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Leaf cuticle characteristics and foliar nutrient uptake by a cool-season and warm-season turfgrass

Dissertation
Author: James Christopher Stiegler
Abstract:
A series of field, greenhouse, growth chamber, and laboratory studies were conducted to increase our understanding of foliar absorption in high-maintenance turfgrasses and evaluate how various seasonal, anatomical and physiological dynamics may affect the permeation process. The following objectives were proposed on creeping bentgrass and hybrid bermudagrass putting green turf: (1) to comprehensively analyze the morphology and chemical make-up of the leaf cuticle; (2) to directly measure the seasonal uptake of foliar-applied nitrogen, applied as 15 N urea, under field conditions; (3) to document the extent of N loss via ammonia volatilization following foliar-applied urea; (4) and to investigate the use of various inorganic and organic sources of N and their effect on foliar N absorption efficiency. Older leaves possessed significantly greater cuticle proper thickness compared to younger leaves. Presence of epicuticular wax crystalline structures highlighted potential impact on absorption efficiency of foliar-applied chemicals and fertilizers. The long-chain primary alcohol (1-hexacosanol) comprised 90 % of creeping bentgrass leaf cuticle wax and variably influenced foliar N absorption efficiency. Foliar uptake of urea-N and absorption into plant tissues occurred rapidly, generally peaking at 4 h after treatment. Foliar absorption of N supplied as urea was affected by month of application and year, ranging variably from 36-69 % for creeping bentgrass and 38-62 % for hybrid bermudagrass and volatile loss of NH 3 -N was negligible (< 3%). Foliar uptake of the various N compounds by creeping bentgrass ranged from 31-56 % of the N applied at 8 h after application. Foliar absorption of KNO3 into aerial plant parts was lower than most of the organic and inorganic sources tested, while many of the compounds supplied N to the plant in similar proportions.

TABLE OF CONTENTS List of Tables xi List of Figures xii Chapter I: Introduction and Literature Review Introduction and Literature Review 2 Literature Cited 13 Chapter II: Leaf Surface Morphology and Cuticle Charicteristics of a Cool-season and Warm- season Putting Green Turfgrass Species: An Electron and Light Microscope Study Abstract 20 Introduction 21 Materials and Methods 23 Results and Discussion 27 Conclusions 32 Literature Cited 34 Chapter III: Direct Measurement of Foliar Absorbed Nitrogen Following Application of Urea to Putting Green Turfgrass Species Abstract 45 Introduction 46 Materials and Methods 48 Results and Discussion 56 Conclusions 61 Literature Cited 63 viii

Chapter IV: Indirect Field-Based Measurement of Ammonia Volatilization Following Foliar Applications of Urea to Putting Green Turf Abstract 73 Introduction 74 Materials and Methods 76 Results and Discussion 81 Conclusions 86 Literature Cited 88 Chapter V: Foliar Absorption of Nitrogen by Creeping Bentgrass Putting Green Turf Utilizing Select 15N-labeled Inorganic and Organic Sources Abstract 98 Introduction 99 Materials and Methods 101 Results and Discussion 109 Conclusions 115 Literature Cited 117 Chapter VI: Leaf Cuticle Wax Amounts and Compositional Analysis of Putting Green Turf: Influence on Foliar N Fertilizer Absorption Efficiency Abstract 123 Introduction 124 Materials and Methods 126 Results and Discussion 131 Conclusions 136 ix

Literature Cited 138 Chapter VII: Conclusions Conclusions 147 Appendix 150 x

LIST OF TABLES Page Chapter III Analysis of variance testing the main effects and their interactions on foliar fertilizer N uptake efficiency when supplied by urea 66 Chapter IV Effect of pH on the equilibrium relationship between ammoniacal-N species in solution 91 Analysis of variance testing the main effects (year, month of application, N rate) and their higher order interactions on NH3 volatilization at 24 h after application of foliar applied urea-N 92 Chapter VI Hexane-extractable cuticular wax loads obtained from representative composite sampling of observational unit area (total of 183.22 cm"2 of turfgrass verdure), as affected by month and year 140 XI

LIST OF FIGURES Figure Page CHAPTER II 2.1 (A and B) SEM micrographs of chemically dehydrated creeping bentgrass leaf tissue specimens (A = 39x magnification); (B = 35Ox magnification). (C and D) SEM micrographs of freeze-dried creeping bentgrass specimens (C = 150x magnification); (D = 350x magnification) 38 2.2 (A and B) SEM micrographs of Perm Al creeping bentgrass specimens showing basic leaf surface cuticle morphology (A = adaxial view at 150x magnification; B = adaxial view at 500x magnification). (C and D) SEM micrographs of Tifeagle bermudagrass specimens showing basic leaf surface cuticle morphology (top = adaxial view at 200x magnification; bottom = abaxial view at 500x magnification) 39 2.3 Effects of 8 h of day or night foliar absorption on 15N-enriched urea fertilizer uptake efficiency by Perm Al creeping bentgrass when spray applied at 0.5 g N m"2. Each bar represents an average from four replicates over two separate treatment dates. Means followed by the same letter are not significantly different using Fisher's protected LSD at a = 0.05 40 2.4 (A) TEM micrograph (13,000x magnification) of Tifeagle bermudagrass showing evidence of an internal cuticle wax layer surrounding guard cells. (B) TEM micrograph (16,000x magnification) showing cuticular ledge connecting guard cells of Tifeagle bermudagrass and enclosing the stomatal aperture. (C and D) SEM micrographs of Perm Al creeping bentgrass (C = adaxial view at 3500x magnification) and Tifeagle bermudagrass (D = adaxial view at 6500x magnification) showing wax-occluded stomatal aperture and presence of crystalline structures arising from the underlying cuticle proper (CP) layer of both species 41 2.5 (A) Light microscopy image of hand sectioned leaf tissue piece taken from Perm Al creeping bentgrass then subjected to methylene blue staining. (B and C) Representative TEM micrographs from Tifeagle bermudagrass sections displaying differences in cuticle proper thickness due to leafage (B = newer leaf at 16,000x magnification; C = older leaf at 16,000x magnification). Abbreviations placed at author-interpreted areas: NU, nucleus; CP, cuticle proper; CL, cuticle layer; CW, cell wall of epidermal cell...42 2.6 Cuticle proper thickness (nm) of Perm Al creeping bentgrass and Tifeagle bermudagrass, as affected by leaf age 43 xn

CHAPTER III 1 Percentage of Arkansas golf course superintendents (n = 31; 2007 survey) indicating their range of foliar fertilization use on putting greens with respect to total annual N inputs 67 2 Percentage of foliar fertilizer N absorption (applied as urea) by Perm Al creeping bentgrass and Tifeagle hybrid bermudagrass as affected by sampling time. Each data point represents a total of 80 observations. (* indicates significant difference at P < 0.05 from previous sampling time) 68 3 Percentage of foliar fertilizer N absorption (applied as urea) by Perm Al creeping bentgrass (n = 160) as affected by N rate. Bars with different letters are significantly different at P < 0.05 69 4 Percentage of foliar fertilizer N absorption (applied as urea) by Tifeagle hybrid bermudagrass as affected by year, month of application, and N rate. Each data point represents a total of 16 observations. LSD bars indicate the unique value given for this three-way interaction and can be used to make comparisons among treatment factors 70 5 Percentage of foliar fertilizer N absorption (applied as urea) by Perm Al creeping bentgrass as affected by year and month of application. Each bar represents a total of 32 observations averaged across N application rates and sampling times. Bars with different letters are significantly different at P<0.05 71 CHAPTER IV 1 Apparatus used for in-field ammonia volatilization estimates 93 2 Ammonia volatilization during 24 h period from a hybrid bermudagrass putting green as affected by the following: (left) foliar urea-N application rate and sampling month; (right) year and sampling month. (LSD bars denote significance at the 0.05 probability level) 94 3 Ammonia volatilization during 24 h period from a creeping bentgrass putting green as affected by foliar urea application rate and sampling month, during 2007 and 2008. (LSD bars denote significance at the 0.05 probability level) 95 4 Tracing the fate of NH3-N over a 24 h period following alkali liberation from a known amount of 15NH4SC>4 solution within enclosed chambers covering creeping bentgrass and hybrid bermudagrass putting green canopies 96 Xl l l

CHAPTER V 1 Chemical structures of the synthetic and natural organic N compounds used in the study: (A) urea, (B) L-glutamic acid, (C) glycine, and (D) L-proline 119 2 Foliar uptake of 15N supplied by six different inorganic or organic N compounds (UR = urea, AS = (NH4)2S04, KN = KN03, GLY = glycine, GLU = L-glutamic acid, PRO = L-proline) sampled from Perm G2 creeping bentgrass at 1 h and 8 h after treatment on (A) 18 September 2008 (B) 14 October 2008. Means followed by the same letter are not significantly different using Fisher's protected LSD at a = 0.05 120 3 Foliar N absorption efficiency by Perm G2 creeping bentgrass following application of six different inorganic or organic N compounds (UR = urea, AS = (NH4)2S04, KN = KNO3, GLY = glycine, GLU - L-glutamic acid, PRO = L-proline) sampled at different time intervals on 14 October 2008. Note the vast differences among the direct (tissue) and indirect (rinsate) methods for quantification. Means followed by the same letter are not significantly different using Fisher's protected LSD at a = 0.05 121 CHAPTER VI 1 Yield (mg) of each successive one minute solvent extraction on composite verdure plugs, establishing the basis of our hexane extraction protocol. Extractions were stopped when the seventh extraction event yielded 1 % of the total accumulated. It was determined that four extractions provided sufficient (90 %) hexane-extractable cuticle wax extraction 141 2 Linear regression analysis examining the relationship between Penn Al creeping bentgrass leaf cuticle wax loads and foliar N fertilizer uptake efficiency determined at 4 h, 8 h, and 24 h after soluble urea treatment, along with an average of all temporal analysis intervals (24 h average) 142 3 Linear regression analysis examining the relationship between Tifeagle hybrid bermudagrass leaf cuticle wax loads and foliar N fertilizer uptake efficiency determined at 4 h, 8 h, and 24 h after soluble urea treatment, along with an average of all temporal analysis intervals (24 h average) 143 4 Representative GC trace showing (top) creeping bentgrass subsample with 1- docosanol (C22 primary alcohol - peak elution at 15.9 min) internal standard added to bulk leaf cuticular wax extract (bottom) external standard mixture of 1-docosanol (C22 primary alcohol - peak elution at 15.9 min) and 1 -hexacosanol (C26 primary alcohol - peak elution at 20.6 min) 144 xiv

6.5 Figure 6.5. Linear regression analysis examining the relationship between Penn Al creeping bentgrass 1-hexacosanol amounts (ng) and foliar N fertilizer uptake efficiency determined at 4 h, 8 h, and 24 h after soluble urea treatment, along with an average of all temporal analysis intervals (24 h average) 145 xv

Chapter I: Introduction and Literature Review 1

Foliar fertilization is a common practice on today's intensively managed golf courses. Its strategic use as a supplement to traditional root-feeding programs has been utilized in turfgrass maintenance for many years, but its widespread popularity and adoption by golf course superintendents has only truly developed over the last 10-15 years. A recent survey of golf course superintendents in Arkansas (31 respondents) indicated that nearly all of those responding are using foliar fertilization on their putting greens and many superintendents apply over half of the total annual nitrogen (N) inputs to greens in this fashion (see Chapter III; Fig. 3.1). Foliar fertilization refers to the process of nutrient uptake through the foliage or other aerial plant parts and is often utilized to deliver nutrients during periods when root uptake may be compromised. There are a host of well-documented chemical and physical inhibitors of turfgrass root growth at the soil level. Improper irrigation frequency or depth of water in the rootzone (Doss et al., 1962; Madison and Hagan, 1962), nutrient deficiencies (Beard, 1973), soil pH issues (Rieke, 1969), soil compaction and/or limited soil oxygen (Waddington and Baker, 1965; Carrow, 1980), supraoptimal air/soil temperatures (Beard and Daniel, 1965; Xu and Huang, 2000), and excessive thatch accumulation (Carrow, 2004a; 2004b) have all been shown to hinder root development. Anything which restricts root growth or function can potentially lead to reduced nutrient uptake, even in a nutrient-rich environment. Applying nutrients directly to plant foliage can effectively bypass any absorption deficiencies associated with roots or soils and adequately supply plant nutrients during critical periods. Foliar fertilization also affords turfgrass managers with increased flexibility, precision, and convenience of application compared to traditional granular fertilizer 2

application methods. The ability to quickly supply plant nutrients, especially nitrogen, in small doses and at more frequent intervals promotes more uniform growth (Bowman, 2003) and color that can lead to enhanced playing conditions, turf performance and aesthetics. In addition, golf course superintendents are generally striving to be better environmental stewards. Use of foliar fertilization methods has been touted as one possible way for turfgrass managers to produce better turf with fewer inputs (Middleton, 2001; Liu etal., 2008). Whether driven by the purported benefits presented above, or simply from recent advances and availability in soluble fertilizer technology, it seems evident that increased reliance upon foliar feeding has become a trend among golf course superintendents. Unfortunately, despite its prevalent use, there is a paucity of scientific research pertaining to foliar absorption of nutrients by turfgrasses. While there continues to be investigations into simple, practical growth and color response from various foliar and liquid-applied fertilizers (Spangenberg et al., 1986; Hardeback et al., 2003; Harrell et al., 2004; Totten et al., 2008), few studies have investigated foliar nutrient uptake dynamics or efficiency and only recently have scientific efforts been put forth to attempt this work in a real-world, field setting (Gaussoin et al., 2009; Henning et al., 2009). The majority of the earlier foliar uptake turfgrass research came from a small group of researchers, looking at nitrogen absorption into cool-season turfgrass leaves grown in controlled, moderate temperature environments (Wesely et al., 1985; Bowman and Paul, 1989; Bowman and Paul, 1990; Bowman and Paul, 1992). Whether using differences between plant tissue Kjeldahl-N before and after application, leaf washing procedures, or 15N direct measurement to 3

determine foliar uptake efficiency, the aforementioned studies have revealed absorption values ranging between 30-60 % of the N applied. While these contributions have been significant, there are clearly many gaps of knowledge that need to be bridged in regard to turfgrass foliar nutritional strategies. Historical investigations dealing with foliar application of nutrients can be traced all the way back to the mid-19th century when iron sprays were used to correct plant chlorosis (Gris, 1844). Over 100 years later, artificial radioisotopes were discovered. While the ability to use these isotopes as tracers had exciting applications to numerous research disciplines, it was not until the early 1950's that scientists began to implement them for studying plant nutrition. More specifically, these compounds opened the door for accurate quantification and transport studies of various foliar-applied nutrients. One such investigation was the classic study of Bukovac and Wittwer (1957), which led to confirmation that most of the essential plant nutrients, including some beneficial elements, are absorbed by foliage to some degree. In order for a foliar fertilizer nutrient to be utilized by the plant for growth and other necessary functioning, it must first diffuse into the leaf before it can reach the cytoplasm of the epidermal cell (Lyshede, 1982; Marschner, 1995). During this process it must traverse through several different distinct layers which are schematically represented in Jetter et al. (2000): epicuticular wax layer, cuticle proper, cutinized layer between the epidermal cell wall and the cuticle proper, and finally the pectin and cellulose layer of the epidermal cell wall. Once penetration into the cytoplasm has been achieved, the absorption of that particular nutrient can be considered a success because at this point the mechanism of uptake and utilization within the plant resembles that of the 4

typical root absorption pathway. The leaf cuticle is the primary barrier that must be overcome (Kirkwood, 1999) when attempting to drive nutrients or agrochemicals into the plant via leaf tissue absorption. Lipophilic in nature and comprised of cutin and associated waxes (Schonherr and Riederer, 1989), the cuticle serves as a natural protection mechanism limiting evaporative water loss, leaching of nutrients via rain or irrigation, insect and fungal attack, and foreign chemical penetration (Oosterhuis et al., 1991a). In addition to the cuticle proper, there is another hydrophobic covering of wax spicules overlying the cuticular membrane layer. These epicuticular waxes have been described as a plant acclimation feature in response to an earlier drought stress for use in a subsequent water stress event (Bondada and Oosterhuis, 2000). When viewed under an electron microscope, Bondada and Oosterhuis (2000) described the epicuticular wax structure of cotton {Gossypium hirsutum L.) leaf as intricate ridges or striations following the pattern of the underlying epidermal cell wall. However, previous scanning electron microscope (SEM) investigations of various plant species revealed a fascinating diversity in the shape, size, and arrangement of epicuticular waxes (Jeffree, 1986; Barthlott et al., 1998). We know of no similar SEM observations that have been made to detail the epicuticular surface waxes on leaves of turfgrass species commonly utilized on golf course putting greens. When viewed with the naked eye, these same leaf surface morphological features have also been reported in scientific literature as being responsible for imparting a bluish-white cast or coating of glaucousness (Jeffree, 1996). Kirkwood (1999) proposed that these epicuticular waxes were a major rate-limiting barrier to solute penetration. 5

From a plant management perspective, the leaf cuticle and, more specifically, the epicuticular surface wax/film layer is the initial point of contact for foliar-applied chemicals and fertilizers and its structure and chemical properties have a significant effect on the absorption of sprayed solutions. Logically, any attempt at increasing the efficiency of foliar fertilization should begin with a detailed understanding of the cuticular surface and its effects on nutrient uptake. The use of various analytical microscopes to study anatomy of turfgrass leaf surfaces has been limited to date and deserves more attention (Shearman and Beard, 1972; Johnson and Brown, 1972; Akin and Burdick, 1973; Karnok and Beard, 1985; Marcum, 1999; Williams and Harrell, 2004). Plant physiologists have spent considerable time investigating the movement of solutes through the leaf, as penetration of solutes is important for pesticide efficacy, nutrient studies, and water movement in and out of the leaf. Originally it was proposed that penetration of polar substances occurred in hydrophilic micro-pores protruding through epidermal cell walls, called ectodesmata (Franke, 1961). However, it is now more widely accepted that cuticles are traversed by numerous hydrophilic pathways permeable to water and small solute molecules (Marschner, 1995). These pores have a diameter of < 1 nanometer, with a density of about 10 pores cm" (Schonherr, 1976), and are lined with negative charges increasing in density toward the inside, facilitating movement of cations (Tyree et al., 1990). Collectively, penetration of foliar sprays of nutrients through the plant cuticle is a complex movement process governed by nutrient concentration, molecular size, organic or inorganic form, time as a solution on the leaf cuticle, and charge density across the cuticle. 6

The effectiveness of foliar fertilization is also confounded by influences from the environment, as well as the health and vigor of the plants receiving the application. Studies in cotton have demonstrated that leafage (Bondada et al., 1997) and water (deficit) stress (Oosterhuis et al. 1991a; Oosterhuis et al. 1991b) cause dynamic changes in cuticle thickness and increases in epicuticular waxes in cotton. Similar effects of water (deficit) stress on leaf cuticle characteristics have more recently been shown in other crop species (Cameron et al., 2006; Kim et al., 2007a; Kim et al., 2007b). In a golf course putting green system, irrigation is almost always present and would likely prevent the potential drought effects observed in dryland agricultural systems. However, turfgrasses, especially cool-season species, can exhibit temporary heat and water deficit stress during hot summer days between irrigation events. Hence, it seems plausible that turfgrasses could exhibit changes in cuticle structure similar to those documented in other crops (Leece, 1976; Johnson, et al. 1983; Oosterhuis et al., 1991a; Oosterhuis et al., 1991b; Bondada et al., 1996). Unfortunately, there have been no studies that have investigated seasonal or environmental effects on the turfgrass cuticle. Foliar nutrition is particularly useful and effective when implemented on the predominant turfgrass species grown for golf course greens, creeping bentgrass (Agrostis stolonifera var. palustris (Huds.) Farw.). Cool-season grasses maintain their maximum growth rate at temperatures ranging from 15 to 24° C for shoots and 10 to 18° C for roots (Beard, 1973). During the summer months, especially in USD A Plant Zones 7-9, these optimum soil and air temperature ranges are often exceeded. Subsequently, creeping bentgrass is only marginally adapted to a large area of the United States where it is used extensively as a putting green turf. Automated irrigation systems to replace ET deficits, 7

syringing for evaporative cooling in isolated dry spots and/or hand watering throughout the summer months are routine maintenance practices crucial to its persistence in these areas. When other stress factors such as high foot traffic, disease and insect pressure, and low mowing heights are added on top of the previously mentioned metabolic energy shortage associated with supraoptimal temperatures > 30° C (Huang, 2003), it is not difficult to imagine a putting green turfgrass system that is compromised in terms of root uptake of essential plant nutrients. In fact, it is well documented that roots of creeping bentgrass during the summer actually shorten, decline, or slough off to varying degrees, dependent on cultivar (Carrow, 1996; Wang et al., 1998; Liu and Huang, 2001; Huang and Liu, 2003) Today's turfgrass practitioners are also expanding the use of foliar fertilization beyond its most prominent use on creeping bentgrass putting greens. In many situations, warm-season (C4) turfgrasses such as bermudagrass {Cynodon dactylon (L.) Pers. and zoysiagrass (Zoysiajaponica) are also receiving precision applications of foliar sprayed products. There is no known scientific research that has been done on direct measurement of foliar N uptake in the various warm-season turfs typically used on golf courses. There are obviously some distinct differences between the leaves of turfgrass species, as well as the standard management practices applied to them, when compared to the various agricultural, horticultural, and forest species which have been commonly used in select foliar nutrient absorption studies to date (Volk and McAuliffe, 1954; Cain, 1956; Impey et al., 1960; Vasilas et al., 1980; Thorn et al., 1981; Karasuyama et al., 1985; Reickenberg and Pritts, 1996; Bondada et al., 1997; Bondada et al., 2001). Due to the 8

extreme density of the plants in a high-maintenance turfgrass stand, the first point of contact for a sprayed solution with a turfgrass leaf can be either the adaxial or abaxial side of the leaves, dependent upon individual leaf orientation. As reported in Liu and Hull (2009), there is evidence from research performed in other crop species that foliar uptake efficiency may be affected due to positioning of spray droplets on one side of the leaf or the other. However, in comparison to crop species, the ultra-small leaf area per plant exhibited by turfgrass species and the millions of plants that receive an over-the- canopy spray, calls into question the relative importance of leaf orientation on foliar absorption by high maintenance turfgrasses. Turfgrasses appear to be exceptionally adapted to foliar uptake due to their dynamic nature of leaf growth. While the crowns and certain parts of the verdure remain in place once established, the cultural practice of mowing creates a constant regeneration of new, young leaves. In studies of foliar uptake by cotton and citrus leaves, absorption of foliar products and defoliants were found to be reduced as leaves aged along with concomitant increases in leaf cuticular waxes (Oosterhuis et al., 1991b; Bondada et al., 1997; Bondada et al., 2001). This effect of leaf ontogeny would suggest that leaves of turfgrass systems may be easier to penetrate with foliar sprays, as leaves are not determinate and do not age in the same manner as many agricultural or horticultural crops. However, there have been no studies that have looked at cuticle characteristics or foliar uptake of turfgrass leaves, as affected by leafage or environmental stress. Inherent characteristics of foliar fertilization, such as soluble urea treatments made directly over the top of the plant canopy with low carrier rates, should negate the possibility of denitrification and/or leaching losses, as these are strictly soil/rootzone 9

phenomena. Therefore, ammonia volatilization should be the most important N loss mechanism associated with typical N foliar fertilizer practices (McCarty, 2005). Urea and/or urea-ammonium nitrate (UAN) are common sources of nitrogen (N) included in foliar fertilizer products and, when applied to the plant surface, there is risk of considerable N loss to the atmosphere as ammonia (NH3) with these N sources. The presence of the urease enzyme both on the leaf surface, and within most plants (Witte et al., 2002), underlies ammonia volatilization N loss potential. Urease catalyzes the hydrolysis of urea into ammonia (NH3) and carbon dioxide. Under certain conditions, the NH3 then undergoes protonation (NH3 + H+ «-• NtL^). While this is a highly important process for plants to assimilate urea-N into a plant available form of ammonium (NH4+), NH3 gas may also escape from the system (volatilize) during the process. Factors known to favor NH3 volatilization include increased soil pH, along with increased surface temperature, moisture or relative humidity, and wind speed (Joo, 1987; Knight et al., 2007). Atmospheric losses of N as NH3 gas, following the application of N fertilizers, have been well studied in agricultural research, while, in comparison, this same N loss pathway from turfgrass stands has received considerably less research attention. Several investigations into NH3 volatilization from turfgrass stands have been reported, as shown in a monograph review by Turner and Hummel (1992). A compilation of results obtained from NH3 volatilization from turfgrass stands following N fertilizer application have varied widely from near 0 % to greater than 60 % volatile loss (Knight et al., 2007). Each of these studies implemented different collection methodologies, environmental and soil conditions, methods of application, N source, and management associated with the 10

Full document contains 172 pages
Abstract: A series of field, greenhouse, growth chamber, and laboratory studies were conducted to increase our understanding of foliar absorption in high-maintenance turfgrasses and evaluate how various seasonal, anatomical and physiological dynamics may affect the permeation process. The following objectives were proposed on creeping bentgrass and hybrid bermudagrass putting green turf: (1) to comprehensively analyze the morphology and chemical make-up of the leaf cuticle; (2) to directly measure the seasonal uptake of foliar-applied nitrogen, applied as 15 N urea, under field conditions; (3) to document the extent of N loss via ammonia volatilization following foliar-applied urea; (4) and to investigate the use of various inorganic and organic sources of N and their effect on foliar N absorption efficiency. Older leaves possessed significantly greater cuticle proper thickness compared to younger leaves. Presence of epicuticular wax crystalline structures highlighted potential impact on absorption efficiency of foliar-applied chemicals and fertilizers. The long-chain primary alcohol (1-hexacosanol) comprised 90 % of creeping bentgrass leaf cuticle wax and variably influenced foliar N absorption efficiency. Foliar uptake of urea-N and absorption into plant tissues occurred rapidly, generally peaking at 4 h after treatment. Foliar absorption of N supplied as urea was affected by month of application and year, ranging variably from 36-69 % for creeping bentgrass and 38-62 % for hybrid bermudagrass and volatile loss of NH 3 -N was negligible (< 3%). Foliar uptake of the various N compounds by creeping bentgrass ranged from 31-56 % of the N applied at 8 h after application. Foliar absorption of KNO3 into aerial plant parts was lower than most of the organic and inorganic sources tested, while many of the compounds supplied N to the plant in similar proportions.