J.E. Raymond Use of Stable Isotopes to Trace the Fate of Applied Nitrogen in Forest Plantations to Evaluate Fertilizer Efficiency and Ecosystem Impacts Jay Edwards Raymond Dissertation submitted to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy In Forestry Thomas R. Fox, Chair John E. Barrett Brian D. Strahm Valerie A. Thomas February 3 rd , 2016 Blacksburg, VA Keywords: 15 N; forest fertilization; nitrogen cycle; plantation forestry Copyright 2016, Jay Edwards Raymond J.E. Raymond Use of Stable Isotopes to Trace the Fate of Applied Nitrogen in Forest Plantations to Evaluate Fertilizer Efficiency and Ecosystem Impacts Jay Edwards Raymond ABSTRACT This study assessed five fertilizer treatments (control – no fertilizer, urea, urea treated with N-(n-butyl) thiophosphoric triamide (NBPT), coated urea + NBPT (CUF), polymer coated urea (PCU) ) during two application seasons (spring, summer) to: 1) compare fertilizer nitrogen (N) losses (see Chapter 2); 2) evaluate temporal N uptake patterns of loblolly pine (see Chapter 3); and 3) evaluate fertilizer N cycling and partitioning in a loblolly pine ecosystem (see Chapter 4). Chapter 2 results showed enhanced efficiency fertilizers (EEFs) significantly reduced ammonia (NH 3) volatilization losses compared to urea. Mean NH 3 volatilization after spring fertilization ranged from 4% to 26% for EEFs versus 26% to 40% for urea, and 8% to 23% for EEFs versus 29% to 49% for urea in summer. Chapter 3 results showed an increase in timing and development of foliage in fertilized compared to unfertilized plots. In addition, the cumulative N uptake by loblolly pines increased over the entire growing season from N originating from fertilizer and natural sources. Chapter 4 results showed greater fertilizer N recovery for EEFs in both spring and summer (80%, 70-80% respectively) compared to urea (60%, 50% respectively) with most fertilizer N recovered from mineral soil (20% to 50%) and loblolly pines (10% to 50%). Three primary conclusions come from this research: 1) EEFs reduce NH 3 volatilization after N fertilization compared to urea regardless of application timing and weather conditions (see Chapter 2); 2) N uptake by loblolly pines increases over the entire growing season after N fertilization (see Chapter 3); more fertilizer N remains in the ecosystem with EEFs compared to urea with most fertilizer N remaining in the soil (see Chapter 4). From these findings, we hypothesize that the EEFs in this study: 1) reduce ammonia volatilization which 2) translates to an increase in fertilizer nitrogen remaining in the loblolly pine plantation system that 3) increases the amount of plant available nitrogen for an extended period into the stand rotation and 4) increases fertilizer nitrogen use efficiency (FNUE) for all enhanced efficiency fertilizers investigated in this study compared to the conventional form of fertilizer N used in forestry, urea. i J.E. Raymond Dedication To my wife Anja Whittington. Without her understanding, patience and support at every level, this process would have been less enjoyable and less meaningful. Thank you for everything you have done for me and for us over the last several years. iii J.E. Raymond Acknowledgements I would like to extend my sincerest gratitude to my advisor, Dr. Thomas R. Fox, who provided the guidance, advice, and support during this entire process. I would like to thank my committee member Dr. Brian D. Strahm, who also provided guidance and advice during this process. I would like to thank my committee members, Dr. John E. Barrett and Dr. Valerie A. Thomas, for their support and guidance during the development of my dissertation research. I would like to thank Dave Mitchem for always making time in the laboratory to assist me. I would like to thank Eric Carbaugh, Andy Laviner, and Kevan Minick for the numerous conversations on the meaning of science, and their friendships during this process. I would like to thank Dr. Ivan Fernandez for his mentoring and advice during various phases of moving through this process. I would also like to thank Dr. Anja Whittington for her input and review during all stages of this process. I finally would like to thank the Forest Productivity Cooperative, the Center for Advanced Forestry Systems, and the United States Department of Agriculture National Institute of Food and Agriculture for their support of this research. iv J.E. Raymond Contributing Authorship Chapter 2. Chapter 2 will be submitted to Soil Biology and Biochemistry in 2016 J.E. Raymond T.R. Fox B.D. Strahm J.L. Zerpa Chapter 3. Chapter 3 will be submitted to Forest Ecology and Management in 2016 J.E. Raymond T.R. Fox B.D. Strahm J.L. Zerpa Chapter 4. Chapter 4 will be submitted to Ecology in 2016 J.E. Raymond T.R. Fox B.D. Strahm J.L. Zerpa v Table of Contents Abstract ........................................................................................................................................... ii Dedication ...................................................................................................................................... iii Acknowledgements ........................................................................................................................ iv Contributing Authorship ..................................................................................................................v Table of Contents ........................................................................................................................... vi List of Tables ................................................................................................................................. ix List of Figures ............................................................................................................................... xii Chapter 1. Introduction 1.1. Justification ...........................................................................................................................1 1.2. Literature Review 1.2.1. The Nitrogen Cycle in Forest Ecosystems .....................................................................4 1.2.2. Productivity of Intensively Managed Pine Plantations ..................................................6 1.2.3. Assessment Methods for Nutrient Deficiencies in Loblolly Pine ..................................7 1.2.4. Nitrogen Fertilization of Pine Plantations ......................................................................8 1.2.5. Cycling of Fertilizer Nitrogen in Pine Plantations .......................................................10 1.2.6. Enhanced Efficiency Fertilizers ...................................................................................13 1.2.7. Use of Stable Isotopes to Trace Nitrogen in Forest Ecosystems ..................................16 1.3. Objectives ............................................................................................................................20 Literature Cited ..........................................................................................................................21 Chapter 2. Ammonia volatilization following nitrogen fertilization with enhanced efficiency fertilizers and urea in loblolly pine (Pinus taeda L.) plantations of the southern United States Abstract ......................................................................................................................................41 2.1. Introduction .........................................................................................................................42 2.2. Materials and Methods 2.2.1. Experimental Design ....................................................................................................46 2.2.2. Fertilizer Treatments ....................................................................................................46 2.2.3. Site Description ............................................................................................................47 2.2.4. Experimental Method ...................................................................................................47 2.2.5. Laboratory Processing ..................................................................................................48 2.2.6. Weather Data ................................................................................................................49 2.2.7. Calculations ..................................................................................................................50 2.2.8. Statistical Analysis .......................................................................................................51 2.3. Results 2.3.1. Differences in NH 3 Volatilization Among Fertilizers Treatments – Spring .................52 2.3.2. Differences in NH 3 Volatilization Among Fertilizers Treatments – Summer .............52 2.3.3. NH 3 Volatilization Among Fertilizer Treatments – Spring + Summer ........................53 2.3.4. Correlation Between NH 3 Volatilization from Urea and Weather Data ......................53 2.4. Discussion ...........................................................................................................................54 vi J.E. Raymond 2.5. Conclusion ...........................................................................................................................62 2.6. Acknowledgements .............................................................................................................64