Citation
Effects of Polymer-Coated Urea and Irrigation Scheduling on N Leaching and Yield for a Potato-Millet-Sweet Corn-Cereal Rye Cropping Sequence

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Title:
Effects of Polymer-Coated Urea and Irrigation Scheduling on N Leaching and Yield for a Potato-Millet-Sweet Corn-Cereal Rye Cropping Sequence
Creator:
Desormeaux, Amanda
Place of Publication:
[Gainesville, Fla.]
Florida
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University of Florida
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english
Physical Description:
1 online resource (110 p.)

Thesis/Dissertation Information

Degree:
Master's ( M.S.)
Degree Grantor:
University of Florida
Degree Disciplines:
Interdisciplinary Ecology
Committee Chair:
HOCHMUTH,GEORGE J,II
Committee Co-Chair:
BENNETT,JERRY M
Committee Members:
ROWLAND,DIANE L
Graduation Date:
8/9/2014

Subjects

Subjects / Keywords:
Agricultural seasons ( jstor )
Corn ( jstor )
Crops ( jstor )
Fertilizers ( jstor )
Irrigation ( jstor )
Leaching ( jstor )
Nitrogen ( jstor )
Planting ( jstor )
Rain ( jstor )
Soils ( jstor )
Interdisciplinary Ecology -- Dissertations, Academic -- UF
budget -- controlled-release -- corn -- cycling -- irrigation -- leaching -- management -- nitrate -- nitrogen -- polymer-coated -- potato -- sweet -- urea
City of Gainesville ( local )
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bibliography ( marcgt )
theses ( marcgt )
government publication (state, provincial, terriorial, dependent) ( marcgt )
born-digital ( sobekcm )
Electronic Thesis or Dissertation
Interdisciplinary Ecology thesis, M.S.

Notes

Abstract:
Potato (Solanum tuberosum L.) and sweet corn (Zea mays var. rugosa) are two economically important crops grown in a typical N Florida cropping sequence, but the sandy soils characteristic of this area make these crops at-risk to nitrate leaching. The objectives of this project were to determine the effects of irrigation management and fertilization with polymer-coated urea (PCU) on the fates and flows of nitrogen for a potato-millet-sweet corn-cereal rye cropping sequence. Treatments consisted of three N management programs (urea-ammonium nitrate (UAN) applied at the rate of 224 kg ha-1 N, and polymer-coated urea applied at the rates of 224 kg ha-1 N or 196 kg ha-1 N) and three sprinkler irrigation management treatments (maintenance of field capacity at or above 100% with daily sprinkler irrigation replacing 100%ETc and 125% ETc, and maintenance of soil moisture at 75% field capacity), which were arranged factorially in a completely randomized design with three replicates. PCU196 was more efficient for potato production, resulting in significantly less leaching than current grower practices (UAN224) without negative impacts on yield. However, PCU196 resulted in lower yields and higher fertilizer N costs during the sweet corn season than UAN224 or PCU224, so PCU196 was not a viable fertilizer alternative for late-season sweet corn production. Irrigation treatments had no effect on nitrate-N leaching during either growing season. Maintaining the soil moisture at 75% field capacity instead of 100% resulted in water savings that translate into savings on irrigation costs without any yield reductions for either crop. ( en )
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.
Thesis:
Thesis (M.S.)--University of Florida, 2014.
Local:
Adviser: HOCHMUTH,GEORGE J,II.
Local:
Co-adviser: BENNETT,JERRY M.
Electronic Access:
RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2016-08-31
Statement of Responsibility:
by Amanda Desormeaux.

Record Information

Source Institution:
UFRGP
Rights Management:
Applicable rights reserved.
Embargo Date:
8/31/2016
Classification:
LD1780 2014 ( lcc )

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EFFECTS OF POLYMER COATED UREA AND IRRIGATION SCHEDULING ON N LEACHING AND YIELD FOR A POTATO MILLET SWEET CORN CEREAL RYE CROPPING SEQUENCE By AMANDA DESORMEAUX A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2014

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© 2014 Amanda Desormeaux

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To my mother

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4 ACKNOWLEDGMENTS I would like to thank my a dvisor and mentor, Dr. George Hochmuth, for giving me the opportunity to complete this research at the University of Florida. I would also like to thank my committee members, Dr. Jerry Bennett and Dr. Diane Rowland , for their guidance and expertise in the classroom and throughout my research process . I would like to thank Dr. John Erickson for serving as a substitute member of my committee and for enhancing my understanding of crop nutrition. I have been extremely lucky to work with such skilled and dedicat ed professors that have taught me so much during my two years at the University of Florida. I would like to thank Dawn Lucas , Connie Johnson , and Andressa Freitas for all of their help with field and lab work, as well as Annie Couch, Rajendra Gautam , and Rishi Prasad for th eir help during plant sampling. I would like to thank my family for their continued support throughout this program , especially my mother for her love and constant encouragement . I would like to thank all of my new friends in Gainesville for their love and support during my time here. Finally, I would like to thank George Johnson for sparking my interest in soil science and encouraging me to apply to this program.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .............. 4 LIST OF TABLES ................................ ................................ ................................ ......................... 7 LIST OF FIGURES ................................ ................................ ................................ ..................... 10 LIST OF ABBREVIATIONS ................................ ................................ ................................ ...... 11 ABSTRACT ................................ ................................ ................................ ................................ . 12 CHAPTER 1 LITERATURE REVIEW ................................ ................................ ................................ ...... 14 Introduction ................................ ................................ ................................ .......................... 14 Nitrate Leaching and D ownstream Effects ................................ ................................ ...... 14 Regulatory Framework ................................ ................................ ................................ ....... 16 Nutrient Management BMPs ................................ ................................ ............................. 17 Irrigation Management ................................ ................................ ................................ ....... 20 Joint Management ................................ ................................ ................................ .............. 23 Social Barriers to Grower Adoption ................................ ................................ .................. 23 Goals and Objectives ................................ ................................ ................................ ......... 27 2 MATERIALS AND METHODS ................................ ................................ .......................... 29 Site Description ................................ ................................ ................................ ................... 29 Treatments ................................ ................................ ................................ ........................... 29 Lysimeter Design and Sampling Methods ................................ ................................ ...... 32 Testing the Accuracy of the Lysimeter Leachate Collection System .......................... 33 Cropping Sequence ................................ ................................ ................................ ............ 36 Potato ................................ ................................ ..... 36 Millet ................................ ................................ ................. 39 Sweet Corn ................................ ........................... 39 ................................ ............................. 41 Partial N Budget ................................ ................................ ................................ .................. 42 Statistical Analysis ................................ ................................ ................................ .............. 42 3 RESULTS AND DISCUSSION ................................ ................................ ......................... 46 ................................ ................................ ............ 46 Yield ................................ ................................ ................................ ............................... 47 Leachate ................................ ................................ ................................ ........................ 48 Soil ................................ ................................ ................................ ................................ . 50

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6 Crop Biomass and N Uptake ................................ ................................ ..................... 51 Leaf N Concentration ................................ ................................ ................................ .. 54 Partial N Budget ................................ ................................ ................................ ........... 55 ................................ ................................ ........................ 57 Leachate ................................ ................................ ................................ ........................ 57 Soil ................................ ................................ ................................ ................................ . 58 Biomass and N Uptake ................................ ................................ ............................... 58 Partial N Budget ................................ ................................ ................................ ........... 59 ................................ ................................ ... 60 Yield and Quality ................................ ................................ ................................ .......... 60 Leachate ................................ ................................ ................................ ........................ 61 Soil ................................ ................................ ................................ ................................ . 63 Crop Biomass and N Uptake ................................ ................................ ..................... 63 Leaf N Concentration ................................ ................................ ................................ .. 65 Partial N Budget ................................ ................................ ................................ ........... 66 ................................ ................................ .... 67 Leachate ................................ ................................ ................................ ........................ 68 Soil ................................ ................................ ................................ ................................ . 68 Biomass and N Uptake ................................ ................................ ............................... 68 Partial N Budget ................................ ................................ ................................ ........... 69 Total Season ................................ ................................ ................................ ........................ 69 Leachate ................................ ................................ ................................ ........................ 70 Par tial N Budget ................................ ................................ ................................ ........... 71 Cost Analysis ................................ ................................ ................................ ................ 72 4 CONCLUSIONS ................................ ................................ ................................ .................. 92 Future Resear ch ................................ ................................ ................................ .................. 93 APPENDIX: ANOVA TABLES ................................ ................................ ................................ . 95 LIST OF REFERENCES ................................ ................................ ................................ ........... 99 BIOGRAPH ICAL SKETCH ................................ ................................ ................................ ..... 110

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7 LIST OF TABLES Table page 2 1 Lysimeter sampling dates. ................................ ................................ ............................ 44 2 2 Initia l chemical properties of top 20 cm of soil. ................................ .......................... 44 2 3 UAN224 side dress schedule for sweet corn. ................................ ........................... 44 3 1 Irrigation treatment main eff ects on soil moisture tension averaged over the potato season. ................................ ................................ ................................ ................ 74 3 2 Irrigation and nitrogen fertilizer main effects on total yield, marketable yield, size A4 and B tubers, and tuber quality. ................................ ................................ ..... 74 3 3 Total leached N load for potato season. ................................ ................................ ..... 74 3 4 N main effects on leached N load from 15 March and 12 April samples. ............. 75 3 5 Interaction effects for 24 April and 23 May leached nitrate N loads. ..................... 75 3 6 Soil mineral N content as affected by N fertilizer tre atment for all potato season sampling dates. ................................ ................................ ................................ . 76 3 7 Treatment main effects on end of season plant dry biomass partitioning. ........... 76 3 8 Main effects for irrigation and N fertilizer treatments on whole plant N content at the end of the season on 17 May. ................................ ................................ ........... 77 3 9 N main effects on potato fertilizer N use efficiency. ................................ .................. 77 3 10 Dried potato whole leaf total Kjeldahl nitrogen concentration by sampling date. ................................ ................................ ................................ ................................ .. 77 3 11 N main effects on potato petiole sap NO 3 N by sa mpling date. ............................. 78 3 12 Potato season unaccounted for N. ................................ ................................ .............. 78 3 13 Main effects for total millet/crabgrass leached N load. ................................ ............. 78 3 14 Main effects on millet/crabgrass cover crop end of season soil N. ........................ 79 3 15 Main effects for total millet/crabgrass N uptake. ................................ ....................... 79 3 16 Main effects for dry plant biomass for the millet cover crop. ................................ ... 80 3 17 Millet/crabgrass cover crop unaccounted for N. ................................ ........................ 80

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8 3 18 Average soil moisture tension for sweet corn soil by irrigation treatment. ............ 80 3 19 Main effects of irrigation and N fertilization on swee t corn yield. ............................ 81 3 20 Main effects of irrigation and fertilization on sweet corn ear quality measurements. ................................ ................................ ................................ ............... 81 3 21 Treatment main effects on seasonal leached N load for sweet corn. .................... 82 3 22 N fertilizer treatment main effects on leached N for 27 September lysimeter sample. ................................ ................................ ................................ ............................. 82 3 23 Main effects of N fertilization on soil inorganic N content over the sweet corn season. ................................ ................................ ................................ ............................. 82 3 24 Irrigation and N treatment main effects on total season sweet corn dry plant biomass. ................................ ................................ ................................ ........................... 83 3 25 Seasonal total plant N uptake and stover, ear, and root N uptake. ....................... 83 3 26 Irrigation and N treatment main effect s on sweet corn FNUE. ............................... 83 3 27 Treatment interactions for sweet corn leaf total Kjeldahl nitrogen concentration 27 DAP. ................................ ................................ ................................ ... 84 3 28 Swe et corn leaf total Kjeldahl nitrogen by sampling date. ................................ ....... 84 3 29 Main effects on sweet corn unaccounted for N. ................................ ........................ 85 3 30 Final soil in organic N content during the cereal rye cover crop period. ................. 85 3 31 Main effects on cereal rye whole plant, shoot, and root N uptake. ........................ 85 3 32 Main effects on cereal rye unaccounted for N budget. ................................ ............ 86 3 33 Main effects on unaccounted for N over the potato millet sweet corn cereal rye cropping sequence. ................................ ................................ ................................ . 86 3 34 Potato fertilizer program costs. ................................ ................................ .................... 86 3 35 Sweet corn fertilizer program costs. ................................ ................................ ............ 87 A 1 ANOVA table for the effect of sample date on NO 3 N concentration of leachate in the lysimeter reservoir. ................................ ................................ .............. 95 A 2 ANOVA table for the effects of drainage through the lysimeter basin and experi ment run on leachate NO 3 N concentration. ................................ ................... 95 A 3 ANOVA table for potato season tensiometer readings. ................................ ........... 95

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9 A 4 ANOVA table for market able tuber yield. ................................ ................................ ... 95 A 5 ANOVA table for total tuber yield. ................................ ................................ ................ 96 A 6 ANOVA table for potato quality. ................................ ................................ ................... 96 A 7 ANOVA table for total season leached N load for potato season. ......................... 96 A 8 ANOVA table for end of season soil N. ................................ ................................ ...... 96 A 9 ANOVA table for final potato root biomass. ................................ ............................... 97 A 10 ANOVA table for final potato shoot biomass. ................................ ............................ 97 A 11 ANO VA table for final potato tuber biomass. ................................ ............................. 97 A 12 ANOVA table for end of season whole plant N uptake. ................................ ........... 97 A 13 ANOVA table for total leached N load for the millet cover crop. ............................. 98 A 14 ANOVA table for cumulative sweet corn leached N load. ................................ ....... 98 A 15 ANOVA table for c umulative leached N during rye cover crop. .............................. 98 A 16 ANOVA table for cumulative leached N over all crops. ................................ ............ 98

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10 LIST OF FIGURES Figure page 2 1 Sections of the field sampled for initial Mehlich 1 soil testing (see Table 2 2 for results of soil testing). ................................ ................................ .............................. 4 5 3 1 Cumulative irrigation , ET c , rainfall, and historic rainfall over the potato season. ................................ ................................ ................................ ............................. 87 3 2 Rainfall over the potato season at Citra, FL. ................................ ............................. 87 3 3 N main effects on leached N load and cumulative rainfall from previous sampling date. ................................ ................................ ................................ ................. 88 3 4 N main effects on potato dry plant biomass accumulation. ................................ ..... 88 3 5 N main effects on potato whole plant N uptake. ................................ ....................... 89 3 6 Cumulative irrigation by treatment, ET c , rainfall, and historic rainfall during sweet corn season. ................................ ................................ ................................ ........ 89 3 7 Rainfall over the sweet corn season at Citra, FL. ................................ ..................... 90 3 8 N main effects on sweet corn season leached N load and cumulative rainfall from previo us sampling date. ................................ ................................ ....................... 90 3 9 N main effects on sweet corn dry matter accumulation over the season. ............. 91 3 10 N main effects on total pla nt N uptake over the sweet corn season. ..................... 91 3 11 Total inorganic leached N load, February 2013 February 2014. ............................ 91

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11 LIST OF ABBREVIATIONS BMP Best Management Prac tices CRF Controlled Release Fertilizer DAP Days After Planting ESN Environmentally Smart Nitrogen FNUE Fertilizer Nitrogen Use Efficiency N Nitrogen PCU Polymer Coated Urea PSREU University of Florida Plant Science Research and Education Unit PVC Polyvinyl Chloride TKN Total Kjeldahl Nitrogen UAN Urea ammonium nitrate UF/IFAS Sciences

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1 2 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science EFFECTS OF POLYMER COATED UREA AND IRRIGATION SCHEDULING ON N LEACHING AND YIELD FOR A POTATO MILLET SWEET CORN CEREAL RYE CROPPING SEQUENCE By Amanda Desormeaux August 201 4 Chair: George Hochmuth Major: Interdisciplinary Ecology Potato ( Solanum tuberosum L. ) and sweet corn ( Zea mays var. rugosa ) are two economically important crops grown in a typical N Florida cropping sequence, but the sandy soils characteristic of this area make these crops at risk to nitrate leaching. The objectives of this project were to determine the effects of irrigation management and fertilization with polymer coated urea (PCU) on the fates and flows of nitrogen for a potato millet sweet corn cere al rye cropping sequence . Treatments consisted of three N management programs (urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N, and polymer coated urea applied at the rates of 224 kg ha 1 N or 196 kg ha 1 N) and three sprinkler irrigation management treatments (maintenance of field capacity at or above 100% with daily sprinkler irrigation replacing 100%ET c and 125% ET c , and maintenance of soil moisture at 75% field capacity), which were arranged factorially in a completely randomized design with three replicates . PCU196 was more efficient for potato production, resulting in significantly less leaching than current grower practices (UAN224) without negative impacts on yield. However, PCU196 resulted in lower yields and higher fertilizer N co sts during the sweet

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13 corn season than UAN224 or PCU224 , so PCU196 was not a viable fertilizer alternative for late season sweet corn production . Irrigation treatments had no effect on nitrate N leaching during either growing season . Maintaining the soil mo isture at 75% field capacity instead of 100% resulted in water savings that translate into savings on irrigation costs without any yield reductions for either crop.

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14 CHAPTER 1 LITERATURE REVIEW Introduction Global population is expected to reach over 9 b illion by 2050, creating the challenge for agriculture to double global production to meet projected food and fiber demands (Tilman et al., 2011 ) . Sustainable i ntensification of current production systems has been argued as a strategy to meet future yield increases within an environmentally sustainable context (Cassman et al., 1999; Foley et al., 2011; Godfray and Garnett, 2014 ; Tilman et al., 2011) . C losing yield gaps in low yielding producti on systems and maintaining high yields in current intensive produ ction systems are necessary, which will require a continued reliance on inorganic nitrogen (N) sources (Davidson et al., 2012; Sutton et al., 2013; Tenkorang and Lowenberg De Boer, 2009). However, N loss from agricultural land is the largest pollution thre at to surface water and groundwater (Billen et al., 2013), impacting water quality and ecosystem health (Sutton et al., 2011; Vitousek et al., 1997). It is therefore critical to investigate site specific management practices that allow for environmentally sustainable maintenance of high yielding agriculture by increasing N use efficiency in crop production (Billen et al., 2013; Galloway et al., 2008; Sutton et al., 2013). Nitrate Leaching and Downstream Effects Fertilizer application is a major source of N in agricultural systems and is typically applied in the form of urea or various ammonium N forms (FAO, 201 3) ; urea and ammonium N forms are rapidly transformed to nitrate in coarse textured soils, but nitrate ions are not retained on the soil cation exchan ge sites because of their negative charge. Nitrate is therefore extremely mobile in the soil and is subject to leaching when

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15 rainfall or irrigation is in excess of the water holding capacity of the soil . N itrate leaching is most pronounced on sandy soils a nd can be a significant pathway of N loss (Bergstrom and Johansson, 1991; Gaines and Gaines, 1994; Lind et al., 1995; Sogbedji e t al. , 2000; van Es et al., 2006 ). Agriculture is considered a major non point source of N (Katz, 2004 ; Livingston Way, 2001), which can have many negative impacts on human and ecosystem health. High nitrate concentrations in drinking water can increase the risk of certain cancers (DeRoos et al., 2003; Wolfe and Patz, 2002 ; Weyer et al., 2001 ) and can resu lt in the irreversible oxidation of hemoglobin to methemoglobin in infants, which prevents the transport of oxygen in the blood (Craun et al., 1981; Knobeloch et al., 2000) . Methemoglobinemia has also been demonstrated in aquatic animals subject to high ni trate concentrations (Jensen, 2003). Increases in surface water nitrate concentrations have been linked to nitrate toxicity in sensitive aquatic animals, resulting in marked changes in aquatic species composition and function ( Camargo et al., 2005 ; Camargo and Alonso, 2006; Vitousek et al., 1997 ). In addition, increases in N loading in coastal, marine, and estuarine systems can result in algae blooms and toxic Pfiesteria outbreaks ( Paerl, 2002 ; Smith et al., 1999 ; Anderson et al., 2002 ), which have negative economic impacts on commercial fisheries, recreation , and tourism (Hoagland and Scatasta, 2006). The negative impacts on human and ecosystem health associated with excessive N loading into aquatic systems emphasize the importance of monitoring N concentr ations in both surface and groundwater. Section 303(d) of the Federal Clean Water Act (2002 ) requires every state to assess the quality of water resources, as well

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16 as maintain lists of impaired water bodies. To date, over 90% of assessed water bodies in Fl orida have been declared impaired and over 50% of these impaired water bodies are the result of excess nutrient concentrations (FDEP, 2012 ) . Nitrate concentrations have continued to increase over the past 40 years ; this is con cerning because and n itrate can persist in groundwater for decades (Katz, 2004) . This prolonged persistence of nitrates in the groundwater increases the response time of groundwater quality to reductions in N leaching and can impact both public health and ecosystem services for decades after the initial contamination. The long term impact of nitrate contamination in water resources and the direct and indirect consequences of increasing nitrat e concentrations on human health and aquatic ecosystems substantiate the need for projects that investigate strategies to reduce N losses from non point agricultural sources. Regulatory Framework The Federal Clean Water Act ( 3 U.S.C. § 1251 1376, 200 2) wa s enacted to quality and implement restoration strategies for impaired water bodies. Total maximum daily loads (TMDLs) are restoration targets that quantify the maximu m amount of a pollutant that can safely enter a water body and be assimilated, without exceeding the water quality standards set by the state and are developed to protect the designated use of the water body . W atersheds that contain impaired water bodies r equire the development of Basin Management Action Plans (BMAPs), which are plans to restore impaired waters and reduce nutrient loads to below the established TMDL. These BMAPs include best management practices (BMPs) for agricultural operations , which

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17 are science based practices that aim to reduce non point nutrient loading. While BMPs are constantly being developed and tested to refine nutrient and irrigation management on farms, the formation of TMDL numeric nutrient criteria and the development of BMAPs for impaired waters are creating even more pressure for growers to reduce nitrate loss to comply with these regulatory standards. While the adoption of BMPs is voluntary, growers who refuse to implement BMPs must drill wells and monitor water quality to p rove their practices are not impacting water quality . G rowers who voluntarily implement BMPs obtain a pr standards , creating an incentive for the voluntary adoption of BMPs. Nutrient Management BMPs Best management practices (BMPs) are scientifically validated, field tested agricultural practices that increase the efficiency , productivity, and sustainability of agricultural production (Griffith and Murphy, 1991) , allowing Florida producers to reduce N loa ds and maintain productivity (FDACS, n.d. ) . BMPs are derived from field research and communicated to the agricultural community in the form of extension recommendations , which are both site and crop specific. UF/IFAS E xtension Service provides nutrient man agement recommendations for the crops in the state of Florida . Potato ( Solanum tuberosum L.) and sweet corn ( Zea mays var. rugosa ) are two principal crops grown in a typical cropping sequence in north Florida, representing 35% of total planted area ( 35,170 hectares ) and 17% ($219 million) of total crop value for Florida vege t able s, watermelon, pot atoes and berries (USDA, 2009 ). These two crops and the current UF/IFAS recommended N rates are 224 k g ha 1 for both crops (Ozores Hampton et al., 2011; Zotarelli et al., 2011 ). The large N applications necessary for the production of potato

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18 and sweet corn paired with the combined 35,170 planted hectares make the development and adoption of BMPs critical for reducing agricultural N loading by keeping N in the root zone. Nutrient management refers to the efficient and appropriate use of nutrients in agricultural production and there are many BMPs related to managing nutrients on the farm . T he ( Roberts, 2007 ) is a framework that emphasizes the four key components of BMPs for N management : right rate, right time, right place, and right source. Early research focused on refining fertilizer recommendations to allow growers to reac h optimal potato and sweet corn yields without applying N in excess (Hochmuth et al. , 1992 ; Hochmuth et al., 1993; Locascio and Hensel, 1990 ; Patel et al. , 1988 ; Rudert and Locascio , 1979 ; White et al. , 1996; Yuan et al ., 1985). Recommended fertilizer rate s for optimal yields have continued to change over time, but current recommended N rates for both potato and sweet corn are 224 kg ha 1 N ( Ozores Hampton et al., 2012; Zotarelli et al., 2012 ). In addition to rate, research has shown the importance of appli cation timing on both yield and N loss. Munoz Arb oleda et al. (2008) concluded that pre plant N application led to increased N leaching and research has shown that delaying N application until potato emergence can significantly reduce early season N loss w ithout reducing potato yield (Hochmuth and Jones, 2004). Rather than applying all N at emergence, split application of soluble N has shown to further reduce N loss in both potato and sweet corn production (Elkashif et al., 1983 ; Hochmuth et al., 1992; Pate l et al., 1988 ; Robertson, 196 2 ) and increase potato N utilization (Errebhi et al., 1998; Vos,

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19 1999) compared with a single N application. While delayed and split applications of N can minimize vulnerability to N loss from leaching rains by minim izing the window that soluble N is available in the soil, leaching rains still have the potential to leach N from the soil after fertilizer application. Fertilizer placement is another key component of N management; appropriate fertilizer placement ensures maximum crop uptake and protects from leaching losses by placing fertilizer where the roots will be able to access the applied nutrients. Banding fertilizer along the crop rows increase d potato tuber yield compared with broadcast application (Khan et al., 2007; Ne ubaur, 1993 ; Rahman et al., 2004; Westermann and Sojka, 2006) . N source is the final component of the nutrient stewardship framework. Soluble sources of N are the dominant fertilizers used for potato and sweet corn production in Florida, which require mul tiple applications throughout the season to ensure efficient potato and sweet corn focus on N rate and ti ming of soluble sources, research has shown the potential of controlle d release fertilizers (CRF s ) to control N availability and limit N loss without reducing the yield of vege t able crops. There are many different types of CRFs (Guertal, 2009), which all rely on a release mechanism that controls the diffusion of N into the s oil water. Polymer coated urea is a type of CRF that consists of a urea prill coated with a biodegradable plastic resin and gradual diffusion of N through the coating is driven by soil temperature and the thickness of the coating . Polymer coated urea allow s producers to apply 100% of the crop N requirement at planting, eliminating the need for split applications and saving producers both time and money.

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20 focus on N rate, controlled release N sources have shown promise for reducing N losses without impacting yield. Hutchinson et al. (2003), Wilson et al. (2009), and most recently Bero et al. (2014) found that polymer coated urea resulted in similar yields of potatoes grown on sandy so ils when compared with soluble N sources . CRF research has shown that controlling the N release can lower potato fertilizer N requirements by keeping more of the applied N in the root zone for plant uptake (Hutchinson et al., 2003; Simonne and Hutchinson, 2005). This direction aims at reducing the risk of N loss by both controlling the release and reducing the rate of N sources and can make the use of CRFs more economical for vege t able production. Irrigation Management While applied N is the major source o f nutrients in agricultural production systems, excess water is the driver of nutrient loss. The role of irrigation management in reducing the risk of N leaching has been emphasized as environmental protection becomes increasingly important in the manageme systems (Simonne et al., 2010). However, irrigation practices that minimize environmental impacts must be economically viable to the producer. Both irrigation scheduling and infrastructure can impact the efficiency of irrigation application. The soil acts as a reservoir to store water in the root zone and irrigation scheduling allows the grower to maintain adequate water availability to meet crop needs . A common method of irrigation scheduling is called the checkbook method, which is an accounting method that allows the grower to estimate soil water content and inform irrigation decisions , based on soil water holding capacity, amount of rain, crop growth period, and water loss from the crop and soil .

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21 for the accounting system . If the soil water balance is too low, crop water stress can have negative impacts on growth. However, excessive irrigation application can trigger leaching through the soil profile, moving mobile nutrients below t he root zone. Additionally, different irrigation application methods have varying degrees of efficiency, which has an impact on irrigation delivery and uniformity. Inefficient irrigation delivery can have major impacts on growth and N losses. Studies have shown greater efficiency of sprinkler irrigation over furrow irrigation for potato and sweet corn production. Sprinkler irrigated fields held more water in the root zone and lead to greater N use efficiency and water use efficiency for potato (Kurunc et a l., 2011; Lv et al., 2011) and resulted in greater sweet corn yields (Ebrahimi et al., 2011) compared with furrow irrigated fields. While drip irrigation has been shown to result in the greatest water savings and lowest N leaching because of a high irrigat ion application efficiency , it is still not economical for potato and sweet corn farmers to adopt this method (Sharma et al., 2012). Vico and Porporato (2011) concluded that mild deficit irrigation schemes using sprinkler irrigation create an optimal balan ce of reducing water application and maximizing profitability in cases where water costs are low and drip i rrigation is not cost efficient. Deficit irrigation is a strategy that aims to optimize the use of water in agricultural production by reducing irri gation below an optimal threshold. While deficit irrigation schedules have the potential to increase the sustainability of agricultural production by reducing water application and minimizing N leaching, it is critical that deficit irrigation does not nega tively impact productivity or farm economy by reducing yield. Adequate water availability is essential for crop growth; producing optimal yields is dependent on

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22 reducing water stress to keep the stomata open for maximum carbon fixation. Both the timing and severity of the irrigation deficit have the potential to initiate water stress and reduce yields, so they must be carefully considered when developing a deficit irrigation schedule. Deficit irrigation scheduling that replaced 80% of crop ET (ET c ) had no i mpact on tuber biomass compared with 100% ET c replenishment (Alva and Moore, 2012), while Shahnazari et al. (2008) and Alva et al. (2002) reported potato yield reduction under irrigation deficit treatments of 70% and 85% of ET c , respectively. Ertek and Ka ra (2013) found no reduction in sweet corn yield irrigated at 70% ET c or 85% ET c compared with 100% ET c . Ahmadi et al. (2010) observed an increase in plant water use efficiency in later growth stages when potatoes were irrigated with 65% ET c , concluding th at later growth stages offer a potential for water savings. Byrd (2013) and Ahmadi et al. (2011) found that deficit irrigation initiated after tuber bulking maintained tuber yield compared with full irrigation . However, Jefferi es and Mackerron (1993) found that deficit irrigation at tuber initiation and tuber bulking decreased potato yields. Shock et al. (1998) found that deficit irrigation reduced tuber yield and total farm profits, while researchers in Italy who reduced irrigation of potato to 50% of ET c found the reduction of yield minor compared to the water savings (Ierna et al., 2011). The large range of crop responses to deficit irrigation schemes emphasize the importance of careful water management practices that increase water use efficiency and inc rease the storage capacity of the soil to hold rainfall, without causing water stress that can reduce crop yields. However, impacts on yield must be weighed against other production costs and the effects of deficit irrigation strategies on the farm economy depend on many factors. The disparity in results for deficit irrigation studies

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23 emphasizes the importance of studying deficit irrigation strategies among different soil types to optimize site specific management practices . Joint Management Both irrigation scheduling and fertilizer management have an effect on N leaching; e xcess irrigation contributes to the total volume of water leached through the soil profile and excess fertilizer contributes to t he total N concentration of leachate. Fiebert et al. (1998) found that careful irrigation scheduling reduced N fertilizer requirements for potato by reducing N leaching losses. Joint management of fertilizer and irrigation practices is crucial to producing optimal potato and sweet corn yield s while minimizing field N loss. However, there is a need for research that directly measures N fates and flows and relates it back to different combinations of irrigation and fertilization practices. Social Barriers to Grower Adoption Research on the contribution of N management and irrigation efficiency in reducing N loss from potato and sweet corn production systems is crucial in understanding soil nutrient water crop dynamics. However, the identification of more effi cient management practices must be coupled with widespread grower adoption. Therefore, understanding water quality issues related to Florida potato production practices requires understanding farmer behavior, economic barriers, stakeholder interactions and Florida potato and sweet corn production supports grower livelihoods, but current practices that increase N losses pose a threat to environmental quality. Rational choice theory can be used as a framework to enco urage the adoption of more sustainable practices by reframing the issue to emphasize the economic vulnerability that growers

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24 face as the risk of N loss increases (Scott, 2000). The price of fertilizer has risen with increasing fuel costs (Lui et al., 2012) , so fertilizer lost from wasteful applications or inefficient irrigation management should rationalize the choice of moving towards more nutrient efficient production systems; however, this relies on the translation of N loss into monetary terms. Cost ana lyses between traditional and controlled release programs (Simonne & Hutchinson, 2005) are outdated and fail to value either ecosystem services or N loss, illustrating the current perceived economic advantage of traditional practices. However, more recent analyses have attributed value to N loss in the form of societal costs of clean up or lost ecosystem services (Brink et al., 2011; van Grinsven et al., 2013). Up to date information on cost differences that represent current prices, as well as the quantifi cation of social benefits from water conservation and environmental protection, are crucial for accurate cost benefit analyses of agricultu ral technologies (Casey et al. , 1996). This relies on the identification of methods to quantify the value of ecosyste m services and costs of environmental degradation (de Groot, 2010) . Because of the difficulty of accurate quantification of ecosystem services and environmental protection, shifting farmer attitudes based on cost analyses that focus on individual rational choice is a more likely strategy to encourage adoption of high cost technologies . R esearch on irrigation and N fertilizer management should therefore aim to include a discussion of the economic dimensions of alternative production practices . Stakeholder c onflict is another barrier to the successful transition of Florida vege table growers to more sustainable production systems. The development of TMDLs and BMAPs has allowed for regulation of nutrient loading and more government protection of ecosystem servi ces, but this has only increased government grower

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25 conflict. For example, growers in the Tri County Agricultural Area, a large potato producing agricultural area in northeastern Florida, cited increasing government regulation as a reason for the decreasing trend of agricultural production in the area (Borisova et al., 2009). This suggests that the top down strategy of Florida environmental regulation is pushing people out of agricultural production, rather than encouraging their transition to more sustainab le practices. As algal blooms gain public attention, pressure on growers to reduce nutrient inputs while maintaining yields adds additional conflict between environmentalists and local potato growers (Borisova et al., 2009). Simonne et al. (2010) identifie d the need for discussions between key stakeholders as a key principle for keeping water and nutrients in the root zone of Florida vege table s, supporting the inclusion of stakeholders as a strategy to encourage sustainable natural resource management . Both social and ecological components influence the adoption and spread of nutrient and irrigation management strategies. These two components have different mechanisms, constraints, and effects on behavior, with the institutional domain acting as a hinge that reconciles the two incompatible sides (Porzecanski et al., 2012). Institutional mechanisms that encourage in the evolution of grower production systems toward s environmental sustainability. Education guides individual decision making and social networks facilitate the spread of this knowledge to influence collective decis ion making (Munchhausen et al. , 2012). The UF/IFAS E xtension Program strengthen s universit y grower networks and disseminate s the most curre nt research and recommendations in a field setting, which

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26 has been shown as a successful strategy for encouraging the adoption of alternative practices within practice networks (Chiffoleau, 2005) . While ther e is no one size fits all strategy that will apply to each grower, increasing the tools available to growers to make informed decisions as well as encouraging the adoption of these systems through education are potential strategies to orient growers toward s more sustainable production systems. Variability and unpredictability of future climate conditions, as well the possible increase of intense precipitation events ( Groisman et al., 2005) , all have implications on Florida potato and sweet corn producers. How they respond to and manage agricultural production in a changing climate relies on the adaptive capacity of growers, as well as the ability of policy makers to develop incentives to manage production systems for unpredictability. It is not total amount of rainfall over the season, but the increase of identification, inclusion, and participation can increase social capital and help encourage long term changes to ad apt to a changing climate. Resilience based ecosystem stewardship relies on the ability of Florida producers to adapt production systems in the face of change (Chapin, 2009); the development of multiple strategies that can reduce the risk of N leaching und er different scenarios increases the tools available to growers for coping with change. The diverse nature of Florida vege table production systems requires a toolbox filled with various strategies that can be applied according to specific social and ecolo gical circumstances; in the case of Florida potato and sweet corn production, ecological constraints in the form of sandy soil texture and heavy rainfall patterns

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27 require irrigation and N management strategies that minimize the risk of N leaching through t he development of more efficient application strategies. However, changing practices often requires substantial investments and the economic dimensions of management practices must be considered. When practices are beneficial, but costly, widespread adopti on will depend on local cost share initiatives, which can be facilitated by grower regulatory interactions. Because the crop soil interface has many intricacies, communication of key research findings to growers is crucial. UF/IFAS E xtension programs are a n important tool for involving growers with current research and encouraging BMP implementation and research on irrigation and N management should aim to inform and update UF/IFAS recommended practices . Goals and Objectives The goal of this project was to increase N fertilizer use efficiency by reducing N loss from the root zone and leaving it available for maximum crop uptake. Understanding the fundamental processes of N cycling under the experimental management practices will help to sustain the profitabi lity of potato and sweet corn production, as well as protect surrounding water resources that are impacted by non point source N inputs. The objective s of this st udy were to 1) determine the effects of irrigation scheduling and fertilization programs on cr op production and amounts of NO 3 N leached from the root zone and 2) develop partial N budgets for each component of the cropping system (irrigated potato millet irrigated sweet corn cereal rye sequence). Standard crop production practices were developed with consideration of current grower

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28 Researchable questions include d : 1. What are the effects o n crop yield and nitrate leaching of changing the allowable depletion threshold for irrigation scheduling? More specifically, what are the effects of changing typical grower irrigation practice , from one which keeps the soil close to field capacity, to one allowing for water depletion to a certain threshold above the permanent wilting point before irrigation? The h ypothesis was that m aintaining soil moisture below field capacity will reduce the risk of NO 3 N leaching due to rain by increasing the rain water storage capacity of the soil. 2. How do the different fertilizer programs differ in regards to impacts on yield and NO 3 N leaching? The hypothesis was that polymer coated controlled release N fertilizer programs at both the UF/IFAS recommended rate and reduc ed rate will maintain yield and minimize NO 3 N leaching. 3. Are there interactions between irrigation and N treatments ? The h y pothesis was that i rrigation management will have a greater impact on the reduction of NO3 N leaching and the benefits of CRF will b e most pronounced under greater irrigation applications.

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29 CHAPTER 2 MATERIALS AND METHODS Site Description One year of field research was conducted between February 2013 and February 2014 at the University of Florida Plant Science Research and Education Unit (PSREU) in Citra, FL on a soil classified as Tavares sand (hyperthermic, uncoated Typic Quartzipsamment) with a measured bulk density of 1.59 g cm 3 . A cropping sequence of potato and sweet corn was the basis for investigation, which is a typical rot ation in north Florida. In addition to the principal vegetable crops, millet ( Panicum ramosum L. ) and cereal rye ( Secale cereale L . ) cover crops were pl anted in the summer and winter periods, respectively . Disease and pest control was managed by the PSREU staff and pest and disease prevention measures were applied as needed , based upon field scouting . The experiment was arranged in a completely randomized design with 3 replications and treatments consisted of three irrigation treatments and three N manageme nt treatments. Treatments were only applied to the two principal vege t able crops. Treatments Irrigation treatments were chosen to manage the avai lable water content of the soil. Rainfall is common during crop production seasons and can trigger nitrate N leaching. Most commercial vegetable growers use irrigation to maintain the soil moisture at 100% field capacity , leavi ng little capacity to hold rainfall and therefore increasing the chance of nitrate N leaching. Maintain ing the soil moisture at less than 100% field capacity should reserve some water storage capacity for rain yet still provide adequate water for the crop. Irrigation treatments consisted of three different irrigation

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30 schedules ; maintenance of 75 % field capacity (FC) with daily sprinkler irr igation (75FC), maintenance of 100 % FC with daily sprinkler irrigation that replaced 100% ET c (100 ET ) , and an over irrigation treatment with daily irrigation that replaced 125 % ET c ( 125ET ) . One 1 804 P ressure R egulating S pray (PRS) head (Rain Bird Corporati on, Azusa , CA), fitted with an R VAN 1724 adjus t able rotary nozzle (Rain Bird Corporation, Azusa , CA) set to 90° was installed in each corner of every plot , giving an irrigation application rate of 1.8 cm of water per hour with a distribution uniformity of 82% . The four sprinklers in each plot were inter connected by 3 .8 cm polyethylene tubing and 5 cm lay flat discharge hose was used to connect plots within the same treatment to a timer controlled valve attached to a constantly pressurized irrigation syste m that averaged 60 psi. The irrigation system was installed in the early part of the season and disassembled prior to cover crop planting after each principal crop; installation was completed on 7 March 2013 for the potato season and 19 August 2013 for the sweet corn season. The i rrigation events were scheduled using reference evapotranspiration (ET 0 ) reported on the Florida Automated Weather Network website (fawn.ifas.ufl.edu) multiplied by a crop coefficient ( K c ) for each crop growth stage (Ozores Hampton et al., 2011; Zotarelli et al., 2011) to determine crop water use (ET c ). C heck book water budgeting methods were used to maintain soil water content for each irrigation treatment level . I n the top 30 cm of the soil profile, field capacity was measured to be 5.5 percent by volume and permanent wilting point was 2.0 percent . Ch anges to scheduling were also guided by tensiometer readings (Irrometer Co., Riverside , CA) , which were logged three times per week into a spreadsheet to validate irrigation scheduling . For 75FC , soil moisture was maintained at 75% field capacity with daily sprinkler irrigation . When crop ET (ET c )

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31 reduced available soil moisture to 6 0% of the soil water holding capacity, an irrigation amount was applied to bring soil moisture back to 75 % of field capacity ; this approach maintained a soil water reservoir for rainfall . For the 100ET treatment , which mimicked grower irrigation practices, soil was first irrigated to 100% FC, followed by daily irrigation to replace 100% of ET c and keep soil m oisture at 100% field capacity. The 125 ET treatment consisted of daily irrigation events that supplied 125% of ET c to explore the effect of over irrigation relative to other treatments on nitrate N leaching . The irrigation treatments were not set up as an irrigation study and the differences in irrigation applications were intentionally mild. Treatments were developed to evaluate , in combinations with N management treatments, the impacts on N losses. Irrigation treatments were not hypothesized to have any n egative impacts on crop growth or yield. In addition to three irrigation management treatments, there were also three N fertilization treatments. The first treatment was polymer coated urea (PCU) applied at the reduced rate of 196 kg ha 1 ( PCU196 ) , which is 2 8 kg ha 1 below the UF/IFAS recommended rate for potato and sweet corn. The second treatment was polymer coated urea at the rate of 224 kg ha 1 ( PCU224 ) , which is the UF/IFAS recommended rate for potato and sweet corn. Environmentally Smart Nitrogen ([ ESN] , A grium Inc., Calgary, AB, Canada) was the polymer coated urea applied to the potato crop, while a 50/50 blend of ESN and Duration 120 ( Agrium Inc., Calgary, AB, Canada) was applied to t he sweet corn crop. Duration 120 (43 0 0) has a slower releas e rate than ESN (44 0 0) and was used in the sweet corn season because of higher temperatures during the fall growing season . B oth polymer coated urea fertilizers supplied 100% of the seasonal N in a single application at planting for each principal crop . The final

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32 fertilizer treatment was split applied urea ammonium nitrate (UAN) , banded on both sides of the row at the UF/IFAS recommended (best Management Practice [ BMP ]) rate of 224 kg ha 1 ( UAN224 and was designed to rep resent current grower pra ctices. Application schedules were different for the potato and sweet corn crops and are detailed in the corresponding cropping sequence section below. Lysimeter D esign and S ampling M ethods Each plot contained one drainage lysimeter (Figure 2 2), which co nsisted of a water collection basin constructed from half of a 208 L polyethylene drum and a storage reservoir constructed from 15 cm PVC sewer pipe and two 15 cm PVC sewer caps, which were connected by 2 cm flex PVC. The basin was fitted with a thru hull that allowed drainage from the basin to the reservoir , filled with pea gravel, and covered with window screen to prev ent blockage of the connection. A 2.5 cm hole was drilled in the top cap of each reservoir, threaded, and attached with a threaded 2.5 cm P VC adapter. 2.5 cm PVC was attached to the adapter and brought to the soil surface . A 0 .96 cm hole was drilled into a 2.5 cm cap and placed at the end of the 2.5 cm PVC, which allowed for 0 .95 cm tygon tubing to be lowered into the reservoir through the PV C pipe to evac uate the leachate from the reservoir . Lysimeters were buried in each plot with the top edge of the basin at 6 1 c m below the soil surface, under the middle of either the 4 th or 5 th row in the 8 row plot . The basin measured 88 cm x 54 cm and c aught leachate from an area of 0 .475 m 2 . The leachate was collected from the lysimeters bi weekly using a 12 volt transfe r pump, which was attached to the tygon tubing using a 1.7 cm x 0 .95 cm brass adapter. The volume of leachate was measured using a 2 L graduated cylinder and as the reservoir was being drained, one sample for nitrate N analysis was taken 3 to 4 seconds after the evacuation began and was stored in a 20 ml scintillation

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33 vial. Every 6 to 7 plots, a duplicate leachate sample was taken, along with a sample of deionized water run through the pump as an equipment blank and another sample of deionized water as a field blank. Each sample received one drop of half strength sulfuric acid to maintain a pH < 2 and stored in a cooler full of an ice /wate r mixture to keep sample temperatures at or below 4°C. Samples were taken to the University of Florida Analytical Research Lab and analyzed for NH 3 N and NO 3 N concentrati ons (EPA method 350 .1 and 353.2). A schedule of lysimeter sampling dates for each cro p can be found in Table 2 1. Testing the A ccuracy of the L ysimeter L eachate Collection S ystem The use of drainage lysimeters as an accurate method of measuring nitrate load may be limited by the potential N transformations before the leachate is sampled. T he leachate flows through the soil until it reaches the bottom of the lysimeter , where pea gravel lines the area above the drainage hole that leads to the leachate reservoir. This area of textural discontinuity could potentially lead to anaerobic condition s before the soil water drains to the reservoir, creating one of the conditions necessary for denitrification. Additionally, the leachate in the reservoir is potentially subject to losses of N from denitrification between sampling events. Denitrification l osses in both cases were hypothesized to be non significant, and the following experiments were performed with the aim of determining the accuracy using d rainage lysimeters to measure the N leaching load in the field . The objective of the first experiment was to measure NO 3 N concentrations in the leachate over a three week period to test the hypothesis that denitrification losses from leachate in the reservoir before sampling were not significant. Immediately after a rainfall event, lysimeters were sampled and the leachate samples were submitted to the

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34 ARL for analysis. Leachate from one re servoir was saved and eight 125 mL bottles were each filled with a pproximately 100 mL of leachate. D eionized water was poured into two additional 125 mL bottles. A hole w as dug on the edge of the field outside of the plots to a depth of 1 m, a bucket was placed into the bottom of the hole, and all ten uncapped bottles were placed at the bottom of the bucket. The lid was secured to the top of the bucket and the bucket was b uried to mimic the conditions of the lysimeter reservoir . E very three days , the bucket was uncovered and one bottle of both leachate and deionized water were removed. Two samples were poured from each bottle into 20 mL scintillation vial s and o ne drop of h alf strength H 2 SO 4 was added to each vial . Samples were placed in ice water to keep temperatures at or below 4°C to avoid any nitrate transformations between sampling and lab analysis. The bottle of deionized water was returned to the bucket, the lid was r eattached, and the bucket was reburied after each sampling event. The experimental unit was the lysimeter leachate and treatments were sampling dates. Means were analyzed by performing an ANOVA (JMP Pro 10, SAS Institute, Cary, NC). Sampling date had no e ffect on NO 3 N concentrations ( Table A 1) and there were no differences between NO 3 N concentrations for any sampling date and the initial measurement. These results support the accuracy of NO 3 N concentrations measured up to 21 days after the initial leac hing event. Deionized water was below the detection limit for all sampling dates, which confirmed the accuracy of ARL lab procedures on measuring NO 3 N leachate concentrations. A second experiment was performed to measure nitrate concentrations of soil po re water before and after it drained through the gravel at the base of the lysime ter.

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35 This experiment tested the hypothesis that denitrification losses as soil pore water drains through the gravel at the bottom of the lysimeter were not significant. After the lysimeters had been sampled and reservoir samples were buried for the first denitrification experiment, one lysimeter was constructed and buried at the edge of the field outside of the plots. The lysimeter was constructed using the same materials and c onstruction methods as described for the cropping sequence research and was buried with the top edge of the basin at 61 cm below the soil surface. A watering can was used to simulate irrigation or rainfall and 18 L of water was poured over the reservoir to flush out soil pore water. The reservoir was drained and leachate was discarded, after which a 2.5 len g th of PVC was used to drive three holes in the soil above the gravel lined drainage hole of the lysimeter basin. One soil solution access tube (SSAT) su ction lysimeter ( Irrometer Co., Riverside, CA ) was inserted into each 2.5 cm hole and soil was compacted around the instrument. A vacuum was applied to the suction lysimeters using a #1102 hand vacuum pump ( Irrometer Co., Riverside, CA ) and 10 mL of UAN wa s added to 1 8 L of water, which was then poured over the lysimeter. The three suction lysimeters were used to sample soil pore water before moving through the gravel lined basin . T he reservoir was pumped and three leachate samples were taken to measure nit rate concentration after moving through the basin . T his process was repeated three times. All samples were poured into 20 mL scintillation vials, one drop of half strength H 2 SO 4 was added to each sample, and samples were stored in a cooler filled with ice water to keep samples at or below 4°C to avoid any nitrate transformations between sampling and lab analysis. Samples were immediately submitted to the ARL and analyzed for NO 3 N concentration.

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36 Data for the second experiment were analyzed by performing a two way ANOVA with replication (JMP Pro 10, SAS Institute, Cary, NC). The experimental unit was the lysimeter leachate and treatments were drainage through the zone of textural discontinuity (before or after) and sample run (1, 2, or 3). There were no sign ificant treatment interactions or main effects on NO 3 N concentration of the leachate ( Table A 2), which supports the uniformity of NO 3 N concentrations before and after passing through the zone of textural discontinuity at the base of the lysimeter basin. A ll d eionized water samples were below the detection limit, which confirmed the accuracy of ARL lab procedures on measuring NO 3 N leachate concentrations. The results of these two experiments show that there was no change in the nitrate N concentration as it moved through the soil in the lysimeter and that there was no change in leachate nitrate N concentration over a two week period in the lysimeter reservoir. Based on these results, we concluded that n itrate N transformations did not affect interpretatio n of nitrate N leachate data from the field studies. Cropping Sequence Principal C P otato On 24 January 2013, soil samples were taken from three even sections in the field ( Figure 2 1) . Eight soil samples were taken in each section, whi ch were combined, sub sample d, and Mehlich 1 nutrient analyses ( Table 2 2 ). determine lime, phosphorus, potassium, magnesium, and micronutrient fertilizer needs for the subsequent research crops. The field was then divided into 27 plots , with 3.7 m alleys between all plots . E ach individual plot consisted of eight 7.3 m long rows ; inter row spacing was 90 cm and intra row spacing was 15 c m , resulting in a plant population

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37 of 71,729 plants ha 1 . Dry a mmonium nitrate (32 N 0 P 0 K ) was applied pre plant on 11 February at a rate of 22 kg ha 1 N for the rower N management treatment ( UAN224 ) , with two additional side dressings of liquid urea ammonium nitrate banded on both sides of the hill each at the rate of 10 1 kg ha 1 N at emergence ( 18 March) and 3 5 days after emergence ( 22 April) . All of the polymer coated urea was placed in beds and incorporated immediately prior to planting for both PCU196 and PCU224 treatments on 12 February . All plots r eceived K 2 Mg 2 (SO 4 ) 3 ( 0 N 0 P 18 K ) at the rate of 4 6 kg ha 1 K at planting on 12 February, with two additional side dressings of the same fertilizer at 4 6 kg ha 1 K on 18 March and 22 April 22, 2013. A cup type potato planter was used to plant potato seed pie ces on 12 February. The irrigation system installation was completed on 7 March and irrigation treatments were initiated. Prior to installation, the PSREU staff applied uniform irrigation to all plots as needed to maintain moisture fo r seed piece sprouting and emergence . On 11 March, o ne tensiometer (Irrometer Co., Riverside, CA) w as randomly placed in each plot with the ceramic tip at a depth of 2 0 cm and readings w ere manually logged three times per week . On 22 March, 5 April, 19 Ap ril, 3 May, and 17 May , two plant samples were taken by harvesting two randomly selected potato plants , including roots, from each plot to measure N uptake throughout the season. Plants were dug to a depth of 30 cm using a round point shovel and placed int o labeled bags. Plant samples were taken from the 2 nd , 3 rd , 6 th , and 7 th rows, to avoid sampling near the lysimeter and avoid the outer edges on the plot. After sampling, p lant samples were separated into roots, shoots , and tubers (when available) and w ere washed thoroughly to remove any sand. Separated

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38 samples were placed into labeled bags and dried in a 65°C oven. After drying, samples were weighed and ground in a Wiley mill to pass through a 2mm screen. A representative sample was taken from the ground p lant material for each plant sub sample and stored in a 20 ml scintillation vial. Plant tissue was analyzed for Total Kjeldahl Nitrogen (TKN) by preliminary acid digestion and semi automated colorimetry (EPA method 351.2 ). Whole plant samples were used to develop a seasonal N uptake profile for plants growing with the irrigation and N fertilizer treatments. In addition to whole plant samples, whole leaf samples from the first fully expanded leaf were taken on 5 April, 19 April, and 3 May; each sample consis ted of ten randomly selected leaves from each plot. Leaf samples were dried in a 65°C oven and processed as described above. Whole leaf samples were used to test the N sufficiency concentrations of potato plants. Soil samples were taken from each plot on 2 2 February, 25 March, 5 April, 7 May, and 28 May 2013; samples consisted of 6 sub sample s that were taken using a soil probe to a depth of 30 cm, combined, sub sampled, and submitted as one representative sample. Samples were submitted to the University of Florida Analytical Research Lab , where they were extracted with 1N KCl , and analyzed for NH 4 N and NO 3 N concentrations (EPA method 350 .1 and 353.2). On 22 May, tubers from three 4.5 m sections from uniform rows were harvested and graded into four size c lasses : A4 > 11.4 cm, A1 3=1 1.4 to 5.7 cm, B= 5 . 7 to 3.8 cm and C=3.8 to 1. 9 cm ( USDA, 2011 ). Potatoes in each class were counted and weighed to determine yield. Quality was rated b y counting and weighing tubers with shape deformities and defects such as enla rged lenticels that result from excess soil moisture .

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39 Cover C Millet After harvest of the potatoes, a drill planter was used to plant a cover crop of millet at the rate of 22 kg ha 1 seed on 29 May 2013. On 13 June, a fertilizer blend ( 16 N 0 P 6K ) at the rate of 22 kg ha 1 N was applied to all plots to enhance the early growth and establishment of the cover crop . On 31 July , two randomly selected samples from each plot were harvested using a 0 .5 m 2 quadrat ring and a round point shovel was used to dig up the roots to a depth of 30 cm. Samples were washed free of soil and separated into roots and shoots, placed into labeled paper bags, and o ven dried at 65°C. After the samples were dried, they were weighed and ground in a Wiley mill to pass t hrough a 2 mm screen and analyzed for TKN by prel iminary acid digestion and semi automated colorimetry (EPA method 351.2 ) to determine N recovery. Soil samples were taken from each plot at the end of the season on 30 July and consisted of 6 sub sample s tha t were taken using a soil probe to a depth of 30 cm, combined, sub sampled , and submitted as one representative sample. Samples were submitted to the University of Florida Analytical Research Lab , w here they were extracted with 1N KCl , and analyzed for NH 4 N and NO 3 N concentrations (EPA method 350 .1 and 353.2). Principal C rop 2: S weet C orn On 1 August , all plots w ere mowed . sweet corn seeds (Seminis Inc., Saint Louis, MO) were planted 15 cm apart in a row using a strip till, d rill plant er, with 90 cm between rows. All plots r eceived 50% of K soil test recommendations from K 2 Mg 2 (SO 4 ) 3 ( 0N 0P 18K ) at the rate of 4 6 kg ha 1 K at planting , with an additional application of K 2 Mg 2 (SO 4 ) 3 ( 0 N 0 P 22 K ) at the rate of 4 6 kg ha 1 K on 22 Au gust . Ammonium nitrate was applied at a rate of 1 6 kg ha 1 N at planting for all treatments , and again on 12 September after a series of large rainfall events . PCU at the rate of 180

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40 and 208 kg ha 1 N for PCU196 and PCU224, respectively, was hand applied a s PCU in the tilled row area and incorporated by an initial pass with the strip tiller prior to planting . Two side dressings of 42 kg ha 1 N from liquid urea ammonium nitrate (32 N 0 P 0 K ) were banded on both sides of the row UAN2 24 ) on 16 Aug and 22 Aug, with two additional side dressings of 62 kg ha 1 N on 6 Sept and 17 Sept ( Table 2 3 ) . Grower side dressings were planned for 5 ev enly split applications every 7 to 10 days. However, early applications had to be postponed due to pr ojected rainf all, which led to 4 split applications instead , but the total N for the treatment was maintained . One tensiometer (Irrometer Co., Riverside, CA) was randomly placed in a uniform section of each plot to a depth of 2 0 cm and r eadings were manua lly logged three times per week . On 22 August, 5 September, 19 September, and 10 October 2013 , plants from two randomly selected 1 m lengths of row from each plot were sampled by excavating to the depth of 30 cm using a round point shovel . Plant s amples w ere washed thoroughly and separated into shoots, roots, and ears (when present ) immediately after harvesting . After being washed and separated, samples were placed into labeled bags and oven dried at 65° C . After drying, samples were weighed and ground for nutrient analyses. In addition to wh ole plant samples, leaf samples from the first fully expanded leaf from the top of the plant were taken during tass e li n g on 5 September and at silking on 12 September; each sample consisted of ten randomly selected who le leaves from each plot. Leaf samples were dried in a 65°C oven and processed as described above.

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41 On 3 October and 1 8 October (63 days after planting [ DAP ] and 78 DAP, respectively) , marke t able sweet corn ears w ere harvested from three 4.5 m lengths of row , counted , and weighed to determine yield . Ear q uality was evaluated by removing the husks from 5 random ears from each plot sample, weighing the 5 ears, and measuring them for ear length , as well as rating tip fill on a scale from 0 to 5 , with 0 = top 5 cm unfi lled , 1 = top 4 cm unfilled , 2 = top 3 cm unfilled , 3 = top 2 cm unfilled, 4 = top 1 cm entire ear filled, and 5=all kernels filled (Kwabiah, 2004). Soil samples were taken from each plot on 27 August, 3 September, and 3 October consist ing of 6 samples that were taken using a soil probe to a depth of 30 cm, combined, sub sample d and submitted as one representative sample. Samples were submitted to the University of Florida Analytical Research Lab, w here they were extracted with 1N KCl an d analyzed for NH3 N and NO 3 N concentrations (EPA method 350 .1 and 353.2). Cover C C ereal R ye On 17 October , sweet corn stalks w ere mowed down and roto tilled into the soil. On 29 October , a drill planter was used to plant rye at the rate of 56 kg ha 1 seed. A mmonium nitrate (32 N 0 P 0 K ) was appli ed to all plots on 19 November at the rate of 28 kg ha 1 N . Representative plant and soil samples were taken at the end of the season on 30 January 2014 from two 0 .5m 2 sections of each plot to a depth of 30 cm. Samples were washed and separated into roots and shoots. Tissue was dried at 65 ° C , ground, and analyzed for TKN by prel iminary acid digestion and semi automated colorimetry (EPA method 351.2 ) to determine N recovery. S oil samples were ta ken from each pl ot at the end of the season on 7 February 2014 to determine final soil N content. Each plot was sampled with a soil probe 6 times to a depth of 30 cm, which were mixed

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42 in a bucket and sub sample d as one representative sample; representative samples from each plot were then dried at 38 ° C and sieved. Samples were submitted to the University of Florida Analytical Research Lab, w here they were extracted with 1N KCl and analyzed for NH3 N and NO 3 N concentrations (EPA method 350 .1 and 353.2). Par tial N Budget N budgeting is a strategy to account for the fates and flows of N inputs in agricultural systems by measuring total N inputs and outputs for a crop. Budgeting approaches and measured components can range in complexity and depend on the budge s increases the total accounted for N in the system and can more accurately determine the major N sources and sinks (Watson and Atkinson, 1999) . A partial N budget was calculated for each crop throughout the cropping season by summing total measured N out puts and subtracting them from the total measured N in puts. Measured inputs consisted of initial soil inorganic N content and inorganic fertilizer , while measured outputs were final so il N content, crop uptake, and N leaching. Unaccounted for N was assumed to be gaseous losses. Runoff was a ssumed to be negligible on this level, sandy field and was not included in the budget. Atmospheric deposition data was unavailable for 2013 to 2014, but values averaged over the period of 2000 to 2012 were only 8.4 kg ha N yr 1 and accounted for less than 2% of the average total N inputs ( NADP, 2012 ) . Statistical Analysis A two way analysis of variance was conducted ( JMP Pro 10 , SAS Institute, Cary, NC ) to determine treatment interactions and main effects o n yield for each primary crop , and N uptake, fertilizer N use efficiency (FNUE) , soil N stocks, and total leached N load

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43 for all crops; the total mass balance at the end of the cropping sequence for e ach treatment was also analyzed by subtracting the measured outputs from the measured inputs each season for each plot . Treatment effects were tested for significance at 0.05 . Means were The constant variance assumption was checked for each analysis by plotting residuals by fitted values and the normality assumption was checked by analyzing the distribution of the res iduals . Both constant variance and normality assumptions were met for all statistical analyses.

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44 Table 2 1. Lysimeter sampling dates. Crop Sampling dates Potato 3/1/13, 3/15/13, 3/29/13, 4/12/13, 4/25/13, 5/9/13, 5/23/13 Millet 6/7/1 3, 6/21/13, 7/3/13, 7/17/13, 7/26/13 Sweet corn 8/15/2013, 8/27/13, 9/5/13, 9/12/13, 9/27/13, 10/8/13, 10/24/13 Rye 11/20/13, 12/5/13, 12/17/13, 1/10/14, 2/14/14 Table 2 2 . Initial chemical properties of top 20 cm of soil. Section of Field Property 1 2 3 pH a 6.3 5.9 5.7 OM% b .82 1.02 .88 K ppm c 118 101 80 Mg ppm c 25 23 20 Ca ppm c 627 518 345 Cu ppm c 1.01 1.09 .69 Mn ppm c 2.73 2.47 2.14 Zn ppm c 2.52 2.62 1.61 a EPA Method 150.1 b Walkley Black Method ( Nelson and Sommers, 1982 ) c Mehlich 1 (Mehlich, 1953 ) Table 2 3. UAN224 side dress schedule for sweet corn. Date N rate kg ha 1 N 16 Aug 2013 42 22 Aug 2013 42 6 Sept 2013 62 17 Sept 2013 62

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45 Figure 2 1. Sections of the field sampled fo r initial Mehlich 1 soil testing (see Table 2 2 for results of soil testing) . Figure 2 2. Drainage lysimeter design. A ) water collection basin, B) storage reservoir, C) 2 cm flex PVC connection, D) thru hull, E) pea gravel, F) window screen, G out er diameter tygon tubing, H ) 2.5 cm PVC attached to the top of reservoir

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46 CHAPTER 3 RESULTS AND DISCUSSION Potato P otatoes were planted on 12 February , 2013 and were harvested for yield measurements 99 DAP on 22 May. Irrigati on t reatments were initiated on 7 March and ended on 21 May. Totals of 17.5 cm, 21 . 5 cm, and 26.9 cm of irrigation were applied to 75FC, 100ET , and 125 ET treatments, respectively, and there was a total of 27.6 cm of rainfall over the season (Figure 3 1 ). A verage daily soil water content in the irrigation checkbook for 75FC was maintained at 78% FC. Irrigation treatments had a significant effect on soil moisture tension ( P= .0002 ) , averaged over the season, with a significant difference between soil moisture tension with 75FC treatments compared with 100ET and 125ET treatments ( Table A 3 ) . Soil moisture tension with the 75ET treatment was 11.5 kPa , which indicated significantly drier soil than soil moisture in 100ET and 125 treatments ( 10.0 and 9.0, respe ctively) . Recommended soil moisture tension range for sandy soils used for crop production in Florida is 6 to 1 5 k Pa ( Dukes et al., 2012 ) , with 10 kPa representing the field capacity of sandy soils (Stewart et al., 1963 ) . There was no difference in soil moisture tension with 100ET and 125ET ( 10 kPa and 9 kPa, respectively) . Both of these soil moisture situations are representative of soils maintained at field capacity. Irrigation main effects for average soil moisture tension over the season are shown in Table 3 1 . The goal of the irrigation treatments was to have a soil moisture treatments that differed in the amount of reserve water holding capacity. These soil moisture tension readings demonstrate that selected irrigation treatments were effective in maintaining minor differences between soils at field

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47 capacity with the 100ET and 125ET compared with the soil with the 75% field capacity, over the season. Yield There were no significant treatment interactions or treatment main effects for total yield, marke t able yield ( grades A1 4, B , C) or culls , or tuber quality . ANOVA t ables are presented in the Appendix tables ( A 4 , A 5 , and A 6 ). Treatment m ain effects for total and marke t able yield are show i n Table 3 2. The grand means for marketable and total t uber yields were 2 8.9 Mt ha 1 and 29.6 Mt ha 1 , respectively, which were within the range of published acceptable commercial yields for the potato variety used in this study . The total yields were greater total yields reported by Pack (20 0 4 ), which ranged from 20.8 24.7 Mt ha 1 . marketable yields from the UF r esearch and demonstration farm in Hastings, FL ranged from 17 .3 52.4 Mt ha 1 over the period of 1998 to 2012 (Zotarelli et al., 2013). There were no treatment interaction s or irrigation main effects on tuber size , but N fertilizer treatments had a significant effect on sized A4 (P=.004) and B tubers (P=.004) (Table 3 2) . UAN resul ted in significantly less A4 sized tubers and significantly more B sized tubers than either PC U treatment . Large tubers are often valued in the potato industry. These results are in line with those published by Zvomuya and Rosen (2001 ) and Zvomuya et al. (2003 ), who reported that soluble N sources resulted in a smaller portion of large tubers compared with PCU . However, in the current study, A1 A3 sized tubers accounted for 70 % of the marketable yield and there were no differences between N treatments for combined A1 A3 sized tubers or size A1 A4 tubers when A4 sized tubers were grouped together with A1 3 sizes . This result is similar to result s reported by Wilson et al. (20 0 9 ) , who found no differences in grade A yields with PCU and soluble N fertilizer applied at

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48 the rates of 180 and 270 kg ha 1 N, which cover ed the range of N rates used in this study . PCU at the reduced rate of 196 kg ha 1 N rate resulted in yields similar to both PCU at the recommended rate of 224 kg ha 1 N and the standard grower practice with UAN at the recommended rate . This result is similar to findings from Bero et al. (2014) , Wilson et al. (20 0 9 ), and Zvomuya et al. (2003) who found that optimal N rates with PCU were lower than the optimal rates with soluble N sources. This suggests that PCU allows for a reduction of total N required for maximum tuber yield , which can increase the economic viability of the more expensive PCU fertilizer use for potato pro duction . Leachate L eachate volume (L), N concentration ( mg L 1 NO2 N + NO 3 N) of the leachate , and the area of the lysimeter ( 0 .475 m 2 ) were used to determine the total leached N load . While NH 3 N was measured for all leachate samples, NH 3 N was only ab ove the detection limit for only one plot on two sampling dates. T his amounted to less than .01 kg ha 1 N; therefore, NH 3 N values were omitted and N leaching load was determined from NO 2 N + NO 3 N concentrations. There were no treatment interactions for t otal season leached N load. I rrigation treatments d id not influence season total leached N load (grand mean=4.9 kg ha 1 N) , but N treatments had a significant effect ( P= .003) on total potato season leached load ( Table s 3 3 and A 7 ) . UAN224 resulted in a gr eater leached N load than PCU196 treatments, but was not significantly different than leaching with PCU224 (Table 3 3) . UAN224 treatments involved two split applications of 101 kg ha 1 N each , compared with PCU which was all applied at planting. Polymer co ated urea has been shown to release N more in synchrony with plant uptake ( Wilson et al., 20 0 9 ). T otal NO 3 N leached during the current season was low , compared with results from other studies. Wilson et al. (2010) found 24.3 to 29.3 kg ha 1 NO 3 N

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49 leached for potatoes with PCU applied at emergence and split applied soluble N . Zvomuya et al. ( 2003) reported values ranging from 7 to 98 kg ha 1 N for PCU and soluble N applied to potatoes at the rate of 140 kg ha 1 N and values ranging from 28 to 228 kg ha 1 N for PCU and soluble N applied to potatoes at the rate of 280 kg ha 1 N . While cumulative rainfall was greater during the current study than the 2000 2012 historical average (Figure 3 1), the majority of rain fell during the second half of the season (Figu re 3 2). Figure 3 3 shows the leached N load and cumulative rainfall from the previous sampling date. Most of the N was leached early in the season ( Figure 3 3 ) when the plants were small, while the majority of rainfall occurred near the end of the season ( Figure 3 3) when most N had already been taken up by the plants (Figure 3 5 ) . These two factors can explain the low leached N load for the season . Minshew et al. (2002) also found that leachate was not well correlated with rainfall, suggesting that N surp lus is a more important driver of N leaching. N leaching varied across sampling dates. Most of the N leaching occurred near the 15 March and 12 April dates (Table 3 4). N main effects were significant for the 15 March ( P= .0 4 ) and 12 April ( P= .04) samplin g dates. More N was leached with the UAN224 fertilizer treatment compared with the two PCU treatments. There was a significant interaction between irrigation and N treatments for N leaching on the 2 4 April ( P= .006) and 23 May ( P= .05) sampling dates ( Table 3 5 ) , with UAN224 at the excessive irrigation rate (125ET) resulting in a significantly greater leached N load than all other treatment combinations for both sampling dates ( Table 3 5 ). T otal leached N from these sampling dates was very low.

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50 These results showed that N fertilizer treatments had a larger impact on N leaching than irrigation treatments. Even though irrigation treatments led to variation in soil moisture, there were few rain events that triggered substantial leaching early in the season when N is most vulnerable to leaching losses . Rainfall later in the season triggered leaching events, resulting in an interaction between irrigation and N treatments, but a very low leached N load. Larger rainfall events in the early part of the season could re sult in a larger effect of irrigation treatments on the cumulative leached N load. Soil Soil inorganic N was measured in each plot throughout the season on four sampling dates, in addition to initial soil sampling on 7 February. Bulk density was used in t he calculations to determine total soil mineral N stocks in kg ha 1 N. Soil N measurements were used to determine N build up in the soil due to treatment. Soil N build up could lead to increased N losses upon leaching rain events. There were no treatment i nteractions and irrigation treatments had no effect on soil inorganic N stock for any sa mpling date. N treatments had a significant effect on soil inorganic N for 25 March ( P= .0002), 7 May ( P= .03), and end of season ( P= .004) sampling dates ( Table s 3 6 and A 8 ). Both PCU treatments resulted in significantly higher soil N for the 25 March sampling date (Table 3 6 ), which was one week after the fi rst split application of UAN . UAN was banded on both sides of the row and bands were avoided during soil sampling, in contrast to PCU which was broadcast and incorporated into the bed. This could explain why UAN224 treatments led to significantly lower soil N than PCU treatments on 25 March, as there were no differences on 5 April suggesting UAN had fully diffused into the bed. N fertilizer treatment main effects were significant for 7 May

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51 soil samples, with UAN resulting in lower soil N than PCU224 treatmen ts (Table 3 6 ). These samples were taken only 15 days after the last application of UAN for UAN224 treatments and measured N leaching was minimal during this time, suggesting that the final UAN application resulted in large gaseous N losses . End of season residual soil N was significantly lower in UAN224 than either PCU224 or PCU196 (Table 3 6 ), but all plots had resi dual N greater than the initial soil N values. This result is similar to results reported by Zvomuya et al. (2003), who found that PCU resulted in greater residual soil NO 3 N than soluble N after potato harvest. Wilson et al. (2010) also found that both PC U and soluble N resulted in residual soil NO 3 N after harvest. The results with soil N content showed that soil N built up during the season in response to N fertilization with more mineral N associated with controlled release fertilizer compared with sol uble N. Soil N content increased early in the season when N was applied and plants were small, but then decreased after mid season due to plant uptake. More N was present in the soil at the end of the season than was present in the soil before fertilizatio n began. N left over at the end of the season could be leached with summer rains, emphasizing the importance of cover crops that scavenge residual soil N for all treatment scenarios. Crop B iomass and N U ptake There were no significant interactions or treat ment main effects for potato plant biomass for any sampling dates including the final sampling (Table 3 7 and Figure 3 4 ) , further emphasizing that reduced rates of PCU provided adequate N for optimal potato growth . Average end of season shoot, root, and t uber dry weight s across all treatments w ere 2 .3 Mt ha 1 , 0 .05 Mt ha 1, and 5 .2 Mt ha 1 , respectively. These results are consistent with those re ported by Zvomuya et al. (2003) who found that PCU did not

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52 result in differences between shoot or tuber dry matt er amounts compared with soluble urea fertilizer . Meas ured shoot dry weights were similar to the 2.5 Mt ha 1 average shoot dry weights reported by Vos (1999). P otato tuber dry weights reported by Vos (1999) were 3 times higher than those found in this stud y , which was likely due to differences in potato variety . N treatments had a significant effect (P=.003) on the final sample whole plant N uptake (Table A 12 and 3 8). Polymer coated urea applied at the recommended rate of 224 kg ha 1 N ( PCU224 ) resulted in significantly higher whole plant N uptake than urea ammonium nitrate applied at the same rate (UAN224) (Table 3 8). Wilson et al. (2010) reported higher potato whole plant N uptake values, ranging from 133 to 294 kg ha 1 N; however, they found similar d ifferences between PCU and soluble N whole plant N uptake, reporting that PCU resulted in higher N recovery than split applied soluble N. There were no interactions or irrigation treatment main effects on N on shoot N uptake, but N treatments affected shoo t N uptake (P=.01). Shoot N uptake ranged from 52 to 78 kg ha 1 N, which is within the range of shoot N uptake values reported by Wilson et al. (2010). Both shoot N uptake and whole plant N uptake were within the ranges reported by Pack et al. (2006), whic h were 41 to 100 kg ha 1 N and 133 to 204 kg ha 1 N, respectively. There were no treatment interactions or main effects on root N uptake, which contributed very little (1%) to the total N uptake. Plants absorbed N from a combination o f fertilizer and miner alized soil N, but unfertilized plots were not included in this study to determine the proportion of mineralized N uptake versus fertilizer N uptake. There were no significant treatment interactions for effects on whole plant N uptake and there were no tre atment main

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53 effects for any sampling date until the final plant sample on 17 May (Table 3 8) . Figure 3 5 shows N main effects on whole plant N uptake over the season, which illustrates rapid crop uptake early in the season . To be a viable fertilizer source for potato production, PCU should have a release rate that corresponds with this period of rapid uptake. Figure 3 5 shows that ESN at both the recommended and reduced rates (PCU224 and PCU196) was able to perform as well as split applied UAN during the ve getative growth stage . Furthermore, PCU196 supplied adequate N suggesting that fertilizer N rate recommendations could be slightly lowered when using PCU N sources. Additionally, soluble fertilizer split applications should be applied during the period of rapid N uptake during vegetative growth . Figure 3 5 shows that the timing of UAN224 fertilizer applications for this study was suit able to supply adequate N for optimal N uptake. Fertilizer N use efficiency (FNUE) was calculated for each plot by dividing the total whole plant N uptake by the total applied N (Table 3 9) . The uptake values include N taken up from the unmeasured soil mineralized N pool, which explains why the values are higher than N use efficiency values of 29 to 52% for potato reported by B ero et al. (2014) . However, uptake of mineralized N was assumed to be similar across treatments, so differences in calculated FNUE between treatments are still valuable measurement s . There were no treatment interactions and irrigation treatm ents had no eff ect on FNUE. N treatment had a significant effect on FNUE ( P= .001). The FNUEs ranged from 55 to 71% and were comparable to those reported for potato by V os (1999), which ranged from 48 to 72%. Both PCU196 and PCU224 resulted in a signifi cantly higher FNUE than UAN224 , which is consistent with findings that PCU

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54 result ed in a higher N recovery than soluble N applied at the same N rate ( Wilson et al., 2010) . PCU 224 fertilization resulted in a higher whole plant N uptake (Table 3 8 ) , but due to the higher total applied N (224 kg ha 1 N) compared with PCU196 (196 kg ha 1 N), the FNUEs for both PCU196 and PCU224 were the same. PCU224 treatments resulted in greater shoot N uptake than UAN224 treatments ( Table 3 8) and no additional benefit to yield , which suggests luxury consumption of N with PCU224 treatments . While FNUE was similar between PCU196 and PCU224, the higher application of N that did not result in an increase in yield represents an economic disadvantage to potato producers for PCU224. Leaf N C oncentrat ion Whole l eaf samples taken on 5 April (52 DAP), 19 April (66 DAP), and 3 May (80 DAP) were analyzed for TKN to determine plant N nutrient status. There were no significant interactions or treatment main effect s on leaf N concentration for the first two sampling dates (52 DAP and 66 DAP) and average leaf N concentrations were above the adequate range ( Zotarelli et al., 2012 ). However, N treatment main effects were significant ( P= .01) for the third sampling date on 3 May (80 DAP). Leaf N concentrations wit h PCU196 and PCU224 were greater than leaf N concentrations with the UAN224 treatment , but whole leaf N concentrations with all treatments were within the adequate range (Table 3 10) . The leaf N concentrations at 66 DAP were consistent with values reported by Pack (2004). Results for all sampling dates are shown in Table 3 10 . Results of w hole leaf N concentration show that potato plants contained adequate N with all N fertilizer treatments and yield was not affected by N supply to the plant. In addition to whole leaf TKN concentrations , fresh p etiole sap measurements were made on 5 April (52 DAP) and 19 April (66 DAP) (Table 3 11) . There were no

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55 significant treatment interactions or irrigation main effects, but N treatments ha d a significant effect on 19 Ap ril petiole sap NO 3 N ( P= .00 5 ) . Both polymer coated urea treatments (PCU196 and PCU224) resulted in significantly higher ( P= .005) petiole sap NO 3 N than UAN224 ( Table 3 1 1 ). These results agree with those pu blished by Wilson et al. (2010) who reported that PCU resulted in higher potato petiole sap N O 3 N later in the season when compared with soluble N sources. While the leaf TKN was within the adequate range for all N treatments on 19 April, UAN224 petiole sap dropped slightly below the published adequate r ange for plants at the full flower growth stage (Zotarelli et al., 2012). Whole leaf tissue and petiole sap measurements were taken as diagnostic measure s of plant nutrition and health. Both PCU treatments resulted in whole leaf and petiole fresh sap conc entrations within the adequate ranges, showing that PCU at both the recommende d and reduced rate led to adequate plant N and equal yields compared with the conventional grower practice and reduced rates of PCU resulted in a lower leached N load . Irrigation treatments resulted in differences in s oil moisture and irrigation application and did not result in negative impacts on yield. This suggests that there is a potential to manage soil moisture below field capacity without causing water stress, which would allow for more conservative water applications for potato production. Partial N Budget A partial N mass budget was calculated for the potato season, subtracting the total outputs (whole plant N uptake, residual soil inorganic N, and leached N) from the t otal inputs (fertilizer N and initial soil inorganic N) for each plot (Table 3 12) . Results from the 7 February soil test were used for initial soil inorganic N content and final

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56 inorganic soil N was determined from the 28 May soil test. There w as no signi ficant treatment interaction for effects on the N balance, but both N treatment and irrigation main effects were significant ( P <.0001 and P= .0 4 , respectively). PCU treatments at both the recommended and reduced rate resulted in a lower unaccounted for N co mpared with the grower UAN treatment, suggesting higher gaseous losses in UAN treatments. Mattos et al. (2003) reported N losses from NH 3 volatilization of 33% for urea based fertilizers on an Entisol in Florida, which is comparable to the gaseous losses o f 13 to 38% calculated from the current study partial N budget . PCU196 resulted in a significantly lower leached N load than UAN224, but there were no differences in yield. Paired with the assumption that the unaccounted for N is an estimate of gaseous los ses, PCU applied at the rate of 196 kg ha 1 N result ed in the most efficient N program for potatoes by supplying enough N to produce optimal tuber yields and minimizing both leaching and gaseous N losses. While the effects of irrigation treatment on leach ed N and soil N stock were not significant , irrigation treatments had a significant effect o n the unaccounted for N at the end of the season. 75FC treatments resulted in less unaccount ed for N compared with 100 and 125% ET treatments , suggesting that maint aining soil moisture below field capacity can reduce gaseous N losses. Elmi et al. (2000) reported that increases in denitrification in sandy soils were associated with higher soil moisture content and Mahmood et al. (199 8) found that water filled pore spa ce was highly correlated with denitrification rates in a sandy soil under maize production . The 100ET and 125ET treatments maintained field capacity with daily irrigation, which could have led to saturated conditions , especially after rainfall events and led to greater rates of

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57 denitrif i cation compared with 7 5FC treatments. UF/IFAS recommends that irrigation scheduling use both crop water requirements and soil moisture measurements to keep soil moisture close to field capacity (Dukes et al., 2012), but the se results show that maintaining soil moisture slightly below field capacity can reduce unaccounted for N and total irrigation application without negative impacts on tuber yield. Additionally, reducing irrigation applications by maintaining soil moisture below field capacity will result in reduced irrigation pumping that translates to a reduction in energy usage and irrigation costs for the grower. Recommended irrigation practices should reflect the potential to maintain tuber yields, reduce irrigation cos ts, conserve water, and decrease gaseous N losses by maint aining soil moisture between 75 to 80% FC. Millet Millet was planted on 29 May , following the potato harvest, as a cover crop to scavenge the residual soil N left from the potato crop. B y the cover crop harvest date on 31 July , the plots contained a mix of 47 % rowntop millet, 5 3 % crabgrass ( Digitaria sanguinalis L.) . Soil N results at the end of the potato season showed that there was still residual soil N from the potato season (Table 3 6). No N fertilizer or irrigation treatments were applied during the cover crop season , but all plots received 22 kg ha 1 N early in the season to support cover crop establishment . Leachate During the millet /crabgrass cover crop growing p eriod , there were 5 leachate sampling events. NH 3 N was below the detection limit for any of the lysimeter samples during the millet cover crop, so leaching load was determined from NO 2 N + NO 3 N concentrations.

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58 There were no significant interactions and no treatment main effects on l eached N load for any of the sampling dates during the cover crop period (Table A 13 ) . T he cumulative leached N load for the millet /crabgrass crop averaged 2.8 kg ha 1 N across all treatments (Table 3 13) . Soil There were no significant treatment interactions or treatment effec ts on millet end of season soil N. Soil inorganic N averaged 7.7 kg ha 1 N across all treatments (Table 3 1 4 ) , illustrating the effectiveness of the cover crops in scavenging residual soil N . The soil N content at the end of the potato season (Table 3 6) was elevated , but declined further during the cover crop season. This value was close to the soil N at the beginning of the potato season, suggesting that soil N return ed back to a background N level. T his result is consistent with the conclusion made by Vos (1999) that little of the N excess from potato production returns to the pool of labile soil N in sandy soils . Biomass and N Uptake Plant samples were taken at the end of the millet cover crop to me asure any differences in N uptake resulting from differences in residual soil N from the potato season. There were no treat ment interactions and treatment effects were not significant for tota l millet /crabgrass total biomass, N uptake , or biomass partition ing . Average plant biomass (shoots + roots) was 3.7 Mt ha 1 , which was between the average browntop millet biomass of 5.6 Mt ha 1 fertilized with 82 kg ha 1 N and unfertilized biomass of 2.4 Mt ha 1 reported by Stewart and Daniels (1995). The average end of season N uptake across all treatment combinations was 29.7 kg ha 1 N . Main effects for N uptake are shown in T able 3 1 5 and main effects for biomass partitioning are shown in T able 3 1 6 . Average N uptake was slightly above the applied N rate, suggesting t hat millet absorbed

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59 N from a combination of residual soil N and the small amount of fertilizer N applied at the start of the millet period. This brought plots back to background soil N levels and allowed for sweet corn treatments (the next crop in the crop ping sequence) to be applied without any carry over effects from potato season treatments. Partial N Budget There were no treatment interactions and irrigation treatments had no effect on the unaccounted for N amount at the end of the millet/crabgrass cov er crop . N treatment main effects were sig nificant ( P= .003) for the unaccounted for N and main effects are shown in T able 3 17 . Both PCU treatments resulted in a significantly larger unaccounted for N than UAN224 treatments, which led to effectively 0 kg h a 1 N unaccounted for at the end of the season. The negative result was due to unmeasured inputs, such as atmospheric deposition and soil N mineralization, but was not significantly different from 0. While the fertilized cover crop was successful at scaven ging excess soil N for UAN 224 treatments, the unaccounted for N for PCU treatments was close to the amount of fertilizer N applied at the beginning of the cover crop. This could result from urea release from PCU after the potato harvest or from gaseous los ses of soil N from prior to cover crop establishment, as soil N was significantly higher in both PCU196 and PCU224 than UAN224. Wilson et al. (2009) found that 100% of PCU was released by 125 DAP, but millet was planted only 105 days after the potato plant ing and 125 DAP corresponds with 20 days into the millet cover crop . Zvomuya et al. (2003) reported that only 60% of PCU had released by potato harvest and Pack (2004) reported PCU release of 60 80% by harvest, confirming that there is a potential for smal l to moderate amounts of N release from PCU after

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60 potato harvest. These results suggest that fertilization may be unnecessary for cover crops following crops supplied with N from PCU. Sweet C orn Sweet corn was planted on 1 August , 2013 and w as harvested for yield measurements on 3 October and 18 October (63 and 78 DAP, respectively) . Two harvest dates were used to capture late maturing ears on some plants. Irrigation treatments were initiated on 19 August and ended on 17 Oct ober. Totals of 13.9 cm, 17.6 cm, and 2 2 cm of irrigation were applied with the 75FC, 100ET , and 125 FC treatments, respectively, and there was a total of 17.9 cm of rainfall over the season (Figure 3 6 ). Rainfall and irrigation combined to maintain soil m oisture at 77% FC for the targeted 75FC treatment. Average soil moisture tension over the season is shown in Table 3 18 . Differences in s oil moisture tension values w ere not significant ly different between 75FC and 100 ET treatments ( 11.5 and 10.5 kPa, re spectively) , but 75FC resulted in significantly greater soil moisture tension than with the 125 ET treatment ( 9.9 kPa) . Soil moisture tension was within the recommended soil moisture tension range for sandy soils in Florida with all treatments (Dukes et al ., 2012). Yield and Qualit y Sweet corn was harvested on 3 October and 18 October and results from both harvest dates were combined for total yield ear yield (with husk) and quality measurements. There were no treatment interactions or irrigation main ef fects on ear yield (grand mean=9.6 Mt ha 1 ). N treatments had a significant effect on yield and treatment main effects are shown in Table 3 19 . PCU196 result ed in lower sweet corn yields (7.8 Mt ha 1 ) than PCU224 or UAN224 (9.9 and 11.1 Mt ha 1 , respective ly) which were similar . PCU224 and UAN224 resulted in y ields that were comparable to yields of

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61 9.1 to 10.1 Mg ha 1 reported by Teasdale et al. (2008) and yields of 11.2 Mt reported by Rangarajan et al. (2002) , but greater than sweet corn yields of 3.4 to 3 .9 Mt ha 1 reported by Cherr (2004) . Treatment main effects for quality results are shown in Table 3 20. There were no treatment interactions or irrigat ion treatment main effects on either ear quality parameter. N treatments had a significant effect on ear weight and tip fill, with UAN224 resulting in greater ear weights and greater degree of tip fill than either PCU treatment. However, UAN224 yields were only greater than the PCU196 yields, indicating that reducing N rate to 196 kg ha 1 N for the PCU blend used in this study was not viable for sweet corn production . This result is different than for potato , which resulted in no differences in yield betwe en PCU196 and 224 kg ha 1 N. However, the potato season PCU treatments were only supplied with ESN, while the PCU blend used for sweet corn included a PCU with a slower release rate. This could have impacted the differences in response to PCU196 between th e potato and sweet corn . These results suggest that in regards to yield and quality, PCU196 release was not in sync with crop uptake and was not a viable option for sweet corn production . PCU N rele ase rate is temperature dependent , so a PCU with a slower release rate (Duration 120) was blended with the ESN because of warmer summer temperatures. However, the release could have been too slow during the early part of the season to supply adequate N for PCU196 treatments. The slower release may have negativel y affected ear tip fill and average ear weight. Leachate While NH 3 N was measured for all leachate samples, NH 3 N was only above the detection limit for only three plot s on two sampling dates. As this amounted to less than

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62 0 .01 kg ha 1 N, these values wer e omitted and the N leaching load was determined from NO 2 N + NO 3 N concentrations. There were no treatment interactions or irrigation or fertilization main effects on sweet corn season cumulative N leaching load ( Table A 1 4 and 3 21 ), which is consistent with findings of Bero et al. (2013) that N leaching was similar between PCU and soluble N at similar N rates, as well as at reduced PCU N rates . There were no treatment effects on seasonal cumulative leached N load, but N treatments had a significant effe ct ( P= .01 ) on N leaching for the 27 September sampling date ( Table 3 2 2 ). On 27 September, UAN224 resulted in significantly greater N leaching than either PCU treatment. Figure 3 8 shows the N main effects for each sampling event; cumulative rainfall refer s to the total rainfall since the previous sampling event. There w ere 7.2 cm of rainfall between planting and the first sampling event, but very little N leaching; only 16 kg ha 1 N had been applied with UAN224 treatments and it is likely that PCU had not fully released so early in the season. N leaching was generally higher with PCU treatments for the next three sampling dates, but differences were not significant. However, by 27 September all of the UAN had been applied and UAN224 resulted in significantl y more leaching than either PCU treatments ( F igure 3 8 ). The average cumulative inorganic N leached across all treatments was 22.1 kg ha 1 N (Table 3 21) , which was three to four times greater than N leaching during the potato season and slightly lower tha n the 32 kg N ha 1 N leaching predicted for sweet corn by the CERES Maize model ( He , 2008) . However, Minshew et al. (2002) found that modeling of N leaching typically over predicted N leaching compared with observed measurements. Th ese results suggest that sweet corn production late in the summer is

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63 more at risk for N leaching losses, emphasizing the need for PCU technologies that release more in sync with plant needs in warm temperatures than the 50/50 ESN/Duration blend used in this project. Soil There were no treatment interactions and irrigation treatments had no effect on soil N on any sampling date . N main effects were significant ( P= .02 ) for final soil inorganic N amounts near the end of the sweet corn season (Table 3 2 3 ) . Soil N content at the end of the sweet corn showed an opposite pattern from soil N at the end of the potato season, with UAN224 resulting in significantly higher residual soil N than either PCU treatment at the end of the sweet corn season . Soil N with both PCU treatments peaked on 27 August (26 DAP), dropping significantly by 3 September. This is in contrast with UAN224 soil N, which remained more consistent, peaking much lower on 27 August and increasing after 3 September in response to the final N applications. The soil N peak in PCU treatments was much lower in the sweet corn season than the potato season, which suggest s that N release from PCU was not rapid enough throughout the sweet corn season to provide adequate N for the sweet corn at the reduced rate . However, the four spl it applications of UAN result ed in more constant soil N content throughout the season. Crop B iomass and N Uptake There were no interactions and treatments had no e ffect on plant biom ass ( dry weight of stover + ears + roots), which averaged 5. 5 Mt ha 1 ac ross treatments (Table 3 24) . This wa s within the range of sweet corn dry matter production reported by Zotarelli et al. (2008), which was 2.0 to 6.1 Mt ha 1 . Total N uptake was the sum of stover, ear, and root N uptake and was the product of dry weight an d TKN for each sample . N

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64 treatments had a significant effect ( P= .05) on total N uptake and N treatment main effects are shown in Table 3 2 5 . Whole plant N uptake ranged from 69.7 to 96.9 kg ha 1 N, which was consistent with published values for early seaso n sweet corn varieties that ranged from 59 to 12 6 kg ha 1 N (Heckman, 2007; Zotarelli et al., 2008). UAN224 resulted in significantly greater N uptake than PCU196, which was related to the significantly higher yields of UAN224. Figure 3 10 shows N main eff ects on whole plant uptake over the sweet corn season, illustrating constant N uptake throughout the season similar to results from Zotarelli et al. (2008) . This emphasizes the importance of maintaining N availability throughout the sweet corn season and h elps to explain the underperformance of PCU 196 compared with UAN 224 . There were no treatment interactions or irrigation main effects on root N uptake, but N main effects were significant . Root N uptake ranged from 2.0 to 4.0 kg ha 1 N a nd were within the r ange of 1.8 to 5.3 kg ha 1 N reported by Zotarelli et al. (2008) for sweet corn roots. UAN224 resulted in significantly higher root N uptake than either PCU treatment, but only resulted in an additional N removal of 2 kg ha 1 N. Agreement between the measu red N uptake values in this study and published values shows that plant sampling was effective in harvesting sweet corn roots. While roots were only harvested to the depth of 30 cm, Cherr et al. (2006) found that 85 to 95% of sweet corn roots on an Entisol in Florida were in the upper 30 cm of the soil profile. There were no treatment interactions or main effects on stover N uptake, which ranged from 49 to 64 kg ha 1 N (Table 3 25) . This range was higher than the range of 12.1 to 39 kg ha 1 N reported by Z otarelli et al. (2008) for sweet corn stover, but

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65 consistent with the 46 kg ha 1 N stover removal reported by Heckman for early season sweet corn varieties (2007). There were no treatment interactions or irrigation main effects on root N uptake, but N mai n effects were significant for ear N upta ke (Table 3 25) . Ear N uptake ranged from 19 to 29 kg ha 1 N , which was on the lower end of the range of 12.4 to 53.9 kg ha 1 N reported by Zotarelli et al. (2008) for sweet corn ear N uptake, but consistent with th e 28 kg ha 1 N ear removal reported by Heckman (2007). These results suggest that stover N uptake remains consistent, while differences in whole plant N uptake are largely influenced by differences in ear N uptake. Sweet corn cultivar can impact yield (Ran garajan et al., 2002) and N uptake (Heckman, 2007), which could account for differences between published values for yield and N uptake between sources. There were no treatment interactions or main effects on FNUE, which averaged 32% across all treatment c ombinations (Table 3 2 6 ) . This is lower than the NUE of 51% reported by He (2008) and lower than the FNUE for both PCU treatments during the potato season. This can be attributed to the higher N applications and lower N uptake compared with the potato sea son and suggests that there is large potential to increase FNUE for fall grown sweet corn. Leaf N Concentration Leaf samples taken at tasseling on 5 September ( 35 DAP) and silking on 12 September (42 DAP) were analyzed for TKN to determine plant N nutrie nt status. There was a significant treatment interaction on leaf N concentration for the first sampling date ( Table 3 2 7 ). PCU224 resulted in significantly lower TKN than UAN22 4 within 100ET irrigation treatments, while UAN224 resulted in significantly gre ater TKN than either PCU treatment within 125ET irrigation treatments . These results indicate that UAN224

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66 treatments resulted in a better plant N status than PCU treatm ents at excessive irrigation rates . Irrigation main effects were not significant for th e first sampling date, but were significant for the second samp l ing date ( Table 3 2 8 ). 75FC treatments resulted in significantly greater leaf TKN than 125ET, which maintained soil moisture above field capacity with excessive irrigation. This also suggests that higher irrigation rates resulted in greater N losses towards the end of the season. N treatment main effects were significant (P=. 01) for both sampling dates ( Table 3 25 ). Leaf N concentrations with PCU196 and PCU224 were significantly higher than for UAN224 , but all treatments were within the adequate range. The leaf N concentrations for both sampling dates were higher than values of 10 to 18 g kg 1 N reported by Cherr (2006), which were lower than the adequate range likely due to the lower N fertiliz ation rate of 133 kg ha 1 N . Average leaf N concentrations were above the adequate range (Ozorez Hampton., 2012) for all treatments on all sampling dates. Partial N Budget T here wer e no treatment interactions or irr igation main effects on the end of season unaccounted for N, but N treatment effects were significant ( Table 3 29 ). PCU224 treatments resulted in a larger unaccounted for N than either PCU196 or UAN224. The unaccounted for N was much higher for the sweet corn season compared with the potato seaso n, which could be attributed to the warmer temperatures and wetter conditions of the sweet corn season. While UAN224 led to higher N uptake and greater yields than PCU 196 , as well as lower unaccounted for N than PCU applied at the same rate, the high unacc ounted for N and low FNUE across treatments suggest that the efficiency of N fertilizer use can be greatly improved for late summer sweet corn

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67 production. The results from the sweet corn season suggest that, despite using a 50/50 mixture of ESN and Duratio n 120 , N release was too slow to be used effectively at a reduced rate for late summe r sweet corn production. A blend that uses a sma ller proportion of Duration 120, or a 100% ESN program, could be a potential alterative that should be investigated . From a yield , environmental , and economic perspective, PCU was not a viable alternative for sweet corn production. Yields were reduced with PCU 196 and there were no differences in N leaching among treatments. Additionally, there was no economic benefit to reduc ing N rates with PCU, as PCU196 reduced yield resulted in more expensive fertilizer N programs (Table 3 34) . PCU224 was a viable alternative to UAN224, as it did not lead to differences in yield, although there was no environmental or economic benefit due to no measured differences in leached N load and a higher fertilizer cost (Tables 3 21 and 3 34) Soil N and N uptake suggest that PCU release was not well suited for the sweet corn crop at the reduced rate , with UAN224 outperforming PCU196 due to a greater and more constant N supply throughout the season. The low N uptake values suggest that there is a large potential to increase FNUE for sweet corn, which could result in the reduction of recommended N application rates with more efficient use of N for swee t corn production . Cereal Rye Rye was planted on 29 October, following the sweet corn harvest, but crop establishment was delayed due to nematode damage and warm fall temperatures. No N fertilizer or irrigation treatments wer e applied during the cover crop season, but all plots received 16 kg ha 1 N early in the season to support cover crop establishment.

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68 Leachate Measurements of N leaching were continued to test for leaching of residual N from the sweet corn crop. During the cereal rye cover crop growing period, there were 4 leachate sampling events. NH 3 N was not above the detection limit for any of the lysimeter samples during the cereal rye cover crop, so leaching load was determined from NO 2 N + NO 3 N concentrations. Ther e were no significant interactions and no treatment main effects on leached N load for any of the sampling dates , cumulative cereal rye leached load, or cumulative sweet corn + cereal rye leached load. T he ANOVA table for total leached load is shown in tab le A 1 5 . Average leached N during the cereal rye cover crop was 5.9 kg ha 1 N across all treatments , which was greater than the 1.9 kg ha 1 N leaching measured for a rye ryegrass mixture (Hellmuth, 2013) . Soil There were no treatment interactions or main effects on inorganic soil N at the end of the cereal cover crop . R esidual soil N ranged from 15.2 to 29.4 kg ha 1 N at the end of the sweet corn season, but average final inorganic soil N across all treatments with the rye cover crop was 11.4 kg ha 1 N (T able 3 30 ) . This is slightly higher than the initial potato season soil N and the end of millet season soil N, which could be due to cooler winter temperatures, but overall the pattern of cover crop scavenging of residual soil N was consistent for both the millet and cereal rye cover crop. At the end of both summer and winter cover crop periods the soil N stocks had returned to the same level as in March 2013 when the potato crop was established. Biomass and N Uptake There were no treatment interactions or main effects on total plant biomass or dry matter partitioning . Average plant biomass (shoots + roots) was 1.2 kg ha 1 , which is

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69 consistent with the 1.0 Mt ha 1 dry matter reported by Garwood et al. (1999). T otal N uptake was the sum of shoot and root N up take and was determined b y multiplying the dry weight by TKN for each sample. There were no treatment interactions or main effects on whole plant, shoot, or root N uptake. Main effects are shown in Table 3 31 . Average N uptake across all treatments was 12. 5 kg ha 1 N, which was lower than the 27 kg ha 1 N uptake reported for cereal rye by Garwood et al. (1999), despite similar dry matter values. Total N uptake was less than applied N and the benefits of N application to cover crop establishment were unreali zed due to poor crop growth . Partial N B udget There were no trea tment interactions or main effects on the end of season unaccounted for N . The average unaccounted for N at the end of the cereal rye cover crop was 16.6 kg ha 1 N, whi ch was similar to the 16 kg ha 1 N that was applied at the beginning of the season (Table 3 32) . The warm winter temperature s result ed in a poor stand and very low biomass , which resulted in a low total N uptake ( Table 3 31 ). Initial soil inorganic N was greater in UAN224 than either PCU treatment , but there were no differences between treatments for final soil inorganic N content. This could explain the larger unaccounted for N in UAN224 treatments, despite no statistical difference between the unaccounted for N of UAN224 and e ither PCU treatment. Total Season This study evaluated N and irrigation practices and their e ffects on crop growth, N leaching, and N efficiency. One objective of this study was to evaluate N leaching and N use efficiency over the entire cropping system . Total leached N load was summed over the entire season, to evaluate differences in leached N loads over the entire cropping sequence. Additionally, the partial nutrient budget for each treatment

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70 over the entire cropping sequence was compared to gain a ful ler understanding of N fates and flows throughout a potato millet sweet corn cereal rye cropping sequence. Leachate The average cumulative leached N over the cropping system from February 2013 through February 2014 for all crops was 35.6 kg ha 1 N. Ther e were no treatment interactions and irrigation treatments had no effect on cumulative leached N. N main effect s were not significant ( P= . 10 ) , and are shown on Figure 3 11 . T he variability of measurements of leached N load in these experiments (CV= 47%) mad e it difficult to determine N treatment effects on total inorganic l eached N load over the entire cropping sequence . Leached load was highest for UAN224, followed by PCU224, and lowest with PCU196, although the differences were not significant at =.05 . Th ese results suggest a potential of reducing leached N load over the cropping sequence, but future investigations should use higher re plications in an attempt to reduce variability and increase significance. Other researchers have noted the challenges with variability in measuring nitrate leaching in field experiments (Bero et al., 2014). On 20 November 2013, a leachate sample submitted to the ARL was analyzed for inorganic N ( NH3 N + NO 3 N), as well as TKN. D ata were analyzed in JMP (SAS Institute, Cary, N C) using a two sample t test. The null hypothesis that the difference between our standard leachate analysis ( NH3 N + NO 3 N) and total N (NO 3 N + TKN) was zero was rejected (p<.0001) and the average difference between NH3 N + NO 3 N and total N was 0 .88 mg L 1 . While this is a minor difference, it could account for un derestimates in leached N load; however, treatments had no significant interactions or main effect s on the differences between the leachate analysis methods used in this study and total N result s , so any underestimat ion was consistent across treatments .

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71 Irrigation treatments had no effect on cumulative total N leached, but occasionally had significant main effects on sampling dates. However, this was typically at the end of the season, when cro p uptake had peaked and soil N differences were minimal between treatments . Additionally, while there were differences in soil moisture over the season for both principal crops, 80% of rainfall events were followed by one or more days of additional rainfal l. Initial rainfall events likely filled the water reservoir in 75FC treatments, resulting in no differences between 75FC and 100FC treatments during the subsequent rainfall events. Partial N B udget There were no treatment interactions or main effects on the end of cropping system unaccounted for N , other than significant N main effects on fertilizer N input across N treatments (Table 3 33 ) . The average unaccounted for N at the end of the cropping sequence was 195 kg ha 1 N, which was 40% of the average t otal N inputs (Table 3 3 3 ) . N treatment m ain effects were not considered significant (P=.10), which is likely due to the lack of consistent treatment effects on N uptake and N leaching across the different crops. PCU196 and PCU224 resulted in similar unacc ounted for N during the potato season, while PCU196 and UAN224 resulted in similar unaccounted for N during the sweet corn season, which reduced the differences between treatments over the entire cropping system. These results allow for the identification of the major fates and flows in N within a potato millet sweet corn cereal rye cropping sequence, showing that unaccounted for N ma de up a large percentage of N inputs in irrigated Florida cropping systems. While this study focused on the effects of N and irrigation management on N leaching, which represented 11% of total outputs, these results suggest that gaseous losses were the largest N loss pathway. The unaccounted for N

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72 appears to be largely influenced by the unaccounted for N from the sweet corn seas on, which contributed to 62% of total unaccounted for N. The cumulative N budget suggest s that all crops within a cropping system should be managed to reduce both leaching and gaseous N losses , as crops differ in their impacts on various components of the N budget . The budget is a useful tool for identifying where improvements can be made in increasing FNUE and decreasing N losses for each crop. Total crop FNU Es ranged from 50 to 55%, which are typical of global average values, but suggests there is still m uch room for improvement . Reducing whole season N losses and increasing FNUE will require the synchronization of N application and crop demand via integrated crop management (Fageria and Baligar, 2005) . Cost Analysis The price of the N fertilization progra ms for both the potato and sweet corn seasons were determined from a fertilizer quote given for all products on the same day from the same supplier (Crop Production Services Inc., Mulberry, FL) . Cost comparison of the potato fertilizer programs show ed that ESN applied at the rate of 196 kg ha 1 N reduced N fertilizer costs compared with UAN (Table 3 34 ) , which also minimized inorganic N leaching , increased potato FNUE, and maintained potato yields. Reducing fertilizer application by 28 kg ha 1 N for the ent ire 14,266 planted hectares of potatoes (USDA, 2012) would reduce applied N by 400 M t and lead to a total savings of $100,000. Additionally, the reduction in fuel costs resulting from a single application of PCU compared with the recommended split applicat ions of soluble fertilizer further incentivizes the use of PCU for potato production. Significant financial savings could result from the use of controlled release N in potato production in Florida.

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73 While the use of PCU at the rate of 196 kg ha 1 N re duced N leaching, increased FNUE, and reduced total fertilizer costs for potato , the 50/50 ESN/Duration 120 PCU blend was not a viable fertilizer alternative for sweet corn production. The release rate from t he PCU blend (ESN and Duration 120 ) was not well suit ed for fall planted sweet corn at the reduced rate of 196 kg ha 1 N, resulting in reduced yields and did not reduce N leaching. Additionally, the f ertilizer blend used was more expensive than the liquid UAN because of the higher price of Duration 120, whic h was three times the price of UAN by weight and double the cost of ESN (Table 3 35 ) . While measurements of plant physiological stress were outside the scope of this project, t he reduced irrigation treatment (75FC) had no negative impact on potato or swee t corn yield . While variability of leached N load and rainfall patterns likely contributed to the lack of significant irrigation effects on leached N, there were still differences in irrigation application and 75FC resulted in water savings of 770,000 L pe r ha over the entire cropping sequence compared to 100ET treatments . Managing soil moisture below field capacity can reduce irrigation costs, without reducing yields, and represents an economic advantage to the producer.

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74 Table 3 1. Irrigation treatment main effects on soil moisture tension averaged over the potato season. Irrigation Treatment Soil Moisture Tension kPa 75FC z 11.5a 1 100ET y 10.0b 125ET x 9.0b Significance P=.0002*** 1 Levels not connected by the same letter are significantly diffe . ***Significant at P=.001 z Maintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET Table 3 2. Irr igation and nitrogen fertilizer main effects on total yield, marketable yield, size A4 and B tubers, and tuber quality. Treatment Marke table Yield t Total Yield s Size A4 Tubers Size B Tubers Quality Reduction r Mt ha 1 % Irrigation P=.71 NS P=.42 NS P= .98 NS P=.49 NS P=.61 NS 75FC z 29 . 7 30 .3 3.0 4.7 0 100ET y 29 . 7 30 .2 3.0 5.1 2 125ET x 27 . 4 28 .2 3.1 4.5 2 N itrogen P=.46 NS P=.20 NS P=.004** P=.00 4** P=.28 NS PCU196 w 28 . 9 29 .8 3.0ab 4.4b 1 PCU224 v 29 . 4 30 . 2 4.3a 4.0b 2 UAN224 u 28 . 5 28 . 7 1.7b 6.0a 2 NS Nonsignificant , **significant at P z Maintenance of 75% field capa city (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET, w Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, v PCU applied at plant ing at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications, t size A1 A4, B, and C tubers, s marketable yield plus culls, r y ield reductions as a percent of total yields due to shape deformities an d defects. Table 3 3. Total leached N load for potato season. Nitrogen Treatment Total Leached N Load kg ha 1 PCU196 z 2. 1b 1 PCU224 y 4. 7 ab UAN224 x 7. 9 a Significance P=.003** 1 Levels not connected by the same letter are signifi . z Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, y PCU applied at planting at the rate of 224 kg ha 1 N, x urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications . * *S ignificant at P

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75 Table 3 4. N main effects on leached N load from 15 March and 12 April samples. N Treatment 3 / 15 /2013 4 / 12 /2013 kg ha 1 N PCU196 z 1.3b 0 .07b PCU224 y 3.9ab 0 .33b UAN224 x 5.2a 1.4a Significance P=.01** P=.04* 1 . z Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, y PCU applied at planting at the rate of 224 kg ha 1 N, x urea ammonium ni trate (UAN) applied at the rate of 224 kg ha 1 N in split applications. * Significant at P .05, **significant at P Table 3 5. Interaction effects for 24 April and 23 May leached nitrate N loads. Irrigation Treatment Nitrogen Treatment NO 3 N Load by Sample Date 4/24/13 5/23/13 kg ha 1 N 75FC z PCU196 w 0 .099b 1 0b 75FC PCU22 4 v 0 .70b 0b 75FC UAN224 u 0 .0029b 0b 100ET y PCU196 0b 0b 100ET PCU224 0 .007b 0b 100ET UAN224 0b 0b 125ET x PCU196 0 .00067b 0b 125ET PCU224 0 .029b 0b 125ET UAN224 1.9a .096a Significance P=.006** P=.05* 1 Levels not connected by the same . * Significant at P .05, **significant at P z Maintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET, w Polymer coated urea (PCU) applied at p lanting at the rate of 196 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications.

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76 Table 3 6. Soil mineral N content as affected by N fertilize r treatment for al l potato season sampling dates. N itrogen Treatment 2/7/2013 3/25/2013 4/5/2013 5/7/2013 5/28/2013 kg ha 1 N PCU196 z 8.70 176a 135 62.2ab 38.3a PCU224 y 8.70 207a 182 104a 40.5a UAN224 x 8.70 108b 151 27.9b 17.2.6b Significance P= .9 NS P= .0002*** P= .7 NS P= .03* P= .004** 1 . NS Nonsignificant,*significant at P .05, **significant at P z Polymer coated urea (PCU) applied at pla nting at the rate of 196 kg ha 1 N, y PCU applied at planting at the rate of 224 kg ha 1 N, x urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. Table 3 7. Treatment main effects on end of season plant dry biomass parti tioning. Treatment Shoot Root Tuber g plant 1 Irrigation P=.4 NS P=.9 NS P=.3 NS 75FC z 33 t 0 .67 74 100ET y 33 0 .68 76 125ET x 32 0 .56 68 N itrogen P=.3 NS P=.2 NS P=.6 NS PCU196 w 36 0 .63 71 PCU224 v 31 0 .56 72 UAN224 u 29 0 .72 75 NS Nonsignificant z Maintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET w Polymer coated urea (PCU) a pplied at planting at the rate of 196 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. t Plant spacing resulted in a plant population of 71, 729 plants ha 1 .

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77 Table 3 8. Main effects for irrigation and N fertilizer treatments on whole plant N content at the end of the season on 17 May. Treatment Total Plant N Content Shoot Root Tuber kg ha 1 N Irrigation P= .6 NS P= .9 NS P= .8 NS P= .6 NS 75FC z 144 66 0 .9 77 100ET y 141 64 1 76 125ET x 135 62 0 .9 72 N itrogen P= .003** P= .01 ** P= .9 NS P= .2 NS PCU196 w 140.2ab 1 63ab 1 77 PCU224 v 158.5a 78a 0 .9 80 UAN224 u 122.2b 52b 0 .9 70 1 . NS Nonsignificant, **significant at P z Maintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET, w Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. Table 3 9. N main effects on potato fertilizer N use efficiency. N Treatment FNUE % PCU196 z 71a 1 PCU224 y 71a UAN224 x 55b Significance P=.001*** ** *Significant at P 1 HSD test . z Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, y PCU applied at planting at the rate of 224 kg ha 1 N, x urea ammonium nitrate (U AN) applied at the rate of 224 kg ha 1 N in split applications. Table 3 10. Dried potato whole leaf total K jeldahl nitrogen concentration by sampling date. N Treatment 52 DAP w 66 DAP v 80 DAP u g kg 1 N PCU196 z 62a 1 57a 42ab PCU224 y 63a 56a 44a UAN224 x 67a 54a 38b Significance P=.11 NS P=.3 NS P=.01** 1 . z Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N , y PCU applied at planting at the rate of 224 kg ha 1 N, x urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. w Plants at 20 cm height growth stage, v plants at first flower growth stage, u plants at full flower growth stag e

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78 Table 3 11. N main effects on potato petiole sap NO 3 N by sampling date. N Treatment Petiole sap NO 3 N 52 DAP 66 DAP mg L 1 PCU196 z 990 1150a 1 PCU224 y 980 1120a UAN224 x 1100 800b Significance P=.06 NS P= .005** 1 Levels not co . NS Nonsignificant , **significant at P , z p olymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, y PCU applied at planting at the rate of 224 kg ha 1 N, x urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. Table 3 12 . Potato season unaccounted for N . Treatment Unaccounted for N kg ha 1 N Irrigation P= .04* 75FC z 31.6b 1 100ET y 55.6a 125ET x 51.6a N itrogen P <.0001**** PCU196 w 26.4b PCU224 v 27.0b UAN224 u 85.4a 1 test . * Significant at P 5, * ***significant at P 001 z Maintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET, w Polymer c oated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. Table 3 13. Main effects for total millet/cr abgrass leached N load. Treatment Leached N kg ha 1 N Irrigation P=.18 NS 75FC z 1. 6 100ET y 3. 3 125ET x 3.5 Nitrogen P=.07 NS PCU196 w 4.3 PCU224 v 2.4 UAN224 u 1.7 NS Nonsignificant z Maintenance of 75% fie ld capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET, w Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, v PCU applied a t planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications.

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79 Table 3 1 4 . Main effects on millet/crabgrass cover crop end of season soil N. Treatment Soil N (NO 3 N + NH3 N) kg ha 1 N Irrigation P=.47 NS 75FC z 7.43 100ET y 8.41 125ET x 7.26 Nitrogen P=.13 NS PCU196 w 7.04 PCU224 v 7.14 UAN224 u 8.93 NS Nonsignificant z Maintenance of 75% field capacity (FC), y maintenance of 100% FC wi th daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET, w Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u ure a ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. Table 3 15. Main effects for total millet/crabgrass N uptake. Treatment Whole plant N Uptake kg ha 1 N Irrigation P=.55 NS 75FC z 32 100ET y 30 125E T x 27 N itrogen P=.69 NS PCU196 w 28 PCU224 v 32 UAN224 u 29 z Maintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 1 00% FC with daily irrigation at 125% crop ET, w Polymer coated urea (PCU) at 196 kg ha 1 N applied at planting, v PCU at 224 kg ha 1 N applied at planting, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. NS Nonsignifi cant

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80 Table 3 16. Main effects for dry plant biomass for the millet cover crop. Treatment Shoot Root Mt ha 1 Irrigation P=.54 NS P=.83 NS 75FC z 3.6 0 .4 100ET y 3.2 0 .3 125ET x 3.2 0 .4 Nitrogen P=.44 NS P=.33 NS PCU196 w 3.1 0 .4 PCU224 v 3.6 0 .3 UAN224 u 3.3 0 .3 NS Nonsignificant z Maintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop evapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET, w Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. Table 3 17 . Mill et/crabgrass cover crop unaccounted for N. Treatment Balance kg ha 1 N Irrigation P= . 18 NS 75FC z 16.4 100ET y 3.33 125ET x 13.9 Nitrogen P<.003 ** PCU196 w 19.7a PCU224 v 19.6 a UAN224 u 5.76b NS Nonsignificant z Maintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET, w Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. Table 3 18. Average soil moisture tension for sweet co rn soil by irrigation treatment. Irrigation Treatment Soil Moisture Tension kPa 75FC z 11.5a 100ET y 10.5ab 125ET x 9.9b Significance P=.05 1 Levels not connected by the same letter are significant . *Significant at P=.05 z Maintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET

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81 Table 3 19 . Main effects of irrigation and N fertilization on sweet corn yield . Treatment Yield Mt ha 1 Irrigation P= .29 NS 75FC z 10.3 100ET y 9.5 125ET x 9.0 Nitrogen P=.002** PCU196 w 7.8b PCU224 v 9.9a UAN224 u 11.1a NS Nonsignificant, **significant at P z Maintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigat ion at 125% crop ET, w Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. Table 3 20 . M ain effects of irrigation and fertilization on s weet corn ear quality measurements. Treatment Weight Tip Fill Ear Length g ear 1 Scale 1 5 cm ear 1 Irrigation P=.11 NS P=.16 NS P=.09 NS 75FC z 178 4.6 18.8 100ET y 179 4.7 18 .8 125ET x 169 4.5 18.0 Nitrogen P=.004** P=.01** P=.86 NS PCU196 w 167b 1 4.5b 18.5 PCU224 v 170b 4.5b 18.4 UAN224 u 190a 4.8a 18.6 1 Levels not connected by the same letter are significantly different . NS Nonsignificant, **significant at P z Maintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET, w Polymer coated urea (PCU) applied at planting at the rate of 1 96 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications.

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82 Table 3 21. Treatment main effects on seasonal leached N load for sweet corn. Treatment Leached N kg ha 1 Irrigation P=.68 NS 75FC z 18.4 100ET y 24.9 125ET x 21.4 Nitrogen P=.62 NS PCU196 w 22.3 PCU224 v 17.7 UAN224 u 24.7 NS Nonsignifican t z Maintenance o f 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET, w Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. Table 3 22. N fertilizer treatment main effects on leached N for 27 September lysimeter sample. Treatment Leached N kg ha 1 PCU196 z 4.8b 1 PCU224 y 5.2b UAN224 x 12.6a Significance P=.01** 1 . **significant at P z Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, y PCU applied at planting at the rate of 224 kg ha 1 N, x urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. Table 3 2 3 . Main effects of N fertilization on soil inorganic N content over the sw eet corn season. Sample Date N Treatment 8/27/2013 9/3/2013 10/3/2013 kg ha 1 N PCU196 z 65.0 21.6 19.4b 1 PCU224 y 70.2 23.0 15.2b UAN224 x 42.1 25.4 29.4a Significance P= .17 NS P= .78 NS P= .02* 1 . NS Non significant, *significant at P z Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, y PCU applied at plan ting at the rate of 224 kg ha 1 N, x urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications.

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83 Table 3 24. Irrigation and N treatment main effects on total season sweet corn dry plant biomass. Treatment Stover Ear Root Mt ha 1 Irrigation P=.48 NS P=.47 NS P=.33 NS 75FC z 1.9 2.8 0.4 100ET y 1.9 3.1 0.4 125ET x 2.0 3.2 0.4 Nitrogen P=.50 NS P=.54 NS P=.11 NS PCU196 w 1.9 2.8 0.4 PCU224 v 1.9 3.2 0.4 U AN224 u 2.0 3.2 0.4 NS Nonsignificant z Maintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET, w Polymer coated urea (PCU) appl ied at planting at the rate of 196 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. Table 3 2 5 . Seasonal t otal plant N uptake and stover, ear, and ro ot N uptake. N Treatment Whole plant Stov er Ear Root kg ha 1 N PCU196 z 69.7b 49 19b 1 2.0b PCU224 y 82.6ab 59 21b 2.8b UAN224 x 96.9a 64 29a 4.0a Significance P= .05* P= .65 NS P <.0004*** P <.0001**** 1 . NS Nonsignificant,* ** significant at P .001, * *** significant at P .0001 z Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, y PCU applied at planting at the rate of 224 kg ha 1 N, x urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. Table 3 26. Irrigation and N treatment main effects on sweet corn FNUE. Treatment FNUE % Irrigation P=.78 NS 75FC z 31 100ET y 34 125ET x 32 Nitrogen P=.20 NS PCU196 w 29 PCU224 v 31 UAN224 u 36 NS Nonsignificant z Maintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET, w Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications.

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84 Table 3 27. Treatment interactions for sweet corn leaf total K jeldahl nitrogen concen tration 27 DAP. Irr Treatment N Treatment g kg 1 N 75FC z PCU196 w 36ab 1 75FC PCU224 v 32abc 75FC UAN224 u 34abc 100ET y PCU196 32abc 100ET PCU224 29c 100ET UAN224 38a 125ET x PCU196 29bc 125ET PCU224 30bc 125ET UAN224 38a Significance P=.03* 1 . * significant at P .05, *significan t at P z Maintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET, w Polymer coated urea (PCU) applied at planting at the rat e of 196 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. Table 3 28. Sweet corn leaf total K jeldahl nitrogen by sampling date. Treatment 35 DAP t 42 DAP s g kg 1 N Irrigation 75FC z 3.4 2.7a 100ET y 3.3 2.6ab 125ET x 3.2 2.4b Significance P=.39 NS P=.05* Nitrogen PCU196 w 3.2b 1 2.5a PCU224 v 3.0b 2.5a UAN224 u 3.7a 2.7a Significance P < .0001**** P=.04 NS 1 . NS Nonsignificant, * significant at P .05, * ***significant at P .0001 z Maintenance o f 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET, w Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. t Tasseling growth stage, s s ilking growth stage

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85 Table 3 2 9 . Main effects on sweet corn unaccounted for N. Treat ment Unaccounted for N kg ha 1 N Irr Treatment P= . 32 NS 75FC z 127 100ET y 111 125ET x 51.6 N Treatment P=.009 ** PCU196 w 114b 1 PC U224 v 142a UAN224 u 106b 1 . NS Nonsignificant,* *significant at P .0 1 z Maintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET, w Polymer coated urea (PCU) applied at planting at the rate of 1 96 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. Table 3 30. Final soil inorganic N content during the cereal rye cover crop period. NS Nonsignificant z Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, y PCU applied at planting at the rate of 224 kg ha 1 N, x urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. Table 3 31. Main effects on cereal rye whole plant, shoot, and root N uptake. Treatment Whole plant N uptake Shoot N Uptake Root N Uptake kg ha 1 N Irrigation P=.50 NS P=.47 NS P=.95 NS 75FC z 12.0 9.6 2.4 100ET y 13.5 11.1 2.4 125ET x 12.0 9.6 2.4 Nitrogen P=.72 NS P=.58 NS P=.64 NS PCU196 w 1 2.2 9.7 2.5 PCU224 v 13.2 10.9 2.2 UAN224 u 12.1 9.6 2.4 NS Nonsignificant z M aintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET, w Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applicat ions. N Treatment 2/7 /20 14 kg ha 1 N PCU196 z 11.2 PCU224 y 11.3 UAN224 x 11. 7 Significance P=.93 NS

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86 Table 3 32 . Main effects on cereal rye unaccounted for N b udget. Treatment Balance kg ha 1 N Irrigation P= . 85 NS 75FC z 17.4 100ET y 17.6 125ET x 14.7 N itrogen P=.13 NS PCU196 z 14.7 PCU224 y 11.5 UAN224 x 23.5 NS Nonsignificant z Maintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET , w Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. Table 3 33 . Main effects on una ccounted for N over the potato millet sweet corn cereal rye cropping sequence. Inputs Outputs Balance t Treatment Fertilizer N Initial soil N Uptake Residual soil N Leached N kg ha 1 N Irr igation P=1 NS P=.08 NS P=.57 NS P=.55 NS P=.97 NS P= . 52 NS 75FC z 483 81.8 260 75.7 37.3 192 100ET y 483 62.9 263 56.5 39.2 187 125ET x 483 64.2 247 57.8 37.8 205 Nitrogen P .0001**** P=.54 NS P=.09 NS P=.07 NS P=.10 NS P=.10 NS PCU196 w 446 71.2 243 64.8 30.4 179 PCU224 v 502 73.5 277 67.2 34.9 197 UAN224 u 502 64.2 250 57.9 49.0 209 NS Nonsignificant , z Maintenance of 75% field capacity (FC), y maintenance of 100% FC with daily irrigation at 100% crop e vapotranspiration (ET), x maintenance of 100% FC with daily irrigation at 125% crop ET, w Polymer coated urea (PCU) applied at planting at the rate of 196 kg ha 1 N, v PCU applied at planting at the rate of 224 kg ha 1 N, u urea ammonium nitrate (UAN) applied at the rate of 224 kg ha 1 N in split applications. u U naccounted for N. Table 3 3 4 . Potato fertilizer program costs. N Treatment Analysis N P K Application rate kg ha 1 N Price $ kg 1 Price $ kg 1 N Cost $ ha 1 PCU196 z 44 0 0 1 196 0.74 1.68 329 PCU224 y 44 0 0 1 224 0.74 1.68 376 U AN224 x 32 0 0 224 0.48 1.50 336 1 ESN

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87 Table 3 3 5 . Sweet corn fertilizer program costs. N Treatment Analysis N P K Application rate kg ha 1 N Price $ kg 1 Price $ kg 1 N Cost $ ha 1 PCU196 z 44 0 0 1 /43 0 0 2 196 0.74 1 /1.3 2 2 1.68 1 /3.08 2 466 PCU224 y 44 0 0 1 /43 0 0 2 224 0.74 1 /1.32 2 1.68 1 /3.08 2 533 UAN224 x 32 0 0 224 0.48 1.50 336 1 ESN 2 Duration 120 Figure 3 1. Cumulative irrigation, ET c , rainfall, and historic rainfall ov er the potato season. Figure 3 2. Rainfall over the potato season at Citra, FL. 0 5 10 15 20 25 30 23 29 35 41 47 53 59 65 71 77 83 89 95 cm Days after planting FC75 FC100 FC125 Cumulative ETc Cumulative Rainfall Cumulative Rainfall 2002-2012 0 10 20 30 40 50 3/7/2013 3/21/2013 4/4/2013 4/18/2013 5/2/2013 5/16/2013 mm

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88 Figure 3 3. N main effects on leached N load and cumulative rainfall from previous sampling date. Figure 3 4. N main effects on potato dry plant biomass accum ulation. 0 2 4 6 8 10 12 14 0 1 2 3 4 5 6 3/1/13 3/15/2013 3/29/2013 4/12/2013 4/24/2013 5/9/2013 5/23/2013 Rainfall (cm) Leached N load (kg ha 1 ) PCU196 PCU224 UAN224 Rainfall 0 1 2 3 4 5 6 7 22-Mar 5-Apr 19-Apr 3-May 17-May Mt ha 1 PCU196 PCU224 UAN224

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89 Figure 3 5. N main effects on potato whole plant N uptake. Figure 3 6. Cumulative irrigation by treatment, ET c , rainfall, and historic rainfall during sweet corn season. 0 20 40 60 80 100 120 140 160 180 22-Mar 5-Apr 19-Apr 3-May 17-May kg ha 1 N PCU196 PCU224 UAN224 0 5 10 15 20 25 18 25 32 39 46 53 60 67 cm DAP FC75 FC100 FC125 Cumulative ETc Cumulative Rainfall

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90 Figure 3 7. Rainfall over the sweet corn season at Citra, FL. Figure 3 8. N main effects on sweet corn season leached N load and cumulative rainfall from previous sampling date. 0 5 10 15 20 25 30 35 40 45 8/19/2013 9/2/2013 9/16/2013 9/30/2013 mm

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91 Figure 3 9. N main effects on sweet corn dry matter accumulation over the season. Figure 3 10 . N main ef fects on total plant N uptake over the sweet corn season. Figure 3 11 . Total inorganic leached N load, February 2013 February 2014. 0 1 2 3 4 5 6 7 8 22-Aug 31-Aug 9-Sep 18-Sep 27-Sep 6-Oct Mt ha 1 PCU196 PCU224 UAN224 0 20 40 60 80 100 22-Aug 31-Aug 9-Sep 18-Sep 27-Sep 6-Oct kg ha 1 N PCU196 PCU224 UAN224 0 10 20 30 40 50 60 PCU196 PCU224 UAN224 kg ha 1 N Total Season Inorganic N Leached Load N Treatment Main Effects

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92 CHAPTER 4 CONCLUSIONS T he goal of this project was to update best management practices for potato and swee t corn to include more economically viable and resource efficient irrigation and nitrogen fertilizer management practices. The objectives of this project were to determine the effects of irrigation management and fertilizer N source on crop yield and amoun t of nitrate leached from the root zone and to compare the partial nutrient budgets for each treatment combination. The results of this project suggest that growers should be encouraged to adopt PCU as an alternative fertilizer N source for potato producti on, as this resulted in a lower N application requirement that maintained tuber yields and reduced N leaching. Additionally, fertilizer N costs were reduced with the use of ESN, a low cost PCU. Results also suggested that maintaining soil moisture between 75 to 80% FC likely minimized the gaseous N losses and led to a large redu ction in water use, so irrig ation management BMPs should recommend keeping soil moisture below field capacity, rather than at or above field capacity. The adoption of these more reso urce efficient management practices can minimize N losses and increase the fertilizer nitrogen use efficiency of Florida potato production through the joint management of irrigation and nitrogen. PCU was a viable fertilizer alternative that increased the efficiency of potato production when compared with conventional fertilizer N management, but the PCU fertilizer blend used in this study was not a viable alternative for fall sweet corn production. Sweet corn yield was reduced with the PCU blend at the red uced rate of 196 kg ha 1 N, w ith no differences in N leaching among treatments. Soil N and N uptake

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93 suggested that the PCU N release was not well suited to the fall sweet corn crop to allow for a reduced N rate. While the results of this project aid in the development of more efficient N fertilizer and irrigation management practices, there are still many barriers that prevent the movement of Florida growers to alternative production systems. PCU has the potential to reduce N loss and maintained potato yiel d, but there are still perceived economic barriers that prevent the widespread adoption of controlled release fertilizer technologies in Florida potato production systems. Cost analysis of the fertilizer programs showed that reduced N rates offset the high er cost of PCU for potatoes, but not for the PCU blend used for the sweet corn season. While there are instances when the cost of polymer coated urea is comparable to or below the cost of liquid UAN, the price differences will vary between products and ove r time. Government cost sharing programs are important in encouraging shifts in production systems toward BMPs and will be necessary to support the adoption of more expensive controlle d release fertilizer programs. D espite its limitations, ascribing value to the preservation of water quality should still be encouraged as it could support policy makers in the development of such programs. Future R esearch Nitrate losses from agricultural systems can negatively impact ecosystem health, degrade water quality, and represent an economic loss to growers. While the downstream effects of agricultural nitrate losses threaten ecosystem services around the world, agriculture faces the challenge of increasing production to feed a growing population. Maintaining high yi elds must be done in a more environmentally sustainable

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94 context, so understanding N cycling will continue to remain a priority for agricultural research. Evaluating site specific management practices that target the main pathways of N loss for Florida pot ato and sweet corn production will impact the sustainability of future agricultural production in the state of Florida. While the unaccounted for N for each crop in the current study suggest differences in gaseous losses, direct measurement of denitrificat ion and volatilization were outside the scope of this project. Future research should include direct measurements of gaseous N losses and soil N mineralization to develop a complete N budget for typical Florida cropping systems. Additionally, future resear ch including with PCU fertilizers should include experiments to evaluate N release from controlled release fertilizers in the field over the season. Future research should focus on strategies for increasing N use efficiency for early sea son sweet corn va rieties. Whole plant N uptake was consistent with published values for early season sweet corn varieties, but the low uptake resulting from lower biomass suggests that increases in N use efficiency could result in a reduction of the recommend ed N rates for fall grown sweet corn varieties.

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95 APPENDIX ANOVA TABLE S Table A 1. ANOVA table for the effect of sample date on NO 3 N concentration of leachate in the lysimeter reservoir. Source DF SS MS F P > F Sample Date 7 0.309 0.044 1.00 6 0.49 1 Error 8 0.351 0 .043 Total 15 0.66 1 Table A 2. ANOVA table for the effects of drainage through the lysimeter basin and experiment run on leachate NO 3 N concentration. Source DF SS MS F P > F Model 5 23.835 4.767 0.63 7 0.67 7 Drainage 1 1.55 6 1.555 0.207 0.65 7 Run 2 7.236 3.618 0.48 3 0.62 9 Drain*Run 2 15.04 4 7.52 2 1.003 0.395 Error 12 89.96 2 7.49 7 Total 17 113.79 7 Table A 3 . ANOVA t able for potato season tensiometer readings. Source DF SS MS F P > F Model 8 31.287 3.911 2.986 0.0257 N 2 1.246 0.623 0.476 0.629 Irr 2 27.843 13.922 10.629 0. 0009 N*Irr 4 2.198 0.549 0.420 0.792 Error 18 23.575 1.310 Total 26 54.863 Table A 4 . ANOVA t able for marke t able tuber yield. Source DF SS MS F P > F Treatments 8 299.529 3 7.441 1.771 0.1 49 N 2 38.666 19.333 0.914 0.419 I 2 75.031 37.515 1.775 0.198 N*Irr 4 185.832 46.458 2.198 0.110 Error 18 380.535 21.141 Total 26 680.064

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96 Table A 5 . ANOVA t able for total tuber yield. Source DF SS MS F P > F Treatments 8 204.53 7 25.567 1.083 0.417 N 2 16.296 8.148 0.345 0.71 3 I 2 38.840 19.420 0.823 0.455 N*Irr 4 149.400 37.350 1.582 0.22 2 Error 18 424.845 23.603 Total 26 629.382 Table A 6 . ANOVA t able for potato quality. S ource DF SS MS F P > F Treatments 8 7.042 0.880 0.88 2 0.5 50 N 2 1.023 0.512 0.513 0.607 I 2 2.75 3 1.376 1.379 0.277 N*Irr 4 3.266 0.817 0.8180 0.530 Error 18 17.96 7 0.998 Total 26 25.009 Table A 7 . ANOVA t able for total seas on leached N load for potato season. Source DF SS MS F P > F Treatments 8 269.842 33.730 3.689 0.010 N 2 153.984 76.992 8.420 0.002 I 2 22.793 11.396 1.244 0.311 N*Irr 4 93.066 23.266 2.544 0.075 Error 18 164.597 9.144 Total 26 43 4.440 Table A 8 . ANOVA t able for end of season soil N. Source DF SS MS F P > F Treatments 8 269.843 33.730 3.689 0.010 N 2 153.984 76.992 8.420 0.003 I 2 22.793 11.396 1.246 0.311 N*Irr 4 93.06 6 23.266 2.544 0.075 Error 18 164 .597 9.144 Total 26 434.440

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97 Table A 9 . ANOVA t able for final potato root biomass. Source DF SS MS F P > F Treatments 8 0.34 7 0.043 1.101 0.40 7 N 2 0.110 0.05 5 1.39 7 0.27 3 I 2 0.082 0.041 1.045 0.37 2 N*Irr 4 0.154 0.03 9 0 .981 0.442 Error 18 0.708 0.039 Total 26 1.055 Table A 10 . ANOVA table for final potato shoot biomass. Source DF SS MS F P > F Treatments 8 676.956 84.620 1.326 0.293 N 2 226.209 113.105 1.772 0.198 I 2 3.969 1.984 0.031 0.969 N*Irr 4 446.778 111.694 1 .750 0.183 Error 18 1148.882 63.827 Total 26 1825.838 Table A 11 . ANOVA table for final potato tuber biomass. Source DF SS MS F P > F Treatments 8 1281.46 5 160.183 1.300 0.304 N 2 109.615 54 .808 0.445 0.648 I 2 320.137 160.068 1.299 0.297 N*Irr 4 851.713 212.928 1.728 0.188 Error 18 2218.506 123.250 Total 26 3499.971 Table A 1 2 . ANOVA t able for end of season whole plant N uptake. Source DF SS MS F P > F Treatments 8 8473.27 2 1059.15 9 2.754 0.035 N 2 5932.65 7 2966.328 7.714 0.004 I 2 356.16 2 178.081 0.463 0.637 N*Irr 4 2184.45 4 546.113 1.420 0.268 Error 18 6921.361 384.520 Total 26 15394.632

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98 Table A 1 3 . ANOVA t able for total leached N load for the mill et cover crop. Source DF SS MS F P > F Treatments 8 93.250 11.656 2.08 1 0.0 94 N 2 20.652 10.326 1.843 0.187 I 2 34.063 17.031 3.040 0.073 N*Irr 4 38.536 9.634 1.720 0.190 Error 18 100.838 5.602 Total 26 194.088 Table A 1 4 . ANOVA t able for cumulative sweet corn leached N load. Source DF SS MS F P > F Treatments 8 1857.533 232.192 1.101 0.40 2 N 2 556.689 278.344 1.330 0. 289 I 2 541.803 270.902 1.295 0.298 N*Irr 4 759.041 189.760 0.907 0.481 Error 18 3766 .172 209.232 Total 26 5623.704 Table A 1 5 . ANOVA t able for cumulative leached N during rye cover crop. Source DF SS MS F P > F Treatments 8 116.658 14.582 1.593 0.19 6 N 2 42.507 21.25 4 2.323 0.127 I 2 35.131 17.565 1.919 0.176 N*Irr 4 39.020 9.755 1.066 0.402 Error 18 164.765 9.154 Total 26 281.424 Table A 1 6 . ANOVA t able for cumulative leached N over all crops. Source DF SS MS F P > F Treatments 8 2759.001 344.875 1.3 70 0.274 N 2 1420.172 710.086 2.821 0 .086 Irr 2 137.593 68.797 0.273 0.764 N*Irr 4 1201.236 300.309 1.1 93 0.348 Error 18 4531.453 251.747 Total 26 7290.453

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110 BIOGRAPHICAL SKETCH Amanda Desormeaux was born and raised in DeLand, FL, where she attended Stetson University and earned a B.A. in e nvironmental s cience and a B.S. in g eo graphy. quantity issues at Stetson University, she thought it natural to explore the issue of water quality for her m