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Nutrient Release Patterns of Controlled Release Fertilizers Used in the Ornamental Horticulture Industry of South Florida

Permanent Link: http://ufdc.ufl.edu/UFE0042253/00001

Material Information

Title: Nutrient Release Patterns of Controlled Release Fertilizers Used in the Ornamental Horticulture Industry of South Florida
Physical Description: 1 online resource (80 p.)
Language: english
Creator: Mayer, Henrique
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: controlled, ficus, nitrogen, slow, temperature
Soil and Water Science -- Dissertations, Academic -- UF
Genre: Soil and Water Science thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Use of controlled release fertilizer (CRF) is one of the Best Management Practices (BMPs) utilized by the ornamental horticulture industry in South Florida to improve nutrient use efficiency (NUE) and reduce detrimental environmental effects. CRF manufacturers generally claim nutrient release will last for a specific period of time (4, 6, 9, or 12 months). The prevalence of relatively high temperatures throughout the year, a typical feature of South Florida climatic conditions, could result in faster nitrogen (N) release rates than those stated by CRF manufacturers and published in their application guidelines. In Florida, no official laboratory method exists that can verify the N release rates provided on CRF product labels. A laboratory study was conducted to investigate the effect of temperature on the N release patterns of five polymer-coated fertilizers (Nutricoteregistered trademark 18-6-8 Type 140, Multicoteregistered trademark 4 Extra 15-7-15 +1.2 Mg, Kingentaregistered trademark 20-8-10 six months, Osmocoteregistered trademark Plus 15-9-12 3-4 months, and Harrell?sregistered trademark Polyon 16-6-11 5-6 months). A long term fertilizer incubation method (180 days), in water at 25degree Celsius (C), was employed to attain polynomial equations of N release as a function of time. A short term or quick extraction method (168 hours or 7 days), in water at 100degreeC, has also been developed to assess N release under accelerated laboratory conditions using a Constant Temperature Extractor (CTE). A nitrogen release prediction equation was developed, using regression analysis, for each of the CRFs with high accuracy (R2 > 0.97). Results suggested that all CRFs tested have shorter N release longevities than the label claimed. High correlation (R2 > 0.97) values indicate N release patterns can be predicted accurately at 25degreeC. The quick laboratory method (100degreeC) shows a high correlation to 25degreeC methods and can be used to predict N releases from CRFs within a few days. In order to evaluate N uptake by plants, liners of Ficus elastica ?Robusta? were grown in a greenhouse in 3.8 L containers with Premier Promix BX / Mycorise Pro 3.8 potting media for 180 days. Plant biomass and N uptake were measured every 30 days. All tested fertilizers increased plant biomass compared to the control treatment which did not receive supplemental nutrition. F. elastica leaf N concentrations ranged from 1.2% at the mature stage (150 days after planting (DAP)) to 3.4% at the juvenile stage (30 DAP). The ranges of N concentrations were 0.8-1.5 for both stems and roots. The highest nitrogen use efficiency (NUE) came from F5 (an alkyd resin-based product) treatment with 40% while the lowest was from F6 (a Polyonregistered trademark material) treatment with 31%. Plant biomass and N uptakes were highly correlated to N release from CRFs measured at 25degreeC (r > 0.94). This study indicated that CRFs hold great promise to improve plant growth and NUE but additional research on characterization, plant response, environmental effects, and economics is needed.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Henrique Mayer.
Thesis: Thesis (M.S.)--University of Florida, 2010.
Local: Adviser: Li, Yuncong.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2012-08-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0042253:00001

Permanent Link: http://ufdc.ufl.edu/UFE0042253/00001

Material Information

Title: Nutrient Release Patterns of Controlled Release Fertilizers Used in the Ornamental Horticulture Industry of South Florida
Physical Description: 1 online resource (80 p.)
Language: english
Creator: Mayer, Henrique
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: controlled, ficus, nitrogen, slow, temperature
Soil and Water Science -- Dissertations, Academic -- UF
Genre: Soil and Water Science thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Use of controlled release fertilizer (CRF) is one of the Best Management Practices (BMPs) utilized by the ornamental horticulture industry in South Florida to improve nutrient use efficiency (NUE) and reduce detrimental environmental effects. CRF manufacturers generally claim nutrient release will last for a specific period of time (4, 6, 9, or 12 months). The prevalence of relatively high temperatures throughout the year, a typical feature of South Florida climatic conditions, could result in faster nitrogen (N) release rates than those stated by CRF manufacturers and published in their application guidelines. In Florida, no official laboratory method exists that can verify the N release rates provided on CRF product labels. A laboratory study was conducted to investigate the effect of temperature on the N release patterns of five polymer-coated fertilizers (Nutricoteregistered trademark 18-6-8 Type 140, Multicoteregistered trademark 4 Extra 15-7-15 +1.2 Mg, Kingentaregistered trademark 20-8-10 six months, Osmocoteregistered trademark Plus 15-9-12 3-4 months, and Harrell?sregistered trademark Polyon 16-6-11 5-6 months). A long term fertilizer incubation method (180 days), in water at 25degree Celsius (C), was employed to attain polynomial equations of N release as a function of time. A short term or quick extraction method (168 hours or 7 days), in water at 100degreeC, has also been developed to assess N release under accelerated laboratory conditions using a Constant Temperature Extractor (CTE). A nitrogen release prediction equation was developed, using regression analysis, for each of the CRFs with high accuracy (R2 > 0.97). Results suggested that all CRFs tested have shorter N release longevities than the label claimed. High correlation (R2 > 0.97) values indicate N release patterns can be predicted accurately at 25degreeC. The quick laboratory method (100degreeC) shows a high correlation to 25degreeC methods and can be used to predict N releases from CRFs within a few days. In order to evaluate N uptake by plants, liners of Ficus elastica ?Robusta? were grown in a greenhouse in 3.8 L containers with Premier Promix BX / Mycorise Pro 3.8 potting media for 180 days. Plant biomass and N uptake were measured every 30 days. All tested fertilizers increased plant biomass compared to the control treatment which did not receive supplemental nutrition. F. elastica leaf N concentrations ranged from 1.2% at the mature stage (150 days after planting (DAP)) to 3.4% at the juvenile stage (30 DAP). The ranges of N concentrations were 0.8-1.5 for both stems and roots. The highest nitrogen use efficiency (NUE) came from F5 (an alkyd resin-based product) treatment with 40% while the lowest was from F6 (a Polyonregistered trademark material) treatment with 31%. Plant biomass and N uptakes were highly correlated to N release from CRFs measured at 25degreeC (r > 0.94). This study indicated that CRFs hold great promise to improve plant growth and NUE but additional research on characterization, plant response, environmental effects, and economics is needed.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Henrique Mayer.
Thesis: Thesis (M.S.)--University of Florida, 2010.
Local: Adviser: Li, Yuncong.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2012-08-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0042253:00001


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1 NUTRIENT RELEASE PATTERNS OF CONTRO LLED RELEASE FERTILIZERS USED IN THE ORNAMENTAL HORTICULTURE INDUSTRY OF SOUTH FLORIDA By HENRIQUE MAYER 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 2010

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2 2010 Henrique Mayer

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3 To my family: Ingrid, Patr icia, Gabriela, and Melanie

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4 ACKNOWLEDGMENTS I would like to give m y sin cere gratitude and appreciati on to Dr. Yuncong Li and Dr. Xiaohui Fan for their guidance, problem solv ing, good comments, and inspiration. Achieving this degree would not have been possible without their support. I would also like to thank the other members of my supervisory committee, Dr George Fitzpatrick, Dr. Samira Daroub, Dr. Rafael Muoz-Carpena, Dr. Qi ngren Wang, and Dr. Kati W. Migliaccio whose knowledge and comments contributed significantly to this research project. Further, my special thanks go to Yu Guigin, Laura Rosado, Sikavas Na-Lampang, Gu dong Liu, Daniel Irick, Nick Kiggundu, Gaelan Jones, and all the personnel of the Tropical Research and Education Center Soil and Water laboratory for their friendly assistance thr ough laboratory analysis and field tasks for my research. Thanks also go to BWI, Harrells, and Kerry Bromeliads for providing materials for this research. Finally, I would lik e to thank all the members of my family, especially my wife, for their constant support and help during these long years.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS...............................................................................................................4 LIST OF TABLES................................................................................................................. ..........7 LIST OF FIGURES.........................................................................................................................8 ABSTRACT...................................................................................................................................10 CHAP TER 1 INTRODUCTION..................................................................................................................12 2 LITERATURE REVIEW.......................................................................................................15 History of Slow Release Fertilizers and Controlled Release Fertilizers .................................15 Definitions and Types of Slow Release Fert ilizers and Controlled Release Fertilizers ......... 16 Advantages of Controlle d Release Fertilizer .......................................................................... 18 Increase Nitrogen Use Efficiency.................................................................................... 18 Less Leaching and Runoff...............................................................................................18 Less Ammonia Volatilization a nd Nitrous Oxide Em issions.......................................... 19 Less Toxicity and Salt Content........................................................................................ 19 Low Labor Cost...............................................................................................................20 Disadvantages of Controlle d Release Fertilizers .................................................................... 20 Lack of Standardized Methods........................................................................................20 Accumulation of Salts..................................................................................................... 20 High Cost.........................................................................................................................21 Consumption of Controlled Release Fertilizers...................................................................... 21 Globally....................................................................................................................... ....21 United States....................................................................................................................22 Florida..............................................................................................................................22 Factors Affecting Consumption of Cont rolled Release Fertilizers Release ........................... 23 Temperature.................................................................................................................... .23 Other Factors...................................................................................................................24 Predicting Nutrient Release.................................................................................................... 25 Mechanism of Nutrient Release...................................................................................... 25 Traditional Field and Laboratory Methods for Nitrogen Release ...................................26 Regulations and Registration.................................................................................................. 27 Federal Level...................................................................................................................28 State Level.......................................................................................................................28 3 NITROGEN RELEASE RATES FROM CONTROLLED RELEASE FERTILIZERS PREDICTED BY DIFFERENT METHODS. ........................................................................ 31 Introduction................................................................................................................... ..........31

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6 Materials and Methods...........................................................................................................33 Determination of Release Pattern and Duration from Controlled Release Fertilizers in Water at 25C.......................................................................................................... 33 Determination of Release Pattern and Duration from Controlled Release Fertilizers in Water at 100C........................................................................................................ 33 Determination of Nutrients Release by a Weight Loss Method...................................... 34 Regression Analysis of the Releas e Tim es at 25C and at 100C................................... 34 Results and Discussion......................................................................................................... ..35 Nitrogen Release Rates from Controll ed Release Fertilizers at 100C ........................... 36 The Predication of Nitrogen Release Rate at 25C from Nitrogen Release Rates at 100C...........................................................................................................................36 Nitrogen Release Rates Measured by W eight Loss Method under Greenhouse Conditions....................................................................................................................37 Conclusions.............................................................................................................................39 4 RESPONSE OF GROWTH AND NITROGEN UPTAKE BY FICUS EL ASTICA ROBUSTA TO NITROGEN RELEAS ES FROM CONT ROLLED RELEASED FERTILIZERS........................................................................................................................48 Introduction................................................................................................................... ..........48 Materials and Methods...........................................................................................................49 Results and Discussion......................................................................................................... ..51 Plant Growth or Biomass................................................................................................. 51 Nitrogen Uptake in Plants...............................................................................................51 Correlation between Nitrogen Uptake / Biom ass and Nitrogen Release from Controlled Release Fertilizers...................................................................................... 53 Conclusions.............................................................................................................................54 5 SUMMARY AND CONCLUSIONS.....................................................................................73 Nitrogen Release Rate from Controlled Re lease F ertilizers Predicted by Different Method Study......................................................................................................................73 Response of Plant Growth Study............................................................................................74 APPENDIX LIST OF REFERENCES...............................................................................................................76 BIOGRAPHICAL SKETCH.........................................................................................................80

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7 LIST OF TABLES Table page 2-1 World consumption in metric tons (MT) of m anufactured slow release fertilizers and controlled release fertilizers............................................................................................... 302-2 Historical total fertilizer cons umption in tons (T) in Florida............................................. 303-1 Characteristics of controlled release fertilizers (CRFs) used in the experiment................ 403-2 The regression equations of cumulative N release rates from controlled release fertilizers (CRFs) at 25C.................................................................................................. 423-3 Longevity claimed (days) and duration te sted (days) for five controlled release fertilizers (CRFs) used....................................................................................................... 423-4 Regression equations and coe fficients of determination (R 2) for 5 controlled release fertilizes (CRFs) in wa ter incubation at 100C.................................................................. 443-5 Regression equations and coe fficients of determination (R2) between times of nitrogen release at 25C (d ays) and at 100C (hours)....................................................... 443-6 Regression equations between cumulative N release rates from the weight loss method in a greenhouse and the water in cubation at 25C in a laboratory.......................464-1 Cumulative N uptakes and N use efficiency (NUE) of Ficus elastica Robusta throughout the growing season (150 days)........................................................................ 564-2 Significant levels for means of dry biomass (g/plant)....................................................... 564-3 Correlation (r) between biomass of Ficus elastica Robusta vs. N release of controlled release fertilizers ( CRFs), and N uptake vs. N release Error! Bookmark not defined.4-4 Regression equations and coe fficients of determination (R2) between biomass of Ficus elastica Robusta vs. N release of controlle d release fertilizers (CRFs), and N uptake vs. N release........................................................................................................... 574-5 Nitrogen uptake per unit of dry weight (mg N/g biomass) of different controlled release fertilizers (CRFs) during the growing season........................................................58

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8 LIST OF FIGURES Figure page 3-1 Nitrogen release rates from controlled release fertilizers in w ater at 25C....................... 413-2 Nitrogen release rates from controlled rele ase fertilizers (CRFs) in water at 100C........ 433-3 Percentage of weight lo ss of controlled release fert ilizers (CRFs) incubated in a greenhouse.........................................................................................................................453-4 A mesh bag of a controlled release fertilizer (CRF) in a 250 mL-bottle........................... 463-5 A constant temper ature extractor (CTE)............................................................................473-6 A bag of a controlled release fertilizer (CRF) for the weight loss method........................ 474-1 Ficus elastica Robusta grown in a greenhouse............................................................... 554-2 Ficus elastica Robusta treated with controlled release fertiliz ers (CRFs) F1, F2, F3, F4, F5, and F6 from left to right at 180 days afte r planting (DAP)...................................554-3 Leave biomass (g/plant) of Ficus elastica Robusta treated with five controlled release fertilizes (CRFs) plus control (C) in a greenhouse................................................ 594-4 Stem biomass (g/plant) of Ficus elastica Robusta treated with five controlled release fertilizers (CRFs) plus a control (C) in the greenhouse......................................... 604-5 Biomass in the roots (g) of Ficus elastica Robusta treated with five controlled release fertilizers (CRFs) plus a co ntrol (C) and grown in the greenhouse....................... 614-6 Total biomass (g) of Ficus elastica Robusta treated with five controlled release fertilizers (CRFs) plus a control (C).................................................................................. 624-7 Daily biomass (g) of Ficus elastica Robusta treated with five controlled release fertilizers (CRFs) plus a control (C).................................................................................. 634-8 Leaf nitrogen concentration (% ) (A) and nitrogen uptake (B) of Ficus elastica Robusta treated with five controlled release fertilizer s (CRFs) plus a control............... 644-9 Stem nitrogen concentration (%) (A) and nitrogen uptake (B) of Ficus elastica Robusta treated with five c ontrolled release fertilizers (CRFs) and a control (C).......... 654-10 Root nitrogen concentration (%) (A) and nitrogen uptake (B) of Ficus elastica Robusta treated with five c ontrolled release fertilizers ( CRFs) plus a control (C)......... 664-11 Total nitrogen concentra tion (%) (A) and uptake (B) of Ficus elastica Robusta treated with five controll ed release fertilizers (CRF s) plus a control (C).......................... 67

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9 4-12 Comparison of nitrogen uptakes (A) of Ficus ela stica Robusta (mg N / plant) vs. nitrogen release (% ) from F1 (B)....................................................................................... 684-13 Comparison of nitrogen uptakes (A) of Ficus elastica Robusta (mg N/plant) vs. nitrogen release (% ) from F3 (B)....................................................................................... 694-14 Comparison of nitrogen uptakes (A) of Ficus elastica Robusta (mg N/plant) vs. nitrogen release (% ) from F5 (B)....................................................................................... 704-15 Comparison of nitrogen uptakes (A) of Ficus elastica Robusta (mg N / plant) vs. nitrogen release (% ) from F4 (B)....................................................................................... 714-16 Comparison of nitrogen uptakes (A) of Ficus elastica Robusta (mg N / plant) vs. nitrogen release (% ) from F6 (B)....................................................................................... 72

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10 Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science NUTRIENT RELEASE PATTERNS OF CONTRO LLED RELEASE FERTILIZERS USED IN THE ORNAMENTAL HORTICULTURE INDUSTRY OF SOUTH FLORIDA By Henrique Mayer August 2010 Chair: Yuncong Li Major: Soil and Water Science Use of controlled release fertilizer (CRF) is one of the Best Manage ment Practices (BMPs) utilized by the ornamental hor ticulture industry in South Fl orida to improve nutrient use efficiency (NUE) and reduce detrimental enviro nmental effects. CRF manufacturers generally claim nutrient release will last for a specific period of time (4, 6, 9, or 12 months). The prevalence of relatively high temperatures through out the year, a typical feature of South Florida climatic conditions, could result in faster nitr ogen (N) release rates than those stated by CRF manufacturers and published in thei r application guidelines. In Florida, no official laboratory method exists that can verify the N release rates provided on CRF product labels. A laboratory study was conducted to investigate the effect of temperature on the N release patterns of five polymer-coated fertilizers (Nut ricote 18-6-8 Type 140, Multic ote 4 Extra 15-7-15 +1.2 Mg, Kingenta 20-8-10 six months, Osmocote Plus 15-9-12 3-4 months, and Harrells Polyon 16-6-11 5-6 months). A long term fertilizer in cubation method (180 days), in water at 25 Celsius (C), was employed to attain polynomial e quations of N release as a function of time. A short term or quick extraction method (168 hours or 7 days), in water at 100C, has also been developed to assess N release under accelerated laboratory conditions using a Constant Temperature Extractor (CTE). A nitrogen rel ease prediction equation was developed, using

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11 regression analysis, for each of the CRFs with high accuracy (R2>0.97). Results suggested that all CRFs tested have shorter N release longe vities than the label claimed. High correlation (R2>0.97) values indicate N release patterns can be predicted accurately at 25C. The quick laboratory method (100C) shows a high correlation to 25C methods and can be used to predict N releases from CRFs within a few days. In order to evaluate N upt ake by plants, liners of Ficus elastica Robusta were grown in a greenhouse in 3.8 L containers with Premier Promix BX / Mycorise Pro 3.8 potting media for 180 days. Plan t biomass and N uptake were measured every 30 days. All tested fertilizers in creased plant biomass compared to the control treatment which did not receive supplemental nutrition. F. elastica leaf N concentrations ranged from 1.2% at the mature stage (150 days after planting (DAP)) to 3 .4% at the juvenile stage (30 DAP). The ranges of N concentrations were 0.8-1.5 for both stems a nd roots. The highest nitrogen use efficiency (NUE) came from F5 (an alkyd resin-based product ) treatment with 40% while the lowest was from F6 (a Polyon material) treatment with 31%. Plant biomass and N uptakes were highly correlated to N release from CR Fs measured at 25C (r>0.94). This study indicated that CRFs hold great promise to improve plant growth and NUE but additional research on characterization, plant response, environmental effe cts, and economics is needed.

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12 CHAPTER 1 INTRODUCTION Florida nursery and landscap e plant industries include a wide range of businesses, including field nurseries, greenhouses, shad ehouses, landscape de sign, installation and m aintenance service, lawn and garden stores, re tail establishments and others. The 2005 Florida Nursery Growers and Landscape Association (FNG LA) and University of Florida (UF) study showed that the State of Florida produces the se cond largest nursery crop in the United States (US) after California (Hodges and Haydu, 2005). Total annual sales of this industry totaled $15 billion with nurseries, landscape, and garden and retail centers accounting for $3, $5 and $7 billion, respectively. Cumulatively, these businesses generate more than 320,000 job opportunities. Nursery crops, along with fruits, ve getables, and forestry productions, are one of the largest agricultural commodity groups in Flor ida. There are 7,952 registered nurseries in the state, which represent 24,000 hectares (ha) of container production and 10,000 ha of field production. Almost half of the produc tion facilities are lo cated within 2 kilome ters (km) of an urban center. The close proximity to urban centers can result in undesired o ff-site effects. MiamiDade, Palm Beach, Orange, and Hillsborough counties are the top four counties for employment impact and sales related to the nursery industry. Use of fertilizers, pesticides, and other inputs also are very high in these counties. Excessive use of fertilizers presents potential problems especially with container-grown plants because roots are confined to small volum es, and the storage capacity of growth media for nutrients and water are limited. Frequent irrigati on and fertilization are necessary to maintain the soil moisture and nutrient level, which may e nhance leaching and runoff losses (Oertli, 1980). Therefore, it is very important to select a proper fertilizer type, rate, and application technique in

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13 order to match the plants nutrient and growth re quirements as precisely as possible (Trenkel, 1997). In an effort to improve water quality and prevent groundwater cont amination the Florida Department of Agriculture and Consumer Se rvice (FDACS) created the Best Management Practices (BMP) program for cont ainer plant producti on in 1994. Fertilization management is very important for plant production and the use of controlled release fertilizer (CRF) is now recommended in the BMP document (Sartain and Kruse, 2001). The Florida Department of Environmental Protection (DEP) creat ed the Green-Industry Best Management Practices fo r Protection of Water Resources ( GI-BMP) for the professional landscaper in 2001. The program encourages the use of fertilizers with a minimum of 50% nitrogen (N) as a slow release. Today some cities like Naples, Fort Myers, Port Charlotte, and Orlando are enforcing the program. The goal is to make the program mandatory in all of Florida by 2014 (UF, 2009). CRFs have the potential to synchronize nutrient release patterns w ith crop demand. This will optimize nutrient uptake efficiency and increase plant biomass while reducing nutrient losses to the environment. CRFs product labels usually include a claim quantifying the nutrient release rate (e.g. 3, 6, 9 and 12 mont hs). Verification of the nutrient release pattern is critical for evaluation of the effectiveness of these ferti lizers; however, there ar e no official laboratory methods that can verify such claims. The main fact or that controls the nutr ient release rate from CRFs is the temperature (Oertli and Lunt, 1962; Broschat and Moor e, 2007). Climatic conditions of South Florida, specifically the relatively high temperature throughout most of the year, can result in the longevity of CRFs to be lower than the manufacturer label cl aims. Furthermore, it is important to determine the longevity of the CRF s because they are becoming increasingly more

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14 popular in South Florida. Approximately 60% of the bigand middlesize nurseries in MiamiDade County use CRFs, which account for approximat ely 7% to 20% of the total farming related business expenses, excluding labor (Cla rence Chamorro, unpublished data, 2010). The objectives of this study were to (1) establ ish N release curves of selected CRFs using a standard water extraction method (6 months) at 25 Celsius (C), (2) develop a quick laboratory method (one that would require le ss than 7 days) for N release pa tterns from CRFs at 100C, (3) build a relationship between the laboratory incubation method and the weight loss method within a greenhouse, and (4) evaluate th e relationship between N release patterns of five CRFs and biomass and N uptake of Ficus elastica Robusta grown in a greenhouse.

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15 CHAPTER 2 LITERATURE REVIEW History of Slow Release Fertilizers and Controlled Release Fertilizers Slow release fertilizers (SRFs) and controlled release fertilize r (CRFs) have been available since the 1950s, although most of the advances in the developmen t of these products were made in the 1980s and 1990s. The first CRF sources to b ecome commercially available were strictly nitrogen (N). CRF technology has expanded to incl ude potassium (K), phosphorus (P), and other nutrients including micronutrients. SRF/CRF empl oys several mechanisms to reduce the amount of nutrient available from the fertilizer at any one time (Obreza et al., 2006). Elemental sulfur (S) is commonly used as a coating material because it is inexpensive and has a low melting point (Trenkel, 1997). Molten sulfur c ould be sprayed over the prills of urea creating sulfur-coated urea (SCU). The product was first produced co mmercially by the Tennessee Valley Authority (TVA) for almost 40 years (Trenkel, 1997). In or der to seal cracks in the coating and reduce microbial degradation, a layer of wa x sealant is applied to SCU. At the end, attapulgite, a type of clay, is added as a conditioner. One disadvantage of the product is that th e release rate is not uniform because the coating has cracks as imperf ections (Shaviv, 2001). On average, one third of the product is released too fast (burst), and about one third is released too slow (lock-off) (Shaviv, 2001). To have more control over the N release from the SCU, an additional layer of resin was added. The final product is called pol ymer sulfur-coated urea (PSCU). Although the product has better properties than SCU, PSCU s till has a burst and tailing effect on plants (Shaviv, 2001). Another type of resin coating is an alkyd-type called osmocote (Scotts-Sierra Horticultural Products, Marysville, OH), which was introduced in California in 1967. The resin consists of a copolymer of dicyclopentadiene with a glycerol ester (Sartain et al ., 2001). Manufacturers can

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16 control the nutrient release rate by varying th e coating thickness or composition of the CRFs. This technology could be applied to a large variety of fertilizer like N-P-K, urea, and others. Normally, the coating weight varies from 10% to 20% of the total weight. The osmocote market has mainly been limite d to high value plants such as commercial ornamental nurseries, greenhouses, citrus and strawberry producti on. Another type of coating is based on a polyurethane-like coating. It is ob tained by reacting poly-is ocyanates with polyols on the surface of the fertilizer and forming an at trition-resistant CRF. This technology is called Reacted Layer Coated Fertilizer (RLCF). The RLCF can be applied to many prilled materials. It has the advantage to accomplish good control over the nutrient release patte rn and rate. Some commonly marked products with this technology are: Polyon (Pursell Technologies, Sylacauga, AL), Plantacote (Aglukon GmbH, Dusseldorf, Germ any), and Multicote (Haifa Chemical, Haifa, Israel) (Trenkel, 1997; Shaviv, 2001). Other technology for coating granular fertili zers is through utilizati on of thermoplastic resins as coating substances. Th e coatings are dissolved in fa st-drying chlorinated hydrocarbon solvent. Because the thermoplastic polymers used are highly impermeable in water, to obtain the desired diffusion characteristics ethylene-vinyl acetate and surfactants must be added as a release controlling agents. The release pa ttern is controlled by the level of release-cont rolling agents. Release rates can also be altere d by blending talc into the coati ng. The coating could be applied to many granular and prilled fertilizers (Sar tain and Kruse, 2001). Some commonly marketed products are Meister products (Chisso Asahi Fertilizer Corp., Tokyo, Japan), and Nutricote (Chisso Asahi Fertilizer Corp., Tokyo, Japan). Definitions and Types of Slow Release Fert ilizers and Controlled Release Fertilizers The Association of Am erican Plant Food Cont rol Officials (AAPFCO) define SRFs and CRFs as fertilizers as products that contain a plan t nutrient in a form which; a) after application,

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17 the plant uptake is delayed, or b) longer availabi lity of the products compared with other quick release fertilizers such as urea (AAPFCO, 1995). The main difference between CRF and SRF is that in the CRF, the factors affecting the rate pattern, and duration of release are well known and controllable, while in the case of SRFs, the pa ttern, rate, and duration of release are not well controlled. Release charact eristics are affected by conditions su ch as manipulation, storage, and transportation. Soil moisture content and biological activity also could have an effect (Shaviv, 2001). The Comit Europen de Normalisation proposed that for a fertilizer to be described as SRF it needs to follow three criteria under 25 Celsius (C); (i) less than 15% of the nutrients release in 24 hours, (ii) less than 75% release in 28 da ys, and (iii) at leas t about 75% release by the stated release time (Trenkel, 1997). CRFs and SRFs can be classified into four types; (i) materials with low solubility with organic-N compounds that can be biologically or chemically decomposed, e.g. ureaformaldehyde, and isobutyledene-diurea (IBDU), ( ii) low-solubility, inorganic compounds such as partially acidulated phospha te rock (PAPR) and metal a mmonium phosphates, (iii) water soluble or relatively water soluble materials that gradually decompos e and release the plant nutrients (e.g. guanylurea salts), and (iv) fertilizers in which the release is controlled by a physical barrier. The barrier can be further divi ded into three groups; a) organic polymer coated fertilizer (PCF) such as osmocote, polyon, multic ote, nutricote, which are widely used in container nursery plant production (Husby et al., 2003), b) inorganic such as sulfuror mineralbased coatings materials (e.g. SCU), and c) fert ilizers with a combined coating of Polymer/ Sulfur-Coating (e.g. PSCF, PSCU) (Shaviv, 2005; Trenkel, 1997). PCFs represent the fastest growing segment of controlled release fertilizer technology because of their improved flexibility in nutri ent release patterns compared with other CRF

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18 products and the flexibility in controlling the releas e of other nutrients in addition to N (Sartain, 1999). Several technologies have been produced de pending on the coating material and coating process. Some examples of coating technolog ies are polyurethane-base d, like Reactive Layers Coating (RLC, Pursell) or Polyon Multicote (Haifa Chemicals Inc.), polyolefin-based, like Meister, and Nutricote (Chisso); alkyd resin-based like Osmoco te (Scotts). In general, the coating material represents 3% to 4% of the to tal weight of the finish ed product in the case of reactive layer coating (RLC) technology and 15% in the case of conventional coating polymers (Trenkel, 1997). Advantages of Controlled Release Fertilizer Increase Nitrogen Use Efficiency For container nursery growers, m aintaining continuous optim um nutrient level is very important for rapid production of quality plants. Growers use slow release fertilizers to make sure that mineral nutrients do not restrict plant growth. Fertilizer nutrient recovery is defined as the total nutrient absorbed by the plant as a perc entage of total nutrient supplied by that fertilizer for a given time (Craig, et al., 2003). The use of CRF can improve nitrogen use efficiency (NUE) while reducing environmental hazard. This is mainly because CRF can couple nutrient delivery with plant demand by having a pattern of supply congruent to plant growth. Less Leaching and Runoff In m ost cases, due to the microbial activity mine ral N is likely to be oxidized to nitrate. Due to the high water solubility of nitrate, relatively high quantities of the applied N may potentially be leached and cause surface and ground water contamination. This happens more often in nurseries that use soil less growing substrates that are irrigated more than once a day (Foster et al., 1983). In the United States (US), nitrate concentration stan dards in potable water have been set at 10 milligrams of nitrogen per liter (mg N/L). Any technology or nutrient

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19 management system that reduces the detrimental effect of nitrogen is desirable (Shaviv, 2001). Due to the gradual release of nutrients, CRFs can significantly reduce possible leaching of nitrate between applications and plant uptake. Less leac hing and volatilization d ecrease the risk of environmental pollution (Oer tli, 1980; Trenkel, 1997). Less Ammonia Volatilization and Nitrous Oxide Emissions In calcareou s and alkaline soils of South Fl orida, surface applied products like ammonium and urea fertilizers are potent ial sources of ammonia (NH3) volatilization. The emission can cause damage to vegetation or may be oxidized into nitric acid and form acid rain when coupled with sulfuric acid (Shaviv, 2001). CRFs reduce volatilization losses of ammonia since only a small fraction of the total application is present in a readily available form at any one moment. Reduction in volatilization losses decreases the risk of enviro nmental pollution (Oertli, 1980; Trenkel, 1997). Use of standard N fertilizers in agriculture e ffects traces gas emissi on, particularly nitrous oxide (N2O) and nitrogen monoxide (NO) Soil microbial processes, temperature, soil water content, and mineral-N content control N trace gas emission. Duri ng the process of nitrification and de-nitrification, only a small fraction of ammonium is converted to NO, N2O, and N2. Emission of N2O is the main concern for causing ozone depletion, atmospheric holes and global warming (Shaviv, 2001). CRFs c ontribute to reduce gas emissions (N2O) due to the slow release of N. Less Toxicity and Salt Content It is im portant for a grower to understand how a particular fertilizer works and to know its designed release rate before applying it. For greenhouse and nursery crop s, controlled release fertilizers are typically incorporated into the growing media or top dre ssed after planting (Obreza and Sartain, 2010). Because of the slow dissoluti on of nutrients, CRFs reduce the toxicity to

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20 plants, particularly to seedlings. Due to less t oxicity and salt content, substantially larger amounts of CRFs can be applied less frequently as compared to conventional soluble fertilizers. Low Labor Cost Plant nutrient m anagement is intensive when producing high value horticultural crops that demand high fertilizer inputs. Controlled release fertilizers can meet the crop nutrient demand for the entire season through a singl e application. Saving on labor cost constitutes the main benefit for CRF use. Decreased application frequency re sults in saving in labor cost, time and energy. The utilization of CRF could be increased be cause they provide good qu alities like increased nutrient efficiency, maintained yields, and reduction of nutrient po llution (Shaviv, 2001). Disadvantages of Controlled Release Fertilizers Lack of Standardized Methods As Trenkel (1997) m ention there are no standard ized methods for reliab le determination of nutrient release pattern available ye t. There appear to be a lack of correlation between data from the laboratory which are available to the consumer and actual data collected from the field Lack of standardized methods for determination of nut rient release patterns is a huge disadvantage of the CRF because it is difficult to assure complia nce with the label claims by the manufacturers. Existence of an appropriate methodology to eval uate a wide range of materials will allow regulators and producers monitor more efficien tly, and faster CRF nutrient release patterns (Cabrera, 1997; Sartain et al., 2004). Accumulation of Salts Another disadvantage is the possibility that nutrient re lease from CR F may continue during the non-cropped season and result in leaching loss es or accumulation of toxic levels of salts (Oertli, 1980). A study by Meadows and Fuller (1983) revealed th at the release curve of the product could be too short to meet the plants de mands for nutrients. The nutrient release periods

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21 of several CRFs were shorter than those clai med by their manufacturers. The release of the S-coating may occur too fast (burst), causing damage to th e crop and to the environment compared with non-coated water so luble fertilizers. While if the co ating is too closely applied, it could cause the nutrients contained in the granules to not be released qui ckly (lock-off) (Lamont et al., 1987; Trenkel, 1997; Shavi v, 2001; Rosen et al., 2006). In so me cases, S-coated fertilizers may increase the acidity of the soil, and the coat ing agents may decompose very slowly leaving undesired residues of syntheti c materials in the soil. High Cost The greatest disadvan tage for CRF is the hi gh manufacturing cost as compared with conventional fertilizers, which may be as mu ch as three to ten times higher than the corresponding standard fertilizer products. The higher production costs are due to the expensive coating material, equipment and energy cost. Th e coating process requires a more complicated technical process. The higher cost limits the CRF use to high value crops such as ornamentals, vegetables, rice, fruits, and turf (Trenkel, 1997; Simonne et al., 2005). Consumption of Controlled Release Fertilizers Globally Use of CRF is growing faster than soluble m aterials alt hough CRF use represents only 3% to 4% of the total fertilizer used. The US and Canada account for about 66% of the total amount used. All European countries and Japan consum e the rest at the same proportion. In Japan, almost all CRFs are used for vegetables, rice, and fruits. In Canada, US, and Europe, the situation is different. Ninety percent of the total consumption is used in golf courses, nurseries, lawn and landscape. Only 10% is used for f ood production such as vegetables, strawberries, melons, citrus, and other fruits. However, the increase use of CRF in food production is more important than in non-food markets. Approximately 75% of the fertilizers used for food crops are

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22 coated CRFs with an annual average increase rate of 10% in the use of polymer coated fertilizers (PCFs). The supply of fertilizers from 1983 to 1996 grew 76% in the US, and 257% in Japan during the same period (Trenkel, 1997). For 1996, Trenkel (1997) estimate d the total amount of SRF/CRF consumed worldwide at 562,000 tons (Table 2-1). In Japan from 1985 to 1994, the consumption increased by 470%. Polymer-coate d N-P-K products have become the most important fertilizer used in Ja panese agriculture. The annual grow th rate in Europe from 1980 to 1996 is only 1% (Trenkel, 1997). United States In the US, the production of SRFs and CRFs increased by 76% from 1983 to 1996 (Trenkel, 1997). During the last 15 years, the consumption of CRF s has increased more than any other type (about 10% per year ). Nursery production and greenhous es, landscape, golf courses, and home yards are the main user s (Landels, 1994; Trenkel, 1997). Florida Table 2-2 illustrates the historical co nsump tion of fertilizer in Florida from 1998 to 2006. The farm category includes fertilizers for citrus growers, cattle ranchers, farmers, vegetable growers, and others. The non-farm category includes fertilizers for lawn turf, golf-athletic field, garden, container and greenhouse nurseries. The majority of SRF and CRF used in Florida is within the container and gree nhouse nursery category. The non-farm category has increased from 1998 to 2006 from 10% to 27% of the total. On the other hand, the farm portion showed a decrease from 90% to 75%. These data reflect the enormous grow th of the SRF and CRF market consumption in Florida. South Florida (south of Lake Okeechobee) has the biggest growth in the state (non published, Gary Bird, 2010)

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23 Factors Affecting Consumption of Co ntrolled Release Fer tilizers Release Temperature CRFs nutrient release is m ainly affected by temperature (Oertli and Lunt, 1962; Lamont et al., 1987; Kochba et al., 1990; Hu ett et al., 2000; Husby et al., 2003). Ingram (1981) found that the temperatures within black plastic nursery cont ainers in Florida increased from 21C to 40C or more when exposed to the sun. Increase in te mperature significantly increases nutrient release (e.g. an increase in temperature from 10C to 20C almost doubled the initial rate). Oertli and Lunt (1962) speculated that prope rties of the coating material s could possibly change with temperature because the release rate increased gr eater than expected from a simple diffusion mechanism. Husby et al. (2003) studied the nutri ent release patterns of three PCFs placed in sand-filled columns under differe nt temperatures. When temper ature increased from 20C to 40C, they found an increase of nutrient release. When the temp erature decreased from 40C to 20C, the nutrient release rate decreased. They su ggested that the changes in the daily nursery container temperature may have rapid effects on container nutrient leve l and nutrient release longevity of CRFs. Ahmed et al. (1963) showed in a study that nutri ent release rate was directly related to temperature. Kochba et al. (1990) determined in a so il incubation study that the change of nutrient release rate with temperature is expected to be an exponential function since vapor pressure is exponential function of temperature. Cabrera (1997) studied the N leaching patterns of different CRFs in containers under gree nhouse conditions. It was found that some CRFs exhibited N leaching patterns that closely followed changes in average daily ambient temperature over the season. Lamont et al. (1987) investigated the nutrient release rate of CRFs in beakers with distilled water at temperat ures between 5C and 45C. It wa s found that the nutrient release rate was affected by both incuba tion temperature and time. Genera lly, as temperature increased, nutrient release rate also increa sed. After a high initial release rate, nutrient release decreased

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24 with time. They also found that high temperatur es during the first month following planting can cause salt problems to the crop due the high nutrien t release; conversely, lo w temperatures could cause nutrient deficiency due to the slow nutrient release. Other Factors Nutrient release is m ainly dependent on the soil temperature and moisture permeability of fertilizer polymer coating. It is not appreciably affected by ot her factors such as pH, cation exchange, salt, texture, biologi cal activity, and red ox (Trenkel, 1997; Sartain and Kruse, 2001). The moisture permeability can be controlled by the manufacturer by varying the coating material, but the soil temperature is still variab le. Oertli and Lunt (1962) found that the release rate was independent of pH, as well as microbial activity. Thickne ss of the coating has a direct effect on the release rate. Heavily coated fertilizer formulations have low release rates and lightly coated ones have higher release rates. They also found that nitr ate and ammonia were released more rapidly than potassium and phosphate under comparable environmental conditions. Cabrera (1997) found a decrease of nutrien t release rates when the product is applied as a top-dressing instead of incorporated. The release rate from CRFs can also be affected by composition of the coating and the fertilizer N source being coated (Sartain and Kruse, 2001). Lunt and Oertli (1962) found that moisture levels exceeding the range of permanent wilting percentage to field capacity in a loam soil did not significantly affect the rate of nutrient transfer through the membrane of coated fertilizers mixed in the soil. Kochba et al. (1990) hypothesized that in the nutrient rele ase rate the substrate vapor pre ssure is the rate limiting step, since lowering the substrate moisture level within range of field capacity does not have a marked effect on the substrate vapor pressure.

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25 Predicting Nutrient Release Effective utilization and proper m anagement of nutrient application require tools for predicting the nutrient release under various soil and environmen tal conditions. Efforts have been made in the past to predict and measur e the nutrient release pattern from CRF using different models and techniques. Most of the mo dels assume that the nut rient release from CRFs is either controlled by the rate of water vapor that pe netrate through the coati ng or by the rate of solute diffusion from the fertilizer (Shaviv, 2001). Because CRF release pattern is most affected by temperature and not significantly affected by soil properties, it is possible to predict the nutrient release. Mechanism of Nutrient Release The m echanism of nutrient release from CRF wa s described by Shaviv (2001) as water in the form of vapor passes through the coating and then the vapo r condenses and dissolves the fertilizer core inducing an increase in the intern al pressure. At this point, two events can occur. The coating can break and the entire content of the granule is released immediately. Goertz (1995) called this sequence the failure mechanism or catastrophic release. It is more typical in the inorganic type of coati ng such as S, which are fragile and non-elastic coatings. If the coating resists the internal pressure, the fertiliz er could be released e ither by diffusion forced by a concentration gradient across the coating, by mass flow driven by a pressure gradient, or by a combination of the two. This is called the diffusion mechanism and is more characteristic in PCFs with polyurethane, polyolefi n, and alkyd resin coatings. The main characteristic of the diffusion mechanism is the gradual fertilizer rele ase which has a sigmoidal shape when plotted. However, different properties in a group of granules could cause a different release pattern when compared with an individual granule (Shaviv, 2001; 2005). Shaviv (2001) reported that nutrient release consists of three stages: (1) the initial stages or lag period during which almost no

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26 release is observed, (2) the constant release stage, and (3) the last or mature stage where a gradual reduction of rele ase rate occurs. Oertli and Lunt (19 62) used several elution and leaching experiments and observed that the mechanism contro lling the nutrient releas e is the diffusion of salts out of the fertilizer prills. Traditional Field and Laboratory Methods for Nitrogen Release Sartain et al. (2004) used se veral soil incubation m ethodologi es at room temperature to measure N release from CRFs. Initially they worked with a mixture of sand, organic matter, soil, and CRFs inside plastic bags. The media within the plastic bags was leached, and the leachate was analyzed for N. The initial results of th ese experiments were variable because the N recovery was very poor due to high ammonia vol atilization. They subseque ntly introduced an ammonium trap and the plastic bags were replace d with jars. After leaching the media, only 60% to 80% of the N was recovered. The poor recovery was due to a fixation of ammonium N by the organic matter. They eliminated the organic matter from the incubation media using only sand. Finally, they introduced the lysi meter technique to characterize nutrient release from CRFs under standard soil, temperature, and moisture conditio ns. After 270 days, leachates were collected and N was analyzed. Medina et al. (2008) conducted a one year experi ment with CRFs in mesh bags under citrus trees in ambient temperature and moist conditions. Medina et al. (2009) working with SRFs and combinations of slow-release/wate r soluble fertilizers in the laboratory developed a regression model that allows pr ediction of the N release from the SRFs in a short period of time. They worked in the laborat ory with a mixture of sand and so il with the N source inside a lysimeter and used an extraction so lution under different temperatures. The nutrient release profile of most comm ercial SRF materials can be generated by accelerating their natura l release mechanism in a laboratory setting. Various increasingly aggressive solvent extraction procedures were performed, such as a jacketed chromatography

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27 column (Sartain et al., 2004). This procedure pr ovided the ability to maintain temperature and allow a flexible continuous extraction flow sc heme. Extraction solutions used were water and 0.2% citric acid both at 25C and 65C. It appears that the accelerate d laboratory extraction procedur e could successfully predict the N release rate of slow-release N sources. This procedure will allow manufacturers to increase quality control of SRF and CRF products and re gulators to make judgments of SRF and CRF efficiency. However, it has proven to be more di fficult to estimate N release curves for some types of SRF materials, as well as mixtures of slow release and soluble release materials. More data is needed to establish reproducible predictive equations (Medina et al., 2009) Regulations and Registration During the last few decades, several unique technologies have been developed to characterize the release properties of SRF m aterials. These technologies are product-specific and based on the regulation and analysis of each material. However, w ith the constant introduction of new SRF products, an individualized approach to regulation is inad equate to verify manufacturer claims regarding material performance. The use of several technologies to evaluate nutrient release properties also creates consumer confus ion regarding choices when purchasing SRFs and lack of protection against ineffective products. An SRF and CRF task force was established in 1994 by the AAPFCO to address issu es regarding the effective regulation and analysis of SRF materials. Soil incubation methodology and shor t-term laboratory nutri ent extraction methods have been developed to overcome these regulatory issues (Sartain et al., 2004). Regardless of this important market, no universally established le gislation exists yet in the US nor in Western Europe or Israel to protect the consumer. Only Japan has in troduced required test methods. However, in the future, more legislation and regulation will be needed as the use of CRFs become more popular (AAPFCO, 1995)

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28 Until more appropriate methods are developed, the Association of Analytical Chemists International (AOACI) method 970.04 ( 15th Edition) is used to c onfirm the coated slow-release rate and occluded slow-release nutrients whose slow-release characterist ics depend on particle size. AOACI method 945.01 (15th Edition) shall be us ed to determine the water insoluble part when working with inorganic N materials (AAPFCO, 1995) These methods only utilize a 2 hour time frame and do not standardize temperature. They are also hampered by examining what is not released over time instead of measuring what is released. Analytical methodology to measure nutrient release rates is essential to lessening the affect of regulatory inconsiste ncies (Sartain et al., 2004). Federal Level In the US, each state reg ulates its own agricu ltural policies, including fertilizers. However, if state policy does not meet or exceed the fe deral regulation, the Federal Environmental Protection Agency (EPA) could impose their polic ies. The slow release materials have been marketed using many differing names, claims or de scriptions for the higher efficiencies of their products. All of these materials have been referr ed to as a single class of materials called Enhanced Efficiency by the AAPFCO. Within th e Enhanced Efficiency class of materials there are two broad categories: inhibitor material s and slow release materials. The last one is described as materials that delay their nutrient availability for plant uptake relative to a reference soluble material. Historically n itrogen has been the focus of most slow release technology and products developed (Sartain et al., 2004). State Level The Florida Departm ent of Agriculture a nd Consumer Service (FDACS) Bureau of Compliance Monitoring, under the Fertilizer Section, is charged with the enforcement and administration of Florida's Commercial Fertili zer Law, Chapter 576, F.S., and Chapter 5E-1,

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29 Florida Administrative Code (F.A .C) (http://www.doacs.state.fl.us/ onestop/aes/fertilizer.html). Any company that intends to market fertilizer in Florida needs to be li censed with FDACS. They will be required to pay an insp ection fee of $1.00 per ton for mixe d fertilizer, and $0.50 per ton if the fertilizer contains N or phospha te. Specialty fertilizer sold in packages of less than 49 pounds for home and garden use also are required to comply with the Fertilizer Law. Chapter 5E-1.003 of the Florida Commercial Fertilizer Law defines slow or controlled release fertilizer as a fertilizer containing a plant nutri ent in a form which delays its availability for plant uptake and use after a pplication, or which extends its availability to the plant significantly longer than a referenc e "rapidly available nutrient fertilizer," such as ammonium nitrate or urea, ammonium phosphate, or potass ium chloride. When one or more slow or controlled release nutrients are cl aimed or advertised, the list of source materials shall be shown as a footnote and shall be expresse d as percent of the ac tual nutrient. No claim or advertisement shall be made, if the slow or control release nutrient is less than 15% of the total guarantee analysis (Sartain, 1980). In order to train and educate the consumer about the better use of fertilizers, to encourage and promote the prope r use of fertilizers, and to improve standards regarding nonagricultural fertilizers, the Florida Legislature cr eated the Consumer Fertilizer Task Force. The University of Florida Institute of Food and Agricultural Sciences (IFAS) has one representative on this task for ce (Florida Commercial Law, 2009).

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30 Table 2-1. World consumption in metric tons (MT) of manufactured slow release fertilizers and controlled release fertilizers Region 1983 (MT) % 1996 (MT) % US 202,000 62 356,000 64 Western Europe 76,000 24 87,000 15 Japan 44,000 14 119,000 21 Total 322,000 100 562,000 100 Note: Adapted from Trenkel, M. A. 1997. Cont rolled release and stabilized fertilizers in agriculture. International Fertilizer Industry Assn., Paris. Table 2-2. Historical total fertilizer consumption in tons (T) in Florida Note: Adapted from Florida Department of Agri culture and Consumer Service (FDACS), Bureau of Compliance Monitoring. (2004). Ar chive fertilizer tonnage data. Year Total (T) Farm (T) % Non-Farm (T) % 1998/99 1,698,000 1,524,000 90 174,000 10 1999/00 2,200,000 1,985,000 90 214,000 10 2000/01 2,178,000 1,760,000 81 417,000 19 2001/02 2,110,000 1,768,000 84 342,000 16 2002/03 2,129,000 1,785,000 84 344,000 16 2003/04 2,038,000 1,614,000 79 424,000 21 2004/05 2,022,000 1,471,000 73 551,000 27 2005/06 1,992,000 1,496,000 75 495,000 25

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31 CHAPTER 3 NITROGEN RELEASE RATES FROM CONTROLLED RELEASE FERTILIZERS PREDICTED BY DIFFERENT METHODS. Introduction Controlled release fertilizers ( CRFs) are widely used for the production of nursery plants in South Florida. CRFs have the abili ty to re lease nutrients that can optimally match the pattern and duration of nutrients uptake by crops, which ma y reduce nutrients loss and improve nutrients efficiency (Gandeza et al., 1991; Shaviv, 2001). The duration of nutrient release can vary and depends on type and ratio of mate rials coated on the nutrients (G andeza et al., 1991). The rate of nutrients release from CRFs is dependent on temperature and is less affected by other factors such as pH and moisture conten t of the growing medium (Lamont et al., 1987; Fan et al., 2010). The pattern and duration of nutri ents release from CRFs are th e important factors which are considered by consumers when they choose the ty pe of CRFs to apply to particular crops. In recent years, several t echnologies have been develope d to characterize the release properties of CRFs materials (Medin a et al., 2009). However, there is not one universal standard method for determining the patter n and duration of nutrients re lease from CRFs (Dai et al., 2008). Trenkel (1997) indicated that dissolving in pure water followed by incubation at 25 Celsius (C) is a trad itional method to measure the release characteristics and the number of days required for 75% release of nutrients was co nsidered as the release duration of CRFs. Since pure water dissolving incubation at 25C may require several months to get one release curve for a CRF product, some researchers have investig ated the accelerated laboratory extraction methodology by increasing incubation temperature (S artain et al., 2004; Dai et al., 2008; Medina et al., 2009; Wang et al., 2009). Me dina et al. (2009) predicted constants for a model that characterizes nutrient re lease as a function of time from l ong term incubation method. Also, they estimate nutrient release rates under a short period of time and established release constants that

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32 were useful in the prediction of the CRF longe vity. Dai et al. (2008) predicted the release patterns of CRFs by use of both the cumulative nut rient release equation at 80C and regression equation of release time needed for some cumu lative release rates between 25C and 80C. The highest incubation temperatures used in the two experiments were 60C and 80C, respectively, and the prediction of nutrient re lease from CRFs still took long er than 1-3 months. Increasing testing temperature could reduce the time needed fo r prediction of release rates. At the current time, there is no published study on predicting nutrie nt release rates using incubation method at 100C with a short period of time. Laboratory incubation methods provide the release pattern information under constant temperature condition. However, temperature vari es in greenhouse and field situations. Although many types of CRFs are available to crop producers, there is a l ack of knowledge about nitrogen (N) release patterns under field conditions (Wilson et al., 2009) Trenkel (1997) pointed out that there was a lack of correlation between laboratory and field meas urement. There is no standard method to test N release characteristics in the fiel d. To test N release rate from CRFs in the field, the most common technique is to enclose an amount of CRF into a nylon mesh bag and bury it in the field. These mesh bags are removed over time to estimate N loss (Wilson et al., 2009). Medina et al. (2008) used this weight loss met hod to determine N release from CRFs used in citrus production. Wilson et al. (2009) determined N release from CRFs in potato fields using the weight loss method. Their research indicated this method can be reliably used as a substitute for chemical analysis to determine N release charac teristics of CRFs (Wilson et al., 2009; Medina et al., 2008).

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33 The objectives of this study were to (1) veri fy an accelerated test procedure at 100C for prediction of nutrient release at 25C from CRFs and (2) determine the relationship between the laboratory incubation method and weight loss method in greenhouse. Materials and Methods Five CRF products used in this study were obt ained from local ferti lizer distributors and their basic properties are listed in Table 3-1. All nitrogen was de rived from ammonium nitrate, (AN), ammonium phosphate (AP) and potassium nitrate (PN). There was no urea in the ingredients. The release claimed in the label vari es from 90 days (F3) to 180 days (F6). Nitrogen release from these products was determined in water over 180 days at 25C and 7 days (168 hours) at 100oC. Determination of Release Pattern and Duration from Controlled Release Fertilizers in Water at 25C Ten gram s (g) of each CRF were weighed, transf erred into a nylon bag and then placed in a plastic bottle containing 250 milliliters (mL) of deionized (DI) water (F igure 3-4). All bottles were incubated at 25C. Each treatment was repl icated three times. The samples were collected at 1, 3, 7, 14, 30, 60, 90, 120, 150, and 180 days after incubation began. At each sampling time, all water in the bottles was collected and then 25 0 mL of new, fresh deionized water was added. Determination of Release Pattern and Duration from Controlled Release Fertilizers in Water at 100C Ten gram s of the control release fertilizer was weighed into a small (5 centimeter (cm) x 3 cm) stainless steel wire mesh container. The co ntainer was placed in a tight incubation chamber (250 mL) which was located in a water bath of a constant temperatur e extractor (Model HKQT assembled at Shangdong Agricultural Universiy, Taian, China) (Figure 3-5). The wire mesh container was submerged into 250 mL of dei onized water in the incubation chamber. The incubation chamber was preheated to 100C. The extractions (250 mL) were collected at each

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34 sampling time. These times were at approximately 1, 3, 5, 7, 10, 24, 30, 36, 48, 54, 60, 72, 96, 144 and 168 hours following incubation initiation fo r analysis of N release from CRFs. After each sampling time, all extracted water that was in the incubation chamber was collected and another 250 mL of DI water was added for the subsequent extraction. Cumulative percent of N release as a function of time were plotted to generate the N re lease curve for the CRFs (Figure 3-9). Determination of Nutrients Release by a Weight Loss Method A pot experim ent in a greenhouse was conducted at the University of Florida Tropical Research and Education Center (TREC), Homest ead, FL in 2009. Three grams of a CRF were weighted into a nylon mesh bag; each fertilizer treatment has 24 replicate bags (Figure 3-6). All bags were buried 5 cm below the soil surface in the pots without plants. All these pots were irrigated in the same rate as the pots grow ing nursery plants, whic h was 0.25 liter (L) per container every day. The sampling time was at 3, 7, 30, 60, 90, 120, 150, and 180 days after the bags were buried in pots. Three replicate mesh bags were retrieved at each sampling time. Each mesh bag was placed in a paper bag and then ai r dried. CRF prills in the bag were removed by hand and then weighed. Based on the amount of we ight loss from the CRFs in the bag, the N release rate was estimated with the assumption th at N release will be equivalent to the loss of weight of the prills. Regression Analysis of the Rele ase Times at 25C and at 100C The regression analysis between the release tim e at 25C and the time at 100C for the same CRF was analyzed. A factor quadratic an d logarithmic equation were developed, where h represented the hour and d represented the days needed for cumulative re lease rate of 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100% at 100C and at 25C. The regression equations were developed

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35 by using SAS (v9.1; SAS Institute Inc., Cary NC) and Microsoft Office Excel version 2003 (Microsoft Corp., USA). Results and Discussion Cum ulative data from five CRFs (F1, F3, F4, F5, and F6; see Table 3-1 for specific characteristics for each CRF) indicated N release rate s varied with the type of fertilizers (Figure 3-1). At 2 weeks incubation, F5 and F3 released quickly. The cumulative percentage of N release for the two CRFs was 29.6%. F6 and F1 released moderately, which accounted for about 12% of N released during this time period. F4 released slowly; only 3.5% of N was released. From 2 weeks to 60 days, 93.3% of N in F3 was releas ed. The release rates from F5, F1 and F4 were similar (about 71% of N release); the lowest N release was from F6 at 59.2%. After 90 days incubation, more than 91% of N release was obse rved from F5, F3, F1 and F4. F3 released 99.8% of applied N, which means F3 had a 3 mo nth release period. After 120 days of incubation, N release from F5, F1 and F4 was close to 100%. These three CRFs had 4 month release period. After 180 days incubation, cumulative N released from F6 reached 98.7%. F6 had a 6 month release period, which was the longest among the five CRFs. Cumulative N release rates from 5 CRFs and incubation time at 25C could be adequately described by a quadratic e quation in the general form: y = a+bd+cd2 (3-1) where y is the cumulative N released at any day (d ), and a, b, and c are constants (Table 3-2). The correlation coefficient R2 was greater than 0.97 for all of the CRF products and showed a significant correlation between the days of inc ubation and cumulative N release rate. Regression equation and the coefficient of determination (R2) for each of the CRFs are listed in Table 3-2. Assuming that y = 100, and solving the equation: 100 = a+bd+cd2 (3-2)

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36 the value of d was obtained. The value is the dur ation (days) in which the CRF will release 100% of the N. All values of duration of nutrient rele ase (except F6) were less than the duration claim by the products manufacturer (Table 3-3). Nitrogen Release Rates from Controlled Release Fertilizers at 100C Figure 3-2 shows the cumulative N release pe rcentage from 5 CRFs incubated at 100C. In 24 hours of incubation, the cumulative N release rate was over 80% for CRFs F1, F3, F5 and F6, but for F4, the N released rate was below 60%. During 168 hours of incubation, F6, F5 and F1 had similar N release patterns and the N release rate from F4 was the slowest among the five CRFs. N release rates at 25C a nd 100C were compared (Figures 3-1 and 3-2). Increasing the temperature from 25C to 100C accelerated the N release rate. After 72 hours (3 days) of incubation, the N release rate at 100C was 6.5, 9.7, 23, 42.2 and 81 fold than that at 25C for F5, F3, F1, F6 and F4, respectively. Cumulative N release rates from 5 CRFs and incubation time at 100C could be adequately described by a non linear regressi on equation in the general form: y = aLn(h)+b (3-3) where y is the cumulative N released at any hour (h), and a, b are constants (Table 3-4). The correlation coefficient R2 was greater than 0.90 for all CRF products and showed significant correlations between the hour s of incubation and cumu lative N release rates. The Predication of Nitrogen Release Rate at 25C from Nitrogen Release Rates at 100C From the Regression Equation 3-1 at 25C, th e time (d) for cumulative N release of 10, 20, 30, 40 50, 60, 70, 80, 90, and100% was calculated for each CRF, the different times from d1 to d10 were obtained respectively. In the same wa y, the time (h) for cumulative N release of 10, 20, 30, 40 50, 60, 70, 80, 90, and100% was calculated fo r each CRF at 100C from Equation 3-2.

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37 Using the above two pair times calculated from 25 and 100C, the relationship between the N release times at 25C as a function of th at at 100C can be developed as follows: D = aLn(H)+b (3-4) where D = release time (days) at 25C; H = release time (hours) at 100C (Table 3-5). If an unknown coated product has similar coatin g characteristics with the product that is tested at 25C, a short term test at 100C can be performed for the product. The release time for a given percent of N release at 100C can then be used to predict the time required to release a similar percent of N release at 25C. Thus, the N release duration (about several months) at 25C can be predicted by using a fast N release test at 100C within hours. Nitrogen Release Rates Measured by Weig ht Loss Metho d under Greenhouse Conditions The weight loss methods of determining the pe rcent of N released in greenhouse indicated the value of N release was lowe r than that incubated 25C. Af ter the 180 day incubation, the percent of N release was 28, 71, 51, 69 and 41 for F 1, F3, F4, F5 and F6, respectively (Figure 33). Under the greenhouse condition, th e temperature varied daily for the incubation period of six months. The lowest was 4C on January 10, 2010 and the highest was 27C on September 25, 2009. The average air temperature in the gr eenhouse was 21.1C which was below 25C in laboratory water incubation. Cooler temperatures inside the greenhouse might be one reason for lower N release rates. The weight loss and laboratory incubation (25C) methods of determin ing the percent of N release were highly correlated fo r the 5 CRFs (Table 3-6). The R2 was greater than 0.89 for all CRF products examined in this study. Through the regression equation for each CRF, N release characteristics from CRFs in greenhouse can be predicted from N release test for CRF in the laboratory.

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38 The release pattern and duration of N release from CRFs is an important quality index of CRFs. The pure water incubation at 25C in the laboratory is comm only recognized as a traditional method to describe the N release ch aracteristics from CRFs. Evaluating N release patterns from CRFs enables farmers to choose the most suitable CRFs to be applied to the particular crops, based on the pattern of N upt ake. Many researchers tried to predicate the N release rate in the field from N release rate tested in a labo ratory through mathematical and statistical methods. Despite a variety of predicat ion models and methods being developed in the recent years (Shaviv, 2001; Dai et al., 2008; Tren kle, 1997), there is no consistent and standard method being recognized at pres ent. Nutrient release from CRFs is mostly temperature dependent (Gandeza et al., 1991; Shaviv, 2001). The N release rates from CRFs were greatly enhanced by higher temperatures. The temperature coefficient (Q10), which is defined as the rate of change of a chemical or biological reaction as a consequence of increasing the temperature by 10C, could be greater than 2 (Gandeza et al., 199 1). Because measuring N releases rates in the field or in the laboratory at 25C requires several months to one year for completion, many researchers have endeavored to develop different models of pr ediction (Shaviv, 2001; Dai et al., 2008). Gandeza et al. (1991) used a quadratic equation corresponding to the mean air or soil temperature to describe the cumulative N rele ase from CRFs over time. He found that the cumulative N release of CRFs could be determ ined by using the corresponding relationship between cumulative temperature a nd cumulative N release. Dai et al. (2008) showed N release from CRFs at 25C can be predicated precise ly from accelerated incubation method at 80C. Research work by Medina et al. (2009) indicated that an accelerated laboratorial extraction procedure could successfully predict the N releas e rate of CRFs which can allow manufactures and regulators to make judgments of CRF label claims and effectiveness. The current study

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39 indicated the rapid test with accelerated inc ubation at 100C is accurate and time saving for determining the release duration of CRFs. Conclusions Nitrogen release patterns and dur ations from five CRFs were measured with different methods in this study. The results demonstrated th at a nutrient release test conducted in water at 100C was a useful, acceptable quick testing method for predication of N release rates and duration at 25C. Compared with the traditio nal method, the acceleration incubation method at 100C would greatly save time for testing N releas e rate from CRFs. This study also indicated there was a good relation in N re lease rates between the labora tory incubation method at 25C and the weight loss method in a greenhouse. It is possible to predict N release patterns from CRFs in a greenhouse from la boratory incubation method.

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40 Table 3-1. Characteristics of controlled release fertilizers (CRFs) used in the experiment Product Stated NPK Analysis N derived from Release claimed (days) F1 18-6-8 AN, AP, PN 140 F3 15-7-15 AN, AP, PN 90-120 F4 20-8-10 AN, AP, PN 180 F5 15-9-12 AN, AP, PN 120-150 F6 16-6-11 AN, MonoAmmonium Phosphate 150-180

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41 2D Graph 1Time of incubation (d) 020406080100120140160180 N released (% applied) 0 20 40 60 80 100 120 F5 F3 F6 F1 F4 Figure 3-1. Nitrogen release rates from controll ed release fertilizers in water at 25C

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42 Table 3-2. The regression equations of cumulative N release rates from controlled release fertilizers (CRFs) at 25C CRFs Regression Equation Coefficient of Determination (R2) F1 y = -0.0042d2 + 1.4127d 1.2976 0.9962 F3 y = -0.0059d2 + 1.5835d + 8.964 0.97 F4 y = -0.0051d2 + 1.5243d 7.3609 0.99 F5 y = -0.004d2 + 1.2358d + 11.224 0.99 F6 y = -0.0035d2 + 1.1783d 2.0249 0.99 Table 3-3. Longevity claimed (days) and duration tested (days) for five controlled release fertilizers (CRFs) used CRFs Longevity Claimed (days) Tested (days) F1 140 104 F3 90-120 84 F4 180 114 F5 120-150 114 F6 150-180 168

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43 2D Graph 2Incubation time (h) 020406080100120140160180 N released (%applied) 0 10 20 30 40 50 60 70 80 90 100 110 F1 F3 F5 F4 F6 Figure 3-2. Nitrogen release rates from controlled release fertiliz ers (CRFs) in water at 100C

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44 Table 3-4. Regression equations a nd coefficients of determinati on (R2) for 5 controlled release fertilizes (CRFs) in water incubation at 100C CRFs Equation R2 F1 y = 19.765Ln(h) + 13.031 0.95 F3 y = 14.526Ln(h) + 26.95 0.92 F4 y = 20.942Ln(h) 10.675 0.98 F5 y = 18.204Ln(h) + 24.636 0.90 F6 y = 22.031Ln(h) + 10.338 0.92 Table 3-5. Regression equations and coefficients of determination (R2) between times of nitrogen release at 25C (days) and at 100C (hours) CRFs Equation R2 F1 D = 14.297Ln (H) + 10.094 1.00 F3 D = 12.6Ln(H) + 13.11 0.98 F4 D = 21.288Ln(H) 11.831 0.97 F5 D = 22.233Ln(H) + 9.2974 0.97 F6 D = -0.374H2 + 4.5844H + 15.508 0.98

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45 2D Graph 1Incubation time (d) 020406080100120140160180200 Weight loss (%) 0 20 40 60 80 100 F1 F3 F4 F5 F6 Figure 3-3. Percentage of weight loss of controlled release fertilizers (CRFs) incubated in a greenhouse

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46 Table 3-6. Regression equations between cumulativ e N release rates from the weight loss method in a greenhouse and the water in cubation at 25C in a laboratory CRFs Equation R2 F5 y = 0.7354x 12.481 0.89 F3 y = 0.6556x 3.0186 0.99 F6 y = 0.4031x 0.8021 0.97 F1 y = 0.2597x 2.6743 0.98 F4 y = 0.4219x + 1.7244 0.91 Figure 3-4. A mesh bag of a controlled release fertilizer (CRF) in a 250 mL-bottle

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47 Figure 3-5. A constant temp erature extractor (CTE) Figure 3-6. A bag of a controlled release fe rtilizer (CRF) for the weight loss method

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48 CHAPTER 4 RESPONSE OF GROWTH AND NITROGEN UPTAKE BY FICUS EL ASTICA ROBUSTA TO NITROGEN RELEASES FROM CONTROLLED RELEASE D FERTILIZERS Introduction The ornam ental horticulture industry faces a fine line to maintain economical production while simultaneously protecting the environmen t from excessive nutrient leaching and runoff (Obreza et al., 2010). It is critical to improve nutrient use efficien cy (NUE) to ensure sustainable crop production. The efficient use of fertilizers is influenced by soil, plant, and environmental conditions (Rose et al., 1994; Crai g et al., 2003). Controlled rel eased fertilizers (CRFs) are possible alternatives to quick re lease water soluble fertilizers. Their use could minimize nitrogen (N) losses to the environment and increase N uptak e efficiency. It is important for growers to understand how particular CRFs work and to know th eir designed release rate before application. Sometimes certain CRFs release the nutrients too slow or too fast (Craig et al., 2003). The ideal approach would be to match th e release curve with the crop nu trient demand during the crops growing season. For greenhouse and nursery crops, CRFs are typically incorporated into the potting media or top dressed after planting. When the CRFs are incorporated into the media, continuous nutrient release is more likely to have intermittent periods of dry-wet cycles (Obreza, 2010). Nitrogen not released to the soil remains in an insoluble form or is protected from dissolution by a coating, therefor e it cannot be leached. Moreover, N released but not taken by the crop could be lost through leaching or runoff to groundwater or surface water. Knowledge of plant N requirements, fertilizer release propertie s, and expected temperatures would allow the best opportunity to apply CRFs most efficiently for container plant production. Little attention has been gi ven to identifying nutrient requi rements of co ntainer-growth plants as related to plant age or stage of deve lopment (Tolman et al., 1990). As a root system develops, nutrient uptake by the plant becomes more efficient and less sensitive to fluctuations in

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49 nutrient release from CRFs. During rapid growth stages, fast-growing plants like Ficus require relatively high amounts of nutrients. Because CRFs must supply enough plant nutrients to support season-long growth of the crop in one application, matching nutrient releas e with plant requirements is a major challenge for both gr owers and CRF manufact urers (Yeager, 2010). Another challenge preventing efficient fertilizer management use is the one size fits all. Per example, a CRFs rate of 0.8 kilo grams of nitrogen per meter (kg N m-3) of media could be enough for a shrub in an 11-liter (3 gallons) cont ainer for 1 year, but maybe is too much for a shrub in a 3.8-liter (1 gallon) container for 3 mo nths. A grower may tend to over fertilize because quality plays a major role in consumer preference for ornamental crops and high fertilizer rates produce dark green foliage. The added cost of applying additional fertilizer may provide a measure of insurance against producing under fertilized plants and could allow for extended growth during times when crops cannot be sold (Yeager et al., 2010). Cultivars of Ficus elastica Roxb. Ex Hornem (Bailey and Ba iley, 1976) have been popular houseplants for the last 50 years. Most of the production today in the United States (US) comes from vegetative propagation. Standard or multitru nked trees are also produced from cuttings or air layers. The plants are frequently grown in sh adehouses with 47% to 63% shade. They need a well-drained growing medium and grow best when irrigated regularly (Griffith, 1998). The objective of this research was to evaluate the relationship between N rele ase patterns of five CRFs and biomass and N uptake of Ficus elastica Robusta grown in a greenhouse. Materials and Methods A greenhouse experim ent was conducted fr om August 27, 2009 to February 27, 2010 at the University of Florida Tropical Research a nd Education Center, Homestead, FL. Liners of Ficus elastica Robusta were obtained from a local nursery and transplanted on August 27, 2009 into 3.8-liter plastic containers using premier Pr omix BX / Mycorise Pro 3.8 as containing media

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50 (Sungro, Vancouver, Canada) (Figure 4-1). The gr owing medium consisted of Sphagnum peat moss (85%) and perlite + vermiculite + limestone (15%). Five CRFs were incorporated (mixed) with the growing medium at the rate of the equivalent of 0.8 kg N m-3according to a University of Florida IFAS recommendation (Broschat, 2005; Obreza et al., 2010; Yeager, 2010). Th ese CRF products were obtained from local fertilizer distributors and their formula, ch emical composition and claimed release period are listed in Table 3-1. Nitrogen release rates for these products were dete rmined in water over a 180 day period at 25 Celsius (C) and are described in Chapter 3. The containers were placed on raised benches inside a greenhouse with a daily irrigation of approximately 0.25 liter/plant a day (Figure 4-2) The irrigation was supplied with a drip irrigation system (1 liter per hour (L h-1)). Roots, stems, and leav es were collected 30, 60, 90, 120, 150, and 180 days after planting (DAP). At each harvest, the medium was gently washed from the root system, and the plant was separate d into roots, stems, and leaves portion. These portions were dried at 80C until constant weight was recorded (approximately 7 days). The dry tissue samples were weighed for biomass and ground using a 4 canister ball-mill pulverizer (Kleco, model 4200, CA. USA). The N concentration was analyzed using a CN analyzer (Vario Max CNS, Elemental Americas, Mt. Laurel, NJ). Results were statistically analyzed using the general linear model procedure of SAS (v9.1; SA S Institute Inc., Cary, NC) as a completely randomized design with six treatments (F1, F3, F4, F5, F6, and no-fertilizer control), six harvesting time (30, 60, 90,120,150, and 180 DAP), and f our replicates. Treatment means from the experiment were compared with Duncans Multiple Range Test ( = 0.05).

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51 Results and Discussion Plant Growth or Biomass Plant biom ass levels were evaluated for leaf stem and root tissue and are presented in Figures 4-3, 4-4, 4-5, and 4-6. Stat istics of the dry weight showed that there are not significant differences between fertilizer treatments at P<0.05. However, dry weights for 5 fertilizer treatments are significantly higher than those ob tained from control (no fertilizer) treatment. Biomass for F5 has the greatest biomass with 142 .1 grams/plant (g/plant), the control has the lowest with 17.7 g/plant and F1, F 3, F4, and F6 have 126.2, 121.1, 124.2, and 132.5 g respectively, after 180 DAP. The daily or increm ental biomass showed some variation in the growing rate mainly with F1 (Fi gure 4-7). This may be due to the characteristics of the release of the fertilizer or climatic variati on (e.g. temperature in the winte r). The leaves were responsible for the majority of the plants overall weight. The roots and stems had approximately the same proportion of the dry weight. Nitrogen Uptake in Plants There were no significant diffe rences of N concentrations in leaves, stem s, and roots between treatments of CRFs (P = 0.05). However, it was interesting to find out that Ficus elastica Robusta N leaf concentrations were high with 3.4% in the juvenile stages (30 DAP) and decreased to 1.2 % in the mature stag es (150 DAP) (Figure 4-8A). The average concentrations for N in the leaves were 3.4, 2.4, 1.7, 1.1, and 1.2 % after 30, 60, 90, 120, and 150 DAP, respectively. Similarly, N concentrations were 1.5, 1.3, 1.0, 0.8, and 0.8 percent for stems and 1.5, 1.3, 1.0, 0.8, and 0.8 percent for ro ots after 30, 60, 90, 120, and 150 DAP (Figures 4-9A and 4-10A). The nitrogen conc entration tends to decrease fast er as the plants mature. This is because as the plant grows, the N will be d iluted in more tissue (Figure 4-11A). Griffith (1998), working with the Ficus cultivar Decora found simila r values with very high N

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52 concentration >3.51%, medium co ncentration as 1.3% to 2.25%, and very low concentration <1.0%. Nitrogen uptakes were calculated by multiplyi ng N concentrations by the plant biomass, thus: UL = LN x BL x 1000 Where, UL = uptake by leave (milligrams of nitrogen per plant (mg N/plant)); LN = N concentration in the leave (milligrams per kilogram (mg kg-1)), and BL = leave biomass (g/plant). In this experiment, leaf fraction was responsible for the majority of the total plant N gains with 59, 67, 70, 65, and 70 percent for the 30, 60, 90, 120, and 150 DAP. Roots were responsible for approximately 26% and the rest was due to the stem portion (Figures 4-8B, 4-9B, and 4-10B, and 4-11B). The total plant incremental N gain s (mg N/plant) between 30 and 150 DAP for F1, F3, F4, F5, F6, and control were 779, 769, 772, 867, and 767 for 53 mg N/plant, respectively, (Figure 4-11B). There were no significant diffe rences in N gains attributable to the CRF treatment (P = 0.05). A plants nutrient requirement increases w ith age and size during periods of growth, therefore the supply and uptake of nutrients must increase to maintain maximum plant growth. This is in accordance with what Tolman (1990) found while working with marigold plants and Yeager (1991) working with Ilex. Nitrogen not utilized immediat ely by a container plant can leach, volatilize, or adsorb on the container medi um. Leaching is considered the greatest avenue of nutrient loss. Up to 90% of leachable nitroge n is lost when irrigation or rainfall volume exceeds container volume (Craig, 2003). Applying fe rtilizer during active root growth increases nutrient efficiency. Thus, if nut rient addition (source) remains constant, nutrient efficiency changes as nutrient uptake patterns changes. Nitrogen use efficiency is a measure of the crops

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53 ability to take up the fertilizer N applied to the so il. It is defined as the total nitrogen absorbed by the plant as a percentage of total nitrogen supplied by that fertilizer for a given time interval. Thus, NUE at 150 DAP = N uptake {[(N source) N uptake (control)] x 100} / (Total fertilizer N applied) Where, N uptake (N source) is the weight of N taken up by the Ficus plant after 150 DAP N uptake (control) is the wei ght of N taken up by the non treated control after 150 DAP, and total N applied is the weight of N applied to container after 150 DAP. The NUE in the experiment was 34, 32, 35, 40, and 31 for the CRFs F1, F3, F4, F5, and F6, respectively (Table 4-1). These numbers ar e a little low comparing to other CRFs studies such as Obreza et al. (2010) and Fan (unpublished data, 2010). Correlation between Nitrogen Uptake / Biomass and Nitrogen Release from Controlled Release Fer tilizers Tolman et al. (1990) suggested than young marigold plants may require higher N concentrations than mature plants because of a smaller root system. King and Stimart (1990) found that chrysanthemums had higher N uptake pe r unit dry weight in the first 4 weeks of growth than in later growth st ages. This is similar to the F. elastica data in the current study (Table 4-5). The first 30 days had an N accumula tion (mg N per gram of dry weight) ratio of 25, 10, 31, 25, 30, and 26 for F1, control, F3, F4, F5, and F6, respectively, which decrease after 180 days to 6, 3, 6, 6, 6, and 6 for the same products This suggests the importance to fertilize container crops early and heavily after potting when root growth is critical (Rose et al., 1994). Figures 4-12, 4-13, 4-14, 4-15, and 4-16 s how the correlation between N uptake by F. elastica Robusta and the N release in water at 25 C from F1, F3, F4, F5, and F6, respectively. In all the cases, the correlation and the coefficient of determination were high which means a

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54 good relation between the two vari ables and a strong fit between N uptake vs. N release (r>0.94 and R2>0.83) (Tables 4-3 and 4-4). The cumulative per centage of N release from the F1, F3, F4, F5, and F6 after 180 days of incubation was 117, 110, 104, 106, and 110 percent, respectively. The N uptake by the plants were 908, 938, 940, 1127, 918 mg N/ plant, respectively from F1, F3, F4, F5, and F6 after 150 days of planting. There wa s no significant differen ce attributable to the CRF treatment ( = 0.05). Conclusions All tes ted fertilizers increased plant biomass compared to the control treatment. However, there is no significant difference between the biom ass of plants attributable to the different CRFs. By the end of growing period, the highest biomass (142 g/plant) ca me from the treatment F5 and the lowest (17.7 g/plant) was from the c ontrol. All CRFs except F1 have similar patterns with slow growth in early season and quick growth in later season. Ficus leaf N concentrations ranged from 1.2% at mature stage (150 DAP) to 3.4% at juvenile stage (3 0 DAP). The ranges of N concentrations were 0.8 to 1.5 for both stems and roots. The cumulative N uptake by the end of growing season ranged from 90 g/plant (contro l) to 1069 g/plant (F5). The highest NUE came from F5 treatment with 40% and the lowest is F6 treatment with 31%. Low NUE values for all fertilizers may be caused by quick releasing of N from CRFs and over irrigation. Plant biomass and N uptakes were highly correlated to N re lease from CRFS measured at 25C (r>0.94). The linear regression analysis also showed the bioma ss and N uptake can be predicted with N release of CRFs (R2>0.83). This study indicated that CRFs hold great promise to improve plant growth and NUE, but additional research on characterizati on, plant response, environmental effects, and economics is needed.

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55 Figure 4-1. Ficus elastica Robusta grown in a greenhouse Figure 4-2. Ficus elastica Robusta treated with controlled release fertiliz ers (CRFs) F1, F2, F3, F4, F5, and F6 from left to right at 180 days af ter planting (DAP)

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56 Table 4-1. Cumulative N uptakes and N use efficiency (NUE) of Ficus elastica Robusta throughout the growing season (150 days) Net cumulative N uptake (mg/plant) NUE Treatment 30 d 60 d 90 d 120 d 150 d (%) Control 39 52 64 68 90 F1 110 458 545 752 932 34 F3 187 551 646 724 877 32 F4 173 520 717 736 953 35 F5 246 581 672 898 1069 40 F6 183 532 624 838 849 31 Table 4-2. Significant levels for means of dry biomass (g/plant) CRF 30 days 60 days 90 days 120 days 150 days 180 days F1 5.2 a 21.9 a 31.6 a 61.0 a 73.4 a 126.2 a F2 3.4 a 4.6 b 9.7 b 13.1 b 14.6 b 17.8 b F3 5.5 a 24.9 a 38.4 a 66.5 a 65.3 a 121.1 a F4 6.8 a 19.0 a 34.8 a 62.3 a 78.0 a 124.2 a F5 8.7 a 24.6 a 33.6 a 66.3 a 75.2 a 142.2 a F6 5.8 a 24.5 a 40.0 a 76.4 a 76.4 a 132.5 a Significant (P = 0.05)

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57 Table 4-3. Correlation (r) between biomass of Ficus elastica Robusta vs. N release of controlled release fertilizers ( CRFs), and N uptake vs. N release CRF Biomass vs. N Release N Uptake vs. N Release F1 0.94 0.97 F3 0.90 0.98 F4 0.91 0.98 F5 0.91 0.96 F6 0.94 0.94 Table 4-4. Regression equations and coefficients of determination (R2) between biomass of Ficus elastica Robusta vs. N release of controlled release fertilizers (CRFs), and N uptake vs. N release Biomass vs. N uptake Biomass vs. N release CRF Equation R2 Equation R2 F1 y = 0.0878x-10.459 0.9478 y = 0.0476x 36.912 0.8761 F3 y = 0.0943x 16.18 0.8604 y = 0.0957x 86.054 0.8037 F4 y = 0.0922x 16.925 0.8313 y = 0.0523x 28.548 0.8206 F5 y = 0.0869x 18.58 0.945 y = 0.0712x 48.175 0.8223 F6 y = 0.1113x 21.083 0.9645 y = 0.0657x 25.682 0.8813

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58 Table 4-5. Nitrogen uptake per unit of dry wei ght (mg N/g biomass) of different controlled release fertilizers (CRFs) during the growing season CRF 30 d 60 d 90 d 120 d 150 d 180 d F1 25 21 1 12 12 6 F2 10 12 6 6 6 3 F3 31 22 16 11 14 6 F4 25 30 22 12 12 6 F5 30 24 16 13 15 6 F6 26 16 15 11 12 6

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59 dry weight (g / plant 0 20 40 60 80 100 0306090120150180 F1 C F3 F4 F5 F6 Days after planting Figure 4-3. Leave biomass (g/plant) of Ficus elastica Robusta treated with five controlled release fertilizes (CRFs) plus control (C) in a greenhouse

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60 dry weight (g / plant) 0 5 10 15 20 25 0306090120150180 F1 C F3 F4 F5 F6 Days after planting Figure 4-4. Stem biomass (g/plant) of Ficus elastica Robusta treated with five controlled release fertilizers (CRFs) plus a control (C) in the greenhouse

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61 d r y wei g ht (g / p lant ) 0 10 20 30 40 0306090120150180 F1 C F3 F4 F5 F6 Days after planting Figure 4-5. Biomass in the roots (g) of Ficus elastica Robusta treated with five controlled release fertilizers (CRFs) plus a co ntrol (C) and grown in the greenhouse

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62 d r y wei g ht (g / p lant ) 0 20 40 60 80 100 120 140 160 0306090120150180 F1 F2 F3 F4 F5 F6 Days after planting Figure 4-6. Total biomass (g) of Ficus elastica Robusta treated with five controlled release fertilizers (CRFs) plus a control (C)

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63 d r y wei g ht (g / p lant ) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0306090120150180 F1 F2 F3 F4 F5 F6 Days after planting Figure 4-7. Daily biomass (g) of Ficus elastica Robusta treated with five controlled release fertilizers (CRFs) plus a control (C)

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64 N uptake (mg N / plant) leaf nitrogen (%) A 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 0306090120150 F1 F2 F3 F4 F5 F6 Days after planting B 0 200 400 600 800 0306090120150 F1 F2 F3 F4 F5 F6 Days after planting Figure 4-8. Leaf nitrogen concentrati on (%) (A) and nitrogen uptake (B) of Ficus elastica Robusta treated with five controlled release fertilizer s (CRFs) plus a control

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65 N uptake (mg N / plant) stem nitrogen (%) A 0.0 0.5 1.0 1.5 2.0 2.5 0306090120150 F1 F2 F3 F4 F5 F6 Days after planting B 0 40 80 120 160 200 0306090120150 F1 F2 F3 F4 F5 F6 Days after planting Figure 4-9. Stem nitrogen concentrati on (%) (A) and nitrogen uptake (B) of Ficus elastica Robusta treated with five controlled release fertilizer s (CRFs) and a control (C)

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66 N uptake (mg N / plant) roots nitrogen (%) A 0 0.5 1 1.5 2 2.5 0306090120150 F1 F2 F3 F4 F5 F6 Days after planting B 0 50 100 150 200 250 0306090120150 F1 F2 F3 F4 F5 F6 Days after planting Figure 4-10. Root nitrogen concentra tion (%) (A) and nitrogen uptake (B) of Ficus elastica Robusta treated with five c ontrolled release fertilizers (CRFs) plus a control (C)

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67 N uptake (mg N / plant) Nitro g en ( % ) A 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 0306090120150 F1 F2 F3 F4 F5 F6 Days after planting B 0 200 400 600 800 1000 1200 0306090120150 F1 F2 F3 F4 F5 F6 Days after planting Figure 4-11. Total nitrogen concen tration (%) (A) and uptake (B) of Ficus elastica Robusta treated with five controlled release fertilizers (CRFs) plus a control (C)

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68 cumulative % N release N uptake (mg N / plant) A 0 200 400 600 800 1000 1200 0306090120150 F1 Days after planting B 0 20 40 60 80 100 120 0306090120150180 F1 Days after incubation Figure 4-12. Comparison of nitrogen uptakes (A) of Ficus elastica Robusta (mg N / plant) vs. nitrogen release (%) from F1 (B)

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69 cumulative % N release N uptake (mg N / plant) A 0 200 400 600 800 1000 0306090120150 F3 Days after planting B 0 20 40 60 80 100 120 0306090120150180 F3 Days after incubation Figure 4-13. Comparison of nitrogen uptakes (A) of Ficus elastica Robusta (mg N/plant) vs. nitrogen release (%) from F3 (B)

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70 cumulative % N release N uptake (mg N / plant) A 0 200 400 600 800 1000 1200 1400 0306090120150 F5 Days after planting B 0 20 40 60 80 100 120 0306090120150180 F5 Days after incubation Figure 4-14. Comparison of nitrogen uptakes (A) of Ficus elastica Robusta (mg N/plant) vs. nitrogen release (%) from F5 (B)

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71 cumulative % N release N uptake (mg N / plant) A 0 200 400 600 800 1000 1200 0306090120150 F4 Days after planting B 0 20 40 60 80 100 120 0306090120150180 F4 Days after incubation Figure 4-15. Comparison of nitrogen uptakes (A) of Ficus elastica Robusta (mg N / plant) vs. nitrogen release (%) from F4 (B)

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72 Cum cumulative % N release N uptake (mg N / plant) A 0 200 400 600 800 1000 0306090120150 F6 Days after planting B D a y s a f Days after incubation Figure 4-16. Comparison of nitrogen uptakes (A) of Ficus elastica Robusta (mg N / plant) vs. nitrogen release (%) from F6 (B) 0 20 40 60 80 100 0306090120150180 F6

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73 CHAPTER 5 SUMMARY AND CONCLUSIONS Due to the p revalent high temperatures a nd rainfall that characterize South Floridas weather, the large numbers of nur series located close to urban cen ters, and the sensitivity of the groundwater to nitrogen (N) po llution, Best Management Prac tices (BMP) guidelines are essential. In the actually very competitive horticulture market, th ere is a tremendous potential for container nurseries to become more efficient with their fertilizer use. Although today the controlled release ferti lizers (CRFs) are increasing in popul arity and are used by many growers in South Florida, there is a n eed to develop new methodologies and techniques to allow accurate predictions of N release patterns in the short te rm. Also, it is important to match plant growth characteristics with the N release pattern of the fertilizers used. This research includes in Chapter 3 the prediction for N release rates by different me thods, and in Chapter 4, the response of plant growth to different CRFs. Nitrogen Release Rate from Controlled Releas e Fertiliz ers Predicted by Different Method Study Although many types of CRFs are available to cr op producers, there is a lack of knowledge about N release patterns under field conditions. In Florida, there has been no quick and accurate test for determining N release rates. In th e laboratory, the standard methodology for CRFs N release is at 25 Celsius (C) in soil or water in cubation, but this procedure is very slow and can take several months or more than one year to be completed, which is inconvenient for practical purposes. The objective of this study was to find an accelerated procedure to determine N release that could be correlated with the st andard procedure in order to ob tain N release results in short periods of time in hours or days. The research results of this study demonstrated that the N release test at 100C was useful for prediction of N rate at 25C. This procedure can be used by

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74 growers, manufacturers or regulat ors who want to test an unknow n coated CRF product. We can conduct a short term test at 100C for the product and use the regression equation found in this study. The release time for a given percent of N rel ease at 100C can then be used to predict the time required to release similar percent of N rele ase at 25C. Thus, the N release duration (about several months) at 25C can be predicted by using a fast N release test at 100C within hours. By using the accelerated incubati on method, users can have a more accurate idea about the actual longevity of the CRF products used under Sout h Florida conditions. This can save time and money. The field mesh bag study showed high correlation between the prill loss weight and the N release pattern; however it need s more research to be perfecte d, because environmental factors could have caused different values. Response of Plant Growth Study Supplying adequate nutrients for producing quality plants in containe rs poses interesting challenges to growers. CRFs can supply, in one application, enough plant nutrients to support a season long growth of crop, but m atching nutrient release with plant requirements is a major challenge for both growers and CRF manufactur ers. The objective of this research was to evaluate the relationship between N release patterns and plant growth (biomass and N Uptake). Ficus elastica Robusta, which is a popular indoor and outdoor plant in Florida, was used as testing plants. All tested fertilizers that increas ed plant biomass were compared to the control treatment. However, there is no significant differe nce between the biomass of plants treated with various CRFs. We also tested nitrogen use effi ciency (NUE), which show low values for all fertilizers. This may be caused by quick releasing of N from CRFs due to high temperature and over irrigation. Plant biomass and N uptakes were highly correlated to N release from CRFs measured at 25C (r>0.94). The lin ear regression analysis also s howed the biomass and N uptake can be predicted with N release of CRFs (R2>0.83). This study indicated that CRFs hold great

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75 promise to improve plant growth and NUE but additional research on characterization, plant response, environmental effects, and economics is needed before CRFs use can be established in a much broader base.

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76 LIST OF REFERENCES Ahm ed, I.U., O.J. Attoe, L.E. Engelbert, and R.E. Corey. 1963. Factors affecting the rate of release from fertilizers fro m capsules. Agron. J. 55:495-499. Association of American Plan t Food Control Officials (AAPFC O). 1995. Official Publication No. 48. Published by Association of American Plant Food Control Officials, Inc.; West Lafayette, Indiana, USA. Broschat, T. K., and K. Moore. 2007. Release rates of ammonium-nitrogen, nitrate-nitrogen, phosphorus, potassium, magnesium, iron, and ma nganese from seven controlled-release fertilizers. Commun. Soil Sc i. Plan. Anal. 38: 843-850. Cabrera, R.I. 1997. Comparative evaluation of nitr ogen release patterns from controlled release fertilizers by nitrogen leachi ng analysis. HortScience. 32:669-673. Craig, J.L., B.A. Birrenkott, and D.K. Struve. 2003. Nutrient uptake and dr y weight patterns of three container-grown woody speci es. J. Environ. Hort. 21: 209-215. Dai, J.J., X.L. Fan, J.G. Yu, F. Liu, and Q. Zhang. 2008. Study on the rapid method to predict longevity of controlled release fertilizer coated by water so luble resin. Agri. Sci. China 7(9):1127-1132. Fan. X.H., and Y.C. Li. 2010. Nitrogen release fro m slow-release fertilizers as affected by soil type and temperature. Soil Sci. Soc. Am. J. 74:1082-1089. Florida Department of Agriculture and Consum er Service. Bureau of Compliance Monitoring. 2004. Archive fertilizer tonnage data. Retrieved May 27, 2010, from http://www.flaes.org/complimonitoring/reports.html. Florida Comm ercial Fertilizer Law. 2004. Florid a Department of Agriculture and Consumer Service. Bureau of Compliance Monitoring Fer tilizer Section. Chapter 576 Florida Statutes and Chapter 5E-1 Florida Administrative Code. Retrieved June 1, 2010 from http://www.doacs.state.fl.us /onestop/aes/fertilizer.htm l. Florida Container Nursery BMP Guide. 2006. Container Production Guidelines. Retrieved June 3, 2010 from http://hort.ufl.edu/bmp/containerBMP.pdf. Florida Department of Environmental Protection. 2002. Florida Green Industry. Best Management Practices for Protection of Water Resources in Florida. Retrieved June 4, 2010 from http://www.dep.state.fl.us/water /nonpoint/docs/nonpoi nt/BMP_Book_final.pdf Foster, W. J., R.D Wright, M.M. Alley, and T.H. Yeager. 1983. Ammonium adsorption on a pinebark growing medium. J. Am. Soc. Hortic. Soc. 108:548-551. Gandeza, A.T., S. Shoji, and L. Yamada. 1991. Simu lation of crop response to polyolefin-coated urea: I. Field dissolution. Soil Sci. Soc. Am. J. 55:1462-1467.

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77 Goertz, H.M. 1995. Technology development in coated fertilisers. In: Pro c. Dahlia Greidinger Memorial Goertz, Int. Workshop on Contro lled/Slow Release Fertilisers Technion Institute of Technology, Haifa, Israel. Griffith, L.P. 2006. Tropical foliage plants A growers guide. 2nd edition. pp.182-189. Ball Publishing, Batavia, IL, U.S.A. Hodges, A.W., and J.J. Haydu. 2005. Economic impacts of the Florida environmental horticulture industry in 2005.Uni v. of Florida-Institute of Food and Agricultural Science, Food and Resource Econ. Dep. EDIS document FE 675. Huett, D.O. 1997. Fertiliser use efficiency by containerized nursery plants.1. Plant growth and nutrient uptake. Aust. J. Agric. Res. 48:251-258. Huett, D.O., and B.J. Gogel. 2000. Longevities and nitrogen, phosphorus, and potassium release patterns of polymer-coated cont rolled release fertilizers at 30C and 40C. Commun. Soil Sci. Plant Anal. 31:959-973. Husby, C.E., A.X. Niemiera, J.R. Harris, and R.D. Wright. 2003. Influence of diurnal temperature on nutrient release patterns of th ree polymer-coated fertilizers. HortScience. 38(3):387-389. Ingram, D.I. 1981. Characterization of temperature fluctuations a nd woody plant growth in white poly bags and conventional black co ntainers. HortScience. 16:762-763. King J., and D. Stimart. 1990. Quantities and forms of N uptake throughout development in chrysanthemum. HortScience. 25:170. Kochba, M., S. Gambash, and Y. Avnimelech. 1990. Studies on slow release fertilizers:1.Effects of temperature, soil moisture, and wa ter vapor pressure. Soil Sci. 149:339-343. Lamont, G.P., R.J. Worrall, and M.A. OConne ll. 1987. The effects of temperature and time on the solubility of resin-coated controlled-re lease fertilizers under laboratory and field conditions. Scientia Hort. 32:265-273. Landels, S.P. 1994. Controlled release fertiliz ers: Supply and demand trends in US nonfarm markets. Proc. American Chemical Society Na tional Meeting, Divisi on of Fertilizers and Soil Chemistry. August 1994. Meadows, W.A., and D.L. Fuller. 1983. Nitroge n and potassium release patterns of five formulations of Osmocote fertilizers and two micronutrients mixes for container grown woody ornamentals. Proc. Southern Nu rserymens Assn. Res. Conf. 9:28-34. Medina, C. L., T.A. Obreza, and J.B. Sartain. 2008. Nitrogen releas e patterns of mixed controlled release fertilizer and it s components. Hort Technology. 18:475-480. Medina, C.L., J.B. Sartain, T.A. Obreza. 2009. Es timation of release properties of slow-release fertilizer materials. HortTechnology. 19:13-15.

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78 Obreza, T.A, R. Rouse, and E.A. Hanlon. 2006. Adva ncement with controlled-release fertilizers for Florida citrus production: 1996-2006. Univ. of Florida-Institute of Food and Agricultural Sciences, Soil and Water Science Dept. SL-243. Obreza, T.A, and J.B. Sartain. 2010. Improving nitr ogen and phosphorus fertil izer use efficiency for Floridas horticultural crops. HortTechnology. 20:23-33. Oertli, J.J., and O.R. Lunt. 1962. Controlled-relea se of Fertilizer Mine rals by Encapsulating Membranes: I. Factors Influencing the Rate of Release. Soil Sci. Soc. Am. Proc. 26:579583. Oertli, J.J., and O.R. Lunt. 1962. Controlled re lease of fertilizer minerals by encapsulating membranes: II. Efficiency of recovery, influen ce of soil moisture, mode of application, and other considerations rela ted to use. Soil Sci. Soc. Am. Proc. 26:584-587. Oertli, J.J. 1980. Controlled-release fertilizers. Fert. Res. 1:103-123. Rose, M. A., and J. W. White. 1994. Nitrogen ra te and timing of nitrogen application in poinsettia (Euphorbia pulcherrima Willd. Ex Klotz). HortScience. 29:1309-1313. Rosen, C.J., P. Bierman, and M. McNearney. 2006. Kingenta controlled releas e fertilizer trial 2006. Department of Soil, Water, and Climate. University of Minnesota. unpublished. Shaviv, A. 2001. Advanced in controlled-release fertilizers. Adv. Agron. 71:1-49. Shaviv, A. 2005. Controlled-release fertilizer s. IFA International Workshop on enhancedefficiency fertilizers. pp 15.Israel In stitute of Technology, Haifa, Israel. Sartain, J.B. 2008. The Florida Label. Univ. of Florida-Institute of Food and Agricultural Sciences, Soil and Water Science Dept. SL 3. Sartain, J.B, and J.K. Kruse. 2001. Selected fertil izers used in turfgrass fertilization. Univ. of Florida-Institute of Food and Agricultural Sciences, Soil and Water Science Dept. CIR 1262. Sartain, J.B., W.L. Hall, R.C.Littell, and E. W. Hopwood. 2004. New tools for the analysis and characterization of slow-release fertilizers, p. 180-195. In : Environmental impact of fertilizer on soil and water. Amer. Ch em. Soc. Symo. Ser. 872. Washington. DC. Simonne, E.H., and C.M. Hutchinson. 2005. Cont rolled release fertilizers for vegetable production in the era of best management pr actices: teaching new tricks to an old dog. HortTechnology. 15(1):36-46. Tolman, D.A., A.X. Niemiera, and R.D. Wr ight. 1990. Influence of plant age on nutrient absorption for marigold seedli ngs. HortScience. 25:1612-1613. Trenkel, M. A. 1997. Controlled re lease and stabilized fertilizer s in agriculture International Fertilizer Industry Assn., Paris.

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79 Yeager, T.H., R.H. Harrison, and D.L. Ingram. 1991. Rotundifolia Holy growth and nitrogen accumulation influenced by supraoptimal root-zone temperatures. HortScience. 26:13871388. Yeager, T., J. Million, C. Larsen, and B. Stamps. 2010. Florida nursery best management practices: past, present, and future. HortTechnology. 20:82-88. Wang, S.S., A.K. Alva, Y.C. Li, and M. Zh ang. 2010. A rapid techniqu e for prediction of nutrient release from controlled release fe rtilizers. Soil Sci. Soc. Am. J. Document submitted. Wilson, M.L., C.J. Rosen, and J.F. Moncrief. 2009. A comparison of techniques for determining nitrogen release from polymer-coated urea in the field. HortScience. 44:492-494.

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80 BIOGRAPHICAL SKETCH Henrique Mayer was born in Caracas, Venezuela. He attended the Central University of Venezuela for five years wh ere he received his bachelors degree in agricultural engineering in 1984. In 1999, he moved with his wife and three daughters to the United States where he began working at th e University of Florida / Institute of Food and Agricultural Sciences Extension office in Broward County. Actually, he works with the Miami-Dade Extension Service as a Commercial Urban Horticulture Extension Agent. He continued further studies in th e Soil and Water Science Department at the University of Florida and will graduate with a Master of Science degree in August 2010.