Yield, biomass and nitrate leaching potential for cauliflower grown on a sandy loam with organic and conventional fertilizers

YIELD, BIOMASS AND NITRATE LEACHING POTENTIAL FOR CAULIFLOWER GROWN ON A SANDY LOAM WITH ORGANIC AND CONVENTIONAL FERTILIZERS Nitrate contamination in drinking water continues to be a significant unresolved environmental issue worldwide, and in agricultural regions of California. Cauliflower is a shallow rooted crop with high demand for Nitrogen (N), thereby providing a challenge to optimizing yield while minimizing the potential for nitrate leaching. Hence, this study focused on comparing the effects of different fertilizer types and rates on biomass, yield and nitrate leaching potential for drip irrigated cauliflower grown on a sandy loam soil. The experimental layout was a two factor randomized complete block design, with organic soybean meal (ORG) and conventional UAN32 applied at rates of 0, 75, 150 and 225 lbs N/acre. In the study, UAN32 and the ORG fertilizers increased the biomass production by 61% and 30%, respectively, at the two highest application rates. Marketable yields were higher in response to 150 and 225lbs N/acre compared to the 0 and 75lbs N/acre, regardless of the fertilizer type. Postharvest soil nitrate levels within the top 4 feet increased with application rates for both UAN32 and ORG. Overall, application rates of 225lbN/acre intensified the potential to leach nitrates below the root zone, with an insignificant economic return from adding extra nitrogen. Hence, for the sandy loam soil used in this study it is recommended that N application rates for cauliflower should not exceed 150lbs/N acre, regardless if it is being applied as an organic soybean meal or UAN32 synthetic fertilizer. Josué Sámano Monroy May 2016 YIELD, BIOMASS AND NITRATE LEACHING POTENTIAL FOR CAULIFLOWER GROWN ON A SANDY LOAM WITH ORGANIC AND CONVENTIONAL FERTILIZERS by Josué Sámano Monroy A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Plant Science in the Jordan College of Animal Sciences and Agricultural Education California State University, Fresno May 2016 APPROVED For the Department of Plant Science: We, the undersigned, certify that the thesis of the following student meets the required standards of scholarship, format, and style of the university and the student's graduate degree program for the awarding of the master's degree. Josué Sámano Monroy Thesis Author Dave Goorahoo (Chair) Plant Science Florence Cassel Sharma Plant Science John Bushoven Plant Science For the University Graduate Committee: Dean, Division of Graduate Studies AUTHORIZATION FOR REPRODUCTION OF MASTER’S THESIS X I grant permission for the reproduction of this thesis in part or in its entirety without further authorization from me, on the condition that the person or agency requesting reproduction absorbs the cost and provides proper acknowledgment of authorship. Permission to reproduce this thesis in part or in its entirety must be obtained from me. Signature of thesis author: ACKNOWLEDGMENTS I offer my sincere gratitude to Dr. Dave Goorahoo, Dr. Florence Cassel and Dr. John Bushoven for their continuous support and guidance during the process of my research project and thesis writing. Special thanks to Dr. Dave Goorahoo to serve as chair of my committee and advisor, encouraging me to participate in research projects and scientific conferences that contributed to my academic and professional development. Thanks to the Jordan College of Agricultural Sciences and Technology for the funding provided through the Harvey Jordan Scholarship, and to Dr. Sharon Benes for her guidance in the process of admission and completion of the Master’s program. Thanks to the Plant Science Department for its support and to the Division of Graduate Studies for funding part of my research. I want to thank the Agricultural Research Initiative (ARI) for funding the project “Managing High-Nitrate Irrigation Water in Agriculture”. Acknowledge the CIT for the opportunities and to the staff for their constant support. Recognize the “Gradlab Team”: Janet Robles, Charles Cochran, Touyee Thao, and other students who helped me in the sampling and completion of the field project, and to Dr. Bacon for his expertise and guidance in lab analysis. I am very grateful to my parents Mónica Monroy Bear and José Sámano Guzmán for their unconditional support and to my fiancée Maria Kimei Callieri for her encouragement. TABLE OF CONTENTS Page LIST OF TABLES . vii LIST OF FIGURES . ix INTRODUCTION . 1 LITERATURE REVIEW . 5 Cauliflower Production in California . 5 Nitrogen . 5 Nitrogen Cycle . 7 Green Revolution . 9 Nitrogen Fertilization . 10 Organic Fertilizers . 12 Nitrogen (N) Balance . 13 Nitrate Leaching . 14 Nitrate Contamination in Water and Environment . 15 Elevated Nitrate