MANAGEMENT EFFECTS ON HERBAGE RESPONSES, SIZE OF NUTRIENT POOLS, AND LITTER DYNAMICS IN GRAZED ‘TIFTON 85’ BERMUDAGRASS (CYNODON SPP.) PASTURES By KESI LIU A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2009 1 © 2009 Kesi Liu 2 To my parents and wife, for all their support and encouragement through the year. 3 ACKNOWLEDGMENTS I would like to begin by giving my special thanks to Dr. Lynn E. Sollenberger, my supervisory committee chair. His guidance throughout the graduate program has been invaluable and greatly appreciated. Thanks also go to the other members of the supervisory committee, Dr. Kenneth S. Boote, Dr. Donald A. Graetz, Dr. Yoana C. Newman, and Dr. João M.B. Vendramini, for their willingness to serve on the committee, their input and direction during the program, and for reviewing the dissertation. Special thanks go to those who helped during field and laboratory activities. This includes fellow graduate students Sindy Interrante, Renée White, and Miguel Castillo for their great support. Thanks go to the Beef Research Unit staff, Sid Jones and Dwight Thomas, for their help and support at the experimental station. In the Forage Evaluation Support Laboratory, Richard Fethiere and his crew gave the support needed for the forage analyses. Thanks are also due to Dr. Maria Silveira and Dr. Adegbola T. Adesogan and their lab staff for their help and support with laboratory sample preparation and analysis. For the friendship and company during my life in Gainesville, I would like to thank Ming Liu, Zhiwei Chen, and Qien Yang. Last but not least, I would like to give my thanks to my family and wife for their constant support and advice. 4 TABLE OF CONTENTS page ACKNOWLEDGMENTS ...............................................................................................................4 LIST OF TABLES...........................................................................................................................9 LIST OF FIGURES .......................................................................................................................13 ABSTRACT...................................................................................................................................14 CHAPTER 1 INTRODUCTION ..................................................................................................................16 2 LITERATURE REVIEW .......................................................................................................21 Bermudagrass .........................................................................................................................21 Origin and Characteristics of ‘Tifton 85’ ........................................................................21 Tifton 85 Response to N Fertilization .............................................................................22 Tifton 85 Response to Grazing........................................................................................23 Grazing Systems and Grazing Management...........................................................................25 Grazing Systems..............................................................................................................25 Grazing Management ......................................................................................................25 Grazing intensity ......................................................................................................26 Grazing frequency ....................................................................................................26 Plant Responses to Grazing Management ..............................................................................27 Grazing Intensity .............................................................................................................27 Herbage accumulation..............................................................................................27 Reserve status and persistence .................................................................................29 Nutritive value..........................................................................................................30 Grazing Frequency ..........................................................................................................31 Herbage accumulation..............................................................................................31 Persistence................................................................................................................32 Nutritive value..........................................................................................................33 Nutrient Pools in Grasslands ..................................................................................................33 Carbon .............................................................................................................................34 Nitrogen...........................................................................................................................35 Phosphorus ......................................................................................................................36 Potassium.........................................................................................................................37 Nutrient Cycling in Grasslands...............................................................................................38 Carbon .............................................................................................................................38 Nitrogen...........................................................................................................................39 Phosphorus ......................................................................................................................39 Potassium.........................................................................................................................40 Effects of Management Practices on Nutrient Cycling Among Pools ...................................40 Grazing Management ......................................................................................................41 5 Fertilization......................................................................................................................45 Litter Dynamics in Grazed Grasslands...................................................................................46 Role of Litter in Grassland Ecosystems ..........................................................................46 Management Effects on Litter Responses .......................................................................47 Litter deposition .......................................................................................................47 Litter chemical composition.....................................................................................48 Litter decomposition and nutrient release ................................................................48 Summary.................................................................................................................................51 3 GRAZING MANAGEMENT EFFECTS ON PRODUCTIVITY, NUTRITIVE VALUE, AND PERSISTENCE OF ‘TIFTON 85’ BERMUDAGRASS PASTURE ...........52 Introduction.............................................................................................................................52 Materials and Methods ...........................................................................................................54 Study Site.........................................................................................................................54 Experimental Design .......................................................................................................55 Pasture Management .......................................................................................................55 Pasture Sampling.............................................................................................................56 Statistical Analysis ..........................................................................................................59 Results and Discussion ...........................................................................................................60 Herbage Accumulation....................................................................................................60 Herbage Nutritive Value..................................................................................................64 Herbage Persistence.........................................................................................................67 Stem base and root-rhizome mass............................................................................67 Stem base and root-rhizome N concentration and content.......................................69 Stem base and root-rhizome TNC concentration and content..................................71 Percent cover after three years of grazing................................................................75 Conclusions.............................................................................................................................76 4 PASTURE MANAGEMENT EFFECTS ON NUTRIENT DISTRIBUTION AMONG NUTRIENT POOLS IN ‘TIFTON 85’ BERMUDAGRASS PASTURES............................79