it does not appear that application of high rates of N to St. Augustinegrass will result in nitrat e leaching, particularly when th e grass is maintained in a healthy condition.

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12 CHAPTER 1 INTRODUCTION St. Augustinegrass ( Stenotaphrum secundatum [Walt.] Kuntze) is one of the most popular choices for lawns throughout the southern United States. St. Augustinegrass represents 64.5% of all sod production in Florida, with 75% used for new residential land scapes (Haydu et al., 2002, 2005). St. Augustinegrass is believed to be native to the coastal regions of the Gulf of Mexico and the Mediterranean a nd perform s best in well drained so ils (Trenholm et al., 2000a). It has relatively good salt tolerance a nd certain cultivars have good shade tolerance. There are numerous cultivars of St. Augustinegrass that are produced in Florida including Palmetto, Delmar, Bitterblue and Flo ratam. Of these, Floratam is the most widely produced, comprising 75% of all St. Augustinegrass in production. Floratam is an improved St. Augustinegrass that was released jointly in 1973 by the University of Florida and Texas A & M University (Trenholm et al., 2000a). St. Augustinegrass prefers modera te cultural practices with a fertility requirement ranging from 10 to 30 g N m-2 yr-1 (Trenholm et al., 2002). In some regions, regular irrigation is needed due to poor drought tolerance (Christians 1998). Environmental Concerns with Nitrogen Use Increasing urbanization and an increasing number of hom e lawns throughout Florida may contribute to problems associ ated with nitrate-N (NO3-N) contamination of water. Nitrogen is the nutrient applied to turfgrass in the greatest quantity and frequency. Nitrate nitrogen is a water soluble form of N, which may leach through the soil if applied at excessive rates especially when accompanied by excess water from either irrigation or rainfall. In Florida, NO3-N leaching from home lawns has been implicated as a source of N pollution to streams, lakes, springs and bays (Erickson et al., 2001, Flipse et al., 1984). Sandy soils commonly found in Florida have low wate r holding capacity which may increase leaching

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13 of N fertilizer from the turfgrass when water drains through the soil prof ile into the groundwater. Burgess (2003) said that N entering the ground and surface water can cause eutrophication, and can cause health risk wher e that water is used for drinking. A high uptake of NO3-N is known to be hazardous to human health (Hornsby, 1999). Nitr ate nitrogen is converted to nitrite (NO2-N), which combines with hemoglobin in human body to form toxic methemoglobin. This decreases the ability of blood to carry oxygen, which cause s the syndrome known as methemoglobinemia, also called "blue baby syndrome" (The Nitrate Elimination Co., Inc. 2001). The United States Environmental Protection Agency (EPA) limit for NO3-N in drinking water is 10 mg L-1 which is easy to exceed if enough attention when applying fertilizers is not provided. Research has shown that fertilizer manageme nt is a factor in re ducing non-point source pollution (Gross et al., 1990), which has led to th e development of Best Management Practices (BMPs) (Trenholm et. al. 2002). BMPs have been developed for the commercial lawn care and landscape industries in Florida to minimize any potential adverse impacts from fertilization and lawn care activities. BMPs ar e the guidelines for implementation of environmentally sound agronomic practices to reduce potential contamination of ground or surface water due to commercial lawn care practices. These BMPs were developed in 2002 by regulatory, academic and industry professionals and are intended to pr eserve Floridas water resources. Practical N management techniques such as the use of controlled-release fertiliz ers, fertigation, and irrigation management have been shown to provide quality turfgrass with little leaching (Snyder et al., 1984; Snyder, et al., 1989). Annual N leaching rates for Kentucky bluegrass ( Poa pratensis L .), perennial ryegrass ( Lolium perenne L.) and St.Augustinegrass range from 0 to 160 kg N ha-1, and represent up to 30% of fertilizer applied N (B arton and Colmer, 2006). These authors observed that pollution

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14 occurs when less than adequate management prac tices are used. They observed less than 5% of the applied N was lost from established turfgras s that was not over-irrigated and had received a moderate amount of N fertilizer (200 kg N ha1 year1). Gross et al. (1990) studied surface runoff losses of nutrients and sediment s from established tall fescue (Festuca arundinacea Schrub.) and Kentucky bluegrass mixed stands for two consecutive years and observed that total N loss in turf averaged 0.14 kg N ha-1 which was lower when compared to most agronomics row crops like tobacco (11.7 kg N ha-1). Bowman et al. (2002) compared Raleigh St. Augustinegrass with five other warm season grasses (common bermudagrass [ Cynodon dactylon (L.) Pers.], T ifway hybrid bermudagrass ( Cynodon dactylon transvalensis ), centipedegrass (Eremochloa ophiuroides (Munro) Hack.), Meyer zoysiagrass (Zoysia japonica Steud.), and Emerald zoysiagrass ( Zoysia japonica x Zoysia tenuifolia Willd.ex Thiele) for NO3-N leaching and N use efficiency. They applied ammonium nitrate at the rate of 50 kg N ha-1 and found that Raleigh St. Augustinegrass produced the highest amount of leaf tissue and root ma ss compared to the other species. They found differences among the species for leaching of NO3-N ranging from a low of 24% of applied N in Raleigh St. Augustinegrass and a high of 56% in Meyer zoysiagrass. They concluded that the higher root mass might increase the abil ity of St. Augustinegrass to absorb NO3-N from the soil. In spite of some reports that propose turfgrass fertilization to be a significant contributor of NO3-N to ground water (Flipse et al., 1984), some, research has shown that properly managed and fertilized turf is not a significant source of groundwater contamination (Erickson et al., 2001). The authors studied Floratam St. Augustin egrass vs. a mixed species (ornamental ground cover, shrubs and trees) landscape. N was applied at a rate of 50 kg N ha-1per application to both plant systems for a total of 300 kg N ha-1 yr-1 to St. Augustinegrass and 150 kg N ha-1yr-1 to the

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15 mixed species landscapes. They found that more than 30% of applied fertilizer N leached from the mixed species landscapes, whereas less than 2% leached from St Augustinegrass. Frank (2007) showed nitrate leaching from Kentucky bl uegrass decreased as th e turf matured. When fertilizer was applied at the rate of 196 kg N ha-1 in 2003, averaged NO3-N leached was 31.6 mg L-1 and in 2006 averaged NO3-N leached was 11.2 mg L-1. Leaching may also depend on the source of N fertilizer applied. Shuman (2001) determined that supplying turf with N in a c ontrolled fashion greatly reduced the potential for leaching and runoff. According to Sartain (2002), slow-release fertilizers release their nutrient contents at more gradual rate s that enhance uptake and uti lization of the nutrient while minimizing losses due to leaching, volatilization or excessive turf growth. Benette (1996) verified that slow release N releases nutrients at a slower ra te throughout the season, thus, less frequent application is required. Th e author noted that this would al so reduce fertilizer burn, even when N was applied at high rates. Brown et al ( 1978) studied golf green s with sandy rooting media and found that NO3-N concentrations in leachate re sulting from isobutylidene diurea (IBDU) application were low (0.2% to 1.6% of applied N) but con tinuous throughout the study, whereas concentrations remained above 20 mg L-1 up to 35 days after application of ammonium nitrate. Saha (2004) found that St. A ugustinegrass treated with of 4.9 g N m-2 of quick release N sources had higher visual quality sc ores than those that received the same amount of slow release N for the first two weeks following fertilizer appli cation. After that, no significant differences in turf quality were found due to N source. There we re no differences in leaf nutrient concentration due to N treatments in this research. Quiroga et al. (2001) applied three N sources at two rates (100 and 200 kg N ha-1) and two different frequencies (eve ry 20 or 40 days) to bermudagrass.

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16 They found that urea and sulfur coated urea (SCU) enhanced vigor and greening and provided rapid N availability and uptake, but also increa sed the risk of N loss from leaching. Conversely, the sparingly soluble hydroform did not promote as much turf vigor and color but tended to minimize the risk of NO3-N leaching loss. Other research has disagreed with these results. Park (2006) applied urea and a blend of ur ea and IBDU at the rate of 30 g m-2 yr-1 and 15 g m-2yr-1 and found that leaching was affected by the fertilizer rates but not by the fe rtilizer sources. Previous research on N leaching from bermudagrass has shown that N rates, N sources, N application methods, and irrigati on all influence the amount of NO3-N leaching beyond the root zone and subsequently to groundwater (Snyder et al., 1989; Cisar et al., 1992). Mowing Heights and Nitrogen Leaching Turfgrass mowing is known to be one of the ma jor cultural practices that can influence turf health and vigor. Turfgrass undergoes physiological stress with each mowing, particularly if too much leaf tissue is removed (Trenholm et al., 2002). These authors state that it is important to leave as much leaf surface as possible to e nhance photosynthesis and to promote deep rooting. If turf is mowed too short, it tends to become denser, but has less root and rhizome growth (May et al., 2004). According to the authors, remova l of excess leaf area ma y increase the risk of fertilizers leaching through the soil or running o ff and endangering water reserves. The relatively high mowing height of St. Augustinegrass compared to other grasses produces a deeper root system, which can reduce NO3-N leaching (Bowman et al., 2002). Clark (2006) determined that gra ss species like blue flag iris ( Iris virginica L var shrevei), eastern gamma grass (Tripsacum dactyloides L.), and big blue stem ( Andropogon gerardii Vitman.) maintained at higher heights removed more pesticides from runoff water than those maintained at lower heights. Guertal and Evan s (2006) noted that berm udagrass color, rhizome and stolon weight were often reduced at a mowi ng height of 3.2 mm. When mowed at 3.9 mm

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17 and 4.8 mm, turf grew rapidly and maintained go od stolon, rhizome, and root dry weights, as well as good total nitrogen cont ent (TNC) and turf color. Biran et al. (1981) found that perennial ryeg rass mowed at 6 cm showed an increase in water use and yield than when mowed at 3 cm. Bermudagrass also showed a rapid and significant increase in water consumption and gr owth when the mowing height was increased from 3 cm to 6 cm but they slowly declined over time. Multispectral Reflectance and Chlorophyll Measurements Multispectral radiometry (MSR) provides a me thod for assessing plant light reflectance at various wavelengths of light energy where the percentage of light not reflected is either absorbed by the plant or transmitted downward to the so il surface (Trenholm et al., 1999). To assess the growth, or to compare treatment responses, quali tative responses are comm only used in turfgrass research, where quality might be expressed by visual and functional characteristics (Turgeon 1991). Qualitative responses are often described as the combination of shoot density, color, and growth habit (Beard, 1973). MSR may be used to quantify these subj ective parameters and provides a reliable method for comparison of turf response to treatments (Trenholm et al., 1999). Plants use varying amount of light at differe nt wavelengths for physiological processes. Some of the light is assimilated for that use, while some is reflected off the leaf surface. Measurement of the amount of light reflected at various wavelengths can be correlated with crop health, chlorophyll content, fertility, and stre ss (Carter 1993; Carter a nd Miller 1994; Trenholm et al., 2000b). Wavelengths within the visible spectrum (400 nm) are strongly absorbed by plant pigments. Near-infrared (NIR) ra diation (700 nm) is highly re flected due to low absorption (Knipling, 1970; Asrar et al., 1984 ). Leaf physical characteristic, such as cell structure, water

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18 content, and pigment concentration affect plant canopy reflectance, transmittance, and absorption (Maas and Dunlap, 1989). Leaf chlorophyll conten t was negatively correl ated to green light reflection (500 nm) and positively correl ated to NIR reflection in soybean ( Glycine max L .) and corn ( Zea mays L .) (Blackmer et al., 1994; Adcock et al., 1990). Measurement of chlorophyll concentration ma y be used to assess plant physiological response. Chlorophyll concentration may be considered as a measure of plant vitality, or may be viewed as an indirect measure of turf colo r (Pocklington et al., 1974). The Field Scout CM1000 Chlorophyll Meter (Spectrum Technology, Plainfield, IL) uses ambient and reflected light at 700 nm and 840 nm to calculate a rela tive chlorophyll index. It senses light at wavelengths of 700 nm and 840 nm to estimate the quantity of chlorophyll in leaves. The ambient and reflected light at each wavelength is measured. Chlorophyll a absorbs 700 nm light and, as a result, the reflection of that wavelength from the leaf is reduced compared to the re flected 840 nm light. Light having a wavelength of 840 nm is unaffected by leaf chlo rophyll content and serves as an indication of how much light is reflected due to leaf physical ch aracteristics such as the presence of a waxy or hairy leaf surface. ( www.specmeters.com). Few studies have been conducted regarding th e relationship of mo wi ng height and N rate on NO3-N leaching in warm season grasses. Theref ore, the objectives of this study were to evaluate the effect of nitroge n rates and mowing heights on NO3-N leaching of St. Augustinegrass, and to evaluate the res ponse of N rates and mowing heights on St. Augustinegrass turf quality and physiological responses.

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19 CHAPTER 2 MATERIALS AND METHODS The experime nt was conducted in a greenhous e at the Turfgrass Research Envirotron Laboratory at the University of Florida in Gainesville. Floratam St. Augustinegrass was harvested from the University of Florida G.C. Horn Turfgrass Research plots at the Plant Science Research and Education Unit (PSREU) located in Citra and established in poly vinyl chloride (PVC) tubs with dimensions of 0.6 m by 0.5 m and a volume of 42.5 L. Tubs were placed on metal tables in the gree nhouse. Five cm of gravel was placed at the bottom of the tubs and was covered with a mesh cloth to prevent soil migr ation into the gravel layer. Tubs were then filled with a sandy loam soil (Hyperthermic, uncoated, Quartzipsamments under the Candler series) obtained from the PSREU. Sod was planted on 25 September 2007. The sod was allowed to establish for two-months period before fertilizer treatments started. Urea (46-0-0) was applied at th e rate of 2.5, 4.9, 7.4 and 9.8 g N m-2 every two month (21 February 2008, 17 April 2008 and 26 June 2008). Each interval between fertilizer applications was considered a fertilizer cycle (FC). Turf grass mowing height treatments were 7.6 and 10.2 cm. Turf that was maintained at 7.6 cm wa s mowed once every week and turf that was maintained at 10.2 cm mowing height was mowed once every two weeks. Irrigation was applied twice a week thr oughout the experimental period at 1.27cm of water per application. Leachate was collected every 15 days. To fac ilitate leachate collecti on, a hole was drilled in one side of the tub. A polyethylene tube with an internal diameter of 6.35 mm was attached to the tub to allow leachate to drain into a white 2.5 L plastic bucket. Samples were acidified with sulfuric acid (conc. 96.3%) to lowe r pH (<2) and were cooled to less than 4 C. Samples were submitted to the Analytical Research Laboratory (ARL) in Gainesville for NO3-N analysis. The

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20 volume of total leachate collect ed was measured on each sampling date. Results are presented based on both Total Nitrogen c ontent (TNC) leached (mg m-2) and nutrient concentration in leached water (mg L-1). TNC was calculated by multiplyi ng the nutrient concentration by the corresponding leachate volume and dividi ng by the surface area of the tub. Turf visual quality ratings we re taken every 15 days using sc ale of 1 to 9, with 9 being outstanding or ideal turf and 1 be ing poor or dead turf. A rating of 6 or above was considered acceptable. Reflectance measurements were taken m onthly using a Cropscan model MSR 16R (CROPSCAN, Inc., Rochester, MN). Reflectance was measured at the following wave lengths: 450, 550, 660, 694, 710, 760, 835, and 930 nm. From these measurements, the following indices were used to assess tu rfgrass performance: NDVI (normalized difference vegetation index) which is measured as (R930-R660)/ (R930+R660) Stress-1, which is measured as R710/R760 Stress 2, which is measured as R710/R835 Chlorophyll measurements were taken monthly using a Field Scout CM-1000 Chlorophyll meter (Spectrum Technologies, Plainf ield, IL). Measurements were taken holding the meter approximately 1.5 m from the turf canopy. This yielded a circular area of evaluation of approximately 180 cm2 per measurement. All measurements were ta ken in full sun between 1100 and 1300 h with the meter facing away the sun. Canopy temperature was measured monthly with a Raytek Raynger infrared thermometer (Raytek, Santa Crtuz, CA). Temperature was m easured by point and shoot operation sequence by aiming the thermometer at the top of the turf canopy for couple seconds. Accurate monitoring of

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21 the difference between leaf (or canopy) temper ature and air temperature has been used to indicate plant water stress (Ehrle r, 1973; Idso and Ehrler, 1976). Shoot tissue clippings were coll ected 4 weeks after fe rtilizer application for each FC. Base line clippings were collected prio r to treatment initiation. Samples were dried in the oven for 48 hours at 75 C, ground, and analyzed for total nitr ogen content. Analysis of N was done by total Kjeldahl nitrogen (TKN) procedur e. Roots were harvested after the research was completed on 3 September 2008. Supplemental nutrients were provided to the turfgrass during the re search period. On 3 June 2008 and 18 July 2008, a micronutrient blend (Lesco Inc, Marysville, OH) (Magnesium (Mg) 1%, Sulfur (S) 5.78%, Iron (Fe) 3% and Ma nganese (Mn) 4%) was a pplied at the rate of 2.5 g m-2. Phosphorous (P) was applied as 0-45-0 on 17 June 2008 at the rate of 2.5 g m-2. On 5 June 2008 4.9 g m-2 potassium (K) was applied. Insecticid es were applied as needed throughout the experiment to control scale insects and mites. Experimental design was a randomized complete block with four replications. Data were analyzed with the SAS analytical program (SAS institute, Inc. 2008) to determine treatment differences at the 0.05 signifi cance level by General Linear Method (GLM) and means were separated by Waller-D uncan means separation. Data are presented by FC and averaged across all FCs. Correlation analysis was done to dete rmine degree of associ ation between data

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22 CHAPTER 3 EFFECT OF FERTILIZER RATES AND MOWI NG HEIGHTS ON NITRATE LEACHING FROM ST. AUGUSTINEGRASS Introduction St. Augustinegrass ( Stenotaphrum secundatum [Walt.] Kuntze) is one of the most popular choices for lawns throughout the southern United States. St. Augustinegra ss is believed to be native to the coastal regions of the Gulf of Mexico and the Mediterranean and perf orms best in well drained soils (Trenholm et al., 2000a). It has relatively good salt tolerance bu t has poor cold tolerance. St. Augustinegrass is more shade tolerant than many other warm season turfgrass species, although there is a wide range of shade tolerance within the species (Trenholm et al., 2002). St. Augustinegrass is characterized as a st oloniferous perennial, ro oting at nodes, with coarse-textured leaf blades that are 6 to 8 mm wide and up to 15 cm in length (Hitchcock, 1950; Duble, 1989). Commonly produced cultivars of St. Augustineg rass include Palmetto, Delmar, Bitterblue and Floratam, among which Floratam is the most widely produced, comprising 75% of all St. Augustinegrass in production in Florida. Floratam is an improved St. Augustinegrass that was released jointly in 1973 by the University of Florida and Texas A & M. University While St. Augustinegrass can grow in unfertile sand soils (Chen, 1992), depending on the aesthetics and uses requ ired, St. Augustinegrass requires fert ilization to maintain a healthy turfgrass stand. St. Augustinegrass prefers mode rate cultural practices with a fertility requirement ranging from 10-30 g N m-2 yr-1 (Trenholm et al., 2002). University of Florida recommendations for St. Augustineg rass fertilization vary, depending on location in the state. In northern Florida, 10-20 g N m-2 yr-1 is recommended, while in cen tral and south Florida 10-25 g N m-2 yr-1 and 20-30 g N m-2 yr-1, respectively, are recommended (Trenholm et al., 2002).

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23 St. Augustinegrass does not remain green unde r drought conditions and may die without supplemental irrigation. When irrigating St. Auges tinegrass, it is recommended that water be applied on an as needed basis (Trenholm et al., 2003). In some regions, St. Augestinegrass requires regular irrigation because of its poor drought tolerance (Christians, 1998). Increasing urbanization and an increasing number of home lawns throughout Florida may contribute to problems associated with NO3-N contamination of water. N is the nutrient applied to turfgrass in the greatest quantity and freque ncy to provide green co lor and healthy growth. NO3-N is a water soluble form of N, which may l each through the soil if applied at excessive rates, especially when accompanied by excess water from either irrigation or rainfall. In Florida, NO3-N leaching from home lawns has been implicated as a source of N pollution to streams, lakes, springs and bays (Erickson et al., 2001; Flipse et al., 1984). Sandy soils commonly found in Florida have low wa ter holding capacity, whic h may increase leaching of N from turfgrass when water drains thr ough the soil profile into the groundwater. Burgess (2003) said that N entering the ground and surfac e water can cause eutrop hication, and can cause health risk where that water is us ed for drinking. A high uptake of NO3-N is known to be hazardous to human health (Hornsby, 1999). The United States Environmental Protection Agency (EPA) limit for NO3-N in drinking water is 10 mg L-1. Bowman et al., (2002) compared Raleigh St. Augustinegrass with five other warm season grasses (common bermudagrass, Tifway hybrid bermudagrass, centipedegrass, Meyer zoysiagrass, and Emerald zoysiagrass). They appl ied ammonium nitrate at the rate of 50 kg N ha1 and found that Raleigh St. A ugustinegrass produced the highest amount of leaf tissue and the root mass compared to the other species. They found differences among the species for leaching of NO3-N ranging from a low of 24% of applied N in Raleigh St. Augustinegrass and a high of

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24 56% in Meyer zoysiagrass. They concluded that the higher root mass mi ght increase the ability of St. Augustinegrass to absorb NO3-N from the soil. In spite of some reports that propose turfgrass fertilization to be a significant contributor of nitrates to ground water (Flipse et al., 1984), some research has show n that properly managed and fertilized turf is not a significant source of groundwater contamination (Erickson et al., 2001). The authors studied Floratam St. Augustin egrass vs. a mixed species (ornamental ground cover, shrubs and trees) landscape. N was applied at the a of 50 kg N ha-1 per application to both plant types for a total of 300kg N ha-1 yr-1 to St. Augustinegrass and 150 kg N ha-1yr-1 to the mixed species landscape. They found that more than 30% of applied fertilizer N leached from the mixed species, whereas less than 2% leached from St. Augustinegrass. Previous research on N leaching from bermudagrass golf course turf in Florida has shown that N rates, N sources, N app lication methods, and ir rigation all influence the amount of N leached beyond the root-zone, and subsequently to groundwater (Snyder, et al., 1984; Snyder, et al., 1989; Cisar, et al., 1992). Frank (2007) showed NO3-N leaching from Kentucky bluegrass decreased as the turf matured. When fertilizer was applied at rate of 196 kg N ha-1 in 2003, averaged NO3-N leached was 31.6 mg L-1 and in 2006 averaged NO3-N leached was 11.2 mg L-1. Some claim that turf use s hould be minimized to avoid pollution, but research has shown that properly applied fertilizer will be assim ilated by the grass (Snyder et al., 1984; Erickson et al., 2001) and that proper fertilizer management is a factor in reducing non-point source pollution (Gross et al., 1990). The authors no ted that application of high rates of quick release fertilizers combined with high irrigation or rainfall re sulted in higher N losses due to leaching. Leaching may also depend on the source of N fertilizer applied. Saha (2004) found that St. Augustinegrass treated with 4.9 g N m-2 of quick release N sources had higher visual quality

PAGE 25

25 scores than those that received the same am ount of slow release N for the first two weeks following fertilizer application. After that, no diff erences in turf quality due to the N source were found. There were no differences in leaf nutrient concentration due to N treatments in this research. Shuman (2001) determined that supplyi ng turf with N in a controlled fashion greatly reduced the potential for leaching and runoff. Si milar results had previously been obtained by Killian et al. (1966), who found that concentration of NO3-N in leachate from turfgrass was found to be dependent on N source, with greater leaching and runoff from quick release sources. Brown et al. (1982) observed NO3-N losses of 8.6 to 21.9% in golf course greens fertilized with ammonium nitrate at the rate of 163 kg N ha-1. When slow release sources [isobutylidene diurea (IBDU) and ureaformaldehyde (UF)] were used at the rate of 146 kg N ha-1, only 0.2 to 1.6% NO3-N was leached. Other research has disagreed with these results. Park (2006) applied urea and a blend of urea and IBDU at the rate of 30 g m-2 yr-1 and 15 g m-2yr-1 and found that leaching was affected by the fertilizer rates but not by the fert ilizer sources. The Green Industries Best Management Practices (BMPs) have been developed for the commercial lawn care service in Florida to minimize any potential adverse impacts from fertilization and lawn care activities. BMPs are the guidelines for implementation of environmentally sound agronomic practices to reduce potential contam ination of ground or surface water due to commercial lawn care prac tices. These BMPs were developed in 2002 by regulatory, academic and industry professionals a nd are intended to preserve Floridas water resources. There is an outreach program for the BMPs to provide education on fertilizer management to the landscape maintenance industrie s of Florida. The objective of this study was to evaluate the effect of N rates and mowing heights on NO3-N leaching and turf quality of St. Augustinegrass.

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26 Materials and Methods The experime nt was conducted in a greenhous e at the Turfgrass Research Envirotron Laboratory at the University of Florida in Gainesville. Floratam St. Augustinegrass was harvested from the University of Florida G.C. Horn Turfgrass Research plots at the PSREU located in Citra and established in PVC tubs with di mensions of 0.6 m by 0.5 m and a volume of 42.5 L. Tubs were placed on metal tables in the greenhou se. Five cm of gravel was placed at the bottom of the tubs and was covered with a mesh cl oth to prevent soil migr ation into the gravel layer. Tubs were then filled with a sandy loam soil (Hyperthermic, uncoated, Quartzipsamments under the Candler series) obtained from the PSREU. Sod was planted on 25 September 2007. The sod was allowed to establish for two months period before fertilizer treatments started. Urea (46-0-0) was applied at th e rate of 2.5, 4.9, 7.4 and 9.8 g N m-2 every two month (21 February 2008, 17 April 2008 and 26 June 2008). Each interval between fertilizer applications was considered a fertilizer cycle (FC). Turf grass mowing height treatments were 7.6 and 10.2 cm. Turf that was maintained at 7.6 cm wa s mowed once every week and turf that was maintained at 10.2 cm mowing height was mowed once every two weeks. Irrigation was applied twice a week thr oughout the experimental period at 1.27cm of water per application. Leachate was collected every 15 days. To fac ilitate leachate collecti on, a hole was drilled in one side of the tub. A polyethylene tube with an internal diameter of 6.35 mm was attached to the tub to allow leachate to drain into a white 2.5 L plastic bucket. Samples were acidified with sulfuric acid concentration to lower pH (<2) an d were cooled to less than 4 C. Samples were submitted to the Analytical Research Laboratory (ARL) in Gainesville for NO3-N analysis. The volume of total leachate collected was measured at each sampli ng date. Results are presented

PAGE 27

27 based on both nutrient concentra tion in leached water (mg L-1) and TNC (mg m-2). TNC was calculated by multiplying nutrient concentration by the corresponding leachate volume and dividing by the surface area of the tub. Shoot tissue clippings were coll ected 4 weeks after fe rtilizer application for each FC. Base line clippings were collected prio r to treatment initiation. Samples were dried in the oven for 48 hours at 75 C, ground, and analyzed for total nitr ogen content. Analysis of N was done by total Kjeldahl nitrogen (TKN) procedur e. Roots were harvested after the research was completed on 3 September 2008. Turf visual quality ratings we re taken every 15 days using sc ale of 1 to 9, with 9 being outstanding or ideal turf and 1 being poor or dead turf. A ratin g of 6 or above is generally considered acceptable. Supplemental nutrients were provided to the turfgrass during the re search period. On 3 June 2008 and 18 July 2008, a micronutrients blend (Lesco Inc, Marysville, OH) (Magnesium (Mg) 1%, Sulfur (S) 5.78%, Iron (Fe) 3% and Ma nganese (Mn) 4%) was a pplied at the rate of 2.5 g m-2. Phosphorous (P) was applied as 0-45-0 on 17 June 2008 at the rate of 2.5 g m-2. On 5 June 2008 4.9 g m-2 potassium (K) was applied. Insecticid es were applied as needed throughout the experiment to control scale insects and mites. Experimental design was a randomized complete block with four replications. Data were analyzed with the SAS analytical program (SAS institute, Inc. 2008) to determine treatment differences at the 0.05 signifi cance level by General Linear Method (GLM) and means were separated by Waller-Dun can mean separation.

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28 Results and Discussion Nitrate Leaching (mg m-2) The amount of NO3-N leached (mg m-2) is presented in Table 3-1. The amount of NO3-N leached increased with increasing N rate in FC3 and when averaged across all three FCs (Figure 3-1). There were no differences in the NO3-N leached due to N rate in FC1 and FC2. This result may be because the turfgrass in these two cycles was healthy and dense, and was therefore able to filter and take up N at even the high rates. Increased NO3-N leaching in FC3 in this study is likely due to insect damage during later fertiliza tion cycles. Loss of turf cover and density and stress due to insect (scale insects and mites) damage decreased th e capacity of the turf to absorb nutrients, thus increasing the NO3-N content in the leachate in FC3. Porter et al. (1980) hypothesized that the capacity of the soil to store fertilizer N is a function of the age of the turfgrass and that older turf sites lose the abil ity to store additional N in the soil, which might also account for greater leaching at higher rate s. There was no difference in N leaching due to mowing heights (Table 3-1). Nitrate-N leaching data showed increased NO3-N in the leachate following fertilizer application in every FC for the three highest N rates (Figure. 3-2). This increase in N leaching was not seen in the samples collected at the subs equent collection dates in each FCs. Park (2006) found that regardless of season and N sources in all cycles, NO3-N leaching peaked shortly after fertilization and did not follow any consistent trend. Other studies have also found similar results (Petrovic, 2004; Johnston et al., 2003; Geron, et al., 1993, Sheard et al., 1 985). If irrigation rates and frequencies do not cause water to move be yond the active rooting zone, this will also decrease N leaching (Brown et al., 1977; Snyder et al., 1984; Morton et al., 1988). The interaction between mowing height and N ra te (fig 3-3) was si gnificant only in FC3 ( P-value = 0.04 ). At the lower mowing height, maximum NO3-N leaching was reached at 7.3 g

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29 N m-2, and then it declined at the 9.8 g N m-2 level. The decrease of NO3-N leaching at the highest N rate is hard to expl ain. At the higher mowing height, NO3-N leaching was constant through the 7.3 g N m-2 rate and then increased sharply at the 9.8 g N m-2. This means that at the higher mowing height, turf grass filters more NO3-N, except when N is applied at the highest rate. At the rate of 9.8 g N m-2 mowing height is not sufficien t to effectively filter NO3-N. Percent of total NO3-N leached is shown in tabl e 3-2. The percentage of NO3-N leached increases with increasing N rate in FC3 only. Less percentage of NO3-N was leached from higher mowed grass when the data was averaged over al l FCs. Interaction betw een mowing height and N-rate was found in FC3 which was very similar to fig 3-3. Nitrate Leaching by Concentration (mg L-1) Table 3-3 shows the average NO3-N concentration (mg L-1) in the leachate collected during the study period. Where there were differences in N leachi ng due to N rate, the most NO3N was leached from the highest N treatment rate a nd the least from the lowest N rate. There were differences due to N rate in all cycles except for FC2. There was a difference in the amount of NO3-N leached due to the mowing height difference in FC1 and when averaged across all three FCs, with higher NO3 leaching at the lower mowing height. An interaction was seen between the mowing heights and fertilizer rate in FC3 (figure not provided) which was very similar to the interaction of nitrate leaching (mg m-2).At the lower mowing height, maximum NO3-N leaching was reached at 7.3 g N m-2, and then it declined at the 9.8 g N m-2 level. The decrease of NO3-N at the highest N rate is hard to ex plain. At the higher mowing height, NO3-N leaching was low and steady through the 7.3 g N m-2 rate and then increased at the 9.8 g N m-2.This shows that turfgrass with higher mowing heights has better potential to absorb nutrients, thereby reducing the NO3-N leaching loss.

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30 Visual Color and Quality Higher visual color scores (Table3-4) were obtained from the turf treated with 9.8 g N m-2 and lower scores were obtained from the 2.4 g N m-2 treated turf in all FCs and when averaged over the study period. Visual color scores of the turfgrass mowed at 10.2 cm were better in FC1 and FC3 than the turfgrass mowed at 7.6cm. Significant differences were seen in the interaction between the mowing heights and fertilizer rates in FC1 and when averaged over all the FCs. In FC1 (fig 3-5a), whenever there was a difference, better color scores were seen in higher mowing heights and th e score increased with increasing fertilizer rate for both mowing heights. This indicates the positive influence of higher mowing heights. Similar to the visual color score, higher visual quality scores were obtained from turf treated with 9.8 g N m-2 than those treated with 2.4 g N m-2 in all three cycles and when averaged over the study period (table 3-5). There was a di fference in the visual quality due to mowing height in FC1 only, with higher sc ores at the higher mowing hei ght. An interaction in FC1 was also observed between mowing height and N rate with respect to turf quality (Fig 3-5b). Whenever there was a difference, better quality sc ores were seen in hi gher mowing heights and the score increases with the increase in fertilizer rate for both mowing heights.

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31 Total Kjeldahl Nitrogen Content in Leaf Tissue Leaf tissue nutrient analysis showed no di fference in TKN in FC1 due to N treatment (Table 3-6). The TKN increased as N rate increas ed in all other FCs and when averaged over the study period. Higher TKN values we re observed at the lower mowi ng height in all FCs (except FC1) and when averaged over all cycles. No inte raction was seen between fertilizer rate and mowing height due to th e total N content. Shoot and Root Growth Shoot growth differed in all FCs (except FC1) and when averaged over all cycles due to N treatme nt (Table 3-7). Greater shoot growth per unit area was found from 9.8 g N m-2 rate and the least was from the 2.4 g N m-2. Trenholm et al., (1998) obtain ed highest shoot growth per unit area in two cultivars of bermudagrass when fertilized at a rate of 9.8 g N m-2 then when they were fertilized at rate of 1.2, 2.4 and 4.9 g N m-2. Differences in shoot mass due to mowing height were seen in all FCs. Greater shoot tissue was harveste d from the 10.2 cm mowing height in FC2 and FC3, with less growth at the higher height in FC1. This difference in FC1 may be attributed to the fact that thes e grasses were still establishing. There was an interaction between mowing height and N rate only in FC2 (fig 3-4) Shoot mass was always greater at the higher mowing height at all N rates, while both mo wing rates showed increased shoot as N rate increased. However, shoot mass of turf mowed at 10.2 cm height reached a plateau with 7.3 g N m-2, while the tissue mass of grass mowed at 7.6 cm continued to increase as N rates increased (Fig 3-4). There were no differences in root growth due to N treatment; however, there was difference due to mowing height (Table 3-8). Root weight was 66% greater in turf maintained at 10.1 cm height than in the turf maintained at 7.6 cm height. Better root growth was supported by the higher mowing heights.

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32 Correlation Correlation analysis indicated that there we re significant relationship between average quality and color (Table 3-9) There was no correlation betwee n visual scores and nitrate leached This was somewhat surprising, since the treatm ents with lower quality ratings tended to be those that had the most damage from insect s, which would increase susceptibility to nitrate leaching.

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33 Conclusions From the results of this research, we concl ude that even with higher N rates and lower mowing heights, healthy turfgrass can efficiently use nitrogen, allowing lo w levels of nitrate leaching. The turfgrass that became infested with insects had less ability to absorb nitrogen as efficiently and increased the potential of leaching, particularly at the higher N rates. The higher mowing heights lessened nitrate-N leaching when insect damage became a factor. High nitrate leaching peaks were observed after the fertiliz ation events, which supports the potential for higher N leaching with quick-release urea nitrogen if applied at higher N rates. Higher nitrogen rates and higher mowing hei ghts produced better qua lity turfgrass and increased shoot mass. Additionally, higher NO3-N leaching losses may occur at lower mowing heights due to less shoot and root tissue to take up the nitrogen. Recommended mowing heights should be followed for optimal turfgrass h ealth and mitigation of nutrient leaching. From this greenhouse research, it appears th at healthy St. Augustin egrass provides an excellent filter to absorb applie d N and that, proper cultural practi ces to ensure turf vigor is an important factor in reducing NO3-N leaching. Field plot research should be conducted to determine if similar results would be found outside of a controlle d greenhouse setting.

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34 Table 3-1. Nitrate leaching (mg m-2) from Floratam St. Augustineg rass in response to N rates and mowing heights in a greenhouse experiment N-rate (g N m-2) FC1 FC2 FC3 Average 2.4 0.58 2.69 2.69 1.98b* 4.9 8.61 3.43 11.64 7.90b 7.3 10.61 7.21 51.25 23.02ba 9.8 16.44 36.95 66.95 40.11a Mow Ht (cm) 7.6 17.36 22.42 40.07 26.61 10.2 0.76 2.72 26.21 9.90 ANOVA N-rate NS NS 0.01 0.02 Mow Ht NS NS NS NS NrateMow Ht NS NS 0.04 NS *Means followed by the same letter do not diffe r significantly at the 0.05 probability level. Means are averaged for fertilizer cycles. Table 3-2. Percentage Nitrate leached from Floratam St. Augustinegrass in response to N rates and mowing heights in a greenhouse experiment N-rate (g N m-2) FC1 FC2 FC3 Average 2.4 0.02 0.11 0.11 0.08 4.9 0.17 0.07 0.23 0.16 7.3 0.14 0.10 0.70 0.31 9.8 0.17 0.38 0.68 0.40 Mow Ht (cm) 7.6 0.24 0.27 0.55 0.36a* 10.2 0.01 0.05 0.31 0.13b ANOVA N-rate NS NS 0.01 NS Mow Ht NS NS NS 0.02 N-rateMow Ht NS NS 0.01 NS *Means followed by the same letter do not diffe r significantly at the 0.05 probability level. Means are averaged for fertilizer cycles.

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35 Table 3-3. Nitrate leaching (mg L-1) from Floratam St. Augustinegrass in response to N rates and mowing heights in a greenhouse experiment N-rate (g N m-2) FC1 FC2 FC3 Average 2.4 0.08b* 0.12 0.13 0.11b 4.9 0.73ba 0.13 0.38 0.41b 7.3 0.88ba 0.47 1.61 0.99b 9.8 2.40a 1.60 2.81 2.27a Mow Ht (cm) 7.6 1.95a 0.99 1.32 1.42a 10.2 0.10b 0.16 1.15 0.47b ANOVA N-rate NS NS 0.0005 0.0008 Mow Ht 0.004 NS NS 0.009 NrateMow Ht NS NS 0.003 NS *Means followed by the same letter do not differ significan tly at the 0.05 probability level. Means are averaged for fertilizer cycles. Table 3-4. Visual color score of Floratam St. Augustinegrass in response to N rates and mowing heights in a greenhouse experiment N-rate (g N m-2) FC1 FC2 FC3 Average 2.4 6.5 6.3c* 6.5d 6.4 4.9 6.6 6.4b 6.5c 6.5 7.3 6.8 6.6a 6.6b 6.7 9.8 7.0 6.7a 6.7a 6.8 Mow Ht (cm) 7.6 6.6 6.5 6.6a 6.6 10.2 6.8 6.5 6.5b 6.6 ANOVA N-rate <0.0001 <0.0001 <0.0001 <0.0001 Mow Ht 0.011 NS 0.019 NS NrateMow Ht 0.033 NS NS 0.04 *Means followed by the same letter do not differ significantly at the 0.05 probability level. Means are averaged for fertilizer cycles.

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36 Table 3-5. Visual quality score of Floratam St. Augustinegrass in response to N rates and mowing heights in a greenhouse experiment N-rate (g N m-2) FC1 FC2 FC3 Average 2.4 6.4 6.2d* 6.4c 6.4b 4.9 6.5 6.4c 6.5bc 6.5b 7.3 6.7 6.5b 6.5ba 6.5ba 9.8 6.8 6.6a 6.6a 6.6a Mow Ht (cm) 7.6 6.5 6.5 6.5 6.5 10.2 6.7 6.4 6.5 6.5 ANOVA N-rate <0.0001 <0.0001 0.0006 0.009 Mow Ht 0.002 NS NS NS NrateMow Ht 0.04 NS NS NS *Means followed by the same letter do not differ significantly at the 0.05 probability level. Means are averaged for fertilizer cycles. Table 3-6. Total Kjeldahl Nitr ogen percentage Floratam St. Augustinegrass in response to N rates and mowing heights in a greenhouse experiment N-rate (g N m-2) FC1 FC2 FC3 Average 2.4 1.00 1.08c* 1.50b 1.20c 4.9 1.06 1.30b 1.74ba 1.36b 7.3 1.22 1.60a 1.86a 1.54a 9.8 1.07 1.61a 1.91a 1.53a Mow Ht (cm) 7.6 1.18 1.47a 1.87a 1.50a 10.2 1.00 1.30b 1.66b 1.31b ANOVA N-rate NS <.0001 0.01 <.0001 Mow Ht NS 0.0004 0.02 0.0006 NrateMow Ht NS NS NS NS *Means followed by the same letter do not differ significantly at the 0.05 probability level.

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37 Table 3-7. Turf shoot weight (g m-2) Floratam St. Augustinegrass in response to N rates and mowing heights in a greenhouse experiment N-rate (g N m-2) FC1 FC2 FC3 Average 2.4 2.75 4.65 9.07b* 5.49c 4.9 3.35 4.66 12.40a 6.80b 7.3 2.88 6.06 12.26a 7.07b 9.8 3.08 6.43 14.20a 7.91a Mow Ht (cm) 7.6 3.47a 4.59 10.65b 6.24b 10.2 2.56b 6.31 13.31a 7.39a ANOVA N-rate NS <.0001 0.0006 0.0006 Mow Ht 0.0004 <.0001 0.001 0.0008 NrateMow Ht NS 0.02 NS NS *Means followed by the same letter do not differ significantly at the 0.05 probability level. Table 3-8. Turf root weight (g m-2) Floratam St. Augustinegrass in response to N rates and mowing heights in a greenhouse experiment N-rate (g N m-2) root wt (gm) 2.4 20.47 4.9 18.78 7.3 21.81 9.8 17.59 Mow Ht (cm) 7.6 14.78a* 10.2 24.55b ANOVA N rate NS Mow Ht 0.004 NrateMow Ht NS *Means followed by the same letter do not differ significantly at the 0.05 probability level.

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38 Table 3-9. Correlation matrix of average color, average quality and average nitrate leached from Floratam St. Augustinegrass in response to N rates in a greenhouse experiment Average color Average quality Average N leached Average color 1 0.96 0.23 Average quality 0.96 1 0.18 Average N leached 0.23 0.18 1

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39 Figure 3-1. Average NO3-N leached from the turf at different fertilization cycles. Means are averaged for fertilizer cycles Figure 3-2. Observations NO3-N (mg m-2) leaching with respect to th e three fertilization dates. Black arrows indicate fert ilizer application dates

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40 Figure 3-3. Interaction between mowing height and N rate with respect to NO3-N leaching from Floratam St. Augustinegrass in FC3 Figure 3-4. Interaction between mowing height and N rate with respect ot shoot growth of Floratam St. Augustinegrass

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41 (a) (b) Figure 3-5. Interaction between mowing height and N rate with respect to visual color (a) and quality (b) ratings at FC1.

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42 CHAPTER 4 EFFECT OF FERTILIZER RATES AND MOWI NG HEIGHTS ON SPECTRAL REFLECTANCE OF ST. AUGUSTINEGRASS Introduction St. Augustinegrass is one of the most popular choices for lawns throughout the southern United States. St. Augustinegrass is believed to be native to the coastal re gions of the Gulf of Mexico and the Mediterranean a nd perform s best in well draine d soils (Trenholm et al., 2000). It has relatively good salt tolerance but has poor cold tolerance. St. Augustinegrass is more shade tolerant than many other warm s eason turfgrass species, although th ere is a wide range of shade tolerance within the species (Trenholm et al., 2002). St. Augustinegrass is characterized as a stoloniferous perennial, rooting at nodes, with coarse-t extured leaf blades that are 6 to 8 mm wide and up to 15 cm in length (Hitchcock, 1950; Duble, 1989). Commonly produced cultivars of St. Augustineg rass include Palmetto, Delmar, Bitterblue and Floratam, among which Floratam is the most widely produced, comprising 75% of all St. Augustinegrass in production in Florida. Floratam is an improved St. Augustinegrass that was released jointly in 1973 by the University of Florida and Texas A & M University. While St. Augustinegrass can grow in unfertile sand soils (Chen, 1992), depending on the aesthetics and uses requ ired, St. Augustinegrass requires fert ilization to maintain a healthy turfgrass stand. St. Augustinegrass prefers mode rate cultural practices with a fertility requirement ranging from 10-30 g N m-2 yr-1 (Trenholm et al., 2002). University of Florida recommendations for St. Augustineg rass fertilization vary, depending on location in the state. In northern Florida, 10-20 g N m-2 yr-1 is recommended, while in cen tral and south Florida 10-25 g N m-2 yr-1 and 20-30 g N m-2 yr-1, respectively, are recommended (Trenholm et al., 2002). St. Augustinegrass does not remain green unde r drought conditions and may die without supplemental irrigation. When irrigating St. Auges tinegrass, it is recommended that water be

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43 applied on an as needed basis (Trenholm et al., 2003). In some regions, St. Augestinegrass requires regular irrigation because of its poor drought tolerance (Christians 1998). Increasing urbanization and an increasing number of home lawns throughout Florida may contribute to problems associated with NO3-N contamination of water. N is the nutrient applied to turfgrass in the greatest quantity and freque ncy to provide green co lor and healthy growth. NO3-N is a water soluble form of N, which may l each through the soil if applied at excessive rates especially when accompanied by excess water from either irrigation or rainfall. Turfgrass mowing is known to be one of the major cultural practices that can influence turf health and vigor. Turfgrass undergoes physiological stress with each mowing, particularly if too much leaf tissue is removed (Trenholm et al., 2002). These authors state that it is important to leave as much leaf surface as possible so th at photosynthesis can occur and to promote deep rooting. If turf is mowed too s hort, it tends to become denser but has less root and rhizome growth (May et al., 2004). Accord ing to the authors, removal of excess leaf area may increase the risk of fertilizers leaching through the soil or running o ff and endangering water reserves. To assess the growth, or to compare treat ment responses, qualitative responses are commonly used in turfgrass research, where qualit y might be expressed by visual and functional characteristics (Turgeon 1991). Qualitative response s are often described as the combination of shoot density, color, and growth habit (Beard 1973). Multispectral radi ometry (MSR) may be used to quantify these su bjective values and provides a reliable method for comparison of turf response to treatments (Trenholm et al., 1999). Plants use varying amount of light at differe nt wavelengths for physiological processes. Some of the light is assimilated for that use, while some is reflected off the leaf surface. Measurement of the amount of light reflected at various wavelengths can be correlated with crop

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44 health, chlorophyll content, fertility, and stre ss (Carter 1993; Carter a nd Miller 1994; Trenholm et al., 2000). Wavelengths in th e visible range (400 nm can be absorbed by plant pigments. Near-infrared (NIR) ra diation (700 nm) is highly re flected due to low absorption (Knipling, 1970; Asrar et al., 1984 ). Leaf physical characteristics such as cell structure, water content, and pigment concentration affect plant canopy reflectance, transmittance, and absorption (Maas and Dunlap, 1989). Leaf chlorophyll conten t was negatively correl ated to green light reflection (500 nm) and positively correlated to NIR reflection in soybean and corn (Blackmer et al., 1994; Adcock et al., 1990). Measurement of chlorophyll concentration ma y be used to assess plant physiological response. Chlorophyll concentration may be considered as a measure of plant vitality, or may be viewed as an indirect measure of turf colo r (Pocklington et al., 1974). The Field Scout CM1000 Chlorophyll Meter (Spectrum Technology, Plainfield, IL) uses ambient and reflected light at 700 nm and 840 nm to calculate a rela tive chlorophyll index. It senses light at wavelengths of 700 nm and 840 nm to estimate the quantity of chlorophyll in leaves. The ambient and reflected light at each wavelength is measured. Chlorophyll a absorbs 700 nm light and, as a result, the reflection of that wavelength from the leaf is reduced compared to the re flected 840 nm light. Light having a wavelength of 840 nm is unaffected by leaf chlo rophyll content and serves as an indication of how much light is reflected due to leaf physical ch aracteristics such as the presence of a waxy or hairy leaf surface. ( www.specmeters.com). The objective of this study was to evaluate the physio logical responses of St. Augustinegrass as measured through various instru m entation in response to N rates and mowing heights.

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45 Materials and Methods The experime nt was conducted in a greenhous e at the Turfgrass Research Envirotron Laboratory at the University of Florida in Gainesville. Floratam St. Augustinegrass was harvested from the University of Florida G.C. Horn Turfgrass Research plots at the PSREU located in Citra and established in PVC tubs with di mensions of 0.6 m by 0.5 m and a volume of 42.5 L. Tubs were placed on metal tables in the gree nhouse. Five cm of gravel was placed at the bottom of the tubs and was covered with a mesh cloth to prevent soil migr ation into the gravel layer. Tubs were filled with a sandy loam soil (Hyperthermic, uncoated, Quartzipsamments under the Candler series) obtained from the PSREU. Sod was planted on 25 September 2007. The sod was allowed to establish for two mont hs before fertilizer treatments started. Urea (46-0-0) was applied at th e rate of 2.5, 4.9, 7.4 and 9.8 g N m-2 every two month (21 February 2008, 17 April 2008 and 26 June 2008). Each interval between fer tilizer applications was considered a fertilizer cycle (FC). Turf grass mowing height treatments were 7.6 and 10.2 cm. Turf that was maintained at 7.6 cm wa s mowed once every week and turf that was maintained at 10.2 cm mowing height was mowed once every two weeks. Irrigation was applied twice a week throughout the experimental period at 1.27cm of water per application. Chlorophyll measurements were taken mont hly using Field Scout CM-1000 Chlorophyll meter (Spectrum Technologies, Plainfield, IL). Measurements were taken holding the meter approximately 1.5 m from the turf canopy. This yielded a circular ar ea of evaluation of approximately 180 cm2 per measurement. All measurements were ta ken in full sun between 1100 and 1300 h with the meter facing away from the sun.

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46 Canopy temperature was measured monthly with a Raytek Raynger infrared thermometer (Raytek, Santa Crtuz, CA). Temperature was m easured by point and shoot operation sequence by aiming the thermometer at the top of the turf canopy for couple seconds. Accurate monitoring of the difference between leaf (or canopy) temper ature and air temperature has been used to indicate plant water stress (Ehrle r, 1973; Idso and Ehrler, 1976). Reflectance measurements were taken m onthly using a Cropscan model MSR 16R (CROPSCAN, Inc., Rochester, MN). Reflectance was measured at the following wave lengths: 450, 550, 660, 694, 710, 760, 835, and 930 nm. From these measurements, the following indices were used to assess tu rfgrass performance: NDVI (normalized difference vegetation index) which is measured as (R930-R660)/( R930+R660) Stress-1, which is measured as R710/R760 Stress 2, which is measured as R710/R835 Visual quality measurements were taken every other week (data in Chapter 3). These measurements were used for correlation analysis with instrumentation data collected here. Supplemental nutrients were provided to the tu rfgrass during the research period. On 3 June 2008 and 18 July 2008, micronutrients blend (Lesco Inc.) (Magnesium (Mg) 1%, Sulfur (S) 5.78%, Iron (Fe) 3% and Manga nese (Mn) 4%) was applie d at the rate of 2.5 g m-2. Phosphorous (P) was applied as 0-45-0 on 17 June 2008 at the rate of 2.5g m-2. On 5 June 2008 4.9g m-2 potassium (K) was applied. Insecticides were ap plied as needed throughout the experiment to control scale insects and mites. Experimental design was a randomized complete block with four replications. Data were analyzed with the SAS analytical program (SAS institute, Inc. 2008) to determine treatment

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47 differences at the 0.05 signifi cance level by General Linear Method (GLM) and means were separated by Waller-Dun can mean separation.

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48 Results and Discussion Multispectral Reflectance There were no differences in reflectance valu es due to N rate in FC1 but there were differences in indices NDVI, Stress 1 and Stress 2 (Table 4-1). Refl ectance values at 450 nm and 660 nm were lower, indicating greater plant assi milation of light, at 10.2 cm mowing height than at 7.6 cm. Trenholm et al. (1999) showed that re flectance in the visible range (400-700 nm) is relatively low due to increased chlorophyll absorptance in this range. There was an interaction between N rate and mowing height for NDVI, Stress 1 and Stress 2 (fig 4-1) In FC2, there were differences due to N rate for all the wavelengths and indices excluding Stress 2 (Table 4-2). Although no difference was found in FC2 due to mowing height, there was an interaction between N rate and mowing height for wavelengths 450, 660, 694, and 710 nm (fig 4-2). At 450 nm, reflectance from the turf at 10.2 cm height decreased when N rate was increased from 2.4 g N m-2 to 7.3 g N m-2, while for 7.6 cm, reflectance increased from 2.4 to 4.9 g N m-2 and declined from 4.8 to 7.3 g N m-2. Reflectance at 450 nm increased for both mowing heights when N rate was increased to the highest rate but the increase was much greater for 7.6 cm as compared to the 10.1 cm height. In FC3 there were no differences due to N rate, with the exception of Stress2 index, where better values were seen at the lower N rates (Table 4-3). Thisresult may be due to the insect damage in FC3. In the NIR range of 710 to 935 nm, reflectance is typically increased across the visible range because of internal scattering of light within the leaf that results in greater reflective surfaces (Gupta and Woolley, 1971; Knipling, 1970). If stress is sufficient to inhibit chlorophyll produc tion, increased reflectance becomes detectable first as chlorophyll content decreases. Thus, reflectan ce sensitivity to stress-induced chlorosis is high in the 690-700 nm range (Cibula and Carter, 1992; Carter, 1993)

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49 Canopy Temperature Canopy temperature decreased with increasi ng N rate in all FC s (Table 4.4). No difference was seen due to mowing height excep t for in FC1, where temperature was higher at the lower mowing height. Interaction between mo wing height and N rate was seen only in FC3 (fig 4.3). At the lower mowing height, canopy temper ature increased as the N rate increased from 2.4 to 4.9 g N m-2 and then steadily decreased as the N rate increased. At the higher mowing height, canopy temperature decreased when N rate increased from 2.4 to 7.3 g N m-2 but increased slightly when the N rate was increased to 9.8 g N m-2. These responses are not unexpected, since evapotranspirati on (ET) in a turf system has been shown to have a cooling effect and this would be expected to increase as shoot growth is increased, either due to N or mowing height (Fig 4-4). In addition, poor turf often did not fill the whole tub leaving exposed soil which would lead to increased canopy temperat ure. Throssell et al. (1987) found that wellwatered Kentucky bluegrass turf had lower canopy temperature than slightly stressed turf and that moderately stressed turf had the highest temperatures. Chlorophyll Index The Chlorophyll Ind ex (CI) increased with increasing N rates (Table 4.5). In all FCs, chlorophyll readings were highest for the turf that received 9.8 g N m-2 and lowest in the turf receiving 2.4 g N m-2 treated turf (Fig.4.5). Th is response to N is logi cal, since higher N rates produce more chlorophyll, which is the green pi gment that induces green-up of turf. This research agrees with Madison and Anderson (1 963), who reported th at increasing N rate, increased the chlorophyll index si gnificantly in Seaside bentgrass ( Agrostis palustris Huds Seaside). There were differences in CI due to mowing height in FC1 and when averaged throughout the cycles. Chlorophyll index in creased at higher mowing heights.

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50 Correlation Growth index NDVI had strong associations with color ( r = 0.73) (Table 4.6 and Fig. 4.6) and quality ( r = 0.75). Stress2 had strong negative associations with color and quality with limited association between Stress1 and quality a nd color. Previous research has shown that Stress2 is the more reliable indicator of quality and color in bermudagrass and seashore paspalum (Trenholm et al., 1999). These results indi cate that these indices, particularly Stress2, can alternatively be used to indicate qualitative factors as well as respons es to stress (Carter, 1994; Carter and Miller, 1994). NDVI had strong negative associations with canopy temperature and CI (r = 0.68 and r = 0.77 respectively) (Table 4.7 and Fig. 4.7). Ther e was a slight association between canopy temperature and Stress1 (r = 0.43) and stronger associat ion with Stress2 ( r=0.73).

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51 Conclusions From the results of this research, we concl ude that som e instrume ntation may provide an indication of the physiological func tioning of the turfgrass. Spectral reflectance readings at some of the visible range wavelengths can be useful in determining health, cover, and stress level of the turfgrass. Indices NDVI and Stress2 appear to have the best potentia l for determination of stress symptoms. Canopy temperature and chlorophy ll may have some ability to indicate stress or health in a turfgrass system. Field plot research should be conducted to determine if similar results would be found outside of a controlle d greenhouse setting.

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52 Table 4-1. Multispectral reflectance values of Floratam St. Augustinegrass in a greenhouse experiment in response to N ra tes and mowing heights in FC1. N-rate WV450 WV550 WV660WV694WV710NDV1 Stress1 Stress2 2.4 2.54 7.88 5.51 7.75 9.36 0.73 0.35 0.31 4.9 3.00 9.59 6.62 9.44 12.23 0.78 0.31 0.28 7.3 2.66 8.93 5.81 8.06 10.61 0.79 0.27 0.24 9.8 3.00 9.29 6.44 8.88 12.58 0.80 0.27 0.24 Mow Ht 7.6 3.24a* 9.86 7.33a 9.70 13.18 0.74 0.32 0.29 10.2 2.35b 7.98 4.86b 7.37 9.20 0.81 0.30 0.25 ANOVA N-rate NS NS NS NS NS 0.0003 <.0001 <.0001 Mow Ht 0.03 NS 0.04 NS NS <.0001 <.0001 0.0003 N-rateMow Ht NS NS NS NS NS 0.03 0.002 0.001 *Means followed by the same letter do not differ significantly at the 0.05 probability level. Means are averaged for fertilizer cycles. Table 4-2. Multispectral reflectance values of Floratam St. Augustinegrass in a greenhouse experiment in response to N ra tes and mowing heights in FC2 N-rate WV450 WV550 WV660 WV694 WV710NDV1 Stress1 Stress2 2.4 4.62 12.15b* 9.79 12.63 18.89 0.64b 0.47 0.46a 4.9 4.05 10.71b 7.87 10.53 17.19 0.70a 0.41 0.46a 7.3 3.30 9.33b 6.08 8.24 13.71 0.73a 0.50 0.37ba 9.8 5.53 17.95a 13.99 18.69 24.66 0.73a 0.39 0.33b Mow Ht 7.6 4.65 12.69 10.09 13.06 19.14 0.68b 0.45 0.43 10.2 4.09 12.38 8.78 11.98 18.08 0.72a 0.43 0.38 ANOVA N-rate 0.014 0.002 0.002 0.006 0.042 0.0006 NS 0.01 Mow Ht NS NS NS NS NS 0.03 NS NS NrateMow Ht 0.03 NS 0.02 0.05 0.03 NS NS NS *Means followed by the same letter do not differ significantly at the 0.05 probability level. Means are averaged for fertilizer cycles.

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53 Table 4-3. Multispectral reflectance values of Floratam St. Augustinegrass in a greenhouse experiment in response to N ra tes and mowing heights in FC3 N-rate WV450 WV550 WV660WV694 WV710 NDV1 Stress1 Stress2 2.4 3.83 11.23 9.70 13.60 16.57 0.69 0.41 0.43a* 4.9 3.99 12.31 11.14 15.15 18.08 0.70 0.55 0.36b 7.3 3.32 10.71 8.64 11.75 15.96 0.75 0.39 0.31b 9.8 3.51 10.68 8.69 12.32 15.92 0.74 0.44 0.34b Mow Ht 7.6 3.84 11.35 10.05 14.20 16.69 0.72 0.47 0.36 10.2 3.49 11.11 9.03 12.21 16.56 0.73 0.43 0.36 ANOVA N-rate NS NS NS NS NS NS NS 0.005 Mow Ht NS NS NS NS NS NS NS NS NrateMow Ht NS NS NS NS NS NS NS NS *Means followed by the same letter do not differ significantly at the 0.05 probability level. Means are averaged for fertilizer cycles. Table 4-4. Canopy temperature re ading (C) of Floratam St. Augustinegrass in a greenhouse experiment in response to N rates and mowing heights N-rate Cycle 1 Cycle 2 Cycle 3 Average 2.4 32.2a* 32.2a 36.7 34.0a 4.9 31.5b 32.1a 36.4 33.4ba 7.3 30.8b 30.8b 36.0 32.5bc 9.8 30.9b 30.5b 35.8 32.4c Mow Ht 7.6 32.2a 31.1 36.4 33.3 10.2 30.9b 31.6 36.1 32.9 ANOVA N-rate 0.017 0.014 0.011 0.001 Mow Ht 0.034 NS NS NS NrateMow Ht NS NS 0.02 NS *Means followed by the same letter do not differ significantly at the 0.05 probability level. Means are averaged for fertilizer cycles.

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54 Table 4-5. Chlorophyll reading Floratam St. Au gustinegrass in a greenhouse experiment in response to N rates and mowing heights N-rate Cycle 1 Cycle 2 Cycle 3 Average 2.4 218.37b* 156.43c 201.00b 191.93b 4.9 226.43b 190.06b 215.75b 210.75b 7.3 288.68a 241.56a 240.5a 256.91a 9.8 296.00a 256.06a 254.81a 268.96a Mow Ht 7.6 230.81b 211.09 223.75 221.88b 10.2 283.93a 210.96 232.28 242.39a ANOVA N-rate <0.0001 <0.0001 0.0004 <0.0001 Mow Ht <0.0001 NS NS 0.012 NrateMow Ht NS NS NS NS *Means followed by the same letter do not differ significantly at the 0.05 probability level. Means are averaged for fertilizer cycles. Table 4-6. Correlation matrix of visual color and quality (fro m chapter 3) with reflectance values of Floratam St. Augustineg rass in a greenhouse experiment Color Quality WV 450 WV 550 WV 660 WV 694 WV 710 NDVI Stress1 Stress2 Color 1.00 0.96 -0.12 0.09 -0.09 -0.03 -0.03 0.73 -0.27 -0.75 Quality 0.96 1.00 -0.11 0.11 -0.09 -0.02 -0.01 0.75 -0.25 -0.75 Table 4-7. Correlation matrix of canopy temperat ure (CT) and chloroph yll index (CI) with reflectance values of Floratam St. A ugustinegrass in a grass experiment CT CI WV 450 WV 550 WV 660 WV 694 WV 710 NDVI Stress1 Stress2 CT 1.00 -0.81 0.34 0.16 0.27 0.18 0.21 -0.68 0.43 0.63 CI -0.81 1.00 -0.21 0.01 -0.19 -0.13 -0.08 0.77 -0.37 -0.76

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55 Figure 4-1. Interaction between N rate and mowi ng height of Floratam St. Augustinegrass in a greenhouse experiment with respect to (a) NFVI (b) Stress1 (c) Stress2 during FC1

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56 (a) (b) (c) (d) Figure 4-2. Interaction between N rate and mowi ng height of Floratam St. Augustinegrass in a greenhouse experiment with respect to MS R at different wave lengths in FC2. (a) 450nm (b) 660nm (c) 694nm (d) 710nm Figure 4-3. Interaction between N rate and mowi ng height of Floratam St. Augustinegrass in a greenhouse experiment with respec t to canopy temperature during FC3

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57 Figure 4-4. Average canopy temperature (oF) of Floratam St. Augustinegrass in a greenhouse experiment with different N tr eatments during the study period Figure 4-5. Average chlorophyll readings of Floratam St. Augustinegrass in a greenhouse experiment with different N tr eatments during the study period

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58 (a) (b) (c) (d) Figure 4-6. Relationships between visual color and quality of Floratam St. Augustinegrass in a greenhouse experiment with different reflec tance ratios. (a)NDVI and color (b) NDVI and quality (c) Stress2 and co lor (d) Stress2 and quality

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59 (a) (b) (c) (d) Figure 4-7. Relationship of canopy temperature and chlorophyll in dex with reflectance ratios of Floratam St. Augustinegrass in a greenhous e experiment (a) NDVI and chlorophyll (b) NDVI and canopy tempertature (c) Stress2 and chlorophyll (d) Stress2 and canopy temperature

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60 CHAPTER 5 CONCLUSIONS Four different N rates and two mowi ng height treatments were studied for their effects on NO3-N leaching, turf visual color and quality, chlorophyll in dex, canopy temperature, and multispectral reflectance in Floratam St. Augustinegrass. From the results of this research, we conclude that even at high N rates and low mowing heights, healthy turfgrass can absorb virtually the entire applied N, with very low NO3-N leaching rates. When the turfgrass was in poor condition and injured by insect s in FC3, it did not absorb N as well as when it was growing in a healthy condition. Grass maintained at a higher mowing height leached less N than when mowed at a lower height. High NO3-N leaching peaks were observed after the fertilization events, which supports the potential for leaching of quick release fertilizer s such as urea if applied at higher N rates. Higher N rates and higher mowing heights produced better quality turfgrass and increased shoot growth but do not compensate enough to reduce NO3-N leaching. Additionally, higher NO3-N leaching losses may occur at lower mowing height s due to less shoot and root tissue to take up the N. Recommended mowing heights should be followed for optimal turfgrass health and mitigation of nutrient leaching. Some instrumentation may provi de an indication of the phys iological functioning of the turfgrass. Spectral reflectance readings at some of the visible range wavelengths can be useful in determining health, cover, and st ress level of the turfgrass. Indi ces NDVI and Stress2 appear to have the best potential for dete rmination of stress symptoms in turfgrass. Canopy temperature and CI may have some ability to indicate stress or health in a turfgrass system.

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61 The results obtained from this study indica te responses under cont rolled environmental conditions. Therefore, recommendations for a natu ral landscape cannot be made based solely on these findings. However, these results indicate th at the amount of N loss from St. Augustinegrass can be lowered or minimized if they are maintained at higher mowing heights and lower N levels.

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62 REFERENCES Adcock, T.E., F.W. Nutt er, Jr., and P.A. Banks. 1990. Measuring herbicid e injury to soybean ( Glycine max) using a radiometer. Weed Sci. 38: 625-627. Asrar, G., M. Fuchs, E.T. Kanemaru, and J.L. Hatfi eld. 1984. Estimating absorbed photosynthetic radiation and leaf area index from spectral re flectance in wheat. Agron. J. 76:300-306. Barton, L., & Colmer, T. D. (2006). Irrigation and fertiliser strategies for minimising nitrogen leaching from turfgrass. Agricultural Water Management, 80(1-3): 160-175. Beard, J.B. 1973. Turfgrass: science and cultu re. Prentice Hall, Englewood Cliffs, NJ. Benette, E. 1996. Slowrelease fertilizers. Vi rginia Gardeners Newsletter. Vol. 11. No. 4. Biran, I., B. Bravado, I. Bushkin-Harav, and E. Rawitz. 1981. Water consumption and growth rate of 11 turfgrasses as affected by mo wing height, irrigation frequency, and soil moisture. Agron. J. 75: 85-90. Blackmer, T.M., J.S. Schepers, and G.E. Barv el. 1994. Light reflectance compared with other nitrogen stress measurements in corn leaves. Agron. J. 86:934-938. Bowman, D.C., C.T. Cherney, a nd T.W. Rufty, Jr. 2002. Fate and transport of nitrogen applied to six warm season turfgrasses. Crop Sci. 42: 833-841. Brown, K.W., R.L. Duble, and J.C. Thomas. 1977. Influence of management and season on fate of N applied to golf greens. Agron. J. 69: 667-671. Brown, K.W., J.C. Thomas, and R.L. Duble. 1982. Nitrogen source effect on nitrate and ammonium leaching and run off losses from greens. Agron. J. 74: 947-950. Burgess, C. 2003. Reporoa nitrogen leaching tr ail 1998-2002: final. Environmental Waikato Technical Report: 15. Carter, G.A. 1993. Response of leaf spectral reflect ance to plant stress. Am. J. Bot. 80: 230-243. Carter, G.A. and R.L. Miller. 1994. Early detec tion of plant stress by digital imaging within narrow stress-sensitive wavebands. Re mote Sense. Environ. 50: 295-302. Chen, C. P. 1992. Plant resources of South-East Asia no 4. Forages. Pudoc-DLO, Wageningen, the Netherlands. Pg. 208-209.

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66 Snyder, G. H., B. J. Augustin, and J. L. Cisar. 1989. Fertigation for stabil izing turfgrass nitrogen nutrition. p. 217-219 In H. Takatoh (ed.) Proc. 6th Int. Turfgrass Res. Conf. (Tokyo), Japanese Soc. Turfgrass Sci., Tokyo. Snyder, G.H., B.J. Augustin, and J.M. Davidson. 1984. Moisture sensor-controlled irrigation for reducing N leaching in bermudagrass turf. Agron. J. 76: 964-969. The Nitrate Elimination Co., Inc. 2000. Nitrate: Health risks to consumer. The Nitrate Elimination Co., Inc. Lake Linden, MI. Accessed in November, 2003 at http://www.nitrate.com. Trenholm, L. E., J.L. Cisar, and J.B. Unruh. 2000a. St. Augustinegrass for Florida lawns. Univ. of Fla. Coop.Ext. Serv., ENH 5. Un iv. of Florida, Gainesville, FL. Trenholm, L. E., M.J. Schlossberg, G. Lee, W. Parks, and S.A. Geer. 2000b. An evaluation of multispectral responses on selected turf grass species. Int. J. Remote Sens. 21(4): 709721. Trenholm, L. E., A. E. Dudeck, J. B. Sartain, and J. L. Cisar. 1998. Bermudagrass growth, total nonstructural carbohydrate con centration, and quality as influenced by nitrogen and potassium. Crop Sci. 38:168-174. Trenholm, L. E., R.N. Carrow, and R.R. Dun can. 1999. Relationship of multispectral radiometry data to qualitative data in turfgr ass research. Crop Sci. 39: 763-769. Trenholm, L.E., E.F. Gilman, G.W. Knox, and R.J. Black. 2002. Fertilization and irrigation needs for Florida lawns and landscapes. Univ. of Fla. Coop. Ext. Serv., ENH 860. Univ. of Florida, Gainesville, FL. Trenholm, L. E., J.B. Unruh, and J.L. Cisar. 2003. Watering your Florida lawn. Univ. of Fla. Coop. Ext. Serv., ENH 9. Univ. of Florida, Gainesville, FL. Throssell, C.S., R.N. Carrow, and G.A. Milliken. 1987. Canopy Temperature based irrigation scheduling indices for Kentucky blue grass turf. Crop. Sci. 27: 126-131. Turgeon, A.J. 1991. Turfgrass management. Prentice-Hall, Englewood Cliffs, NJ.

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67 BIOGRAPHICAL SKETCH Shweta Sharma was born in 1982 in Chitwa n, Nepal. She completed her undergraduate from Institute of Agriculture and Animal Sciences Rampur, Nepal. She joined the University of Florida in spring 2007 and gradua ted with M.S. degree in environmental horticulture in 2009. After graduating she continued for doctorate degr ee in Department of Plant medicine at the University of Florida.