YIELD AND NITROGEN USE EFFICIENCY FOR LETTUCE (LACTUCA SATIVA) GROWN WITH AIRJECTION® AND NON-AERATED IRRIGATION

YIELD AND NITROGEN USE EFFICIENCY FOR LETTUCE (LACTUCA SATIVA) GROWN WITH AIRJECTION AND NON-AERATED IRRIGATION Nitrogen (N) use efficiency (NUE) is an important factor to consider for the improvement of crop yield and the minimization of nitrate leaching potential (NLP). AirJection Irrigation is one method proposed for increasing yield and NUE for shallow rooted crops, such as lettuce, that have a high demand of N. Optimizing NUE while minimizing soil residual nitrate presents a challenge for lettuce growers mandated to comply with the Irrigation and N Management Plan (INMP). This study focused on the yield and NUE of two head lettuce varieties subjected to different rates of N and two irrigation treatments. Two separate experiments were conducted in the San Joaquin Valley (SJV) of California in a Panoche clay loam soil. The experimental layout consisted of a randomized complete block design (RCBD) with 3 replications. Treatments within each experiment were composed of four N fertilizer rates and either an AirJection Irrigation (AI) or Non-Aerated Irrigation (NA) treatment. Lettuce yield increased with higher rates of N applied over two seasons under both irrigation treatments. However, NUE decreased with increased fertilizer rates over both seasons under the two irrigation regimes. Trends in plant tissue NO3-N, total leaf N along with post-harvest soil NO3-N concentrations suggest NLP was mitigated by plant N uptake. Hence, in an effort to comply with the INMP for iceberg lettuce grown on a Panoche clay loam, producers should consider these parameters along with yield and economic returns, when increasing their N application rates from 200 to 250 kg N per ha. Daniel A. Gutiérrez December 2020 YIELD AND NITROGEN USE EFFICIENCY FOR LETTUCE (LACTUCA SATIVA) GROWN WITH AIRJECTION AND NON-AERATED IRRIGATION by Daniel A. Gutiérrez A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Plant Science in the Jordan College of Agricultural Sciences and Technology California State University, Fresno December 2020 © 2020 Daniel A. Gutiérrez 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. Daniel A. Gutiérrez 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 would like to thank the faculty and staff at the Plant Science Department at Fresno State University for their support during my graduate studies. I would like to offer my sincere gratitude to my thesis committee Dr. Dave Goorahoo, Dr. Florence Cassel and Dr. John Bushoven for their expertise and guidance in the completion of this thesis. Dr. Dave Goorahoo, thank you for your mentorship, guidance, support, and advice during this process! Dr. Bushoven and Dr. Cassel, thank you for your support in my graduate courses and for being part of my thesis committee. Thank you to the Grad Lab Team, Janet Robles, Charles Cochran, and all students who helped me process and analyze samples. I appreciate all your help and hard work! Marlene, thank you for your support and assistance during my studies. You were always there to answer all my questions and concerns! I thank my parents, Jesús and Briselda Gutiérrez for their unconditional support and encouragement throughout my life. Finally, I dedicate this thesis to my wife and children, Julia, Melody and Dylan. I am forever grateful to have you in my life! TABLE OF CONTENTS Page LIST OF TABLES . viii LIST OF FIGURES . ix INTRODUCTION . 1 LITERATURE REVIEW . 4 Head Lettuce Production in California . 4 The Nitrogen Cycle . 5 Nitrogen in Plants . 6 Nitrogen in Soil.7 Inorganic Nitrogen . 8 Lettuce Irrigation & Fertilization . 8 Sub-Surface Drip Irrigation . 10 AirJection® Irrigation . 10 Irrigation and Nitrogen Management Plan (INMP) . 12 STATEMENT OF THE PROBLEM . 14 OBJECTIVES . 15 MATERIALS AND METHODS . 16 Location . 16 Agronomic Practices . 16 Experimental Design . 17 Irrigation . 17 Fertilization. 18 Yield . 19 Tissue Sampling & Analysis . 19