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The Effects of Irrigation and Nitrogen Management on Potato Tuber Yield, N Recovery and Leaching in Northeast Florida

Permanent Link: http://ufdc.ufl.edu/UFE0041587/00001

Material Information

Title: The Effects of Irrigation and Nitrogen Management on Potato Tuber Yield, N Recovery and Leaching in Northeast Florida
Physical Description: 1 online resource (115 p.)
Language: english
Creator: Fan, Yandi
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: crf, drip, irrigation, nitrogen, potato, seepage
Soil and Water Science -- Dissertations, Academic -- UF
Genre: Soil and Water Science thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: THE EFFECTS OF IRRIGATION AND NITROGEN MANAGEMENT ON POTATO TUBER YIELD, N RECOVERY AND LEACHING IN NORTHEAST FLORIDA Nitrate leaching from agricultural fields under potato production in northeast Florida is a potential water quality concern in the St. Johns River watershed. A 3-year study was conducted to investigate the effect of an alternate seepage irrigation method and a controlled-release N source, polymer sulfur coated urea (PSCU), on potato tuber yield, crop N recovery and N leaching loss into the shallow water table. The experimental plots were arranged in a split-split-plot design. The whole plot factors were two irrigation treatments: traditional seepage irrigation (TSI) and intermittent seepage irrigation (ISI). A factorial design with two N sources (PSCU and urea) and two N rates (168 and 224 kg ha-1) constituted the split plot factors, where the subplots included two potato cultivars (Atlantic and Fabula). The average total and marketable yields in 3 years were 31.9 and 25.2 Mg ha-1, 32.1 and 28.5 Mg ha-1, and 22.4 and 16.4 Mg ha-1, respectively. Compared with the 20-year (1990 to 2009) average yield (28.3 Mg ha-1) in Florida, yield in 2007 was similar yield while yields in 2006 and 2008 were lower. In both 2006 and 2007, both N factors had little effect on tuber yields and crop N recovery. In 2008, a ?leaching rainfall? (9 cm in 3 days) occurred 2 days after planting, which resulted in a lower N recovery, lower tuber yield, and higher N leaching loss compared with 2007. Higher marketable and total yield were produced with PSCU compared with urea in a single fertilizer application. There was no benefit of higher N rate in increasing tuber yield. Based on this study, we concluded PSCU has a potential to improve tuber yield, even with the occurrence of a leaching rainfall in the spring season. Also, increasing N rate from 168 to 224 kg ha-1 did not benefit tuber yields, but increased the potential of N leaching losses. Overall, the ISI system successfully reduced water use by 59%, 50% and 43% compared with TSI method in three experimental years. In 2006, the TSI had a better impact on potato tuber yield than the ISI. Potato tuber yield was maintained by ISI treatment in 2007 and increased in 2008. Irrigation strategy was critical in minimizing nitrate leaching under ISI. In the first 2 years, irrigation water was supplied at night for 12 hours whereas, the irrigation schedule was changed to supply water during the day for 12 hours in the last experimental year. Nitrate concentrations in the shallow water table were minimized by supplying irrigation during the day due to less fluctuation of the water table depth under ISI. Another 3-year study was conducted to investigate the feasibility of fertigation method for potato production. Five N rates (0, 112, 168, 224, 280 kg N ha-1) were used as the whole plot factor in a split-plot design, while the split plot factor was two potato cultivars (Atlantic and Fabula). An average of 28.8 cm irrigation water was applied by drip throughout 3 experimental years, compared with 45 to 50 cm of the average irrigation applied with seepage irrigation systems. Water use was reduced 35 to 42% of that use by seepage irrigation. However, potato marketable yields were not maintained when the UF-IFAS recommended N rate (224 kg N ha-1) was applied. The undesirable yields were resulted from the late application of fertilizers and water through drip, which was because drip tapes could not be installed until potato emerged. Therefore, a booster dose of fertilizer at planting to meet the nutrient requirement and establishment of potato plants is probably necessary to overcome the delayed fertigation problem.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Yandi Fan.
Thesis: Thesis (Ph.D.)--University of Florida, 2010.
Local: Adviser: Mylavarapu, Rao S.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0041587:00001

Permanent Link: http://ufdc.ufl.edu/UFE0041587/00001

Material Information

Title: The Effects of Irrigation and Nitrogen Management on Potato Tuber Yield, N Recovery and Leaching in Northeast Florida
Physical Description: 1 online resource (115 p.)
Language: english
Creator: Fan, Yandi
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: crf, drip, irrigation, nitrogen, potato, seepage
Soil and Water Science -- Dissertations, Academic -- UF
Genre: Soil and Water Science thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: THE EFFECTS OF IRRIGATION AND NITROGEN MANAGEMENT ON POTATO TUBER YIELD, N RECOVERY AND LEACHING IN NORTHEAST FLORIDA Nitrate leaching from agricultural fields under potato production in northeast Florida is a potential water quality concern in the St. Johns River watershed. A 3-year study was conducted to investigate the effect of an alternate seepage irrigation method and a controlled-release N source, polymer sulfur coated urea (PSCU), on potato tuber yield, crop N recovery and N leaching loss into the shallow water table. The experimental plots were arranged in a split-split-plot design. The whole plot factors were two irrigation treatments: traditional seepage irrigation (TSI) and intermittent seepage irrigation (ISI). A factorial design with two N sources (PSCU and urea) and two N rates (168 and 224 kg ha-1) constituted the split plot factors, where the subplots included two potato cultivars (Atlantic and Fabula). The average total and marketable yields in 3 years were 31.9 and 25.2 Mg ha-1, 32.1 and 28.5 Mg ha-1, and 22.4 and 16.4 Mg ha-1, respectively. Compared with the 20-year (1990 to 2009) average yield (28.3 Mg ha-1) in Florida, yield in 2007 was similar yield while yields in 2006 and 2008 were lower. In both 2006 and 2007, both N factors had little effect on tuber yields and crop N recovery. In 2008, a ?leaching rainfall? (9 cm in 3 days) occurred 2 days after planting, which resulted in a lower N recovery, lower tuber yield, and higher N leaching loss compared with 2007. Higher marketable and total yield were produced with PSCU compared with urea in a single fertilizer application. There was no benefit of higher N rate in increasing tuber yield. Based on this study, we concluded PSCU has a potential to improve tuber yield, even with the occurrence of a leaching rainfall in the spring season. Also, increasing N rate from 168 to 224 kg ha-1 did not benefit tuber yields, but increased the potential of N leaching losses. Overall, the ISI system successfully reduced water use by 59%, 50% and 43% compared with TSI method in three experimental years. In 2006, the TSI had a better impact on potato tuber yield than the ISI. Potato tuber yield was maintained by ISI treatment in 2007 and increased in 2008. Irrigation strategy was critical in minimizing nitrate leaching under ISI. In the first 2 years, irrigation water was supplied at night for 12 hours whereas, the irrigation schedule was changed to supply water during the day for 12 hours in the last experimental year. Nitrate concentrations in the shallow water table were minimized by supplying irrigation during the day due to less fluctuation of the water table depth under ISI. Another 3-year study was conducted to investigate the feasibility of fertigation method for potato production. Five N rates (0, 112, 168, 224, 280 kg N ha-1) were used as the whole plot factor in a split-plot design, while the split plot factor was two potato cultivars (Atlantic and Fabula). An average of 28.8 cm irrigation water was applied by drip throughout 3 experimental years, compared with 45 to 50 cm of the average irrigation applied with seepage irrigation systems. Water use was reduced 35 to 42% of that use by seepage irrigation. However, potato marketable yields were not maintained when the UF-IFAS recommended N rate (224 kg N ha-1) was applied. The undesirable yields were resulted from the late application of fertilizers and water through drip, which was because drip tapes could not be installed until potato emerged. Therefore, a booster dose of fertilizer at planting to meet the nutrient requirement and establishment of potato plants is probably necessary to overcome the delayed fertigation problem.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Yandi Fan.
Thesis: Thesis (Ph.D.)--University of Florida, 2010.
Local: Adviser: Mylavarapu, Rao S.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0041587:00001


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1 THE EFFECTS OF IRRIGATION AND NITROGEN MANAGEMENT ON POTATO TUBER YIELD, N RECOVERY AND LEACHING IN NORTHEAST FLORIDA By YANDI FAN A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULF ILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2010

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2 2010 Yandi Fan

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3 To my husband Guang and my daughter, Lerong

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4 ACKNOWLEDGMENTS I would like to gratefully thank Dr. Rao Mylavarapu, my major adv isor, for his guidance, patience, understanding, and encouragement. I would also like to thank my committee members, Dr. Yu n cong Li, Dr. Thomas Obreza, Dr. Michael Dukes, and Dr. George Hochmuth, for their support for this work. I thank Dr. Fernando Munoz for his help on the project proposal and the first year I thank Kelley Hines and Subodh Acharya for all the help they gave me on the field and laboratory work. I would like to thank my husband, Guang. His support, patience and love were unde niably my force to get through all this. I also thank my parents, Wei and Xiufen, for their faith in me and allowing me to be what I wanted to be.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 7 LIST OF FIGURES ................................ ................................ ................................ .......... 8 ABSTRACT ................................ ................................ ................................ ................... 11 CHAPTER 1 I NTRODUCTION ................................ ................................ ................................ .... 14 Best Management Practices ................................ ................................ ................... 14 Seepage Irrigation ................................ ................................ ................................ .. 15 Drip I rrigation ................................ ................................ ................................ .......... 15 Irrigation Scheduling ................................ ................................ ......................... 16 Irrigation Scheduling Methods ................................ ................................ .......... 18 Evapotranspiration ................................ ................................ ..................... 19 Soil water storage ................................ ................................ ...................... 20 Soil moisture monitoring ................................ ................................ ............ 20 Controlled R eleased Fertilizers ................................ ................................ ............... 21 Application Timing ................................ ................................ ............................ 22 Polymer Coated Sulf ur Coated Urea ................................ ................................ 22 Objectives of This Study ................................ ................................ ......................... 23 Hypotheses of This Study ................................ ................................ ....................... 23 2 M ATERIALS AND M ETHODS ................................ ................................ ................ 26 Controlled Released Fertilizer and Alternate Seepage Irrigation Experiment ......... 26 Site Descript ion ................................ ................................ ................................ 26 Experimental Design ................................ ................................ ........................ 26 Irrigation S ystems ................................ ................................ ............................. 27 Irrigation V olumes C alculation ................................ ................................ .......... 27 Planting ................................ ................................ ................................ ............ 28 Fertilizing ................................ ................................ ................................ .......... 28 Soil Sampling a nd Analysis ................................ ................................ .............. 28 Tissue Sampling and Analysis ................................ ................................ .......... 29 Shallow Water Table Depth and Water Sampling ................................ ............ 29 Soil Moisture ................................ ................................ ................................ ..... 29 Harvesting ................................ ................................ ................................ ........ 30 Data Analysis ................................ ................................ ................................ ... 30 Drip Irrigation Experiment ................................ ................................ ....................... 30 Irrigation Water Treatment ................................ ................................ ................ 31 Drip Fertigation ................................ ................................ ................................ 32

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6 Calculation of Irrigation Volumes ................................ ................................ ...... 32 3 THE EFFECT OF N MANAGEMENT ON POTATO TUBER YIELD, N RECOVERY AND LEACHING ................................ ................................ ................ 37 Weather and Irrigations ................................ ................................ ........................... 37 Tuber Yield and Quality ................................ ................................ .......................... 38 Nitrogen Recovery ................................ ................................ ................................ .. 40 Nitrogen U se E fficiency ................................ ................................ ........................... 42 NO 3 N and NH 4 N C oncentrations in the S hallow W ater T able .............................. 43 Contents o f NO 3 N and NH 4 N in the Surface Soil ................................ .................. 45 4 T HE EFFECT OF AN ALTERNATE SEEPAGE IRRIGATION SYSTEM ON POTATO YIELD AND N CONCENTRATIONS IN THE SHALLOW WATER TABLE ................................ ................................ ................................ .................... 61 Rainfall and Irrigation ................................ ................................ .............................. 61 Tuber Yield and Quality ................................ ................................ .......................... 63 N R ecovery ................................ ................................ ................................ ............. 65 Concentrations of NO 3 N and NH 4 N in the S hallow W ater T able .......................... 66 Contents of NO 3 N and NH 4 N in the Surface Soils ................................ ................ 68 Soil Moisture and Water Table Depth ................................ ................................ ..... 69 5 T HE EFFECT OF DRIP IRRIGATION SYSTEM ON POTATO YIELD AND THE FEASIBILITY OF FERTIGATION METHOD ON POTATO PRODUCTION ............ 81 Irrigation Volumes and Weather Conditions ................................ ............................ 81 Tuber Yield ................................ ................................ ................................ ............. 82 Nitrogen Recovery ................................ ................................ ................................ .. 84 NH 4 N and NO 3 N Contents in Surface Soil ................................ ............................ 85 NH 4 N and NO 3 N Concentrations in Observation Wells ................................ ........ 86 6 CONCLUSIONS ................................ ................................ ................................ ..... 99 APPENDIX A ANOVA TABLE FOR POTATO YIELD UNDER SEEPAGE IRRIGATION ............ 101 B ANOVA TABLES FOR POTATO YIELD UNDER DRIP IRRIGATION .................. 103 C IRRIGATION SCHEDULE FOR DRIP IRRIGATION ................................ ............ 105 D FLOW METER RECORD FOR SEEPAGE IRRIGATION ................................ ..... 110 LIST OF REFERENCES ................................ ................................ ............................. 111 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 115

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7 LIST OF TABLES Tabl e page 3 1 Mean monthly rainfall and soil temperature ( 10 cm) for three growing seasons. ................................ ................................ ................................ ............. 47 3 2 Comparison of tuber y ield, quality and distributions for various N sources, rates and cultivars during 2006. ................................ ................................ .......... 47 3 3 Comparison of tuber yield, quality and distributions for various N sources, rates and cultivars d uring 2007. ................................ ................................ .......... 48 3 4 Comparison of tuber yield, quality and distributions for various N sources, rates and cultivars during 2008. ................................ ................................ .......... 49 3 5 Effects of N source, N rate and potato cultivars on N recovery by potato vines and tubers during three growing seasons. ................................ .......................... 50 4 1 Rainfall and irrigation volumes under traditional and inte rmittent seepage systems ................................ ................................ ................................ .............. 69 4 2 Comparison of tuber yield, distribution and specific gravity as related to irrigation management during 2006 to 2008. ................................ ...................... 70 4 3 Effect of irrigation method on N recovery by potato vines and tubers during the 2006, 2007 and 2008 growing seasons. ................................ ....................... 70 5 1 Irrigation water for drip irrigation an d ET at each potato growth stage measured during 2006, 2007 and 2008. ................................ ............................. 89 5 2 Effect of N rate on N uptake by potato vines and tubers compared among N rates during 2006, 2007 and 2008. ................................ ................................ ..... 89 A 1 ANOVA table for potato total yield under seepage irrigation ............................ 101 A 2 ANOVA table for potato marketable yield under seepage irrigat ion .................. 102 B 1 ANOVA table for potato total yield under drip irrigation ................................ .... 103 B 2 ANOVA table for potato marketable yield under drip irrigation ......................... 103 C 1 rrigation schedule for drip system in 2006 ................................ ........................ 105 C 2 rrigation schedule for drip system in 2007 ................................ ........................ 107 C 3 Irrigation schedule for drip system in 2008 ................................ ....................... 108 D The record of the flow meter under TSI in 2008 ................................ ............... 110

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8 L IST OF FIGURES Figure page 1 1 The harvested areas for potatoes from 1991 to 2008 in TCAA and Florida. ....... 25 1 2 Potato y ields and production values from 1990 to 2009 in Florida. .................... 25 2 1 Experimental design used for seepage irrigation during 3 years. SF1: soluble urea at rate of 168 kg ha 1 SF2: soluble urea at rate of 224 kg ha 1 CR1: control released fertilizer at rate of 168 kg ha 1 CR2: control released fertilizer at rate of 224 kg ha 1 V1: Atlantic. V2: Fabula. ................................ ..... 33 2 2 Diagram of seepage irrig ation system used for potato production. ..................... 34 2 3 Sampling schedules used for 3 years. ................................ ................................ 35 2 4 Experimental design used for drip ir rigation during 3 years. N1=112 kg ha 1 N2=168 kg ha 1 N3=224 kg ha 1 N4=280 kg ha 1 V1: Atlantic; V2: Fabula. ...... 36 3 1 Total rainfall and irrigation under traditional and intermittent seepa ge irrigation systems in 3 years. ................................ ................................ .............. 51 3 2 Nitrogen use efficiency with different N sources and rates in 3 years. ................ 51 3 3 NO 3 N and NH 4 N concentrations in the shallow water table separated by N sources and N rates under TSI during 2006. The vertical bars represent the standard error of the mean. ................................ ................................ ................ 52 3 4 NO 3 N and NH 4 N co ncentrations in the shallow water table separated by N sources and N rates under ISI during 2006. The vertical bars represent the standard error of the mean. ................................ ................................ ................ 53 3 5 NO 3 N and NH 4 N concentrati ons in the shallow water table separated by N sources and N rates under TSI during 2007. The vertical bars represent the standard error of the mean. ................................ ................................ ................ 54 3 6 NO 3 N and NH 4 N concentrations in th e shallow water table separated by N sources and N rates under ISI during 2007. The vertical bars represent the standard error of the mean. ................................ ................................ ................ 55 3 7 NO 3 N and NH 4 N concentrations in the shallo w water table separated by N sources and N rates under TSI during 2008. The vertical bars represent the standard error of the mean. ................................ ................................ ................ 56 3 8 NO 3 N and NH 4 N concentrations in the shallow water t able separated by N sources and N rates under ISI during 2008. The vertical bars represent the standard error of the mean. ................................ ................................ ................ 57

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9 3 9 NO 3 N and NH 4 N content in the top 20 cm of the soil profile separated by N sources and N rates during 2006. The vertical bar at each data point represents the standard error of the mean. ................................ ........................ 58 3 10 NO 3 N and NH 4 N content in the top 20 cm of the soil prof ile separated by N sources and N rates during 2007. The vertical bar at each data point represents the standard error of the mean. ................................ ........................ 59 3 11 NO 3 N and NH 4 N content in the top 20 cm of the soil profile separated by N sources and N rates during 2008. The vertical bar at each data point represents the standard error of the mean. ................................ ........................ 60 4 1 Rainfall distribution through potato seasons in 20 06, 2007 and 2008. The X axis shows the sampling days after planting. ................................ ..................... 71 4 2 Observed and predicted NO 3 N and NH 4 N concentrations in the shallow water table compared between two irrigation me thods in 2006. TSI, traditional seepage irrigation; ISI, intermittent seepage irrigation. The X axis shows the sampling days after planting. ................................ ............................. 72 4 3 Observed and predicted NO 3 N and NH 4 N conce ntrations in the shallow water table compared between two irrigation methods in 2007. TSI, traditional seepage irrigation; ISI, intermittent seepage irrigation. The X axis shows the sampling days after planting. ................................ ............................. 73 4 4 Observed and predicted NO 3 N and NH 4 N concentrations in the shallow water table compared between two irrigation methods in 2008. TSI, traditional seepage irrigation; ISI, intermittent seepage irrigation. The X axis shows the sam pling days after planting. ................................ ............................. 74 4 5 Observed and predicted NO 3 N and NH 4 N content in soils under two irrigation methods during 2006. TSI, traditional seepage irrigation; ISI, intermittent seepa ge irrigation. The horizontal axis shows the days after planting where negative number indicates the days before planting. ................. 75 4 6 Observed and predicted NO 3 N and NH 4 N content in soils under two irrigation methods during 2007. TSI, traditional seepage irrigation; ISI, intermittent seepage irrigation. The horizontal axis shows the days after planting where negative number indicates the days before planting. ................. 76 4 7 Observed and predicted NO 3 N and NH 4 N content in soils under two irrigation methods during 2008. TSI, traditional seepage irrigation; ISI, intermittent seepage irrigation. The horizontal axis shows the days after planting where negative number indicates the days before planting. ................. 77 4 8 The dynamic changing of soil moisture under two irrigation systems during the potato season in 2006. The soil moisture was mea sured at 10, 20, 30, 40, 60 and 100 cm below the top of the row. ................................ ...................... 78

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10 4 9 The dynamic changing of soil moisture under two irrigation systems during the potato season in 2007. The soil moisture w as measured at 10, 20, 30, 40, 60 and 100 cm below the top of the row. ................................ ...................... 79 4 10 Water table depth under seepage irrigation systems and drip irrigation in 2006, 2007 and 2008. The vertical axes represent days after planting. ............. 80 5 1 Total rainfall and drip irrigation volumes in 3 years. ................................ ............ 90 5 2 Total and marketable yields compared among N rates under drip irrigation system in 2006. ................................ ................................ ................................ .. 90 5 3 Total and marketable yields compared among N rates under drip irrigation system in 2007. ................................ ................................ ................................ .. 91 5 4 Total and marketable yields compared among N rates under drip irrigation system in 2008 ................................ ................................ ................................ ... 91 5 5 Total and marketable yields compared between two potato culti vars under drip irrigation in 2006, 2007 and 2008 ................................ ................................ 92 5 6 Soil NH 4 N and NO 3 N contents under drip irrigation system compared among N rates during 2006. ................................ ................................ ............... 93 5 7 Soil NH 4 N and NO 3 N contents under drip irrigation system compared among N rates during 2007. ................................ ................................ ............... 94 5 8 Soil NH 4 N, NO 3 N and TKN contents under drip irrigation sy stem compared among N rates during 2008. ................................ ................................ ............... 95 5 9 NH 4 N and NO 3 N concentrations compared among N rates in the observation wells under drip irrigation system during 2006. ............................... 96 5 10 NH 4 N and NO 3 N concentrations compared among N rates in the observation wells under drip irrigation system during 2007. ............................... 97 5 11 NH 4 N and NO 3 N concentrations compared among N rates in the observation wells under drip irrigation system during 2008. ............................... 98

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11 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Par tial Fulfillment of the Requirements for the Degree of Doctor of Philosophy THE EFFECTS OF IRRIGATION AND NITROGEN MANAGEMENT ON POTATO TUBER YIELD, N RECOVERY AND LEACHING IN NORTHEAST FLORIDA By Yandi Fan December 2010 Chair: Rao Mylavarapu Major: Soil an d W ater S cience Nitrate leaching from agricultural fields under potato production in northeast Florida is a potential water quality concern in the St. Johns River watershed. A 3 year study was conducted to investigate the effect of an alternate s eepage irrigation method and a controlled release N source, polymer sulfur coated urea (PSCU), on potato tuber yield, crop N recovery and N leaching loss into the shallow water table. The experimental plots were arranged in a split split plot design. The w hole plot factor s w ere two irrigation treatments : traditional seepage irrigation (TSI) and intermittent seepage irrigation (ISI). A factorial design with two N sources (PSCU and urea) and two N rates (168 and 224 kg ha 1 ) constituted the split plot factors where the subplot s included two potato cultivars ( Atlantic and Fabula ). The average total and marketable yields in 3 years were 31.9 and 25.2 Mg ha 1 32.1 and 28.5 Mg ha 1 and 22.4 and 16.4 Mg ha 1 respectively. Compared with the 20 year (1990 to 2009 ) average yield (28.3 Mg ha 1 ) in Florida, yield in 2007 was similar yield while yields in 2006 and 2008 were lower. In both 2006 and 2007, both N factors had little effect on tuber yields and crop N recovery In 2008, a leaching rainfall (9 cm in 3 days ) occurred 2 days after planting, which resulted in a lower N recovery, lower tuber yield, and higher N leaching loss compared

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12 with 2007. H igher marketable and total yield were produced with PSCU compared with urea in a single fertilizer application. There was no benefit of higher N rate in increasing tuber yield Based on this study, we concluded PSCU ha s a potential to improve tuber yield, even with the occurrence of a leaching rainfall in the spring season. Also, increasing N rate from 168 to 224 kg ha 1 d id not benefit tuber yields, but increase d the potential of N leaching losses. Overall, the ISI system successfully reduce d water use by 59%, 50% and 43% compared with TSI method in three experimental years. In 2006, the TSI had a better impact on potato tuber yield than the ISI. Potato tuber yield was maintained by ISI treatment in 2007 and increased in 2008. Irrigation s trategy was critical in minimizing nitrate leaching under ISI. In the first 2 years, irrigation water was supplied at night for 12 hour s whereas, the irrigation schedule was changed to supply water during the day for 12 hours in the last experimental year. Nitrate concentrations in the shallow water table were minimized by supplying irrigation during the day due to less fluctuation of the water table depth under ISI. A nother 3 year study was conducted to investigate the feasibility of fertigation method for potato production. Five N rates (0, 112, 168, 224, 280 kg N ha 1 ) were used as the whole plot factor in a split plot design, while th e split plot factor was two potato cultivars ( Atlantic and Fabula ). An average of 28.8 cm irrigation water was applied by drip throughout 3 experimental years, compared with 45 to 50 cm of the average irrigation applied with seepage irrigation systems. Wat er use was reduced 35 to 42% of that use by seepage irrigation. However, potato marketable yields were not maintained when the UF IFAS recommended N rate (224 kg N ha 1 ) was applied. The undesirable yields were resulted from the late application of fertili zers and water through drip, which

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13 was because drip tapes could not be installed until potato emerged. Therefore, a booster dose of fertilizer at planting to meet the nutrient requirement and establishment of potato plants is probably necessary to overcome the delayed fertigation problem.

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14 CHAPTER 1 INTRODUCTION Potatoes are an important economic crop in Tri County Agricultural Area (TCAA) in northeast of Florida. In this area approximately 9,000 ha of potatoes are grown annually on coarse sandy soils (Fi gure 1 1), which was a potatoes with an average annual value of 74 million dollars (Figure 1 2). The averaged potato yield from 1990 to 2009 in Florida State was 28.3 Mg ha 1 which valued 123.2 million dollars averagely The c oncern over increasing NO 3 N concentrations in the St. Johns River became a great challenge for competitive agricultural production, particularly potatoes, due to their high N requirement and low N recovery. Munoz et al. (2006) reported that more than 90% of potato root length for Atlantic cultivar was confined to the top 25 cm of the soil hills The s hallow root system associated with coarse sandy texture can result in a high potential for N leaching loss into the shallow water table. Best Management Prac tices Best Management Practices (BMPs) for potato production such as appropriate N rate with proper application time, optimum crop and irrigation management and control of N release are being developed by the University of Florida/Institute of Food and Agr icultural Sciences (UF/IFAS) to minimize N losses from agricultural fields (Cockx et al., 2003). An N rate of 224 kg ha 1 is the standard recommendation for potato production in the state ( Hutchinson et al. 2009 ). Hochmuth et al. (2008) found that optimum potato yields were obtained at 196 kg N ha 1 and that yield decrease d with N rates greater than 224 kg ha 1 Feibert et al. (1998) found that potato yield was

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15 maximized at the application N rate of 211 and 175 kg ha 1 with proper sprinkler irrigation man agement in 2 study years. Seepage Irrigation Seepage irrigation is commonly used in Florida due to cost effectiveness and low maintenance requirement. Under this type of irrigation system, a shallow water table is maintained approximately 45 to 60 cm below the top of the row during the potato grow ing season Water is pumped from a well and is then distributed to individual water furrows. Drainage ditches are usually arranged at the other end of the field to carry off excess water that could occur due to hea v y rainfall. In a typical rainfall year, growers usually start irrigati ng about 30 days after planting, and turn off the system except around heavy rainfall events only at harvest Proper management of the shallow water table was considered necessary to increase water use efficiency and tuber yields when seepage irrigation was used for potato production (Campbell et al., 1978). Drip I rrigation Applying both fertilizer and irrigation water through drip tubing has the potential to reduce both fertilizer ap plication rate and water use. Sammis (1980) found that highest potato yields were produced with subsurface drip irrigation and achiev ed high water use efficienc y by delivering uniform soil moisture in the root zone, compared with sprinkler, surface drip an d furrow irrigation method s Advances in drip tubing design allow the system to be installed below the tillage depth for use across multiple seasons. Additionally, drip tubing can be installed either in or above the root zone and can be removed after each crop. Equipment is available that will retrieve drip tubing from the field before harvest. Retrieved drip tubing can be used for multiple seasons. Simonne et al. (2002) showed that drip irrigation can be an economical practice for potato

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16 production in sou theastern United State s due to an addition profit from costs and returns using drip irrigation. Smajstrla et al. (1995) studied the effect of an automatically controlled subsurface drip irrigation system on potato yield compared with a conventional semi cl osed seepage irrigation system. In their work, drip tubing was installed below the tillage depth with laterals spaced every 6 m. Similar potato yield was reported with subsurface drip irrigation compared with seepage irrigation but with 33% less water use The water saving was assumed to come from the fact that the shallow water table was maintained just below the bottom of the water furrow reducing run off during the season. No fertilizer s were applied through the buried drip tubing in their study Howev er, in our study, the drip tubing was installed in each potato row. No shallow water table was maintained. Irrigation was based on estimated evapotranspiration rates for each 24 hour period during the season. The act of applying fertilizer through the dri p tubing is called fertigation a combination of irrigation and fertilization. Fertigation allows pr e c is e applications of fertilizers. Fertilizer rates can be altered on a daily basis if needed. Certainly, with this system, one can adjust fertilizer appli cation rates based on plant size, plant demand, and/or physiological state. When fertilizer application can be matched with plant demand, fertilizer use efficiency is improved, which means more of the applied fertilizer is taken up by the plant and does no t leach beyond the root zone. Irrigation Scheduling I making activity that the farm manager or operator of an irrigated farm is involved in before and during most of the growing season for each crop that is grown process by which an irrigator determines the timing and quantity of water to be applied

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17 to the crops. With proper irrigation scheduling, crop yields will not be limited by water stress from droughts, and the wastage of water and the energy used in pumping will be minimized. Other benefits include reduced loss of nutrients from leaching as a result of excess water applications, and reduced pollution of groundwater or surface water from the leaching of nutrients It is essential to know exactly how much water the plant is using by accurately measuring the wate r use for the particular site. Traditional crop factors and evaporation may give a general indication but the actual water use varies significantly from si te to site depending on climatic factors, the growth stage of crops bed spacing or crop density, the terrain etc. It is important to develop irrigation scheduling techniques that are suited to local climatic conditions. To irrigate correctly knowing of t he amount of water using by plants and the water holding capacity of the soil is necessary Because the objective of irrigation is to meet crop water requirement, the plants themselves are the best indicators of the need for irrigation. Irrigators should schedule the irrigation carefully to avoid losses from under or over watering. Insufficient water can lead to fruit quality and yield reduction, whereas over watering can lead to losses of water, leaching nutrients and reduction in yield and quality. Van loon (1981) found that water stress could result in yield reduction by limiting leaf area and/or photosynthesis/unit leaf area. Potato yield could be diminished more greatly due to water deficit during tuber bulking stage than at any other growth stage. Water is used in a crop production in several ways: 1) assimilation into the plants, 2) direct evaporation from the soil or other surfaces, 3) transpiration, and 4) other beneficial uses such as leaching of salts, crop cooling, and freeze protecti on. Most of

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18 the water applied to meet the water requirements of a crop is used in evaporation and transpiration. Evaporation and transpiration are important for cooling a crop in order to maintain temperatures in the range that permits optimal photosynthet ic activity and crop growth to occur. Transpiration also helps transport nutrients into and through the plants. T he crop root zone can be visualized as a reservoir where water is temporarily stored for use by the crop. I nputs to that reservoir occ ur from both rainfall and irrigation. U nfortunately, rainfall is relatively unpredictable, and any rain that immediately follows irrigation is not very effective. Irrigation can be minimized by anticipating rainfall and providing soil storage capacity to i ncrease rainfall effectiveness. I f the capacity of soil water content and daily rates of ET are known, the date of next irrigation and the amount of water to be applied can be determined. T herefore, the soil water storage capacity in the root zone and ET c omprise the basic information needed for irrigation scheduling. Irrigation Scheduling Methods To avoid under or over irrigation, it is important to estimate how much water is required by crops and how efficiently the y can use it. Shock et al. (1998) conc luded that deficit irrigation (70% of accumulated ET or less) for potato production in Oregon was not a feasible management scheme due to the risk of tuber yield reduction. There are many methods to measure these factors. They include direct measurements s uch as plant observation, feel and appearances of the soil, and using the soil moisture monitoring devices; or through indirect measurements that estimate available water using weather data. Among these methods, the indirect way is the most recommended. A crop coefficient (Kc) relates crop water use at particular development stage to the amount of reference crop evapotranspiration (ET o ) as calculated from automatic or

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19 manually collected weather data (Simonne et al, 2006) Crop coefficients are seasonally ad justed values that take into account the crop type, stage of growth, and crop cover. Water evaporates from soil and transpires from plant leaves. Together, these two phenomena are referred to as evapotranspiration ( ET ). ET c or ET crop is the water use rate of the crop that is being scheduled or managed. ET c is the amount of water that evaporates from the soil surface and transpires from the leaf surface to the atmosphere. Crop water use (ETc) = Crop coefficient (Kc) Evapotranspiration (ETo) Or, ET c = Kc ETo E vapotranspiration E vaporation is the change of water from liquid to vapor form. E nergy is required for evaporation to occur. S olar radiation intensity is the main climatic factor that determines the ET rate, although air temperature, humidit y, and wind also affect ET rates. T he most significant crop factors that affect ET from a well irrigated crop are crop species, the stage of growth, and the plant size or leaf area on which radiation is incident. ET rates are greatest when the entire soil surface is covered by the crop canopy. W hen the crop canopy is not complete, the ET rate is strongly influenced by the area of the leaf surface that intercepts sunlight. A s growth increases, ET reaches its maximum at nearly complete ground cover. Alva et a l. (2002) found that effects of irrigation management on potato yield were mainly significant with high ET than with lower ET growing conditions. Hang and Miller (1986) concluded that potato yield and quality were maintained when irrigation rate was near e stimated ET on sandy soils. Yield and quality would not be increased if water application was higher than 100% ET.

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20 S oil water storage D uring irrigation, water infiltrates the soil and then distribute s within the soil by gravity and soil capillary forces. W hen soils become wetter, gravitational forces dominate and water drains downward through. D rainage is rapid at first, but after 1 or 2 days it decreases to a very low rate. A t this time, soil moisture in the root zone may be considered to be in storage and available for deplet ion primarily by evapotranspiration. T his upper limit of water storage is called field capacity (FC). A practical lower limit of soil water is defined as the soil water content below which severe crop water stress and perm anent wilting occurs. T his lower limit is defined as the permanent wilting point (PWP). T he difference between FC and PWP is called the available water capacity (AWC). O nce AWC is known, the total depth of water available, and thus the capacity of the soil water storage can be obtained by multiplying AWC by the crop effective root zone depth. T he allowable soil water depletion is the fraction of the available soil water that will be used to meet ET demands. S ince a lower ET will generally reduce yields, gro wer s should irrigate before the root zone water content reaches a level that restricts ET. Soil moisture monitoring Soil moisture monitoring is used as a basis for irrigation scheduling as it can provide accurate information about the extraction of availab le water by the crop. Soil moisture can be measured as a suction or volume of water. Soil moisture suction can be used as a measure of plant stress and for that reason it is a handy tool for growers to use in scheduling their irrigations. S oil moisture mon itoring instruments are most effectively used in combination with ET data. T he instruments are read to determine when to irrigate, and the ET data are used to calculate the volume of water lost since

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21 the last irrigation. F rom this information the volume t o be replaced can be determined. Stieber and S hock (1995) concluded that soil moisture should be maintained between 50 and 60 J K 1 to achieve optimum potato yield. The potato plants w ere found to be particularly sensitive to soil water potential during tuber development, and tuber yield was positively related to mean soil moisture (Harris, 1978) Control led R eleased Fertilizers Nitrate N is considered as a high potential source of non point source pollution due to its negative charge repelled by soil co lloids and its high solubility in water. Therefore, ammoniacal nitrogen fertilizers are recommended for use in sandy soils (Bundy et al., 1986). However, the potato plants have a preference for NO 3 N over NH 4 N (Havlin et al., 1999) Therefore use of cont rolled release fertilizers (CRF) and slow release fertilizers (SRF) may help reduce nitrate leaching and increase nut rient use efficiency. T he CRF s have been found to have certain negative effects on tuber yields. Lorenz et al. (1974) found lower yields we re produced with sulfur coated urea (SCU) than potatoes fertilized with (NH 4 ) 2 SO 4. Liegel and Walsh (1976) also found that SCU produced lower yields compared with the use of urea in single or split applications. Cox and Addiscot (1976) compared SCU and cal cium nitrate in potato production They found no advantage to SCU in maintaining tuber yields Lower yields were also found by Elkashif et al. (1983) with both 100% pre plant isobutylidene diurea (IBDU) and SCU due to reduced N release from these sources d uring cold winter and cooler spring soil temperatures. Reduced yields with SCU could be attributed to lack of synchronization between N release and potato demand (Waddell et al., 1999). A slow initial release of N was not sufficient to meet the high N dema nd of potato plant s early in the growing season, whereas N may have been released late in the season when crop did not need

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22 it. Improved N recovery and tuber yield with polyolefin coated urea (POCU) was reported by Zvomuya et al. (2003). Due to a more sync hronous association between availability and demand of N, Zvomuya et al. (2001) found that POCU had a potential to increase N uptake efficiency. Application Timing Kidder et al. (1992) proposed that since N could be easily leached in a sandy soil following a leaching rainfall ( defined as 7.6 cm in 3 days or 10.2 cm in 7 days ) a supplemental application of 34 kg ha 1 N should be applied to the crop Wang and Alva (1996) found that the first rainfall event after application may be critical for urea N losses from both urea and urea based slow release fertilizers. Therefore, the timing of N application is critical to successful potato production. Hutchinson et al. ( 2009 ) suggested that two thirds of the recommended N should be applied at planting and the remain der should be applied between 30 and 40 days after planting Reduced amounts of N applied at planting were also recommended by Errebhi et al. (1998) to reduce NO 3 N leaching and improve N recovery and tuber yield. Munoz et al. (2008) suggested that use of sorghum as a summer cover crop could reduce the risk of nitrate leaching after potato harvesting by recovering the residual N from the potato season. Polymer C oated Sulfur C oated Urea A polymer coated sulfur coated urea (PSCU) consists of two coatings an external polymer coating and an internal sulfur coating. The nutrient release from PSCU mostly depends on soil temperature rather than soil moisture or microbial activity (Paramasivam and Alva, 1997). The nutrient release rate from PSCU i s regulated by th e thickness of coating Polymer provides a more uniform cover than sulfur. Sharma (1979) indicated that most sulfur coated products contain about 10 15% imperfectly coated

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23 particles which allows nutrients to diffuse rapidly. Zvomuya et al., (2001 ; 2003) u sed a 70 day release POCU, which was designed to release N at a faster rate than SCU, with however only 60% of N released by harvest time (about 150 days after application). Wilson et al. (2009) reported that more than 90% of the applied N had been release d by 100 days after planting ( DAP ) using a 90 d release polymer coated urea (PSU). Nutrient release rate from PSCU was not determined in this study H owever, referring to Paramasivam and Alva (1997), it was established that 80% of N from PSCU had been rele ased by about 100 days. Objectives of T his S tudy In order to determine the feasibility of alternate irrigation systems in conjunction with nutrient management to improve water and N fertilizer use efficiencies in potato production in the S t. J ohns River wa tershed area, a 3 year study was established at the Hastings research center with the following objectives : i) D etermine the feasibility of the Intermittent Seepage Irrigation and Drip Irrigation for successful potato production as an alternate method to t raditional seepage in conserving water resource s ii) D etermine the potential of PSCU as a control led release N source for optimum potato production, efficient N uptake and minimize d N leaching, and iii ) D etermine if fertigation through the drip irrigation tubes is effective for optimum potato production and N use efficiency. Hypotheses of This Study The hypotheses of this study were: 1) The ISI is a more efficient irrigation method in reducing water use, increasing potato yield and N uptake as well as mi nimizing N leaching compared with the TSI, 2) The PSCU increases potato yield and N uptake and

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24 reduces N leaching compared with urea, and 3) Fertigation increases N use efficiency and reduces water use compared with seepage irrigation.

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25 Figure 1 1. The harvested areas for potatoes from 1991 to 2008 in TCAA and Florida. Figure 1 2. Potato yields and production values from 1990 to 2009 in Florida.

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26 CHAPTER 2 MATERIALS AND METHOD S Control led Released Fertilizer and Alternate Seepage Irrigation Experiment Site Description This study was conducted during 2006 to 2008 growing seasons on Ellzey fine sand at the UF/IFAS Plant Science and Education Unit, Hastings Farm in Hastings, FL. The soil at this site has a loamy fine sand layer (Bt layer) at a depth of 90 to 150 cm (USDA, 1983), which contribute s to poor water drainage and may preventing downward movement of N. Seepage irrigation in conjunction with rainfall during the spring seasons i s a typical water management practice for growing potatoes in the northea st agricultural production area of Florida. Water was pumped from deep wells and a temporary water table over the Bt layer was built at 40 60 cm depth from the surface, and the root zone was supplied with moisture through capillary rise. Two irrigation met hods were used in this study The TSI commonly used by farmers in northeast Florida pumped water continuously through the crop season, except when a leaching rain event occurred. An alternate seepage irrigation method, the ISI, was also employed during t his study for comparison, which supplied irrigation water 12 hours at nights in 2006 and 2007 and 12 hours during the days in 2008. Experimental Design The experimental plots were arranged in a split split plot design (Figure 2 1) The nature of s eepage irrigation restricted whole plot randomization. The whole plot factors were two irrigation treatments (TSI and ISI), the split plot factors were four N treatments that included a combination of two N sources (uncoated urea and polymer coated sulfur coated urea) and two N rates (168 and 224 kg N ha 1 ), and the split split plot

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27 factors were two potato cultivars ( Atlantic and Fabula ). Nitrogen treatments were arranged in a 2 way factorial design with four replications Irrigation S ystems Along with Tra ditional Seepage Irrigation (TSI), a n alternate seepage irrigation method, I ntermittent S eepage I rrigation (ISI) was also studied, reduc ing irrigation water use while supporting optimum potato yields. Under the ISI water was turned on and off automatica lly at a pre set irrigation schedule to maintain the desired water table depth. Irrigation V olumes C alculation The diagram of seepage irrigation was showed in Figure 2 2 The volumes of irrigation water were monitored by a flow meter at the inlet to the f ield for TSI treatment in 2008. The flow meter was connected to the one of the faucets in TSI plot on April 15 th in 2008, and started recording irrigation volumes until harvesting. The flow meter data was manually collected twice a week. The flow rate of I SI treatment was assumed as same as the rate of TSI treatment because same pumping system was used for both treatment. The duration time of irrigation was manually recorded for both irrigation treatments. The averaged flow rate in liters per minute (L/min) was calculated by dividing total volumes of irrigation water by duration time of TSI treatment in 2008 grow season. Since the record of irrigation volumes were not available in 2006 and 2007, the flow rate was assumed to remain constant throughout all the experimental years, even though it might change in response to changes of pumping pressure or other reasons. Therefore, the total irrigation volumes in 2006 and 2007 were calculated by multiplying the averaged flow rate and duration time in these years. W ater use (cm) was determined by dividing total volumes of irrigation water by the irrigated area of each treatment.

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28 Planting Potato seed pieces weighing approximately 55 g were hand planted on Mar 1 st Feb 23 rd and Mar 5 th in 2006, 2007 and 2008, respectively, with 102 cm spacing between rows and 20 cm spacing within rows. Each individual plot consisted of four 15 m long rows. Furrows used to supply irrigation were located between every 16 potato rows, which formed a bed. Fertilizing Polym er coated sulfur coated urea (PSCU) was compared with uncoated urea, applied at the rates of 168 and 224 kg N ha 1 with four replications the latter rate being the standard N recommendation of UF/IFAS (Hochmuth and Hanlon, 1995) and is considered a signif icant part of the Best Management Practices for potatoes in Florida. All plots received 34 kg P 2 O 5 and 197 kg K 2 O ha 1 pre plant. All fertilizers were banded and incorporated in a single application 10, 2 and 3 days prior to planting in 2006, 2007 and 2008 respectively (Figure 2 3 ) Soil Sampling and Analysis In 2006, s oils were collected 17 days before planting and 56, 76, and 112 DAP. In 2007, soils were sampled 7 days before planting and subsequently at 29, 64, and 91 DAP and in 2008 20 days before pl anting followed by 37, 54, and 81 DAP. A representative consolidated soil sample was collected from twelve points randomly selected in the two center rows within each subplot. A one side open tubular auger with a 1.9 cm diameter was used to collect soil sa mples to a depth of 20 cm below the surface. Samples were collected in labeled plastic bags, air dried, and passed through a 2 mm sieve for subsequent laboratory analyses. Soil samples were analyzed for pH, NO 3 N and NH 4 N. All the laboratory analyses were determined at the UF/IFAS

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29 Analytical Services Laboratories (A S L) as per the standard procedures (Mylavarapu, 2008). Tissue Sampling and Analysis Whole potato plants with tubers were collected around 64 DAP at full flowering in three study years. Two plants were randomly selected from each subplot. Potato vines were separated into leaves and stems, oven dried, weighed and ground for nutrient analyses. Also, two of the tubers selected from each subplot at harvest were diced, fresh weighed, oven drie d, dry weighed and ground for further analysis. All ground tissue and tuber samples were analyzed for total Kjeldahl nitrogen ( TKN ) Shallow Water Table Depth and Water Sampling A 10 cm diameter PVC pipe was installed in each subplot to a depth of 80 cm from the top of the center row after emergenc e (about 40 DAP) in each experimental year Water s amples were taken from the wells at 41, 55, 69, 83 and 97 DAP in 2006, 43, 57, 71, 84, and 99 DAP in 2007 and at 42, 58, 72 and 86 DAP in 2008. The fifth sampling was not done in 2008 due to the early harvest that year. Water samples were collected in 20 mL vials, frozen, and analyzed for NO 3 N and NH 4 N Shallow w ater table depth inside each observation well was measured manually with a meter stick Soil Moisture Soil moisture profile probe access tubes were installed within 30 cm of observation wells in one of two replicated irrigation beds. Volumetric soil moisture was measured at 10, 20, 30, 40, 60 and 100 cm below the top of the potato rows u sing a soil moisture profile probe (PR2) (Delta T Devices, 2005). Both soil moisture and water table depth were recorded at the same time on weekly schedule until harvest.

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30 Harvesting Potatoes were harvested on June 20 th in 2006, June 4 th in 2007 and June 10 th in 2008, which corresponded with 110, 104 and 99 DAP in the three experimental years, respectively. Potato tuber yields were determined by harvesting plants from 7.6 m row length in the two center rows from each subplot and grading the tubers into five size categories based on tuber diameters according to USDA standards for grades of chipping potatoes (B=<4.8, A1=4.8 6.4, A2=6.4 8.3, A3=8.3 1 0.2, A4=>10.2 cm) (USDA, 1978). Categor ies A1 to A3 were considered marketable yield. Total yield was c alculated by the summation of all of the categories as well as culls (greens, cracked, misshapen, sunburn and rotten tubers). A sample of 20 tubers randomly selected from each subplot was used to determine the specific gravity using the weight in air/weigh t in water method. Data Analysis Data for each year were analyzed separately with PROC MIXED (SAS Institute, 2008 multiple comparison method. Drip Irrigation Experiment A split plot design with four replications was used in this experiment (Figure 2 4 ) The whole plot factor was five N rates ( 0, 112, 168, 224, 280 kg N ha 1 ), while the split plot factor was two potato cultivars ( Atlantic and Fabula ). Potato seed pieces weighing approximately 55 g were hand planted on Mar 1 st Feb 23 rd and Mar 5 th in 2006, 2007 and 2008, respectively, with 102 cm spacing between rows and 20 cm spacing within rows. Each individual plot consisted of four 15 m long rows. The drip tub ing (Netafim USA, Inc., Fresno, CA) was placed above the seed piece approximately 6 cm below

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31 the soil surface but was offset from the center of the row. It ha d a drip spacing of 30.5 cm and a dripper flow of 0. 38 mL/s at 69 kpa No shallow water table was maintained. ETc was calculated by multiplying ET 0 by Kc. The ET 0 values were recorded at the Florida Automated Weather Network (FAWN) weather system at the research station The crop coefficient numbers at each crop growth stage were referred to the work of Simonne et al. (2006). The fertilizer treatment delivered 25% of the total nutrients by tuber initialization, 50% between tuber initialization and full flower ing and 25% during tuber bulking. Irrigation W ater T reatment Irrigation water was chemically t reated and filtered to prevent clogging of the drip emitters. Water for the drip irrigation system was taken from a deep well. Water passe d through three filters before delivery to the field. The first one wa s a mesh filter to retain soil particles and two disc filters before adding the fertilizer solution. The drip fertigation system wa s composed basically of a water treatment unit and a fertilizer mixer unit. The objective of the water treatment unit was to flocculate impurities in order to retain them in the filters before deliver ing water to the drip lines. Initially, hydrochloric acid (muriatic acid 31.5% ) was added to decrease water pH from approx imately 7.3 to 6.5. At pH 6.5, hypochlorite added reaches the maximum concentrat ion of free chlorine. Free chlorine concentration after injection of sodium hypochlorite should be 15 mg/L at the injection point and at least 2 mg/L at the end of the drip lines. Hydrochloric acid and hypochlorite solutions were prepared in 208 L plastic drums and injected to the water supply main line through chemical injectors (Chemilizer, HN55) with a mixing ratio of 1:100.

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32 Drip F ertigation In 2006, a liquid 10 0 11 blend fertilizer was used and supplemented with KCl (62%) to maintain the same N:K proportion (1:1.5). Phosphoric acid (59% P 2 O 5 ) was used as P source and applied at a rate of 33.6 kg P 2 O 5 ha 1 in two applications. In 2007 and 2008, a liquid 7 0 7 blend fertilizer was used for K and N source. Fertilizers and water were mixed in 208 L plastic drums and injected to drip tubes for each N treatment. The control treatment was only supplying water throughout the seasons. Fertigation and irrigation schedule was set up weekly regarding to the ET values calculated by multiplying ET 0 and crop factors f or each growth stage. Cal culation of I rrigation V olumes Irrigation volumes were recorded by a flow meter at the inlet to the fertilizer injectors. Irrigation occurrence and durations were automatically controlled and manually recorded. Irrigation schedule was set up once a week ba sed on ET 0 information by FAWN.

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33 Figure 2 1 Experimental design used for seepage irrigation during 3 years. SF1: soluble urea at rate of 168 kg ha 1 SF2: soluble urea at rate of 224 kg ha 1 CR1: control released fertilizer at rate of 168 kg ha 1 CR2 : control released fertilizer at rate of 224 kg ha 1 V1: Atlantic. V2: Fabula.

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34 Figure 2 2 Diagram of seepage irrigation system used for potato production

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35 Figure 2 3 Sampling schedules used for 3 years

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36 Figure 2 4 Experimental design used for drip irrigation during 3 years N1=112 kg ha 1 N2=168 kg ha 1 N3=224 kg ha 1 N4=280 kg ha 1 V1: Atlantic; V2: Fabula.

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37 CHAPTER 3 THE EFFECT OF N MANA GEMENT ON POTATO TUB ER YIELD, N RECOVERY AND LEACHING Weather and Ir rigation s Mean rainfall and soil temperature ( 10 cm) during the 2006, 2007 and 2008 growing season s are presented in Table 3 1 In 2006, only 4.8 cm rainfall occurred from March to May, which was the critical period for potato growth. The total rainfall was 13.8 cm, which was about 10 cm lower than the 10 yr average (24 cm) (FAWN database) Therefore, the 2006 growing season was identified as a dry season. Crop water requirement was supplemented by 79 and 33 cm of irrigation water with TSI and ISI, respec tively (Figure 3 1). In 2007, total rainfall du ring the potato season was 23.4 cm, which wa s sim ilar to the 10 yr average for the same period. This rai nfall was supplemented with 73 cm of TSI and 36 cm of ISI The biggest rai nfall event early in the season was 5.9 cm. It occurred from Mar 1 st to Mar 3 rd which was 1.7 cm less than a leaching rainfall, followed by a deficit of rainfall (3.7 cm) from Mar 17 th through May 13 th In 2008, total rainfall during the growth season was 19 cm, which was approximately 21% below the average. A leaching rainfall (8.7 cm in 3 days) occurred at 2 DAP, which was 7 days after fertilizing. A severe rainfall deficit occurred from Mar 21 st through May 22 nd when only 0.4 cm rain fell in 63 days. Traditional s eepage and ISI supp lied 57 and 34 cm irrigation water respectively, to supplement this deficit during the middle and late season. Soil temperature averaged from planting to emergenc e in 2007 (18.5C) was similar to that in 2008 (18.6C), even though planting was 8 days late r in 2008. However, from emergenc e to tuber initiation, soil temperature in 2007 (20.4C) was 1.4 C lower than that in 2008. This difference was a factor influencing tuber initiation, and subsequently affecting tuber yield s Waddell et al. (1999) reported a lower tuber yield

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38 and crop N uptake in the warmer season, suggesting that warm soil temperature can inhibit or even reverse tuberization. Tuber Yield and Quality After statistic al analysis of the data interactions were found between year and N treatmen ts, as well as year and cultivar treatments. In 2006, similar total and marketable tuber yields were recorded with two N sources (Table 3 2 ). Meanwhile, the higher N rate (224 kg ha 1 ) did not increase tuber yields compared with the lower N rate (168 kg ha 1 ). The only differences in marketable yield were observed between two cultivars; marketable yield of Atlantic was significantly higher than Fabula Besides, N sources and N rates also had similar impact on specific gravity of potato tubers, even though A tlantic had a higher specific gravity than Fabula In 2007, neither N source nor N rate had an effect on any of the tuber yield categories (Table 3 3 ). The only difference in total and marketable yield detected was between the two potato cultivar s. Cultivar Fabula produced a significant ly higher total and marketable yield than var. Atlantic However, Atlantic significantly yielded more A3 (8.3 10.2 cm) tubers, which were consid ered as large sized tubers for marketable yield, compared with Fabula Cultivar Atlantic the standard variety for chipping, had a significant ly higher specific gravity of 1.0958 compared with var. Fabula (1.0759). In 2008, potatoes did not emerge 100% due to heavy rainfall right after planting. Reduction in both total and m arketable yield was recorded in this year. Leaching rainfal l early in the season and poor tuber set was significantly responsible for the lower yields. Compared with urea, PSCU with a single application at pre plant significantly increased total yield from 20.03 to 24.85 Mg ha 1 and marketable yield from 14.98 to 17.90 Mg ha 1 However, it also increased undesirable tubers and culls (Table 3 4 ). There was no

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39 advantage from applying N fertilizer at a higher rate (224 kg N ha 1 ) for total and marketable yiel d. Tubers produced at the application rate of 168 kg N ha 1 had a similar size distribution compared with tubers produced at the higher N rate. Yield respon se to cultivars in 2008 followed th e trend of 2007, except that more medium sized (6.4 8.3 cm) and e quivalent large sized tubers resulted from var. Fabula compared with var. Atlantic Similar to 2007, in 2008 also, var. Atlantic had higher average specific gravity than var. Fabula However, specific gravity values of all treatments in 2008 were numerical ly lower than in 2007. As a controlled release N source, PSCU produced different tuber yields in 3 production years compar ed with uncoated urea. Several factors could be the reason for the difference. The most critical reason was that a significant leachin g rainfall occurred 7 days after fertilizing, which may have contribute d to a significant leaching loss of urea N from uncoated urea than from PSCU. Wang and Alva (1996) found that in sandy soils, leaching of N from a soluble N source may depend on the fir st few leaching events. Paramasivam and Alva (1997) reported after 10 cm rainfall, 19.6% of urea N was leached from uncoated urea 12 days after N application to the soil. However, in case of PSCU, a significant portion of urea N was leached from 18 to 48 d ays after N application. Therefore, early season rainfall gives PSCU an advantage over soluble N for reducing leaching losses. Previous studies have found certain CRFs can produce yields similar to soluble N sources at the equivalent rates. Hutchi nson et al. (2003) found no difference in total and marketable yield by using a combination of 50% PSU and 50% PSCU compared with a combination of 50% ammonium nitrate (AN) and 50% urea at N rate s of either 168 or

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40 224 kg N ha 1 Similar potato yields and t uber sizes with PSCU and AN were also reported by Pack et al. (2005). The average potato yield in Florida from 1990 to 2009 was 28.3 Mg ha 1 (USDA database). In our study, the average total and marketable yields in 3 years were 31.9 and 25.2 Mg ha 1 32.1 and 28.5 Mg ha 1 and 22.4 and 16.4 Mg ha 1 respectively. The highest potato yield was produced in 2007, which was characterized with the highest precipitation and the lowest soil temperature throughout the season. The highest yield probably resulted from slow release of PSCU which supplied more N late in the season after soluble N was leached or used. Leaching from the soluble N source was also reduced since the rainfall events occurred more even compared with the other two years. Total yields in 2006 and 2007 were similar, however, marketable yield in 2006 was approximately 3 Mg ha 1 less than in 2007 and 20 year average in state. The difference was due to more culls produced in 2006, which probably resulted from dry and warm weather conditions in that ye ar. Both total and marketable yields were low in 2008. The undesirable tuber set and excessive leaching influenced by the unpredictable leaching rainfall contributed to the poor production. Besides, side dress of urea about 40 DAP usually required for the typical fertilization practices. However, in our study, in order to compare the impact of CRF and soluble sources with the same field operations, side dresses were not conducted for urea source, which was also resulted in poor potato yields. Nitrogen Recov ery Nitrogen uptake by tubers was higher with PSCU in 2006 (Table 3 5 ) however, the N uptake by vines was lower with PSCU than with urea, which resulted in a significant higher total N recovery with urea. Nitrogen rate did not affect N uptake either

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41 by tu bers or vines. The Atlantic tubers took up more N than the Fabula tubers, however, no differences in N uptake were found in their vines. N itrogen uptake by tubers and vines was unaffected by N sources or N rates in 2007. Cultivar Fabula accumulated more N in vines and tubers than var. Atlantic reflecting the yields obtained. In 2008, the PSCU contributed to higher N recovery by potato tubers compared with urea The N uptake by v ine s, along with the total N uptake increased with N rate. The total N accumul ation by tubers of var. Fabula was higher than the tubers of var. Atlantic although the total accumulation in both cultivars was similar. Similarly, N recovery by the potato cro p varied considerably among years. An average of 130.6 kg N ha 1 was recovered by the crop in 2007, which exceeded the average total N of 76.6 kg N ha 1 recovered in 2008. All the N recovery results agreed with the effect of N and cultivar treatment on total and marketable tuber yield s Nitrogen content in potato roots was not measu red in this study. It is likely that there were some differences of N content in the roots for various N treatments. The difference in N recovery between 2007 and 2008 was a result of higher leaching losses in 2008. Hutchinson et al. (2003) also reported o n the differences of N uptake by plants by using PSCU and urea. Joern and Vistosh (1995) found N rates of 112 168 kg N ha 1 maximized dry matter production and plant tissue N concentration at harvest. Zvomuya et al. (2001) recorded better N use efficiency with polyolefin coated urea ( POCU ) than with urea which could reduce loss of N through leaching. Errebhi et al. (1998) also found higher N recovery associated with higher tuber yield and better tuber quality because the more N taken up by crops and convert ed into organic forms, the less potential for leaching loss.

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42 Nitrogen U se E fficiency In this study, nitrogen use efficiency (NUE) was determined by dividing the marketable yield by the N application rate for each treatment. The PSCU was expected to be a m ore efficient N source in NUE for both N application rates compared with urea, since less leaching with PSCU was expected especially under the condition of uneven distribution of rainfall events. In 2007 and 2008, PSCU at 168 kg N ha 1 rate had the highest NUE compared with other treatments (Figure 3 2). However, the significant difference was not observed in 168 kg N ha 1 rate in 2006 and 224 kg N ha 1 rate in 2007. In 2006, the averaged soil temperature throughout the potato season was 23.4 C, which was h igher than 21.2 C and 22.5 C in 2007 and 2008, respectively. The high soil temperature could result in fast release of N from PSCU and increasing the risk of leaching as urea treatment. In 2007, the low soil temperature throughout the growing season slowed down the N release from PSCU, which reduced the leaching risk with PSCU treatment. Combined with the most rainfall events, PSCU at 168 kg N ha 1 rate had the highest NUE compared with other treatments. However, similar NUE with two N sources at 224 kg N h a 1 rate could result in the late supplying of N from PSCU in the season due to the slow release. In 2008, NUE values with PSCU treatment were significantly higher than urea treatment for both N rates. A leaching rainfall occurred 3 DAP rendered PSCU super iority in increasing NUE values. In 2006 and 2008, the lowest NUE values were recorded with urea at 224 kg N ha 1 rate. Therefore, urea with a single application was not recommended for maintaining marketable yields and NUE values. Hutchinson et al. (2003) demonstrated that NUE for all N sources they used including the PSCU were not significantly different for the 168 and 224 kg N ha 1 rate. However, the PSCU was not tested only as a controlled release source. They used 50%

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43 of polymer coated urea (PCU) and 50% of PSCU as a combined CRF treatment at 168 and 224 kg N ha 1 rate. NO 3 N and NH 4 N C oncentrations in the S hallow W ater T able In 2006, PSCU reduced both NO 3 N and NH 4 N concentrations at the first sampling event under TSI system (Figure 3 3 ). A differen ce in NO 3 N concentrations was also recorded between two N application rates at the first event. Under ISI (Figure 3 4 ), however, no evidence was showed that PSCU contributed to a lower NO 3 N concentration than urea, even though the NH 4 N concentrations wi th PSCU were significantly lower at the first and second sampling events. The NO 3 N concentrations in the shallow water table were barely affected by N sources under both TSI and ISI system for all sampling events in 2007 (Figure s 3 5 3 6 ). Compared with N sources, NO 3 N leaching was influenced more by N rates especially in the earlier sampling event s under TSI system Significant ly higher NO 3 N concentrations were found in the first (43 DAP) and second (57 DAP) sampling event s with the N rate of 224 kg h a 1 under TSI system, however, no effect of N application rate was observed for nitrate concentrations under ISI system. Similar NH 4 N concentrations were determined by both N sources and rates under two seepage systems In 2008, N sources had no effect on NH 4 N concentrations under both TSI and ISI system across the sampling events (Figure 3 7 3 8 ), whereas the lower N application rate (168 kg ha 1 ) reduced NH 4 N loss at the early sampling events for both seepage systems. Different results of NO 3 N concen trations influenced by N sources were found relative to irrigation system. Under TSI system, PSCU barely reduced nitrate loss except for the first sampling event, whereas under ISI system, nitrate concentrations with PSCU were higher than the concentration s with urea at the second and third events. The higher N rate also

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44 contributed to a higher NH 4 N concentration across all sampling events under TSI system. However, no variance in NH 4 N concentration was determined between two N rates under ISI system. The result indicated that the difference of NO 3 N losses with two N application rates could be minimized by reducing water application amounts during the season. The greatest difference in 3 years was observed at the first sampling event, when an average of 0 .75, 4.50 and 7.96 mg L 1 NO 3 N was measured in 2006, 2007 and 2008, respectively. The leaching rainfall in 2008 occurred 2 DAP possibly result ing in the difference of N leaching loss, and in the subsequent lower N recovery by crop and lower tuber yields that year. Pack et al., (2005) found no significant difference in NO 3 N concentration between treatments in shallow water table samples. The authors suggested that no difference was due to a high dilution of nutrients in the large shallow water table below the plots. Besides, wells in our study could not be installed in the field until about 40 days after planting which was too late to observe the leaching losses in the early season. Generally, t he average concentrations of NO 3 N and NH 4 N across all treat ments decreased with sampling dates except for the dynamic of NO 3 N concentrations with 168 kg N ha 1 treatment in 2006 and 2007 and with PSCU treatment in 2006. All of the exceptions were observed under TSI system. Since no early observations of nitrogen loss were available in our study, we assumed that higher nitrogen concentrations might have been determined before the first sampling event in each year, especially after the heavy precipitation events occurring early during each growing season. Besides, PSCU reduced nitrate concentrations at the first sampling event in 2006 and 2008 under TSI system, which suggested with high rate of irrigation, PSCU had the potential to reduce

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45 nitrate leaching compared with urea. It was also assumed that significant vari ance of leaching loss by using PSCU and urea was possibly found early in the season. Wang and Alva (1996) reported up to 30% of the total N applied as slow release fertilizer was leached from sandy soils, whereas, more than 88% of total N was leached whe n AN was used. The authors also suggested that in sandy soils, leaching of urea N could be an important part of total N loss from urea based slow release fertilizers, especially with the first precipitation events. Paramasivam and Alva (1997) found leachin g amounts of total N (sum of urea NH 4 and NO 3 ) in 100 days were 59% and 44% applied as PSCU and urea, respectively. The lower N leaching from urea was the result of loss N through volatilization and denitrification. Bundy et al. (1986) suggested that urea N could be lost by leaching of unhydrolyzed urea, volatilization and greater loss through leaching due to more rapid nitrification compared with an ammonium N source. Zvomuya et al. (2003) found that a single application of PCU improved recovery of N and r educed NO 3 leaching compared with three applications of urea. Similar results were reported by Waddell et al. (2000) when comparing SCU with urea. Contents of NO 3 N and NH 4 N in the Surface Soil In 2006, soil NO 3 N content was affected by both N sources an d application rates at all sampling events after fertilizing and planting (Figure 3 9 ). The urea treatment resulted in a significantly higher NO 3 N concentration in the surface soil before harvesting, compared with the PSCU treatment. On the other side, NO 3 N content with application rate of 224 kg N ha 1 was higher than with 168 kg N ha 1 across three sampling events after fertilizing. Soil NH 4 N content was also influenced by N source and rate at certain sampling events. Generally speaking, soil N content increased more rapidly with urea than with PSCU, especially for soil NO 3 N content. However, more N

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46 was retained in surface soil by using PSCU at the last sampling event, which indicated that PSCU released more slowly than urea. This result rendered PSCU a potential in reducing N leaching into the shallow water table. In 2007, both NO 3 N and NH 4 N residues in the surface soil were affected by N sources in the late season (Figure 3 10 ). High amounts of NO 3 N and NH 4 N remained in the soil with urea at the l ast two sampling events (64 and 91 DAP). There was no effect of higher N rate on residual soil NO 3 N or NH 4 N during the whole season. Similar results were found in 2008, when N rates failed to influence the content of both N forms in the surface soil (Fig ure 3 11 ). A higher NO 3 N content of 27.4 mg kg 1 with PSCU was recorded in the third sampling event (54 DAP). After pre plant sampling, a higher NH 4 N accumulat ion with PSCU than with urea until harvesting was observed Averaged across all treatments, the cumulative NO 3 N content of 111.27 mg kg 1 in 2007 surpassed the 80.52 mg kg 1 amount determined in 2008, while the cumulative residual NH 4 N of 50.49 mg kg 1 in 2007 exceeded the residu al of 34.63 mg kg 1 in 2008. Differences in tuber yields and N uptake by crops were consistent with the difference s in available soil N. In regard to the lower N recovery in 2008, the lower N residue in the surface soils indicated a higher N leaching loss in the early season of that year. Low mineral N contents in the top 20 cm of soil at pre plant were measured as 3.5 mg kg 1 and 5.2 mg kg 1 in 2007 and 2008, respectively. Meyer and Marcum (1998) concluded that higher N rates were needed to be applied to achieve optimum yields if low pre plant soil N concentrations were obs erved

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47 Table 3 1 Mean monthly rainfall and soil temperature ( 10 cm) for three growing season s 2006 2007 2008 Soil Temp (C) Rainfall (cm) Soil Temp (C) Rainfall (cm) Soil Temp (C) Rainfall (cm) Feb 14.7 16.3 15.4 14.0 17.3 9.4 0 Mar 1 8.3 1.5 0 18.8 10.4 18.2 11.3 Apr 22.7 2.5 0 21.1 3.1 0 21.3 0.3 0 May 25.3 0.8 0 23.9 3.2 0 24.3 1.6 0 Jun 27.3 11.9 26.7 12.9 27.2 16.7 Note: Marketable yield was calculated by the summation of A1 through A3 tuber grades. Tubers were graded as B=<4.8, A1=4.8 6.4, A2=6.4 8.3, A3=8.3 10.2, A4=>10.2 cm. No interactions were found between e ither two of the treatments. method at the 0.05 probability level. PSCU, polymer sulfur coated urea. Table 3 2 Comparison of tuber yield, quality and distributions for various N sources, rates and cultivars duri ng 2006. N and cultivar treatment Tuber yield (Mg ha 1) Specific gravity Mkt Total Cull B A1 A2 A3 A4 N source PSCU 25.88 32.86 3.96 3.02 23.09 2.80 0.00 0.00 1.071 Urea 24.67 30.97 4.05 2.25 19.29 5.32 0.06 0.00 1.072 N ra te (kg ha 1) 168 25.51 32.08 3.92 2.65 21.67 3.84 0.00 0.00 1.071 224 25.05 31.76 4.09 2.62 20.71 4.28 0.06 0.00 1.072 Cultivar Atlantic 27.16a 33.20 3.16 2.88 22.45 4.66 0.04 0.00 1.081a Fabula 23.40b 30.63 4.85 2.39 19.93 3.45 0.01 0.00 1.062b

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48 Table 3 3 Comparison of tuber yield, quality and distributions for various N sources, rates and cultivars during 2007. N and cultivar treatment Tuber yield (Mg ha 1 ) Specific gravity Marketable Total Culls B A1 A2 A3 A4 N source PSCU 29.57 33.35 1.28 2.45 18.07 7.67 3.83 0.05 1.0856 Urea 27.47 30.84 1.00 2.36 17.02 7.01 3.45 0.01 1.0859 N rate (kg ha 1 ) 168 28.90 32.45 1.15 2.39 17.51 7.69 3.70 0.01 1.0852 224 28.15 31.73 1.12 2.41 17.57 6.99 3.59 0.05 1.0864 Cultivar Atlantic 26.56b 30.15b 1.01 2.52 14.03b 7.78 4.75a 0.06 1.0958a Fabula 30.49a 34.04a 1.27 2.28 21.05a 6.90 2.53b 0.00 1.0759b Note: Marketable yield was calculated by the summation of A1 through A3 tuber grades. Tubers were graded as B=<4.8, A 1=4.8 6.4, A2=6.4 8.3, A3=8.3 10.2, A4=>10.2 cm. No interactions were found between either two of the treatments. method at the 0.05 probability l evel. PSCU, polymer sulfur coated urea.

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49 Table 3 4 Comparison of tuber yield, quality and distributions for various N sources, rates and cultivars during 2008. N and cultivar treatment Tuber yield (Mg ha 1 ) Specific gravity Marketable Total Culls B A1 A2 A3 A4 N source PSCU 17.90a 24.85a 3.74a 3.21a 15.89a 3.06 2.09 0.00 1.0675 Urea 14.98b 20.03b 2.60b 2.38b 12.32b 3.01 1.87 0.01 1.0692 N rate (kg ha 1 ) 168 16.34 22.50 3.28 2.83 14.36 2.88 1.88 0.01 1.0683 224 16.54 22.38 3.06 2.76 13.85 3.19 2.08 0.00 1.0685 Cultivar Atlantic 13.90b 19.78b 3.31 2.57b 12.17b 2.61b 1.90 0.00 1.0737a Fabula 18.98a 25.11a 3.03 3.02a 16.04a 3.46a 2.07 0.01 1.0630b Note: Ma rketable yield was calculated by the summation of A1 through A3 tuber grades. Tubers were graded as B=<4.8, A1=4.8 6.4, A2=6.4 8.3, A3=8.3 10.2, A4=>10.2 cm. No interactions were found between either two of the treatments. Treatment means were compared wit method at the 0.05 probability level. PSCU, polymer sulfur coated urea.

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50 Table 3 5 Effects of N source, N rate and potato cultivars on N recovery by potato vines and tubers during three growing season s 2006 2007 2008 Treatment N recovery (kg ha 1 ) N recovery (kg ha 1 ) N recovery (kg ha 1 ) tuber vine Total tuber vine Total tuber vine Total N source PSCU 91.0a 79.6b 170.6b 61.0 67.4 128.4 56.1a 22.0 78.2 Urea 80.8b 103.3a 184.1a 60.5 72.3 132.8 48.3b 26.6 74.9 N rate (kg ha 1 ) 168 83.8 83.8 167.6 62.2 68.2 130.5 51.8 20.6b 72.4b 224 88.0 99.1 187.1 59.3 71.5 130.8 52.6 28.0a 80.6a Cultivar Atlantic 100.6a 94.0 194.5a 58.6b 51.3b 109.9b 47.7b 23.0 70.7b Fabula 71.2b 88.9 160.1b 63.0a 88.4a 151.4a 56.7a 25.6 82.4a Note: No interactions were found between eithe r two of the treatments. Treatment means were compared within columns sulfur coated urea.

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51 Figure 3 1. Total rainfall and irrigation un der traditional and intermittent seepage irrigation systems in 3 years Figure 3 2. Nitrogen use efficiency with different N sources and rates in 3 years.

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52 Fig ure 3 3 NO 3 N and NH 4 N concentrations in the shallow water table separated by N sources and N rates under TSI during 200 6. The vertical bars repre sent the standard error of the mean. NH 4 N concentrations (mg L 1 ) N O 3 N concentrations (mg L 1 )

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53 Figure 3 4 NO 3 N and NH 4 N concentrations in the shallow water table separated by N sources and N rates under ISI during 200 6 The vertical bars repre sent the standard error of the mean. NH 4 N concentrations (mg L 1 ) N O 3 N concentrations (mg L 1 )

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54 Figure 3 5 NO 3 N and NH 4 N concentrations in the shallow water table se parated by N sources and N rates under TSI during 200 7 The vertical bars repre sent the standard error of the mean. NH 4 N concentrations (mg L 1 ) N O 3 N concentrations (mg L 1 )

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55 Figure 3 6 NO 3 N and NH 4 N concentrations in the shallow water table separated by N sources and N rates under ISI during 200 7 The v ertical bars repre sent the standard error of the mean.

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56 Figure 3 7 NO 3 N and NH 4 N concentrations in the shallow water table separated by N sources and N rates under T SI during 200 8 The vertical bars represent the standard error of the mean NH 4 N concentrations (mg L 1 ) N O 3 N concentrations ( mg L 1 )

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57 Figure 3 8 NO 3 N and NH 4 N concentrations in the shallow water table separated by N sources and N rates under ISI during 2008. The vertical bars represent the standard error of the mean NH 4 N concentrations (mg L 1 ) N O 3 N concentrations (mg L 1 )

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58 Figure 3 9 NO 3 N and NH 4 N con tent in the top 20 cm of the soil profile separated by N sources and N rates during 200 6 The vertical bar at each data point repre se nts the standard error of the mean. 2006 NO 3 N co ntent (mg kg 1 ) NH 4 N content (mg kg 1 )

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59 Figure 3 10 NO 3 N and NH 4 N content in the top 20 cm of the soil profile separated by N sources and N rates during 2007. The vertical bar at each data point repre se nts the standard error of the mean.

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60 Figure 3 11 NO 3 N and NH 4 N content in the top 20 cm of the soil profile separated by N sources and N rates during 200 8 The vertical bar at each data point repre se nts the standard error of the mean.

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61 CHAPTER 4 THE EFFECT OF AN ALT ERNATE SEEPAGE IRRIG ATION SYSTEM ON POTA TO YIELD AND N CONCENTR ATIONS IN THE SHALLOW WATER TABLE Rainfall and I rrigation Rainfall distribution through the p otato seasons in 3 years is presented in Figure 4 1. In 2006, only 13.8 cm of rainfall was recorded during the growing season, which was about 10 cm lower than the 10 yr average (24 cm) for the same period ( Table 4 1 ). This rainfall was supplemented with 7 9 and 33 cm of irrigation by TSI and ISI, respectively, which resulted in ISI supplying approximately 41% of TSI In 2007, total rainfall during the potato season was 23.4 cm, which was similar to the 10 yr average. The biggest rainfall event early in the season was 5.9 cm which occurred from Mar 1 st to Mar 3 rd which was 1.7 cm less than a leaching rainfall, followed by a deficit of rainfall (3.7 cm) from Mar 17 th through May 13 th Traditional seepage supplied 72 cm of irrigation compared with 36 cm by IS I. In 2008, total rainfall during the grow ing season was 19 cm, which was approximately 21% below the 10 year average. A leaching rainfall (8.7 cm in 3 days) occurred 2 DAP, which was 7 days after fertiliz er application A severe rainfall deficit occurred from Mar 21 st through May 22 nd when only 0.4 cm rain fell in 63 days. Intermittent irrigation delivered 34 cm of water, which was 57% of TSI water use ( 57 cm). The unfavorable weather condition resulted in a depressed emergence of potato sets in 2008, sig nificantly affect ing the tuber yields The averaged potato irrigation requirement reported by St. Johns River Water Management District (SJRWMD) is 45.7 to 50.8 cm per year (Smajstrla, 1995). An investigation of potato water use in TCAA reported an averag e amount of 50 cm irrigation water use for potatoes in 1985 and 1986 (Singleton, 1990). In this study, the range in water use of 23 monitored potato farms was 22 to 100 cm in two years. The

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62 author suggested different soil types, farm management practices, and periods of the crop growing season probably resulted in the wide range of water use. In our study, water use varied in years, especially under TSI system, which was mostly due to the different growing periods and weather conditions in three experimenta l years. Water use was expected to be more when potatoes planted later in a season because evapotranspiration increases as temperature and length of daylight hour increase. In 2006, potato growing season was 110 days, which was longer than 104 and 99 days in 2007 and 2008, respectively. The late harvest resulted in more irrigation water use in 2006 than in other two years. The leaching rainfall which occurred early in 2008 season delayed the beginning of irrigation schedule for both TSI and ISI systems. The late startup of irrigation combined with shortest growing season led to less water use under TSI system compared with the other 2 years. However, the total volume of irrigation under TSI in 2008 (56.5 cm) was close st to the number reported by SJRWMD (45.7 to 50.8 cm). The most possible reason that the amounts of irrigation in 2006 and 2007 were higher than the TCAA average was that the total volumes were over calculated. Since no flow rate data available in 2006 and 2007, we assumed that the pumping rate g enerally remained constant throughout all experimental years. The variable pumping rates may occur in the other two years and resulted in different irrigation volumes. The other reason was that duration of irrigation was miscalculated due to manually recor ding irrigation hours other than using timers. The crop water requirement (ET) during each season was calculated by multiplying estimated evapotranspiration (ET 0 ) by crop factors at each growth stage. The total ET of potato plants in three experimental ye ars were 28.4, 24.2 and 25.2 cm,

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63 respectively. The efficiency of TSI systems was approximately 30 to 70% (Smajstrla, 1991), which suggested that potatoes under TSI systems needed ranging from 35 to 95 cm of irrigation to meet growth requirement over three seasons. At this point, although irrigation water use in 2006 and 2007 was higher than the average number in TCAA, it was still not over irrigated due to the variable irrigation efficiency of seepage systems. Tuber Yield and Quality In 2006, potato tuber yield was affected by irrigation method (Table 4 2). The marketable yield with TSI (28.5 Mg ha 1 ) was significantly higher than with ISI (22.1 Mg ha 1 ) Total yield followed the same trend as marketable yield even though more culls and small size tubers ( size B) were recorded with ISI than the TSI The differences in tuber yield were a result of the different amount s of irrigation applied for the two systems. Potatoes under ISI treatment only received 41% of irrigation water compared with the TSI treatment Besides, rainfall in that growing season was 10 cm less than the 10 year average, which did not complement the irrigation deficiency. A verage specific gravity of potato tubers with ISI treatment was significantly higher than TSI treatment. This result pr obably revealed that over irrigating could affect the tuber quality by reducing tuber specific gravity. In 2007, irrigation method did not have an influence on total or marketable tuber yield. However, more middle size tubers (size A1) and less large size tubers ( size A2 and A3) were recorded with TSI than ISI Similar yields were possibly due to sufficient rainfall during this growing season. Also, irrigation supplied by ISI was 50% of that received from TSI, which was 9% higher than in 2006. Increased wat er supply improved tuber yield under ISI system. Similar specific gravities were also found with two irrigation treatments. In 2008, potatoes did not emerge 100% due to the heavy rainfall right after planting. Reduction of both total and marketable yield w as

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64 recorded in this year. Leaching rainfall early in the season and poor tuber set s was responsible for the lower yields compared with the yields in the other two years. Compared with TSI, ISI increased marketable tuber yields from 16.9 to 21.4 Mg ha 1 Th is result was possibly due to more irrigation water applied by ISI treatment compared with the other 2 years. Similar specific gravities were recorded under two irrigation methods; however, both of them were about 0.02 lower than in 2007. The early leachin g rainfall was one of the reasons that affected the tuber quality. Seepage irrigation treatments had different effects on tuber yields in three experimental years. In 2006, the average rainfall during the growing season was 42% lower than the 10 yr averag e. Intermittent seepage supplied only 41% of irrigation water compared with traditional irrigation as the system was operated manually. The lower yield was resulted from the deficiency of water application by ISI. In 2007, intermittent seepage supplied mo re irrigation water than that in 2006. Combin ed with more rainfall during the growing season, similar tuber yield was observed with ISI compared with TSI. In 2008, irrigation supplied by intermittent seepage was increased to 57% of the TSI, which could be a reason that higher tuber yield was obtained with ISI than TSI Besides, irrigation schedule was changed from nights to days, which resulted in lesser fluctuation in the water table level in 2008. Therefore, the changing of irrigation timing was another r eason that ISI resulted in increased yield in 2008. The average potato yield in Florida from 1990 to 2009 was 28.3 Mg ha 1 (USDA database). In our study, the average total and marketable yields in 3 years were 31.9 and 25.2 Mg ha 1 32.1 and 28.5 Mg ha 1 and 22.4 and 16.4 Mg ha 1 respectively. The highest potato yield was produced in 2007, which was characterized with the highest

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65 precipitation and the lowest soil temperature throughout the season. The highest yield was probably resulted from slow release of PSCU which supplied more N late in the season after soluble N was leached or used. Leaching from the soluble N source was also reduced since the rainfall events occurred more even compared with the other 2 years. Total yields in 2006 and 2007 were simil ar, however, marketable yield in 2006 was approximately 3 Mg ha 1 less than in 2007 and 20 year average in state. The difference was due to more culls produced in 2006, which was probably resulted from dry and warm weather conditions in that year. Both tot al and marketable yields were low in 2008. The undesirable tuber set and excessive leaching influenced by the unpredic table leaching rainfall contributed to the poor production. Besides, side dress of urea about 40 DAP usually is required according to typi cal fertilization practices. However, in our study, in order to compare the impact of CRF and soluble sources with the same field operations, side dress ings were not conducted for urea, which was also resulted in poor potato yields. N R ecovery The two irri gation systems had different effects on N uptake by potato tubers and vines in 3 years (Table 4 3). In 2006, differences in N uptake were recorded in potato tubers, where TSI resulted in a higher N accumulation than ISI. Consequently, a higher N accumulati on in entire potato plants with the TSI treatment was observed since no differences were found in vines. The lower N recovery under ISI system was due to an insufficient irrigation supply. In particular, precipitation in 2006 was quite low compared with th e average of the last 10 yrs. In 2007, significantly higher N recovery was found in both tubers and vines by using ISI system. However, the tuber yields under two irrigation systems were similar. In 2008, potato tubers under ISI system recovered more

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66 N tha n tubers under TSI system, even though no difference in N accumulation by vines was observed. Also, total N recovery under both irrigation systems in 2008 was lower than in other 2 years, which was possibly due to the massive leaching loss of N early in th e season after the leaching rainfall. To sum up, ISI system successfully increased tuber N recovery when sufficient irrigation was supplied. Over irrigating in a normal or a wet season would possibly reduce N accumulations in tubers and vines. Concentratio ns of NO 3 N and NH 4 N in the S hallow W ater T able The concentrations of NO 3 N in the shallow water table were significantly affected by irrigation method in 2006 and 2007, when the ISI treatment was scheduled to irrigate overnight. In 2006, minim al fluctuations were observed in NO 3 N concentrations under TSI system across the five sampling events and all of them were < 1.5 mg L 1 ( F igure 4 2 ). However, compared with TSI treatment, NO 3 N concentrations under ISI were found to be significantly highe r for the first two sampling events. Also, unlike the concentrations with TSI treatment, concentrations of NO 3 N with ISI treatment were significantly decreased across five sampling events. In 2007, NO 3 N concentrations in the well water samples were simil ar for both the irrigation systems ( F igure 4 3 ). However, average concentrations of NO 3 N under ISI were higher in 2007 than in 2006, which was a result of the differences in rainfall during the 2 years. In 2007, rainfall was more than 40% higher compared with 2006. Rainfall could have easily move d NO 3 N downward into the shallow water table in sandy soils. In 2008, however, no significant differences in NO 3 N concentrations in shallow water table were found between two of the irrigation methods ( F igure 4 4 ). Unlike the first two years, concentrations of NO 3 N under TSI system in 2008 significantly decreased across sampling events and the change of irrigation timing for ISI was the reason for the

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67 differences in NO 3 N concentrations. In 2006 and 2007, the sch edule for ISI was set up to irrigate potato over night at 12 hrs per day. However, i n 2008, the schedule was changed to supply water during the day at the same 12 hrs per day rate The change was introduced to minimize water table fluctuation under ISI sys tem, since daytime fluctuations in water table depth due to higher ET compared with night time can be substantial. Such a change in irrigation timing would subsequently reduce NO 3 N leaching into shallow water table Pack et al. (2005) found no significant difference in NO 3 N concentration between CRF and urea treatments in shallow water table samples. The authors suggested that their result may have been due to a high dilution of nutrients in the large shallow water table below the plots. Besides, wells we re not installed in the field until about 40 days after planting a period during which early leaching probably occurred. The concentrations of NH 4 N in the shallow water table were significantly higher with TSI method than with ISI method in 200 6 and 2007 ( F igure 4 2 and 4 3 ), which showed that the concentrations of NH 4 N in the shallow water table were not affected by the fluctuation in the water table depth. Higher NH 4 N concentrations with TSI treatment was the result of more water being suppl ied with this treatment. No differences in NH 4 N concentrations were observed between two irrigation methods in 2008 ( F igure 4 4 ), which was also due to the change of ISI schedule to daytime irrigation In all 3 years, concentrations of NH 4 N in the shallo w water table were reduced gradually with sampling events for both of the irrigation systems. The reduction could be the result of nitrification and uptake by the crop.

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68 Contents of NO 3 N and NH 4 N in the Surface Soils In all years, NO 3 N residue s in the surface soil were affected by irrigation treatments ( F igure 4 5 4 6 and 4 7 ). Residues of NO 3 N were significantly higher with TSI treatment than with ISI treatment all 3 years. However, change s in soil NO 3 N concentrations w ere different. In 200 6, concentration differences between irrigation methods were found at the sampling events at 56 and 76 DAP. However, n o difference of NO 3 N con centration was recorded after harvesting. Also, the NO 3 N concentrations in the surface soils decreased following the second sampling event Crop uptake and leaching were the reason s for the decline in soil nitrate content. However, in 2007 and 2008, the only difference in NO 3 N content between two irrigation treatments was found at the last sampling event The diffe rence might indicate that TSI and ISI affected nitrate leaching differently. In 2006 and 2007, nitrate leaching with ISI was significantly higher than leaching with TSI, which resulted in the higher nitrate concentrations in surface soil with TSI treatment The significant higher residue of NO 3 N with TSI treatment in 2008 was a reason for the lower tuber yield with this treatment The soil NH 4 N contents under ISI treatment were significant ly higher compared with the contents under TSI treatment in 2006 and 2007, but significantly lower in 2008. This result indicated that frequent fluctuation s in water table depth under ISI treatment could reduce nitrification in soils in 2008. Therefore, more NH 4 N and less NO 3 N were retained in surface soils w ith ISI treatment in the first 2 years. In 2008, significant ly higher NH 4 N content was found with TSI treatment. Combined with the higher NO 3 N residues with TSI treatment, the higher N concentrations in the surface soil could illustrate lower N uptake by potato plants, since leaching was low due to the low precipitation during the potato growth stages.

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69 Soil Moisture and Water Table Depth In 2006, the water table depth fluctuated considerably during the growing season under ISI system compared wi th TSI system (Figure 4 10 ), due to irrigation timing for ISI and deficient rainfall. While a n average water table depth of 49 cm was maintained with TSI treatment, with the ISI method the average depth was 58 cm. The differences in water table depth obvio usly influenced soil moisture at various soil depths. With TSI treatment, the average of soil moisture at 20 and 30 cm below the surface was 20.1% and 24.8%, respectively, compared with the average of 10.9% and 17.1% with ISI treatment (Figure 4 8 ) In TCA A production areas, 63% of the potato root system is located between 12 and 24 cm below the soil surface (Munoz, 2004). Therefore, soil moisture differences at 20 and 30 cm depth would greatly affect the crop growth. In 2007, the fluctuation in water table depth under ISI system was not high as it was in 2006. L ess fluctuation in water table was due to abundant rainfall during 2007 A verage water table depth in 2007 was 50 cm with TSI treatment and 57 cm with ISI treatment during the potato season. In 2008 however, average water table depth was 52 cm with TSI and 56 cm with ISI. The fluctuation in water table depths was minimized by switching the irrigation timings from night time to day time for ISI treatment. Table 4 1. Rainfall and irrigation volumes und er traditional and intermittent seepage systems Year Treat ment Irrigation area (m 2 ) Duration (h) Flow rate (L/min) Total irrigation volume (m3) Total irrigation (cm) Rainfall (cm) 2006 TSI 2650.7 1711.0 20.4 2094.3 79.0 13.8 ISI 2650.7 703.8 0 20.4 861. 5 0 32.5 2007 TSI 2650.7 1560.0 20.4 1909.4 72.0 24.3 ISI 2650.7 780.0 0 20.4 954.7 0 36.0 2008 TSI 2650.7 1224.0 20.4 1498.2 56.5 18.5 ISI 2650.7 732.0 0 20.4 896.0 0 33.8

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70 Table 4 2 Comparison of tuber yield, distribution and specific gravity as re lated to irrigation management during 2006 to 2008 Year Irrigation Tuber yield (Mg ha 1 ) Specific gravity Mkt Total Cull B A1 A2 A3 A4 2006 TSI 28.47a 33.93a 3.22b 2.24b 22.59a 5.82a 0.06 0.00 1.067b ISI 22.08b 29.91b 4.80a 3.03a 19.79b 2 .29b 0.00 0.00 1.074a 2007 TSI 28.53 32.09 1.19 2.37 19.31a 6.56b 2.66b 0.01 1.0844 ISI 28.52 32.09 1.09 2.43 15.78b 8.13a 4.62a 0.05 1.0872 2008 TSI 16.90b 21. 70b 2.65b 2.15b 12.19b 2.68b 2.03 0.01 1.0696 ISI 21.35a 28.49a 3.69a 3.44a 16.02a 3.39a 1.94 0.00 1.0671 Note: method at the 0.05 probability level. TSI, traditional seepage irrigation; ISI, intermittent seepage irrigation. Table 4 3. Effect of irrigation method on N recovery by potato vines and tubers during the 2006, 2007 and 2008 growing season s 2006 2007 2008 Treatment N recovery ( kg ha 1 ) N recovery (kg ha 1 ) N recovery (kg ha 1 ) T uber vine Total tuber vine Total tuber vine Total Irrigation TSI 95.0a 89.8 184.8a 53.3b 64.5b 117.8b 50.0b 25.2 75.2 ISI 76.8b 93.1 169.9b 68.8a 75.3a 144.0a 53.4a 23.4 76.8 Note: method at the 0.05 probability level. TSI, traditional seepage irrigation; ISI, intermittent seepage irrigation.

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71 Figure 4 1. Rainfall distribution through potato seasons in 2006, 2007 and 2008. The X axis shows the sampling days after planting. 2006 2007 2008 Rainfall (cm)

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72 Figure 4 2 Observed and predicted NO 3 N and NH 4 N concentrations in the shallow water table compar ed between two irrigation methods in 2006. TSI, traditional seepage irrigation; ISI, intermittent seepage irrigation. The X axis shows the sampling days after planting.

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73 Figure 4 3 Observed and predicted NO 3 N and NH 4 N concentrations in the shallow w ater table compared between two irrigation methods in 2007. TSI, traditional seepage irrigation; ISI, intermittent seepage irrigation. The X axis shows the sampling days after planting.

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74 Figure 4 4 Observed and predicted NO 3 N and NH 4 N concentrations in the shallow water table compared between two irrigation methods in 2008. TSI, traditional seepage irrigation; ISI, intermittent seepage irrigation. The X axis shows the sampling days after planting

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75 Figure 4 5 Observed and predicted NO 3 N and NH 4 N content in soils under two irrigation methods during 2006. TSI, traditional seepage irrigation; ISI, intermittent seepage irrigation. The horizontal axis shows the days after planting where negative number indicates the days before planting.

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76 Figur e 4 6 Observed and predicted NO 3 N and NH 4 N content in soils under two irrigation methods during 2007. TSI, traditional seepage irrigation; ISI, intermittent seepage irrigation. The horizontal axis shows the days after planting where negative number indi cates the days before planting.

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77 Figure 4 7 Observed and predicted NO 3 N and NH 4 N content in soils under two irrigation methods during 2008. TSI, traditional seepage irrigation; ISI, intermittent seepage irrigation. The horizontal axis shows the days after planting where negative number indicates the days before planting.

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78 Figure 4 8 The dynamic changing of soil moisture under two irrigation systems during the potato season in 2006. The soil moisture was measured at 10, 20, 30, 40, 60 and 100 cm b elow the top of the row.

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79 Figure 4 9 The dynamic changing of soil moisture under two irrigation systems during the potato season in 200 7 The soil moisture was measured at 10, 20, 30, 40, 60 and 100 cm below the top of the row.

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80 Figure 4 1 0 Water table depth under seepage irrigation systems and drip irrigation in 2006, 2007 and 2008. The vertical axes represent days after planting. 2006 2007 2008 Water Table Depth (cm)

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81 CHAPTER 5 THE EFFECT OF DRIP I RRIGATION SYSTEM ON POTATO YIELD AND THE FEASIBLILITY OF FERT IG A TION METHOD ON POTAT O PRODUCTION Irrigation V olumes and W eather C onditions The system we used has several innate benefits. First, no shallow water table drained from the field and entered the watershed. Smajstrla et al. (2000) found that the water table responded more quickly to irrigation with subsurface drip irrigation than with seepage irrigation. Secondly, irrigation rate was based on evapotranspiration rate, i.e., less when the plant was small and more when the plant matured. With seepage irrigation, the irrigation rate usually remains the same during the entire season. Thirdly, soil moisture can be maintained at reduced levels during late bulking to improve tuber quality. Excess water during the bulking period can suffocate tubers causing a disorder above ground drip irrigation for potato production and water use efficiency in Nor th Dakota. The SDI was found to be the most water use efficient while also maintaining potato yield and quality. W ith drip irrigation, 27.3 cm of water w as applied during 2006, supplemented by 14.0 cm of rainfall (Figure 5 1). In 2007, the water applied th rough drip irrigation was 28.0 cm In 2008, the total irrigation amount through the drip system (31.0 cm) was similar to the previous two experimental years The average potato irrigation requirement reported by St. Johns River Water Management District (S JRWMD) is 45.7 to 50.8 cm per year (Smajstrla, 1995). Compared with the averaged potato irrigation amounts, drip irrigation in our study reduced 35 to 42% of irrigation water use. One of

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82 the reasons for the reduction in water use with drip irrigation was t hat no runoff occurred, whereas runoff occurred under both seepage irrigation systems since water furrows with small slopes are used to distribute water particularly for drainage after heavy rain. Crop water requirements (ET) and water applied at each pot ato growth stage are shown in Table 1 In 2006, the amount of irrigation water applied through drip system was less than the crop water requirements at stage 2 and 3, which are the critical growth stages for plant water requirement. This occurrence was pos sibly the reason for lower tuber yields with drip irrigation compared with the seepage irrigation systems. In 2007, the water applied with drip was similar to the ET requirement at stage 2 and more than the ET at stage 3 and 4, which resulted in the higher tuber yields compared with the yields in the other 2 years. In 2008, even though the total water applied with drip system was higher than the other two years, potato crops were under irrigated at stage 2 and over irrigated at stage 3. Combined with the le aching rainfall in the early season, the tuber yields were severely low under both drip and seepage irrigation in this year. Our study was not set up to determine the effects of adjustment of the amounts of water delivered during different physiological st ages using drip irrigation based on the ET requirement for crop growth and yield. A separate experiment designed with specific objectives for gathering such information could possibly help gain better understanding. Tuber Y ield The drip irrigation system d id not perform well in both total and marketable yields except for the second experimental year compared with the seepage irrigation systems (Figure 5 2 5 3 5 4 ). The heaviest rainfall occurred in 2007, which was similar to the 10 year average, resulting in the highest total and marketable potato yields compared

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83 with the yield in the other two years. Both total and marketable yields, when fitted with linear regression models relating to the different N rates, resulted in R 2 s ranging from 0.67 to 0.97 duri ng the three experimental years. In 2006, no significant differences in marketable yield with any N rate were found except for the control. However, marketable yields with all N rates were below 10 Mg ha 1 which were lower than marketable yields under the traditional seepage systems. One of the reasons was that there were no fertilizers applied to the field until after the drip tapes were set up for fertigation. The potato crops need N at planting and in the early season for shoot growth and tuber initiali zation, which is critical for tuber yields. The other reason was the lower irrigation amount supplied through the drip system, especially during growth stages 2 and 3. Total yields with each N rate were much higher than the marketable yields in 2006, which indicated that a lot of small sized tubers were produced with drip irrigation due to the inefficient water and N fertilizer management. In 2007, the marketable yields with N rates of 168 and 280 kg ha 1 were significantly higher than the yields with othe r N rates. Also, average marketable and total yields in this year were higher than the yields in the other 2 years. Adequate rainfall was one of the reasons for higher yields. In addition, improved efficiency in managing the drip system during 2007 could b e another reason for higher yields. In 2008, total and marketable yields increased significantly with the N rates. The average marketable yield during this year was similar to the yield in 2006 and lower than the yield in 2007. Even though total rainfall in 2008 was more than the total rainfall in 2006, the distribution through the growing season was extremely uneven. More than 83% of rainfall occurred within 10 DAP and after 80 DAP, which was not effective in

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84 sustaining or improving optimum tuber yields. Therefore, the drip system did not produce more yields in 2008 compared with 2006. Fabeiro et al. (2001) concluded that tuber bulking and ripening stages were found to be the most sensitive stages to water stress with drip irrigation. Water deficit occurri ng at these two growth stages could result in yield reductions. The two potato cultivars had remarkably different marketable and total tuber yields during the 3 study years (Figure 5 5 ) In 2006, significantly higher marketable and total tuber yields of va r. Atlantic were produced than var. Fabula whereas, in 2007 and 2008, var. Fabula harvested more marketable and total tubers than var. Atlantic The differences in irrigation rates along with precipitation during 3 years contributed to the yield variances The data further suggested that var. Atlantic would have higher tuber yields during a dry season, whereas var. Fabula would produce more tubers if there was normal rainfall combined with adequate irrigation. Nitrogen R ecovery Nitrogen recovery by plants under drip irrigation was generally low irrespective of the N rates in all experimental years (Table 5 2 ). Compared with N recovery at the corresponding equivalent N application rates under seepage irrigation systems, N recovery by both potato tubers and vines was lower all 3 years. In 2006, N recovery by potato tubers and vines with control N treatment which was the treatment with no fertilizer applied, was significantly lower than the recovery with other N treatments. No differences in N uptake by tub ers were found except at the highest N application rate (280 kg N ha 1 ). N itrogen uptake by vines was significantly highest at 224 kg ha 1 N compared with 112 k g ha 1 N and control. The highest N

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85 application rate contributed to the highest total N recovery which was significantly higher than the other N treatments except for the N rate of 224 kg ha 1 In 2007, no significant differences in N recovery by potato tubers were found at any N application rate. The variance in total N recovery among control and other N treatments could not be compared during this year as the data on N uptake by potato vines were not available for the control However, no significant differences in vine and total N uptake were found at any of the N application rates. The potato tu ber and total N recovery was consistent with the trend of potato tuber yields, where also no differences were found among all N application rates. In 2008, similar to the N recovery under seepage irrigation system s N uptake by tubers and vines at all N application rates was lower compared with the uptake at corresponding equivalent rates in the other 2 years. N itrogen recovery by potato tubers was highest with the 280 kg ha 1 N rate treatment, which was significantly higher than the other N treatments ex cept for the 224 kg ha 1 N treatment. D ifferences in N uptake by vines were only recorded between control treatment and the 224 and 280 kg ha 1 N treatments. Total N uptake with control treatment was significantly lower than the other N treatments, and the 280 kg ha 1 treatment had a higher total N recovery than the other N treatments except for the 224 kg ha 1 treatment. The lower N recovery of both tubers and vines in 2008 was a result of the deficient irrigation at the early growth stage, which also cont ributed to the lower tuber yields in this experimental year. NH 4 N and NO 3 N C ontents in S urface S oil The highest NH 4 N and NO 3 N contents in surface soil across sampling events after planting in three experimental years were found in 2006 ( Figure 5 6 ). At the second sampling event in 2006, the NO 3 N contents in surface soil exceeded 30 mg kg 1

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86 with 168 and 280 kg ha 1 N treatments, which were significantly higher than the contents with other two N treatments. At the third sampling event (76 DAP), the nit rate residues in surface soil were highest in the 280 kg ha 1 N treatment, which was significantly higher than the residu al soil N in other treatments. No differences in soil NO 3 N and NH 4 N residues among all N treatments were found after harvesting (112 DAP). In 2007, the NH 4 N and NO 3 N contents in surface soil barely varied with each N treatment across sampling events, including the event before planting ( Figure 5 7 ). S ignificantly lowe r NO 3 N contents were measured with the 112 kg ha 1 treatment at the last two sampling events. No differences in NH 4 N contents at any N rate were found across sampling events except for the lower contents at 112 kg ha 1 treatment at the last event. In 2008, both NO 3 N and NH 4 N residues in soil were relatively lower than the residues across sampling events in the other 2 years ( Figure 5 8 ). Also, relatively higher soil NO 3 N contents were found before planting during this year At the second sampling event, both NH 4 N and NO 3 N contents with each N treatment were significa ntly lower compared with contents in the corresponding samples in the other 2 years. The low soil N content at this sampling event resulted from the late N fertilizer application with drip irrigation, which also contributed to low potato tuber yields that year. The soil TKN contents were tested in 2008, but no differences among N treatments were found over the sampling events. NH 4 N and NO 3 N C oncentrations in O bserv ation W ells The NH 4 N and NO 3 N concentrations in the observ ation wells showed marked variat ion during the three experimental years. In 2006, no differences in the well water NO 3 N concentrations among N application rates were observed at the first two sampling events ( Figure 5 9 ), and the concentrations were extremely low ( less than 1.0

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87 mg L 1 ) for the first three events. At the last two sampling events, lower NO 3 N concentrations were observed with 112 kg ha 1 N compared with the other N rates except with 224 kg ha 1 N rate. H igh standard deviations were also observed between replications within each N treatment at the last two sampling events. Unlike the NO 3 N concentrations across sampling events, NH 4 N concentrations in the wells decreased from the first to the fo u rth sampling At the first two sampling events, higher NH 4 N concentrations with high standard deviations were found with 112 kg ha 1 N. At the third and fo u rth sampling events, no differences in NH 4 N concentrations were measured among all N treatments, and all concentrations were less than 0.5 mg L 1 At the last event, the only dif ference observed was that between 112 and 280 kg ha 1 N treatments. In 2007, higher NO 3 N concentrations were measured acrss sampling events ( Figure 5 10 ) compared with the concentrations in 2006. Since the amount of water delivered through the drip system in both the years was the same, higher precipitation in 2007 should be the only reason for the differences in the nitrate concentrations in the observ ation wells. The nitrate concentrations also increased with N application rates except for the last sampl ing event. High standard deviations were also measured within each N treatment, especially with the 224 and 280 kg ha 1 N rates. Similar patterns of NH 4 N concentrations were observed across sampling events in 2006 and 2007. The NH 4 N concentrations decrea sed from the first event to the fo u rth event in all N treatment s However, the highest N application rate contributed to the lower NH 4 N concentrations in wells, especially for last three sampling events.

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88 In 2008, NO 3 N concentrations increased with N ap plication rates except for the first sampling event ( Figure 5 1 1 ). There were no differences in nitrate concentrations measured among N treatments at the first event, including the control. Compared with the nitrate concentrations in 2007, the concentratio ns in 2008 were lower through all sampling events, which were similar to the concentrations in 2006. The precipitation differences were the reason for the variances of nitrate concentrations in wells. The NH 4 N concentrations with all N treatments were les s than 1.0 mg L 1 across sampling events, and the highest concentrations with each N treatment were found at the first sampling event, which were similar to the patterns of NH 4 N concentrations in the other 2 years.

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89 Table 5 1 Irrigat ion water for drip ir rigation and ET at each potato growth stage measured during 2006, 2007 and 2008. Year Growth Stage ET0 (cm/d) Kc ET (cm/d) Irrigation water (cm/d) 1 0.34 0.4 0.13 0.14 2006 2 0.36 0.7 0.25 0.14 3 0.41 1.1 0.45 0.35 4 0.43 0.7 0.30 0.36 2 0. 33 0.7 0.23 0.22 2007 3 0.38 1.1 0.42 0.53 4 0.41 0.7 0.28 0.46 2 0.35 0.7 0.24 0.15 2008 3 0.41 1.1 0.45 0.65 4 0.45 0.7 0.32 0.33 Table 5 2 Effect of N rate on N uptake by potato vines and tubers compared among N rates during 2006, 200 7 and 2008. N rate 2006 2007 2008 N recovery (kg ha 1 ) N recovery (kg ha 1 ) N recovery (kg ha 1 ) Tuber Vine Total Tuber Vine Total Tuber Vine Total 0 11.49c 9.02c 20.51c 30.96 ns ns 6.69c 3.15b 9.84c 112 49.31b 58.70b 108.02b 44.01 24.19 68.21 13.22bc 23.03ab 36.25b 168 41.52b 75.04ab 116.56b 64.49 27.10 91.59 16.85b 23.34ab 40.19b 224 39.43b 97.18a 136.60ab 46.70 30.36 77.07 28.26a 35.15a 63.41ab 280 69.57a 80.42ab 149.99a 63.62 32.53 96.15 35.41a 37.30a 72.72a

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90 Fig ure 5 1. Total rainfall and drip irrigation volumes in 3 years Figure 5 2 Total and marketable yields compared among N rates under drip irrigation system in 2006.

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91 Figure 5 3 Total and marketable yields compared among N rates under drip irrigation system in 2007. Figure 5 4 Total and marketable yields compared among N rates under drip irrigation system in 2008

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92 Figure 5 5 Total and marketable yields compared between two potato cultivars under drip irrigation in 2006, 2007 and 2008

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93 Figure 5 6 Soil NH 4 N and NO 3 N contents under drip irrigation system compared among N rates during 2006.

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94 Figure 5 7 Soil NH 4 N and NO 3 N contents under drip irrigation system compared among N rates during 2007.

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95 Figure 5 8 Soil NH 4 N, NO 3 N and TKN contents under drip irrigation system compared among N rates during 2008.

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96 Figure 5 9 NH 4 N and NO 3 N concentrations compared among N rates in the observation wells under drip irrigation system during 2006.

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97 Figure 5 10 NH 4 N and NO 3 N con centrations compared among N rates in the observation wells under drip irrigation system during 2007.

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98 Figure 5 11 NH 4 N and NO 3 N concentrations compared among N rates in the observation wells under drip irrigation system during 2008.

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99 CHAPTER 6 CO NCLU S IONS In this study, potato yield s in 2006 and 2007 w ere similar to the 20 year average in Florida. However, yield in 2008 was lower than the average number. The weather conditions, especially uneven rainfall distribution, had important impacts on pota to production Particularly, the distribution of rainfall events throughout the growing season was more important than the total precipitation on potato production. In 2008, a leaching rainfall event occurred 3 DAP which greatly damaged the potato tuber se ts and maximized N leaching early in the season. The unpredictable rainfall events reduced tuber yields and increased the potential of nitrate leaching as well. In order to avoid yield reduction, certain amount of fertilizers should be applied after big ra infall events. Planting time also influenced nitrogen uptake and leaching potentials by determining the release rate of CRFs. From our study, potatoes planted in the middle of February produced higher yields than those planted in the early March. Intermitt ent seepage irrigation reduce d water use by approximately 50% compared with TSI throughout 3 study years, and maintain ed potato yield in 2007, when the tuber yield was the highest in 3 years and very similar to the 20 yr average in State. Even though tuber yield with ISI was higher than the yield with TSI in 2008, the total and marketable yields were much lower than long term average yield Therefore, f urther studies are required to investigate whether ISI could increase tuber yields as well as significantl y reduce water use. C ompared with the TSI the ISI also had the potential to reduce nitrate leaching if appropriate irrigation timing and schedul ing are used. Applying irrigation water from 6am to 6pm during a day successfully reduced the fluctuation of th e shallow water table, which subsequently minimized n itrate leaching under ISI.

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100 As a controlled release N source, PSCU has the potential to increase total and marketable tuber yields compared with urea with a single pre plant application. However, there m ay be still a risk of leaching of urea N from PSCU particularly after the first few leaching events in sandy soils. Heavy early season rainfall can deplete available soil N; th us, side dress fertilizers m ay still be required to produce optimum tuber yield s for both PSCU and urea treatments. Besides leaching loss, urea and urea based controlled release fertilizers can also be los t through volatilization and denitrification, which can result in lower N uptake and poor er tuber yields. Increase of N rate from 168 to 224 kg ha 1 barely benefit ted tuber yields, but increase d the potential of N leaching losses. F ertigation in this study was unsuccessful in maintain ing potato yields as fertilizer application was delayed as a delay in laying down drip tapes could n ot be avoided for the potato crop A booster dose of fertilizer at planting to meet the nutrient requirement for germination and establishment of potato plants may help overcome the delayed fertigation problem. Besides, i n this study, fertigation schedule was changed weekly, which could not match the daily ET sometimes. Therefore, daily schedules are probably needed to obtain the optimum potato yield. This study was not set up to determine the effects of adjustment of the amounts of water delivered during different physiological stages using drip irrigation based on the ET requirement for sufficient crop growth and yield. A separate experiment designed with specific objectives for gathering such information could possibly help gain better understanding.

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101 APPENDIX A ANOVA TABLE FOR POTATO YIE LD UNDER SEEPAGE IRR IGATION Table A 1. ANOVA table for potato total yield under seepage irrigation Source DF Sum of Squares Mean Square F Value Pr > F rep 3 968.11 322.70 5.28 0.1026 year 2 3704.73 1852.36 39.94 <.0 001 irri 1 61.07 61.07 1.02 0.3759 N 3 886.01 295.34 4.26 0.0171 year*irri 2 1437.05 718.52 15.49 <.0001 year*N 6 975.21 162.54 3.50 0.0024 irri*N 3 570.73 190.24 2.74 0.0692 year*irri*N 6 210.96 35.16 0.76 0.6035 var 1 327.23 327.23 7.06 0.0084 ye ar*var 2 659.32 329.66 7.11 0.001 irri*var 1 58.01 58.01 1.25 0.2645 var*N 3 186.33 62.11 1.34 0.2622 year*var*N 6 234.06 39.01 0.84 0.5392 year*irri*var 2 232.09 116.05 2.50 0.084 irri*var*N 3 22.74 7.58 0.16 0.9209 year*irri*var*N 6 104.08 17.35 0. 37 0.8951 rep(irri) 3 183.36 61.12 0.85 0.4845 N*rep(irri) 18 1294.14 71.90 1.55 0.0738 Residual 248 11502.00 46.38

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102 Table A 2 ANOVA table for potato marketable yield under seepage irrigation Source DF Sum of Squares Mean Square F Value Pr > F r ep 3 1062.36 354.12 7.01 0.0721 year 2 5767.00 2883.50 78.06 <.0001 irri 1 29.80 29.80 0.61 0.4855 N 3 447.55 149.18 1.85 0.1705 year*irri 2 1268.73 634.37 17.17 <.0001 year*N 6 687.05 114.51 3.10 0.006 irri*N 3 400.21 133.40 1.66 0.2086 year*irri*N 6 160.16 26.69 0.72 0.6317 var 1 204.63 204.63 5.54 0.0194 year*var 2 869.23 434.61 11.77 <.0001 irri*var 1 86.08 86.08 2.33 0.1281 var*N 3 102.09 34.03 0.92 0.4311 year*var*N 6 149.74 24.96 0.68 0.6694 year*irri*var 2 159.12 79.56 2.15 0.1182 irri *var*N 3 34.26 11.42 0.31 0.8188 year*irri*var*N 6 76.33 12.72 0.34 0.9127 rep(irri) 3 151.64 50.55 0.59 0.6281 N*rep(irri) 18 1536.25 85.35 2.31 0.0023 Residual 248 9160.63 36.94

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103 APPENDIX B ANOVA TABLES FOR POT ATO YIELD UNDER DRIP IRRIGATION T able B 1. ANOVA table for potato total yield under drip irrigation Source DF Sum of Squares Mean Square F Value Pr >F rep 3 313.43 104.48 6.88 0.0002 year 2 8931.28 4465.64 294.26 <.0001 N 4 1995.22 498.81 32.87 <.0001 year*N 8 430.62 53.83 3.55 0.0009 var 1 465.67 465.67 30.69 <.0001 year*var 2 1195.98 597.99 39.40 <.0001 N*var 4 46.73 11.68 0.77 0.5465 year*N*var 8 164.16 20.52 1.35 0.2224 Residual 147 2230.85 15.18

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104 Table B 2 ANOVA table for potato marketable yield under drip irrigation S ource DF Sum of Squares Mean Square F Value Pr > F rep 3 267.60 89.20 6.13 0.0006 year 2 9892.65 4946.32 340.06 <.0001 N 4 1378.06 344.51 23.69 <.0001 year*N 8 362.60 45.33 3.12 0.0028 var 1 218.33 218.33 15.01 0.0002 year*var 2 1122.55 561.27 38.59 <.0001 N*var 4 67.47 16.87 1.16 0.3311 year*N*var 8 204.27 25.53 1.76 0.0904 Residual 147 2138.19 14.55

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105 APPENDIX C IRRIGATION SCHEDULE FOR DRIP IRRIGATION Table C 1. Irrigation schedule for drip system in 2006 Date Activity Stage Gallons Duration comments Initial final (min) 27 Mar Irrigation 1 4074 4207 28 28 Mar Irrigation 1 4234 4512 50 28 Mar Irrigation 1 4512 4701 50 Filter clogged 28 Mar Irrigation 1 4701 4818 50 Filter clogged 29 Mar Irrigation 1 4824 5184 50 Filter cleaned (1 0 am) 29 Mar Irrigation 1 5184 5494 50 29 Mar Irrigation 1 5494 5732 50 30 Mar Irrigation 1 5732 6634 50 31 Mar Irrigation 1 6634 weekend 2 Apr Irrigation 1 8916 weekend 3 Apr Fertigation 1 8927 9336 80 First injection fertilizers (10 0 11) 3 Apr Fertigation 1 9336 9734 80 Afternoon 3 Apr Fertigation 1 9734 10176 80 3 Apr Fertigation 1 10176 3 Apr Fertigation 1 10952 4 Apr Fertigation 1 10952 5 Apr Fertigation 1&2 13064 Overlapping stage 1 and 2 7 Apr Ferti gation 2 13108 13429 65 7 Apr Fertigation 2 13429 13752 65 8 Apr Fertigation 2 13407 14407 130 10am and 2pm 9 Apr Fertigation 2 Valve closed for rain 10 Apr Fertigation 2 14407 14743 65 Morning 10 Apr Fertigation 2 14743 65 Noon 10 Apr Fe rtigation 2 15622 65 Afternoon 11 Apr Fertigation 2 15622 15956 52 11 Apr Fertigation 2 15956 65 Additional applic at 5:00pm 12 Apr Fertigation 2 16467 65 Additional applic at 8:00am 12 Apr Fertigation 2 16467 17246 65 applic at 10am & 2pm 13 Apr Fertigation 2 17246 17530 65 13 Apr Fertigation 2 17530 17831 65 13 Apr Fertigation 2 17831 18259 90 Applic morning 14 Apr Fertigation 2 18259 18673 90 Applic afternoon 15 Apr Fertigation 3 18741 16 min each period

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106 Irrigation schedule for drip system in 2006 Continued. Date Activity Stage Gallons Duration comments Initial final (min) 16 Apr Fertigation 3 20133 16 min each period 17 Apr Fertigation 3 20133 Applic K to control (1.76 lb) 17 Apr Irrigation 3 17 Apr F ertigation 3 20790 18 Apr Fertigation 3 20790 60 morning 18 Apr Fertigation 3 22084 50 Afternoon 19 Apr Fertigation 3 22084 22370 50 Morning 19 Apr Fertigation 3 22370 22674 50 Afternoon 20 Apr Fertigation 3 22674 23156 100 20 Apr Irrigati on 3 23156 23460 50 Additional applic (3:30pm) 21 Apr Fertigation 3 23460 23774 50 21 Apr Fertigation 3 23774 22 Apr Fertigation 3 25194 23 Apr Fertigation 3 25194 25765 24 Apr Fertigation 3 25765 25 Apr Fertigation 3 30873 26 Apr Fertigation 3 30873 34200 3 May Fertigation 3 34200 55583 Additional applic at 4:00 am 3 May Fertigation 3 55583 55770 3 May Fertigation 3 55770 9 May Fertigation 3 78396 15 May Fertigation 3 17 May Fertigati on 4 102732 18 May Irrigation 4 102732 16 Jun Irrigation 4 149731

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107 Table C 2. Irrigation schedule for drip system in 2007 Date Activity Stage Gallons Duration comments Initial final (min) 30 Mar Irrigation 2 153721 153967 30 31 Mar Irrigation 2 Weekend 1 Apr Irrigation 2 Weekend 2 Apr Fertigation 2 154456 158042 95 Calibrated injectors 3 Apr Irrigation 2 30 4 Apr Fertigation 2 158835 161489 60 Calibrated injectors 5 Apr Fertigation 2 6 Apr Ferti gation 2 162545 165671 60 7 Apr Fertigation 2 Weekend 8 Apr Fertigation 2 Weekend 9 Apr Fertigation 2 166882 167438 10 Apr Fertigation 2 11 Apr Fertigation 2 168042 168796 30 12 Apr Fertigation 2 13 Apr Fertigatio n 2 170175 14 Apr Fertigation 2 Weekend 15 Apr Fertigation 2 Weekend 16 Apr Fertigation 2 60 17 Apr Fertigation 2 18 Apr Fertigation 2 60 19 Apr Fertigation 2 20 Apr Fertigation 2 21 Apr Fertiga tion 2 Weekend 22 Apr Fertigation 2 Weekend 23 Apr Fertigation 2 178409 24 Apr Fertigation 2 25 Apr Fertigation 2 90 26 Apr Fertigation 2 2 May Fertigation 3 188721 240 11 May Irrigation 3 214264 15 May Irrigation 3 224702 17 May Irrigation 3 231057 300 21 May Irrigation 4 258934 4 Jun Irrigation 4 303423

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108 Table C 3 Irrigation schedule for drip system in 200 8 Date Activity Stage Gallons Duration comments Initial final (min) 1 Apr Irrigation 2 329258 2 Apr Irrigation 2 3 Apr Irrigation 2 4 Apr Irrigation 2 330758 5 Apr Irrigation 2 weekend 6 Apr Irrigation 2 weekend 7 Apr Irrigation 2 8 Apr Irrigation 2 332725 Injection of N 9 Apr Irrigation 2 10 Apr Irrigation 2 60 11 Apr Irrigation 2 12 Apr Irrigation 2 weekend 13 Apr Irrigation 2 weekend 14 Apr Irrigation 2 15 Apr Irrigation 2 339500 340837 Injection of N 16 Apr Irrigation 2 340837 342237 17 Apr Irrigation 3 342242 120 18 Apr Irrigation 3 19 Apr Irrigation 3 weekend 20 Apr Irrigation 3 weekend 21 Apr Irrigation 3 22 Apr Irrigation 3 346394 348320 Injection of N 23 A pr Irrigation 3 24 Apr Irrigation 3 354838 25 Apr Irrigation 3 26 Apr Irrigation 3 weekend 27 Apr Irrigation 3 weekend 28 Apr Irrigation 3 29 Apr Irrigation 3 378678 383159 Injection of N 30 Apr Irrigation 3 1 May Irrigation 3 387723 2 May Irrigation 3 3 May Irrigation 3 weekend 4 May Irrigation 3 weekend 5 May Irrigation 3 6 May Irrigation 3 414557 Injection of N

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109 Irrigation schedule for drip system in 2 008. continued. Date Activity Stage Gallons Duration comments Initial final (min) 7 May Irrigation 3 8 May Irrigation 3 423438 9 May Irrigation 3 10 May Irrigation 3 weekend 11 May Irrigation 3 weekend 12 May Ir rigation 3 13 May Irrigation 3 436400 437886 Injection of N 14 May Irrigation 3 15 May Irrigation 3 446415 16 May Irrigation 4 17 May Irrigation 4 weekend 18 May Irrigation 4 weekend 19 May Irrigation 4 20 May Irrigation 4 459034 Injection of N 5 Jun Irrigation 4 490299 10 Jun Irrigation 4 494847

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1 10 APPENDIX D FLOW METER RECORD FO R SEEPAGE IRRIGATION Table D. The record of the flow meter under TSI in 2008 Date Flow meter Initial record time Volumes (gal) Final record time Volumes (gal) 15 Apr 10:00 AM 433 2:00 PM 1271 16 Apr 17 Apr 9:30 AM 10560 1:00 PM 11238 18 Apr 19 Apr 20 Apr 21 Apr 22 Apr 11:00 AM 37006 2:30 PM 37748 23 Apr 24 Apr 8:45 AM 46654 1:00 PM 47361 25 Apr 26 Apr 27 Apr 28 Apr 29 Apr 9:00 AM 69372 12:30 PM 70107 30 Apr 1 May 9:15 AM 79756 12:30 PM 80583 2 May 3 May 4 May 5 May 6 May 10:00 AM 107282 1:00 PM 107923 7 May 8 May 10:00 AM 118113 12:30 PM 118681 9 May 10 May 11 May 12 May 13 May 11:00 AM 143003 1:00 PM 143431 14 May 15 May 10:00 AM 152831 1:30 PM 153535 16 May 20 May 10:00 AM 177293 1:00 PM 177885 22 May 10:30 AM 187427 10 Jun 10:00 AM 227712

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111 LIST OF REFERENCES Allen, R.G., L. S. Pereira, D. Raes, and M. Smith. 1998. Crop Evapotranspiration: Guidelines for Computing Crop Water Requirements. FAO Irrigation and Drainage Paper No. 56. Rome. Alva, A.K., T. Hodges, R.A. Boydston, and H.P. Collins. 2002. Effects of Irrigation and Tillage Practices on Yield of Potato Under High Production Conditions in the Pacific Northwest. Commun. Soil Sci. Plan t Anal. 33(9&10): 1451 1460. Bundy, L.G., R.P. Wolkowski, and Weis, G.G. 1986. Nitrogen Source Evaluation For Potato Production on Irri gated Sandy Soils. Am. Potato J. 63: 385 397. Campbell, K.L., J.S. Rogers, and D.R. Hensel. 1978. Water Table Contr ol for Potatoes in Florida. Transactions of the ASAE. 21: 701 705. Cockx, Eve Marie and E.H. Simonne. 2003. Reduction of the Impact of Fertilization and Irrigation on Processes in the Nitrogen Cycle in Vegetable Fields with BMPs. EDIS, Fla. Coop. Ext. Ser v. HS948. Cox, D., and T.M. Addiscott. 1976. Sulphur C oated U rea as a F ertilizer for P otatoes. J. Sci. Food Agri. 27: 1015 1020. Elkashif, M.E., and S.J. Locascio. 1983. Isobutylidene and Sulfur Coated Urea as N Sources for Potatoes. J. Am. Soc. Hort. Sci. 108(4): 523 526. Errebhi, M., C. J. Rosen, S.C. Gupta, and D. E. Birong. 1998. Potato Yield Response and Nitrate Leaching as Influenced by Nitrogen Management. Agron. J. 90: 10 15. Faberio C., F. Martin de Santa Olalla, and J.A. de Juan. 2001. Yield and Size of Deficit Irrigated Potatoes. Agri. Water Management. 48: 255 266 Feibert E.B. C.C. Shock, and L.D. Saunders. 1998. Nitrogen Ferti lizer Requirements of Potatoes U sing Carefully Scheduled Sprinkler Irrigation. Hort Sci. 33(2):262 265 Hang, A .N., and D.E. Miller. 1986. Yield and Physiological Responses of Potatoes to Deficit, High Frequency Sprinkler Irrigation. Agron. J. 78:436 440 Harris, P.M. 1978. Mineral Nutrition. In the Potato Crop: the Scientific Basis for Improvement, ed. P.M. Harri s, 195 243. New York: Chapman & Hall. Havlin, J.L., J.D. Beaton, S.L. Tisdale, and W.L. Nelson. 1999. Soil Fertility and Fertilizers: An Introduction to Nutrient Management, 6 th edition. Englewood Cliffs, NJ. Prentice Hall. Hochmuth, G. and K. Cordasco. 2008. A Summary of N, P and K Research on Potato in Florida. EDIS, Fla. Coop. Ext. Serv. HS756.

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112 Hutchinson, C., E. Simonne, P. Solano, J. Meldrum, and P. Livingston Way. 2003. Testing of Controlled R elease Fertilizer Programs for Seep Irrigated Irish Potat o Production. J. Plnt. Nutr. 26(9):1709 1723. Hutchinson C.M., E.H. Simonne, W.M. Stall, S.M. Olson, S.E. Webb, T.G. Taylor, S.A. Smith, and P.D. Roberts. 2009. Potato Production in Florida. EDIS, Fla. Coop. Ext. Serv. HS733. Jensen, M.E. 1981. Summary a nd Challenges in Irrigation Scheduling for Water and 231. Joern, B.C. and M.L. Vitosh. 1995. Influence of Applied Nitrogen on Potato Part I: Yield, Quality, and Nitrogen Uptake. Am. Potato J. 72: 51 63. Kidder, G., G. Hochmuth, D.R. Hensel, E.A.Hanlon, W.A.Tilton, J.D. Dilbeck, and D.E. Schrader. 1992. Horticulturally and Environmentally Sound Fertilization of Hastings Area Potatoes. EDIS, Fla. Coop. Ext. Serv. Brochure. Leigel, E.A., and L.M Walsh. 1976. Evaluation of Sulfur Coated Urea (SCU) Applied to Irrigated Potatoes and Corn. Agron J. 68: 457 463. Lorenz, O.A., B.L. Weir, and J.C. Bishop. 1974. Effect of Sources of Nitrogen on Yield and Nitrogen Absorption of Potatoes. Am. Potato J. 51: 56 65. Meyer, R. D. and D.B. Marcum. 1998. Potato Yield, Petiole Nitrogen, and Soil Nitrogen Response to Water and Nitrogen. Agron. J. 90: 420 429 Munoz Arboleda, F R.S. Mylavarapu, C.M. Hutchinson, and K. M. Portier. 2006. Root Distribution under Seepage I rrigated Potatoes in Northeast Florida. Am. J. Potato Res. 83: 463 472. Munoz Arboleda, F., R. Mylavarapu, and K. Portier. 2008. Nitrate Nitrogen Concentrations in the Perched Ground Water under Seepage Irrigated Potato Cropping Systems. J. Env iron. Qual. 37:387 394 Munoz Arboleda, F. and C.M. Hutchinson. 2006. Soil Moisture in the Potato Root Zone under Seepage Irrigation. Proc. Fla. State Hort. Soc. 119: 218 220. Mylavarapu, R.S. 2008. UF/IFAS Extension Soil Testing Laboratory. Analytical Procedures and Training Manual. EDIS, Fla. Coop. Ext. Serv. Circ. 1248. Univ. of Florida, IFAS, Gainesville, FL. Pack, J.E., C.M. Hutchinson, and E.H. Simonne. 2006. Evaluation of Controlled R elease Fertilizers for Northeast Florida Chip Potato Production J. Plnt. Nutr. 29:1301 1313.

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113 Paramasivam, S., and A.K. Alva. 1997. Nitrogen Recovery form Controlled R elease Fertilizers under Intermittent Leaching and Dry Cycles. Soil science. 162: 447 453. SAS institute Inc. NC, USA. The SAS S ystem for W indows. Rel ease 9.2 2002 2008. Sammis, T.W. 1980.Comparison of Sprinkler, Trickle, Subsurface, and Furrow Irrigation Methods for Row Crops. Agron. J. 72: 701 104. Shae, J.B., D.D. Steele, and B.L. Gregor. 1999. Irrigation Scheduling Methods for Potatoes in the Nort hern Great Plains. Am. Soc. Agri. Engineers. 42(2): 351 360 Sharma, G.C. 1979. Controlled R elease Fertilizers and Horticultural Applications. Scientia Hort. 11:107 129. Shock, C.C., E.B.G.Feibert, and L.D. Saunders. 1998. Potato Yield Quality Response t o Deficit Irrigation. Hort Sci. 33(4): 655 659 Shock, C.C., E.B.G.Feibert, and L.D. Saunders. 2003. 'Umatilla Russet' and 'Russet Legend' Potato Yield and Quality Respones to Irrigation. Hort Sci. 38(6):1117 1121. Shock, C.C., A.B. Pereira, and E.P. Eld redge. 2007. Irrigation Best Management Practices f or Potato. Am J. Potato Res. 84:29 37 Simonne E., N. Ouakrim, and A. Caylor. 2002 Evaluation of a Irrigation Scheduling Model for Drip irrigated Potato in Southeastern United States. Hort Sci. 37(1):104 107. Simonne, E.H., M.D. Dukes, and D.Z. Haman. 2006. Principles and Practices of Irrigation Management for Vegetables. EDIS, Fla. Coop. Ext. Serv. AE206. Singleton, V.D. Investigation of Potato Water Use in the Tri County Area of Putnam, St. Johns, and Flagler Counties, Florida. 1990. Technical Publication SJ 90 13. St. Johns River Water Management District Palatka, Florida. Smajstrla, A.G., S.J. Locascio, and D.R. Hensel. 1995. Subsurface Drip Irrigation of Potatoes. Proc. Fla. State Hort. Soc. 108:1 93 195. Smajstrla, A.G., B.J. Boman, G.A. Clark, D.Z. Haman, D.S. Harrison, F.T. Izuno, D.J. Pitts, and F.S. Zazueta. 1991. Efficiencies of Florida Agricultural Irrigation Systems. Fla. Coop. Ext. Serv. Bul.247. Smajstrla, A.G., S.J. Locascio, D.P. Weing artner, and D.R. Hensel. 2000. Subsurface Drip Irrigation for Water Table Control. Am. Sci. Agri. Engineers. 16(3):225 229.

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114 Smajstrla, A. G., B.J. Boman, D.Z. Haman, F.T. Izuno, D.J. Pitts and F.S. Zazueta. 1997. Basic Irrigation Scheduling in Florida. EDI S, Fla. Coop. Ext. Serv. BUL249. Stieber, T., and C.C. Shock. 1995. Placement of Soil Moisture Sensors in Sprinkler irrigated Potatoes. Am. Potato J. 72: 533 543. USDA. 1978. United States Standards for Grades of Potatoes for Chipping. United States Depa rtment of Agriculture, Agricultural Marketing Servic e, Fruit and Vegetable Division. Washington, D. C. USDA. 1983. Soil Survey of St. Johns County. Florida Soil Conservation Service, Washington, D. C. Waddell, J., S.C. Gupta, J.F. Moncrief, C.J. Rosen, and D. Steele. 1999. Irrigation and Nitrogen Management Effects on Potato Yield, Tuber Quality, and Nitrogen Uptake. Agron. J. 91: 991 997. Wang, F.L. and A.K. Alva. 1996. Leaching of Nitrogen from Slow Release Urea Sources in Sandy Soils. Soil. Sci Soc. Am. J. 60: 1454 1458 Wilson, M.L., C.J. Rosen, and J.F. Moncrief. 2009. Potato Response to a Polymer C oated Urea on an Irrigated, Coarse textured Soil. Agron. J. 101: 897 905. Zvomuya, F., and C.J. Rosen. 2001. Evaluation of Polyolefin C oated Ur ea for Potato Production on a Sandy Soil. HortScience 36: 1057 1060. Zvomuya, F., C.J. Rosen, M.P. Russelle, and S.C. Gupta. 2003. Nitrate Leaching and Nitrogen Recovery Following Application of Polyolefin Coated Urea to Potato. J Environ. Qual. 32: 480 489.

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115 BIOGRAPHICAL SKETCH Yandi Fan was born in Zhongwei City, Ningxia, China in 1983. She graduated from China Agricultural University with a Bachelor of Science degree in soil science and plant nutrient management in 2004. After two years of graduate stud y in the China Agricultural University on agricultural ecology, she came to the University of Florida to pursue a Doctor of Philosophy degree in soil and water science in August 2006