<%BANNER%>

Controlled-Release Nitrogen Fertilizer Release Characterization and Its Effects on Potato (Solanum tuberosum) Production...

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CONTROLLED-RELEAS E NITROGEN FERTILIZER RELEASE CHARACTERIZATION AND ITS EFFECTS ON POTATO ( Solanum tuberosum ) PRODUCTION AND SOIL NITROGEN MOVEMENT IN NORTHEAST FLORIDA By JEFFERY EARL PACK A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2004

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Copyright 2004 by Jeffery Earl Pack

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This thesis is dedicated to my loving wife Jerami, and three daughters, Sarah, Rachel, and Elisabeth, for following me wherever I needed to go.

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iv ACKNOWLEDGMENTS I thank my advisor, Dr. Chad Hutchinson, for his mentor-like spirit. He provides guidance y et al lows me room to teach myself. I thank my other committee members Dr. George Hochmuth, Dr. Rao Mylavarapu, Dr. Johan Scholberg, and Dr. Michael Dukes for their support of this work. I thank my sweetheart, Jerami, for her patience and unwavering support and ennobling confidence as well as my children, Sarah, Rachel, and Elisabeth, and those yet unborn, for trusting and simple love. We can only get through this together. Finally, I thank our Father for agency to choose, opportunities to grow, truth to guide us home, and a veil of forgetfuln ess to allow it to come from within.

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v TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES.............................................................................................................ix LIST OF FIGURES.........................................................................................................xiii ABSTRACT....................................................................................................................... xv CHAPTER 1 INTRODUCTION........................................................................................................1 2 LITERATURE REVIEW.............................................................................................2 Best Management Practices..........................................................................................3 Florida BMPs................................................................................................................4 Nutrient Use Efficiency................................................................................................6 Potato Growth Stages...................................................................................................7 Growth Stage I.......................................................................................................7 Growth Stage II.....................................................................................................8 Growth Stage III....................................................................................................8 Growth Stage IV....................................................................................................9 Growth Stage V.....................................................................................................9 Cultural Practice Influences on N Fertilization Efficacy............................................10 N Application Timing..........................................................................................10 Irrigation Management........................................................................................11 N Source..............................................................................................................11 N Placement.........................................................................................................12 CRF Products..............................................................................................................12 Sulfur-Coated Urea..............................................................................................13 Isobutylidene Diurea and N itrification Inhibitors...............................................14 Polymer-Coated Urea..........................................................................................15 PCU Release........................................................................................................16 Summary and Research Objectives............................................................................17 3 MATERIALS AND METHODS...............................................................................19 CRF Release from the Incubato r and Meshbag Experiments.....................................19

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vi Incubator Experiment..........................................................................................19 CRF fertilizer products.................................................................................20 Incubators.....................................................................................................20 Duration........................................................................................................21 Setup and procedure.....................................................................................21 Sample analysis............................................................................................22 Statistical design and analysis......................................................................22 Meshbag Experiment...........................................................................................23 CRF fertilizer treatments..............................................................................23 Setup and procedure.....................................................................................23 Sample analysis............................................................................................24 Statistical analysis........................................................................................24 Field Production..........................................................................................................24 General Production..............................................................................................25 Soils..............................................................................................................25 Irrigation.......................................................................................................25 Planting.........................................................................................................25 Fertilizer treatments......................................................................................26 Seasonal management..................................................................................26 Soil analysis..................................................................................................27 Tissue Sampling and Analysis.............................................................................27 Nitrogen Recovery Efficiency.............................................................................28 Harvest.................................................................................................................28 Statistical Analysis..............................................................................................29 Nitrogen Leaching Experiment...................................................................................30 Lysimeters...........................................................................................................30 Wells....................................................................................................................31 Statistical Analysis..............................................................................................31 4 RELEASE CHARACTERISTICS OF CONTROLLED-RE LEASE NITROGEN FERTILIZERS UNDER CONSTANT TEMPERATURE AND FIELD CONDITIONS............................................................................................................32 Incubator Experiment Results.....................................................................................33 Incubator Experiment Weekly and Cumulative N Release.................................33 Ammonium Nitrate..............................................................................................35 Urea.....................................................................................................................35 CRF1....................................................................................................................38 CRF2a..................................................................................................................38 CRF2b..................................................................................................................41 CRF3....................................................................................................................41 CRF4....................................................................................................................44 CRF5....................................................................................................................44 CRF6....................................................................................................................47 No N Control.......................................................................................................49 Variable Temperature Incubator Release............................................................49 Q10........................................................................................................................51

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vii Residual Fertilizer...............................................................................................53 Total N Recovery................................................................................................56 Meshbag Experiment..................................................................................................56 Meshbag Experiment Results..............................................................................59 CRF Release Discussion.............................................................................................62 Incubator CRF Release and Mes hbag Experiment Correlation..........................62 Fertilizer Release Characteristics........................................................................64 AN and urea.................................................................................................64 CRF1............................................................................................................65 CRF2a...........................................................................................................66 CRF2b..........................................................................................................66 CRF3............................................................................................................67 CRF4............................................................................................................68 CRF5............................................................................................................68 CRF6............................................................................................................69 Nitrification and denitrification....................................................................70 Plant uptake requirements............................................................................70 Methodology improvement..........................................................................71 Summary......................................................................................................72 5 COMPARISON OF CONTROLLED-RELEA SE NITROGEN FERTILIZERS TO AMMONIUM NITRATE ON POTATO PRODUCTION ........................................74 CRF Production Experiment.......................................................................................74 Total and Marketable Yields...............................................................................75 Specific Gravity...................................................................................................77 Tuber Quality.......................................................................................................79 Stand Establishment............................................................................................81 Plant tissue...........................................................................................................83 Plant Biomass......................................................................................................86 Tuber Nitrogen Uptake and Recovery Efficiency (NRE)...................................87 Replacement Experiment............................................................................................88 Total and Marketable Yields...............................................................................90 Specific Gravity...................................................................................................92 Tuber Quality.......................................................................................................94 Stand Establishment............................................................................................94 Tissue Analysis....................................................................................................95 Plant Biomass......................................................................................................95 Tuber Nitrogen Recovery Efficiency..................................................................95 CRF Production Studies Discussion...........................................................................97 CRF Production Experiment...............................................................................97 Ammonium nitrate.......................................................................................97 CRF..............................................................................................................98 Fertilizer rate..............................................................................................100 Replacement Experiment...................................................................................101 Summary............................................................................................................101

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viii 6 NITROGEN MOVEMENT IN A SU B-SURFACE IRRIGATED POTATO PRODUCTION SYSTEM UTILIZING CONVENTIONAL AND CONTROLLEDRELEASE NITROGEN SOURCES........................................................................104 Precipitation and Temperature..................................................................................104 Precipitation.......................................................................................................104 Temperature.......................................................................................................105 Soil Nitrogen.............................................................................................................107 Pre-plant Soil Nitrogen......................................................................................107 Seasonal Soil Nitrogen......................................................................................107 Well Water Nitrogen.................................................................................................113 Seasonal Well Nitrogen.....................................................................................113 Periodic Well Nitrogen......................................................................................116 Lysimeter Nitrogen...................................................................................................121 Nutrient Movement Discussion................................................................................122 7 CONCLUSIONS......................................................................................................124 Incubator and Meshbag Experiments.......................................................................125 Incubator Experiment........................................................................................125 Meshbag Experiment.........................................................................................126 CRF Production and Replacement Experiments......................................................126 CRF Production Experiment.............................................................................126 Replacement Experiment...................................................................................127 Leaching Experiment................................................................................................127 Lessons for Future Work..........................................................................................128 Summary...................................................................................................................129 LIST OF REFERENCES.................................................................................................131 BIOGRAPHICAL SKETCH...........................................................................................136

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ix LIST OF TABLES Table page 3-1 Characteristics of fer tilizer products evaluated in the various CRF release, production, and leaching experiments......................................................................20 3-2 Incubator 7 temperature settings used for the incubator experiment.......................21 4-1 Incubator temperatures dur ing the incubator experiment.........................................34 4-2 ANOVA table for CRF incubator release by sampling date, temperature setting and fertilizer product main effects...........................................................................35 4-3 N release from ammonium nitrate at va rious incubator settin gs for each sampling date........................................................................................................................... 36 4-4 N release from urea at various incu bator settings for each sampling date...............37 4-5 N release from CRF1 at various inc ubator settings for each sampling date............39 4-6 N release from CRF2a at various incubator settings for each sampling date..........40 4-7 N release from CRF2b at various incubator settings for each sampling date..........42 4-8 N release from CRF3 at various inc ubator settings for each sampling date............43 4-9 N release from CRF4 at various inc ubator settings for each sampling date............45 4-10 N release from CRF5 at various inc ubator settings for each sampling date............46 4-11 N release from CRF6 at various inc ubator settings for each sampling date............48 4-12 N release from fertilizer products in th e variable temperature incubator for each sampling date............................................................................................................50 4-13 ANOVA table for residual N by incubato r temperature and fertilizer product main effects..............................................................................................................53 4-14 Residual N recovery (% of applied) from CRF products after 13 weeks of release for each incubator.........................................................................................54

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x 4-15 Residual N recover (% of applied) from CRF products after 13 weeks of release at each temperature setting...........................................................................54 4-16 Total N recovery (% of applied) fr om fertilizer treatments from solution and residual sources for each temperature setting...........................................................57 4-17 ANOVA table for released N (% of applie d) by fertilizer treatment and sampling date main effects.......................................................................................................60 4-18 Cumulative N release (%) from CRF pr oducts at each sampling date for each fertilizer....................................................................................................................6 1 5-1 ANOVA table for total yields by fe rtilizer and rate main effects............................75 5-2 ANOVA table for marketable yield by fertilizer rate and main effects...................75 5-3 Total and marketable yield simple effects................................................................76 5-4 ANOVA table for specific gravity by rate and fertilizer source main effects..........78 5-5 Potato tuber specific gravity by simple effects........................................................78 5-6 Potato tuber quality by fert ilizer source main effect................................................80 5-7 Potato tuber quality by rate main effect...................................................................80 5-8 Potato tuber quality by treatment.............................................................................81 5-9 Potato stand establishment for the CRF production experiment..............................82 5-10 ANOVA table for most recently matured leaf TKN by rate and fertilizer product main effects..............................................................................................................83 5-11 Most recently mature leaf percent TKN of potato plants by fertilizer source main effect at 36 and 64 DAP...........................................................................................84 5-12 Most recently mature leaf percent TKN of potato plants by rate main effect at 36 and 64 DAP..............................................................................................................84 5-13 Most recently mature leaf tissue percen t TKN of potato plants by fertilizer and rate simple effects.....................................................................................................85 5-14 Plant biomass and tissue nitrogen at full flower (61 DAP) by fertilizer source main effect................................................................................................................86 5-15 Plant biomass and tissue nitrogen at fu ll flower (61 DAP) by rate main effect.......86 5-16 ANOVA table for N recovery (kg ha-1 N) by fertilizer pr oduct and rate main effects.......................................................................................................................8 8

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xi 5-17 ANOVA table for NRE by fertilizer product and rate main effects.........................88 5-18 Tuber nitrogen uptake and nutrient recovery efficiency by treatment.....................89 5-19 Total and marketable yields of 'Atlantic' and 'Red LaSoda' potatoes by CRF4 blend.........................................................................................................................9 1 5-20 Total and marketable yields of 'Atlantic' and 'Red LaSoda' potatoes by CRF6 blend.........................................................................................................................9 1 5-21 Atlantic and Red LaSoda tuber specific gravity by CRF4 blend........................93 5-22 'Atlantic' and 'Red LaSoda' tube r specific gravity by CRF6 blend..........................93 5-23 Plant stand establishment data in the replacement experiment................................94 5-24 Plant biomass and tissue nitrogen by CRF4 blend...................................................95 5-25 Plant biomass and tissue nitrogen by CRF6 blend...................................................96 5-26 Tuber nitrogen uptake and nutrient recovery efficiency by CRF4 blend.................96 5-27 Tuber nitrogen uptake and nutrient recovery efficiency by CRF6 blend.................96 6-1 ANOVA table for soil NH4-N over all sampling dates..........................................108 6-2 ANOVA table for soil NO3-N over all sampling dates..........................................108 6-3 Soil NH4-N by fertilizer source main effect over all N rates and sampling dates..108 6-4 Soil NO3-N simple effects by fertilizer source and rate over all sampling dates...109 6-5 Soil NO3-N by fertilizer source main effect for each sampling date......................110 6-6 Soil NH4-N by fertilizer source main effect for each sampling date......................111 6-7 Soil NO3-N by treatment for each sampling date...................................................112 6-8 Soil NH4-N by rate main effect for each sampling date.........................................114 6-9 Soil NO3-N by rate main effect for each sampling date.........................................115 6-10 ANOVA table for well NO3-N over all sampling dates.........................................115 6-11 ANOVA table for well NH4-N over all sampling dates.........................................115 6-12 NH4-N and NO3-N concentrations in wells by treatment.......................................116 6-13 Well NH4-N fertilizer source main eff ects at each sampling date.........................118

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xii 6-14 Well NO3-N fertilizer source main eff ects at each sampling date.........................119 6-15 NO3-N concentrations in wells for each sampling date.........................................120 6-16 Well NH4-N rate main effect at each sampling date..............................................121 6.17 Well NO3-N rate main effect at each sampling date..............................................121

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xiii LIST OF FIGURES Figure page 4-1 Release profile of ammonium nitrate at each incubator setting over the duration of the CRF release experiment.................................................................................36 4-2 Release profile of urea at each incuba tor setting over the duration of the incubator experiment................................................................................................37 4-3 Release profile of CRF1 at each incu bator setting over the duration of the incubator experiment................................................................................................39 4-4 Release profile of CRF2a at each in cubator setting over the duration of the incubator experiment................................................................................................40 4-5 Release profile of CRF2b at each inc ubator setting over the duration of the incubator experiment................................................................................................42 4-6 Release profile of CRF3 at each incu bator setting over the duration of the incubator experiment................................................................................................43 4-7 Release profile of CRF4 at each incu bator setting over the duration of the incubator experiment................................................................................................45 4-8 Release profile of CRF5 at each incu bator setting over the duration of the incubator experiment................................................................................................46 4-9 Release profile of CRF6 at each incu bator setting over the duration of the incubator experiment................................................................................................48 4-10 N found in the no fertilizer control wi thin each incubator for various sampling dates.......................................................................................................................... 49 4-11 Release profile of fertilizer product at the variable incubator setting over the duration of the CRF release experiment...................................................................51 4-12 Q10 values for various CRF products.......................................................................52 4-13 Residual TKN (% of applied) for various CRF products as affected by temperature...............................................................................................................56 4-14 Total N recovery from dissolution and re sidual analysis across all temperatures...58

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xiv 4-15 Graphical breakdown of th e total recovery of fertilizer treatments at various temperatures.............................................................................................................58 4-16 Cumulative N release (% of applied) fr om CRF products at each sampling date....61 4-17 Cumulative N release (% of applied) of each fertilizer product as a function of growing degree days with 5C base temperature.....................................................62 4-18 Comparison of release rates of CRF products between the CRF release experiment and the meshbag experiment on a degree day basis, base temperature of 5C.......................................................................................................................63 5-1 Total and marketable tuber yields by treatment.......................................................77 5-2 Potato tuber specific gravity by treatment................................................................79 5-3 Total and marketable potato tube r yields by AN:CRF ratio by variety...................92 5-4 Atlantic and Red LaS oda tuber specific gravity by fertilizer treatment.............93 6-1 2003 daily precipitation in Hasti ngs, FL from 13 Feb to 28 May..........................105 6-2 2003 and historical air and soil temperat ures in Hastings, FL over the potato growing season.......................................................................................................106 6-3 Nitrogen in wells by treatm ent over all sa mpling dates.........................................117 6-4 Well NH4-N concentrations from each ferti lizer product for each sampling date over the growing season.........................................................................................118 6-5 Well NO3-N concentrations from each ferti lizer product for each sampling date over the growing season.........................................................................................119

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xv Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science CONTROLLED-RELEAS E NITROGEN FERTILIZER RELEASE CHARACTERIZATION AND ITS EFFECTS ON POTATO ( Solanum tuberosum ) PRODUCTION AND SOIL NITROGEN MOVEMENT IN NORTHEAST FLORIDA By Jeffery Earl Pack December 2004 Chair: Chad M. Hutchinson Major Department: Horticultural Science The Tri-County Agricultural Area of nor theast Florida is home to nearly 8,000 ha of potato ( Solanum tuberosum L.) production, valued at approximately $64M annually. The combination of sandy soils, perched water tables, and unpredictable rainfall together with nitrogen fertilizer app lications as high as 390 kg ha-1 N increases the potential for nutrient loading into lo cal watersheds, including the St. Johns River. As mandated by the 1987 Florida SWIM Act, the St. Johns River Water Management District directs the development of agricultural best management practices (BMP) for the area. Within the BMP program the potential of c ontrolled-release fertilizers (CRF ) as alternative fertilizers was evaluated. The specific research objectiv es were to 1) characterize nutrient release from CRF under laboratory and field condi tions, 2) determine potato production and nutrient recovery efficiency for soluble ferti lizer and CRF treatments, and 3) estimate soil nutrient levels in the potato bed a nd in the perched water table.

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xvi Seven CRF products (polymer coated ureas ) were compared to ammonium nitrate (AN). Lab and field experiments evaluate d nutrient release bo th at controlled temperature and under field conditions. Fiel d experiments evaluated CRF products at three application rates (112, 168, and 224 kg ha-1 N); 224 kg ha-1 N is the current potato BMP rate, adopted from the University of Fl oridas Institute of Food and Agricultural Sciences Extension Services recommendati on. Two CRF products and AN blends were included to evaluate ideal combinations. Leaching studies evaluated nitrate (NO3-N) and ammonium (NH4-N) movement into nearby wells and lysimeters under field conditions. Results from the nutrient release expe riments revealed that CRF2b, CRF4, CRF5, and CRF6 all exhibited temperature-based, co mplete release over time. While initial release from CRF products was somewhat hi gher under field conditions compared to lab conditions, subsequent sustained release fr om the two experiments was similar. From the field production experiments, CRF fertilized plants produced comparable total and marketable potato yields to AN fe rtilized plants. Plants within CRF2 (224 kg ha-1 N) and CRF4 (224 kg ha-1 N) had the highest total and marketable yields and specific gravity (SG) of all treatment s. Applications of 224 kg ha-1 N did not result in yield or SG increases over the 168 kg ha-1 N rate, independent of N source. For percent AN:CRF blends evaluated with two CRF products, no blend was advant ageous for either Atlantic or Red LaSoda potato production. NO3-N and NH4-N movement into the perched wa ter table was significantly lower with CRF than with AN treatments, particularly early in the season. Potatoes fertilized with CRF products have similar yields and qua lity to AN fertilized potatoes while soil nitrogen movement into waters heds is significantly reduced.

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1 CHAPTER 1 INTRODUCTION Agricultural associations with Florida usually involve images of orange trees full of fruit. However, Florida produces a wide vari ety of fruit and vegetable crops, not the least of which is potatoes. Florida potatoes ( Solanum tuberosum L.) are grown primarily for the fresh market and chip market, with Atlan tic variety being the most widely grown. In northeast Florida, pota to production approaches 8,000 ha at approximately $64M per year in value. The soils in northeast Florida are sandy w ith a shallow perched water table. In combination with unpredictable rainfall and hi gh fertilizer rates, this increases the potential movement of nutrients into local wa tersheds, thus degrading the environment. Local endeavors under mandate from state a nd federal law have encouraged cultural practices called BMPs or best management practices which aim to allow farmers to maintain high yielding and high-value cr ops while protecting the environment. This research project evaluates the suitability of controlled-release fertilizers (CRF) as an alternative nitrogen (N) fertilizer source to commonly utilized ammonium nitrate (AN) for potato production in northeast Florida. It evaluates the e ffects of CRF products on potato production including tuber yields and quality as well as their effects on nutrient leaching into local watersheds. It further exam ines the release charac teristics of selected CRF products under controlled and field condit ions. Our hypothesis is that appropriate use of CRF products may provide an alternat ive to AN fertilizer sources including equal or improved potato tuber yi elds with less negative im pacts on the environment.

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2 CHAPTER 2 LITERATURE REVIEW Potato ( Solanum tuberosum L.) nitrogen (N) fertiliza tion strategies to improve tuber yield and/or quality have greatly evol ved during the past cen tury. Methods have included additions of organic fertilizer amendments like manures and green manures; the application of N in various soluble forms (e.g., ammonium, nitrate, and urea), alone and in blends; the appl ication of N in slowly sol uble forms (e.g., urea formaldehyde, methylene urea, and isobutylid ene diurea); and the applicatio n of coated soluble N (e.g., sulfur-coated urea, polymer-coated urea). Research has expl ored the timing of application (e.g., pre-plant, at planting, at hilling), placement (e.g., banded, broadcast, surface applied, incorporated, side-dressed), ap plication method (e.g., solid prills, liquid through irrigation lines), rate, and virtually every combination thereof. Research has evaluated the growth characteri stics of the plant and linked this to nitrogen accumulation patternslittle N demand very early, to heavy N demand during vegetative growth and bulking stages, to little N demand during matu ration and senescence. New, N-efficient cultivars have been compared to reliable favorite varieties. Climate (e.g., rainfall, temperature), soil conditions (e.g., texture, stru cture, CEC), and seasons have been linked to fertilizer management. Nitrogen manage ment is increasingly subject to market demands, legal constraints, and economic cons iderations. N fertilization of potatoes has become a highly specialized science, with di fferent applications for any given set of conditions.

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3 However, as society advances, so does the need to adapt to new circumstances, new needs, new laws, new considerations, etc. Increasing concerns over fossil fuel supplies, polluted water supplies, and environmental degradation have forced the agricultural industry to re-evaluate how it manages production inputs. It has been obliged to seek out more environmentally responsible methods of production while striving to remain profitable with an increasingly competitiv e economy and ever more environmentally conscious public. This review will discuss the evolution and implementation of best management practices (BMP) across the United States with sp ecial reference to Florida. It will then outline the basic potato plant growth cy cle and strategies to maximize production efficiency. It will then narrow its focus to potato fertilizer research, particularly with slowor controlled-release fertilizers. Fi nally, it will present the research justification and objective of the current project. Best Management Practices Agricultural best management practices (BMP) are scientifically-based cultural farming practices that should maintain or increase crop yields and/or profits while protecting the environment (Simonne et al ., 2003). One common BMP goal is to reduce the contamination of water bodies by chemical s or other pollutants such as nitrogen. Nitrogen (N), particularly in the form of nitrate (NO3 -), is the most common contaminant in aquifer systems (Freeze and Cherry, 1979). Hallberg (1989) states that agriculture is the largest human-caused source of nitrate and Keeney (1986) s uggests that this is caused by activities associated with crop and anim al production. Burkart and Stoner (2002) report that shallow unconfined a quifers associated with agricultural systems, particularly under irrigation, are the most susceptible wa tersheds to nitrate contamination.

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4 Individual BMPs differ according to sp ecific regional, climatic, geographic, governmental, and growing requirements. Th ough BMPs differ, the following aspects commonly appear in BMP programs: 1) soil or tillage management to reduce runoff and erosion of nutrients and/or nutrient coated soils, 2) irri gation management to reduce runoff, deep percolation, and soil salinization, 3) mulching practices to reduce soil losses and, in the case of some organic mulches, partially or completely replace fertilizer applications, reduce evaporation rates, and e nhance soil water storage, and 4) fertilizer scheduling to apply only the types and quanti ties of nutrients requi red by crops at the right time to produce optimal yields and minimize negative environmental impacts. Florida BMPs In 1987, the Florida legislature, under th e mandate of the Federal Clean Water Quality Act of 1977, passed the Florida Su rface Water Improvement and Management (SWIM) Act (Florida, 2004). The SWIM Ac t created a program that focused on the preservation and/or restorat ion of the state's water bodies through the development and implementation of Best Management Practices (BMPs) (Simonne et al ., 2003). Since its passage, state and local regulatory agencies ha ve worked to improve water bodies in need of restoration thr oughout the state. The St. Johns River watershed in northeas t Florida has been identified as a water body in Florida in need of re storation. Nitrate leaching in to the river has generated concern. The lower St. Johns River basin is encompassed by three counties: St. Johns, Putnam, and Flagler counties. These countie s comprise the Tri-County Agricultural Area (TCAA) and feature predominate agricultural land use. The major crop in the TCAA is potato, and this area produces nearly half of Floridas annual 15,000 hectare crop with a value of $130M (Bronson, 2003). Soils in th e area are generally sandy with low water-

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5 holding capacity. This, together with the shallow root system of potatoes and the possibility of excessive seas onal rains, increases the poten tial for movement of water soluble plant nutrients into th e surrounding watersheds, includ ing the St. Johns River. State and local regulatory agencies in c ooperation with growers in the TCAA have developed a BMP program which has been in place for over three years. The BMP program is the TCAA Water Quality Protecti on Cost Share Program which is managed by the St. Johns River Water Management District (SJRWMD). The TCAA Water Quality Protection Cost Share Program enc ourages growers to adopt environmentally responsible practices by partially offsetting the implementation cost s of those practices (Livingston-Way, 2000). The nitrogen BMP rate for potato produc tion in the TCAA ranges from 224 to 280 kg ha-1 N. This contrasts with growers in the TCAA, who apply an average of 280 kg ha-1 N, ranging from 195 kg ha-1 N on fresh market potato to 390 kg ha-1 N for some chipping potatoes. The base rate of 224 kg ha-1 N was adopted from the University of Floridas Institute of Food and Agricultural Science (IFAS) recommended rate (Hochmuth and Cordasco, 2000; Hochmuth et al. 2003). The IFAS recommended BMPs for potato production also suggest split applicatio n of N fertilizer. Approximately 30% of the total N should be applie d at planting and the remai nder banded 35-40 days after planting. N rates should be based on plant nutrient status analysis. IFAS recommendations also include the installati on and monitoring of water table observation wells, control structures to trap sediment from the field, and conservation crop rotations (Hutchinson et al. 2002).

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6 Nutrient Use Efficiency One possible benefit of BMPs is an impr ovement in production efficiencies. As system efficiency increases, productivity per unit of energy increases while loss and environmental impacts decrease. The efficient use of nutrients is referred to in this thesis as nutrient use efficiency (NUE), and refers to the percentage recovery of an applied nutrient. NUE has different definitions depending on the goals of the research program. Prihar et al. (2000) divided NUE into the followi ng categories: Agronomic NUE is expressed as the amount of yield increase obt ained per unit of fertilizer applied when compared to the yield of an unfertilized cr op. Economic NUE refers to the returns on investment in added nutrients, where the cost of the last unit of fertilizer applied equals the value of the yield increase obtained by that add ition. Apparent nutrient recovery is the amount of nutrient taken up by the cr op and divided by the amount applied as fertilizer, independent of the source from wh ich the nutrient may have been obtained. Actual NUE is similar to apparent NUE in th at it measures the amount of fertilizer taken up by a crop. However, actual NUE differs from apparent NUE in that actual NUE measures the amount of fertiliz er-supplied nutrients that ar e actually taken up by the crop using tracers like depleted 15N or phosphorus-32 (32P) in the fertilizer source (Prihar et al ., 2000). In some cases where the amount of nutrient s available for movement from the site is of interest, the nutrien t recovery efficiency (RE) is calculated (Zvomuya et al. 2003; Westermann et al. 1988). Nutrient RE is defined as the fraction of an applied nutrient that is recovered or removed from the s ite, usually in the form of a product.

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7 Baligar et al. (2001), reviewed several factor s affecting NUE including soil characteristics, fertilizer types and qu antities, plant uptake and use mechanisms, agronomic considerations such as tillage, cr op rotation, and cover cr op usage, biological contributions of mycorrhizal fungi symbiosi s and rhizobial nitrogen fixation, and climate factors. Their review also stressed that highest NUEs (apparent, agronomic, economic, etc.) can only be obtained thr ough the appropriate integration of all of these factors. Potato Growth Stages In order to maximize productivity and NUE, it is useful to review the life cycle of the potato plant. This is because by understand ing the life cycle of the plant, its uptake capacity, peak uptake periods, etc., fertilizer products can be designed to maximize NUE and minimize waste. The life cycle of a potato plant can be di vided into five gene ral growth stages during each of which, the plant will carry on generally different metabolic activities (Rowe, 1993). Once understood, effective prac tices can be implemented which work together with the plant maximizi ng production and uptake efficiency. Growth Stage I Growth stage I is characterized by sprout development. During this stage sprouts form from eyes on seed tubers and grow upward to emerge from the soil. No photosynthesis takes place during this stage as the entire plant is underground and all of the plant nutritional requirements are supplied by the seed tuber. Because the plant has only begun developing functional roots during this stage, l ittle or no nitrogen uptake occurs.

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8 Growth Stage II Growth stage II is characterized by vege tative growth. The plant begins to photosynthesize and products of photosynthesis provide energy to the plant as the seed tuber becomes depleted of both energy and nut rients. Leaves and branch stems develop from aboveground nodes along emerged sprouts a nd roots and stolons develop at belowground nodes. Growth stages I and II are re ported to last from 15 to 30 days (Ojala et al. 1990) to as long as 60 or 70 days (K leinkopf, 1983; Westermann, 1993) depending on planting date, planting depth, soil temperat ure and other environmental factors, the physiological age of the seed tubers, and the characteristics of particular cultivars. Approximately 15% of the total nitrogen uptake by Russet Burbank occurs during stages I and II (Ojala et al. 1990). Nitrogen deficiency during this stage is easily corrected without appreciable yield losses if addressed early. Nutr ient excesses during this stage promote assimilate partitioning to vines, prolonging this vegetative growth stage and delaying tuber in itiation and expansion. Growth Stage III Growth stage III is characterized by tuber initiation and typically lasts from 10 to 14 days (Westermann, 1993; Ojala et al. 1990). During this stage, tubers form at the end of stolons but are not yet en larging. Marketable-sized t ubers at harvest are usually initiated at this time. The end of this st age typically coincides with early flowering. Approximately 30% of the total plant nitrogen uptake occurs by the middle of this stage of growth (Ojala et al. 1990). Nitrogen stress during this stage re duces leaf area and canopy development but may stimulate early tube r initiation; excess nitrogen stimulates vegetative growth and may delay the initiation of stage IV tuber growth for up to ten days (Allen and Scott, 1980; Ojala et al. 1990).

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9 Growth Stage IV Growth stage IV is characterized by tuber bulking (expansion) and lasts from 30 to 60 days (Kleinkopf, 1983) to as high as 120 days (Ojala et al. 1990). During this stage tuber cells expand and become the major si nks for photosynthetic products, water, and nutrients. Much of the tota l nitrogen uptake (58 to 71%) by the crops occurs through early and mid tuber bulk ing, respectively (Ojala et al. 1990), and most of the nutrients used by the plant are taken up during growth stage IV (Westermann, 1993). Westermann et al. (1988) reported that the nitrogen taken up du ring this stage is in itially concentrated in the stems and leaves and later translocated to the tubers. Nitrogen deficiencies during this stage reduce tuber yield a nd size; excesses decrease tube r specific gravity, delay vine senescence, and hamper tuber maturation (Ojala et al. 1990). Growth Stage V Growth stage V is the maturation stage, a nd little additional n itrogen is taken up from the soil. During this stage, representi ng the final 10 to 24 days of growth, mobile nutrients are translocated from vegetative plan t portions into the enlarging tubers [for N, up to 90% or more is translocated to the t ubers (Westermann, 1993)]. Also during this stage, tuber dry weight reaches its highest level, canopy photosynthesis decreases, and above-ground parts senesce and die, and tube r skin matures (Rowe, 1993). Excessive nitrogen during this stage can promote late-season vegetative growth and delay tuber maturity and also result in poor net development of tuber skins, which is a concern for russet-type potato growers (Ojala et al. 1990). Early season cult ivars reach maturity in 90-100 days while late season cultivars may take 150 or mo re days (Kleinkopf, 1983). Atlantic potatoes grown for chip production in Florida mature between 85 and 110 days (Hochmuth et al ., 2003).

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10 Cultural Practice Influences on N Fertilization Efficacy By understanding the life cycle of the potato plant, effec tive fertility management and fertility related cultural practices can be adopted. As stated by Westermann (1993), the goal in managing potato crop nutrition is to promote uniform and continuous growth of plants and tubers throughout all growth stages. Most soils need nitrogen applications to produce maximum yields of potatoes. However, the efficacy of that application may be highly dependent on th e control of other soil and environmental factors. Cultural practices that influen ce uniform, continuous growth are in turn influenced by nitrogen, and include N a pplication timing, irrigation management, N source, and N placement. N Application Timing Westermann and Kleinkopf (1985) showed that on Russet Burbank potatoes, for maximum early tuber growth, the above ground portion of the plant s hould contain 79 to 100 kg ha-1 N at the start of tuber bulking (gro wth stage IV), and that a preplant N fertilizer application between 67 and 134 kg ha-1 would provide adequate N, while excessive preplant N would delay tuber forma tion and result in lower marketable yield (Westermann and Kleinkopf, 1985). Errebhi et al. (1998) reported that as the percentage of total N applied pre-plant increased, total marketable yield decreased while total yields remained the same on Russet Burbank potatoes grown on a sandy loam in Minnesota. They also reported that split applications of N fertilizer reduced nitrate leaching and increased recovery because less ferti lizer was applied preplant. Stark et al (1993) showed that split biweekly N applications pr oduced higher marketable tuber yields than did weekly applications. Depending on potato variety and local conditions, fertilizer applications should be terminated from two or three weeks (Ojala et al. 1990) to four to

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11 six weeks (Westermann, 1993), before the start of maturation (stage V) growth to avoid tuber immaturity at harvest. Irrigation Management Ojala et al. (1990) reported that when growi ng Russet Burbank potatoes with reduced irrigation and seasonal water application rates rang ing from 160 mm (severely water-stressed) to 590 mm (adequate water) were applied, that maximum tuber yields were attained with 247 kg ha-1 N. They also reported that under optimal irrigation, specific gravity was greatest at the lowest N application rate wher eas higher N levels decreased specific gravity. For excessive ir rigation (1.2 and 1.4 times the estimated evapotranspiration rate), Stark et al. (1993) reported no significant plant N uptake effects, or late-season tuber or plant dry weight diffe rences, but did find si gnificant reductions in marketable yields in two seasons, and re duced total yields in one season. N Source Nitrogen source is important for optim al potato growth. Commonly used N fertilizer sources are nitrate, urea, and a mmonium, though plants only take up N as either NO3-N or NH4-N (Westermann, 1993). N applied as urea is converted into NH4-N by the ubiquitous enzyme urease (B enson and Barnette, 1939). This is a rapid process, reaching a rate up to 90% conversion within 4 da ys of application at soil temperatures of 21C (Benson and Barnette, 1939). Francis and Haynes (1991) repor ted similar results with urea transforming to NH4-N within 48 hours under field conditions in New Zealand. Polizotto et al. (1975), testing Red Pontiac and PU 66-142 potatoes in solution cultures found that growth of tops, roots, and t ubers was greatest with N supplied as NO3, intermediate with NH4 + NO3, and least with NH4, for both cultivars. Davis et al. (1986) reported similar findings for Russet Burba nk potatoes. Changing the N source from

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12 NO3 or NH4 + NO3 to NH4 reduced both shoot and root growth while changing the N source from NH4 to NH4 + NO3 improved growth. They concluded that some NO3-N should be available to potatoes for proper growth and development and that when NH4-N was the sole form of N available to the plant, it was detrimental to potato growth, regardless of stage of development (Davis et al. 1986). N Placement Nitrogen placement can influence the N us e efficiency, plant health, and tuber yields in potatoes. In Idaho, Wester mann and Sojka (1996) reported for Russet Burbank potato production, that banding N increased average plant dry weight 6.4%, total tuber yield 9%, and N uptake 28% compared with broadcast N. They reasoned that these results were consistent with predicti ons because potato root s would be unable to exploit a certain percentage of broadcasted N due to spatia l limitations, whereas banded applications would tend to be in a region of th e soil accessible to plan t roots. This would be consistent regardless of irrigation method. Waddell et al. (1999), working with Russet Burbank potato in central Minne sota, reported no significant tuber yield differences except for lower yields with burie d drip irrigation and the control treatment regardless of irrigation a nd N source treatments. CRF Products One approach to potato fertilization that may limit nutrient leaching involves the use of slowor controlled-rel ease fertilizers (CRF). These are products that theoretically reduce nitrogen leaching by limiting the solubility and availability of a fertilizer (e.g., sulfur-coated urea (SCU), isobutylidene diurea (IBDU), pol ymer-coated urea (PCU), others) or by limiting its convers ion to mobile forms (e.g., nitrif ication inhibitors (NI)).

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13 These slowor controlled-release strategies have been used successfully to reduce nitrogen applications in numerous crops. These incl ude Yolo Wonder bell peppers ( Capsicum annuum L.) with IBDU and SCU (Locascio et al., 1981), Jupiter bell peppers with resin-coated-urea/potassium n itrate blends (Csizinszky, 1994), green bell peppers with PCU, SCU, or AN (Guertal, 2000), tomatoes ( Lycopersicon esculentum Mill.) with IBDU or SCU/ammonium nitrate blends (Locascio et al. ,1984), strawberries ( Fragraria x ananassa Weston), with SCU and IBDU (Locascio and Martin, 1985), potted chrysanthemums ( Chrysanthemum x morifolium ) with Osmocote (a PCU) (Hershey and Paul, 1982), and barley ( Hordeum vulgare L.) with PCU and NI (Shoji et al. 2001). These products have been evaluate d for potato production over the years in different parts of the country w ith varying degrees of success. Sulfur-Coated Urea In studies conducted over several years in three locations in California, Lorenz et al. (1972, 1974) showed that ammonium sulfate was generally superior to SCU or ureaformaldehyde (a slowly availabl e N source) for White Rose potatoes, and that while in some cases SCU produced yields equal to am monium sulfate, in no case were yields greater with SCU. In both st udies, the lower yields of CRF treatments were attributed to too-slow release of the fertilizer products. Cox and Addiscott (1976) using SCU on King Edward potatoes in Rothamsted, England, determined that for rates up to 200 kg ha-1 N, potato tuber yi elds were greater for ammonium nitrate than for SCU and at higher rates no significant difference between nitrogen sources was found. They attributed these findings to incomplete or too slow release of SCU over the potato growth period.

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14 Liegel and Walsh (1976) in Hancock, Wisc onsin reported that Russet Burbank potatoes, grown on a loamy sand with SCU, produced higher tuber yields than plants grown with urea or AN. However, this was at tributed to excessive rainfall in May which leached the water soluble fertilizer and reduced yields for the entire year. In central Minnesota, Waddell et al. (1999), growing Russet Burbank potatoes on a sandy loam soil, found that SCU applied at a rate of 224 kg ha-1 N resulted in lower tuber yields than did urea under either drip or sprinkler irriga tion. This was attributed to slow availability of the SCU product. Elkashif et al. (1983) reported similar results in Florida where yields of Atlantic potatoes grown on two sandy soils fertilized w ith SCU or a SCU/ammonium nitrate (AN) blend were lower than treatments with only AN. These results were consistent for rates from 134 to 201 kg ha-1 N and either as preplant or split applications. Maynard and Lorenz (1979), in reviewing the work done on SCU, concluded that N release rates from SCU are too slow to meet the high N dema nd of the potato crop early in the growing season. Isobutylidene Diurea and Nitrification Inhibitors Though evaluated, isobutylidene diurea (IBDU) and nitrificati on inhibitors (NI) have not been adopted for commercial pot ato production. Under potato production in Florida, Elkashif et al (1983) reported lowest total tuber yields and 25% lower marketable yields using IBDU as the N s ource compared to either AN or IBDU/AN blends. NI evaluated in five studies on pot ato in Northeast Florid a gave no tuber yield increases in four of the five tests. As a result, the researchers did not recommend NI for potato production on hyperthermic, irrigated, sandy soils (Martin et al. 1993).

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15 Polymer-Coated Urea One relatively new CRF technology that ha s shown promising preliminary results for potato production and reduced leaching is polymer-coated water soluble fertilizers. Polymer-coated ureas (PCU) are CRFs with a polymer coating. Zvomuya and Rosen (2001), growing Russe t Burbank potatoes on a sandy soil in Minnesota, reported higher marketable yields using PCU applied at planting compared to urea applied at emergence and hilling for a pplication rates ranging from 110 to 290 kg ha1 N. In other research invol ving a three-year study, Zvomuya et al. (2003) reported that at 280 kg ha-1 N, NO3-N leaching was 34 to 49% lower with PCU treatments than three split applications of urea while nitrogen rec overy efficiency (RE) for PCU averaged 50%, 7% higher than urea (43%). To tal and marketable tuber yields with the CRF treatments were between 12 and 19% higher than thr ee applications of urea under leaching or excessive irrigation conditions. This was attributed to a prolonged N release period and reduced leaching of PCU trea tments compared to urea treatments under excessive irrigation conditions. Shoji et al. (2001) demonstrated that PCU could markedly increase the NUE and tuber yields of Centennial ru sset potatoes, reporting that a single basal application of 112 kg ha-1 N PCU at planting produced total tuber yields comparable to traditional fertilizer practices totaling 269 kg ha-1 N in 9 split applications. They also reported that plant nitrogen NUE values of CRF products we re nearly doubled compared to that of urea N. These results were attributed to the ability of CRF products to supply N synchronously with plant requirements. In northeast Florida on Atla ntic potatoes, Hutchinson et al. (2003) reported that at low N rates (112 kg ha-1 N), marketable tuber yields a nd nutrient use efficiency (NUE)

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16 were higher for PCU than AN, though marketable yields were lower than acceptable local levels. At higher rates (168 to 224 kg ha-1 N), tuber yields and NUE were similar. PCU Release One characteristic of PCU that has made it a successful fertilizer is the degree of control of nutrient release. The controlled-r elease is obtained thr ough varying either the thickness or composition of the fertilizer coating. Though the specifics of coating composition are held by individu al manufacturers and are proprietary secrets, the general list of chemicals is similar. Polymer-coating films are typically composed of blends of water permeable and impermeable resins and surfactants (e .g. polyolefin or polyethylene), ethylene vinyl ac etate, and talc occurring as la yered plates (Shoji, 1999). Regulating the composition of the coating gives it a controlled moisture permeability and release rate (Fujita et al ., 1983). Shoji (1999) and Gandeza et al (1991) characterized the release mechanism as following three general steps: 1) Water m oves into the fertilizer granule by osmotic potential, 2) the water soluble fertilizer inside the granule di ssolves, and 3) the nutrient solution diffuses out of the granule due to a ch emical concentration gr adient. The rate of water penetration is proportiona l to the differences in wate r vapor pressures between the inside and outside of the capsule. This gradient potential determines the rate of release of the nutrient (Kochba, 1990). The talc component of the coati ng aids in control over the rate of nutrient diffusion because the talc forms voids in the polymer coating. These voids become larger with increasing talc co ntent, increasing the distance which the water must move through, slowing diffusion (Shoji, 1999) Talc can also be used to adjust the Q10 (the rate increase of a reacti on over a 10 C rise) of release. As the talc content of the coating increases, the Q10 of diffusion decreases (Shoji, 1999 ). Generally, fertilizers are

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17 formulated to maintain a Q10 of around 2, matching typical Q10 values for chemical reactions occurring in plants and microbial activity in many soils (Shoji, 1999). Soil temperature and moisture affect nutri ent release rates. Maeda (1990) studied the contributions of various soil factors aff ecting N release of one particular PCU product and found that temperature accounted for about 83% while moisture content, about 11%. Other soil factors such as mi crobial activity, pH, etc., and th eir interactions accounted for less than 1% each. Having a nutrient release rate that is highly depe ndent on one variable enables good prediction of release. Gandeza et al. (1991) showed that N release from PCU was primarily affected by temperature. In that study, cumulative air temperature (CAT) and cumulative soil temperature (CST) were highly correlated (r2= 0.99) so either could be used for predicting nutrient releas e rates. This is useful because soil temperature data is not always readily available, air temperatur e data can be used instead. Fujita et al. (1983) and Fujita (1989) reported that th e rate of PCU release is affected most by moisture when soil moisture is less than the incipient plant wilting point of the plant (10 kPa). This was addressed by S hoji (1999) who report ed that at any soil moisture content greater than wilting point, th e relative humidity of the soil is 100%. He did report that some observed values from a PCU product were somewhat lower than temperature-predicted values in some co arse-textured upland soils, possibly due to reduced diffusion under exceedingly dry soil conditions. Summary and Research Objectives Polymer-coated CRFs have the potential to revolutionize the way potato crops are being grown. With predictable release rate s, polymer-coated CRFs are very suitable for BMP programs by allowing growers to produce acceptable crop yields while eliminating the need for frequent applic ations of water soluble nutri ents, thus reducing excessive

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18 fertilizer applications and labor costs as we ll as the potential for nutrient movement. As nutrient release rates could be formulated to match crop requirements, nutrients would be available at times and in quantities required by the plant. This woul d result in potential reduction in nutrient losses asso ciated with high intensity rain fall events and thereby also enhance nutrient use efficiency. Release rates of nitrogen from polymer-coate d fertilizers have not been determined for TCAA growing conditions. Neither have the effects of various current commerciallyavailable PCU CRFs on potato production been examined. Once these are established, fertilizer blends can be formulated to ma tch crop uptake requirements, reducing excesses of fertilizer being applied. The objectives of this work were to: 1) determine nutrient release characteristics of various controlled-r elease fertilizers under controlled and field conditions, 2) determine potato production and nutrient recovery efficiency data for soluble and controlled-release fertilizer treatmen ts, and 3) estimate soil nutrient levels in potato beds and underlying perched water tables.

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19 CHAPTER 3 MATERIALS AND METHODS This chapter describes the materials a nd methods of the various experiments conducted. In broad categories, the experiments can be brok en down into three sections, each of which addresses one of the three objectives of this re search project. The three categories are: 1) CRF release through the incubator and meshbag experiments, 2) field production of potatoes in the CRF production an d replacement experiments, and 3) soil nitrogen movement in the leaching experiment utilizing wells and lysimeters. The fertilizer products evaluated through all of the experiments performed are shown in Table 3-1. The CRF products utilized for these experiments were labeled CRF1 through CRF6 with CRF2 being broken into CRF2a and CRF2b. CRF2 was sub-divided because in the production experiment, CRF2 was a blend of two fertilizer products, CRF2a, and CRF2b. AN and urea were provide d by Gator Fertilizer (Hastings, FL), CRF1, CRF2a, and CRF2b were provided by Sc otts Chemical Company (Marysville, OH), and CRF5 and CRF6 were provided by Pu rsell Technologies, Inc. (Sylacauga, AL). The University of Florida has signed a s ecrecy agreement with the manufacturers of CRF3 and CRF4. CRF Release from the Incubator and Meshbag Experiments Incubator Experiment The goal of the incubator experiment was to evaluate the release characteristics of selected CRF products under aqueous conditions at controlled temperatures over a 13

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20 Table 3-1. Characteristics of fertilizer products evaluated in the various CRF release, production, and leaching experiments. Fertilizer Formulation Manufacturer N Form Characteristics AN 30-0-0 Gator Fertilizer 16% NH4, 14% NO3 water soluble Urea 46-0-0 Gator Fertilizer Urea water soluble CRF1 44-0-0 Scotts Chemical Co. Urea 45-day release CRF2a 37-0-0 Scotts Chemical Co. Urea 120-day release CRF2b 43-0-0 Scotts Chemical Co. Urea 75 day release CRF3 42-0-0 Product 31 Urea CRF, unknown CRF4 41-0-0 Product 41 Urea CRF, unknown CRF5 44-0-0 Purcell Technologi es, Inc. Urea CRF, unknown CRF6 43-0-0 Purcell Technologi es, Inc. Urea CRF, unknown 1 The manufacturer of these products has a secrecy agreement w ith the University of Florida to remain anonymous. week period. Weekly and cumulative releas e were measured together with residual fertilizer, Q10 values, and total recovery. CRF fertilizer products The incubator experiment had a total of ten fertilizer treatments: a no fertilizer control (No N), ammonium nitrate (AN), urea, and seven CRF products. The two products in CRF2 were separated fo r individual characterization. Incubators Six cooled incubators (Sanyo Electric Biom edical Co., Ltd., Osaka, Japan) were set at constant temperatures of 5, 10, 15, 20, 25, and 30C. A seventh incubator was set at variable temperatures based on the averag e soil temperature (10 cm depth) for a given week of a typical growing season. The variab le temperatures were established using 25 years (1975 to 2000) of historical soil temperat ure data for the area (Table 3-2). Each week, prior to sampling, the temperature of each incubator was recorded as well as that of an American Society for Testing and Materi als (ASTM) certified thermometer inside

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21 Table 3-2. Incubator 7 temperature setti ngs used for the incubator experiment. Average soil temperature Incubator setting for week beginning (C) 25-Jan 15 1-Feb 15 8-Feb 15 15-Feb 16 22-Feb 18 1-Mar 18 8-Mar 19 15-Mar 19 22-Mar 21 29-Mar 21 5-Apr 23 12-Apr 22 19-Apr 23 26-Apr 24 each incubator for temperature verification. The variable temperature incubator was adjusted for the next weeks temperature after sampling. Duration The experiment lasted for 13 consecutive weeks, with samples taken each week. Setup and procedure Three grams of nitrogen (varying amounts of fertilizer based on formulation) were placed inside 200 ml sterile glass bottles wi th screw caps and added to 100 ml of deionized (DI) water. These bottles were then placed inside each incubator. At one week intervals, the bottles were shaken to ensu re solution homogeneity and a 20 ml sample aliquot removed. The fertilizer prills were filtered out of the remaining solution and returned to the sampling bottle; the excess so lution was discarded. The bottles were then refilled with 100 ml of fresh DI water. After 13 weeks, the fi ltered fertilizer prills were

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22 ground with a mortar and pestle and residual fe rtilizer was dissolved in 100 ml DI water and an aliquot taken. Sample analysis Aqueous samples were stored at -5C pr ior to analysis. Solution from weekly samplings was analyzed at the University of Florida Analytical Research Laboratory (ARL) for nitrogen by TKN and for EC usi ng standard protocols (Mylavarapu and Kennelley, 2002). The TKN method used measures NH4-N but not NO3-N, so the AN treatment percent recovery was based on 1.6% applied N. Residual fertilizer samples were analyzed by Waters Analytical La boratories (Camilla, GA) for N by the Dumas method (Dumas, 1831; Watson and Galliher, 2001). Statistical design and analysis Treatments were arranged in a completely randomized design with three replicates. Data were treated in three major categories: weekly and cumulative release, residual fertilizer, and total N recovery. Weekly and cumulative release data were analyzed factorially for sampling date, incubator temperature, and fertilizer source ma in effects and their interactions. Further factorial analysis was perfor med on weekly and cumulative release samples by analysis of fertilizer product main effect N release wi thin each temperature setting, analysis of temperature main effect release within each fertilizer product, and analysis of fertilizer product main effect release for each sampling date. Residual fertilizer can be defined as th e amount of N which would be available after plants had been harvested or ceased nutri ent uptake. In this experiment it was the amount of N remaining in prills after 13 w eeks of release. Residual fertilizer was

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23 evaluated for fertilizer main effects at each temperature setting and for temperature main effects with each fertilizer. Total N recovery evaluated the fertilizer products at each incubator temperature setting. All statisti cal analyses were performed usi ng SAS ANOVA and software (SAS, 1999). Treatment significance and mean se paration were performed using ANOVA and the Tukeys mean separation tests with = 0.05. Meshbag Experiment CRF fertilizer treatments The meshbag experiment consisted of eight fertilizer treatments: AN, and seven CRF products (CRF1 through CRF6). CRF 2 was divided into CRF2a and CRF2b. Setup and procedure Meshbags were prepared by mixing appr oximately 200 g of soil with 3 g of fertilizer (varying amounts of N). The mix was then tied into porous cheesecloth bags, and labeled at the end of an attached string. The bags were then buried at 10 cm depth from the top of the potato row at the resear ch farm at the Plant Science Research and Education Unit (PSREU) in Hastings, FL with no potato plants present. The meshbags were subject to the same temperature and mo isture conditions as plants. They were buried on 13 Feb 2003 with samplings at 20, 35, 48, 62, 76, 91, and 104 days. Due to limited space, meshbags were placed at a pproximately 20 cm in-ro w spacing and 100 cm between-row spacing. At two week intervals, three replicates of each fertilizer material were removed from the ground and air-dried. Once dry, the soil was sieved (30-mesh) to remove soil and to retain the fertilizer prills. Prills were ground with a mortar and pestle and any fertilizer was dissolved with DI wa ter. The solution was filtered with #3

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24 Whatman (Whatman International, LTD, Middl esex, UK) filter paper and diluted to 100 ml with DI water in class A volumetric flasks. Sample analysis Aqueous samples were stored at -5C prior to analysis. Samples were analyzed at the University of Florida Analytical Re search Laboratory (ARL) for nitrogen by TKN and for EC according to standard protoc ol (Mylavarapu and Kennelley, 2002). Statistical analysis Treatments were arranged in a randomi zed complete block design with three replicates. Data were analysed factorially for fertilizer product and sampling date main effects. Fertilizer source ma in effects were analyzed both over all sampling dates as well as for each sampling date. Sampling date main effects were analyzed over all fertilizer products. All analyses were performed usi ng SAS ANOVA software (SAS, 1999). Treatment significance and mean separati on were performed using ANOVA and the Tukeys mean separation tests with = 0.05. Field Production Two field experiments were conducted at the University of Floridas Hastings Plant Science Research and Education Unit (PSR EU). The first experiment was a CRF production experiment evaluating tuber yield, tu ber quality, and plant nutritional status over the course of the season as affected by six different CRF pr oducts plus ammonium nitrate (AN) all at three nitrogen application rates together with a no fertilizer control. The second experiment was a replacement expe riment in which two potato varieties were evaluated for tuber yield and tuber quality a nd plant nutritional st atus, as affected by applying two different CRF products in combin ation with AN at diffe rent ratios (100:0,

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25 75:25, 50:50, 25:75, and 0:100). Weather data was collected and recorded with the Florida Agricultural Weather Network (FAWN) weather station located on the research farm. As production was essentially the same for both experiments with the exception of N fertilization, the production practices de scribed below apply to both experiments except as specified. General Production Soils Soil at the field site is an Ellzey fine sand (sandy, siliceious, hyperthermic Arenic Ochraqualf; sand 90-95%, <2.5% clay, <5% silt, 1% OM). Irrigation Subsurface irrigation was used during the s eason for irrigation. A perched water table was maintained by flooding the growi ng field with water pumped from wells. A clay hardpan approximately 1 meter below the soil surface prevented deep percolation of this water. The water level was maintained at historical cultural levels (45-60 cm) by controlling the drainage of wate r from the growing beds in ditches (18.3 m apart) at the bottom of the field. Planting Seed potatoes for both trials were cut to approximately 71 g (2.5 oz) pieces and dusted with fungicide (1.1 g (0.04 oz) a.i. fludioxonil and 21.8 g (0.77 oz) a.i. mancozeb per 45.4 kg (100 lb) seed pieces; Maxim MZ, Sy ngenta Crop Protection, Inc. Greensboro, N.C.) prior to planting. In the CRF production trial, Atlantic potatoes were planted on 13 Feb 2003 and in the replacement experiment, Atlantic and Red LaSoda potatoes were planted on 20 Feb 2003. Seed potatoes were planted using 20-cm in-row spacing with 24 seed potatoes

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26 per row in each plot of the production expe riment and 36 seed potatoes per row in each plot of the replacement experiment. Plots in both trials were four rows wide with between-row spacing of 102 cm. The CRF tria l plots were 4.6 m long with 1.2 m in-row border space between plots and the replacemen t experiment plots were 7.3 m long with 1.8 m in-row border space between plots. Fertilizer treatments In the CRF production experiment, treatment s consisted of a no nitrogen control (No N) and 7 nitrogen sources (6 CRFs and AN) at three rates (112, 168, and 225 kg ha-1 N), representing 50%, 75%, and 100% of the recommended IFAS (or BMP) rate. CRF2 was a blend of CRF2a and CRF2b with 50% of the N coming from each fertilizer source. In the replacement experiment, fertilized treatments consisted of a no nitrogen control (No N) and two CRF products (CRF4 and CRF 6) blended with AN at AN:CRF percent N applications of 100:0, 75:25, 50:50, 25:75, and 0:100 totaling 168 kg ha-1 N. The nitrogen source in all CRF products was urea. All fertilizer treatments were incorporated into the plot the day of planting. Thirty-four kg ha-1 P (76 kg ha-1 P2O5) and168 kg ha-1 K (202 kg ha-1 K2O) were incorporated into all plots prior to planting. Seasonal management Pesticide applications were made dur ing the growing season following IFAS extension recommendations (Aerts and Ne sheim, 2000; Weingartner and Kucharek, 2004). Soil was fumigated with 1,3-di chloropropene (Telone II, 56 L ha-1, Dow Chemical Company, Indianapolis, IN) in early January prior to planting. Aldicarb (Temik 22.5 kg ha-1, Bayer Chemical Company, Kansas City, MO) was applied at planting. Metribuzin (Sencor, 2.9 L ha-1, Bayer Chemical Company, Kansas City, MO) was broadcast at hilling (approximately 21 days after planting) for weed cont rol. Fungicides were applied

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27 as needed for control of early and late blight following integrated pest management practices. Soil analysis A composite soil sample (20 cores of the upper 30 cm) from the entire potato bed was taken on 5 Feb 2003, before planting and prio r to fertilizer appl ication. Soil was airdried, sieved through a 30-mesh sieve, and an alyzed by the University of Floridas ARL for pH, nitrate (NO3-N) and ammonium (NH4-N) concentrations, phosphorus, calcium, magnesium, electrical conductiv ity (EC), and soil organi c matter (OM) according to standard protocol (Mylavara pu and Kennelley, 2002). Soil samp les (8 cores of the upper 30 cm) were taken from each plot in the pr oduction experiment at two-week intervals over the growing season at 15, 29, 41, 55, 69, 84, and 97 days after planting (DAP). The final soil samples (97 DAP) were taken one day before final harvest. The replacement experiment was sampled pre-plant and after harvest. All soil samples were dried and sieved as described above. Mid-season soil samples were tested for the same parameters as pre-plant soil samples. Tissue Sampling and Analysis Tissue samples consisting of both the leaflets and petiole of the most recently matured (expanded) leaf which had reached fu ll size and had turned a dark-green color (Hochmuth, 1991) were sampled in the production experiment at bi-weekly intervals at 36, 47, 64, and 82 DAP. Six samples from each plot were dried at 70 C until a constant weight was measured. They were then ground in a Wiley mill (Thomas Scientific, Swedesboro, NJ) to pass through a 20 mesh sieve, and analyzed for total Kjeldahl nitrogen (TKN) at the ARL. Petiole/leaflet tissue samples were not taken from the replacement experiment.

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28 At full flower, at 64 days after planting (DAP), one plant taken at random from each plot in both the production and the re placement experiments was cut at the soil surface. Leaves and stems were separate d, dried, and ground. Samples were then submitted to the ARL for TKN analysis using a standard protocol (Mylavarapu and Kennelley, 2002). Data were us ed to calculate percent leaf and stem TKN, and leaf, stem, and leaf + stem (total) dry matter accumulation (DM). At harvest in both the production and the re placement experiments, four marketable tubers from each plot were skinned. The remaining center was then diced into 1 cm cubes, dried, and ground. Tuber samples we re analyzed for TKN at the ARL using standard procedures (Myl avarapu and Kennelley, 2002). Nitrogen Recovery Efficiency Nitrogen recovery efficiency reflects the amount of applied nitrogen recovered from the field in tubers. Nitrogen recovery efficiency (NRE) was calculated after the method used by Zvomuya et al (2003) by the following equation: NRE = 100 (Ntreat Ncontrol) / Napplied where Ntreat represents the amount of nitrogen removed in the t ubers of a given fertilizer treatment, Ncontrol is that removed in the tubers of the no fertilizer control plot, and Napplied is the amount of nitrogen applied as fertilizer. Harvest The center two rows of each plot were mechanically harvested on 28-29 May 2003 at 106 DAP in the production experiment and 2 Jun 2003 at 103 DAP in the replacement experiment using commercial equipment.

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29 Potatoes were washed and graded into five size classes (size 1 4.8 cm, 4.8 cm size 2 6.4 cm, 6.4 cm size 3 8.3 cm, 8.3 cm size 4 10.2 cm, size 5 10.2 cm) based on USDA standards (USDA, 1991). Potatoes were grouped according to total yield and marketable yield. Total potato yield is defined as all tubers harvested from the field, independent of size or defects. Marketable yield is defined as no.1 tubers with diameters between 4.8 and 10.2 cm (USDA, 1991) and without any visible blemishes (rotten, green, misshapen, or c ontaining growth cracks). Specific gravity was measured by the weight in air/weight in water method (Edgar, 1951). Specific gravity is a ratio of water to solid content in a potato tuber. Because Atlantic potatoes are used primarily for chipping, a high specific gravity is desired. Specific gravities of at least 1.078 are c onsidered good for production at the PSREU research farm in Hastings, FL (Hutchinson et al ., 2002). Plant physiological disorders reduce tuber yields and qua lity. Tubers unfit for storage or consumption were removed from the total yields and quantified. Tuber external disorders that reduce marketab ility include sunburned (green) potatoes, misshapen potatoes, growth crack potatoes and otherwise rotten potatoes Tuber internal disorders monitored include hollow heart or brown center, and internal heat necrosis. Also evaluated were disease-induc ed tuber disorders in clude corky ring spot and brown rot. Statistical Analysis The CRF production experiment was arranged in a randomized complete block design with four replications Data in the CRF production experiment were analyzed factorially by fertilizer source and rate main effects. Where interactions were significant, simple effects were analyzed. This was follo wed for total and market able yields, specific

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30 gravity, tuber quality, plant biomass, nutrient upt ake, and nutrient recovery efficiency. In the case of plant tissue analyses, data were al so analyzed across all and at each of the sampling dates, and where interactions ex isted, simple effects were evaluated. The replacement experiment was arranged in a split plot design with four replications. Statistical analysis involved the evaluation of the va rious fertilizer blends for each CRF product, though not between products or across potato varieties. This was done for yields, specific gravity, tuber qual ity, plant biomass, and nutrient recovery efficiency. Linear regressi on analysis was performed with in each fertilizer product and potato variety across all AN:CRF blends. All analyses for both the production a nd the replacement experiments were performed using SAS ANOVA software (SAS 1999, Gary NC). Treatment significance and mean separation were performed usi ng ANOVA and the Tukeys mean separation tests with = 0.05. Nitrogen Leaching Experiment The nitrogen leaching experiment was performed within the CRF production experiment mentioned above. One lysimete r and one well were buried in each plot (described below). Samples from both lysi meters and wells were taken at 29, 41, 64, and 78 DAP. Lysimeter and well samples were st ored at -5C until analyzed. All water samples were analyzed at the ARL for NO3-N and NH4-N concentrations following standard procedures (Mylavar apu and Kennelley, 2002). Lysimeters Suction lysimeters, consisting of a PVC tube having a porous ceramic cup affixed to one end and a rubber stopper affixed to the ot her, were buried in each plot to a 30 cm depth below the top of the potato row. At two-week intervals over the season, a vacuum

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31 of approximately 40 kPa, was applied to each lysimeter. After 24 hrs, a water sample was removed from the lysimeter. Excess water from the lysimeter was removed and discarded. Wells Well casings (PVC pipe, 10 cm diameter by 120 cm long) were buried in each plot at a depth of 90 cm below the soil surface from the top of the potato row to access water in the perched water table. Wells were re moved from the field at 104 DAP in order to harvest plots. Statistical Analysis As with the CRF production experiment, data were arranged in a randomized complete block design, though with three replicat es. Data were analyzed factorially by fertilizer product, rate, and sampling date main effects. Where significant interactions were found, simple effects were evaluated. W ith the sampling date effects, fertilizer source and rate were analyzed both for each and across all dates. All statistical analyses were performe d using SAS ANOVA software (SAS, 1999). Treatment significance and mean separati on were performed using ANOVA and the Tukeys mean separation tests with = 0.05.

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32 CHAPTER 4 RELEASE CHARACTERISTICS OF CONTROLLED-RELEASE NITROGEN FERTILIZERS UNDER CONSTANT TEMPERATURE AND FIELD CONDITIONS The laboratory and field release experiments were conducted to evaluate the rate of release of nutrients from various contro lled-release fertilizer (CRF) products. Hypothetically, if release were predictable, fertilizer blends could be formulated that would match crop uptake requirements. To th at end, nitrogen CRF pr oducts from various manufacturers were analyzed for rate of N rel ease. These products were analyzed in two experiments: 1) nitrogen (N) release from CRF in DI water inside incubators at constant temperature and fluctuating temperature and 2) N release from CRF in buried meshbags under field conditions. In the incubator e xperiment, 3 g of N (variable amounts of fertilizer depending on formulati on) were mixed with 100 ml DI water. The prills were filtered weekly for thirteen weeks with aqueous samples taken each week, and fresh DI water added, replacing water from each previous week. Residual fertili zer in prills after thirteen weeks was submitted fo r quantification. In cubator temperatures were 5C, 10C, 15C, 20C, 25C, 30C and a variable temper ature incubator which was adjusted weekly to match average soil temperatures over su ccessive weeks of a typical north Florida growing season. In the meshbag experiment meshbags containing 3 g of CRF (varying amounts of N) mixed with appr oximately 200 g of soil were bur ied in the growing field at planting, and were successively removed at two week intervals ove r the potato growing season and analyzed for residual fe rtilizer remaining in the prills.

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33 Incubator Experiment Results Ten fertilizer treatments were analyzed: a no fertilizer control (No N), ammonium nitrate (AN), urea, and seven CRF pr oducts (CRF1, CRF2a, CRF2b, CRF3, CRF4, CRF5, and CRF6). CRF2 was split into two products because in the production and leaching experiments (Chapters 5 and 6, respec tively) CRF2 was a blend of two fertilizer products, each contributing half of the N a pplied. For this experiment, these two products were analyzed separately to dete rmine the release profile of each. Although AN and urea are water soluble, they were included as controls. These are currently the local prevailing fertilizer sources for potato produc tion. Table 4-1 shows the various incubator settings with readings taken week ly over the experimental period. Incubator Experiment Weekly and Cumulative N Release The weekly release data were analyzed factorially for rate, sampling date, and fertilizer source main effects; the ANOVA ta ble is shown in Table 4-2. Over all temperature settings, fertilizer products, a nd sampling dates, all main effects were significant as were their interacti ons: temperature by fertilizer ( p < 0.0001), temperature by sampling date ( p < 0.0001), fertilizer by sampling date ( p < 0.0001), and the thirdorder interaction, temperature by fertilizer by sampling date ( p < 0.0001). Thus, further analyses were performed within each effect to evaluate the reasons for these results. As the primary purpose of this experiment was to evaluate the release characteristics of certain fertilizer products and to relate that release to field conditions, each fertilizer product was evaluated for differences of rel ease at each temperature for each sampling date and the various fertilizer s were evaluated for differences of release in the variable temperature incubator, also for each sampling date.

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34Table 4-1. Incubator temperatures during the incubator experiment. Incubator Incubator 7 Week 5C 10C 15C 20C 25C 30C Variable setting (C) 01 5.02 5.5 10.0 10.5 14.5 14.6 19.5 19.0 24.5 24.5 30.0 30.6 14.0 15.4 15 1 4.3 4.7 9.8 10.4 14.9 15.2 20.0 19.7 24.9 25.3 30.1 30.0 14.2 14.5 15 2 5.0 5.7 10.0 10.1 15.0 15.1 20.0 20.4 25.0 25.4 30.0 30.2 14.0 15.2 15 3 4.0 5.1 9.7 10.3 14.6 14.4 20.0 20.3 25.0 25.5 30.0 30.3 15.6 15.9 16 4 4.3 5.2 9.9 10.2 14.8 14.9 20.0 20.6 24.8 25.2 30.0 30.4 17.3 18.3 18 5 4.5 5.6 10.0 10.0 14.5 15.2 19.5 19.8 25.0 25.5 30.0 29.9 16.9 17.4 18 6 4.0 4.5 9.8 9.4 14.5 15.3 20.0 20.3 24.9 25.2 30.3 30.1 18.2 18.5 19 7 4.2 4.5 10.0 9.6 14.6 15.2 20.0 20.5 24.6 25.4 30.0 30.0 18.0 18.7 19 8 4.1 5.3 10.0 9.8 14.6 14.9 19.8 19.4 24.9 25.4 29.5 30.0 20.8 21.5 21 9 4.1 5.3 10.0 10.0 14.8 15.2 20.0 20.5 25.0 25.2 29.8 30.0 20.6 20.9 21 10 4.3 4.6 10.0 9.7 14.9 15.3 20.0 20.1 24.3 25.0 30.0 30.0 22.5 23.2 23 11 4.3 4.5 10.0 10.2 14.8 15.3 20.0 20.4 25.0 25.4 30.0 30.4 21.5 22.2 22 12 4.2 5.4 10.0 9.8 14.7 15.2 20.0 19.8 24.5 24.6 29.7 30.0 23.4 23.4 23 13 4.3 5.2 9.8 10.0 14.6 14.7 19.9 20.3 24.8 25.5 29.8 30.0 23.9 23.8 24 1 At week zero, the samples were placed in the incubato r after equilibrating, but no sample was submitted for testing. 2First temperature represents a water-submer ged alcohol thermometer inside incubator; second represents the incubator digital reading.

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35 Table 4-2. ANOVA table for CRF incubato r release by sampling date, temperature setting and fertilizer product main effects. Source DF Type III SS MS F Value Pr > F Date 12 18491427461540952293352.85 < 0.0001 Temp 6 8382264713970441303.97 < 0.0001 Fert 8 625969804782462261702.5 < 0.0001 Rep 2 30250151250.33 0.7196 Temp*Fert 48 118597592247078353.76 < 0.0001 Date*Temp 72 104261826144808131.51 < 0.0001 Date*Fert 96 168106241517511067381.01 < 0.0001 Date*Temp*Fert 576 2375095194123438.97 < 0.0001 Error 1636 7518970445959 Corrected Total 2456 4775586503 Ammonium Nitrate The release profile of ammonium nitrate (AN) is s hown in Table 4-3 and in Figure 4-1. As would be expected for a wate r-soluble fertilizer, release from AN was characterized by a flush of nut rients at the first sampling da te, with little N recovery at subsequent samplings. Further, as AN has no temperature-based release, there was little statistical separation between N in the various sample at any of the sampling dates. There was a significant difference in N found in samples taken at 7 DAP, though this would not be expected, and could be due to experime ntal error. Significant differences found between samples taken at 57 and 64 DAP were not considered of pa rticular use because the concentration of nutrients at this time was practicably zero and within the background range for this experiment. Urea The release profile of urea is shown in Table 4-4 and in Figure 4-2. Similar to ammonium nitrate, urea had hi gh initial N release with little residual fertilizer in subsequent samplings. This is not surprising as urea is a water-soluble product. While there was a significant difference in N concen tration between samples from the variable

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36Table 4-3. N release from ammonium nitrate at various incubator settings for each sampling date. Days (TKN, mg L-1) Temperature (C) 7 14 21 28 35 42 49 57 64 71 78 85 92 5 9471 ab1 621 7 4 5 3 5 2 a 3 a 2 2 1 0 10 9432 ab 238 11 3 2 1 1 1 b 1 b 1 0 0 0 15 9721 ab 280 5 3 2 1 3 1 b 1 b 2 0 0 0 20 9656 ab 282 3 4 3 1 2 1 b 1 b 1 0 0 0 25 10185 a 242 7 2 1 1 31 1 b 1 b 2 1 0 0 30 9550 ab 376 7 2 2 1 1 1 b 1 b 2 3 0 0 Variable 9136 b 329 7 2 1 1 2 1 b 1 b 2 0 0 0 ANOVA p-value 0.0232 0.4397 0.2096 0. 7104 0.0773 0.0619 0.4915 0.0371 < 0.0001 0.3242 0. 0726 0.3126 0.4682 Tukey LSD 817 ns ns ns ns ns ns 0.6 0 ns ns ns ns 1 Means in columns followed by same letters not significantly different. 0 2000 4000 6000 8000 10000 12000 020406080100 DaysTKN (mg L-1) 5C 10C 15C 20C 25C 30C Variable 0 20 40 60 80 100 020406080100 DaysPercentage of N applied 5C 10C 15C 20C 25C 30C Variable Figure 4-1. Release profile of ammonium n itrate at each incubator sett ing over the duration of the CRF release experiment. A) Weekly release, B) Cumulative release. A B

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37Table 4-4. N release from urea at various incubator settings for each sampling date. Days (TKN, mg L-1) Temperature (C) 7 14 21 28 35 42 49 57 64 71 78 85 92 5 2491 440 a1 11 3 4 4 3 2 2 a2 3 a4 0 10 2529 389 a 10 3 4 3 1 1 1 b1 1 b0 0 15 2679 400 a 7 4 2 3 2 2 1 b2 1 b0 0 20 2626 355 a 7 4 3 3 3 1 2 a2 1 b0 0 25 2682 377 a 23 21 5 2 41 1 1 b3 1 b0 0 30 2665 359 a 9 6 6 1 3 1 1 b2 1 b0 0 Variable 2714 217 b 8 3 7 1 2 0 1 b2 0 b3 0 ANOVA p-value 0.0842 <0.0001 0.2220 0.4017 0.6317 0.4166 0. 4235 0.2320 0.0003 0.5848 <0.0001 0.1909 0.4682 Tukey LSD ns 93 ns ns ns ns ns ns 0.6 ns 1 ns ns 1 Means in columns followed by same letters not significantly different. 0 500 1000 1500 2000 2500 3000 020406080100 DaysTKN (mg L-1) 5C 10C 15C 20C 25C 30C Variable 0 20 40 60 80 100 020406080100 DaysPercentage of N applied 5C 10C 15C 20C 25C 30C Variable Figure 4-2. Release profile of urea at each incubator setting over the duration of the incubator experiment. A) Weekly releas e, B) Cumulative release. A B

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38 temperature incubator and all ot her incubators, this is likely due to sample error. The significant separations at 64 and 78 days are artifacts of samples with background concentrations of N and rounding errors rather than actual differences in N. The low percent release (recovery of applied) of N is discussed below (see Total N recovery). CRF1 The release profile of CRF1 is shown in Table 4-5 and in Figure 4-3. While there was significant separation in N release at the first two sampling dates, CRF1 had a generally similar release profile to ur ea and ANhigh initial release with little subsequent release. As with urea and AN, significant separations at 28, 64, and 78 days are likely due to background levels of N coupl ed with low-level contamination in random samples causing some statistical differences. While N release at the first sampling date was greater in the 25C, 30C, and variable temperature incubators than in the 5C and 10C incubators, this temperature-influenced release was not cont inued at subsequent samplings. This would tend to indicate an initial temperature-based release, though not over time. CRF2a The release profile of CRF2a is shown in Table 4-6 and Figure 4-4. Like the water-soluble fertilizer products, CRF2a exhibi ted little temperature-based release. No significance was found for the firs t four sampling dates for N concentration from samples in the various incubators, and the differences found at 35 and 64 days were small. In contrast to AN, urea, and CRF1, CRF2a had c ontinued nutrient rele ase over the entire season, albeit at low levels. Th is would tend to indicate that nutrient inside the fertilizer prills was not entirely depl eted and slowly available.

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39Table 4-5. N release from CRF1 at various incubator settings for each sampling date. Days (TKN, mg L-1) Temperature (C) 7 14 21 28 35 42 49 57 64 71 78 85 92 5 2438 d1 371 ab 17 2 b 1 7 7 4 2 b 1 14 b 0 0 10 2531 cd 343 ab 17 2 b 1 6 8 3 10 a 27 2 b 0 0 15 2624 bc 419 ab 17 3 b 1 4 8 11 1 c 13 1 b 0 0 20 2588 b-d 424 ab 17 2 b 1 4 11 5 1 c 13 1 b 0 0 25 2704 a 516 a 24 3 b 2 5 7 1 1 c 14 7 b 0 0 30 2646 ab 383 ab 16 20 a 9 10 6 1 1 c 14 84 a 0 0 Variable 2841 b 259 b 19 3 b 10 6 5 3 1 c 16 4 b 0 0 ANOVA p-value < 0.0001 0.0117 0.3834 0.0182 0.2218 0.4983 0. 2928 0.2128 < 0.0001 0. 4558 < 0.0001 0.3168 -Tukey LSD 170 183 ns 16 ns ns ns ns 0 ns 14 ns ns 1 Means in columns followed by same letters not significantly different. 0 500 1000 1500 2000 2500 3000 020406080100 DaysTKN (mg L-1) 5C 10C 15C 20C 25C 30C Variable 0 20 40 60 80 100 020406080100 DaysPercentage of N applied 5C 10C 15C 20C 25C 30C Variable Figure 4-3. Release profile of CRF1 at each incubator setting over the duration of the incubator experiment. A) Weekly releas e, B) Cumulative release. A B

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40Table 4-6. N release from CRF2a at various incubator settings for each sampling date. Days (TKN, mg L-1) Temperature (C) 7 14 21 28 35 42 49 57 64 71 78 85 92 5 4043 1183 540 355 317 ab1 251 226 195 220 ab 284 226 207 272 10 4231 1084 529 490 411 ab 250 260 281 260 a 369 196 208 176 15 4065 1052 414 514 332 ab 347 284 351 191 ab 246 262 194 195 20 4543 1288 574 534 473 a 424 243 320 180 ab 183 131 247 153 25 5160 1221 562 457 413 ab 270 238 216 162 b 146 103 150 150 30 4890 1267 714 415 315 ab 239 292 457 165 b 123 126 191 141 Variable 4996 1172 454 379 236 b 198 216 180 142 b 190 131 123 157 ANOVA p-value 0.1711 0.5554 0.1555 0. 0765 0.0565 0.1424 0.6871 0. 4608 0.0047 0.2080 0. 1142 0.6138 0.2041 Tukey LSD ns ns ns ns 233 ns ns ns 82 ns ns ns ns 1 Means in columns followed by same letters not significantly different. 0 1000 2000 3000 4000 5000 6000 020406080100 DaysTKN (mg L-1) 5C 10C 15C 20C 25C 30C Variable 0 20 40 60 80 100 020406080100 Da y s After Startin g Percentage of N applied 5C 10C 15C 20C 25C 30C Variable Figure 4-4. Release profile of CRF2a at ea ch incubator setting over the duration of the incubator expe riment. A) Weekly relea se, B) Cumulative release. A B

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41 CRF2b The nutrient release profile for CRF2b is found in Table 4-7 and Figure 4-5. While CRF2b had the spike of initial N release at the first sampling date, it also continued sustained nutrient release throughout the major ity of the testing pe riod. Of particular interest, at the first sampling date (7 days), an increase in incubator temperature resulted in an increase in N release, thus indicating temperature-based release characteristics. As would be predicted, N release from the variab le incubator was comparable to that from the 15C and 20C incubators. Also of note, total release by the end of the study was similar for fertilizer in incubators set at 20 C, 25C, 30C, and the variable temperature incubator, in that they had a ll approached 90% release of to tal nutrients during the testing period. CRF3 CRF3 exhibited characteristics between t hose of CRF and water-soluble products (Table 4-8 and Figure 4-6). At the first sa mpling date, a large flush of N was observed, while at 14 days, only samples from the 10 C and 30C incubators had substantially comparable release to the first sampling da te. At 21 and 28 days, N release followed a temperature-based trend where significantly gr eatest release was obtained from samples in the 30C incubator and least release from the 5C incubator. Between 42 and 57 days, nutrient release from all samples was substant ially higher than from previous samplings, a phenomenon not seen with either the watersoluble or CRF products. At and after 64 days no trend appeared to describe the data though N concentrations at 71, 78, 85, and 92 days had significant differences.

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42Table 4-7. N release from CRF2b at various incubator settings for each sampling date. Days (TKN, mg L-1) Temperature (C) 7 14 21 28 35 42 49 57 64 71 78 85 92 5 1870 de 1000 e 620 e 537 c 576 e 522 c 515 d 553 e 550 c 530 c 594 de 548 c 514 bc 10 1758 e 1303 de 953 de 946 bc 866 de 828 bc 776 d 971 de 820 c 838 c 855 cd 783 b 792 ab 15 2416 cd 1722 cd 1379 d 1529 a-c 1654 cd 1618 b 1633 bc 1947 bc 1540 b 1618 b 1470 ab 1228 a 1098 a 20 2684 c 2251 bc 2108 c 2220 a-c 2372 bc 2603 a 2480 a 2566 a 1956 ab 1622 b 1183 bc 811 b 663 b 25 4578 b 2420 b 3482 b 3406 a 3623 a 1524 b 2102 ab 1502 cd 894 c 631 c 413 de 278 d 220 cd 30 5741 a 4530 a 5749 a 2818 ab 2744 ab 1377 b 1072 cd 751 e 412 c 317 c 199 e 156 e 112 d Variable 2364 cd 1770 cd 1400 cd 1666 a-c 1814 b-d 1621 b 2436 ab 2250 ab 2163 a 2633 a 1768 a 1250 a 812 ab ANOVA p-value < 0.0001 < 0.0001 < 0.0001 0.0036 < 0.0001 < 0.0001 < 0.0001 < 0. 0001 < 0.0001 < 0.0001 < 0.0001 < 0.0 001 < 0.0001 Tukey LSD 587 552 714 2008 1014 853 827 545 488 703 527 90 371 1 Means in columns followed by same letters not significantly different. 0 1000 2000 3000 4000 5000 6000 7000 020406080100 DaysTKN (mg L-1) 5C 10C 15C 20C 25C 30C Variable 0 20 40 60 80 100 020406080100 Da y s After Startin g Percentage of N applied 5C 10C 15C 20C 25C 30C Variable Figure 4-5. Release profile of CRF2b at each incubator setting over the du ration of the incubator expe riment. A) Weekly relea se, B) Cumulative release. A B

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43Table 4-8. N release from CRF3 at various incubator settings for each sampling date. Temperature Days (TKN, mg L-1) (C) 7 14 21 28 35 42 49 57 64 71 78 85 92 5 1701 654 94 d1 45 c 34 c 228 d 202 c 191 c 75 14 c 135 a 37 c 113 cd 10 1756 1784 100 d 59 bc 39 c 345 cd 290 bc 272 bc 20 205 a-c 91 a-c 183 ab 155 bc 15 1859 460 138 c 78 b 59 c 453 a-c 371 ab 350 b 102 233 ab 79 a-c 215 a 189 ab 20 1926 480 141 c 81 b 80 c 556 ab 439 a 558 a 30 227 ab 100 a-c 173 ab 135 cd 25 1394 522 180 ab 148 a 86 c 501 a-c 383 ab 32 d 22 271 ab 20 bc 116 bc 102 de 30 1968 1362 184 a 132 a 600 a 360 b-d 262 c 19 d 14 92 bc 3 c 76 c 62 e Variable 1713 315 148 bc 127 a 186 b 648 a 445 a 375 b 39 365 a 132 ab 241 a 220 a ANOVA p-value 0.7682 0.2372 < 0.0001 < 0.0001 < 0.0001 0.0002 < 0.0001 < 0.0001 0.3431 0.0008 0.0081 < 0.0001 < 0.0001 Tukey LSD ns ns 34 32 54 204 103 141 ns 194 112 84 46 1 Means in columns followed by same letters not significantly different. 0 500 1000 1500 2000 2500 020406080100 DaysTKN (mg L-1) 5C 10C 15C 20C 25C 30C Variable 0 20 40 60 80 100 020406080100 DaysPercentage of N applied 5C 10C 15C 20C 25C 30C Variable Figure 4-6. Release profile of CRF3 at each incubator setting over the duration of the incubator experiment. A) Weekly releas e, B) Cumulative release. A B

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44 CRF4 The CRF4 release profile is shown in Tabl e 4-9 and Figure 4-7. At the first two sampling dates, no significant difference was found in N concentration between the various incubator temperatures There was, however, at these early sampling dates, a high initial pulse of N release, as seen with both the wate r-soluble and the CRF products previously evaluated. At 21 and 28 days, N release followed temperature-based release patterns; highest N release was obtained from samples in the 25C, 30C, and variable temperature incubators while least release was obtained from the 5C and 10C incubators. After 28 days, though differen ces were found, N concentrations did not appear to follow a strong temperature-based trend. As with CRF2b, by 92 days, total N release samples in the 20C, 25C, 30C, a nd the variable temper ature incubators was roughly equal. As samples from the third and fourth samplings exhibited temperaturecontrolled release, it is possible that temp erature-based control was also controlling release at the first two samplings, with those effects being masked by a large initial N release. CRF5 The release profile and sample N concen trations for CRF5 at each sampling date are found in Table 4-10 and Figure 4-8. Of all of the CRF products evaluated, CRF5 exhibited the greatest degree of temperature-based release as evidenced by the significant decrease in N concentrations from sample s taken at the first sampling date. This controlled-release trend c ontinued through 49 days, where samples from warmtemperature incubators, generally had greater nutrient release than from cool-temperature incubators. The only exception to this was at 14 days, where none of the samples were statistically different from one another. This is likely due to a lack of precision in

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45Table 4-9. N release from CRF4 at various incubator settings for each sampling date. Temperature Days (TKN, mg L-1) (C) 7 14 21 28 35 42 49 57 64 71 78 85 92 5 1701 654 94 d1 45 c 34 c 228 d 202 c 191 c 75 14 c 135 a 37 c 113 cd 10 1756 1784 100 d 59 bc 39 c 345 cd 290 bc 272 bc 20 205 a-c 91 a-c 183 ab 155 bc 15 1859 460 138 c 78 b 59 c 453 a-c 371 ab 350 b 102 233 ab 79 a-c 215 a 189 ab 20 1926 480 141 c 81 b 80 c 556 ab 439 a 558 a 30 227 ab 100 a-c 173 ab 135 cd 25 1394 522 180 ab 148 a 86 c 501 a-c 383 ab 32 d 22 271 ab 20 bc 116 bc 102 de 30 1968 1362 184 a 132 a 600 a 360 b-d 262 c 19 d 14 92 bc 3 c 76 c 62 e Variable 1713 315 148 bc 127 a 186 b 648 a 445 a 375 b 39 365 a 132 ab 241 a 220 a ANOVA p-value 0.7682 0.2372 < 0.0001 < 0.0001 < 0.0001 0.0002 < 0.0001 < 0.0001 0.3431 0.0008 0.0081 < 0.0001 < 0.0001 Tukey LSD ns ns 34 32 54 204 103 141 ns 194 112 84 46 1 Means in columns followed by same letters not significantly different. 0 1500 3000 4500 6000 7500 9000 020406080100 DaysTKN (mg L-1) 5C 10C 15C 20C 25C 30C Variable 0 20 40 60 80 100 020406080100 DaysPercentage of N applied 5C 10C 15C 20C 25C 30C Variable Figure 4-7. Release profile of CRF4 at each incubator setting over the duration of the incubator experiment. A) Weekly releas e, B) Cumulative release. A B

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46Table 4-10. N release from CRF5 at various incubator settings for each sampling date. Temperature Days (TKN, mg L-1) (C) 7 14 21 28 35 42 49 57 64 71 78 85 92 5 720 c1 679 a 391 c 407 d 593 d 576 c 701 d 860 d 810 cd 763 d 790 cd 477 cd 683 b 10 848 c 614 a 530 c 926 d 1027 d 986 bc 1041 c 1231 c 947 c 925 d 841 cd 810 bc 696 b 15 960 c 1114 a 1390 bc 1591 c 1681 c 1445 ab 1307 b 1463 b 1078 bc 1116 c 944 bc 784 bc 801 b 20 1518 bc 2158 a 2354 ab 2414 b 2494 b 1960 a 1760 a 2059 a 1292 ab 1319 b 1060 b 849 b 723 b 25 2648 b 3135 a 3382 a 3396 a 3202 a 1731 ab 1834 a 1578 b 1113 bc 909 d 683 d 583 bc 471 c 30 4530 a 3554 a 3468 a 3492 a 2601 b 1378 a-c 1104 bc 877 d 586 d 467 e 324 e 197 d 228 d Variable 895 c 1267 a 1592 bc 1847 bc 1847 c 1713 ab 1651 a 1625 b 1607 ab 1550 a 1492 a 1375 a 1239 a ANOVA.p-value < 0.0001 0.0224 0.0001 < 0. 0001 < 0.0001 0.0010 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 Tukey LSD 1240 2986 1721 614 509 815 232 218 342 187 167 357 157 1 Means in columns followed by same letters not significantly different. 0 1000 2000 3000 4000 5000 020406080100 DaysTKN (mg L-1) 5C 10C 15C 20C 25C 30C Variable 0 20 40 60 80 100 020406080100 DaysPercentage of N applied 5C 10C 15C 20C 25C 30C Variable Figure 4-8. Release profile of CRF5 at each incubator setting over the duration of the incubator experiment. A) Weekly releas e, B) Cumulative release. A B

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47 samples taken from the 30C incubator where co ncentrations of the th ree replicates were 358, 4700, and 5500 mg L-1 N; it is likely that the first value is a transcriptional error and not a true value. Thus the absence of statisti cal differences is an e rror and true separation would have likely followed trends set both before and after that sampling date, as evidenced by the decreasing N concentration in successively cooler incubators. Of note with CRF5, however, was that independent of temperature, this product never reached greater than 90% release over the course of the experiment. Under field conditions, it would be desirable to have a greater rate of re lease, so as to be useful to the plant during the growing season. It should be noted that nutrient release from this product may have been incomplete as substantial N was releas ed even after 92 days, and illustrated by the positive slope of the cumulative release curves in Figure 4-8, B. CRF6 The release profile for CRF6 with accompanyi ng N concentrations from the various incubators at each sampling date are shown in Table 4-10 and Figure 4-9. CRF6 was the only fertilizer product evaluated th at did not have a substantial initial release of N. Like CRF5, it exhibited good temperatur e-based release. From the data, it appears that this product had somewhat of a sigmoidal-type releasea period of no nutrient release followed by a linear release curve, finally tape ring off as the product was depleted. This is illustrated by the S-pattern in the cumu lative release curve for CRF6 (Figure 4-9, B). Of note with this product was its continued re lease of substantial qua ntities of nutrients through the end of the experiment period. Also after 92 days of release, only product in the 30C incubator had released even 70% of its nutrients; all other temperature regimes had resulted in 60% or less total N release. As with CRF5, the positive slope of the cumulative release curve between 85 and 92 days tends to indicate th at further release

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48Table 4-11. N release from CRF6 at various incubator settings for each sampling date. Temperature Days (TKN, mg L-1) (C) 7 14 21 28 35 42 49 57 64 71 78 85 92 5 331 295 b 113 b 104 e 137 c 134 e 99 d 118 c 150 d 155 e 185 e 193 f 232 d 10 208 270 b 60 b 91 e 149 c 151 e 197 d 289 c 277 d 322 e 322 e 315 e 342 d 15 301 350 b 168 b 229 de 369 c 501 d 647 c 918 b 837 c 912 d 886 d 822 d 900 bc 20 377 451 b 438 b 750 c 998 b 1031 c 1157 b 1664 a 1197 b 1185 c 1113 c 970 c 968 b 25 481 466 b 1179 ab 1826 b 2034 a 1637 b 1777 a 1919 a 1636 a 1540 a 1350 ab 1150 b 989 b 30 650 1591 a 1598 a 2562 a 2466 a 2072 a 1893 a 2028 a 1639 a 1472 ab 1239 bc 1000 c 789 c Variable 562 198 b 237 b 342 d 551 bc 700 d 907 bc 1100 b 1274 b 1350 bc 1436 a 1400 a 1383 a ANOVA p-value 0.1037 < 0.0001 0.0022 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0. 0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 Tukey LSD ns 434 1127 231 448 218 283 477 175 177 163 112 159 1 Means in columns followed by same letters not significantly different. 0 500 1000 1500 2000 2500 3000 020406080100 DaysTKN (mg L-1) 5C 10C 15C 20C 25C 30C Variable 0 20 40 60 80 100 020406080100 DaysPercentage of N applied 5C 10C 15C 20C 25C 30C Variable Figure 4-9. Release profile of CRF6 at each incubator setting over the duration of the incubator experiment. A) Weekly releas e, B) Cumulative release. A B

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49 would occur, although it would be useless with respect to th e typical Atlantic potato growth cycle. No N Control N found from the no fertilizer control at th e various sampling dates is illustrated in Figure 4-10. It serves to illustrate the b ackground degree of contamination that occurred throughout the sampling dates of the experime nt. Early in the experiment, as high quantities of N were found in the various samples, contamination in the control was higher than late in the season when many of the CRF products had been depleted and the water-soluble products had been removed. 0 5 10 15 20 25 30 020406080100 DaysTKN (mg L-1) 5C 10C 15C 20C 25C 30C Variable Figure 4-10. N found in the no fertilizer co ntrol within each in cubator for various sampling dates. Variable Temperature Incubator Release As one of the purposes of this experiment was to evaluate th e release of various CRF products under simulated fi eld conditions, the nutrient re lease of the fertilizer products under varying temperat ure conditions was evaluated. The release profiles and nutrient release from each fertilizer at each sampling date are shown in Table 4-12 and in Figure 4-11. As noted previously with each individual fertilizer, a ll products with the

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50Table 4-12. N release from fertilizer products in the variable temperat ure incubator for each sampling date. Days (TKN, mg L-1) Fertilizer 7 14 21 28 35 42 49 57 64 71 78 85 92 AN 9136 a 329 d 7 e 2 b 1 b 1 c 2 e 1 h 1 d 2 e 0 c 0 f 0 d Urea 2714 d 217 d 8 e 3 b 7 b 1 c 2 e 0 i 1 d 2 e 0 c 3 f 0 d CRF1 2841 d 259 d 19 e 3 b 10 b 6 c 5 e 3 g 1 d 16 e 4 c 0 f 0 d CRF2a 4996 c 1172 c 454 c 379 b 236 b 198 c 216 e 180 f 142 d 190 e 131 c 129 e 157 d CRF2b 2364 de 1770 b 1400 b 1666 a 1814 a 1621 a 2436 a 2250 a 2163 a 2633 a 1768 a 1250 b 812 b CRF3 1713 e 315 c 148 de 127 b 186 b 648 b 445 de 375 e 39 d 365 de 132 c 241 d 220 d CRF4 7270 b 2451 a 1533 ab 1728 a 1475 a 1357 a 1278 bc 1200 c 1109 c 900 cd 751 b 636 c 494 c CRF5 895 f 1267 c 1592 a 1847 a 1847 a 1713 a 1651 b 1625 b 1607 b 1550 b 1492 a 1375 a 1239 a CRF6 562 f 198 d 237 de 342 b 551 b 700 b 907 cd 1100 d 1274 bc 1350 bc 1436 a 1400 a 1383 a ANOVA p-value < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.000 1 Tukey LSD 786 168 182 443 859 438 645 1 403 585 464 53 260 1 Means in columns followed by same letters not significantly different.

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51 0 2000 4000 6000 8000 10000 12000 020406080100 DaysTKN (mg L-1) No N AN Urea CRF1 CRF2a CRF2b CRF3 CRF4 CRF5 CRF6 Figure 4-11. Release profile of fertilizer pr oduct at the variable in cubator setting over the duration of the CRF release experiment exception of CRF6 had substantia l release at the first sampling date. Of the fertilizer products evaluated, CRF2b, CRF4, and CRF6 had the greatest degree of sustained release over the entire experiment. When compared against each other, AN a nd CRF4 had significantly the greatest N release at the first sampling dated, while su stained release from 14 through 49 days was highest with CRF2b, CRF4 and CRF5. Late in the experiment, as CRF4 was depleted, CRF2b, CRF5, and CRF6 had highest release. With the exception of the first two sampling dates, AN, urea, and CRF1 had essent ially zero N release, typical of a watersoluble fertilizer product. Q10 Early in the experiment (7 and 14 day samp ling dates), the releas e of each fertilizer with respect to incubator temper ature provided a good estimate of Q10 values for each product. CRF1 and CRF2a, together with the wa ter soluble fertilizers, AN and urea, had a single flush of N release which was i ndependent of temperature, hence Q10 values for

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52 these products were roughly 1. Q10 values were greatest for CRF5, both at the 7 and 14 day samplings across all temperature compar isons (Figure 4-12, A and B). Also from these data, Q10 values varied considerably over the biological range depending on where one was within that range. For example, CRF5 at the 7 day sampling has a Q10 of 1.3 between 5 and 15C, but a Q10 of 3.0 between 20 and 30C. Q10 values for sampling dates beyond 14 days were not calculated because of a depletion effect that could occur 0 1 2 3 4 5 to 1510 to 2015 to 2520 to 30 Temperature Comparisons (C)Q10 CRF1 CRF2a CRF2b CRF3 CRF4 CRF5 CRF6 0 1 2 3 4 5 to 1510 to 2015 to 2520 to 30 Temperature Comparisons (C)Q10 CRF1 CRF2a CRF2b CRF3 CRF4 CRF5 CRF6 Figure 4-12. Q10 values for various CRF products. A) at 7 days, B) at 14 days. A B

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53 where future fertilizer rel ease if affected by differing am ounts of fertilizer previously released and correspondingly diffe rent remaining concentrations. Residual Fertilizer After 13 weeks of release, the fertiliz er products were ground and the residual fertilizer dissolved and submitted for TKN analysis. No residual analysis was run for urea or AN because of zero residual recover y. The ANOVA table for factorial analysis of incubator temperature and fertilizer sour ce is shown in Table 4-13. As there was a significant interaction ( p < 0.0001) between the main effects and it was not of interest to evaluate each product and temperature se tting with all other product-temperature combinations, differences in residual N from the fertilizer products was evaluated at each temperature setting (Table 4-14) and the effects of the vari ous temperature settings on N release were evaluated for each CRF product (Table 4-15). Table 4-13. ANOVA table for resi dual N by incubator temperat ure and fertilizer product main effects. Source DF Type III SS MS F ValuePr > F Temp 6 176472941333.63< 0.0001 Fert 6 68808114681300.86< 0.0001 Rep 2 24121.380.2565 Temp*Fert 36 1406339144.31< 0.0001 Error 96 8469 Corrected Total 146 101389 Within the coolest three incubators ( 5, 10, and 15C), both CRF2a and CRF6 had the greatest amount of residua l fertilizer after 13 weeks wh ile CRF1 had significantly the least residual N of all products (Table 4-14). Within the warmest constant-temperature incubators (20, 25 and 30C), significantly gr eatest residual was found in CRF2a while CRF1 continued with the least residual N. The lack of residual N in CRF1 and, to a

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54Table 4-14. Residual N recovery (% of applied) from CRF products after 13 w eeks of release for each incubator. TKN (% of applied) Fertilizer 5C 10C 15C 20C 25C 30C Variable CRF1 1.2 e1 1.1f 1.5d 1.1e 2.0d 0.9c 1.0f CRF2a 65.5 b 64.6b66.4a 64.9a 68.1a 65.8a 67.2a CRF2b 62.2 b 47.6c 21.5c 9.0de 4.3cd1.8c 7.9de CRF3 14.4 d 10.4e 14.3cd4.6de 4.0cd3.2c 4.5ef CRF4 36.4 c 28.6d19.3c 12.0cd 7.3c 7.3c 12.5d CRF5 63.9 b 52.2c 39.7b 20.9c 8.5c 3.7c 22.4c CRF6 79.4 a 64.6a 60.5a 49.7b 28.2b 18.3b47.1b ANOVA p -value 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 Tukey LSD 10.5 9.0 12.8 9.4 4.6 7.6 5.3 1 Means in columns followed by same letters not significantly different. Table 4-15. Residual N recover (% of app lied) from CRF products after 13 weeks of release at each temperature setting. TKN (% of applied) Temperature (C) CRF1 CRF2a CRF2b CRF3 CRF4 CRF5 CRF6 5 1.265.562.2a1 14.4a 36.4a 63.9a 79.4a 10 1.164.647.6b 10.4a 28.6b 52.2b 64.6a 15 1.566.421.5c 14.3a 19.3c 39.7c 60.5b 20 1.164.99.0d 4.6b 12.0d 20.9d 49.7c 25 2.068.14.3d 4.0b 7.3d 8.5e 28.2d 30 0.965.81.8d 3.2b 7.3d 3.7f 18.3e Variable 1.067.27.9d 4.5b 12.5d 22.4d 47.1c ANOVA p -value 0.6570.9782< 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 Tukey LSD nsns10.1 5.8 5.9 4.8 9.7 1 Means in columns followed by same letters not significantly different.

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55 lesser degree, CRF3, independent of temperature, is of concern because they imparted no nutrient retentive advantage over AN or ur ea. Having noted a high initial nutrient release, hope might have been maintained all of the fertilizer was not lost, merely locked into the prill. However, with little residual, it becomes apparent that all N was released at the first sampling date. At 30C, CRF2 a and CRF6 had 65.8% and 18% residual N, respectively. This is of concern because after 90-100 days, most potato plants have ceased uptake and even been harvested. This residual fertilizer would remain in the field though with no crop to take it up, again poten tially leading to leaching conditions. Residual N from samples in the incubator te mperature fell perfectly between that found in the 15C and 25C incubators, the predicted response as temperatures in the variable temperature incubator were alwa ys between these two values. Considering each CRF across temperature settings (Table 4-15, Figure 4-13), both CRF1 and CRF2b had little change in nutrient release as temperature was changed. This indicates no temperature-based cont rol. Conversely, CRF2b, CRF4, CRF5, and CRF6 had significant reductions in residual fertilizer as incu bator temperature setting was increased, tending to indicate varying degrees of temperature-based control. CRF3 had intermediate characteristics between CRF and water-soluble products in that residual N was not significantly different for the lower temperature settings or for the higher settings, though a significant decrease in residual was found between the two sets of temperatures. With the exceptions of CRF2a and CRF6, the CRF products had very li ttle residual fertilizer at either 25C or 30C.

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56 0 20 40 60 80 100 05101520253035 Temperature (C)Total applied N (% ) CRF1 CRF2a CRF2b CRF3 CRF4 CRF5 CRF6 Figure 4-13. Residual TKN (% of applied) for various CRF products as affected by temperature. Total N Recovery The total amount of N recovered from the 13 weeks of release added to the amount of N recovered from the residual found still insi de the fertilizer prills constitutes the total recovery of fertilizer. The percentages r ecovered are found in Table 4-16 and illustrated in Figure 4-14 and Figure 4-15. CRF2a, CRF 2b, CRF4, CRF5, and CRF6 all had total recoveries greater than 80%, with CRF2a ha ving total recoveries greater than 90%, across all temperatures. Meshbag Experiment The meshbag experiment consisted of ei ght fertilizer produ cts thoroughly mixed with soil and buried in the growing field. Th e fertilizers consisted of ammonium nitrate (AN) and the seven CRF products as were ev aluated in the incubator experiment. In preparing the meshbags, three grams of fertiliz er (varying amounts of N) were applied to approximately 100 g of field soil, mixed, and pl aced into a cheeseclo th bag, labeled,

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57Table 4-16. Total N recovery (% of applie d) from fertilizer treatments from solution and residual sources for each temperatur e setting. TKN (% of applied)) 5C 10C 15C 20C 25C 30C Variable Fertilizer Soln1 Res Tot Soln Res Tot Soln Res Tot Soln Res Tot Soln Res Tot Soln Res Tot Soln Res Tot AN2 68 0 68 61 0 61 63 0 63 62 0 62 65 0 65 62 0 62 59 0 59 Urea 13 0 13 10 0 10 10 0 10 10 0 10 11 0 11 10 0 10 10 0 10 CRF1 10 1 11 10 1 11 10 2 12 10 1 11 11 2 13 11 1 12 11 1 12 CRF2a 27 65 92 28 65 93 28 66 94 31 65 96 31 68 99 31 66 97 28 67 95 CRF2b 28 62 90 39 48 87 70 21 91 85 9 94 84 4 88 87 2 88 69 8 77 CRF3 11 14 26 18 10 28 15 14 30 16 5 21 13 4 17 17 3 20 21 4 25 CRF4 47 36 83 55 29 83 68 19 87 75 12 87 73 7 80 73 7 80 71 13 84 CRF5 25 64 89 38 52 90 52 40 92 73 21 94 82 8 91 76 4 80 58 22 80 CRF6 7 79 86 10 79 89 26 61 87 41 50 91 56 28 84 67 18 85 32 47 79 1 Soln = solution; Res = residual; Tot = total. All values in % of applied. 2 AN values are corrected for total recovery based on 1.6 g N applied as NH4-N.

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58 0 20 40 60 80 100 05101520253035 Temperature (C)Total N Recovery (%) AN Urea CRF1 CRF2a CRF2b CRF3 CRF4 CRF5 CRF6 Figure 4-14. Total N recovery from di ssolution and residual analysis across all temperatures. 0 20 40 60 80 100AN Urea CRF1 CRF2a CRF2b CRF3 CRF4 CRF5 CRF6Fertilizer ProductsRecovery (%) Residual Solution 0 20 40 60 80 100AN Urea CRF1 CRF2a CRF2b CRF3 CRF4 CRF5 CRF6Fertilizer ProductsRecovery (%) Residual Solution 0 20 40 60 80 100AN Urea CRF1 CRF2a CRF2b CRF3 CRF4 CRF5 CRF6Fertilizer ProductsRecovery (%) Residual Solution 0 20 40 60 80 100AN Urea CRF1 CRF2a CRF2b CRF3 CRF4 CRF5 CRF6Fertilizer ProductsRecovery (%) Residual Solution Figure 4-15. Graphical breakdown of the total recovery of fe rtilizer treatments at various temperatures. A) 5C, B) 10C, C) 15C, D) 20C, E) 25C, F) 30C, G) variable temperatures. A B C D

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59 0 20 40 60 80 100AN Urea CRF1 CRF2a CRF2b CRF3 CRF4 CRF5 CRF6Fertilizer ProductsRecovery (%) Residual Solution 0 20 40 60 80 100AN Urea CRF1 CRF2a CRF2b CRF3 CRF4 CRF5 CRF6Fertilizer ProductsRecovery (%) Residual Solution 0 20 40 60 80 100AN Urea CRF1 CRF2a CRF2b CRF3 CRF4 CRF5 CRF6Fertilizer ProductsRecovery (%) Residual Solution Figure 4-15. Continued. and tied with twine. Enough bags were prepar ed for three replicates of each product to be removed from the field every two weeks ove r the growing season (7 total samplings at 20, 35, 48, 62, 76, 91, and 104 DAP). At two-week intervals, meshbags were removed from the field, air-dried, and sieved with a 20mesh sieve to remove soil particles. The prills were then ground to di srupt the polymer coating a nd the residual fertilizer dissolvedand analyzed by TKN analysis. Also an alyzed were pure fertilizer prills to give a baseline of total availabl e N before field application. Meshbag Experiment Results ANOVA testing for the treatment and samp ling date main effects revealed a significant interaction between th e effects (Table 4-17). As it was not of interest to evaluate every fertilizer product and sampli ng date combination, the various fertilizer products were evaluated at each sampling date (Table 4-18, Figure 4-16). For each of the E F G

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60 Table 4-17. ANOVA table for released N (% of applied) by fertilizer treatment and sampling date main effects. Source DF Type III SS MS F Value Pr > F Trt 5 1.68010.33695.6< 0.0001 Date 6 2.19650.366104.16< 0.0001 Rep 2 0.0070.00350.990.3743 Trt*Date 30 0.4630.01544.39< 0.0001 Error 82 0.28820.0035 Corrected Total 125 4.6347 sampling dates, AN, a water-soluble fertiliz er, and CRF1, a product that breaks up into tiny granules, were not recovered. Accordin gly, no residual analysis was performed. CRF3 had the greatest release of N by day 20, statistically higher than all other CRF products except CRF2b. However, CRF3 at s ubsequent samplings released only 10% of applied more, similar to a water soluble product. At 20 DAP, CRF2a had released only 31% of its N, yet by the 104 DAP, it had releas ed a total of 72% of its total contents 28% was still in the prills after 104 days. CRF6, at 20 DAP, had released less fertilizer than any other product, 23%. However, it continued to releas e steadily throughout the season and by 104 DAP it had released 90% of its contents. For potato production in Florida, it is desirable to have around 70 to 80 % release by full flower which occurs around 60 days after planting. Of the CRF products evaluated, CRF2b, CRF3, CRF4, and CRF5 all met that criteria, though CRF 3 would likely not perform well for potato production because after its initial high release, little fertiliz er was subsequently released for plant use. Figure 4-17 converts Figure 416 from a DAP to a degree-day basis, using a base temperature of 5C. This is us eful for calculating nut rient release based on physiological age of the plan t and adjusts for seasonal temperature variations.

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61Table 4-18. Cumulative N release (%) from CRF pr oducts at each sampling date for each fertilizer. DAP1 Fertilizer 20 35 48 62 76 91 104 CRF2a 31cd2 57b 63b 60c 70d 70c 72c CRF2b 63ab 86a 93a 94a 99a 98a 99a CRF3 85a 89a 89a 90ab 91ab 96a 95ab CRF4 48bc 72ab72ab81b 84bc 88b92ab CRF5 41b-d62b 75ab87ab 89a-c 94a 94ab CRF6 23d 57b 55b 65c 78cd 84b89b ANOVA p -value 0.00010.00020.00100.0001 0.00010.00010.0001 Tukey LSD 24192311 11581 DAP = Days after planting. 2 Means in columns followed by same letters not significantly different. 0 20 40 60 80 100 020406080100120 Days After Planting (DAP)Applied N released from prills (%) CRF2a CRF2b CRF3 CRF4 CRF5 CRF6 Figure 4-16. Cumulative N release (% of applie d) from CRF products at each sampling date.

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62 0 20 40 60 80 100 0500100015002000 Growing Degree Days (GDD), CApplied N released from prills (%) CRF2a CRF2b CRF3 CRF4 CRF5 CRF6 Figure 4-17. Cumulative N release (% of applie d) of each fertilizer product as a function of growing degree days with 5C base temperature. CRF Release Discussion Incubator CRF Release and Meshbag Experiment Correlation When the various CRF release, residual, total recovery, and Q10 data from the incubator experiment are considered together with the data obtained from the meshbag experiment, the general release characterist ics of the evaluated CRF products can be readily ascertained for both controlled-tempe rature and field conditions. As a general rule, the fertilizer products had similar release patterns rela tive to each other between the CRF release experiment and the meshbag study. A comparison of the six CRF products that were evaluated in both the meshbag and CRF release experiments is shown in Fi gures 4-18. As the temperature patterns experienced by the CRF products between 2003 (when the meshbag study was run) and the 30 year average (the temperature regime used in the variable temperature incubator experiment) varied, the releas e of each of the products was converted to growing degree days to obtain a common reference point. As mentioned previously, the base temperature for growing degree day conversion was 5C, whic h is the temperature most often used for

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63 0 20 40 60 80 100 0400800120016002000 GDDN Recover y ( % of a pp lied ) Meshbag Beaker 0 20 40 60 80 100 0400800120016002000 GDDN Recover y ( % of a pp lied ) Meshbag Beaker 0 20 40 60 80 100 0400800120016002000 GDDN Recover y (% of a pp lied) Meshbag Beaker 0 20 40 60 80 100 0400800120016002000 GDDN Recover y ( % of a pp lied ) Meshbag Beaker 0 20 40 60 80 100 0400800120016002000 GDDN Recover y ( % of a pp lied ) Meshbag Beaker 0 20 40 60 80 100 0400800120016002000 GDDN Recover y ( % of a pp lied ) Meshbag Beaker Figure 4-18. Comparison of release rates of CRF products between the CRF release experiment and the meshbag experiment on a degree day basis, base temperature of 5C. A) CRF2a, B) CRF2b, C) CRF3, D) CRF4, E) CRF5, F) CRF6. potato growth equations. The incubator expe riment received a total of 13 samplings compared to 7 in the meshbag experiment, though the total number of degree days accumulated in the CRF release experiment was only 1323 compared to the 1850 accumulated in the meshbag experiment. A B C D E F

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64 On the surface, the release rates of the CRF products under the two sampling regimes appear dissimilar. However, if the first sampling date from each experiment were removed, and the slopes of the remain ing lines compared (representing sustained nutrient release over time), the slopes are re markably similar with the exception of CRF2b. The initial sampling date was obser ved to have a high release, likely due primarily to broken, partially-coa ted, or otherwise incompletely sealed fertilizer prills. So in removing these, the relative release of th e fertilizer products can be evaluated. Also from this data, it is encouraging that, after an initial release, the beaker experiment adequately charts the releas e of coated materials. The higher total release rates observed in the meshbag study compared to the beaker experiment, particularly in the firs t sampling, may be explained by the physical environment in which each was found. In th e meshbag study, the fe rtilizer prills would have been subjected to physical abrasion and pressure from su rrounding soil particles together with microbiological action found in the soil environm ent on the prill coatings. In the beaker experiment, fertilizer prills we re maintained in a pool of water with little physical abrasion, and would not have been s ubjected to a full so il-like environment. Fertilizer Release Characteristics AN and urea AN and urea can be used as baseline indica tors for the behavior of water soluble N productsnear 100% release (though not necessar ily recovery) early in the season with little recovery and no residual th ereafter. The poor total recovery of urea is probably due to analytical difficulties in digesting the matrix resulting in low recoveries. As shown in Figure 4-2, A, fertilizer release occurred in one bu rst. Together with the lack of residual fertilizer (as illustrated in Figure 4-13), these data reveal that most of the fertilizer was

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65 released at the first sample date. The laboratory performing the analyses reported extensive difficulty performing digestions on thes e samples. The lab further reported that upon digestion, the samples formed a brownish semi-gelatinous/semi-crystalline gel. This had never previously b een seen by the laboratory (E lisabeth Kennelley, personal communication). Repeated dilutions were n ecessary to process the samples. It is possible that the low recoveries of these samples were due to an incomplete digestion, together with a compounding dilution factor. The reduced recovery of AN is also so mewhat enigmatic. The actual recovery, based on a 3 g sample of N was approximately 33%. However, TKN analysis will detect NH4 and urea nitrogen, but the me thod used does not convert NO3 nitrogen to NH4. Thus, instead of a full 3 g potential N r ecovery, only 1.6 g (that applied in the NH4 form) was potentially recoverable by the TKN method used. If the recovered N was calculated against the amount recoverable by the analysis utilized, reco very values rose to an average of 63% across all sampling dates for AN. As all of the fert ilizer had dissolved into the first sample and would have been subjected to high dilutions, the difference in theoretical and actual re covery may possibly be attributed to dilution error as with urea. CRF1 In the incubator experiment, CRF1 had a high release at 7 days (80% of total released) and by 14 days had released 96% of total released. This, coupled with no residual fertilizer and a constant Q10 value of 1 leads one to the conclusion that this product behaves like a water soluble fertilizer rather than a CRF. The poor total recovery likely follows the pattern set by ureadifficulty in analysis coupled with high dilutions. As no residual fertilizer was recovered from the meshbag, no meaningful comparisons were performed between the two experiments.

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66 CRF2a Similar to CRF1, CRF2a in the incubator ex periment gave a release characteristic of a water-soluble fertilizer in that initial re lease was high with little subsequent release. CRF2a also had a high initial release of a bout 50% of total release by 7 days. Though some amount of fertilizer continued to rele ase over the successive weeks, this fraction was small. The constant Q10 value of 1 reveals limited re sponse to temperature, and the high residual fertilizer found after 92 days reveals that the coating of this product accounts for a large percentage of lockout wh ich is permanently (over the lifecycle of the plant) unavailable fertilizer to the grow ing crop. Because of the high residual and low release, it is likely that the early fertilizer flus h was due to fertilizer prills that either had damaged coatings or were incompletely coated. In the meshbag experiment, CRF2a followe d a similar release pattern to that observed in the incubator experiment. At 20 DAP, total N release was approximately 30% and by 104 days, total N release was onl y 72%. Thus, even under field conditions, substantial nutrient was retained in the fert ilizer prills, unavailable for nutrient uptake. Correlation between the two experiments (Figure 4-18, A), re vealed a similar release pattern after the first two samplings wi thin each. The difference in initial release may be due to prill degradatio n/abrasion under field conditions. CRF2b CRF2b proved to be one of the best candi dates for further research. The initial fertilizer release from the incubator experi ment was moderate except for high levels at the 25C and 30C temperatures while cont inued release occurred over a number of weeks. Its total cumulative release wa s near 80% by 92 days (for the variable temperature incubator) and re sidual fertilizer at the highe r temperatures was around 10%

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67 or less. Q10 values ranged from 1.3 between 5C and 15C to 2.1 between 20C and 30C. In the meshbag experiment, greater than 60% of the product had been released by 20 DAP, while by 104 days, greater than 99% had been released. CRF2b was the only CRF product evaluated in both release experi ments where a different shaped release curve was obtained for each. The reason for this difference is unknown, though different products may have different responses fiel d conditions. Thus, the involvement of biological activity on fertilizer prills or soil abrasion, both of which were absent in the incubator experiment, may be factors. CRF3 CRF3 appeared to have similar releas e patterns as CRF1 and CRF2a in the incubator experimenta spike of releas e early in the grow ing season and limited response to temperature (Q10 constant at 1). Unlike CRF1 or CRF2a, it had a period of release between 35 and 57 days. The lack of residual fertilizer, especially at warmer temperatures, reveals limited problem with lockout. Q10 values for this product ranged around 1 for all temperature comparisons, indi cating that release was not temperature controlled. From the meshbag experiment, CRF3 had released 85% of applied N by the first sampling date (20 DAP), while 10% was released over the succeeding 84 days. Correlation between the two expe riments revealed that except for the first sampling date at which samples in the meshbag experiment had nearly 8 times as much fertilizer released as in the incubator experiment, sust ained release of the product was very similar between the two experiments.

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68 CRF4 CRF4 had a high initial release (day 7), but exhibited continued steady release up to nearly 40 days. The product had a Q10 of 1 across all temperature comparisons; thus release was not influenced by temperature. Residual fertilizer ranged from nearly 40% at 5C to about 8% at 30C. In the meshbag experiment, CRF4 had releas ed nearly half (48%) of its nutrient by the first sampling date, though an additional 44% was released fairly consistently over the successive weeks. Correlation between the two experiments was very similar with the exception of the amount of N recovered at the first samplinga phenomenon seen with all of the products. CRF5 CRF5 had a moderate nutrient release at day 7, but even higher release (with the exception of the 30C temperature) in subseque nt weeks. Total release approached 80% by 92 days, but the positive slope of the cumu lative release and the positive value on the weekly release curves indicate th at more fertilizer would have been released had the trial period extended for a longer span. Of a ll of the CRF products evaluated, CRF5 also exhibited the greatest Q10 valuesabout 1.4 between 5C and 15C to nearly 3 between 20C and 30C. Thus, the product release coul d closely pattern temperature-related plant growth, though release rates varied with temperature. Because of its high Q10 value, amount of residual fertilizer also indicated a st rong relationship to temperature. At 5C, residual fertilizer was nearly 64% while at 30C residual fertilizer was only 4%. In the variable temperature incubator, total residual N was approximately 22%. In the meshbag experiment, CRF5 had rel eased 41% of its contents by 20 DAP while by 104 DAP, it had released 94%. As wi th the incubator experiment, the lack of

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69 residual is promising in that it was nearly all available during the plant growing season. Further, with nearly 60% of the fertilizer re maining in the prills after 20 DAP, substantial N was available through the middle and late parts of the season. Correlation between the two experiments wa s generally good with the exception of higher initial release in the me shbag experiment. Release fr om the incubator experiment was not yet completed during the time period evaluated whereas it was largely complete in the meshbag experiment after the same number of degree days. CRF6 CRF6 exhibited desirable release character istics. Of all of the CRF products evaluated, it was the only one that did not have a high initial fertilizer release at day 7, and it continued to have slow and controlled-release over the duration of the experiment. This fertilizer in the variable temperature in cubator had peak release at 78 days, resulting in less than 30% total release to date. This is less than half of the desired 75% release desired by 60 DAP. Q10 values averaged 1 between 5 and 15C and approximately 1.6 over between 10C and 20C through 20C and 30C. Residual fertilizer showed a correspondingly sharp decline with increasing temperature with nearly 80% residual fertilizer in the 5C and 10C incubators dow n to less than 20% in the 30C incubator; residual fertilizer in the variable temperature incubator was 47%. In the meshbag experiment, total N release was 23% at 20 DAP which gradually increased to 89% release by 104 DAP. This, re sulted in substantia l release during the middle and late portions of the season, though lik ely too slowly to be useful to plants during peak growth. Correlation between the two experiments was generally good after two samplings. In the field (meshbag experiment) substant ial release was observ ed until 35 DAP, after

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70 which sustained slow release was observe d, whereas in the incubator experiment, substantial initial release never occurred. Rather, slow steady release was observed throughout the entire experiment. Nitrification and denitrification The possibility of N being nitrified or ev en denitrified and hence unavailable for recovery by TKN was evaluated by anal yzing a subset of samples for NH4 and NO3 content. Since the N in all of the CRF pr oducts is from urea, the ubiquitous urease enzyme would be necessary to convert urea to ammonium and the bacteria Nitrosomonas spp. and Nitrobacter spp. would be necessary to convert ammonium to nitrit e then nitrate, respectively. For denitrification, N would have been required to be converted to either nitrate or nitrite by the previously menti oned bacterium species and then reduced by various denitrifying bacteria, c onverting nitrite to nitrous oxid e or nitrogen gas. In the cases of either nitrific ation or denitrification, bacteria would have to be introduced into the environment and they would require a car bon sourceneither of which is likely in a sterile bottle with DI wate r and no substantial carbon supply. From the analysis of the CRF samples, no significant quantity of amm onium was found (the maximum amount in one sample was 100 mg L-1 with the rest bei ng baseline), and no n itrate was found (data not shown). Thus, some small amount of ammonification may have occurred in some samples, but no nitrification or subsequent denitrification likely followed afterwards. Therefore, most of the N in the CRF samp les would have been in a chemical form available for TKN analysis, except for NO3-N in AN as previously discussed. Plant uptake requirements In order for N release characterizations to be useful, the general shape of the N uptake curve for the life cycle of potato shoul d be understood. Thus, the ideal nutrient

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71 release curve for a fertilizer product can matc h the ideal uptake curve. As plants very early in the season (0-10 days) rely solely upon nutrients contained in the seed tuber (no roots have formed in this time), no outside fertilizer nutrients are necessary. After approximately 10 days, when the plant has emerged from the soil and has begun forming a root system, active soil nutrient uptake begi ns. This rate of uptake rapidly increases and continues for nearly 60 days in Atlant ic potato. By full flower, which occurs around 60 days in northeast Florida, approximate ly 75% of the fertilizer nutrients should have been released and available for uptake. During the next 20 days of the season, the remaining 25% of nutrients should be release d, as nutrient uptake after around 85 days is minimal (Ojala et al ., 1990; Westermann, 1993). Of the CRF products evaluated, all excep t CRF6 had high nutrient release very early in the release periods, right when N uptake capacity of the plant is minimal. CRF2b, CRF4 and CRF5 exhibited the best re lease profiles under field conditions (meshbag experiment), although all could be im proved if initial release was delayed for 10-14 days to allow the emerging plant to be come established. CRF6 exhibited sustained release over the experiment t hough total release was too delaye d to be of maximal use to the plant. This product could be improved if initial release occurred earlier in the season, followed by greater sustained re lease rates through 80 DAP. Methodology improvement As already discussed, urea, CRF1, CRF2 a, and CRF3 all had low total N recoveries. These products also had little or no residual fert ilizer and a single large flush of nutrients at day 7. This lik ely created difficulties in anal ysis by TKN. This could be solved by analyzing all samples by combustion by the Dumas method. No digestions or dilutions are necessary with this method. Fu rther, the Dumas method reads N whether in

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72 the nitrate, ammonium, or urea form (all N is atomized), so would read AN as well (Watson and Galliher, 2001). Another possible point of improvement in methodology could be accomplished by adding field soil to the beak ers. This could possibly introduce a more abrasive environment for greater polymer coating disruption and a supply of microorganisms. It would however complicate the taking of week ly samples because of the difficulty of keeping soil out of the sample aliquot. However, if these CRF release data were found to correlate well to data from similar tests perfor med in the field, such adjustments would be unnecessary. Summary Of the CRF products evaluated, CRF 2b, CRF4, CRF5, and CRF6 showed characteristics most favorabl e to potato production. They all released in increasing quantities with temperature (Q10 > 1), had release periods ov er a period of many weeks, and released a high percentage of fertilizer (low residual) indicating low levels of lockout. Though none of the fertilizer produc ts released 75% of total N by full flower in the incubator experiment, CRF2b, CRF3, CRF4 and CRF5 all met that criteria in the meshbag experiment. In the incubator e xperiment, CRF2b, CRF4, and CRF5 appeared to release excessive amounts of N early in the experiment (7 days), while CRF6 had comparatively little release early. All four of them also appeared to have too long of longevity in the incubator experiment. In the meshbag experiment, these four products had even a higher initial releas e of nutrients, though continued release appeared similar to the beaker experiment. CRF1, CRF2a, and CRF3 appeared to release available fertilizer quickly (by day 7), leaving lit tle available nitrogen for subs equent weeks. With CRF1 and CRF3, all of the nitrogen was released in this first week, while CRF2a had large

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73 quantities of N that remained in the prills ove r the entire duration of the experiment. In the meshbag experiment, both CRF2a and CRF3 had higher initial re leases of nitrogen when compared to the incubator experiment at the first sampling date, with no subsequent difference in slope. Of the CRF products evaluated, CRF2b, CRF4, CRF5, and CRF6 would be good products for further evaluation. If the coating characteristics of the prills were modified or if blends were created to bring total N release more in line with crop uptake requirements, the products could provide nutrien ts to plants at times and in quantities needed.

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74 CHAPTER 5 COMPARISON OF CONTROLLED-RELEA SE NITROGEN FERTILIZERS TO AMMONIUM NITRATE ON POTATO PRODUCTION If controlled-release fertilizers (CRF) are to be adopted for use in potato production, they must not compromise either yield quantity or quality. Two field experiments were conducted to evaluate the influence of CRF on potato production. These include the CRF Production Experime nt and the Replacement Experiment. Both experiments evaluated the effect of CRFs on total and marketable yields, tuber quality, plant nutritional stat us, and nutrient recovery. CRF Production Experiment The CRF production experiment evaluated th e potential use of CRFs in place of traditionally-used ammonium nitrate (AN), a nd was set up with six CRF products (CRF1 through CRF6). This experiment was designe d to determine if N from CRF materials remained in the soil longer than a similar ra te of a soluble fertilizer source. The CRF products were also evaluated to determine opt imal N rates by evaluating yield response to N applications at rates of 112 kg ha-1 N, 168 kg ha-1 N, and 225 kg ha-1 N, corresponding to 50%, 75%, and 100% of the current BMP rate for the area. The CRF products evaluated were chosen because they represente d a broad product diversity with respect to N release patterns and were preliminary produc ts from manufacturers aiming to design a fertilizer that meets the specific needs of potato growers. The AN treatment cannot be considered a grower standard treatment because all N was applied at the beginning of the season, whereas growers apply AN in split applications.

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75 Total and Marketable Yields The data were analyzed factorially by fe rtilizer product and rate main effects. ANOVA tables for total and marketable yiel ds are shown in Table 5-1 and Table 5-2, respectively. Because the rate by product ma in effect was significant for both total and marketable yields, their simple effects were evaluated (Table 5-3). Total and marketable yields with the CRF production experiment we re highest with plants in CRF2 (224 kg ha1 N) at 38.3 and 33.8 Mg ha-1, respectively, and with plants in CRF4 (224 kg ha-1 N) at 37.8 and 32.8 Mg ha-1, respectively. Marketable yields from both of these treatments were significantly higher than those achieved from any of the AN treatments. Figure 5-1 illustrates the total and marketable yields obta ined for each fertilizer treatment as well as the no fertilizer control. All plants in fer tilized treatments resulted both in higher total and marketable yields than those in the no fertilizer control (No N). Total yields from CRF fertiliz ed plants were not higher th an with any of the plants fertilized in the AN treatments (see AN, 224 kg ha-1 N, 33.4 Mg ha-1; Table 5-3). When Table 5-1. ANOVA table for to tal yields by fertilizer and rate main effects. Source DF Type III SS MS F Value Pr > F Fert 61060911768214.86< 0.0001 Rate 2731693658430.75< 0.0001 Rep 31090436353.050.0304 Rate*Fert 12140439117039.84< 0.0001 Error 1441713501190 Corrected Total 167501952 Table 5-2. ANOVA table for mark etable yield by fertilizer rate and main effects. Source DF Type III SS MS F Value Pr > F Fert 6 1121441869119.03< 0.0001 Rate 2 1008205041051.33< 0.0001 Rep 3 1437547924.880.0029 Rate*Fert 12 1297881081611.01< 0.0001 Error 144 141415982 Corrected Total 167 498542

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76 Table 5-3. Total and marketable yield simple effects. N rate Total yield Marketable yield1 Fertilizer kg ha-1 Mg ha-1 Mg ha-1 AN 112 23.2fg2,3 16.7hi AN 168 28.9b-f 19.8f-h AN 224 33.4a-d 24.9c-g CRF1 112 28.9b-f 22.6d-h CRF1 168 29.5b-f 25.6c-e CRF1 224 16.7g 13.0i CRF2 112 29.7b-f 22.2d-h CRF2 168 34.4a-c 28.4a-d CRF2 224 38.3a 33.8a CRF3 112 25.6ef 19.2g-i CRF3 168 34.1a-d 28.5a-d CRF3 224 30.7b-e 26.5b-e CRF4 112 28.3c-f 22.1e-h CRF4 168 32.6a-e 26.7b-e CRF4 224 37.8a 32.8ab CRF5 112 28.0c-f 22.5d-h CRF5 168 31.8a-e 26.3c-e CRF5 224 35.5ab 30.0a-c CRF6 112 27.1d-f 21.2e-h CRF6 168 32.5a-e 26.5b-e CRF6 224 34.8a-c 30.3a-c ANOVA p -value < 0.0001< 0.0001 Tukey LSD 6.35.7 1 Marketable Yield: size classes 2 to 4. 2 Means in columns followed by same letters not significantly different. 3 Plants in the control tr eatment yielded 6.0 and 3.8 Mg ha-1 for total and marketable yields, respectively. compared to AN fertilized plants at the BMP rate (224 kg ha-1 N), potatoes with all six CRF products with the 168 kg ha-1 N rate had 3 to 14% higher marketable yields. Marketable yields with five of the CRF treatments (CRF1 excluded) at the 224 kg ha-1 N rate were 7 to 36% higher than marketable yield with the AN at the BMP rate. Low yields with CRF1, 224 kg ha-1 N are due to poor stand establishment with that treatment.

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77 0.0 10.0 20.0 30.0 40.0 50.0No N, 0 AN, 112 AN, 168 AN, 224 CRF1, 112 CRF1, 168 CRF1, 224 CRF2, 112 CRF2, 168 CRF2, 224 CRF3, 112 CRF3, 168 CRF3, 224 CRF4, 112 CRF4, 168 CRF4, 224 CRF5, 112 CRF5, 168 CRF5, 224 CRF6, 112 CRF6, 168 CRF6, 224TreatmentTuber total yiel d (Mg ha-1) 0.0 10.0 20.0 30.0 40.0No N, 0 AN, 112 AN, 168 AN, 224 CRF1, 112 CRF1, 168 CRF1, 224 CRF2, 112 CRF2, 168 CRF2, 224 CRF3, 112 CRF3, 168 CRF3, 224 CRF4, 112 CRF4, 168 CRF4, 224 CRF5, 112 CRF5, 168 CRF5, 224 CRF6, 112 CRF6, 168 CRF6, 224TreatmentTuber marketable yiel d (Mg ha-1) Figure 5-1. Total and marketable tuber yields by treatment. A) total yield, B) marketable yield. Specific Gravity The ANOVA table for specific gravity by pr oduct and rate main effects indicates a significant rate by product interaction (Table 5-4). Simple effects analysis for specific gravity (SG) ranged from a low of 1.074 with AN (112 kg ha-1 N) to a high of 1.084 with CRF2 (224 kg ha-1 N) (Table 5-5, Figure 5-2). Only plants fertilized with CRF2 with 224 A B

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78 kg ha-1 N had SG significantly higher than pl ants fertilized with any of the AN treatments. The control trea tment (no N) had a SG of 1.065. Table 5-4. ANOVA table for spec ific gravity by rate and fert ilizer source main effects. Source DF Type III SS MS F Value Pr > F Fert 6 0.000590.000111.52< 0.0001 Rate 2 0.00010.000056.110.0028 Rep 3 0.000630.0002124.73< 0.0001 Rate*Fert 12 0.000270.000022.610.0036 Error 144 0.001220.00001 Corrected Total 167 0.00281 Table 5-5. Potato tuber specifi c gravity by simple effects. N rate Specific Fertilizer kg ha-1 gravity AN 112 1.074c1,2 AN 168 1.075c AN 224 1.077bc CRF1 112 1.081ab CRF1 168 1.081ab CRF1 224 1.077bc CRF2 112 1.079a-c CRF2 168 1.082ab CRF2 224 1.084a CRF3 112 1.080a-c CRF3 168 1.081ab CRF3 224 1.079a-c CRF4 112 1.077bc CRF4 168 1.081ab CRF4 224 1.081ab CRF5 112 1.078a-c CRF5 168 1.079a-c CRF5 224 1.079a-c CRF6 112 1.075c CRF6 168 1.078bc CRF6 224 1.079a-c ANOVA p -value < 0.0001 Tukey LSD 0.005 1 Means in columns followed by same letters not significantly different. 2 Tubers from the control treatment had a specific gravity of 1.065.

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79 1.060 1.065 1.070 1.075 1.080 1.085No N, 0 AN, 112 AN, 168 AN, 224 CRF1, 112 CRF1, 168 CRF1, 224 CRF2, 112 CRF2, 168 CRF2, 224 CRF3, 112 CRF3, 168 CRF3, 224 CRF4, 112 CRF4, 168 CRF4, 224 CRF5, 112 CRF5, 168 CRF5, 224 CRF6, 112 CRF6, 168 CRF6, 224TreatmentSpecific Gravity Figure 5-2. Potato tuber sp ecific gravity by treatment. SG values were relatively high for the produc tion site in 2003. Potatoes with most treatments had SG of 1.078 or greater, w ith the highest gravities as high as 1.084. Notably, the tubers in treatments with highest SG were also the hi ghest yielding plants. Tuber Quality In the CRF production experiment, no signi ficant rate by produc t interaction was found for the tuber quality parameters of percent green, percent growth crack (GC), percent rotten (Rot), percent hollow heart (HH), percent brown rot (BR), and percent corky ring spot (CRS). Accordingly, main eff ect analysis results for these parameters is shown for fertilizer products (T able 5-6) and for N rates (Table 5-7). Within the fertilizer product main effect, none of the parameters tested were significantly different either within CRF products or compared to AN. However, within the rate main effect, a significantly greater pe rcentage of green and growth crack potatoes was observed with potatoes grown at higher N rates than at the 112 kg ha-1 N rate.

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80 Table 5-6. Potato tuber quality by fertilizer source main effect. Green1GC Rot HH BR CRS Fertilizer % % % % % % AN 1.80.64.24.40.2 0.0 CRF1 2.41.13.54.40.0 0.0 CRF2 1.10.53.71.70.0 0.0 CRF3 2.30.44.13.30.0 0.2 CRF4 1.00.43.92.70.2 0.0 CRF5 1.11.04.31.30.0 0.0 CRF6 1.10.24.11.00.0 0.0 ANOVA p -value 0.03230.04910.97550.0190.5327 0.4278 Tukey LSD nsnsnsnsns ns 1 Green = green, GC = growth cracks, Rot = rotten, HH = hollow heart, BR = brown rot, CRS = corky ring spot. Table 5-7. Potato tuber quality by rate main effect. N rate Green1 GC Rot HH BR CRS kg ha-1 % % % % % % 112 0.7 b2 0.3b 5.3a 2.7 0.1 0.0 168 1.7 a 0.5ab 3.9b 2.9 0.1 0.0 224 2.3 a 0.9a 2.8b 2.5 0.0 0.1 ANOVA p -value 0.00020.01090.00010.9008 0.6012 0.3704 Tukey LSD 0.8 0.5 1.4 ns ns ns 1 Green = green, GC = growth cracks, Ro t = rotten, HH = hollow heart, BR = brown rot, CRS = corky ring spot. 2 Means in columns followed by same letters not significantly different. Significant rate by product interactions were found fo r percent misshapen (MS, p = 0.0059) and percent internal heat necrosis (IHN, p = 0.0115). Results of simple effects analysis are presented in Table 5-8. For MS potatoes, greatest perc entages resulted from AN fertilized treatments at 224 kg ha-1 N, and was statistically similar only to plants fertilized with AN at 168 kg ha-1 N. All CRF products indepe ndent of rate resulted in tubers with similar quantities of misshapes. IHN was highest in tubers with AN fertilized plants at 168 kg ha-1 N at 30.0%. This was significantly higher than all other treatments except AN with 224 kg ha-1 N and CRF6 at 112 kg ha-1 N. None of the CRF products were significantly different from each other in incidence of IHN.

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81 Table 5-8. Potato tuber quality by treatment. N rate Mis1 IHN Fertilizer kg ha-1 % % AN 112 0.2b2,311.3bc AN 168 1.0ab 30.0a AN 224 2.0a 20.0ab CRF1 112 0.5b 6.9bc CRF1 168 0.0b 5.0bc CRF1 224 0.5b 10.0bc CRF2 112 0.3b 7.5bc CRF2 168 0.0b 3.1bc CRF2 224 0.3b 7.5bc CRF3 112 0.3b 10.0bc CRF3 168 0.2b 7.6bc CRF3 224 0.0b 5.6bc CRF4 112 0.0b 5.0bc CRF4 168 0.3b 8.8bc CRF4 224 0.4b 2.5c CRF5 112 0.3b 10.6bc CRF5 168 0.8ab 8.1bc CRF5 224 0.0b 3.8bc CRF6 112 0.4b 16.9a-c CRF6 168 0.1b 6.9bc CRF6 224 0.0b 5.6bc ANOVA p -value 0.0009 < 0.0001 Tukey LSD 1.4 17.4 1 Mis = misshapen potatoes, IHN = internal heat necrosis. 2 Means in columns followed by same letters not significantly different. 3 Tubers from the control treatment had 0.4% Mis and 52.4% IHN. Stand Establishment The CRF production experiment had variable st and establishment, which was influenced by fertilizer treatment (Table 5-9). Pl ants fertilized with CRF1 with 224 kg ha-1 N had the lowest establishment of all treatments w ith 47.9% emergence, while those fertilized with CRF4 with 168 kg ha-1 N had the highest establishment of all at 100%. Other notable treatment-affected sta nds were with CRF1 with 168 kg ha-1 N at 69.2%

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82 Table 5-9. Potato stand establishment for the CRF production experiment. emergence and with CRF3 with 224 kg ha-1 N at 72.1% emergence. With the exception of these three low stand treatments, most pl ants in treatments had stand establishment >95% while two (CRF1, 112 kg ha-1 N and CRF3, 168 kg ha-1 N) had < 90% stand establishment. The reduced stand counts, especially for CRF1 at the high rate likely account directly for the low observed marketab le and total yields. Though not analyzed statistically, it should be noted that this product appeared to reduce plant stands and yields independent of the rate applied, and even at the lowe st fertilizer rate (112 kg ha-1 N rate Stand Fertilizer kg ha-1 % No N 0 98.3 AN 112 97.1 AN 168 97.1 AN 224 95.4 CRF1 112 87.1 CRF1 168 69.2 CRF1 224 47.9 CRF2 112 96.3 CRF2 168 95.4 CRF2 224 96.7 CRF3 112 92.1 CRF3 168 87.5 CRF3 224 72.1 CRF4 112 98.3 CRF4 168 100.0 CRF4 224 96.3 CRF5 112 95.0 CRF5 168 97.1 CRF5 224 97.9 CRF6 112 98.3 CRF6 168 97.1 CRF6 224 96.3

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83 N), the stand was only at 87.1%, considerably lower than the 96.1% av erage stand for all of the other fertilizers at the same rate. Plant tissue Most recently matured (MRM) leaf tissu e samples consisti ng of petioles and leaflets were taken bi-weekly from plants in the CRF production experiment and tested for total Kjeldahl nitrogen (TKN). Th e ANOVA table for sampling date, rate, and fertilizer source main effects (Table 5-10) revealed a significant third-order interaction between sampling dates, fertilizer products, an d rates, as well as a significant secondorder interaction betwee n fertilizer products and sampling da tes. As there was no interest Table 5-10. ANOVA table for most recently ma tured leaf TKN by rate and fertilizer product main effects. Source DF Type III SS MS F Value Pr > F Date 3 48470762397161569207991209.9 < 0.0001 Rate 2 33408740281670437014125.09 < 0.0001 Fert 6 7658970381276495069.56 < 0.0001 Rep 3 42525301014175100310.61 < 0.0001 Rate*Fert 12 254254195211878501.59 0.0957 Date*Rate 6 139699796232832991.74 0.1115 Date*Fert 18 1498614386832563556.23 < 0.0001 Date*Fert*Rate 36 830795456230776521.73 0.0087 Error 249 332512737813353925 Corrected Total 335 59051277683 in evaluating each of the simple effects of th ese three factors individually, the rate and product effects were evaluated at each sampling date. Rate by product interactions were not significant at 36 DAP or 64 DA P, though they were at 47 DAP ( p = 0.0240) and 82 DAP ( p = 0.0010). Accordingly, main effect anal ysis was performed for leaf TKN at 36 DAP and 64 DAP, and results are shown for fertilizer product (Table 5-11) and rate (Table 5-12) main effects. Simple effects analysis results for leaf TKN at 47 DAP and 82 DAP are shown in Table 5-13.

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84 Table 5-11. Most recently mature leaf per cent TKN of potato plants by fertilizer source main effect at 36 and 64 DAP. TKN (x 104 g kg-1) Fertilizer 36 DAP1 64 DAP AN 5.7c2 4.8ab CRF1 6.3ab 5.1a CRF2 6.7a 4.4bc CRF3 6.5ab 4.5bc CRF4 6.5ab 4.3c CRF5 6.5ab 4.4bc CRF6 6.2b 4.3c ANOVA p -value < 0.0001 < 0.0001 Tukey LSD 0.5 0.4 2 DAP = Days after planting. 3 Means in columns followed by same letters not significantly different. Table 5-12. Most recently mature leaf percen t TKN of potato plants by rate main effect at 36 and 64 DAP. N rate TKN (x 104 g kg-1) kg ha-1 36 DAP1 64 DAP 112 6.1c2 4.1c 168 6.4b 4.6b 224 6.6a 5.0a ANOVA p -value < 0.0001< 0.0001 Tukey LSD 0.20.2 1 DAP = Days after planting. 2 Means in columns followed by same letters not significantly different. Leaf TKN at 36 DAP was significantly hi gher in the CRF treatments than in AN treatments. However, at 64 DAP, leaf TKN was significantly highest in CRF1. Also at 64 DAP, leaf TKN in AN treatments was among the highest of all fertilizer products. As might be expected, leaf TKN was affected by fertilizer rate main effect both at 36 and 64 DAP; it was significantly highest with 224 kg ha-1 N across all fertilizer products for both dates. Leaf TKN was also significantly different between plants in 168 and 112 kg ha-1 N treatments, with the lowest rate having the lowest average TKN concentration at both 36 and 64 DAP.

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85 Table 5-13. Most recently mature leaf tissue percent TKN of potato plants by fertilizer and rate simple effects. N rate TKN (x 104 g kg-1) Fertilizer kg ha-1 47 DAP1 82 DAP AN 112 4.9fg2,3 2.8d-f AN 168 5.0e-g 3.4a-e AN 224 5.5a-f 3.7a-c CRF1 112 5.4a-f 2.5f CRF1 168 5.9ab 3.6a-d CRF1 224 5.7a-f 4.2a CRF2 112 5.1d-g 2.5ef CRF2 168 5.7a-e 3.0c-f CRF2 224 5.7a-f 3.1b-f CRF3 112 5.1c-g 2.4f CRF3 168 5.7a-f 3.0c-f CRF3 224 5.9a-d 3.9ab CRF4 112 5.0e-g 2.4f CRF4 168 5.3a-f 2.8d-f CRF4 224 5.9a-c 3.1b-f CRF5 112 5.2b-f 2.9c-f CRF5 168 5.5a-f 3.4a-e CRF5 224 6.1a 3.1c-f CRF6 112 4.4g 2.8d-f CRF6 168 5.4a-f 3.1b-f CRF6 224 5.5a-f 3.2b-f ANOVA p -value < 0.0001< 0.0001 Tukey LSD 0.80.9 1 DAP = Days after planting. 2 Means in columns followed by same letters not significantly different. 3 Plants in the control treatment had average TKN of 3.6 and 2.6 x104 g kg-1, at 47 and 82 DAP, respectively. Leaf TKN simple effects at 47 DAP and 82 DAP indicate that hi ghest leaf TKN at the earlier date was found in plants with CRF5 with 224 kg ha-1 N and lowest with CRF6 with 112 kg ha-1 N. At 82 DAP highest leaf TKN wa s found in plants with CRF1 with 224 kg ha-1 N and significantly lowest in bot h CRF1 and CRF4, both with 112 kg ha-1 N.

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86 Plant Biomass Factorial analysis of plant biomass for rate and fertilizer source main effects provides useful information. No significant interactions between rate and product were observed for leaf TKN, stem TKN, leaf dry matter (DM), stem DM, or total (leaf + stem) DM. Accordingly, fertilizer product main eff ect analysis results are shown in Table 5-14 and rate main effect analysis results are shown in Table 5-15. Table 5-14. Plant biomass and tissue nitrogen at full flower (61 DAP) by fertilizer source main effect. Leaf TKN Stem TKN Leaf DM1 Stem DM Total DM Fertilizer 104 g kg-1 104 g kg-1 g plt-1 g plt-1 g plt-1 AN 4.8 ab22.2ab 28.4 12.1 ab 40.5 CRF1 5.1 a 2.3a 28.4 13.6 ab 41.9 CRF2 4.4 bc 1.7cd 24.3 13.1 ab 37.4 CRF3 4.5 bc 2.0bc 35.1 18.5 a 53.6 CRF4 4.3 c 1.5d 27.3 15.3 ab 42.7 CRF5 4.4 bc 1.8b-d 28.4 16.5 ab 44.8 CRF6 4.3 c 1.7cd 22.2 11.2 b 33.5 ANOVA p -value < 0.0001 < 0.0001 0.0819 0.0279 0.0713 Tukey LSD 0.4 0.4 ns 6.9 ns 1 DM = Dry matter; Total DM = Leaf DM + Stem DM. 2 Means in columns followed by same letters not significantly different. Table 5-15. Plant biomass and tissue nitrog en at full flower (61 DAP) by rate main effect. N rate Leaf TKN Stem TKN Leaf DM1 Stem DM Total DM kg ha-1 104 g kg-1 104 g kg-1 g plt-1 g plt-1 g plt-1 112 4.1 c2 1.5c 22.4b 12.7 35.0 b 168 4.6 b 2.0b 30.6a 16.1 46.7 a 224 5.0 a 2.2a 30.3a 14.2 44.5 ab ANOVA p -value < 0.0001 < 0.0001 0.0037 0.0753 0.0138 Tukey LSD 0.2 0.2 6.4 ns 9.8 1 DM = Dry matter; Total DM = Leaf DM + Stem DM. 2 Means in columns followed by same letters not significantly different. Fertilizer source main effects influenced leaf and stem TKN a nd plant dry weight accumulation. Leaf and stem TKN were signi ficantly higher in plants with the AN and CRF1 treatments than from plants with all ot her treatments. No significant difference

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87 was found between fertilizer sour ces for leaf DM or total DM. Plants fertilized with CRF3 had significantly greater stem DM ( 18.5 g) than CRF6 (11.2 g) (Table 5-14). Within the rate main effect, leaf and stem TKN from plants with the 224 kg ha-1 N rate (5.0 and 2.2 x 104 g kg-1, respectively) plots were si gnificantly higher than from plants in the 112 kg ha-1 N rate (4.1 and 1.5 x 104 g kg-1, respectively) but neither were significantly different from t hose fertilized at the 168 kg ha-1 N rate (4.6 and 2.0 x 104 g kg-1, respectively) (Table 5-15). Fertilizer rate did not influence stem dry weight accumulation. Conversely, leaf dry weights with the 168 and 224 kg ha-1 N (30.6 and 30.3 g, respectively) plots were signif icantly higher than with 112 kg ha-1 N (22.4 g) plots. Total dry weight accumulation wa s statistically higher within the 168 kg ha-1 N (46.7 g) plots compared to plants in the 112 kg ha-1 N (35.0 g) plots (Table 5-15). Tuber Nitrogen Uptake and Recovery Efficiency (NRE) ANOVA tables for total tuber N uptake (kg ha-1) and NRE are shown in Table 5-16 and Table 5-17, respectively. Factorial analysis of the fertilizer source and rate main effects revealed a significant inte raction on total tuber N uptake ( p < 0.0001) and NRE ( p = 0.0012). Thus, the simple effects for each rate by product combination were evaluated (Table 5-18). Treatments having plants with the highest N removal were CRF4 (224 kg ha-1 N), CRF2 (224 kg ha-1 N) and CRF5 (224 kg ha-1 N) with 139.1, 134.8, and 132.3 kg ha-1 N, respectively. The greater N uptake in these tr eatments was a function of the higher yields of potatoes, and not a function of more N in t ubers in those treatments (data not shown). These results would be expected because if th ere is more nitrogen present, more would be available for uptake by plants and eventually movement into tubers. Lowest tuber N uptake was by plants within the no fertilizer control with 16.2 kg ha-1 N.

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88 Table 5-16. ANOVA table for N recovery (kg ha-1 N) by fertilizer pr oduct and rate main effects. Source DF Type III SS MS F Value Pr > F Fert 6714411916.25< 0.0001 Rate 2202061010353.06< 0.0001 Rep 35301770.930.4329 Rate*Fert 12118989925.21< 0.0001 Error 6011424190 Corrected Total 8351203 Table 5-17. ANOVA table for NRE by fertil izer product and rate main effects. Source DF Type III SS MS F Value Pr > F Fert 60.17270.02884.12 0.0016 Rate 20.27400.137019.59 < 0.0001 Rep 30.02540.00851.21 0.3134 Rate*Fert 120.27220.02273.24 0.0012 Error 600.41960.0070 Corrected Total 831.1638 When N recovery values were expressed as a percentage recovery of applied N [(Ntubers Ncontrol) 100 / Napplied], there were no significant differences with the exception of CRF1 (224 kg ha-1 N) which had the lowest nutrient recovery efficiency (NRE) of 19.5%, when compared to NRE valu es of all other treatments (44.5 to 65.8%). This is related to it having the highest rate of applied N and low yields due to poor stand establishment. Replacement Experiment The replacement experiment was performed separate from the CRF production experiment to evaluate the feasibility of blending CRF pr oducts with AN. One of the purposes of this is to partially alleviate th e higher of costs of CRF products (compared to AN) by applying a percentage of N as the ch eaper AN. Theoretically, AN would provide a rapid early N supply to potato plants follo wed by controlled N rel ease by the CRF over the remainder of the season.

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89 Table 5-18. Tuber nitrogen uptake and nutri ent recovery efficiency by treatment. N rate Tuber N uptake NRE1 Fertilizer kg ha-1 kg ha-1 % AN 112 71.0gh2,3 49.0a AN 168 103.5a-g 52.0a AN 224 117.4a-d 45.0a CRF1 112 87.2c-h 63.3a CRF1 168 106.1a-g 53.5a CRF1 224 59.8h 19.5b CRF2 112 89.9b-h 65.8a CRF2 168 118.6a-c 61.0a CRF2 224 134.8a 53.0a CRF3 112 77.2f-h 54.3a CRF3 168 113.6a-f 58.0a CRF3 224 115.5a-e 44.5a CRF4 112 81.5d-h 58.3a CRF4 168 108.3a-f 55.0a CRF4 224 139.1a 54.8a CRF5 112 84.3c-h 61.0a CRF5 168 109.2a-f 55.3a CRF5 224 132.3a 51.8a CRF6 112 80.1e-h 57.0a CRF6 168 112.8a-f 57.5a CRF6 224 124.1ab 48.3a ANOVA p -value < 0.0001 < 0.0001 Tukey LSD 36.4 22.0 1 NRE = Nutrient recovery efficiency. 2 Means in columns followed by same letters not significantly different. 3 Plants in the control treat ment had a total N uptake of 16.2 kg ha-1. Two CRF products, CRF4 and CRF6 were used in the replacement experiment. These CRF products were blended with AN at AN:CRF percent ra tios of 0:100, 25:75, 50:50, 75:25, and 100:0. All fertili zer material was broadcast in the field at a constant N rate (168 kg ha-1 N) at planting and does not repres ent a grower standard treatment, because growers typically apply N in split applications. Red LaSoda and Atlantic potatoes were used to determine CRF infl uences with different potato varieties.

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90 No factorial analysis was performed w ith the replacement experiment. Results from the experiment for the two potato varietie s were analyzed separately as there was no interest in comparing the two varieties them selves. Consequently, all analyses were simple treatment comparisons within each potato variety. Total and Marketable Yields Total and marketable yields for Atlantic potatoes were highest with CRF4 in the AN:CRF4 25:75 plots at 29.7 and 21.0 Mg ha-1, respectively, though di fferences were not significant from other blends in either case (Tables 5-19). CRF6 had highest Atlantic total yields in the AN:CRF6 75:25 blend at 27.9 Mg ha-1, though not significantly different from the other CRF6 blends. Highest CRF6 marketab le yields were observed in the AN:CRF6 25:75 blend at 19.4 Mg ha-1, which was significantly higher than the AN treatment (AN:CRF 100:0) (Table 5-20). The reason for this apparent lack of yield response to CRFs may be due to overall lower stand counts (compared with the production experiment) (Table 5-23), po ssibly due to an overabundance of water observed in that field which may have cause d excessive N leaching and/or seed rot. No significant total or marketable yield di fferences were observed in the Red LaSoda plots between 100% AN and any of the blends for either of the CRF products (Table 5-19 and 5-20, respectively). Highest total and marketable yields for plants with CRF4 were with 100% AN (24.7 Mg ha-1) and AN:CRF4 75:25 (14.2 Mg ha-1) treatments, respectively. Highest total and marketable yields for plants with CRF6 were with AN:CRF6 25:75 (25.4 Mg ha-1) and AN:CRF6 50:50 (14.4 Mg ha-1) treatments, respectively. No significant regression equation was found for either total or marketable yields as a function of percent CRF for eith er CRF product or potat o variety (Figure 5-3, A and B).

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91Table 5-19. Total and marketable yields of 'A tlantic' and 'Red LaSoda' potatoes by CRF4 blend. 'Atlantic' 'Red LaSoda' AN:CRF4 Total yield Marketable yiel d Total yield Marketable yield blend1 Mg ha-1 Mg ha-1 %No N %100:0 Mg ha-1 Mg ha-1 %No N %100:0 100:0 22.6 13.1 400 100 24.7 11.8 704 100 75:25 25.7 16.1 492 123 24.5 14.2 845 120 50:50 22.6 14.8 452 113 23.9 13.6 815 116 25:75 29.7 21.0 641 160 21.3 8.5 506 72 0:100 23.8 14.6 445 111 20.8 10.6 636 90 ANOVA p -value 0.0937 0.0641 0.7094 0.4989 Tukey LSD ns ns ns ns 1 CRF4 = 41-0-0. Blends are % of N applied as AN and CRF, respectively. Table 5-20. Total and marketable yields of 'A tlantic' and 'Red LaSoda' potatoes by CRF6 blend. 'Atlantic' 'Red LaSoda' AN:CRF6 Total yield Marketable yield2 Total yield Marketable yield2 blend1 Mg ha-1 Mg ha-1 %No N %100:0 Mg ha-1 Mg ha-1 %No N %100:0 100:0 22.6 13.1b2 400 100 24.7 11.8 704 100 75:25 27.9 17.3ab530 132 22.4 11.6 693 98 50:50 27.2 17.9ab546 136 23.7 14.4 860 122 25:75 27.7 19.4a 593 148 25.4 14.0 839 119 0:100 27.1 15.9ab487 122 24.7 13.5 803 114 ANOVA p -value 0.2517 0.0566 0.8812 0.9206 Tukey LSD ns 6.0 ns ns 1 CRF6 = 43-0-0. Blends are % of N applied as AN and CRF, respectively. 2 Means in columns followed by same letters not significantly different.

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92 0 5 10 15 20 25 30 0255075100 %CRFYield (Mg ha-1) CRF4, mkt yield CRF4, tot yld CRF6, mkt yld CRF6, tot yld 0 5 10 15 20 25 30 0255075100 %CRFYield (Mg ha-1) CRF4, mkt yield CRF4, tot yld CRF6, mkt yld CRF6, tot yld Figure 5-3. Total and marketable potato t uber yields by AN:CRF ratio by variety. A) Atlantic, B) Red LaSoda. Specific Gravity Tuber SG values from tubers with CRF4 blends ranged from 1.078 to 1.080 for Atlantic potatoes and from 1.064 to 1.067 for R ed LaSoda potatoes (Table 5-21). SG from tubers with CRF6 blends ranged fr om 1.075 to 1.081 for Atlantic potatoes and 1.062 to 1.065 for Red LaSoda potatoes (Table 5-22). No significant tuber SG difference was obser ved with either CRF product for any blend within a potato variety. No significant re gression equation for tuber SG was found for either of the CRF products or potato varie ties tested, though an apparent increasing SG A B

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93 trend was observed with CRF6 as the percen tage of AN in the blend increased for both varieties of potatoes (Figure 54). Atlantic tuber specific gravities were within the accepted grade range for northeast Florida production. Table 5-21. Atlantic and Red LaSoda tuber sp ecific gravity by CRF4 blend. AN:CRF4 Specific gravity blend1 'Atlantic' 'Red LaSoda' 100:0 1.079 1.064 75:25 1.078 1.067 50:50 1.080 1.067 25:75 1.080 1.065 0:100 1.078 1.066 ANOVA p -value 0.7414 0.1562 Tukey LSD ns ns 1 CRF4 = 41-0-0. Blends are % of N applied as AN and CRF, respectively. Table 5-22. 'Atlantic' and 'Red LaSoda tuber specific gravity by CRF6 blend. AN:CRF6 Specific gravity blend1 'Atlantic' 'Red LaSoda' 100:0 1.079 1.064 75:25 1.081 1.065 50:50 1.076 1.065 25:75 1.078 1.062 0:100 1.075 1.062 ANOVA p -value 0.1428 0.2395 Tukey LSD ns ns 1 CRF6 = 43-0-0. Blends are % of N applied as AN and CRF, respectively. 1.060 1.065 1.070 1.075 1.080 1.085 0255075100 % CRFSpecific Gravity CRF4, 'Atlantic' CRF6, 'Atlantic' CRF4, 'Red LaSoda' CRF6, 'Red LaSoda' Figure 5-4. Atlantic and Red LaSoda tuber specific gr avity by fertilizer treatment.

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94 Tuber Quality In the replacement experiment, no signi ficant difference in tuber quality was observed for any internal or external tube r disorders for either CRF product, AN:CRF blend, or for either of the potato varieties, with the exception of pe rcent growth cracks. The AN:CRF4 0:100 treatment had a significantl y higher percentage of Atlantic tubers with growth cracks (5.2%) th an did the 50:50 (1.3%) and 25:75 (0.9%) blends. The AN:CRF4 100:0 (3.2%) and 75:25 (2 .3%) blends were not sign ificantly different from any of the CRF4 treatments. Stand Establishment Atlantic potato stands ranged from 61.1% CRF4 (AN:CRF 50: 50) to 79.2% CRF6 (AN:CRF 25:75). Red LaSoda stand count ranged from 67.4% CRF4 (AN:CRF 25:75) to 90.3% CRF6 (AN:CRF 25:75) (Table 5-23). Lower stand counts observed may in part be explained by the fact that this potato bed is very slightly downhill and relatively wetter than other areas of the farm. Higher water may lead to more rotting of the seed tuber and, in turn, reduced stands. Table 5-23. Plant stand establishment data in the replacement experiment. AN:CRF'Atlantic' 'Red LaSoda' Treatment blend1 % stand % stand No N -64.6 75.0 AN 100:0 63.2 69.4 CRF4 75:25 66.7 76.4 CRF4 50:50 61.1 84.0 CRF4 25:75 77.8 67.4 CRF4 0:100 66.0 70.8 CRF6 75:25 69.4 81.9 CRF6 50:50 69.4 77.8 CRF6 25:75 79.2 90.3 CRF6 0:100 77.1 84.7 1 CRF4 = 41-0-0, CRF6 = 430-0. Blends are % of N applied as AN and CRF, respectively.

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95 Tissue Analysis No periodic tissue sampling was performe d in the replacement experiment. Plant Biomass Whole plant samples were only taken from the Atlantic plots. No significant difference in leaf TKN or leaf, stem, or total (leaf + stem) dry weight was observed between plants within the AN:CRF blends for either of the CRF products (Table 5-24 and 5-25). No significant difference was found in stem TKN with CRF6, though with CRF4, plants with AN:CRF 100:0 had signifi cantly higher TKN concentrations (1.7 x 104 g kg-1) than for with AN:CRF 25:75 blend (1.1 x 104 g kg-1). No significant linear regression equation was found for leaf or stem TKN, or l eaf, stem, or total dry weight for either of the CRF blends or potato varieties evaluated. Tuber Nitrogen Recovery Efficiency There were no significant differences among treatments for the amount of N removed by the tubers. Total N recoveries for CRF4 ranged from 57.9 (AN:CRF 0:100) to 82.9 kg ha-1 N (AN:CRF 25:75) (Table 5-26) a nd from 65.0 (AN:CRF 0:100) to 89.1 kg ha-1 N (AN:CRF 25:75) for CRF6 (Table 5-27). Table 5-24. Plant biomass and tissue nitrogen by CRF4 blend. AN:CRF4 Leaf TKN Stem TKN Leaf DM2 Stem DM Total DM blend1 104 g kg-1 104 g kg-1 g plt-1 g plt-1 g plt-1 100:0 4.0 1.7a3 24.7 15.6 40.3 75:25 3.9 1.5ab 33.7 22.2 55.9 50:50 3.4 1.6ab 35.7 20.0 55.7 25:75 3.0 1.1b 33.0 20.8 53.7 0:100 3.3 1.3ab 28.6 16.0 44.7 ANOVA p -value 0.1106 0.0049 0.38660.2917 0.3772 Tukey LSD ns 0.6 ns ns ns 1 CRF4 = 41-0-0. Blends are % of N applied as AN and CRF, respectively. 2 DM = Dry matter; Total DM = Leaf DM + Stem DM. 3 Means in columns followed by same letters not significantly different.

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96 Table 5-25. Plant biomass and tissue nitrogen by CRF6 blend. AN:CRF6 Leaf TKN Stem TKN Leaf DM2 Stem DM Total DM blend1 104 g kg-1 104 g kg-1 g plt-1 g plt-1 g plt-1 100:0 4.0 1.7 24.7 15.6 40.4 75:25 3.8 1.4 36.5 22.7 59.2 50:50 3.5 1.3 26.9 16.1 43.0 25:75 3.6 1.1 29.2 18.2 47.4 0:100 3.1 1.2 23.4 15.1 38.5 ANOVA p -value 0.1449 0.1182 0.0559 0.1238 0.066 Tukey LSD ns ns ns ns ns 1 CRF6 = 43-0-0. Blends are % of N applied as AN and CRF, respectively. 2 DM = Dry matter; Total DM = Leaf DM + Stem DM. Table 5-26. Tuber nitrogen uptake and nut rient recovery efficiency by CRF4 blend. 'Atlantic' 'Red LaSoda' AN:CRF4 N uptake NRE2 N uptake NRE2 blend1 kg ha-1 % kg ha-1 % 100:0 71.9 42.8 57.2 34.1 75:25 73.5 43.7 56.7 33.7 50:50 62.5 37.2 59.4 35.3 25:75 82.9 49.3 52.8 31.4 0:100 57.9 34.5 52.3 31.1 ANOVA p -value 0.1629 0.1629 0.9588 0.9588 Tukey LSD ns ns ns Ns 1 CRF = controlled-release fertilizer; CRF4 = 41-0-0. Blends are % of N applied as AN and CRF, respectively. 2 NRE = Nutrient recovery efficiency. Table 5-27. Tuber nitrogen uptake and nut rient recovery efficiency by CRF6 blend. 'Atlantic' 'Red LaSoda' AN:CRF6 N uptake NRE2 N uptake NRE2 blend1 kg ha-1 % kg ha-1 % 100:0 71.9 42.8 57.2 34.1 75:25 76.6 45.6 60.1 35.8 50:50 74.6 44.4 56.7 33.7 25:75 82.1 48.9 58.4 34.7 0:100 65.0 38.7 55.3 32.9 ANOVA p -value 0.5224 0.5224 0.9896 0.9588 Tukey LSD ns ns ns Ns 1 CRF6 = 43-0-0. Blends are % of N applied as AN and CRF, respectively. 2 NRE = Nutrient recovery efficiency.

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97 No significant differences in NRE were observed. Percent NRE values for Atlantic tubers 34.5 to 49.3% recovery with CRF4 and 38.7 to 48.9% recovery with CRF6. Red LaSoda NRE results were sim ilar to Atlantic resultsNRE percentages ranged from 31.1% (AN:CRF 0:100) to 35.3% (AN:CRF 50:50) with CRF4, and from 32.9% (AN:CRF 0:100) to 35.8% (AN:CRF 75: 25) with CRF6 (Table 5-26 and 5-27, respectively). No significant linear regres sion equation for N uptake was found for either of the CRF product blends or potato varieties evaluated. CRF Production Studies Discussion CRF Production Experiment The effects of the CRF fert ilizers on potato production gene rally were better than those of AN. There were, however, situations where production parameters were either unimproved or worse with CRF than with AN. These are outlined by fertilizer product. Ammonium nitrate Marketable yields for plants with AN ranged from 16.7 to 24.9 Mg ha-1 for the 112 to 224 kg ha-1 N rates. Overall these yields were somewhat low for the area (Hutchinson et al ., 2003). Specific gravity with AN was al so lower than area averages at 1.077, 1.075, and 1.074 for decreasing fertilizer rates. Plants with AN did not have substantially higher amounts of green, growth cracked, or rotten potatoes, or potatoes with hollow heart, brown rot, or corky ring spot than plants fertilized with CRF. Plants with AN at 224 kg ha-1 N had significantly more misshapen potatoes than with CRF, and tubers with AN at 168 kg ha-1 N had significantly more internal heat necrosis than with CRF, with the exception of CRF6 (112 kg ha-1 N). Stand counts averaged 96% for the three N rates. Leaf tissue N and plant biomass were not grea tly different from CRF treatments. Tuber N uptake and NRE was similar with CRF products.

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98 CRF The CRF products as a whole resulted in higher yields than AN. CRF2 and CRF4, both with 224 kg ha-1 N, had the highest total and mark etable yields of all treatments, while CRF1 (112 kg ha-1 N) had lowest yields (total a nd marketable) of all fertilized treatments. Other products of note were CRF 5 and CRF6, both of wh ich had statistically comparable marketable yields with CRF2 a nd CRF4, at similar rates of application. Specific gravity followed a similar trend to yields. Highest SG were found with CRF2 (224 kg ha-1 N) with 1.084, though most of the other CRF and rate combinations were statistically similar to this. Lowest SG among CRF fer tilized plants was with CRF1 (224 kg ha-1 N). Tuber quality from CRF fertilized plots wa s similar to AN fertilized plots for all measured parameters except misshapen potatoes and potatoes with internal heat necrosis. In the case of these, no CRF product or rate resulted in higher in cidence than another combination, though all CRF-rate combina tions had lower incidence than AN. Stand establishment for the various CRF products averaged 68% for CRF1, 96% for CRF2, 84% for CRF3, 98% for CRF4, 96% for CRF5, and 97% for CRF6. Some possible reasons for the low stands of CRF1, es pecially at the higher rates, may be that the material may have induced dormancy of th e seed tubers, or the fertilizer may have burned back the leading buds and it was not until the fertilizer levels were reduced that the plant could successfully emerge from the soil. One observation was that late in the season some of the potatoes finally emergedi ndicating that at least some of the seed tubers had not rotted, though emergence was delayed. The low observed yields from CRF1 are thus a result of fewer plants produci ng tubers as opposed to fewer tubers per plant.

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99 As mentioned for AN, plant tissue ta ken during the growing season was not outstandingly different between CRF fertilized plants and AN fertilized plants. A trend was observed that early in the season, plan ts with CRF had higher tissue N than AN, whereas late in the season, this trend was re versed. However, considering tuber yield, SG, and quality, it would appear that early ti ssue N concentration is more important to the desirable plant outcome than tissue N concentration late in the season. It is useful to link the various sampling dates to physiological plant age, with sampling date 1 approximately when plants are 20-30 cm tall, sampling date 2 shortly before first flower, sampling date 3 at full fl ower, and sampling date 4 three weeks before harvest. In terms of physiol ogical age, the data from the current study corr elate well to work done by Hochmuth et al (1991), which indicated that at sampling date 1, the most recently matured (MRM) leaf (leaflets + pe tioles) should have a TKN concentration between 3-6 x 104 g kg-1, at sampling date 2, between 3-4 x 104 g kg-1, at sampling date 3, between 2.5-4 x 104 g kg-1, and at sampling date 4, between 2-4 x 104 g kg-1. From this information, the MRM leaf tissue samples take n from the various treatments during the production experiment were somewhat high ea rly in the season and fell to within sufficiency ranges towards the end of the growing season. The increase in leaf TKN concentrations of CRF1 could possibly indicate a late release of that product, fertilizing plants late into the season. The decrease in leaf TKN over the course of the growing season is lik ely due to a depletion of N from the soil coupled with a re-translocation of nutrient s from above ground tissues into developing tubers.

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100 Plant biomass as measured by leaf and stem N, and by leaf, stem, and total DM, revealed that plants with CRF2 through CRF6 we re relatively comparable across all rates (the rate by product interacti on was not significant), though they were different than plants with CRF1 and AN. This may be re lated to the similar observation with plant tissue. In the case of both, it may be due to th e late emergence and growth of plants seen with CRF1, though the reason for this with AN is unknown. Tuber N uptake between the CRF products te nded to decrease with in a fertilizer product with a corresponding decr ease in N rate. Highest N uptake in tubers was from CRF2, CRF4, and CRF5, all with 224 kg ha-1 N. NRE was not different for any of the fertilizer-rate combinations except for CRF1 (224 kg ha-1 N). This was likely due to the poor stands seen with plants in these plots, which resulted in poor yields, indirectly resulting in low NRE. This c ontrasts with results by Zvomuya et al (2003) who reported that nitrogen RE was on average higher with PCU (mean 50%) than urea (mean 43%). Hutchinson et al (2003) reported comparable nutrient use efficiency between CRF and AN products at high rates, but significantly higher efficien cies of CRF products at low rates (112 kg ha-1 N). However, they reported that th at year was fairly dry, resulting in less total fertilizer leach ing away from the root zone for a ll of the products. In this study, the slow release of nutrients did not improve overall efficien cy of use of N between CRF and AN products. Fertilizer rate Despite, many significant interactions resul ting in simple effect s analysis, yields, SG, and tuber quality fro m CRF products at 168 kg ha-1 N did not appear to be substantially less than fr om CRF products at 224 kg ha-1 N. Hutchinson et al (2003)

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101 reported similar results on Atla ntic potatoes. They found that total and marketable yield and SG were not significantly different between 168 and 224 kg ha-1 N. Replacement Experiment No AN:CRF blend from either of the CRF products utilized in the replacement experiment improved yields or SG significantly. CRF6 did in crease marketable yields of Atlantic potatoes some with a 25:75 AN:CRF 6 blend, but this was not observed with Red LaSoda potatoes. No si gnificant effect on tuber qual ity was observed. No effect on stand establishment was observed. No signi ficant effect on leaf TKN, leaf, stem, and total DM was observed. A slightly greater stem TKN level was observed with CRF4 on Atlantic potatoes with 100:0 AN:CRF4. No significant regression equation was found for any of these parameters for either of the CRF products or either of the potato varieties. These results are enigmatic becau se the CRF products are supposed to improve nutrient use and therefore all aspe cts of the plant during its life cycle. This is especially the theoretical outcome under moist conditions. It may be that the absence of change when compared to 100% AN is that the fertiliz er products did not in fact behave as such. Summary In general, all of the CRF products ex cept CRF4 performed better than AN when total and marketable yields were averaged over rate. Presumably this is due to the extended period of availability of the CRF pr oducts. These findings are comparable to those of Zvomuya et al (2003) who reported significantl y higher total and marketable yields with PCU (polymer-coated urea, a CRF) at two rates (148 and 280 kg ha-1 N) than with urea (a water soluble fertilizer) applied in three split applications under excessive irrigation. Fertilization with PCU at 280 kg ha-1 N resulted in higher marketable yields in one study and in higher total and marketable yields in an excessi ve irrigation study

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102 compared to five split applications of ur ea. Zvomuya and Rose n (2001) reported 3.9 and 3.3 Mg ha-1 total and marketable yield increase with POCU over urea alone, respectively. Hutchinson et al (2003) reported highest to tal and marketable yields were obtained either with two different CRF combinations (one at 224 kg ha-1 N and one at 168 kg ha-1 N) or AN + urea (224 kg ha-1 N). Although, tuber quality and quantity were gr eater with the CRF products than with the AN treatments, no comparison can be draw n by comparison to grower yields because the AN treatments did not constitute grower yields as they will typically split their N applications. Typical marketable yi elds for the area range around 36.9 Mg ha-1 (Hutchinson et al ., 2002). Thus, for 2003, marketable yields were somewhat depressed compared to historical averages. Howe ver, as 2003 was a very wet year (see Precipitation, Chapter 6), it was observed that most growers had reduced yields and that the CRF program yielded better than grower programs. Returning to the key question of this st udy, whether CRF products can be used to provide similar total and marketable yields of high-quality potatoes to traditionally-used AN products? It is concluded that CRF products offer no di sadvantage to growers with respect to tuber yield or quali ty, and plant nutritional status when compared to AN. In the recent studies outlined he rein, some CRF-produced pot atoes surpassed AN produced potatoes both in yields and quality. For Florida growers, CRF products provide an alternative to traditional AN fertilizer practices As these products are improved to match crop uptake requirements, future research may find that they are s uperior to AN products under all growing conditions. This may be of particular interest during wet years when nutrient leaching pressures ar e greatest. As this tec hnology is improved, CRF products

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103 may help Florida growers to increase producti vity and profits, thus benefiting the growers and society.

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104 CHAPTER 6 NITROGEN MOVEMENT IN A SU B-SURFACE IRRIGATED POTATO PRODUCTION SYSTEM UTILIZING CONVENTIONAL AND CONTROLLEDRELEASE NITROGEN SOURCES The hypothesis of this research is that controlled-release nitrogen fertilizers (CRF) offer a viable alternative to growers for pr oducing potatoes by main taining or increasing while reducing N contamination of watersheds As part of that hypothesis, if CRF products release nutrients to plants in times and quantities required, little residual will be available for potential movement into water bodi es. This chapter discusses the results of a field experiment designed to determine the timing of nitrogen release from CRF prills and its location in the soil (i.e., soil and water). Soil samples together with well and suction cup lysimeter samples were taken at regular intervals over the growing season. Since the amount of nitrogen found either in so il or aqueous sample s represented only a snapshot of water and soil conditions at the specific time of sampling, it was impossible to quantify how much fertilizer had moved and to where. However, the successive measurements provided trends of amounts of nitrogen found in samples over the growing season. Precipitation and Temperature Precipitation Precipitation quantity and timing coupled w ith temperature over the season, affect potato production and nitroge n fate. Total precipitati on for the 2003 potato growing season (13 Feb through 28 May 2003) was 30.6 cm above the historical average of 28.2 cm (Figure 6-1). Historical averages are based on a 47 year period from 1954 to 2001.

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105 In the first 45 days of the 2003 season, the site received 23.3 cm of precipitation. Historical precipitation averages for this sa me time period are 13.7 cm Thus, the first 45 days of the growing season were more wet th an usual, creating an ideal environment for nutrient leaching. From 45 DAP to harves t at 105 DAP, the 2003 growing season was relatively dry (7.4 cm) compared to the histor ical average (14.2 cm) for the same period. The 7.4 cm precipitation was rece ived mainly during three rain events at 71 DAP (0.9 cm), 77 DAP (1.6 cm), and 98 DAP (4 cm). Th e water table was maintained 56 to 69 cm below the top of the potato row based on historical cultural practices. 0 1 2 3 4 513-Feb 27-Feb 12-Mar 26-Mar 9-Apr 23-Apr 7-May 21-May Calendar Day Precipitation (cm ) Figure 6-1. 2003 daily precipitation in Hastings, FL from 13 Feb to 28 May. Temperature Air temperatures for the 2003 growing season ranged from a low of 1.7C on 31 Mar to a high of 35.7C on 9 May with daily averages shown in Figure 6-2, A. These temperatures are roughly simila r to historical averages, thou gh with greater fluctuations, as would be expected for indivi dual years. Of the two times that air temperatures dipped to near freezing over the season, the first occu rred shortly after plan ting (14 Feb) before

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106 plants had emerged, and was of little con cern. The second event (30-31 Mar) occurred while plants were vigorously growing and c ould have been detrimental to the crop. However, plants appeared not to be affected, and no plant kill was observed. Soil temperatures in 2003 ranged from a low of 12.7C on 14 Feb to a high of 27.2C on 26 May. As with air temperatures 2003 average soil temperatures were roughly similar to historical averages (Figure 6-2, B). 5 10 15 20 25 3013-Feb 27-Feb 12-Mar 26-Mar 9-Apr 23-Apr 7-May 21-MayCalendar DayTemperature (C ) 2003 1975-2000 5 10 15 20 25 3013-Feb 27-Feb 12-Mar 26-Mar 9-Apr 23-Apr 7-May 21-MayCalendar DayTemperature (C ) 2003 1975-2000 Figure 6-2. 2003 and historical air and soil temperatures in Hastings, FL over the potato growing season. A) air, B) soil. B A

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107 Soil Nitrogen Soil samples taken over the duration of the experiment can be separated into two groups: pre-plant soil samples reflecting the N content of th e soil before treatments were implemented, and periodic growing season soil samples reflecting the relative changes in soil N content over the course of the growing season. Both are presented here and are summarized with water data at the end of the chapter. Pre-plant Soil Nitrogen Soils from the experiment area in 2003 contained total of 0.34 mg kg-1 ammonium nitrogen (NH4-N) and 0.29 mg kg-1 nitrate nitrogen (NO3-N) pre-plant. Soil OM levels were 1.06 x 104 g kg-1, pH was 5.82, and the electrical conductivity of the soil was 0.04 dS m-1. Based on those values the amount of N in the top 15 cm of a hectare, there would be about 0.7 kg NH4-N and 0.6 kg NO3-N per hectare of availa ble nitrogen, plus that N tied up in the OM. The N in this OM is not available at proper times or in sufficient quantities to contribute substant ially to the N requirement of the potato crop, as illustrated by the low yields of the non-fertilized c ontrol (No N) (see Table 5-3, footnote 4). Seasonal Soil Nitrogen Soil samples were analyzed factorially by sampling date, fertilizer source, and fertilizer rate. The ANOVA table for NH4-N and NO3-N are shown in Table 6-1 and Table 6-2, respectively. For NH4-N, while the third-order interaction between sampling dates, fertilizer products, and rates, and th e second-order interactions between sampling date and rate and between rate and fertilizer product were not significant, the sampling date by fertilizer product interaction was. For NO3-N, all second-order interactions were significant while the third-order in teraction was not. Accordingly, NH4-N main effect

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108 Table 6-1. ANOVA table for soil NH4-N over all sampling dates. Source DF Type III SS MS F Value Pr > F Date 6191832026.04< 0.0001 Fert 690815112.33< 0.0001 Rate 229814912.12< 0.0001 Rep 3200675.440.0011 Date*Fert 361100312.49< 0.0001 Date*Rate 1210390.70.7525 Fert*Rate 12220181.490.1231 Date*Fert*Rate 7259980.680.9783 Error 438537812 Corrected Total 58710724 Table 6-2. ANOVA table for soil NO3-N over all sampling dates. Source DF Type III SS MS F Value Pr > F Date 6413969023.43< 0.0001 Fert 6336956119.07< 0.0001 Rate 25402270191.76< 0.0001 Rep 34411474.990.0020 Date*Fert 362528702.39< 0.0001 Date*Rate 1214531214.11< 0.0001 Fert*Rate 1222121846.26< 0.0001 Date*Fert*Rate 722721381.280.0705 Error 4381289429 Corrected Total 58735159 Table 6-3. Soil NH4-N by fertilizer source main eff ect over all N rates and sampling dates. Fertilizer NH4-N (mg kg-1) AN 2.30e1 CRF1 2.62de CRF2 4.47bc CRF3 3.24c-e CRF4 3.94b-d CRF5 6.13a CRF6 4.83ab ANOVA p-value 0.0001 Tukey LSD 1.56 1 Means in columns followed by same letters not significantly different. data is shown only for the various fertilizer sources across all sampling dates and rates (Table 6-3). Soils from all plots with CRF2, CRF4, CRF5, and CRF6 had higher

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109 Table 6-4. Soil NO3-N simple effects by fertilizer s ource and rate over all sampling dates. N rate NO3-N Fertilizer kg ha-1 mg kg-1 AN 112 1.10h1,2 AN 168 2.27gh AN 224 4.14e-h CRF1 112 3.12f-h CRF1 168 9.35cd CRF1 224 15.44ab CRF2 112 3.45f-h CRF2 168 5.36c-h CRF2 224 10.44bc CRF3 112 3.15f-h CRF3 168 6.87c-g CRF3 224 18.34a CRF4 112 3.74e-h CRF4 168 4.61d-h CRF4 224 7.59c-f CRF5 112 3.36f-h CRF5 168 8.69c-e CRF5 224 10.14c CRF6 112 2.76f-h CRF6 168 3.61e-h CRF6 224 6.15c-h ANOVA p -value < 0.0001 Tukey LSD 5.21 1 Means in columns followed by same letters not significantly different. 2 Soil from the control treatment had an average NO3-N concentration of 0.82 over all sampling dates. concentrations of NH4-N over the entire season than AN fertilized plots. This may be an effect of prolonged CRF rele ase over the entire growing season, despite numerous rain events that may have leached soil N. Simple effects of each fertilizer source by sampling date interaction on NH4-N for each rate were not of interest and were not analyzed. For NO3-N, rate by product in teractions are shown in Table 6-4. NO3-N was highest in soils with CRF3 at 224 kg ha-1 N over the entire season at 18.3 mg L-1. This

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110 was statistically comparable only to CRF1 at the 224 kg ha-1 N rate. These high soil N concentrations over the entire season are intere sting because yields from these treatments were not the highest. This may be due to hi gh salt concentrations around the seed tubers resulting in dieback of the sprouts. In addition to analysis over all sampli ng dates, soils were also analyzed for differences within each sampling date. No significant interactions between fertilizer source and rate existed for NH4-N at any sampling date during the season. However, interactions were significant at 55 ( p < 0.0001), 69 ( p = 0.0150), and 84 ( p = 0.0011) DAP for NO3-N. The fertilizer source main effects at each sampling date for NO3-N and NH4-N are shown in Table 6-5 and Table 6-6, respectively, while the simple effects for NO3-N at 55, 69, and 84 DAP are shown in Table 6-7. As illustrated by the data, soil NH4-N and NO3-N were lowest in the AN fertilized plots early in the season when it might be expected to be highest. This e ffect may be due to the high mobility of AN which may have moved from the root zone w ith the numerous rainstorms that occurred early in the growing season. Table 6-5. Soil NO3-N by fertilizer source main effect for each sampling date. NO3-N (mg kg-1) Fertilizer 15 DAP1 29 DAP 41 DAP 97 DAP AN 2.38b2 2.36b 1.05b 1.53 CRF1 6.59ab 12.23ab 8.37a 4.35 CRF2 8.05a 17.42a 5.26ab2.61 CRF3 8.08a 14.31a 8.89a 2.76 CRF4 8.15a 13.33a 3.42ab2.21 CRF5 8.00a 16.72a 6.50ab4.31 CRF6 3.95ab 8.35ab 3.12ab3.13 ANOVA p -value 0.0061 0.0003 0.0004 0.1028 Tukey LSD 5.53 10.07 6.56 ns 1 DAP = days after planting 2 Means in columns followed by same letters not significantly different.

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111Table 6-6. Soil NH4-N by fertilizer source main effect for each sampling date. NH4-N (mg kg-1) Fertilizer 15 DAP1 29 DAP 41 DAP 55 DAP 69 DAP 84 DAP 97 DAP AN 1.04 b2 0.88b 0.54 5.67 3.07b 1.80b 3.08ab CRF1 2.89 ab 1.89b 1.03 5.81 2.57b 2.08b 2.05b CRF2 5.58 a 4.85a 1.59 4.73 7.44ab 4.29ab 2.82ab CRF3 3.12 ab 2.52ab1.60 4.57 4.56b 3.80ab 2.49ab CRF4 3.29 ab 3.05ab0.93 5.67 6.80ab 4.73ab 3.13ab CRF5 4.15 ab 5.23a 1.78 7.86 13.20a 5.62a 5.07a CRF6 1.90 ab 2.54ab1.21 5.65 12.47a 6.13a 3.89ab ANOVA p -value 0.0416 0.0004 0.0743 0.8634 0.0015 0.0005 0.0465 Tukey LSD 4.15 2.81 ns ns 7.27 3.04 2.85 1 DAP = Days after planting. 2 Means in columns followed by same letters not significantly different.

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112 Table 6-7. Soil NO3-N by treatment for each sampling date. N rate NO3-N (mg kg-1) Fertilizer kg ha-1 55 DAP1 69 DAP 84 DAP AN 112 0.65c2,31.04c 0.79 c AN 168 2.81c 2.76c 3.44 c AN 224 9.37bc 4.95c 4.74 c CRF1 112 1.27c 1.23c 0.89 c CRF1 168 18.39b 9.98a-c 6.56 bc CRF1 224 20.74ab 23.32a 18.35 ab CRF2 112 3.24c 1.46c 1.75 c CRF2 168 3.20c 2.41c 2.62 c CRF2 224 8.97bc 7.16bc 3.91 c CRF3 112 1.48c 1.37c 1.27 c CRF3 168 6.95bc 4.90c 1.89 c CRF3 224 33.57a 21.80ab 23.21 a CRF4 112 1.62c 1.38c 1.63 c CRF4 168 2.40c 1.80c 2.02 c CRF4 224 9.75bc 5.00c 4.66 c CRF5 112 2.05c 1.62c 1.39 c CRF5 168 7.60bc 4.89c 5.52 bc CRF5 224 9.61bc 8.92a-c 7.22 bc CRF6 112 1.47c 3.01c 1.90 c CRF6 168 1.54c 2.47c 3.23 c CRF6 224 6.70bc 5.62c 6.05 bc ANOVA p -value < 0.0001 < 0.0001 < 0.0001 Tukey LSD 14.35 14.89 13.38 1 DAP = Days after planting. 2 Means in columns followed by same letters not significantly different. 3 Soils from the control treatments had 0.70, 1.03, and 0.92 mg kg-1 NO3-N at 55, 69, and 84 DAP, respectively. Plots fertilized with CRF5 and CRF6 c onsistently had the highest soil NH4-N concentrations from 55 to 97 DAP, while from 41 to 97 DAP, soils in plots fertilized with CRF1 and CRF3 consistently had the highest NO3-N concentrations. This latter phenomenon is particularly evident at the 224 kg ha-1 N rate (Table 6-7). The rate main effects on soil NH4-N and NO3-N concentration are shown in Table 6-8 and Table 6-9, respectively, while NO3-N rate effects at 55, 69, and 84 DAP were

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113 discussed in Table 6-7 due to the significant rate by sour ce interaction. As might be expected, higher NH4-N and NO3-N concentrations were found in soils as N rate increased. This trend conti nued throughout the season for NO3-N, though it was not significant at 15 DAP. This is likely due to the recent rainfall which would have moved any available nutrients below the root zone w/o providing subseque nt time for later N release. Also noteworthy, ear ly in the season, both for NH4-N and NO3-N, soil N was not significantly different be tween the 168 and 224 kg ha-1 N rates. Late in the season, the soils in treatments with the middle N rate had soil N concentrations not higher than those at the low rate. These resu lts would tend to support re duced N application rates considerable N was available early in the seas on while little residual remained late in the season. Combining the soil data together, neither NH4-N nor NO3-N appeared to provide a clear indicator of tuber yiel ds that would result at harv est. No strong trend in N concentration occurred over the season, though this may be due to greatly fluctuating environmental conditions. Well Water Nitrogen Seasonal Well Nitrogen Well samples were analyzed factorially for sampling date, fertilizer source, and rate main effects. The ANOVA tables for NO3-N and NH4-N are shown in Table 6-10 and Table 6-11, respectively. As no main effects can be determined due to interactions, the fertilizer source by rate interaction is of most interest. Accordingly, source by rate simple effects are shown in Table 6-12. From this si mple effect data, highest N concentrations were found in water below plots fertil ized with AN. In the case of NO3-N, highest concentrations were found in AN fertilized plots with 224 kg ha-1 N, while in the case of

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114Table 6-8. Soil NH4-N by rate main effect for each sampling date. Rate NH4-N (mg kg-1) kg ha-1 N 15 DAP1 29 DAP 41 DAP 55 DAP 69 DAP 84 DAP 97 DAP 112 2.83 1.91b2 0.71b5.23 5.23 2.92b2.60 168 3.00 2.93ab1.38a 5.57 7.43 3.83b3.37 224 3.59 4.14a 1.64a 6.32 8.82 5.44a 3.69 ANOVA p -value 0.5791 0.0004 0.0014 0.7024 0.0681 0.0008 0.0974 Tukey LSD ns1.28 0.60 ns ns1.53 ns1 DAP = Days after planting. 2 Means in columns followed by same letters not significantly different.

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115 Table 6-9. Soil NO3-N by rate main effect for each sampling date. Rate NO3-N (mg kg-1) kg ha-1 N 15 DAP1 29 DAP 41 DAP 97 DAP 112 5.95 7.06b2 1.69 c 1.35b 168 6.70 12.65a 4.85 b 2.64b 224 6.71 16.6a 9.15 a 4.97a ANOVA p -value 0.6942 < 0.0001 < 0.0001 < 0.0001 Tukey LSD ns 4.34 2.88 1.72 1 DAP = days after planting. 2 Means in columns followed by same letters not significantly different. Table 6-10. ANOVA table for well NO3-N over all sampling dates. Source DF Type III SS MS F Value Pr > F Date 417754449.65 < 0.0001 Fert 6481380217.43 < 0.0001 Rate 23281643.57 0.0300 Rep 2143871915.63 < 0.0001 Date*Fert 2491153808.25 < 0.0001 Date*Rate 8588731.60 0.1272 Fert*Rate 1222871914.14 < 0.0001 Date*Fert*Rate 482083430.94 0.5826 Error 208957146 Corrected Total 31431999 Table 6-11. ANOVA table for well NH4-N over all sampling dates. Source DF Type III SSMS F Value Pr > F Date 41857464106.37 < 0.0001 Fert 63475813.24 < 0.0001 Rate 21437116.36 < 0.0001 Rep 21681.87 0.1568 Date*Fert 24911388.70 < 0.0001 Date*Rate 8306388.77 < 0.0001 Fert*Rate 1211392.16 0.0146 Date*Fert*Rate 4823351.11 0.2982 Error 2089084 Corrected Total 3144834 NH4-N, statistically highest N concentr ations were found at 224 and 168 kg ha-1 N in AN fertilized plots as well as at 224 kg ha-1 N in CRF1 fertilized plot s. These results are not surprising in that water soluble products like AN would be expected to be mobile in higher quantities than CRF products, and higher rates of such would tend to result in

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116 Table 6-12. NH4-N and NO3-N concentrations in wells by treatment. N rate NH4-N NO3-N Fertilizer kg ha-1 mg L-1 mg L-1 AN 112 1.98b-d1,2 8.20 bc AN 168 4.64ab 13.35 b AN 224 5.68a 23.47 a CRF1 112 1.41cd 0.82 c CRF1 168 1.48cd 6.97 bc CRF1 224 3.88a-c 6.36 bc CRF2 112 0.51d 6.71 bc CRF2 168 1.18cd 4.29 c CRF2 224 1.37cd 3.22 c CRF3 112 0.71d 1.06 c CRF3 168 1.02d 2.99 c CRF3 224 2.16b-d 4.51 bc CRF4 112 0.60d 6.84 bc CRF4 168 0.67d 2.91 c CRF4 224 2.63b-d 3.42 c CRF5 112 0.77d 4.15 c CRF5 168 1.68cd 3.30 c CRF5 224 0.71d 4.39 bc CRF6 112 0.22d 2.17 c CRF6 168 1.58cd 5.69 bc CRF6 224 1.31cd 2.07 c ANOVA p -value < 0.0001 < 0.0001 Tukey LSD 2.76 8.96 1 Means in columns followed by same letters not significantly different. 2 Wells in plots with the control treatment had NH4-N and NO3-N concentrations of 0.18 and 6.03 mg L-1, respectively. greater quantities of nutrient leached. No CRF product at a given rate was significantly different from any other CRF source by rate combination, except for higher NH4-N in CRF1 fertilized plots at 224 kg ha-1 N. Table 6-12 is illustrated graphically in Figure 6-3 and visualizes the increased le aching of nutrients within pl ots fertilized by each product as rate increases. This is pa rticularly well illustrated with NH4-N (Figure 6-3, A). Periodic Well Nitrogen In addition to factorial anal ysis over the entire season, factorial analyses was also performed for each sampling date. Rate by pro duct interactions were not significant for

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117 0 1 2 3 4 5 6No N, 0 AN, 112 AN, 168 AN, 224 CRF1, 112 CRF1, 168 CRF1, 224 CRF2, 112 CRF2 168 CRF2 224 CRF3, 112 CRF3, 168 CRF3, 224 CRF4, 112 CRF4, 168 CRF4, 224 CRF5, 112 CRF5, 168 CRF5, 224 CRF6, 112 CRF6, 168 CRF6, 224Fertilizer, rate (kg ha-1)NH4-N (mg L-1) 0 5 10 15 20 25No N, 0 AN, 112 AN, 168 AN, 224 CRF1, 112 CRF1, 168 CRF1, 224 CRF2, 112 CRF2 168 CRF2 224 CRF3, 112 CRF3, 168 CRF3, 224 CRF4, 112 CRF4, 168 CRF4, 224 CRF5, 112 CRF5, 168 CRF5, 224 CRF6, 112 CRF6, 168 CRF6, 224Fertilizer, rate (kg ha-1)NO3-N (mg L-1) Figure 6-3. Nitrogen in wells by trea tment over all sampling dates. A) NH4-N, B) NO3-N. NO3-N or NH4-N at any of the sampling dates, with the exception of a significant rate by product interaction for NO3-N at 29 DAP ( p = 0.0209). Table 6-13 and Table 6-14 show the fertilizer source main effects across all rates for each sampling date for NH4-N and NO3-N (except 29 DAP), with corresponding fi gures in Figure 6-4 and Figure 6-5, respectively. The simple effects of source by rate for NO3-N at 29 DAP are shown in Table 6-15. A B

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118 Table 6-13. Well NH4-N fertilizer source main e ffects at each sampling date. NH4-N (mg L-1) Fertilizer 29 DAP1 41 DAP 64 DAP 78 DAP 92 DAP AN 16.06a2 4.100.140.18 0.02 CRF1 8.71b 2.100.170.26 0.03 CRF2 3.62bc1.180.040.22 0.04 CRF3 5.16bc1.000.010.22 0.10 CRF4 5.14bc0.930.090.28 0.05 CRF5 3.39bc1.360.130.25 0.14 CRF6 2.69c 2.140.030.27 0.05 ANOVA p-value < 0.0001 0.06390.23410.8321 0.2293 Tukey LSD 5.91 nsnsns ns1 DAP = Days after planting. 2 Means in columns followed by same letters not significantly different. 0 4 8 12 16 20 2941647892 Days After PlantingNH4-N (mg L-1) AN CRF1 CRF2 CRF3 CRF4 CRF5 CRF6 No N Figure 6-4. Well NH4-N concentrations from each fe rtilizer product for each sampling date over the growing season. For NH4-N, highest well concentrations were found below AN fertilized plots early in the season (29 DAP). Subsequent samp lings showed no significant difference between AN treatments and CRF treatments for well NH4-N. Lowest well NH4-N at 29 DAP was found in CRF6 fertilized treatments. NO3-N in wells from AN fertilized plots was significantly greater than in any of the CRF fertilized plots, which were themselves statistically similar to each other. Late in the season no difference was observed between

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119 Table 6-14. Well NO3-N fertilizer source main e ffects at each sampling date. NO3-N (mg L-1) Fertilizer 41 DAP1 64 DAP 78 DAP 92 DAP AN 25.06a2 3.584.93 1.42 CRF1 6.77b 5.204.63 3.84 CRF2 6.92b 6.423.73 3.41 CRF3 4.57b 3.732.33 1.27 CRF4 6.79b 3.725.67 1.73 CRF5 4.85b 6.233.81 2.12 CRF6 3.67b 3.985.77 1.51 ANOVA p-value < 0.0001 0.82530.7825 0.559 Tukey LSD 13.29 nsns ns1 DAP = Days after planting. 2 Means in columns followed by same letters not significantly different. 0 5 10 15 20 25 30 41647892 Days After PlantingNO3-N (mg L-1) AN CRF1 CRF2 CRF3 CRF4 CRF5 CRF6 No N Figure 6-5. Well NO3-N concentrations from each fe rtilizer product for each sampling date over the growing season. AN and CRF treatment well concentrations. At 29 DAP, NO3-N in wells was highest in AN treatments at 224 kg ha-1. Only AN treatments at 168 kg ha-1 N were statistically comparable. AN at the low rate resulted in well NO3-N concentrations not different than any of the CRF products at any rate. No CRF product at any rate was significantly different from any other CRF by rate combination.

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120 Table 6-15. NO3-N concentrations in wells for each sampling date. N rate NO3-N (mg L-1) Fertilizer kg ha-1 29 DAP1 AN 112 21.05bc2,3 AN 168 38.51ab AN 224 60.55a CRF1 112 1.53c CRF1 168 3.84c CRF1 224 4.00c CRF2 112 2.79c CRF2 168 5.01c CRF2 224 1.85c CRF3 112 1.05c CRF3 168 2.17c CRF3 224 3.91c CRF4 112 5.98c CRF4 168 3.46c CRF4 224 2.72c CRF5 112 1.50c CRF5 168 0.22c CRF5 224 6.48c CRF6 112 0.81c CRF6 168 3.46c CRF6 224 0.58c ANOVA p -value < 0.0001 Tukey LSD 26.49 1 DAP = Days after planting. 2 Means in columns followed by same letters not significantly different. 3 NO3-N from wells in the control plot averaged 3.64 mg L-1. Analysis of rate main effects across all fertilizer sources at each sampling date provides additional information. Table 6-16 and Table 6-17 show the results for NH4-N and NO3-N, respectively. As might be expecte d, higher N rates resulted in higher N in wells, particularly early in the season. At no time during the season did wells from plots fertilized at the 168 kg ha-1 rate have significantly higher NH4-N than wells in plots

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121 fertilized with 112 kg ha-1 N. By 64 DAP, well N concentr ations were not significantly different between the various fertilizer rates. Table 6-16. Well NH4-N rate main effect at each sampling date. Rate NH4-N (mg L-1) kg ha-1 N 29 DAP1 41 DAP 64 DAP 78 DAP 92 DAP 112 3.43b2 0.62b 0.060.25 0.07 168 6.17b 2.17ab 0.110.24 0.31 224 9.59a 2.70a 0.100.23 0.07 ANOVA p-value < 0.0001 0.0135 0.59210.8854 0.7673 Tukey LSD 3.43 1.7 nsns ns1 DAP = days after planting. 2 Means in columns followed by same letters not significantly different. Table 6.17. Well NO3-N rate main effect at each sampling date. Rate NO3-N (mg L-1) kg ha-1 N 41 DAP1 64 DAP 78 DAP 92 DAP 112 5.924.234.222.07 168 7.234.985.432.48 224 11.994.873.592.00 ANOVA p-value 0.08720.89030.48960.8846 Tukey LSD nsnsnsns 1 DAP = days after planting. Lysimeter Nitrogen Water sample collection through lysimeters wa s sporadic in 2003 to the extent that no meaningful statistical anal ysis could be performed. This was caused by poor seals on the caps of lysimeters which had been cut to accommodate the desired 30 cm burial depth for water collection. This lack of seal prev ented the maintenance of a vacuum necessary to collect samples. On two sampling dates (20 Mar and 8 May), no solution was obtained from any of the lysimeters. After the 20 Ma r sampling, the lysimeters were re-buried to ensure that there was proper soil-lysimeter contact, but this did not solve the problem. Though no statistical analyses were run, so me trends were noted in the data collected. Highest NO3-N and NH4-N concentrations from any treatment at any sampling date over the season were found in al l three AN treatments (112, 168, and 224 kg ha-1 N)

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122 at 41 DAP, and was as high as 42 mg L-1 for NH4-N and 146 mg L-1 for NO3-N. No comparably high values were found for any CRF treatment at any other time over the season (a high of 11 mg L-1 for NH4-N at 41 DAP, and a high of 17 mg L-1 for NO3-N at 41 DAP). Samples taken at 64 DAP showed no apparent N difference with the AN fertilized plots compared to the CRF fertilized plots. Nutrient Movement Discussion The presence of nitrogen in the soil and wells over the growing season appeared to correlate with observed environmental condi tions. Early in the season, heavy rains translated into nutrient movement into th e perched water table. Work by Zvomuya et al (2003) corroborated these results when they reported that nitrogen fertilizer additions generally increased NO3-N leaching compared with a no fertilizer control. The high concentrations of nitrogen found in wells and lysimeters from the AN treatments early in the season illustrate the relatively high m ovement of nitrogen from the water soluble sources. Early in the season, both air and soil temp eratures were rela tively cool and CRF release may have been correspondingly slow, so it is not unexpected that the relative amounts of nitrogen from the CRF treatments were low early in th e season. Nitrate and ammonium concentrations in th e soil were lower early in the season (15 DAP) than later in the season, the reverse of what would be expected under normal release conditions. However, as the season progressed and rainfall declined, soil nitrogen levels increased as CRF release continued without being leached ou t of the root zone. At the end of the season, all N levels were reduced reflecti ng nitrogen depletion of the bed either by uptake, denitrification, or leaching.

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123 Early in the season (29 DAP), NH4-N in the perched water table below the root zone was 3.4 times as high in the AN treatments as in the CRF while subsequent sampling dates were not significantly differe nt between CRF and AN fertilized plants. Because of a significant rate by product interaction, NO3-N was evaluated at each rate. With 224 kg ha-1 N, NO3-N was 18.9 times as high in the AN versus CRF treatments, with 168 kg ha-1 N, it was 12.6 times as high, and with 112 kg ha-1 N, it was 9.3 times asa high. At 41 DAP, NO3-N from wells with AN treatments was 4.5 times as great as with CRF treatments. This reduced leaching tre nd is consistent with that reported by Zvomuya et al (2003) who reported a 40% reduced nitrate leaching for PCU products compared to urea at a rate of 280 kg ha-1 N. Errebhi et al (1997) reported that 33% N recovery during a wet year (1991) and 56% recovery during 1992 which had fewer leaching events. Returning to the hypothesis that CRF produc ts could reduce the amount of fertilizer leached below the root zones and into wate r bodies during the cropped period. This study showed that CRF products could significantl y reduce the amount of nitrogen moved from the root zone into the perched water table compared to AN. Early in the season this difference was especially marked. CRF produc ts can significantly reduce the amount of leaching of nitrogen into the watershed a nd from there into the St. Johns River.

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124 CHAPTER 7 CONCLUSIONS It is useful to reiterate the three-fold goal of this research proj ect. The first of the three research objectives was to evaluate the release characteristics of controlled-release fertilizers (CRF) under both laboratory and fi eld conditions. This was accomplished with the incubator experiment in cooled incubato rs and with the meshbag experiment at the research farm. The second objective was to determine the effects of different CRF products on potato production. Potato produc tion data evaluated tuber total and marketable yields, specific gravity, internal and external tuber qual ity, plant nutritional status, plant biomass, and nutrient recove ry efficiency. Both the CRF production experiment and the replacement experiment evaluated this objective. The third objective was to determine the effects of different CRF products on soil nitrogen movement below the plant root system and into watersheds. This was accomplished within the CRF production experiment using lysimeters and we lls for aqueous samples together with soil samples. The data from the three i ndividual research objectives outlined in Chapter 4 through Chapter 6 can be combined to draw general conclusions regarding both the characteristics of the CRF products evalua ted and their influence on potato production and nitrogen leaching as well as provide dir ection for future study and research. Each will be briefly summarized here.

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125 Incubator and Meshbag Experiments Incubator Experiment The incubator experiment, which cons isted of seven CRF products, urea, ammonium nitrate (AN), and a no-fertilizer control (No N), was evaluated over 13 consecutive weeks of leaching, revealing se veral important trends All CRF products, with the exception of CRF6, had a high peak of release at the first sampling date. Though this would be expected from the water-soluble AN and urea, the CRF products were not expected to copy this behavior In particular, CRF1, CRF2a, and CRF3 N release curves were shaped like those of water-soluble produc ts. Contrastingly, N release curves from CRF2b, CRF5, CRF6, and to a lesser degree CRF4, exhibited prolonged periods of nutrient release. Temperature-based release of the CRF produc ts varied greatly as well. CRF5 had the highest Q10 of all products across all temper ature comparisons, averaging 2.2 at 7 days and 2.4 at 14 days. CRF1, CRF2a, a nd CRF3, showed no indication of temperaturebased release with Q10 values of approximately 1. Residual fertilizer from each of the CRF products varied considerably. CRF1 and to a lesser degree CRF3 resulted in very little residual fertilizer at the end of the study, independent of temperature. CRF2a, while temperature-independent had nearly 63% of its product and unavailable for release after 13 weeks. CRF2b, CRF4, CRF5, and CRF6 all had decreasing amounts of resi dual fertilizer as temperatur e increased and of the four products, only CRF6 had greater than 20% residu al fertilizer at either the 25C or 30C temperature settings.

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126 Meshbag Experiment The meshbag experiment consisted of the same seven CRF products as the beaker experiment, but was performed in the fi eld and subjected to 2003 moisture and temperature conditions. As with the CRF re lease experiment, the CRF products all had relatively high release by the first sampling date, with CRF6 again having the lowest release. Also, as with the beaker experi ment, CRF2 had the highest percentage of permanently unavailable N, at 28%, while all other CRF products approached 90% or greater release. Though the initial releas e was greater in the meshbag experiment compared to the CRF release experiment, sustained release from the CRF products thereafter was similar between experi ments, with the exception of CRF2b. CRF Production and Replacement Experiments CRF Production Experiment Six CRF products were evaluated for pr oduction parameters in comparison to AN in the CRF production experiment. CRF2 was a blend of CRF2a and CRF2b, thus utilizing the seven products ev aluated in the meshbag and incubator experiments. All products were also evalua ted at three rates kg ha-1 N (the BMP rate), 168 kg ha-1 N, and 112 kg ha-1 N. Of all plants, those fertilized with CRF2 (224 kg ha-1 N) and CRF4 (224 kg ha-1 N) had highest total yields, mark etable yields, and specific gr avity (SG). Plants with treatments at the 168 kg ha-1 N fertilizer rate produced sta tistically similar yields and SG to those grown with the 224 kg ha-1 N rate. Nutrient rec overy efficiency was not different between AN and CRF treatments.

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127 Replacement Experiment CRF4 and CRF6 were blended with AN at differing ratios in the replacement experiment. Atlantic and Red LaSoda potatoes were evaluated for total and marketable yields and SG. No significant difference was ob served between plants with any of the AN:CRF fertilizer ratios for eith er CRF product for total yields, marketable yields, or SG. The only exception to this was with plants fertilized with CRF6 which had statistically higher marketable yields th an AN on Atlantic potatoes at the AN:CRF6 25:75 ratio. Leaching Experiment The leaching experiment was performed within the CRF production experiment and had the same product and fertilizer rate c onditions. Soil, suction lysimeter, and well samples were taken periodically over the growing season. Soil NO3-N concentrations were statistica lly highest over the season with CRF1 (224 kg ha-1 N) and CRF3 (224 kg ha-1 N). Well NH4-N and NO3-N concentrations were statistically higher with AN treatments than with CRF treatments at 29 (NH4-N and NO3N) and 41 DAP (NO3-N). At 29 DAP, well samples fr om under CRF plots had 70% less NH4-N than samples under AN plots. At 224 kg ha-1 N, NO3-N from under CRF plots was 95% less than samples under AN plots, while at 168 kg ha-1 N, it was 92% less, and at 112 kg ha-1 N, it was 89% less. At 41 DAP, well samples from under CRF plots were 78% less than samples from under AN plots for NO3-N while NH4-N was not significantly different between CRF and AN plots. Due to sporadic data collection, lysimeter samples were not an alyzed statistically, though NO3-N and NH4-N concentrations observed in samples from AN fertilized plots were much higher than in

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128 CRF fertilized plots. AN pl ots reached a high of 146 mg L-1 NO3-N and 41 mg L-1 for NH4-N, while CRF plots reach ed a high of 17 mg L-1 NO3-N and 11 mg L-1 for NH4-N. Lessons for Future Work Through the series of experiments conducte d, valuable lessons have been learned which provide a basis for future research, bot h in direction and in quality. By improving this protocol, data from future experiments will be more useful in interpretation and application to the grower. In the CRF release experiment, weekly samples were analyzed for TKN. Though little was converted to nitrat e, the TKN method does not analyze for nitrate. The Dumas method (combustion method) would provide an improved N analysis method, in that all N, independent of chemical form, is analyze d. Also, the Dumas met hod is less sensitive to high N concentrations than the Kjeldahl method, making high dilutions and digestion problems unnecessary (Dumas, 1831; Watson and Galliher, 2001). In the meshbag experiment, the cheesecloth meshbags utilized degraded quickly in the field. This made bi-weekly samplings diffi cult. Alternative bags or containers would save time both in preparation and sampling. In the well and lysimeter experiment, wa ter samplings began later in the season than desirable. This was evidenced by only seeing the tail of the release profilesthe early part of the season, where the most rainfall and the highest amounts of nutrient release occurred, passed without sampling. T hough these data would not influence potato plant uptake (growing plants ut ilize stored nutrients from the seed tuber early in the season), samplings earlier in the season of both the soil solution and the perched water table could provide valuable fertilizer initial-release da ta under growing conditions, which relates to nutrient leaching.

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129 Summary Considering the results of the various studies together provides useful information. From the field production experiments, greatest total and marketable tuber yields were obtained from CRF2, CRF4, CRF5, and CRF6 while highest SG were obtained from CRF1, CRF2, CRF3, and CRF4. Total and ma rketable yields and SG were not significantly different be tween the 168 and 224 kg ha-1 N rates. From the CRF release and meshbag experiments, CRF2b, CRF4, CRF5, and CRF6 exhibited the greatest degree of temperature-based nutrien t release, had prolonged re lease periods, and had little residual fertilizer lockout. All of the CRF fertilized plots had significantly less NO3-N and NH4-N in wells early in the season than did AN fertilized plots. From this combined data, CRF2 (partic ularly CRF2b), CRF4, CRF5, and CRF6 are good candidates for future research. CRF2b and CRF4 produced high yields of quality potatoes with high SG, significantly reduced N leaching into water bodies, and had nutrient release based on temperature. CRF 5 and CRF6 exhibited similar characteristics to CRF2b and CRF4, though SG was somewhat lo wer in tubers from those treatments. Based on the results it is concl uded that this may have been due to too-prolonged nutrient release of these products. Also, a reduced fe rtilizer rate would be useful for future evaluation. Reduced application rates reduc e input costs and qua ntities of nutrient available for leaching, and if tuber yields a nd quality are not compromised, then there is no disadvantage to a reduced rate. The long-term goal of this research projec t is to help potato growers to grow high yields of quality potatoes using environmentally responsible practices. With that goal in mind, controlled-release fertiliz ers provide a viable fertilizer alternative to ammonium nitrate. Yields and tuber quality rema in high while nitrogen leaching into the

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130 environment is reduced, making CRF products good candidates for a BMP program for growers in northeast Florida.

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131 LIST OF REFERENCES Aerts, M.J. and O.N. Nesheim. 2000. Florid a Crop/Pest Management Profiles: Potatoes. EDIS Florida Cooperative Extension Service Publication CIR 1237. Last accessed 11/05/04. http://edis.ifas.ufl.edu/PI030 Allen, E.J. and R.K. Scott. 1980. An Analysis of Growth of the Potato Crop. J. Agric. Sci., Camb. 94, 583-606. Baligar, V.C., N.K. Fageria, and Z.L. He. 2001. Nutrient Use Efficiency in Plants. Commun. Plant Anal. and Soil Sci. 32 (7-8): 921-950. Benson, N. and R.M. Barnett. 1939. Leach ing Studies with Various Sources of Nitrogen. J. Amer. Soc. of Agron. 31:44-54. Bronson, C.H. 2003. Florida Agricultura l Fast Facts 2003 Directory. Florida Department of Agriculture a nd Consumer Services. 90-91. Burkart, M.R. and J.D. Stoner. 2002. Nitrat e in Aquifers Beneath Agricultural Systems. Water Science and Technology. Vol 45, no 9: 19-29. Cox, D. and T.M. Addiscott. 1976. Sulfur-coa ted Urea as a Fertilizer for Potatoes. J. Sci. Fd Agric. 27: 1015-1020. Csizinszky, A.A. 1994. Yield Response of Bell Pepper and Tomato to ControlledRelease Fertilizers on Sand. J. Plant Nutr. 17(9): 1535-1549. Davis, J.M., W.H. Loescher, M.W. Hamm ond, and R.E. Thornton. 1986. Response of Potatoes to Nitrogen Form and to Change in Nitrogen Form at Tuber Initiation. J. Amer. Soc. Hort. Sci. 111(1): 70-72. Dumas, J.B.A. 1831. Procedes de Lanal yse Organique. Ann. Chim. Phys. 47: 198205. Edgar, A.D. 1951. Determining the Specific Gravity of Individual Potatoes. Amer. Potato J. 28: 729-231. Elkashif, M.E., S.J. Locascio, and D.R. Hens el. 1983. Isobutylidene Diurea and Sulfurcoated Urea as N Sources for Potatoes. J. Amer. 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 Nitroge n Management. Agron. J. 90: 10-15.

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132 Florida Senate. 2004. The 2004 Florida Stat utes. Title XXVIII Natural Resources: Conservation, Reclamation and Us e, Chapter 373 Water Resources. Francis, G.S. and R.J. Haynes. 1991. The Leaching and Chemical Transformation of Surface-applied Urea Under Flood Irrigation. Fertilizer Research. 28: 139-146. Freeze, R.A. and J.A. Cherry. 1979. Groundwater Prentice Hall, Inc. Englewood, Cliffs, NJ. 604p. Fujita, T. 1989. Invention and Development of Polyolfin Coated Urea. PhD thesis, Faculty of Agriculture, Tohoku University. Sendai, Japan. Fujita, T., C. Takahashi, T. Ushioda, and H. Shimizu. 1983. Coated Granular Fertilizer Capable of Controlling the Effects of the Temperature Upon Dissolution-out Rate. United States Patent 4,881,963. Gandeza, A.T., S. Shoji, and I. Yamada. 1991. Simulation of Crop Response to Polyolefin-coated Urea: I. Field Dissol ution. Soil Sci. Sci. Am. J. 55: 1462-1467. Guertal, E.A. 2000. Preplant Slow-Releas e Nitrogen Fertilizers Produce Similar Bell Pepper Yields as Split Applications of Soluble Fertilizer. Agron. J. 92: 388-393. Hallberg, G.R. 1989. Nitrate in Groundwater in the United Stat es. In R.F. Follett (ed.) Nitrogen management and groundwater protection. Elsevier, Amsterdam. Hershey, D.R. and J.L. Paul. 1982. Leaching-Losses of Nitrogen from Pot Chrysanthemums with Controlled-Releas e or Liquid Fertilization. Scientia Horticulturae. 17: 145-152. Hochmuth, G.J. and K. Cordasco. 2000. A Su mmary of N, P, and K Research on Potato in Florida. EDIS Florida Cooperative Ex tension Service Publication HS756. Last accessed 11/05/04. http://edis.ifas.ufl.edu/cv233 Hochmuth, G.J., C.M. Hutchinson, D.N. Mayna rd, W.M. Stall, T.A. Kucharek, S.E. Webb, T.G. Taylor, S.A. Smith, and E.H. Simonne. 2003. In S.M. Olsen and E.H. Simonne (eds.) Vegetable Production Guide for Florida Vance Publishing. Last accessed 11/05/04. http://edis.ifas.ufl.e du/pdffiles/CV/CV13100.pdf Hochmuth, G.J., D.N. Maynard, C. Vavrina, and E.Hanlon. 1991. Plant Tissue Analysis and Interpretation for Vegetable Crops in Florida. Florida Cooperative Extension Service Publication SS-VEC42. p.12. Hutchinson, C.M., E. Simonne, P. Solano, J. Meldrum, and P. Livingston-Way. 2003. Development of a Controlled -release Fertilizer Program for North Florida Irish Potato ( Solanum tuberosum) Production. J. Plnt Nutr. 26(9):1709-1723.

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133 Hutchinson, C.M., W.A. Tilton, P.K. Livings ton-Way, and G.J. Hochmuth. 2002. Best Management Practices for Potato Production in Northeast Florida. EDIS, Florida Cooperative Extension Service Publica tion HS877. Last accessed 11/05/04. http://edis.ifas.ufl.edu/cv279 Hutchinson, C.M., J.M. White, and D.P. Weinga rtner. 2002. Chip Potato Varieties for Commercial Production in Northeast Florida. EDIS, Florida Cooperative Extension Service Publication HS 878. Last accessed 11/05/04. http://edis.ifas.ufl.edu/cv280 Keeney, D.R. 1986. Sources of Nitrate to Groundwater. Critical Reviews in Environ. Control. 16(3): 257-304. Kleinkopf, G.E. 1983. Potato. In: J.D. Teare and M.M. Peat (eds.) Crop Water Relations. Wiley and Sons, NY. 287-305. Kochba, M., S. Gambash, and Y. Avni melech. 1990. Studies on Slow Release Fertilizers. 1. Effects of Temperature, Soil Moisture, and Water Vapor Pressure. Soil Sci. 149: 339-343. Liegel, E.A. and L.M. Walsh. 1976. Evaluati on of Sulfur-coated Urea (SCU) Applied to Irrigated Potatoes and Corn. Agron. J. 68: 457-463. Livingston-Way, P. 2000. Tri-County Agricu ltural Area Water Quality Protection Cost Share Program, Applicants Handbook. St. Johns River Water Management District, Palatka, FL USA. Locascio, S.J., J.G.A. Fiskell, and F.G. Martin. 1981. Responses of Bell Pepper to Nitrogen Sources. J. Amer. Soc. Hort. Sci. 106(5): 628-632. Locascio, S.J., J.G.A. Fiskell, and F.G. Martin. 1984. Nitrogen Sources and Combinations for Polyethylene Mulched Tomato es. Proc. Fla. State Hort. Soc. 97: 148-150. Locascio, S.J. and F.G. Martin. 1985. Nitrogen Source and Application Timing for Trickle Irrigated Strawberries. J. Am er. Soc. Hort. Sci. 110(6): 820-823. Lorenz O.A., B.L. Weir, and J.C. Bishop. 1972. Effect of Controll ed-release Nitrogen Fertilizers on Yield and Nitrogen Ab sorption by Potatoes, Cantaloupes, and Tomatoes. J. Amer. Soc. Hort. Sci. 97(3): 334-337. Lorenz, O.A., B.L. Weir, and J.C. Bishop. 1974. Effect of Sources of Nitrogen on Yield and Nitrogen Absorption of Potatoes Amer. Potato J. 51: 56-65. Maeda, S. 1990. Studies on Coated Fert ilizer PhD Thesis, Faculty of Biological Production, Hiroshima University, Hiroshima, Japan. (referenced in S. Shoji, 1999, p. 21).

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134 Martin, H.W., D.A. Graetz, S.J. Locascio, a nd D.R. Hensel. Nitr ification Inhibitor Influences on Potato. Agron. J. 85: 651-655. Maynard, D.N. and O.A. Lorenz. 1979. Cont rolled-release Fertilizers for Horticultural Crops. 1:79-140. Mylavarapu, R.S. and E.D. Kennelley. 2002. UF/IFAS Extension Soil Testing Laboratory (ESTL) Analytical Procedures and Training Manual. EDIS, Florida Cooperative Extension Service Publicati on CIR 1248. Last accessed 11/05/04. http://edis.ifas.ufl.edu/SS312 Ojala, J.C., J.C. Stark, and G.E. Kleinkopf. 1990. Influence of Irr igation and Nitrogen Management on Potato Yield and Qu ality. Am. Pot. J. 67: 29-43. Polizotto, K.R., G.E. Wilcox, and C.M. Jones. 1975. Response of Growth and Mineral Composition of Potato to Nitrate an d Ammonium Nitrogen. 100(2): 165-168. Prihar, S.S., P.R. Gajri, D.K. Benbi, and V.K. Arora. 2000. In Intensive Cropping: Efficient Use of Water, Nutrients and Tillage. 14-15. Rowe, R. 1993. Potato Health Management: A Holistic Approach. In R. Rowe (ed.) Potato Health Management Am. Phytopathol. Soc. SAS Institute. SAS/STST Users Guide, Version 8.02; SAS Inst.: Cary, NC, 1999. Shoji, S. 1999. Meister Cont rolled-release FertilizerPrope rties and Utilization. S. Shoji (ed.). Konno Printing Company, Ltd. Sendai, Japan. Shoji, S., J. Delgado, A. Mosier, and Y. Miura. 2001. Use of Controlled-release Fertilizers and Nitrification Inhibitors to Increase Nitrogen Use Efficiency and to Conserve Air and Water Quality. Commun. Soil Sci. Plant Anal. 32(7-8): 10511070. Simonne, E.H., C.M. Hutchinson, M.D. Dukes, G.J. Hochmuth, R.C. Hochmuth. 2003. Update and Outlook for 2003 of Florida s BMP Program for Vegetable Crops. EDIS, Florida Cooperative Extension Se rvice Publication HS916. Last accessed 11/05/04. http://edis.ifas.ufl.edu/HS170 Stark, J.C., I.R. McCann, D.T. Westermann, B. Izadi, and T.A. Tindall. 1993. Potato Response to Split Application Timing with Varying Amounts of Excessive Irrigation. Am. Pot. J. 70: 765-777. USDA. 1991. United States Standards for Grades of Potatoes. United States Department of Agriculture, Agricultura l Marketing Service, Fru it and Vegetable Division, Fresh Products Branch. Last accessed 11/05/04. http://www.ams.usda.gov/standards/potatoes.pdf

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135 Waddell, J.T., S.C. Gupta, J.F. Moncrief, C.J. Rosen, and D.D. Steele. 1999. Irrigation and Nitrogen Management Effects on Pota to Yield, Tuber Quality, and Nitrogen Uptake. Agron. J. 91: 991-997. Watson, M.E. and T.L. Galliher. 2001. Co mparison of Dumas and Kjeldahl Methods with Automatic Analyzers on Agricultural Samples Under Routine Rapid Analysis Conditions. Commun. Soil Sci. Pl ant Anal. 32(13-14): 2007-2019. Weingartner, P. and T. Kucharek. 2004. 2004 Florida Plant Disease Management Guide: Potato, Irish. EDIS, Florida Cooperativ e Extension Service Publication PDMGV3-46. Last accessed 11/05/04. http://edis.ifas.ufl.edu/PG053 Westermann, D.T. 1993. Fertility Management. In R. Rowe (ed.) Potato Health Management. Am. Phytopathol. Soc. Westermann, D.T. and G.E. Kleinkopf. 1985. Nitrogen Requirements of Potatoes. Agron. J. 77: 616-621. Westermann, D.T., G.E. Kleinkopf, and L.K. Porter. 1988. Nitrogen Fertilizer Efficiencies on Potatoes. Am. Pot. J. 65: 377-386. Westermann. D.T. and R.E. Sojka. 1996. Tillage and Nitrogen Placement Effects on Nutrient Uptake by Potato. Soil Sci. Soc. Am. J. 60: 1448-1453. Zvomuya, F. and C.J. Rosen. 2001. Evaluati on of Polyolefin-coated Urea for Potato Production on a Sandy Soil. HortScience. 36(6): 1057-1060. Zvomuya, F., C.J. Rosen, M.P. Russelle, S.C. Gupta. 2003. Nitrate Leaching and Nitrogen Recovery Following Application of Poly-olefin Coated Urea to Potato. J. Environ. Qual. 32: 489-489.

PAGE 152

136 BIOGRAPHICAL SKETCH Jeffery Earl Pack was born in Salt Lake City, Utah, on November 17, 1974, to Allen E. and Valeen Pack, the oldest of five children. He graduated from West Jordan High School in 1993, from Salt Lake Community College with an Associate of Science degree in 1998, and from the University of Ut ah with a Bachelor of Science degree in biochemistry in 1999. After graduating from the University of Utah, he worked two years before enrolling at the University of Florida to work on a Master of Science degree in horticultural sciences, which was completed in August 2004. Jeffery was married to Jerami Baker in the LDS Salt Lake Temple in Salt Lake City, Utah, on September 4, 1999. They curre ntly have three ch ildren, Sarah, Rachel, and Elisabeth. Jeffery expects to pursue the Doctor of Plant Medicine degree offered at the University of Florida after which he expects to enter industry as a plan t doctor consultant. He is a member of the Church of Jesus Christ of Latter-day Saints and served a two year proselyting mission to Crdoba, Argentina. He currently resides in Gainesville, Florida, with his family.


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Physical Description: Mixed Material
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CONTROLLED-RELEASE NITROGEN FERTILIZER RELEASE
CHARACTERIZATION AND ITS EFFECTS ON POTATO (Solanum tuberosum)
PRODUCTION AND SOIL NITROGEN MOVEMENT
IN NORTHEAST FLORIDA















By

JEFFERY EARL PACK


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA


2004

































Copyright 2004

by

Jeffery Earl Pack
































This thesis is dedicated to my loving wife, Jerami, and three daughters, Sarah, Rachel,
and Elisabeth, for following me wherever I needed to go.















ACKNOWLEDGMENTS

I thank my advisor, Dr. Chad Hutchinson, for his mentor-like spirit. He provides

guidance yet allows me room to teach myself. I thank my other committee members Dr.

George Hochmuth, Dr. Rao Mylavarapu, Dr. Johan Scholberg, and Dr. Michael Dukes

for their support of this work.

I thank my sweetheart, Jerami, for her patience and unwavering support and

ennobling confidence as well as my children, Sarah, Rachel, and Elisabeth, and those yet

unborn, for trusting and simple love. We can only get through this together.

Finally, I thank our Father for agency to choose, opportunities to grow, truth to

guide us home, and a veil of forgetfulness to allow it to come from within.
















TABLE OF CONTENTS

page

A C K N O W L E D G M E N T S ................................................................................................. iv

LIST OF TABLES ....................................................... ............ ....... ....... ix

LIST OF FIGURES .............. ................................. ............. ........... xiii

A B STR A C T ......... .............. ................................................. .. ........ .. xv

CHAPTER

1 IN TRODU CTION ................................................. ...... .................

2 LITERATURE REVIEW ........................................................................2

Best M anagem ent Practices .............................................................. .. ...... .......3
Florida B M Ps........................................................ 4
N utrient U se E efficiency ................................................................ ....................... 6
Potato G row th Stages ..............................................................7
G row th Stage I.............................................................. 7
G row th Stage II ...............................................................8
G row th Stage III ..................................... .............. .......................
G row th Stage IV ............................................................9
G row th Stage V ............................... ...................... ............
Cultural Practice Influences on N Fertilization Efficacy ............... ............ 10
N A application T im ing .................................................................................... 10
Irrigation Management ...................... ......... ............................ 11
N S o u rc e ............................................................. ................................... 1 1
N Placement ............................................................................. ........ ..................12
C R F P ro d u cts ......................................................................................12
Sulfur-Coated U rea............................................................... ........ .... 13
Isobutylidene Diurea and Nitrification Inhibitors ..........................................14
Polym er-Coated U rea ............................................................... ...............15
PCU Release .................. .................................................. ..... 16
Sum m ary and R research Objectives ......................................... .................... ......17

3 MATERIALS AND METHODS ................................................................ 19

CRF Release from the Incubator and Meshbag Experiments ............... ..................19


v









Incubator Experim ent ...................................... ........ ........................ 19
C R F fertilizer products............................................................ ............... 20
In cu b ato rs ............................................................................................... 2 0
D u ra tio n .................................................................................................. 2 1
Setup and procedure .............................................................. .............21
Sam ple analysis .......................................... .................. .. ...... 22
Statistical design and analysis ...........................................22
M eshb ag E x p erim ent..................................................................................... 2 3
CRF fertilizer treatm ents ......................................................... ........ .. 23
Setup and procedure ....................................... ........ ...... ........ .. ...... ... 23
Sam ple analysis .................. .......................... .. ...... .. .......... .. 24
Statistical analysis .............. ...................... .....................................24
F field P ro du action .............................................................................................. 2 4
G general Production ................................................................... ............... 25
S o ils ...................................................... ................... . .. 2 5
Irrigation................... ......... ................. .... .. ... 25
Planting ................................................ ............... ............ 25
Fertilizer treatments .................. ............ ................. .................. 26
Seasonal management .................................................... 26
Soil analysis ................................... ......... 27
Tissue Sam pling and A nalysis............................................... 27
N nitrogen R recovery Efficiency ......................................................................28
H a rv e st ........................................................................................................... 2 8
Statistical A naly sis ...........................................................29
N nitrogen Leaching Experim ent.......................................................... ............... 30
L y sim e ters ................. .................................................................... .. 3 0
W ells........................ ................. .....................
Statistical A n aly sis ............. ..................... ................................................3 1

4 RELEASE CHARACTERISTICS OF CONTROLLED-RELEASE NITROGEN
FERTILIZERS UNDER CONSTANT TEMPERATURE AND FIELD
C O N D IT IO N S ........................................................................................ ..... 32

Incubator Experiment Results.......................... ............ ..............33
Incubator Experiment Weekly and Cumulative N Release .............................33
A m m onium N itrate .............................................................. .. ........................35
U re a .............................................................................. 3 5
C R F .................................................................................. 3 8
C R F 2 a ......................................................... 3 8
C R F 2b ..................................................................................... ........ ......................41
C R F 3 .............................................................................................................. 4 1
C R F 4 .............................................................................................................. 4 4
C R F 5 .............................................................................................................. 4 4
CRF6.................. ............................ ............ 47
N o N C control .................................................. ............... .. ... ................... 4 9
Variable Temperature Incubator Release ...............................................49
Q o ................. ............................................. ....... .. ..... ...... 5 1









R esidual Fertilizer ........................ ................ .. .. .... ........ ......... 53
Total N Recovery .................................. ... .... ..... ............ 56
M eshbag E xperim ent ........................................................................ .......... .......... 56
M eshbag Experim ent R results ................................... ................... ..................59
CR F R release D iscussion.................................... ......... ..... .........................62
Incubator CRF Release and Meshbag Experiment Correlation ........................62
Fertilizer R release Characteristics ............................................. ............... 64
A N an d u rea ................................................. ................ 6 4
C R F 1 ............. ... .............. ...................... .... .... ..... ................ 65
C R F 2 a ................................................... ................ 6 6
C R F 2 b ........................................................................6 6
C R F 3 .........................................................................6 7
C R F 4 .........................................................................6 8
C R F 5 .........................................................................6 8
C R F 6 ................................................ ................. ........... 69
Nitrification and denitrification ......................................... ...............70
Plant uptake require ents ........................................ ........................ 70
M ethodology im provem ent........................................................................71
Su m m ary ......................................................................72

5 COMPARISON OF CONTROLLED-RELEASE NITROGEN FERTILIZERS TO
AMMONIUM NITRATE ON POTATO PRODUCTION .......................................74

C R F P reduction E xperim ent............................................................ .....................74
Total and M arketable Y ields ........................................ .......... ............... 75
Specific Gravity ............... .. ............................... .......... 77
T u b e r Q u a lity ................................................................................................. 7 9
Stand E stablishm ent ............................ ...................... .... ....... .... ....... ..8 1
Plant tissue ................ ....... ...... ....... ......... 83
Plant Biomass ....................................................... ......... 86
Tuber Nitrogen Uptake and Recovery Efficiency (NRE) ..................................87
R eplacem ent E xperim ent ............................................................................................88
Total and M arketable Y ields ........................................ .......... ............... 90
Specific G gravity .................. ............................. ........ .. .......... .. 92
T u b e r Q u a lity ................................................................................................. 9 4
Stand E stablishm ent ........................ .. ...................... .... ....... .... ..... ...... 94
Tissue A nalysis................................................... 95
Plant Biomass .......................... ................ 95
Tuber Nitrogen Recovery Efficiency ...................................... ............ 95
CRF Production Studies D iscussion....................................... ......... ............... 97
CR F Production Experim ent ........................................ .......... ............... 97
A m m onium nitrate ............................................... ........................... ...... 97
C R F ................................................................... 9 8
F e rtiliz e r ra te ........................................................................................ 1 0 0
Replacement Experiment................................................... 101
Summary ......................... ............................................. 101









6 NITROGEN MOVEMENT IN A SUB-SURFACE IRRIGATED POTATO
PRODUCTION SYSTEM UTILIZING CONVENTIONAL AND CONTROLLED-
RELEASE NITROGEN SOURCES ............................................. ............... 104

Precipitation and Tem perature....................................................... ............... 104
Precipitation....................................................................... ....... ..... 104
T em p eratu re .................................................................. ............... 10 5
S o il N itro g en ................................................... ................ 10 7
Pre-plant Soil N itrogen ......................................................... .............. 107
Seasonal Soil N itrogen .............................................. ............................ 107
W ell W after N nitrogen ................................................. .. ....... .. ........ .. .. 113
Seasonal W ell N itrogen ......................................................... ............. .. 113
Periodic W ell N itrogen ............................................................... ............... 116
Lysim eter N nitrogen ........................................................ ................. 121
Nutrient M ovem ent Discussion ................................................... ............... ... 122

7 CONCLUSIONS ................................... .. .. ........ .. ............124

Incubator and M eshbag Experim ents ............................................ ............... 125
Incubator Experim ent ................................................................................. 125
M eshbag Experim ent.................................................................... ............... 126
CRF Production and Replacement Experiments ............................................... 126
CRF Production Experim ent ........................................ ......... ............... 126
Replace ent Experim ent.............. ............................. ............... 127
Leaching Experim ent.................................................................. ............... 127
Lessons for Future W ork ....................... ..... ........ .................................128
Summary ............. ................................................. 129

LIST OF REFEREN CE S ..................................................................... ............... 131

BIOGRAPHICAL SKETCH ........... ............ ......... ..........136
















LIST OF TABLES


Table p

3-1 Characteristics of fertilizer products evaluated in the various CRF release,
production, and leaching experiments....... ................. ...............20

3-2 Incubator 7 temperature settings used for the incubator experiment .....................21

4-1 Incubator temperatures during the incubator experiment.................. .......... 34

4-2 ANOVA table for CRF incubator release by sampling date, temperature setting
and fertilizer product m ain effects. ........................................ ....... ............... 35

4-3 N release from ammonium nitrate at various incubator settings for each sampling
date ................................................................................. 36

4-4 N release from urea at various incubator settings for each sampling date ..............37

4-5 N release from CRF1 at various incubator settings for each sampling date. ...........39

4-6 N release from CRF2a at various incubator settings for each sampling date. .........40

4-7 N release from CRF2b at various incubator settings for each sampling date. .........42

4-8 N release from CRF3 at various incubator settings for each sampling date............43

4-9 N release from CRF4 at various incubator settings for each sampling date. ...........45

4-10 N release from CRF5 at various incubator settings for each sampling date............46

4-11 N release from CRF6 at various incubator settings for each sampling date. ...........48

4-12 N release from fertilizer products in the variable temperature incubator for each
sam p lin g d ate .................................................... ................ 5 0

4-13 ANOVA table for residual N by incubator temperature and fertilizer product
m ain effects. ....................................................... ................. 53

4-14 Residual N recovery (% of applied) from CRF products after 13 weeks of
release for each incubator .................................. ......... ......... ..................... 54









4-15 Residual N recover (% of applied) from CRF products after 13 weeks of
release at each tem perature setting ........................................ ........ ............... 54

4-16 Total N recovery (% of applied) from fertilizer treatments from solution and
residual sources for each temperature setting............... .................................57

4-17 ANOVA table for released N (% of applied) by fertilizer treatment and sampling
date m ain effects................................................... ......................... ....... 60

4-18 Cumulative N release (%) from CRF products at each sampling date for each
fertilize er. .......................................................... ................ 6 1

5-1 ANOVA table for total yields by fertilizer and rate main effects ..........................75

5-2 ANOVA table for marketable yield by fertilizer rate and main effects .................75

5-3 Total and marketable yield simple effects.............. .............................................. 76

5-4 ANOVA table for specific gravity by rate and fertilizer source main effects..........78

5-5 Potato tuber specific gravity by simple effects. ........................................... ........... 78

5-6 Potato tuber quality by fertilizer source main effect.........................................80

5-7 Potato tuber quality by rate main effect. ...................................... ............... 80

5-8 Potato tuber quality by treatm ent. ........................................ ........................ 81

5-9 Potato stand establishment for the CRF production experiment..............................82

5-10 ANOVA table for most recently matured leaf TKN by rate and fertilizer product
m ain effects. ....................................................... ................. 83

5-11 Most recently mature leaf percent TKN of potato plants by fertilizer source main
effect at 36 and 64 D A P. ............................................... ............................... 84

5-12 Most recently mature leaf percent TKN of potato plants by rate main effect at 36
and 64 D A P ...........................................................................84

5-13 Most recently mature leaf tissue percent TKN of potato plants by fertilizer and
rate sim ple effects................................................... ....................... ...... 85

5-14 Plant biomass and tissue nitrogen at full flower (61 DAP) by fertilizer source
m ain effect............................................................................................ 8 6

5-15 Plant biomass and tissue nitrogen at full flower (61 DAP) by rate main effect.......86

5-16 ANOVA table for N recovery (kg ha-1 N) by fertilizer product and rate main
effects. .............................................................................. 88









5-17 ANOVA table for NRE by fertilizer product and rate main effects .......................88

5-18 Tuber nitrogen uptake and nutrient recovery efficiency by treatment. ....................89

5-19 Total and marketable yields of 'Atlantic' and 'Red LaSoda' potatoes by CRF4
b len d ................................................................................ 9 1

5-20 Total and marketable yields of 'Atlantic' and 'Red LaSoda' potatoes by CRF6
b len d ................................................................................ 9 1

5-21 'Atlantic' and 'Red LaSoda' tuber specific gravity by CRF4 blend......................93

5-22 'Atlantic' and 'Red LaSoda' tuber specific gravity by CRF6 blend ........................93

5-23 Plant stand establishment data in the replacement experiment.............................94

5-24 Plant biomass and tissue nitrogen by CRF4 blend ................................................95

5-25 Plant biomass and tissue nitrogen by CRF6 blend ................................................96

5-26 Tuber nitrogen uptake and nutrient recovery efficiency by CRF4 blend ...............96

5-27 Tuber nitrogen uptake and nutrient recovery efficiency by CRF6 blend ...............96

6-1 ANOVA table for soil NH4-N over all sampling dates............... ... ...............108

6-2 ANOVA table for soil N03-N over all sampling dates............... ... ...............108

6-3 Soil NH4-N by fertilizer source main effect over all N rates and sampling dates..108

6-4 Soil N03-N simple effects by fertilizer source and rate over all sampling dates...109

6-5 Soil N03-N by fertilizer source main effect for each sampling date......................110

6-6 Soil NH4-N by fertilizer source main effect for each sampling date....................111

6-7 Soil N03-N by treatment for each sampling date...............................112

6-8 Soil NH4-N by rate main effect for each sampling date..................... ...............114

6-9 Soil N03-N by rate main effect for each sampling date..................... ...............115

6-10 ANOVA table for well N03-N over all sampling dates..................... ...............115

6-11 ANOVA table for well NH4-N over all sampling dates..................... ...............115

6-12 NH4-N and N03-N concentrations in wells by treatment.............. .. ................ 116

6-13 Well NH4-N fertilizer source main effects at each sampling date. ........................118









6-14 Well N03-N fertilizer source main effects at each sampling date. ........................119

6-15 N03-N concentrations in wells for each sampling date. .....................................120

6-16 Well NH4-N rate main effect at each sampling date. ...........................................121

6.17 Well N03-N rate main effect at each sampling date. ........................ .................121
















LIST OF FIGURES


Figure page

4-1 Release profile of ammonium nitrate at each incubator setting over the duration
of the CR F release experim ent. .................................................................... ... .... 36

4-2 Release profile of urea at each incubator setting over the duration of the
incubator experim ent .............................................................................. ... .... 37

4-3 Release profile of CRF 1 at each incubator setting over the duration of the
incubator experim ent ............................ .................................... ............... 39

4-4 Release profile of CRF2a at each incubator setting over the duration of the
incubator experim ent .............................................................................. ... .... 40

4-5 Release profile of CRF2b at each incubator setting over the duration of the
incubator experim ent .............................................................................. 42

4-6 Release profile of CRF3 at each incubator setting over the duration of the
incubator experim ent .............................................................................. ... .... 43

4-7 Release profile of CRF4 at each incubator setting over the duration of the
incubator experim ent..................................................................... ............. 45

4-8 Release profile of CRF5 at each incubator setting over the duration of the
incubator experim ent......... ............................................................ ............. 46

4-9 Release profile of CRF6 at each incubator setting over the duration of the
incubator experim ent ............................................................................ 48

4-10 N found in the no fertilizer control within each incubator for various sampling
d a te s ............................................................................ .4 9

4-11 Release profile of fertilizer product at the variable incubator setting over the
duration of the CRF release experiment........................................... ................. 51

4-12 Qio values for various CRF products. ........................................... ............... 52

4-13 Residual TKN (% of applied) for various CRF products as affected by
tem perature............................................................................................... 56

4-14 Total N recovery from dissolution and residual analysis across all temperatures. ..58









4-15 Graphical breakdown of the total recovery of fertilizer treatments at various
tem peratures. .........................................................................58

4-16 Cumulative N release (% of applied) from CRF products at each sampling date....61

4-17 Cumulative N release (% of applied) of each fertilizer product as a function of
growing degree days with 50C base temperature. .................................................62

4-18 Comparison of release rates of CRF products between the CRF release
experiment and the meshbag experiment on a degree day basis, base temperature
of 50C ..............................................................................63

5-1 Total and marketable tuber yields by treatment. ............................................. 77

5-2 Potato tuber specific gravity by treatment.............. ..........................................79

5-3 Total and marketable potato tuber yields by AN:CRF ratio by variety .................92

5-4 'Atlantic' and 'Red LaSoda' tuber specific gravity by fertilizer treatment ............93

6-1 2003 daily precipitation in Hastings, FL from 13 Feb to 28 May..........................105

6-2 2003 and historical air and soil temperatures in Hastings, FL over the potato
grow ing season .............................................................................. 106

6-3 Nitrogen in wells by treatment over all sampling dates...............................117

6-4 Well NH4-N concentrations from each fertilizer product for each sampling date
over the grow ing season. .......................................................................... ....... 118

6-5 Well N03-N concentrations from each fertilizer product for each sampling date
over the grow ing season. .......................................................................... ....... 119















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

CONTROLLED-RELEASE NITROGEN FERTILIZER RELEASE
CHARACTERIZATION AND ITS EFFECTS ON POTATO (Solanum tuberosum)
PRODUCTION AND SOIL NITROGEN
MOVEMENT IN NORTHEAST FLORIDA

By

Jeffery Earl Pack

December 2004

Chair: Chad M. Hutchinson
Major Department: Horticultural Science

The Tri-County Agricultural Area of northeast Florida is home to nearly 8,000 ha

of potato (Solanum tuberosum L.) production, valued at approximately $64M annually.

The combination of sandy soils, perched water tables, and unpredictable rainfall together

with nitrogen fertilizer applications as high as 390 kg ha-1 N increases the potential for

nutrient loading into local watersheds, including the St. Johns River. As mandated by the

1987 Florida SWIM Act, the St. Johns River Water Management District directs the

development of agricultural best management practices (BMP) for the area. Within the

BMP program the potential of controlled-release fertilizers (CRF) as alternative fertilizers

was evaluated. The specific research objectives were to 1) characterize nutrient release

from CRF under laboratory and field conditions, 2) determine potato production and

nutrient recovery efficiency for soluble fertilizer and CRF treatments, and 3) estimate soil

nutrient levels in the potato bed and in the perched water table.









Seven CRF products (polymer coated ureas) were compared to ammonium nitrate

(AN). Lab and field experiments evaluated nutrient release both at controlled

temperature and under field conditions. Field experiments evaluated CRF products at

three application rates (112, 168, and 224 kg ha-1 N); 224 kg ha-1 N is the current potato

BMP rate, adopted from the University of Florida's Institute of Food and Agricultural

Sciences Extension Service's recommendation. Two CRF products and AN blends were

included to evaluate ideal combinations. Leaching studies evaluated nitrate (N03-N) and

ammonium (NH4-N) movement into nearby wells and lysimeters under field conditions.

Results from the nutrient release experiments revealed that CRF2b, CRF4, CRF5,

and CRF6 all exhibited temperature-based, complete release over time. While initial

release from CRF products was somewhat higher under field conditions compared to lab

conditions, subsequent sustained release from the two experiments was similar.

From the field production experiments, CRF fertilized plants produced comparable

total and marketable potato yields to AN fertilized plants. Plants within CRF2 (224 kg

ha-1 N) and CRF4 (224 kg ha-1 N) had the highest total and marketable yields and specific

gravity (SG) of all treatments. Applications of 224 kg ha-1 N did not result in yield or SG

increases over the 168 kg ha-1 N rate, independent of N source. For percent AN:CRF

blends evaluated with two CRF products, no blend was advantageous for either 'Atlantic'

or 'Red LaSoda' potato production.

NO3-N and NH4-N movement into the perched water table was significantly lower

with CRF than with AN treatments, particularly early in the season. Potatoes fertilized

with CRF products have similar yields and quality to AN fertilized potatoes while soil

nitrogen movement into watersheds is significantly reduced.














CHAPTER 1
INTRODUCTION

Agricultural associations with Florida usually involve images of orange trees full of

fruit. However, Florida produces a wide variety of fruit and vegetable crops, not the least

of which is potatoes. Florida potatoes (Solanum tuberosum L.) are grown primarily for

the fresh market and chip market, with 'Atlantic' variety being the most widely grown.

In northeast Florida, potato production approaches 8,000 ha at approximately $64M per

year in value.

The soils in northeast Florida are sandy with a shallow perched water table. In

combination with unpredictable rainfall and high fertilizer rates, this increases the

potential movement of nutrients into local watersheds, thus degrading the environment.

Local endeavors under mandate from state and federal law have encouraged cultural

practices called BMPs or best management practices which aim to allow farmers to

maintain high yielding and high-value crops while protecting the environment.

This research project evaluates the suitability of controlled-release fertilizers (CRF)

as an alternative nitrogen (N) fertilizer source to commonly utilized ammonium nitrate

(AN) for potato production in northeast Florida. It evaluates the effects of CRF products

on potato production including tuber yields and quality as well as their effects on nutrient

leaching into local watersheds. It further examines the release characteristics of selected

CRF products under controlled and field conditions. Our hypothesis is that appropriate

use of CRF products may provide an alternative to AN fertilizer sources including equal

or improved potato tuber yields with less negative impacts on the environment.














CHAPTER 2
LITERATURE REVIEW

Potato (Solanum tuberosum L.) nitrogen (N) fertilization strategies to improve

tuber yield and/or quality have greatly evolved during the past century. Methods have

included additions of organic fertilizer amendments like manures and green manures; the

application of N in various soluble forms (e.g., ammonium, nitrate, and urea), alone and

in blends; the application of N in slowly soluble forms (e.g., urea formaldehyde,

methylene urea, and isobutylidene diurea); and the application of coated soluble N (e.g.,

sulfur-coated urea, polymer-coated urea). Research has explored the timing of

application (e.g., pre-plant, at planting, at hilling), placement (e.g., banded, broadcast,

surface applied, incorporated, side-dressed), application method (e.g., solid prills, liquid

through irrigation lines), rate, and virtually every combination thereof. Research has

evaluated the growth characteristics of the plant and linked this to nitrogen accumulation

patterns-little N demand very early, to heavy N demand during vegetative growth and

bulking stages, to little N demand during maturation and senescence. New, N-efficient

cultivars have been compared to reliable favorite varieties. Climate (e.g., rainfall,

temperature), soil conditions (e.g., texture, structure, CEC), and seasons have been linked

to fertilizer management. Nitrogen management is increasingly subject to market

demands, legal constraints, and economic considerations. N fertilization of potatoes has

become a highly specialized science, with different applications for any given set of

conditions.









However, as society advances, so does the need to adapt to new circumstances, new

needs, new laws, new considerations, etc. Increasing concerns over fossil fuel supplies,

polluted water supplies, and environmental degradation have forced the agricultural

industry to re-evaluate how it manages production inputs. It has been obliged to seek out

more environmentally responsible methods of production while striving to remain

profitable with an increasingly competitive economy and ever more environmentally

conscious public.

This review will discuss the evolution and implementation of best management

practices (BMP) across the United States with special reference to Florida. It will then

outline the basic potato plant growth cycle and strategies to maximize production

efficiency. It will then narrow its focus to potato fertilizer research, particularly with

slow- or controlled-release fertilizers. Finally, it will present the research justification

and objective of the current project.

Best Management Practices

Agricultural best management practices (BMP) are scientifically-based cultural

farming practices that should maintain or increase crop yields and/or profits while

protecting the environment (Simonne et al., 2003). One common BMP goal is to reduce

the contamination of water bodies by chemicals or other pollutants, such as nitrogen.

Nitrogen (N), particularly in the form of nitrate (NO3s), is the most common contaminant

in aquifer systems (Freeze and Cherry, 1979). Hallberg (1989) states that agriculture is

the largest human-caused source of nitrate and Keeney (1986) suggests that this is caused

by activities associated with crop and animal production. Burkart and Stoner (2002)

report that shallow unconfined aquifers associated with agricultural systems, particularly

under irrigation, are the most susceptible watersheds to nitrate contamination.









Individual BMPs differ according to specific regional, climatic, geographic,

governmental, and growing requirements. Though BMPs differ, the following aspects

commonly appear in BMP programs: 1) soil or tillage management to reduce runoff and

erosion of nutrients and/or nutrient coated soils, 2) irrigation management to reduce

runoff, deep percolation, and soil salinization, 3) mulching practices to reduce soil losses

and, in the case of some organic mulches, partially or completely replace fertilizer

applications, reduce evaporation rates, and enhance soil water storage, and 4) fertilizer

scheduling to apply only the types and quantities of nutrients required by crops at the

right time to produce optimal yields and minimize negative environmental impacts.

Florida BMPs

In 1987, the Florida legislature, under the mandate of the Federal Clean Water

Quality Act of 1977, passed the Florida Surface Water Improvement and Management

(SWIM) Act (Florida, 2004). The SWIM Act created a program that focused on the

preservation and/or restoration of the state's water bodies through the development and

implementation of Best Management Practices (BMPs) (Simonne et al., 2003). Since its

passage, state and local regulatory agencies have worked to improve water bodies in need

of restoration throughout the state.

The St. Johns River watershed in northeast Florida has been identified as a water

body in Florida in need of restoration. Nitrate leaching into the river has generated

concern. The lower St. Johns River basin is encompassed by three counties: St. Johns,

Putnam, and Flagler counties. These counties comprise the Tri-County Agricultural Area

(TCAA) and feature predominate agricultural land use. The major crop in the TCAA is

potato, and this area produces nearly half of Florida's annual 15,000 hectare crop with a

value of $130M (Bronson, 2003). Soils in the area are generally sandy with low water-









holding capacity. This, together with the shallow root system of potatoes and the

possibility of excessive seasonal rains, increases the potential for movement of water

soluble plant nutrients into the surrounding watersheds, including the St. Johns River.

State and local regulatory agencies in cooperation with growers in the TCAA have

developed a BMP program which has been in place for over three years. The BMP

program is the TCAA Water Quality Protection Cost Share Program which is managed

by the St. Johns River Water Management District (SJRWMD). The TCAA Water

Quality Protection Cost Share Program encourages growers to adopt environmentally

responsible practices by partially offsetting the implementation costs of those practices

(Livingston-Way, 2000).

The nitrogen BMP rate for potato production in the TCAA ranges from 224 to 280

kg ha-1 N. This contrasts with growers in the TCAA, who apply an average of 280 kg

ha-1 N, ranging from 195 kg ha-1 N on fresh market potato to 390 kg ha-1 N for some

chipping potatoes. The base rate of 224 kg ha-1 N was adopted from the University of

Florida's Institute of Food and Agricultural Science (IFAS) recommended rate

(Hochmuth and Cordasco, 2000; Hochmuth et al., 2003). The IFAS recommended BMPs

for potato production also suggest split application of N fertilizer. Approximately 30% of

the total N should be applied at planting and the remainder banded 35-40 days after

planting. N rates should be based on plant nutrient status analysis. IFAS

recommendations also include the installation and monitoring of water table observation

wells, control structures to trap sediment from the field, and conservation crop rotations

(Hutchinson et al., 2002).









Nutrient Use Efficiency

One possible benefit of BMPs is an improvement in production efficiencies. As

system efficiency increases, productivity per unit of energy increases while loss and

environmental impacts decrease. The efficient use of nutrients is referred to in this thesis

as "nutrient use efficiency" (NUE), and refers to the percentage recovery of an applied

nutrient.

NUE has different definitions depending on the goals of the research program.

Prihar et al. (2000) divided NUE into the following categories: Agronomic NUE is

expressed as the amount of yield increase obtained per unit of fertilizer applied when

compared to the yield of an unfertilized crop. Economic NUE refers to the returns on

investment in added nutrients, where the cost of the last unit of fertilizer applied equals

the value of the yield increase obtained by that addition. Apparent nutrient recovery is

the amount of nutrient taken up by the crop and divided by the amount applied as

fertilizer, independent of the source from which the nutrient may have been obtained.

Actual NUE is similar to apparent NUE in that it measures the amount of fertilizer taken

up by a crop. However, actual NUE differs from apparent NUE in that actual NUE

measures the amount of fertilizer-supplied nutrients that are actually taken up by the crop

using tracers like depleted 15N or phosphorus-32 (32p) in the fertilizer source (Prihar et

al., 2000).

In some cases where the amount of nutrients available for movement from the site

is of interest, the nutrient recovery efficiency (RE) is calculated (Zvomuya et al., 2003;

Westermann et al., 1988). Nutrient RE is defined as the fraction of an applied nutrient

that is recovered or removed from the site, usually in the form of a product.









Baligar et al. (2001), reviewed several factors affecting NUE including soil

characteristics, fertilizer types and quantities, plant uptake and use mechanisms,

agronomic considerations such as tillage, crop rotation, and cover crop usage, biological

contributions of mycorrhizal fungi symbiosis and rhizobial nitrogen fixation, and climate

factors. Their review also stressed that highest NUEs (apparent, agronomic, economic,

etc.) can only be obtained through the appropriate integration of all of these factors.

Potato Growth Stages

In order to maximize productivity and NUE, it is useful to review the life cycle of

the potato plant. This is because by understanding the life cycle of the plant, its uptake

capacity, peak uptake periods, etc., fertilizer products can be designed to maximize NUE

and minimize waste.

The life cycle of a potato plant can be divided into five general growth stages

during each of which, the plant will carry on generally different metabolic activities

(Rowe, 1993). Once understood, effective practices can be implemented which work

together with the plant maximizing production and uptake efficiency.

Growth Stage I

Growth stage I is characterized by sprout development. During this stage sprouts

form from eyes on seed tubers and grow upward to emerge from the soil. No

photosynthesis takes place during this stage as the entire plant is underground and all of

the plant nutritional requirements are supplied by the seed tuber. Because the plant has

only begun developing functional roots during this stage, little or no nitrogen uptake

occurs.









Growth Stage II

Growth stage II is characterized by vegetative growth. The plant begins to

photosynthesize and products of photosynthesis provide energy to the plant as the seed

tuber becomes depleted of both energy and nutrients. Leaves and branch stems develop

from aboveground nodes along emerged sprouts and roots and stolons develop at below-

ground nodes. Growth stages I and II are reported to last from 15 to 30 days (Ojala et al.,

1990) to as long as 60 or 70 days (Kleinkopf, 1983; Westermann, 1993) depending on

planting date, planting depth, soil temperature and other environmental factors, the

physiological age of the seed tubers, and the characteristics of particular cultivars.

Approximately 15% of the total nitrogen uptake by 'Russet Burbank' occurs during

stages I and II (Ojala et al., 1990). Nitrogen deficiency during this stage is easily

corrected without appreciable yield losses if addressed early. Nutrient excesses during

this stage promote assimilate partitioning to vines, prolonging this vegetative growth

stage and delaying tuber initiation and expansion.

Growth Stage III

Growth stage III is characterized by tuber initiation and typically lasts from 10 to

14 days (Westermann, 1993; Ojala et al., 1990). During this stage, tubers form at the end

of stolons but are not yet enlarging. Marketable-sized tubers at harvest are usually

initiated at this time. The end of this stage typically coincides with early flowering.

Approximately 30% of the total plant nitrogen uptake occurs by the middle of this stage

of growth (Ojala et al., 1990). Nitrogen stress during this stage reduces leaf area and

canopy development but may stimulate early tuber initiation; excess nitrogen stimulates

vegetative growth and may delay the initiation of stage IV tuber growth for up to ten days

(Allen and Scott, 1980; Ojala et al., 1990).









Growth Stage IV

Growth stage IV is characterized by tuber bulking (expansion) and lasts from 30 to

60 days (Kleinkopf, 1983) to as high as 120 days (Ojala etal., 1990). During this stage

tuber cells expand and become the major sinks for photosynthetic products, water, and

nutrients. Much of the total nitrogen uptake (58 to 71%) by the crops occurs through

early and mid tuber bulking, respectively (Ojala et al., 1990), and most of the nutrients

used by the plant are taken up during growth stage IV (Westermann, 1993). Westermann

et al. (1988) reported that the nitrogen taken up during this stage is initially concentrated

in the stems and leaves and later translocated to the tubers. Nitrogen deficiencies during

this stage reduce tuber yield and size; excesses decrease tuber specific gravity, delay vine

senescence, and hamper tuber maturation (Ojala et al., 1990).

Growth Stage V

Growth stage V is the maturation stage, and little additional nitrogen is taken up

from the soil. During this stage, representing the final 10 to 24 days of growth, mobile

nutrients are translocated from vegetative plant portions into the enlarging tubers [for N,

up to 90% or more is translocated to the tubers (Westermann, 1993)]. Also during this

stage, tuber dry weight reaches its highest level, canopy photosynthesis decreases, and

above-ground parts senesce and die, and tuber skin matures (Rowe, 1993). Excessive

nitrogen during this stage can promote late-season vegetative growth and delay tuber

maturity and also result in poor net development of tuber skins, which is a concern for

russet-type potato growers (Ojala et al., 1990). Early season cultivars reach maturity in

90-100 days while late season cultivars may take 150 or more days (Kleinkopf, 1983).

'Atlantic' potatoes grown for chip production in Florida mature between 85 and 110 days

(Hochmuth et al., 2003).









Cultural Practice Influences on N Fertilization Efficacy

By understanding the life cycle of the potato plant, effective fertility management

and fertility related cultural practices can be adopted. As stated by Westermann (1993),

"...the goal in managing potato crop nutrition is to promote uniform and continuous

growth of plants and tubers throughout all growth stages." Most soils need nitrogen

applications to produce maximum yields of potatoes. However, the efficacy of that

application may be highly dependent on the control of other soil and environmental

factors. Cultural practices that influence uniform, continuous growth are in turn

influenced by nitrogen, and include N application timing, irrigation management, N

source, and N placement.

N Application Timing

Westermann and Kleinkopf (1985) showed that on 'Russet Burbank' potatoes, for

maximum early tuber growth, the above ground portion of the plant should contain 79 to

100 kg ha-1 N at the start of tuber bulking (growth stage IV), and that a preplant N

fertilizer application between 67 and 134 kg ha-1 would provide adequate N, while

excessive preplant N would delay tuber formation and result in lower marketable yield

(Westermann and Kleinkopf, 1985). Errebhi et al. (1998) reported that as the percentage

of total N applied pre-plant increased, total marketable yield decreased while total yields

remained the same on 'Russet Burbank' potatoes grown on a sandy loam in Minnesota.

They also reported that split applications of N fertilizer reduced nitrate leaching and

increased recovery because less fertilizer was applied preplant. Stark et al. (1993)

showed that split biweekly N applications produced higher marketable tuber yields than

did weekly applications. Depending on potato variety and local conditions, fertilizer

applications should be terminated from two or three weeks (Ojala et al., 1990) to four to









six weeks (Westermann, 1993), before the start of maturation (stage V) growth to avoid

tuber immaturity at harvest.

Irrigation Management

Ojala et al. (1990) reported that when growing 'Russet Burbank' potatoes with

reduced irrigation and seasonal water application rates ranging from 160 mm (severely

water-stressed) to 590 mm (adequate water) were applied, that maximum tuber yields

were attained with 247 kg ha-1 N. They also reported that under optimal irrigation,

specific gravity was greatest at the lowest N application rate whereas higher N levels

decreased specific gravity. For excessive irrigation (1.2 and 1.4 times the estimated

evapotranspiration rate), Stark et al. (1993) reported no significant plant N uptake effects,

or late-season tuber or plant dry weight differences, but did find significant reductions in

marketable yields in two seasons, and reduced total yields in one season.

N Source

Nitrogen source is important for optimal potato growth. Commonly used N

fertilizer sources are nitrate, urea, and ammonium, though plants only take up N as either

NO3-N or NH4-N (Westermann, 1993). N applied as urea is converted into NH4-N by

the ubiquitous enzyme urease (Benson and Barnette, 1939). This is a rapid process,

reaching a rate up to 90% conversion within 4 days of application at soil temperatures of

210C (Benson and Barnette, 1939). Francis and Haynes (1991) reported similar results

with urea transforming to NH4-N within 48 hours under field conditions in New Zealand.

Polizotto et al. (1975), testing 'Red Pontiac' and PU 66-142 potatoes in solution cultures

found that growth of tops, roots, and tubers was greatest with N supplied as NO3,

intermediate with NH4 + NO3, and least with NH4, for both cultivars. Davis et al. (1986)

reported similar findings for 'Russet Burbank' potatoes. Changing the N source from









NO3 or NH4 + NO3 to NH4 reduced both shoot and root growth while changing the N

source from NH4 to NH4 + NO3 improved growth. They concluded that some NO3-N

should be available to potatoes for proper growth and development and that when NH4-N

was the sole form of N available to the plant, it was detrimental to potato growth,

regardless of stage of development (Davis et al., 1986).

N Placement

Nitrogen placement can influence the N use efficiency, plant health, and tuber

yields in potatoes. In Idaho, Westermann and Sojka (1996) reported for 'Russet

Burbank' potato production, that banding N increased average plant dry weight 6.4%,

total tuber yield 9%, and N uptake 28% compared with broadcast N. They reasoned that

these results were consistent with predictions because potato roots would be unable to

exploit a certain percentage of broadcasted N due to spatial limitations, whereas banded

applications would tend to be in a region of the soil accessible to plant roots. This would

be consistent regardless of irrigation method. Waddell et al. (1999), working with

'Russet Burbank' potato in central Minnesota, reported no significant tuber yield

differences except for lower yields with buried drip irrigation and the control treatment

regardless of irrigation and N source treatments.

CRF Products

One approach to potato fertilization that may limit nutrient leaching involves the

use of slow- or controlled-release fertilizers (CRF). These are products that theoretically

reduce nitrogen leaching by limiting the solubility and availability of a fertilizer (e.g.,

sulfur-coated urea (SCU), isobutylidene diurea (IBDU), polymer-coated urea (PCU),

others) or by limiting its conversion to mobile forms (e.g., nitrification inhibitors (NI)).









These slow- or controlled-release strategies have been used successfully to reduce

nitrogen applications in numerous crops. These include 'Yolo Wonder' bell peppers

(Capsicum annuum L.) with IBDU and SCU (Locascio et al., 1981), 'Jupiter' bell

peppers with resin-coated-urea/potassium nitrate blends (Csizinszky, 1994), green bell

peppers with PCU, SCU, or AN (Guertal, 2000), tomatoes (Lycopersicon esculentum

Mill.) with IBDU or SCU/ammonium nitrate blends (Locascio et al., 1984), strawberries

(Fragraria x aananssa Weston), with SCU and IBDU (Locascio and Martin, 1985),

potted chrysanthemums (C/hl i//h,,/ull,'n x morifolium) with "Osmocote" (a PCU)

(Hershey and Paul, 1982), and barley (Hordeum vulgare L.) with PCU and NI (Shoji et

al., 2001). These products have been evaluated for potato production over the years in

different parts of the country with varying degrees of success.

Sulfur-Coated Urea

In studies conducted over several years in three locations in California, Lorenz et

al. (1972, 1974) showed that ammonium sulfate was generally superior to SCU or urea-

formaldehyde (a slowly available N source) for 'White Rose' potatoes, and that while in

some cases SCU produced yields equal to ammonium sulfate, in no case were yields

greater with SCU. In both studies, the lower yields of CRF treatments were attributed to

too-slow release of the fertilizer products.

Cox and Addiscott (1976) using SCU on 'King Edward' potatoes in Rothamsted,

England, determined that for rates up to 200 kg ha-1 N, potato tuber yields were greater

for ammonium nitrate than for SCU and at higher rates no significant difference between

nitrogen sources was found. They attributed these findings to incomplete or too slow

release of SCU over the potato growth period.









Liegel and Walsh (1976) in Hancock, Wisconsin reported that 'Russet Burbank'

potatoes, grown on a loamy sand with SCU, produced higher tuber yields than plants

grown with urea or AN. However, this was attributed to excessive rainfall in May which

leached the water soluble fertilizer and reduced yields for the entire year.

In central Minnesota, Waddell et al. (1999), growing 'Russet Burbank' potatoes on

a sandy loam soil, found that SCU applied at a rate of 224 kg ha-1 N resulted in lower

tuber yields than did urea under either drip or sprinkler irrigation. This was attributed to

slow availability of the SCU product.

Elkashif et al. (1983) reported similar results in Florida where yields of 'Atlantic'

potatoes grown on two sandy soils fertilized with SCU or a SCU/ammonium nitrate (AN)

blend were lower than treatments with only AN. These results were consistent for rates

from 134 to 201 kg ha- N and either as preplant or split applications. Maynard and

Lorenz (1979), in reviewing the work done on SCU, concluded that N release rates from

SCU are too slow to meet the high N demand of the potato crop early in the growing

season.

Isobutylidene Diurea and Nitrification Inhibitors

Though evaluated, isobutylidene diurea (IBDU) and nitrification inhibitors (NI)

have not been adopted for commercial potato production. Under potato production in

Florida, Elkashif et al. (1983) reported lowest total tuber yields and 25% lower

marketable yields using IBDU as the N source compared to either AN or IBDU/AN

blends. NI evaluated in five studies on potato in Northeast Florida gave no tuber yield

increases in four of the five tests. As a result, the researchers did not recommend NI for

potato production on hyperthermic, irrigated, sandy soils (Martin et al., 1993).









Polymer-Coated Urea

One relatively new CRF technology that has shown promising preliminary results

for potato production and reduced leaching is polymer-coated water soluble fertilizers.

Polymer-coated ureas (PCU) are CRFs with a polymer coating.

Zvomuya and Rosen (2001), growing 'Russet Burbank' potatoes on a sandy soil in

Minnesota, reported higher marketable yields using PCU applied at planting compared to

urea applied at emergence and hilling for application rates ranging from 110 to 290 kg ha-

1 N. In other research involving a three-year study, Zvomuya et al. (2003) reported that

at 280 kg ha-1 N, NO3-N leaching was 34 to 49% lower with PCU treatments than three

split applications of urea while nitrogen recovery efficiency (RE) for PCU averaged 50%,

7% higher than urea (43%). Total and marketable tuber yields with the CRF treatments

were between 12 and 19% higher than three applications of urea under leaching or

excessive irrigation conditions. This was attributed to a prolonged N release period and

reduced leaching of PCU treatments compared to urea treatments under excessive

irrigation conditions.

Shoji et al. (2001) demonstrated that PCU could markedly increase the NUE and

tuber yields of 'Centennial' russet potatoes, reporting that a single basal application of

112 kg ha-1 N PCU at planting produced total tuber yields comparable to traditional

fertilizer practices totaling 269 kg ha-1 N in 9 split applications. They also reported that

plant nitrogen NUE values of CRF products were nearly doubled compared to that of

urea N. These results were attributed to the ability of CRF products to supply N

synchronously with plant requirements.

In northeast Florida on 'Atlantic' potatoes, Hutchinson et al. (2003) reported that at

low N rates (112 kg ha-1 N), marketable tuber yields and nutrient use efficiency (NUE)









were higher for PCU than AN, though marketable yields were lower than acceptable local

levels. At higher rates (168 to 224 kg ha-1 N), tuber yields and NUE were similar.

PCU Release

One characteristic of PCU that has made it a successful fertilizer is the degree of

control of nutrient release. The controlled-release is obtained through varying either the

thickness or composition of the fertilizer coating. Though the specifics of coating

composition are held by individual manufacturers and are proprietary secrets, the general

list of chemicals is similar. Polymer-coating films are typically composed of blends of

water permeable and impermeable resins and surfactants (e.g. polyolefin or

polyethylene), ethylene vinyl acetate, and talc occurring as layered plates (Shoji, 1999).

Regulating the composition of the coating gives it a controlled moisture permeability and

release rate (Fujita et al., 1983).

Shoji (1999) and Gandeza et al. (1991) characterized the release mechanism as

following three general steps: 1) Water moves into the fertilizer granule by osmotic

potential, 2) the water soluble fertilizer inside the granule dissolves, and 3) the nutrient

solution diffuses out of the granule due to a chemical concentration gradient. The rate of

water penetration is proportional to the differences in water vapor pressures between the

inside and outside of the capsule. This gradient potential determines the rate of release of

the nutrient (Kochba, 1990). The talc component of the coating aids in control over the

rate of nutrient diffusion because the talc forms voids in the polymer coating. These

voids become larger with increasing talc content, increasing the distance which the water

must move through, slowing diffusion (Shoji, 1999). Talc can also be used to adjust the

Qio (the rate increase of a reaction over a 100 C rise) of release. As the talc content of the

coating increases, the Qio of diffusion decreases (Shoji, 1999). Generally, fertilizers are









formulated to maintain a Qio of around 2, matching typical Qio values for chemical

reactions occurring in plants and microbial activity in many soils (Shoji, 1999).

Soil temperature and moisture affect nutrient release rates. Maeda (1990) studied

the contributions of various soil factors affecting N release of one particular PCU product

and found that temperature accounted for about 83% while moisture content, about 11%.

Other soil factors such as microbial activity, pH, etc., and their interactions accounted for

less than 1% each. Having a nutrient release rate that is highly dependent on one variable

enables good prediction of release. Gandeza et al. (1991) showed that N release from

PCU was primarily affected by temperature. In that study, cumulative air temperature

(CAT) and cumulative soil temperature (CST) were highly correlated (r2= 0.99) so either

could be used for predicting nutrient release rates. This is useful because soil

temperature data is not always readily available, air temperature data can be used instead.

Fujita et al. (1983) and Fujita (1989) reported that the rate of PCU release is affected

most by moisture when soil moisture is less than the incipient plant wilting point of the

plant (10 kPa). This was addressed by Shoji (1999) who reported that at any soil

moisture content greater than wilting point, the relative humidity of the soil is 100%. He

did report that some observed values from a PCU product were somewhat lower than

temperature-predicted values in some coarse-textured upland soils, possibly due to

reduced diffusion under exceedingly dry soil conditions.

Summary and Research Objectives

Polymer-coated CRFs have the potential to revolutionize the way potato crops are

being grown. With predictable release rates, polymer-coated CRFs are very suitable for

BMP programs by allowing growers to produce acceptable crop yields while eliminating

the need for frequent applications of water soluble nutrients, thus reducing excessive









fertilizer applications and labor costs as well as the potential for nutrient movement. As

nutrient release rates could be formulated to match crop requirements, nutrients would be

available at times and in quantities required by the plant. This would result in potential

reduction in nutrient losses associated with high intensity rainfall events and thereby also

enhance nutrient use efficiency.

Release rates of nitrogen from polymer-coated fertilizers have not been determined

for TCAA growing conditions. Neither have the effects of various current commercially-

available PCU CRFs on potato production been examined. Once these are established,

fertilizer blends can be formulated to match crop uptake requirements, reducing excesses

of fertilizer being applied. The objectives of this work were to: 1) determine nutrient

release characteristics of various controlled-release fertilizers under controlled and field

conditions, 2) determine potato production and nutrient recovery efficiency data for

soluble and controlled-release fertilizer treatments, and 3) estimate soil nutrient levels in

potato beds and underlying perched water tables.














CHAPTER 3
MATERIALS AND METHODS

This chapter describes the materials and methods of the various experiments

conducted. In broad categories, the experiments can be broken down into three sections,

each of which addresses one of the three objectives of this research project. The three

categories are: 1) CRF release through the incubator and meshbag experiments, 2) field

production of potatoes in the CRF production and replacement experiments, and 3) soil

nitrogen movement in the leaching experiment utilizing wells and lysimeters.

The fertilizer products evaluated through all of the experiments performed are

shown in Table 3-1. The CRF products utilized for these experiments were labeled CRF1

through CRF6 with CRF2 being broken into CRF2a and CRF2b. CRF2 was sub-divided

because in the production experiment, "CRF2" was a blend of two fertilizer products,

CRF2a, and CRF2b. AN and urea were provided by Gator Fertilizer (Hastings, FL),

CRF1, CRF2a, and CRF2b were provided by Scotts Chemical Company (Marysville,

OH), and CRF5 and CRF6 were provided by Pursell Technologies, Inc. (Sylacauga, AL).

The University of Florida has signed a secrecy agreement with the manufacturers of

CRF3 and CRF4.

CRF Release from the Incubator and Meshbag Experiments

Incubator Experiment

The goal of the incubator experiment was to evaluate the release characteristics of

selected CRF products under aqueous conditions at controlled temperatures over a 13









Table 3-1. Characteristics of fertilizer products evaluated in the various CRF release,
production, and leaching experiments.
Fertilizer Formulation Manufacturer N Form Characteristics
16% NH4,
AN 30-0-0 Gator Fertilizer 14% NO3 water soluble
Urea 46-0-0 Gator Fertilizer Urea water soluble
CRF1 44-0-0 Scotts Chemical Co. Urea 45-day release
CRF2a 37-0-0 Scotts Chemical Co. Urea 120-day release
CRF2b 43-0-0 Scotts Chemical Co. Urea 75 day release
CRF3 42-0-0 Product 31 Urea CRF, unknown
CRF4 41-0-0 Product 41 Urea CRF, unknown
CRF5 44-0-0 Purcell Technologies, Inc. Urea CRF, unknown
CRF6 43-0-0 Purcell Technologies, Inc. Urea CRF, unknown
The manufacturer of these products has a secrecy agreement with the University
of Florida to remain anonymous.


week period. Weekly and cumulative release were measured together with residual

fertilizer, Qio values, and total recovery.

CRF fertilizer products

The incubator experiment had a total often fertilizer treatments: a no fertilizer

control (No N), ammonium nitrate (AN), urea, and seven CRF products. The two

products in CRF2 were separated for individual characterization.

Incubators

Six cooled incubators (Sanyo Electric Biomedical Co., Ltd., Osaka, Japan) were

set at constant temperatures of 5, 10, 15, 20, 25, and 300C. A seventh incubator was set

at variable temperatures based on the average soil temperature (10 cm depth) for a given

week of a typical growing season. The variable temperatures were established using 25

years (1975 to 2000) of historical soil temperature data for the area (Table 3-2). Each

week, prior to sampling, the temperature of each incubator was recorded as well as that of

an American Society for Testing and Materials (ASTM) certified thermometer inside









Table 3-2. Incubator 7 temperature settings used for the incubator experiment.
Average soil temperature Incubator setting
for week beginning (OC)
25-Jan 15
1-Feb 15
8-Feb 15
15-Feb 16
22-Feb 18
1-Mar 18
8-Mar 19
15-Mar 19
22-Mar 21
29-Mar 21
5-Apr 23
12-Apr 22
19-Apr 23
26-Apr 24


each incubator for temperature verification. The variable temperature incubator was

adjusted for the next week's temperature after sampling.

Duration

The experiment lasted for 13 consecutive weeks, with samples taken each week.

Setup and procedure

Three grams of nitrogen (varying amounts of fertilizer based on formulation) were

placed inside 200 ml sterile glass bottles with screw caps and added to 100 ml of

deionized (DI) water. These bottles were then placed inside each incubator. At one week

intervals, the bottles were shaken to ensure solution homogeneity and a 20 ml sample

aliquot removed. The fertilizer prills were filtered out of the remaining solution and

returned to the sampling bottle; the excess solution was discarded. The bottles were then

refilled with 100 ml of fresh DI water. After 13 weeks, the filtered fertilizer prills were









ground with a mortar and pestle and residual fertilizer was dissolved in 100 ml DI water

and an aliquot taken.

Sample analysis

Aqueous samples were stored at -50C prior to analysis. Solution from weekly

samplings was analyzed at the University of Florida Analytical Research Laboratory

(ARL) for nitrogen by TKN and for EC using standard protocols (Mylavarapu and

Kennelley, 2002). The TKN method used measures NH4-N but not N03-N, so the AN

treatment percent recovery was based on 1.6% applied N. Residual fertilizer samples

were analyzed by Waters Analytical Laboratories (Camilla, GA) for N by the Dumas

method (Dumas, 1831; Watson and Galliher, 2001).

Statistical design and analysis

Treatments were arranged in a completely randomized design with three replicates.

Data were treated in three major categories: weekly and cumulative release, residual

fertilizer, and total N recovery.

Weekly and cumulative release data were analyzed factorially for sampling date,

incubator temperature, and fertilizer source main effects and their interactions. Further

factorial analysis was performed on weekly and cumulative release samples by analysis

of fertilizer product main effect N release within each temperature setting, analysis of

temperature main effect release within each fertilizer product, and analysis of fertilizer

product main effect release for each sampling date.

Residual fertilizer can be defined as the amount ofN which would be available

after plants had been harvested or ceased nutrient uptake. In this experiment it was the

amount of N remaining in prills after 13 weeks of release. Residual fertilizer was









evaluated for fertilizer main effects at each temperature setting and for temperature main

effects with each fertilizer.

Total N recovery evaluated the fertilizer products at each incubator temperature

setting. All statistical analyses were performed using SAS ANOVA and software (SAS,

1999). Treatment significance and mean separation were performed using ANOVA and

the Tukey's mean separation tests with a = 0.05.

Meshbag Experiment

CRF fertilizer treatments

The meshbag experiment consisted of eight fertilizer treatments: AN, and seven

CRF products (CRF1 through CRF6). CRF2 was divided into CRF2a and CRF2b.

Setup and procedure

Meshbags were prepared by mixing approximately 200 g of soil with 3 g of

fertilizer (varying amounts of N). The mix was then tied into porous cheesecloth bags,

and labeled at the end of an attached string. The bags were then buried at 10 cm depth

from the top of the potato row at the research farm at the Plant Science Research and

Education Unit (PSREU) in Hastings, FL with no potato plants present. The meshbags

were subject to the same temperature and moisture conditions as plants. They were

buried on 13 Feb 2003 with samplings at 20, 35, 48, 62, 76, 91, and 104 days. Due to

limited space, meshbags were placed at approximately 20 cm in-row spacing and 100 cm

between-row spacing. At two week intervals, three replicates of each fertilizer material

were removed from the ground and air-dried. Once dry, the soil was sieved (30-mesh) to

remove soil and to retain the fertilizer prills. Prills were ground with a mortar and pestle

and any fertilizer was dissolved with DI water. The solution was filtered with #3









Whatman (Whatman International, LTD, Middlesex, UK) filter paper and diluted to 100

ml with DI water in class A volumetric flasks.

Sample analysis

Aqueous samples were stored at -50C prior to analysis. Samples were analyzed at

the University of Florida Analytical Research Laboratory (ARL) for nitrogen by TKN

and for EC according to standard protocol (Mylavarapu and Kennelley, 2002).

Statistical analysis

Treatments were arranged in a randomized complete block design with three

replicates. Data were analysed factorially for fertilizer product and sampling date main

effects. Fertilizer source main effects were analyzed both over all sampling dates as well

as for each sampling date. Sampling date main effects were analyzed over all fertilizer

products.

All analyses were performed using SAS ANOVA software (SAS, 1999).

Treatment significance and mean separation were performed using ANOVA and the

Tukey's mean separation tests with a = 0.05.

Field Production

Two field experiments were conducted at the University of Florida's Hastings Plant

Science Research and Education Unit (PSREU). The first experiment was a CRF

production experiment evaluating tuber yield, tuber quality, and plant nutritional status

over the course of the season as affected by six different CRF products plus ammonium

nitrate (AN) all at three nitrogen application rates together with a no fertilizer control.

The second experiment was a replacement experiment in which two potato varieties were

evaluated for tuber yield and tuber quality and plant nutritional status, as affected by

applying two different CRF products in combination with AN at different ratios (100:0,









75:25, 50:50, 25:75, and 0:100). Weather data was collected and recorded with the

Florida Agricultural Weather Network (FAWN) weather station located on the research

farm. As production was essentially the same for both experiments with the exception of

N fertilization, the production practices described below apply to both experiments

except as specified.

General Production

Soils

Soil at the field site is an Ellzey fine sand (sandy, siliceious, hyperthermic Arenic

Ochraqualf; sand 90-95%, <2.5% clay, <5% silt, 1% OM).

Irrigation

Subsurface irrigation was used during the season for irrigation. A perched water

table was maintained by flooding the growing field with water pumped from wells. A

clay hardpan approximately 1 meter below the soil surface prevented deep percolation of

this water. The water level was maintained at historical cultural levels (45-60 cm) by

controlling the drainage of water from the growing beds in ditches (18.3 m apart) at the

bottom of the field.

Planting

Seed potatoes for both trials were cut to approximately 71 g (2.5 oz) pieces and

dusted with fungicide (1.1 g (0.04 oz) a.i. fludioxonil and 21.8 g (0.77 oz) a.i. mancozeb

per 45.4 kg (100 lb) seed pieces; Maxim MZ, Syngenta Crop Protection, Inc. Greensboro,

N.C.) prior to planting.

In the CRF production trial, 'Atlantic' potatoes were planted on 13 Feb 2003 and in

the replacement experiment, 'Atlantic' and 'Red LaSoda' potatoes were planted on 20

Feb 2003. Seed potatoes were planted using 20-cm in-row spacing with 24 seed potatoes









per row in each plot of the production experiment and 36 seed potatoes per row in each

plot of the replacement experiment. Plots in both trials were four rows wide with

between-row spacing of 102 cm. The CRF trial plots were 4.6 m long with 1.2 m in-row

border space between plots and the replacement experiment plots were 7.3 m long with

1.8 m in-row border space between plots.

Fertilizer treatments

In the CRF production experiment, treatments consisted of a no nitrogen control

(No N) and 7 nitrogen sources (6 CRFs and AN) at three rates (112, 168, and 225 kg ha-1

N), representing 50%, 75%, and 100% of the recommended IFAS (or BMP) rate. CRF2

was a blend of CRF2a and CRF2b with 50% of the N coming from each fertilizer source.

In the replacement experiment, fertilized treatments consisted of a no nitrogen control

(No N) and two CRF products (CRF4 and CRF6) blended with AN at AN:CRF percent N

applications of 100:0, 75:25, 50:50, 25:75, and 0:100 totaling 168 kg ha-1 N. The

nitrogen source in all CRF products was urea. All fertilizer treatments were incorporated

into the plot the day of planting. Thirty-four kg ha-1 P (76 kg ha-1 P205) andl68 kg ha-1 K

(202 kg ha-1 K20) were incorporated into all plots prior to planting.

Seasonal management

Pesticide applications were made during the growing season following IFAS

extension recommendations (Aerts and Nesheim, 2000; Weingartner and Kucharek,

2004). Soil was fumigated with 1,3-dichloropropene (Telone II, 56 L ha-1, Dow Chemical

Company, Indianapolis, IN) in early January prior to planting. Aldicarb (Temik 22.5 kg

ha-1, Bayer Chemical Company, Kansas City, MO) was applied at planting. Metribuzin

(Sencor, 2.9 L ha-1, Bayer Chemical Company, Kansas City, MO) was broadcast at

hilling (approximately 21 days after planting) for weed control. Fungicides were applied









as needed for control of early and late blight following integrated pest management

practices.

Soil analysis

A composite soil sample (20 cores of the upper 30 cm) from the entire potato bed

was taken on 5 Feb 2003, before planting and prior to fertilizer application. Soil was air-

dried, sieved through a 30-mesh sieve, and analyzed by the University of Florida's ARL

for pH, nitrate (N03-N) and ammonium (NH4-N) concentrations, phosphorus, calcium,

magnesium, electrical conductivity (EC), and soil organic matter (OM) according to

standard protocol (Mylavarapu and Kennelley, 2002). Soil samples (8 cores of the upper

30 cm) were taken from each plot in the production experiment at two-week intervals

over the growing season at 15, 29, 41, 55, 69, 84, and 97 days after planting (DAP). The

final soil samples (97 DAP) were taken one day before final harvest. The replacement

experiment was sampled pre-plant and after harvest. All soil samples were dried and

sieved as described above. Mid-season soil samples were tested for the same parameters

as pre-plant soil samples.

Tissue Sampling and Analysis

Tissue samples consisting of both the leaflets and petiole of the most recently

matured (expanded) leaf which had reached full size and had turned a dark-green color

(Hochmuth, 1991) were sampled in the production experiment at bi-weekly intervals at

36, 47, 64, and 82 DAP. Six samples from each plot were dried at 700 C until a constant

weight was measured. They were then ground in a Wiley mill (Thomas Scientific,

Swedesboro, NJ) to pass through a 20 mesh sieve, and analyzed for total Kjeldahl

nitrogen (TKN) at the ARL. Petiole/leaflet tissue samples were not taken from the

replacement experiment.









At full flower, at 64 days after planting (DAP), one plant taken at random from

each plot in both the production and the replacement experiments was cut at the soil

surface. Leaves and stems were separated, dried, and ground. Samples were then

submitted to the ARL for TKN analysis using a standard protocol (Mylavarapu and

Kennelley, 2002). Data were used to calculate percent leaf and stem TKN, and leaf,

stem, and leaf + stem ("total") dry matter accumulation (DM).

At harvest in both the production and the replacement experiments, four marketable

tubers from each plot were skinned. The remaining center was then diced into 1 cm

cubes, dried, and ground. Tuber samples were analyzed for TKN at the ARL using

standard procedures (Mylavarapu and Kennelley, 2002).

Nitrogen Recovery Efficiency

Nitrogen recovery efficiency reflects the amount of applied nitrogen recovered

from the field in tubers. Nitrogen recovery efficiency (NRE) was calculated after the

method used by Zvomuya et al. (2003) by the following equation:


NRE = 100 (Ntreat Ncontrol) / Napplied

where Ntreat represents the amount of nitrogen removed in the tubers of a given fertilizer

treatment, Ncontrol is that removed in the tubers of the no fertilizer control plot, and Napplied

is the amount of nitrogen applied as fertilizer.

Harvest

The center two rows of each plot were mechanically harvested on 28-29 May 2003

at 106 DAP in the production experiment and 2 Jun 2003 at 103 DAP in the replacement

experiment using commercial equipment.









Potatoes were washed and graded into five size classes (size 1 < 4.8 cm, 4.8 cm <

size 2 < 6.4 cm, 6.4 cm < size 3 < 8.3 cm, 8.3 cm < size 4 < 10.2 cm, size 5 >10.2 cm)

based on USDA standards (USDA, 1991). Potatoes were grouped according to total

yield and marketable yield. Total potato yield is defined as all tubers harvested from the

field, independent of size or defects. Marketable yield is defined as no.1 tubers with

diameters between 4.8 and 10.2 cm (USDA, 1991) and without any visible blemishes

(rotten, green, misshapen, or containing growth cracks).

Specific gravity was measured by the weight in air/weight in water method (Edgar,

1951). Specific gravity is a ratio of water to solid content in a potato tuber. Because

'Atlantic' potatoes are used primarily for chipping, a high specific gravity is desired.

Specific gravities of at least 1.078 are considered good for production at the PSREU

research farm in Hastings, FL (Hutchinson et al., 2002).

Plant physiological disorders reduce tuber yields and quality. Tubers unfit for

storage or consumption were removed from the total yields and quantified. Tuber

external disorders that reduce marketability include sunburned (green) potatoes,

misshapen potatoes, growth crack potatoes, and otherwise rotten potatoes Tuber

internal disorders monitored include hollow heart or brown center, and internal heat

necrosis. Also evaluated were disease-induced tuber disorders include corky ring spot

and brown rot.

Statistical Analysis

The CRF production experiment was arranged in a randomized complete block

design with four replications. Data in the CRF production experiment were analyzed

factorially by fertilizer source and rate main effects. Where interactions were significant,

simple effects were analyzed. This was followed for total and marketable yields, specific









gravity, tuber quality, plant biomass, nutrient uptake, and nutrient recovery efficiency. In

the case of plant tissue analyses, data were also analyzed across all and at each of the

sampling dates, and where interactions existed, simple effects were evaluated.

The replacement experiment was arranged in a split plot design with four

replications. Statistical analysis involved the evaluation of the various fertilizer blends

for each CRF product, though not between products or across potato varieties. This was

done for yields, specific gravity, tuber quality, plant biomass, and nutrient recovery

efficiency. Linear regression analysis was performed within each fertilizer product and

potato variety across all AN:CRF blends.

All analyses for both the production and the replacement experiments were

performed using SAS ANOVA software (SAS, 1999, Gary NC). Treatment significance

and mean separation were performed using ANOVA and the Tukey's mean separation

tests with a = 0.05.

Nitrogen Leaching Experiment

The nitrogen leaching experiment was performed within the CRF production

experiment mentioned above. One lysimeter and one well were buried in each plot

(described below). Samples from both lysimeters and wells were taken at 29, 41, 64, and

78 DAP. Lysimeter and well samples were stored at -50C until analyzed. All water

samples were analyzed at the ARL for NO3-N and NH4-N concentrations following

standard procedures (Mylavarapu and Kennelley, 2002).

Lysimeters

Suction lysimeters, consisting of a PVC tube having a porous ceramic cup affixed

to one end and a rubber stopper affixed to the other, were buried in each plot to a 30 cm

depth below the top of the potato row. At two-week intervals over the season, a vacuum









of approximately 40 kPa, was applied to each lysimeter. After 24 hrs, a water sample

was removed from the lysimeter. Excess water from the lysimeter was removed and

discarded.

Wells

Well casings (PVC pipe, 10 cm diameter by 120 cm long) were buried in each plot

at a depth of 90 cm below the soil surface from the top of the potato row to access water

in the perched water table. Wells were removed from the field at 104 DAP in order to

harvest plots.

Statistical Analysis

As with the CRF production experiment, data were arranged in a randomized

complete block design, though with three replicates. Data were analyzed factorially by

fertilizer product, rate, and sampling date main effects. Where significant interactions

were found, simple effects were evaluated. With the sampling date effects, fertilizer

source and rate were analyzed both for each and across all dates.

All statistical analyses were performed using SAS ANOVA software (SAS, 1999).

Treatment significance and mean separation were performed using ANOVA and the

Tukey's mean separation tests with a = 0.05.














CHAPTER 4
RELEASE CHARACTERISTICS OF CONTROLLED-RELEASE NITROGEN
FERTILIZERS UNDER CONSTANT TEMPERATURE AND FIELD CONDITIONS

The laboratory and field release experiments were conducted to evaluate the rate of

release of nutrients from various controlled-release fertilizer (CRF) products.

Hypothetically, if release were predictable, fertilizer blends could be formulated that

would match crop uptake requirements. To that end, nitrogen CRF products from various

manufacturers were analyzed for rate of N release. These products were analyzed in two

experiments: 1) nitrogen (N) release from CRF in DI water inside incubators at constant

temperature and fluctuating temperature and 2) N release from CRF in buried meshbags

under field conditions. In the incubator experiment, 3 g of N (variable amounts of

fertilizer depending on formulation) were mixed with 100 ml DI water. The prills were

filtered weekly for thirteen weeks with aqueous samples taken each week, and fresh DI

water added, replacing water from each previous week. Residual fertilizer in prills after

thirteen weeks was submitted for quantification. Incubator temperatures were 50C, 100C,

150C, 200C, 250C, 300C and a variable temperature incubator which was adjusted weekly

to match average soil temperatures over successive weeks of a typical north Florida

growing season. In the meshbag experiment, meshbags containing 3 g of CRF (varying

amounts ofN) mixed with approximately 200 g of soil were buried in the growing field at

planting, and were successively removed at two week intervals over the potato growing

season and analyzed for residual fertilizer remaining in the prills.









Incubator Experiment Results

Ten fertilizer treatments were analyzed: a no fertilizer control (No N), ammonium

nitrate (AN), urea, and seven CRF products (CRF1, CRF2a, CRF2b, CRF3, CRF4,

CRF5, and CRF6). CRF2 was split into two products because in the production and

leaching experiments (Chapters 5 and 6, respectively) CRF2 was a blend of two fertilizer

products, each contributing half of the N applied. For this experiment, these two

products were analyzed separately to determine the release profile of each. Although AN

and urea are water soluble, they were included as controls. These are currently the local

prevailing fertilizer sources for potato production. Table 4-1 shows the various incubator

settings with readings taken weekly over the experimental period.

Incubator Experiment Weekly and Cumulative N Release

The weekly release data were analyzed factorially for rate, sampling date, and

fertilizer source main effects; the ANOVA table is shown in Table 4-2. Over all

temperature settings, fertilizer products, and sampling dates, all main effects were

significant as were their interactions: temperature by fertilizer (p < 0.0001), temperature

by sampling date (p < 0.0001), fertilizer by sampling date (p < 0.0001), and the third-

order interaction, temperature by fertilizer by sampling date (p < 0.0001). Thus, further

analyses were performed within each effect to evaluate the reasons for these results. As

the primary purpose of this experiment was to evaluate the release characteristics of

certain fertilizer products and to relate that release to field conditions, each fertilizer

product was evaluated for differences of release at each temperature for each sampling

date and the various fertilizers were evaluated for differences of release in the variable

temperature incubator, also for each sampling date.












Table 4-1. Incubator temperatures during the incubator experiment.
Incubator Incubator 7
Week 50C 100C 150C 200C 250C 300C Variable setting (oC)
01 5.02 5.5 10.0 10.5 14.5 14.6 19.5 19.0 24.5 24.5 30.0 30.6 14.0 15.4 15
1 4.3 4.7 9.8 10.4 14.9 15.2 20.0 19.7 24.9 25.3 30.1 30.0 14.2 14.5 15
2 5.0 5.7 10.0 10.1 15.0 15.1 20.0 20.4 25.0 25.4 30.0 30.2 14.0 15.2 15
3 4.0 5.1 9.7 10.3 14.6 14.4 20.0 20.3 25.0 25.5 30.0 30.3 15.6 15.9 16
4 4.3 5.2 9.9 10.2 14.8 14.9 20.0 20.6 24.8 25.2 30.0 30.4 17.3 18.3 18
5 4.5 5.6 10.0 10.0 14.5 15.2 19.5 19.8 25.0 25.5 30.0 29.9 16.9 17.4 18
6 4.0 4.5 9.8 9.4 14.5 15.3 20.0 20.3 24.9 25.2 30.3 30.1 18.2 18.5 19
7 4.2 4.5 10.0 9.6 14.6 15.2 20.0 20.5 24.6 25.4 30.0 30.0 18.0 18.7 19
8 4.1 5.3 10.0 9.8 14.6 14.9 19.8 19.4 24.9 25.4 29.5 30.0 20.8 21.5 21
9 4.1 5.3 10.0 10.0 14.8 15.2 20.0 20.5 25.0 25.2 29.8 30.0 20.6 20.9 21
10 4.3 4.6 10.0 9.7 14.9 15.3 20.0 20.1 24.3 25.0 30.0 30.0 22.5 23.2 23
11 4.3 4.5 10.0 10.2 14.8 15.3 20.0 20.4 25.0 25.4 30.0 30.4 21.5 22.2 22
12 4.2 5.4 10.0 9.8 14.7 15.2 20.0 19.8 24.5 24.6 29.7 30.0 23.4 23.4 23
13 4.3 5.2 9.8 10.0 14.6 14.7 19.9 20.3 24.8 25.5 29.8 30.0 23.9 23.8 24
1 At week zero, the samples were placed in the incubator after equilibrating, but no sample was submitted for testing.
2First temperature represents a water-submerged alcohol thermometer inside incubator; second represents the incubator digital
reading.









Table 4-2. ANOVA table for CRF incubator release by sampling date, temperature
setting and fertilizer product main effects.
Source DF Type III SS MS F Value Pr > F
Date 12 1849142746 154095229 3352.85 < 0.0001
Temp 6 83822647 13970441 303.97 < 0.0001
Fert 8 625969804 78246226 1702.5 < 0.0001
Rep 2 30250 15125 0.33 0.7196
Temp*Fert 48 118597592 2470783 53.76 < 0.0001
Date*Temp 72 104261826 1448081 31.51 < 0.0001
Date*Fert 96 1681062415 17511067 381.01 < 0.0001
Date*Temp*Fert 576 237509519 412343 8.97 < 0.0001
Error 1636 75189704 45959
Corrected Total 2456 4775586503


Ammonium Nitrate

The release profile of ammonium nitrate (AN) is shown in Table 4-3 and in Figure

4-1. As would be expected for a water-soluble fertilizer, release from AN was

characterized by a "flush" of nutrients at the first sampling date, with little N recovery at

subsequent samplings. Further, as AN has no temperature-based release, there was little

statistical separation between N in the various sample at any of the sampling dates. There

was a significant difference in N found in samples taken at 7 DAP, though this would not

be expected, and could be due to experimental error. Significant differences found

between samples taken at 57 and 64 DAP were not considered of particular use because

the concentration of nutrients at this time was practicably zero and within the background

range for this experiment.

Urea

The release profile of urea is shown in Table 4-4 and in Figure 4-2. Similar to

ammonium nitrate, urea had high initial N release with little residual fertilizer in

subsequent samplings. This is not surprising as urea is a water-soluble product. While

there was a significant difference in N concentration between samples from the variable

















Table 4-3. N release from ammonium nitrate at various incubator settings for each sampling date.
Days (TKN, mg L-)


Temperature ( C)
5
10
15
20
25
30
Variable


7 14 21 28 35 42 49
9471 ab1 621 7 4 5 3 5
9432 ab 238 11 3 2 1 1
9721 ab 280 5 3 2 1 3
9656 ab 282 3 4 3 1 2
10185 a 242 7 2 1 1 31
9550 ab 376 7 2 2 1 1
9136 b 329 7 2 1 1 2


57 64 71 78 85 92
2 a 3 a 2 2 1
1 b 1 b 1 0 0
1 b 1 b 2 0 0
1 b 1 b 1 0 0
1 b 1 b 2 1 0
1 b 1 b 2 3 0
1 b 1 b 2 0 0


ANOVA p-value 0.0232 0.4397 0.2096 0.7104 0.0773
Tukey LSD 817 ns ns ns ns
1 Means in columns followed by same letters not significantly different.


8000


2 6000


- 4000


--5 C

--10C

--15C

20C

25C

--30 C


0.0619 0.4915 0.0371 <0.0001 0.3242 0.0726 0.3126 0.4682


ns ns


0.6 0 ns ns ns ns


80-
C-
C-

60





2


- Variable


-- 5 C

--10C

u--15C

20C

25C

--30C

--Variable


0 20 40 60 80 100

Days


0 20 40 60 80 100

Days


Figure 4-1. Release profile of ammonium nitrate at each incubator setting over the duration of the CRF release experiment. A)
Weekly release, B) Cumulative release.

















Table 4-4. N release from urea at various incubator settings for each sampling date.
Days (TKN, mg L-)
Temperature ('C) 7 14 21 28 35 42 49 57 64 71 78 85 92
5 2491 440 a' 11 3 4 4 3 2 2 a 2 3 a 4 0
10 2529 389 a 10 3 4 3 1 1 1 b 1 1 b 0 0
15 2679 400 a 7 4 2 3 2 2 1 b 2 1 b 0 0
20 2626 355 a 7 4 3 3 3 1 2 a 2 1 b 0 0
25 2682 377 a 23 21 5 2 41 1 1 b 3 1 b 0 0
30 2665 359 a 9 6 6 1 3 1 1 b 2 1 b 0 0
Variable 2714 217 b 8 3 7 1 2 0 1 b 2 0 b 3 0
ANOVA p-value 0.0842 <0.0001 0.2220 0.4017 0.6317 0.4166 0.4235 0.2320 0.0003 0.5848 <0.0001 0.1909 0.4682
Tukey LSD ns 93 ns ns ns ns ns ns 0.6 ns 1 ns ns
1 Means in columns followed by same letters not significantly different.


3000


2500


2000


2 1500


C 1000


500


0


--50C

-*-10oC

--15C

20C

25C

--30 C

-- Variable


80


60
C4-


40


20


-*-5TC


-*-10oC

'-15TC

20C

25C

-N-30C

-- Variable


0 20 40 60 80 100


20 40 60 80 100


Figure 4-2. Release profile of urea at each incubator setting over the duration of the incubator experiment. A) Weekly release, B)
Cumulative release.


B


______ ______I__









temperature incubator and all other incubators, this is likely due to sample error. The

significant separations at 64 and 78 days are artifacts of samples with background

concentrations of N and rounding errors rather than actual differences in N. The low

percent release (recovery of applied) of N is discussed below (see Total N recovery).

CRF1

The release profile of CRF 1 is shown in Table 4-5 and in Figure 4-3. While there

was significant separation in N release at the first two sampling dates, CRF 1 had a

generally similar release profile to urea and AN-high initial release with little

subsequent release. As with urea and AN, significant separations at 28, 64, and 78 days

are likely due to background levels of N coupled with low-level contamination in random

samples causing some statistical differences. While N release at the first sampling date

was greater in the 250C, 300C, and variable temperature incubators than in the 50C and

100C incubators, this temperature-influenced release was not continued at subsequent

samplings. This would tend to indicate an initial temperature-based release, though not

over time.

CRF2a

The release profile of CRF2a is shown in Table 4-6 and Figure 4-4. Like the

water-soluble fertilizer products, CRF2a exhibited little temperature-based release. No

significance was found for the first four sampling dates for N concentration from samples

in the various incubators, and the differences found at 35 and 64 days were small. In

contrast to AN, urea, and CRF 1, CRF2a had continued nutrient release over the entire

season, albeit at low levels. This would tend to indicate that nutrient inside the fertilizer

prills was not entirely depleted and slowly available.


















Table 4-5. N release from CRF1 at various incubator settings for each sampling date.


Temperature ( C) 7 14 21 28
5 2438 d' 371 ab 17 2 b
10 2531 cd 343 ab 17 2 b
15 2624 bc 419 ab 17 3 b
20 2588 b-d 424 ab 17 2 b
25 2704 a 516 a 24 3 b
30 2646 ab 383 ab 16 20 a
Variable 2841 b 259 b 19 3 b

ANOVA p-value < 0.0001 0.0117 0.3834 0.0182
Tukey LSD 170 183 ns 16
1 Means in columns followed by same letters not significantly different.


3000


2500


S2000


S1500


1000


500


0


Days (TKN, mg L-')
35 42 49


1
1
1
1
2
9
10
0.2218
ns


-0- 5C


--10C


--15C


20C


25C


-m-30 C


-- Variable


7
6
4
4
5
10
6
0.4983
ns


C-
C-
60
a

d 40

-
c
_
C^


7
8
8
11
7
6
5
0.2928
ns


57 64
4 2 b
3 10 a
11 1 c
5 1 c
1 1 c
1 1 c
3 1 c
0.2128 <0.0001
ns 0


71 78
1 14 b
27 2 b
13 1 b
13 1 b
14 7 b
14 84 a
16 4 b
0.4558 <0.0001
ns 14


0 20 40 60 80 100


20 40 60 80 100


Figure 4-3. Release profile of CRF1 at each incubator setting over the duration of the incubator experiment. A) Weekly release, B)

Cumulative release.


85 92
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0.3168
ns ns


S-- 5C


--10C


-.-15C


20C


25C


-x-30 C


-- Variable


B


=. -- _

















Table 4-6. N release from CRF2a at various incubator settings for each sampling date.


Temperature ( C) 7 14 21 28 35
5 4043 1183 540 355 317 ab1
10 4231 1084 529 490 411 ab
15 4065 1052 414 514 332 ab
20 4543 1288 574 534 473 a
25 5160 1221 562 457 413 ab
30 4890 1267 714 415 315 ab
Variable 4996 1172 454 379 236 b
ANOVA p-value 0.1711 0.5554 0.1555 0.0765 0.0565
Tukey LSD ns ns ns ns 233
1 Means in columns followed by same letters not significantly different.


6000


5000


S4000


S3000


S2000


1000


0


* 5TC

- 10 C

--~15TC

20C

25C

--30 C

--Variable


Days (TKN, mg L')
42 49 57 64 71 78 85 92
251 226 195 220 ab 284 226 207 272
250 260 281 260 a 369 196 208 176
347 284 351 191 ab 246 262 194 195
424 243 320 180 ab 183 131 247 153
270 238 216 162 b 146 103 150 150
239 292 457 165 b 123 126 191 141
198 216 180 142 b 190 131 123 157
0.1424 0.6871 0.4608 0.0047 0.2080 0.1142 0.6138 0.2041
ns ns ns 82 ns ns ns ns


80
C-
C-

60






20


0 20 40 60 80 100

Days


S5TC

--10 C

- 15C

20C

25C

--- 30C

- Variable


0 20 40 60 80 100

Days After Starting


Figure 4-4. Release profile of CRF2a at each incubator setting over the duration of the incubator experiment. A) Weekly release, B)
Cumulative release.


w









CRF2b

The nutrient release profile for CRF2b is found in Table 4-7 and Figure 4-5. While

CRF2b had the spike of initial N release at the first sampling date, it also continued

sustained nutrient release throughout the majority of the testing period. Of particular

interest, at the first sampling date (7 days), an increase in incubator temperature resulted

in an increase in N release, thus indicating temperature-based release characteristics. As

would be predicted, N release from the variable incubator was comparable to that from

the 150C and 200C incubators. Also of note, total release by the end of the study was

similar for fertilizer in incubators set at 200C, 250C, 300C, and the variable temperature

incubator, in that they had all approached 90% release of total nutrients during the testing

period.

CRF3

CRF3 exhibited characteristics between those of CRF and water-soluble products

(Table 4-8 and Figure 4-6). At the first sampling date, a large flush ofN was observed,

while at 14 days, only samples from the 100C and 300C incubators had substantially

comparable release to the first sampling date. At 21 and 28 days, N release followed a

temperature-based trend where significantly greatest release was obtained from samples

in the 300C incubator and least release from the 5C incubator. Between 42 and 57 days,

nutrient release from all samples was substantially higher than from previous samplings,

a phenomenon not seen with either the water-soluble or CRF products. At and after 64

days no trend appeared to describe the data, though N concentrations at 71, 78, 85, and 92

days had significant differences.


















Table 4-7. N release from CRF2b at various incubator settings for each sampling date.
Days (TKN, mg L ')
Temperature ( C) 7 14 21 28 35 42 49 57

5 1870 de 1000 e 620 e 537 c 576 e 522 c 515 d 553 e

10 1758 e 1303 de 953 de 946 bc 866 de 828 bc 776 d 971 de
15 2416 cd 1722 cd 1379 d 1529 a-c 1654 cd 1618 b 1633 bc 1947 bc
20 2684 c 2251 bc 2108 c 2220 a-c 2372 bc 2603 a 2480 a 2566 a
25 4578 b 2420 b 3482 b 3406 a 3623 a 1524 b 2102 ab 1502 cd
30 5741 a 4530 a 5749 a 2818 ab 2744 ab 1377 b 1072 cd 751 e
Variable 2364 cd 1770 cd 1400 cd 1666 a-c 1814 b-d 1621 b 2436 ab 2250 ab


ANOVA p-value < 0.0001 < 0.0001 < 0.0001 0.0036
Tukey LSD 587 552 714 2008
1 Means in columns followed by same letters not significantly different.



7000

6000 -

5000 I


S4000

S3000 -

2000 "

1000


0.0001
1014






5TC

--10C

-u-15C


20C

25C

-x-30C


--- Variable


0.0001
853


80



60
4

- 40
c
u
_

S20


0.0001
827


0.0001
545


64

550 c

820 c
1540 b
1956 ab
894 c
412 c
2163 a


0.0001
488


71

530 c

838 c
1618 b
1622 b
631 c
317 c
2633 a


0.0001
703


78 85 92

594 de 548 c 514 bc

855 cd 783 b 792 ab
1470 ab 1228 a 1098 a
1183 bc 811 b 663 b
413 de 278 d 220 cd
199 e 156 e 112 d
1768 a 1250 a 812 ab


0.0001
527


0.0001
90


0.0001
371


- 5TC

-4-10 C

--15C


20C

25C

-u- 30TC

-i-Variable


0 20 40 60 80 100


0 20 40 60

Days After Starting


Figure 4-5. Release profile of CRF2b at each incubator setting over the duration of the incubator experiment. A) Weekly release, B)
Cumulative release.


80 100

















Table 4-8. N release from CRF3 at various incubator settings for each sampling date.


Temperature

(C) 7 14 21 28 3
5 1701 654 94 d1 45 c 3
10 1756 1784 100 d 59 bc 3
15 1859 460 138 c 78 b 5
20 1926 480 141 c 81 b 8
25 1394 522 180 ab 148 a 8'
30 1968 1362 184 a 132 a 60(
Variable 1713 315 148 bc 127 a 18'
ANOVA
p-value 0.7682 0.2372 <0.0001 <0.0001 <0.
Tukey LSD ns ns 34 32
1 Means in columns followed by same letters not significantly different.


2500


2000


- 1500


M 1000


500


0


Days (TKN, mg L-')
5 42 49 57
4 c 228 d 202 c 191 c
9 c 345 cd 290 bc 272 bc
9 c 453 a-c 371 ab 350 b
0 c 556 ab 439 a 558 a
6 c 501 a-c 383 ab 32 d
0 a 360 b-d 262 c 19 d
6 b 648 a 445 a 375 b


0001
54


0.0002
204


0.0001
103


-- 5C


--10C

--15C

20C

25C

-x-30C

- Variable


80
C-
C-

60


40


20


64 71
75 14 c
20 205 a-c
102 233 ab
30 227 ab
22 271 ab
14 92 bc
39 365 a


0.0001 0.3431
141 ns


78
135 a
91 a-c
79 a-c
100 a-c
20 bc
3 c
132 ab


85 92
37 c 113 cd
183 ab 155 bc
215 a 189 ab
173 ab 135 cd
116 bc 102 de
76 c 62 e
241 a 220 a


0.0008 0.0081 <0.0001
194 112 84


0.0001
46


-0- 5C

- 10C

.-l15C

20C

25C

-i-30C

- Variable


0 20 40 60 80 100

Days


0 20 40 60 80 100

Days


Figure 4-6. Release profile of CRF3 at each incubator setting over the duration of the incubator experiment. A) Weekly release, B)
Cumulative release.


B









CRF4

The CRF4 release profile is shown in Table 4-9 and Figure 4-7. At the first two

sampling dates, no significant difference was found in N concentration between the

various incubator temperatures. There was, however, at these early sampling dates, a

high initial pulse of N release, as seen with both the water-soluble and the CRF products

previously evaluated. At 21 and 28 days, N release followed temperature-based release

patterns; highest N release was obtained from samples in the 250C, 300C, and variable

temperature incubators while least release was obtained from the 50C and 10C

incubators. After 28 days, though differences were found, N concentrations did not

appear to follow a strong temperature-based trend. As with CRF2b, by 92 days, total N

release samples in the 200C, 250C, 300C, and the variable temperature incubators was

roughly equal. As samples from the third and fourth samplings exhibited temperature-

controlled release, it is possible that temperature-based control was also controlling

release at the first two samplings, with those effects being masked by a large initial N

release.

CRF5

The release profile and sample N concentrations for CRF5 at each sampling date

are found in Table 4-10 and Figure 4-8. Of all of the CRF products evaluated, CRF5

exhibited the greatest degree of temperature-based release as evidenced by the significant

decrease in N concentrations from samples taken at the first sampling date. This

controlled-release trend continued through 49 days, where samples from warm-

temperature incubators, generally had greater nutrient release than from cool-temperature

incubators. The only exception to this was at 14 days, where none of the samples were

statistically different from one another. This is likely due to a lack of precision in

















Table 4-9. N release from CRF4 at various incubator settings for each sampling date.
Temperature Days (TKN, mg L ')
(C) 7 14 21 28 35 42 49 57


654 94 d1
1784 100 d
460 138 c
480 141 c
522 180 ab
1362 184 a


45 c
59 bc
78 b
81 b
148 a
132 a


34 c 228 d
39 c 345 cd
59 c 453 a-c
80 c 556 ab
86 c 501 a-c
600 a 360 b-d


202 c
290 bc
371 ab
439 a
383 ab
262 c


191 c
272 bc
350 b
558 a
32 d
19 d


64 71
75 14 c
20 205 a-c
102 233 ab
30 227 ab
22 271 ab
14 92 bc


78 85 92


135 a
91 a-c
79 a-c
100 a-c
20 bc
3 c


37 c 113 cd
183 ab 155 bc
215 a 189 ab
173 ab 135 cd
116 bc 102 de
76 c 62 e


Variable 1713 315 148 bc 127 a 186 b
ANOVA
p-value 0.7682 0.2372 <0.0001 0.0001 <0.0001
Tukey LSD ns ns 34 32 54
1 Means in columns followed by same letters not significantly different.



9000


7500


6000


S4500


S3000


1500

0 IF-
0


648 a


445 a 375 b


0.0002 <0.0001
204 103





1 -5---C 100
- 5C


- 10C

u--15C


20C

25C

--30'C

--Variable


C-
C-
60
a

| 40

-u
C^


39 365 a 132 ab 241 a 220 a


0.0001 0.3431
141 ns


0.0008
194


0.0081 <0.0001 <0.0001
112 84 46






B

-- 10C

-- 15C

20'C

25C

--30C

Variable


0 20 40 60 80 100

Days


0 20 40 60 80 100


Figure 4-7. Release profile of CRF4 at each incubator setting over the duration of the incubator experiment. A) Weekly release, B)
Cumulative release.

















Table 4-10. N release from CRF5 at various incubator settings for each sampling date.


Temperature

(C) 7 14 21 28
5 720 c' 679 a 391 c 407 d
10 848 c 614 a 530 c 926 d
15 960 c 1114 a 1390 bc 1591 c
20 1518 bc 2158 a 2354 ab 2414 b
25 2648 b 3135 a 3382 a 3396 a
30 4530 a 3554 a 3468 a 3492 a
Variable 895 c 1267 a 1592 bc 1847 bc

ANOVA.p-value <0.0001 0.0224 0.0001 <0.0001
Tukey LSD 1240 2986 1721 614

1 Means in columns followed by same letters not significantly different.



5000-


4000 -


3000 -


2000



1000-


0


35

593 d
1027 d
1681 c
2494 b
3202 a
2601 b
1847 c
<0.0001
509


42

576 c
986 bc
1445 ab
1960 a
1731 ab
1378 a-
1713 ab
0.001
815


--5C

--10C

--15C


20C

25C

-i--30 C

--Variable


Days (TKN, mg L-')
49

701 d 8
1041 c 12.
1307 b 14
1760 a 20
1834 a 15
c 1104 bc 8
1651 a 16
) < 0.0001
S 232


80


60

4
-d 40

C^


0 20 40 60 80 100


57

60 d
31 c
63 b
59 a
78 b
77 d
25 b
0.0001
218


64

810 cd
947 c
1078 bc
1292 ab
1113 bc
586 d
1607 ab
<0.0001
342


71

763 d
925 d
1116 c
1319 b
909 d
467 e
1550 a
<0.0001
187


78
790 cd
841 cd
944 bc
1060 b
683 d
324 e
1492 a
<0.0001
167


0 20 40 60 80 100


Figure 4-8. Release profile of CRF5 at each incubator setting over the duration of the incubator experiment. A) Weekly release, B)
Cumulative release.


92

683 b
696 b
801 b
723 b
471 c
228 d
1239 a
<0.0001
157


85

477 cd
810 bc
784 bc
849 b
583 bc
197 d
1375 a
<0.0001
357


-0- 5C

--10 C

--15C


20C

25C

- -30 C

+- Variable









samples taken from the 300C incubator where concentrations of the three replicates were

358, 4700, and 5500 mg L-1 N; it is likely that the first value is a transcriptional error and

not a true value. Thus the absence of statistical differences is an error and true separation

would have likely followed trends set both before and after that sampling date, as

evidenced by the decreasing N concentration in successively cooler incubators. Of note

with CRF5, however, was that independent of temperature, this product never reached

greater than 90% release over the course of the experiment. Under field conditions, it

would be desirable to have a greater rate of release, so as to be useful to the plant during

the growing season. It should be noted that nutrient release from this product may have

been incomplete as substantial N was released even after 92 days, and illustrated by the

positive slope of the cumulative release curves in Figure 4-8, B.

CRF6

The release profile for CRF6 with accompanying N concentrations from the various

incubators at each sampling date are shown in Table 4-10 and Figure 4-9. CRF6 was the

only fertilizer product evaluated that did not have a substantial initial release ofN. Like

CRF5, it exhibited good temperature-based release. From the data, it appears that this

product had somewhat of a sigmoidal-type release-a period of no nutrient release

followed by a linear release curve, finally tapering off as the product was depleted. This

is illustrated by the S-pattern in the cumulative release curve for CRF6 (Figure 4-9, B).

Of note with this product was its continued release of substantial quantities of nutrients

through the end of the experiment period. Also, after 92 days of release, only product in

the 300C incubator had released even 70% of its nutrients; all other temperature regimes

had resulted in 60% or less total N release. As with CRF5, the positive slope of the

cumulative release curve between 85 and 92 days tends to indicate that further release

















Table 4-11. N release from CRF6 at various incubator settings for each sampling date.

Temperature Days (TKN, mg L-)

(C) 7 14 21 28 35 42 49 57 64
5 331 295 b 113 b 104 e 137 c 134 e 99 d 118 c 150 d
10 208 270 b 60 b 91 e 149 c 151 e 197 d 289 c 277 d
15 301 350 b 168 b 229 de 369 c 501 d 647 c 918 b 837 c
20 377 451 b 438 b 750 c 998 b 1031 c 1157 b 1664 a 1197 b
25 481 466 b 1179 ab 1826 b 2034 a 1637 b 1777 a 1919 a 1636 a
30 650 1591 a 1598 a 2562 a 2466 a 2072 a 1893 a 2028 a 1639 a
Variable 562 198 b 237 b 342 d 551 bc 700 d 907 bc 1100 b 1274 b
ANOVAp-value 0.1037 < 0.0001 0.0022 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001
Tukey LSD ns 434 1127 231 448 218 283 477 175
1 Means in columns followed by same letters not significantly different.


3000


2500


,2000
h;.

S1500


1000


500


0


-*- 5C

--10 C

-15'C

20C

25C

--30 C

- Variable


80


60
4

2 40


20


0 20 40 60 80 100

Days


0 20 40 60 80 100

Days


Figure 4-9. Release profile of CRF6 at each incubator setting over the duration of the incubator experiment. A) Weekly release, B)
Cumulative release.


71
155 e
322 e
912 d
1185 c
1540 a
1472 ab
1350 bc
<0.0001
177


78
185 e
322 e
886 d
1113 c
1350 ab
1239 bc
1436 a
<0.0001
163


85
193 f
315 e
822 d
970 c
1150 b
1000 c
1400 a
<0.0001
112






1 -5C


92
232 d
342 d
900 bc
968 b
989 b
789 c
1383 a
<0.0001
159


--10C

-.-15 C

20C

25C

--30 C

--- Variable










would occur, although it would be useless with respect to the typical 'Atlantic'

potato growth cycle.

No N Control

N found from the no fertilizer control at the various sampling dates is illustrated in

Figure 4-10. It serves to illustrate the background degree of contamination that occurred

throughout the sampling dates of the experiment. Early in the experiment, as high

quantities of N were found in the various samples, contamination in the control was

higher than late in the season when many of the CRF products had been depleted and the

water-soluble products had been removed.


30

25
--- 10oC

20 --150C

15 200C

10 25TC
S---30TC

S--+-- Variable

0 20 40 60 80 100
Days

Figure 4-10. N found in the no fertilizer control within each incubator for various
sampling dates.

Variable Temperature Incubator Release

As one of the purposes of this experiment was to evaluate the release of various

CRF products under simulated field conditions, the nutrient release of the fertilizer

products under varying temperature conditions was evaluated. The release profiles and

nutrient release from each fertilizer at each sampling date are shown in Table 4-12 and in

Figure 4-11. As noted previously with each individual fertilizer, all products with the

















Table 4-12. N release from fertilizer products in the variable temperature incubator for each sampling date.


Days (TKN, mg L-')
14 21 28 35 42 49


9136 a 329 d
2714 d 217 d
2841 d 259 d
4996 c 1172 c
2364 de 1770 b
1713 e 315 c


7 e 2 b b 1 c 2 e 1 h
8 e 3 b 7 b 1 c 2 e O i
19 e 3 b 10 b 6 c 5 e 3 g
454 c 379 b 236 b 198 c 216 e 180 f
1400 b 1666 a 1814 a 1621 a 2436 a 2250 a
148 de 127 b 186 b 648 b 445 de 375 e


57 64 71 78 85 92


1 d 2 e 0 c O f O d
1 d 2 e 0 c 3 f O d
1 d 16 e 4 c 0 f 0 d
142 d 190 e 131 c 129 e 157 d
2163 a 2633 a 1768 a 1250 b 812 b
39 d 365 de 132 c 241 d 220 d


7270 b 2451 a 1533 ab 1728 a 1475 a 1357 a 1278 bc 1200 c 1109 c 900 cd 751 b 636 c 494 c
895 f 1267 c 1592 a 1847 a 1847 a 1713 a 1651 b 1625 b 1607 b 1550 b 1492 a 1375 a 1239 a
562 f 198 d 237 de 342 b 551 b 700 b 907 cd 1100 d 1274 be 1350 be 1436 a 1400 a 1383 a


ANOVA
p-value <0.0001 <0.0001 <0.0001 <0.0001
Tukey LSD 786 168 182 443
1 Means in columns followed by same letters not significantly different.


0.0001
859


0.0001
438


0.0001
645


0.0001
1


0.0001
403


0.0001
585


0.0001
464


0.0001
53


0.0001
260


Fertilizer
AN
Urea
CRF1
CRF2a
CRF2b
CRF3
CRF4
CRF5
CRF6











12000 N
-i-No N

10000 -AN
Urea
8000 --CRF1
-- CRF2a
6000 -
6CRF2b
S4000 CRF3
CRF4
2000 CRF5
0 ~ CRF6

0 20 40 60 80 100
Days

Figure 4-11. Release profile of fertilizer product at the variable incubator setting over the
duration of the CRF release experiment

exception of CRF6 had substantial release at the first sampling date. Of the fertilizer

products evaluated, CRF2b, CRF4, and CRF6 had the greatest degree of sustained release

over the entire experiment.

When compared against each other, AN and CRF4 had significantly the greatest N

release at the first sampling dated, while sustained release from 14 through 49 days was

highest with CRF2b, CRF4 and CRF5. Late in the experiment, as CRF4 was depleted,

CRF2b, CRF5, and CRF6 had highest release. With the exception of the first two

sampling dates, AN, urea, and CRF 1 had essentially zero N release, typical of a water-

soluble fertilizer product.

Qio

Early in the experiment (7 and 14 day sampling dates), the release of each fertilizer

with respect to incubator temperature provided a good estimate of Qio values for each

product. CRF1 and CRF2a, together with the water soluble fertilizers, AN and urea, had a

single flush of N release which was independent of temperature, hence Qio values for










these products were roughly 1. Qio values were greatest for CRF5, both at the 7 and 14

day samplings across all temperature comparisons (Figure 4-12, A and B). Also from

these data, Qio values varied considerably over the biological range depending on where

one was within that range. For example, CRF5 at the 7 day sampling has a Qio of 1.3

between 5 and 150C, but a Qio of 3.0 between 20 and 300C. Qio values for sampling

dates beyond 14 days were not calculated because of a "depletion" effect that could occur


4
Z -.-CRF1

3 -- CRF2a

CRF2b

S2 CRF3
CRF4
1 -*- CRF5

C-RF6

5 to 15 10 to 20 15 to 25 20 to 30
Temperature Comparisons (C)


4
S- CRF1

-- CRF2a
3
CRF2b

2 CRF3

-K CRF4

1 CRF5

CRF6
0
5 to 15 10 to 20 15 to 25 20 to 30
Temperature Comparisons (oC)

Figure 4-12. Qio values for various CRF products. A) at 7 days, B) at 14 days.










where future fertilizer release if affected by differing amounts of fertilizer previously

released and correspondingly different remaining concentrations.

Residual Fertilizer

After 13 weeks of release, the fertilizer products were ground and the residual

fertilizer dissolved and submitted for TKN analysis. No residual analysis was run for

urea or AN because of zero residual recovery. The ANOVA table for factorial analysis

of incubator temperature and fertilizer source is shown in Table 4-13. As there was a

significant interaction (p < 0.0001) between the main effects and it was not of interest to

evaluate each product and temperature setting with all other product-temperature

combinations, differences in residual N from the fertilizer products was evaluated at each

temperature setting (Table 4-14) and the effects of the various temperature settings on N

release were evaluated for each CRF product (Table 4-15).

Table 4-13. ANOVA table for residual N by incubator temperature and fertilizer product
main effects.
Source DF Type III SS MS F Value Pr > F
Temp 6 17647 2941 333.63 < 0.0001
Fert 6 68808 11468 1300.86 < 0.0001
Rep 2 24 12 1.38 0.2565
Temp*Fert 36 14063 391 44.31 < 0.0001
Error 96 846 9
Corrected Total 146 101389


Within the coolest three incubators (5, 10, and 150C), both CRF2a and CRF6 had

the greatest amount of residual fertilizer after 13 weeks while CRF 1 had significantly the

least residual N of all products (Table 4-14). Within the warmest constant-temperature

incubators (20, 25 and 300C), significantly greatest residual was found in CRF2a while

CRF1 continued with the least residual N. The lack of residual N in CRF1 and, to a












Table 4-14. Residual N recovery (% of applied) from CRF products after 13 weeks of release for each incubator.
TKN (% of applied)
Fertilizer 50C 100C 150C 200C 250C 300C Variable
CRF1 1.2 e1 1.1 f 1.5 d 1.1 e 2.0 d 0.9 c 1.0 f
CRF2a 65.5 b 64.6 b 66.4 a 64.9 a 68.1 a 65.8 a 67.2 a
CRF2b 62.2 b 47.6 c 21.5 c 9.0 de 4.3 cd 1.8 c 7.9 de
CRF3 14.4 d 10.4 e 14.3 cd 4.6 de 4.0 cd 3.2 c 4.5 ef
CRF4 36.4 c 28.6 d 19.3 c 12.0 cd 7.3 c 7.3 c 12.5 d
CRF5 63.9 b 52.2 c 39.7 b 20.9 c 8.5 c 3.7 c 22.4 c
CRF6 79.4 a 64.6 a 60.5 a 49.7 b 28.2 b 18.3 b 47.1 b
ANOVAp-value 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001
Tukey LSD 10.5 9.0 12.8 9.4 4.6 7.6 5.3
1 Means in columns followed by same letters not significantly different.

Table 4-15. Residual N recover (% of applied) from CRF products after 13 weeks of release at each temperature setting.
TKN (% of applied)
Temperature (OC) CRF1 CRF2a CRF2b CRF3 CRF4 CRF5 CRF6
5 1.2 65.5 62.2 a1 14.4 a 36.4 a 63.9 a 79.4 a
10 1.1 64.6 47.6 b 10.4 a 28.6 b 52.2 b 64.6 a
15 1.5 66.4 21.5 c 14.3 a 19.3 c 39.7 c 60.5 b
20 1.1 64.9 9.0 d 4.6 b 12.0 d 20.9 d 49.7 c
25 2.0 68.1 4.3 d 4.0 b 7.3 d 8.5 e 28.2 d
30 0.9 65.8 1.8 d 3.2 b 7.3 d 3.7 f 18.3 e
Variable 1.0 67.2 7.9 d 4.5 b 12.5 d 22.4 d 47.1 c
ANOVAp-value 0.657 0.9782 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001
Tukey LSD ns ns 10.1 5.8 5.9 4.8 9.7
1 Means in columns followed by same letters not significantly different.









lesser degree, CRF3, independent of temperature, is of concern because they imparted no

nutrient retentive advantage over AN or urea. Having noted a high initial nutrient

release, hope might have been maintained all of the fertilizer was not lost, merely locked

into the prill. However, with little residual, it becomes apparent that all N was released at

the first sampling date. At 300C, CRF2a and CRF6 had 65.8% and 18% residual N,

respectively. This is of concern because after 90-100 days, most potato plants have

ceased uptake and even been harvested. This residual fertilizer would remain in the field

though with no crop to take it up, again potentially leading to leaching conditions.

Residual N from samples in the incubator temperature fell perfectly between that found

in the 150C and 250C incubators, the predicted response as temperatures in the variable

temperature incubator were always between these two values.

Considering each CRF across temperature settings (Table 4-15, Figure 4-13), both

CRF 1 and CRF2b had little change in nutrient release as temperature was changed.

This indicates no temperature-based control. Conversely, CRF2b, CRF4, CRF5, and

CRF6 had significant reductions in residual fertilizer as incubator temperature setting was

increased, tending to indicate varying degrees of temperature-based control. CRF3 had

intermediate characteristics between CRF and water-soluble products in that residual N

was not significantly different for the lower temperature settings or for the higher

settings, though a significant decrease

in residual was found between the two sets of temperatures. With the exceptions of

CRF2a and CRF6, the CRF products had very little residual fertilizer at either 250C or

300C.










100
CRF1
80 -- CRF2a
6 CRF2b
0 CRF2b
SCRF3
~ 40
CRF4
20 -- CRF5
H 20 -
o -+- CRF6
0
0 5 10 15 20 25 30 35
Temperature (oC)

Figure 4-13. Residual TKN (% of applied) for various CRF products as affected by
temperature.

Total N Recovery

The total amount of N recovered from the 13 weeks of release added to the amount

of N recovered from the residual found still inside the fertilizer prills constitutes the total

recovery of fertilizer. The percentages recovered are found in Table 4-16 and illustrated

in Figure 4-14 and Figure 4-15. CRF2a, CRF2b, CRF4, CRF5, and CRF6 all had total

recoveries greater than 80%, with CRF2a having total recoveries greater than 90%, across

all temperatures.

Meshbag Experiment

The meshbag experiment consisted of eight fertilizer products thoroughly mixed

with soil and buried in the growing field. The fertilizers consisted of ammonium nitrate

(AN) and the seven CRF products as were evaluated in the incubator experiment. In

preparing the meshbags, three grams of fertilizer (varying amounts of N) were applied to

approximately 100 g of field soil, mixed, and placed into a cheesecloth "bag", labeled,















Table 4-16. Total N recovery (% of applied) from fertilizer treatments from solution and residual sources for each temperature
setting.


TKN (% of applied))
5C 100C 15C 200C 25C 300C Variable
Soln1 Res Tot Soln Res Tot Soln Res Tot Soln Res Tot Soln Res Tot Soln Res Tot Soln Res Tot


68 0 68
13 0 13
10 1 11
27 65 92
28 62 90
11 14 26
47 36 83
25 64 89
7 79 86


61 0 61
10 0 10
10 1 11
28 65 93
39 48 87
18 10 28
55 29 83
38 52 90
10 79 89


63 0 63
10 0 10
10 2 12
28 66 94
70 21 91
15 14 30
68 19 87
52 40 92
26 61 87


62 0 62
10 0 10
10 1 11
31 65 96
85 9 94
16 5 21
75 12 87
73 21 94
41 50 91


65 0 65
11 0 11
11 2 13
31 68 99
84 4 88
13 4 17
73 7 80
82 8 91
56 28 84


62 0 62
10 0 10
11 1 12
31 66 97
87 2 88
17 3 20
73 7 80
76 4 80
67 18 85


59 0 59
10 0 10
11 1 12
28 67 95
69 8 77
21 4 25
71 13 84
58 22 80
32 47 79


1 Soln = solution; Res = residual; Tot = total. All values in % of applied.
2 AN values are corrected for total recovery based on 1.6 g N applied as NH4-N.


Fertilizer
AN2
Urea
CRF1
CRF2a
CRF2b
CRF3
CRF4
CRF5
CRF6















--AN

---Urea

CRF1

CRF2a

-- CRF2b

-- CRF3

- CRF4

CRF5

CRF6


0 5 10 15 20 25 30 35

Temperature (oC)


Figure 4-14. Total N recovery from dissolution and residual analysis across all
temperatures.


100

80o

60

40


20
0


Fertilizer Products


100



S60

S40
*R~,fr~1


* Solution


w




* Residual
* Solution


Fet" lize d uc

Fertilizer Products


80

60

40
SResidual
*Solution 20


Fertilizer Products


zm- ~- ~- E-
b- L-
Fertilizer Products


Figure 4-15. Graphical breakdown of the total recovery of fertilizer treatments at various
temperatures. A) 50C, B) 100C, C) 150C, D) 200C, E) 250C, F) 300C, G)
variable temperatures.


* Residual
* Solution


-x--


C~ ~cz






t~
------'


Ii










100
80
S60
S40
4 HResid a1
20 M Solution
20


Fertilizer Products


100
80
60
S40
2


100
80
60

40 Residual
20 J 0 Solution


Fertilizer Products
Fertilizer Products


iU


Fertilizer Products


Figure 4-15. Continued.



and tied with twine. Enough bags were prepared for three replicates of each product to

be removed from the field every two weeks over the growing season (7 total samplings at

20, 35, 48, 62, 76, 91, and 104 DAP). At two-week intervals, meshbags were removed

from the field, air-dried, and sieved with a 20-mesh sieve to remove soil particles. The

prills were then ground to disrupt the polymer coating and the residual fertilizer

dissolvedand analyzed by TKN analysis. Also analyzed were pure fertilizer prills to give

a baseline of total available N before field application.

Meshbag Experiment Results

ANOVA testing for the treatment and sampling date main effects revealed a

significant interaction between the effects (Table 4-17). As it was not of interest to

evaluate every fertilizer product and sampling date combination, the various fertilizer

products were evaluated at each sampling date (Table 4-18, Figure 4-16). For each of the









Table 4-17. ANOVA table for released N (% of applied) by fertilizer treatment and
sampling date main effects.
Source DF Type III SS MS F Value Pr > F
Trt 5 1.6801 0.336 95.6 < 0.0001
Date 6 2.1965 0.366 104.16 < 0.0001
Rep 2 0.007 0.0035 0.99 0.3743
Trt*Date 30 0.463 0.0154 4.39 < 0.0001
Error 82 0.2882 0.0035
Corrected Total 125 4.6347

sampling dates, AN, a water-soluble fertilizer, and CRF 1, a product that breaks up into

tiny granules, were not recovered. Accordingly, no residual analysis was performed.

CRF3 had the greatest release of N by day 20, statistically higher than all other CRF

products except CRF2b. However, CRF3 at subsequent samplings released only 10% of

applied more, similar to a water soluble product. At 20 DAP, CRF2a had released only

31% of its N, yet by the 104 DAP, it had released a total of 72% of its total contents-

28% was still in the prills after 104 days. CRF6, at 20 DAP, had released less fertilizer

than any other product, 23%. However, it continued to release steadily throughout the

season and by 104 DAP it had released 90% of its contents. For potato production in

Florida, it is desirable to have around 70 to 80 % release by full flower which occurs

around 60 days after planting. Of the CRF products evaluated, CRF2b, CRF3, CRF4,

and CRF5 all met that criteria, though CRF3 would likely not perform well for potato

production because after its initial high release, little fertilizer was subsequently released

for plant use. Figure 4-17 converts Figure 4-16 from a DAP to a degree-day basis, using

a base temperature of 50C. This is useful for calculating nutrient release based on

physiological age of the plant and adjusts for seasonal temperature variations.













Table 4-18. Cumulative N release (%) from CRF products at each sampling date for each fertilizer.
DAP1
Fertilizer 20 35 48 62 76 91 104
CRF2a 31 cd2 57 b 63 b 60 c 70 d 70 c 72 c
CRF2b 63 ab 86 a 93 a 94 a 99 a 98 a 99 a
CRF3 85 a 89 a 89 a 90 ab 91 ab 96 a 95 ab
CRF4 48 bc 72 ab 72 ab 81 b 84 bc 88 b 92 ab
CRF5 41 b-d 62 b 75 ab 87 ab 89 a-c 94 a 94 ab
CRF6 23 d 57 b 55 b 65 c 78 cd 84 b 89 b
ANOVAp-value 0.0001 0.0002 0.0010 0.0001 0.0001 0.0001 0.0001
Tukey LSD 24 19 23 11 11 5 8
DAP = Days after planting.
2 Means in columns followed by same letters not significantly different.


Sg80

S3 60
40

1 20


--CRF2a
-- CRF2b
CRF3
CRF4
-- CRF5
- CRF6


0 20 40 60 80 100 120

Days After Planting (DAP)


Figure 4-16. Cumulative N release (% of applied) from CRF products at each sampling date.










100 -
/ --- CRF2a
I 0 --- CRF2b
S60 CRF3
/ CRF3
S40 / CRF4
S 20 -- -- CRF5
-- CRF6

0 500 1000 1500 2000

Growing Degree Days (GDD), C

Figure 4-17. Cumulative N release (% of applied) of each fertilizer product as a function
of growing degree days with 50C base temperature.

CRF Release Discussion

Incubator CRF Release and Meshbag Experiment Correlation

When the various CRF release, residual, total recovery, and Qio data from the

incubator experiment are considered together with the data obtained from the meshbag

experiment, the general release characteristics of the evaluated CRF products can be

readily ascertained for both controlled-temperature and field conditions. As a general

rule, the fertilizer products had similar release patterns relative to each other between the

CRF release experiment and the meshbag study.

A comparison of the six CRF products that were evaluated in both the meshbag and

CRF release experiments is shown in Figures 4-18. As the temperature patterns

experienced by the CRF products between 2003 (when the meshbag study was run) and

the 30 year average (the temperature regime used in the variable temperature incubator

experiment) varied, the release of each of the products was converted to growing degree

days to obtain a common reference point. As mentioned previously, the base temperature

for growing degree day conversion was 50C, which is the temperature most often used for

























0 400 800 1200 1600 2000
GDD
/ ,=
















C


I'

0 400 800 1200 1600 2000
GDD









-
1, "


/[-B







0 400 800 1200 1600 20(
GDD






D




II

0 400 800 1200 1600 20(
GDD


0 400 800 1200 1600 2000 0 400 800


1200 1600


GDD GDD


Figure 4-18. Comparison of release rates of CRF products between the CRF release
experiment and the meshbag experiment on a degree day basis, base
temperature of 50C. A) CRF2a, B) CRF2b, C) CRF3, D) CRF4, E) CRF5, F)
CRF6.


potato growth equations. The incubator experiment received a total of 13 samplings


compared to 7 in the meshbag experiment, though the total number of degree days


accumulated in the CRF release experiment was only 1323 compared to the 1850


accumulated in the meshbag experiment.









On the surface, the release rates of the CRF products under the two sampling

regimes appear dissimilar. However, if the first sampling date from each experiment

were removed, and the slopes of the remaining lines compared (representing sustained

nutrient release over time), the slopes are remarkably similar with the exception of

CRF2b. The initial sampling date was observed to have a high release, likely due

primarily to broken, partially-coated, or otherwise incompletely sealed fertilizer prills.

So in removing these, the relative release of the fertilizer products can be evaluated. Also

from this data, it is encouraging that, after an initial release, the beaker experiment

adequately charts the release of coated materials.

The higher total release rates observed in the meshbag study compared to the

beaker experiment, particularly in the first sampling, may be explained by the physical

environment in which each was found. In the meshbag study, the fertilizer prills would

have been subjected to physical abrasion and pressure from surrounding soil particles

together with microbiological action found in the soil environment on the prill coatings.

In the beaker experiment, fertilizer prills were maintained in a pool of water with little

physical abrasion, and would not have been subjected to a full soil-like environment.

Fertilizer Release Characteristics

AN and urea

AN and urea can be used as baseline indicators for the behavior of water soluble N

products-near 100% release (though not necessarily recovery) early in the season with

little recovery and no residual thereafter. The poor total recovery of urea is probably due

to analytical difficulties in digesting the matrix resulting in low recoveries. As shown in

Figure 4-2, A, fertilizer release occurred in one burst. Together with the lack of residual

fertilizer (as illustrated in Figure 4-13), these data reveal that most of the fertilizer was









released at the first sample date. The laboratory performing the analyses reported

extensive difficulty performing digestions on these samples. The lab further reported that

upon digestion, the samples formed a brownish semi-gelatinous/semi-crystalline gel.

This had never previously been seen by the laboratory (Elisabeth Kennelley, personal

communication). Repeated dilutions were necessary to process the samples. It is

possible that the low recoveries of these samples were due to an incomplete digestion,

together with a compounding dilution factor.

The reduced recovery of AN is also somewhat enigmatic. The actual recovery,

based on a 3 g sample of N was approximately 33%. However, TKN analysis will detect

NH4 and urea nitrogen, but the method used does not convert NO3 nitrogen to NH4.

Thus, instead of a full 3 g potential N recovery, only 1.6 g (that applied in the NH4 form)

was potentially recoverable by the TKN method used. If the recovered N was calculated

against the amount recoverable by the analysis utilized, recovery values rose to an

average of 63% across all sampling dates for AN. As all of the fertilizer had dissolved

into the first sample and would have been subjected to high dilutions, the difference in

theoretical and actual recovery may possibly be attributed to dilution error as with urea.

CRF1

In the incubator experiment, CRF 1 had a high release at 7 days (80% of total

released) and by 14 days had released 96% of total released. This, coupled with no

residual fertilizer and a constant Qio value of 1 leads one to the conclusion that this

product behaves like a water soluble fertilizer rather than a CRF. The poor total recovery

likely follows the pattern set by urea-difficulty in analysis coupled with high dilutions.

As no residual fertilizer was recovered from the meshbag, no meaningful comparisons

were performed between the two experiments.









CRF2a

Similar to CRF 1, CRF2a in the incubator experiment gave a release characteristic

of a water-soluble fertilizer in that initial release was high with little subsequent release.

CRF2a also had a high initial release of about 50% of total release by 7 days. Though

some amount of fertilizer continued to release over the successive weeks, this fraction

was small. The constant Qio value of 1 reveals limited response to temperature, and the

high residual fertilizer found after 92 days reveals that the coating of this product

accounts for a large percentage of "lockout" which is permanently (over the lifecycle of

the plant) unavailable fertilizer to the growing crop. Because of the high residual and low

release, it is likely that the early fertilizer flush was due to fertilizer prills that either had

damaged coatings or were incompletely coated.

In the meshbag experiment, CRF2a followed a similar release pattern to that

observed in the incubator experiment. At 20 DAP, total N release was approximately

30% and by 104 days, total N release was only 72%. Thus, even under field conditions,

substantial nutrient was retained in the fertilizer prills, unavailable for nutrient uptake.

Correlation between the two experiments (Figure 4-18, A), revealed a similar

release pattern after the first two samplings within each. The difference in initial release

may be due to prill degradation/abrasion under field conditions.

CRF2b

CRF2b proved to be one of the best candidates for further research. The initial

fertilizer release from the incubator experiment was moderate except for high levels at

the 250C and 300C temperatures while continued release occurred over a number of

weeks. Its total cumulative release was near 80% by 92 days (for the variable

temperature incubator) and residual fertilizer at the higher temperatures was around 10%









or less. Qio values ranged from 1.3 between 50C and 150C to 2.1 between 200C and

300C.

In the meshbag experiment, greater than 60% of the product had been released by

20 DAP, while by 104 days, greater than 99% had been released. CRF2b was the only

CRF product evaluated in both release experiments where a different shaped release

curve was obtained for each. The reason for this difference is unknown, though different

products may have different responses field conditions. Thus, the involvement of

biological activity on fertilizer prills or soil abrasion, both of which were absent in the

incubator experiment, may be factors.

CRF3

CRF3 appeared to have similar release patterns as CRF1 and CRF2a in the

incubator experiment-a spike of release early in the growing season and limited

response to temperature (Qio constant at 1). Unlike CRF1 or CRF2a, it had a period of

release between 35 and 57 days. The lack of residual fertilizer, especially at warmer

temperatures, reveals limited problem with lockout. Qio values for this product ranged

around 1 for all temperature comparisons, indicating that release was not temperature

controlled.

From the meshbag experiment, CRF3 had released 85% of applied N by the first

sampling date (20 DAP), while 10% was released over the succeeding 84 days.

Correlation between the two experiments revealed that except for the first sampling date

at which samples in the meshbag experiment had nearly 8 times as much fertilizer

released as in the incubator experiment, sustained release of the product was very similar

between the two experiments.









CRF4

CRF4 had a high initial release (day 7), but exhibited continued steady release up to

nearly 40 days. The product had a Qio of 1 across all temperature comparisons; thus

release was not influenced by temperature. Residual fertilizer ranged from nearly 40% at

5C to about 8% at 300C.

In the meshbag experiment, CRF4 had released nearly half (48%) of its nutrient by

the first sampling date, though an additional 44% was released fairly consistently over the

successive weeks. Correlation between the two experiments was very similar with the

exception of the amount of N recovered at the first sampling-a phenomenon seen with

all of the products.

CRF5

CRF5 had a moderate nutrient release at day 7, but even higher release (with the

exception of the 300C temperature) in subsequent weeks. Total release approached 80%

by 92 days, but the positive slope of the cumulative release and the positive value on the

weekly release curves indicate that more fertilizer would have been released had the trial

period extended for a longer span. Of all of the CRF products evaluated, CRF5 also

exhibited the greatest Qio values-about 1.4 between 50C and 150C to nearly 3 between

200C and 300C. Thus, the product release could closely pattern temperature-related plant

growth, though release rates varied with temperature. Because of its high Qio value,

amount of residual fertilizer also indicated a strong relationship to temperature. At 50C,

residual fertilizer was nearly 64% while at 300C residual fertilizer was only 4%. In the

variable temperature incubator, total residual N was approximately 22%.

In the meshbag experiment, CRF5 had released 41% of its contents by 20 DAP

while by 104 DAP, it had released 94%. As with the incubator experiment, the lack of









residual is promising in that it was nearly all available during the plant growing season.

Further, with nearly 60% of the fertilizer remaining in the prills after 20 DAP, substantial

N was available through the middle and late parts of the season.

Correlation between the two experiments was generally good with the exception of

higher initial release in the meshbag experiment. Release from the incubator experiment

was not yet completed during the time period evaluated whereas it was largely complete

in the meshbag experiment after the same number of degree days.

CRF6

CRF6 exhibited desirable release characteristics. Of all of the CRF products

evaluated, it was the only one that did not have a high initial fertilizer release at day 7,

and it continued to have slow and controlled-release over the duration of the experiment.

This fertilizer in the variable temperature incubator had peak release at 78 days, resulting

in less than 30% total release to date. This is less than half of the desired 75% release

desired by 60 DAP. Qio values averaged 1 between 5 and 150C and approximately 1.6

over between 100C and 200C through 200C and 300C. Residual fertilizer showed a

correspondingly sharp decline with increasing temperature with nearly 80% residual

fertilizer in the 50C and 100C incubators down to less than 20% in the 30C incubator;

residual fertilizer in the variable temperature incubator was 47%.

In the meshbag experiment, total N release was 23% at 20 DAP which gradually

increased to 89% release by 104 DAP. This, resulted in substantial release during the

middle and late portions of the season, though likely too slowly to be useful to plants

during peak growth.

Correlation between the two experiments was generally good after two samplings.

In the field (meshbag experiment) substantial release was observed until 35 DAP, after









which sustained slow release was observed, whereas in the incubator experiment,

substantial initial release never occurred. Rather, slow steady release was observed

throughout the entire experiment.

Nitrification and denitrification

The possibility ofN being nitrified or even denitrified and hence unavailable for

recovery by TKN was evaluated by analyzing a subset of samples for NH4 and NO3

content. Since the N in all of the CRF products is from urea, the ubiquitous urease

enzyme would be necessary to convert urea to ammonium and the bacteria Nitrosomonas

spp. and Nitrobacter spp. would be necessary to convert ammonium to nitrite then nitrate,

respectively. For denitrification, N would have been required to be converted to either

nitrate or nitrite by the previously mentioned bacterium species and then reduced by

various denitrifying bacteria, converting nitrite to nitrous oxide or nitrogen gas. In the

cases of either nitrification or denitrification, bacteria would have to be introduced into

the environment and they would require a carbon source-neither of which is likely in a

sterile bottle with DI water and no substantial carbon supply. From the analysis of the

CRF samples, no significant quantity of ammonium was found (the maximum amount in

one sample was 100 mg L-1 with the rest being baseline), and no nitrate was found (data

not shown). Thus, some small amount of ammonification may have occurred in some

samples, but no nitrification or subsequent denitrification likely followed afterwards.

Therefore, most of the N in the CRF samples would have been in a chemical form

available for TKN analysis, except for N03-N in AN as previously discussed.

Plant uptake requirements

In order for N release characterizations to be useful, the general shape of the N

uptake curve for the life cycle of potato should be understood. Thus, the ideal nutrient









release curve for a fertilizer product can match the ideal uptake curve. As plants very

early in the season (0-10 days) rely solely upon nutrients contained in the seed tuber (no

roots have formed in this time), no outside fertilizer nutrients are necessary. After

approximately 10 days, when the plant has emerged from the soil and has begun forming

a root system, active soil nutrient uptake begins. This rate of uptake rapidly increases

and continues for nearly 60 days in 'Atlantic' potato. By full flower, which occurs

around 60 days in northeast Florida, approximately 75% of the fertilizer nutrients should

have been released and available for uptake. During the next 20 days of the season, the

remaining 25% of nutrients should be released, as nutrient uptake after around 85 days is

minimal (Ojala et al., 1990; Westermann, 1993).

Of the CRF products evaluated, all except CRF6 had high nutrient release very

early in the release periods, right when N uptake capacity of the plant is minimal.

CRF2b, CRF4 and CRF5 exhibited the best release profiles under field conditions

(meshbag experiment), although all could be improved if initial release was delayed for

10-14 days to allow the emerging plant to become established. CRF6 exhibited sustained

release over the experiment though total release was too delayed to be of maximal use to

the plant. This product could be improved if initial release occurred earlier in the season,

followed by greater sustained release rates through 80 DAP.

Methodology improvement

As already discussed, urea, CRF1, CRF2a, and CRF3 all had low total N

recoveries. These products also had little or no residual fertilizer and a single large flush

of nutrients at day 7. This likely created difficulties in analysis by TKN. This could be

solved by analyzing all samples by combustion by the Dumas method. No digestions or

dilutions are necessary with this method. Further, the Dumas method reads N whether in









the nitrate, ammonium, or urea form (all N is atomized), so would read AN as well

(Watson and Galliher, 2001).

Another possible point of improvement in methodology could be accomplished by

adding field soil to the beakers. This could possibly introduce a more abrasive

environment for greater polymer coating disruption and a supply of microorganisms. It

would however complicate the taking of weekly samples because of the difficulty of

keeping soil out of the sample aliquot. However, if these CRF release data were found to

correlate well to data from similar tests performed in the field, such adjustments would be

unnecessary.

Summary

Of the CRF products evaluated, CRF2b, CRF4, CRF5, and CRF6 showed

characteristics most favorable to potato production. They all released in increasing

quantities with temperature (Qio > 1), had release periods over a period of many weeks,

and released a high percentage of fertilizer (low residual) indicating low levels of

"lockout". Though none of the fertilizer products released 75% of total N by full flower

in the incubator experiment, CRF2b, CRF3, CRF4 and CRF5 all met that criteria in the

meshbag experiment. In the incubator experiment, CRF2b, CRF4, and CRF5 appeared to

release excessive amounts of N early in the experiment (7 days), while CRF6 had

comparatively little release early. All four of them also appeared to have too long of

longevity in the incubator experiment. In the meshbag experiment, these four products

had even a higher initial release of nutrients, though continued release appeared similar to

the beaker experiment. CRF 1, CRF2a, and CRF3 appeared to release available fertilizer

quickly (by day 7), leaving little available nitrogen for subsequent weeks. With CRF1

and CRF3, all of the nitrogen was released in this first week, while CRF2a had large









quantities of N that remained in the prills over the entire duration of the experiment. In

the meshbag experiment, both CRF2a and CRF3 had higher initial releases of nitrogen

when compared to the incubator experiment at the first sampling date, with no subsequent

difference in slope.

Of the CRF products evaluated, CRF2b, CRF4, CRF5, and CRF6 would be good

products for further evaluation. If the coating characteristics of the prills were modified

or if blends were created to bring total N release more in line with crop uptake

requirements, the products could provide nutrients to plants at times and in quantities

needed.














CHAPTER 5
COMPARISON OF CONTROLLED-RELEASE NITROGEN FERTILIZERS TO
AMMONIUM NITRATE ON POTATO PRODUCTION

If controlled-release fertilizers (CRF) are to be adopted for use in potato

production, they must not compromise either yield quantity or quality. Two field

experiments were conducted to evaluate the influence of CRF on potato production.

These include the "CRF Production Experiment" and the "Replacement Experiment".

Both experiments evaluated the effect of CRFs on total and marketable yields, tuber

quality, plant nutritional status, and nutrient recovery.

CRF Production Experiment

The CRF production experiment evaluated the potential use of CRFs in place of

traditionally-used ammonium nitrate (AN), and was set up with six CRF products (CRF 1

through CRF6). This experiment was designed to determine ifN from CRF materials

remained in the soil longer than a similar rate of a "soluble" fertilizer source. The CRF

products were also evaluated to determine optimal N rates by evaluating yield response to

N applications at rates of 112 kg ha-1 N, 168 kg ha-1 N, and 225 kg ha-1 N, corresponding

to 50%, 75%, and 100% of the current BMP rate for the area. The CRF products

evaluated were chosen because they represented a broad product diversity with respect to

N release patterns and were preliminary products from manufacturers aiming to design a

fertilizer that meets the specific needs of potato growers. The AN treatment cannot be

considered a grower standard treatment because all N was applied at the beginning of the

season, whereas growers apply AN in split applications.









Total and Marketable Yields

The data were analyzed factorially by fertilizer product and rate main effects.

ANOVA tables for total and marketable yields are shown in Table 5-1 and Table 5-2,

respectively. Because the rate by product main effect was significant for both total and

marketable yields, their simple effects were evaluated (Table 5-3). Total and marketable

yields with the CRF production experiment were highest with plants in CRF2 (224 kg ha-

1 N) at 38.3 and 33.8 Mg ha-1, respectively, and with plants in CRF4 (224 kg ha-1 N) at

37.8 and 32.8 Mg ha-l, respectively. Marketable yields from both of these treatments

were significantly higher than those achieved from any of the AN treatments. Figure 5-1

illustrates the total and marketable yields obtained for each fertilizer treatment as well as

the no fertilizer control. All plants in fertilized treatments resulted both in higher total

and marketable yields than those in the no fertilizer control (No N).

Total yields from CRF fertilized plants were not higher than with any of the plants

fertilized in the AN treatments (see AN, 224 kg ha-1 N, 33.4 Mg ha-1; Table 5-3). When

Table 5-1. ANOVA table for total yields by fertilizer and rate main effects.
Source DF Type III SS MS F Value Pr > F
Fert 6 106091 17682 14.86 < 0.0001
Rate 2 73169 36584 30.75 < 0.0001
Rep 3 10904 3635 3.05 0.0304
Rate*Fert 12 140439 11703 9.84 < 0.0001
Error 144 171350 1190
Corrected Total 167 501952

Table 5-2. ANOVA table for marketable yield by fertilizer rate and main effects.
Source DF Type III SS MS F Value Pr > F
Fert 6 112144 18691 19.03 < 0.0001
Rate 2 100820 50410 51.33 < 0.0001
Rep 3 14375 4792 4.88 0.0029
Rate*Fert 12 129788 10816 11.01 < 0.0001
Error 144 141415 982
Corrected Total 167 498542









Table 5-3. Total and marketable yield simple effects.
Marketable
N rate Total yield yield1
Fertilizer kg ha1 Mg ha-1 Mg ha-1


AN
AN
AN
CRF1
CRF1
CRF1
CRF2
CRF2
CRF2
CRF3
CRF3
CRF3
CRF4
CRF4
CRF4
CRF5
CRF5
CRF5


CRF6
CRF6
CRF6
ANOVA p-value


112
168
224
112
168
224
112
168
224
112
168
224
112
168
224
112
168
224
112
168
224


23.2 fg2,3
28.9 b-f
33.4 a-d
28.9 b-f
29.5 b-f
16.7 g
29.7 b-f
34.4 a-c
38.3 a
25.6 ef
34.1 a-d
30.7 b-e
28.3 c-f
32.6 a-e
37.8 a
28.0 c-f
31.8 a-e
35.5 ab
27.1 d-f
32.5 a-e
34.8 a-c
< 0.0001


16.7 hi
19.8 f-h
24.9 c-g
22.6 d-h
25.6 c-e
13.0 i
22.2 d-h
28.4 a-d
33.8 a
19.2 g-i
28.5 a-d
26.5 b-e
22.1 e-h
26.7 b-e
32.8 ab
22.5 d-h
26.3 c-e
30.0 a-c
21.2 e-h
26.5 b-e
30.3 a-c
< 0.0001


Tukey LSD 6.3 5.7
1 Marketable Yield: size classes 2 to 4.
2 Means in columns followed by same letters not significantly
different.
3 Plants in the control treatment yielded 6.0 and 3.8 Mg ha-1 for
total and marketable yields, respectively.


compared to AN fertilized plants at the BMP rate (224 kg ha-1 N), potatoes with all six

CRF products with the 168 kg ha1 N rate had 3 to 14% higher marketable yields.

Marketable yields with five of the CRF treatments (CRF1 excluded) at the 224 kg ha-1 N

rate were 7 to 36% higher than marketable yield with the AN at the BMP rate. Low

yields with CRF1, 224 kg ha- N are due to poor stand establishment with that treatment.










50.0
40.0
30.0
20.0
10.0
0.0


0 (N 00 l-Z (N O 1C N 00 It N 00 'It N 00 'It N 00 'It N OO 0 I-
---- C--Cl-- Cl--Cl-- C1l C'l



Treatment


40.0

30.0

20.0 -

S10.0-

0.0

.,.) 0.,.) c.,. .,. .. .,. .,. c .,. c .,. c .,. .0 .0 .. .. .. .


Treatment

Figure 5-1. Total and marketable tuber yields by treatment. A) total yield, B) marketable
yield.

Specific Gravity

The ANOVA table for specific gravity by product and rate main effects indicates a

significant rate by product interaction (Table 5-4). Simple effects analysis for specific

gravity (SG) ranged from a low of 1.074 with AN (112 kg ha1 N) to a high of 1.084 with

CRF2 (224 kg ha- N) (Table 5-5, Figure 5-2). Only plants fertilized with CRF2 with 224









kg ha-1 N had SG significantly higher than plants fertilized with any of the AN

treatments. The control treatment (no N) had a SG of 1.065.

Table 5-4. ANOVA table for specific gravity by rate and fertilizer source main effects.
Source DF Type III SS MS F Value Pr > F
Fert 6 0.00059 0.0001 11.52 < 0.0001
Rate 2 0.0001 0.00005 6.11 0.0028
Rep 3 0.00063 0.00021 24.73 < 0.0001
Rate*Fert 12 0.00027 0.00002 2.61 0.0036
Error 144 0.00122 0.00001
Corrected Total 167 0.00281

Table 5-5. Potato tuber specific gravity by simple effects.
N rate Specific
Fertilizer kg ha1 gravity
AN 112 1.074 c1'2
AN 168 1.075 c
AN 224 1.077 bc
CRF1 112 1.081 ab
CRF1 168 1.081 ab
CRF1 224 1.077 bc
CRF2 112 1.079 a-c
CRF2 168 1.082 ab
CRF2 224 1.084 a
CRF3 112 1.080 a-c
CRF3 168 1.081 ab
CRF3 224 1.079 a-c
CRF4 112 1.077 bc
CRF4 168 1.081 ab
CRF4 224 1.081 ab
CRF5 112 1.078 a-c
CRF5 168 1.079 a-c
CRF5 224 1.079 a-c
CRF6 112 1.075 c
CRF6 168 1.078 bc
CRF6 224 1.079 a-c
ANOVAp-value < 0.0001
Tukey LSD 0.005
1 Means in columns followed by same
letters not significantly different.
2 Tubers from the control treatment had a
specific gravity of 1.065.










1.085

1.080

t 1.075

S1.070

S1.065

1.060
1 Cl 0 ( C ^- (




Treatment

Figure 5-2. Potato tuber specific gravity by treatment.

SG values were relatively high for the production site in 2003. Potatoes with most

treatments had SG of 1.078 or greater, with the highest gravities as high as 1.084.

Notably, the tubers in treatments with highest SG were also the highest yielding plants.

Tuber Quality

In the CRF production experiment, no significant rate by product interaction was

found for the tuber quality parameters of percent green, percent growth crack (GC),

percent rotten (Rot), percent hollow heart (HH), percent brown rot (BR), and percent

corky ring spot (CRS). Accordingly, main effect analysis results for these parameters is

shown for fertilizer products (Table 5-6) and for N rates (Table 5-7). Within the fertilizer

product main effect, none of the parameters tested were significantly different either

within CRF products or compared to AN. However, within the rate main effect, a

significantly greater percentage of green and growth crack potatoes was observed with

potatoes grown at higher N rates than at the 112 kg ha1 N rate.









Table 5-6. Potato tuber quality by fertilizer source main effect.
Green1 GC Rot HH BR CRS
Fertilizer % % % % % %
AN 1.8 0.6 4.2 4.4 0.2 0.0
CRF1 2.4 1.1 3.5 4.4 0.0 0.0
CRF2 1.1 0.5 3.7 1.7 0.0 0.0
CRF3 2.3 0.4 4.1 3.3 0.0 0.2
CRF4 1.0 0.4 3.9 2.7 0.2 0.0
CRF5 1.1 1.0 4.3 1.3 0.0 0.0
CRF6 1.1 0.2 4.1 1.0 0.0 0.0
ANOVAp-value 0.0323 0.0491 0.9755 0.019 0.5327 0.4278
Tukey LSD ns ns ns ns ns ns
1 Green = green, GC = growth cracks, Rot = rotten, HH = hollow heart,
BR = brown rot, CRS = corky ring spot.

Table 5-7. Potato tuber quality by rate main effect.
N rate Green1 GC Rot HH BR CRS
kg ha-1 % % % % % %
112 0.7 b2 0.3 b 5.3 a 2.7 0.1 0.0
168 1.7 a 0.5 ab 3.9 b 2.9 0.1 0.0
224 2.3 a 0.9 a 2.8 b 2.5 0.0 0.1
ANOVAp-value 0.0002 0.0109 0.0001 0.9008 0.6012 0.3704
Tukey LSD 0.8 0.5 1.4 ns ns ns
1- Green = green, GC = growth cracks, Rot = rotten, HH = hollow heart, BR = brown
rot, CRS = corky ring spot.
2 Means in columns followed by same letters not significantly different.

Significant rate by product interactions were found for percent misshapen (MS, p =

0.0059) and percent internal heat necrosis (IHN,p = 0.0115). Results of simple effects

analysis are presented in Table 5-8. For MS potatoes, greatest percentages resulted from

AN fertilized treatments at 224 kg ha-1 N, and was statistically similar only to plants

fertilized with AN at 168 kg ha-1 N. All CRF products independent of rate resulted in

tubers with similar quantities of misshapes. IHN was highest in tubers with AN fertilized

plants at 168 kg ha-1 N at 30.0%. This was significantly higher than all other treatments

except AN with 224 kg ha-1 N and CRF6 at 112 kg ha-1 N. None of the CRF products

were significantly different from each other in incidence of IHN.









Table 5-8. Potato tuber quality by treatment.
N rate Mis1 IHN
Fertilizer kg ha-1 % %
AN 112 0.2 b2'3 11.3 be
AN 168 1.0 ab 30.0 a
AN 224 2.0 a 20.0 ab
CRF1 112 0.5 b 6.9 be
CRF1 168 0.0 b 5.0 be
CRF1 224 0.5 b 10.0 be
CRF2 112 0.3 b 7.5 be
CRF2 168 0.0 b 3.1 be
CRF2 224 0.3 b 7.5 be
CRF3 112 0.3 b 10.0 be
CRF3 168 0.2 b 7.6 be
CRF3 224 0.0 b 5.6 be
CRF4 112 0.0 b 5.0 be
CRF4 168 0.3 b 8.8 be
CRF4 224 0.4 b 2.5 c
CRF5 112 0.3 b 10.6 be
CRF5 168 0.8 ab 8.1 be
CRF5 224 0.0 b 3.8 be
CRF6 112 0.4 b 16.9 a-c
CRF6 168 0.1 b 6.9 be
CRF6 224 0.0 b 5.6 be
ANOVAp-value 0.0009 < 0.0001
Tukey LSD 1.4 17.4
1- Mis = misshapen potatoes, IHN = internal heat
necrosis.
2 Means in columns followed by same letters not
significantly different.
3 Tubers from the control treatment had 0.4% Mis and
52.4% IHN.

Stand Establishment

The CRF production experiment had variable stand establishment, which was influenced

by fertilizer treatment (Table 5-9). Plants fertilized with CRF1 with 224 kg ha-1 N had

the lowest establishment of all treatments with 47.9% emergence, while those fertilized

with CRF4 with 168 kg ha-1 N had the highest establishment of all at 100%. Other

notable treatment-affected stands were with CRF1 with 168 kg ha-1 N at 69.2%









Table 5-9. Potato stand establishment for the CRF
N rate
Fertilizer kg ha-1
No N 0
AN 112
AN 168
AN 224
CRF1 112
CRF1 168
CRF1 224
CRF2 112
CRF2 168
CRF2 224
CRF3 112
CRF3 168
CRF3 224
CRF4 112
CRF4 168
CRF4 224
CRF5 112
CRF5 168
CRF5 224
CRF6 112
CRF6 168
CRF6 224


production experiment.
Stand
%
98.3
97.1
97.1
95.4
87.1
69.2
47.9
96.3
95.4
96.7
92.1
87.5
72.1
98.3
100.0
96.3
95.0
97.1
97.9
98.3
97.1
96.3


emergence and with CRF3 with 224 kg ha- N at 72.1% emergence. With the exception

of these three low stand treatments, most plants in treatments had stand establishment

>95% while two (CRF1, 112 kg ha- N and CRF3, 168 kg ha- N) had < 90% stand

establishment. The reduced stand counts, especially for CRF 1 at the high rate likely

account directly for the low observed marketable and total yields. Though not analyzed

statistically, it should be noted that this product appeared to reduce plant stands and

yields independent of the rate applied, and even at the lowest fertilizer rate (112 kg ha-









N), the stand was only at 87.1%, considerably lower than the 96.1% average stand for all

of the other fertilizers at the same rate.

Plant tissue

Most recently matured (MRM) leaf tissue samples consisting of petioles and

leaflets were taken bi-weekly from plants in the CRF production experiment and tested

for total Kjeldahl nitrogen (TKN). The ANOVA table for sampling date, rate, and

fertilizer source main effects (Table 5-10) revealed a significant third-order interaction

between sampling dates, fertilizer products, and rates, as well as a significant second-

order interaction between fertilizer products and sampling dates. As there was no interest

Table 5-10. ANOVA table for most recently matured leaf TKN by rate and fertilizer
product main effects.
Source DF Type III SS MS F Value Pr > F
Date 3 48470762397 16156920799 1209.9 < 0.0001
Rate 2 3340874028 1670437014 125.09 < 0.0001
Fert 6 765897038 127649506 9.56 < 0.0001
Rep 3 425253010 141751003 10.61 < 0.0001
Rate*Fert 12 254254195 21187850 1.59 0.0957
Date*Rate 6 139699796 23283299 1.74 0.1115
Date*Fert 18 1498614386 83256355 6.23 < 0.0001
Date*Fert*Rate 36 830795456 23077652 1.73 0.0087
Error 249 3325127378 13353925
Corrected Total 335 59051277683
in evaluating each of the simple effects of these three factors individually, the rate and

product effects were evaluated at each sampling date. Rate by product interactions were

not significant at 36 DAP or 64 DAP, though they were at 47 DAP (p = 0.0240) and 82

DAP (p = 0.0010). Accordingly, main effect analysis was performed for leaf TKN at 36

DAP and 64 DAP, and results are shown for fertilizer product (Table 5-11) and rate

(Table 5-12) main effects. Simple effects analysis results for leaf TKN at 47 DAP and 82

DAP are shown in Table 5-13.









Table 5-11. Most recently mature leaf percent TKN of potato plants by fertilizer source
main effect at 36 and 64 DAP.
TKN (x 104 g kg- )
Fertilizer 36 DAP1 64 DAP
AN 5.7 c2 4.8 ab
CRF1 6.3 ab 5.1 a
CRF2 6.7 a 4.4 bc
CRF3 6.5 ab 4.5 bc
CRF4 6.5 ab 4.3 c
CRF5 6.5 ab 4.4 bc
CRF6 6.2 b 4.3 c
ANOVAp-value < 0.0001 < 0.0001
Tukey LSD 0.5 0.4
2 DAP = Days after planting.
3 Means in columns followed by same letters not
significantly different.

Table 5-12. Most recently mature leaf percent TKN of potato plants by rate main effect
at 36 and 64 DAP.
N rate TKN (x 104 g kg- )
kg ha-1 36 DAP1 64 DAP
112 6.1 c2 4.1 c
168 6.4 b 4.6 b
224 6.6 a 5.0 a
ANOVA p-value < 0.0001 < 0.0001
Tukey LSD 0.2 0.2
1- DAP = Days after planting.
2 Means in columns followed by same letters not
significantly different.

Leaf TKN at 36 DAP was significantly higher in the CRF treatments than in AN

treatments. However, at 64 DAP, leaf TKN was significantly highest in CRF 1. Also at

64 DAP, leaf TKN in AN treatments was among the highest of all fertilizer products.

As might be expected, leaf TKN was affected by fertilizer rate main effect both at

36 and 64 DAP; it was significantly highest with 224 kg ha-1 N across all fertilizer

products for both dates. Leaf TKN was also significantly different between plants in 168

and 112 kg ha-1 N treatments, with the lowest rate having the lowest average TKN

concentration at both 36 and 64 DAP.