
INFLUENCE OF NUTRIENT SOLUTION AND SOLUTION pH ON ONION GROWTH AND MINERAL CONTENT by CHAD D. KANE, B.S. A THESIS IN SOIL SCIENCE Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Approved Chairj^rs(& of the Committee Accepted Dean of the Graduate School August, 2003 ACKNOWLEDGEMENTS I would like to thank my committee members: Dr. Green, Dr. Peffley, and Dr. Thompson for their guidance, direction, and knowledgeable assistance during my graduate career, especially Dr. Green for his unlimited patience and understanding. I appreciate the help Jay M., Jeremy J., Janet H., Brent W., Amanda B., Katie P., Clint S., Amanda H., Marci B. and Brad M. (and anyone else who assisted me in the greenhouse or lab) gave me throughout my career. Thank you Vronka Stoker and Jennifer Collins. All your help with the little things made this research opportunity enjoyable and interesting. I don't believe that another group of people could have accomplished the things that we have, with all the distractions that we frequently encountered. A very special thanks to Dr. Richard Jasoni for serving as a true mentor to myself I don't believe that I have learned as much valuable information from one person throughout my college career as I have from you. Thank you for being extremely patient, understanding, available, and for the endless guidance throughout these past two years. I would also like to thank my family for their endless encouragement and support from the very beginning, especially Mom and Dad. A special thank you to my wife Christy for being exceptionally supportive and for the endless and diligent patience. TABLE OF CONTENTS ACKNOWLEDGEMENTS ii ABSTRACT v LIST OF TABLES vii LIST OF FIGURES viii CHAPTER I. LITERATURE REVIEW 1 Introduction 1 Onions 2 Beneficial Components 3 Hydroponics 5 Nutrient Solution 7 Objectives 12 II. MATERIALS AND METHODS 17 Growth Conditions 17 Phenotypic and Mineral Content Measurements 19 Experimental Design and Analysis 21 III. RESULTS 22 Phenotypic Variables 22 Mineral Content Variables 25 IV. DISCUSSION 36 ill V. CONCLUSIONS 40 REFERENCES 42 APPENDIX 47 IV ABSTRACT This study is a component of a project designed to develop a management strategy for growing onions in a closed growth system on a vehicular space setting. The objective of this research was to evaluate the effects of hydroponic nutrient solution and solution pH on growth and mineral content of green onions. Three onion varieties, Allium cepa L. ('Deep Purple' and 'Purplette') and A. fistulosum L. ('Kinka'), were propagated in three nutrient solutions (Peter's Hydro-Sol, Hoagland's, or half strength Hoagland's), at two pH levels (5.8 and 6.5), in a three by two factorial design applied in a randomized block with three replications. Seeds were germinated in Cropking's Oasis Horticubes™ under greenhouse conditions, and were irrigated with tap water. Once the seedlings reached the flag stage, the plants were placed into hydroponic units within the greenhouse and grown under ambient conditions. Plants were harvested 30 days after transplanting to the hydroponic units. Based on efficient plant growth, the half strength Hoagland's solution is the preferred nutrient solution evaluated in this research. However, Hydro-Sol generally produced onions with highest the mineral content. Mineral content varied with plant part,nutrient, nutrient solution, solution pH, and onion variety. Selection of an appropriate nutrient solution must consider both edible biomass production and mineral content. In the research reported here the solution that produced the greatest biomass did not produce plant material with the mineral content. Future research may lead to the development of a modified nutrient solution that optimizes both edible biomass production and mineral content. VI LIST OF TABLES 1.1 Baseline crops for advanced life support program 14 1.2 Percentage of the Daily Recommended Values (DRV) and Recommended Daily Intake (RDI) of mineral concentrations in onions 15 1.3 Hydroponic nutrient solution compositions 16 3.1 Main effects of nutrient solution, pH, and onion variety on neck diameter (ND), longest leaf midpoint diameter (LLMPD), pseudo-stem length (PL), longest leaf length (LLL), longest root length, and leaf number (LN) 30 3.2 Main effects of nutrient solution, pH, and onion variety on shoot mass (SM), bulb mass (BM), root mass (RM), total biomass (TB), edible biomass (EB), and percentage edible biomass (%EB) 31 3.3 Nutrient solution by pH interaction effects on shoot dry matter percentage, bulb Ca, and Bulb Zn 32 3.4 Main effects of nutrient solution, pH, and onion variety on dry matter percentage, ash percentage, and seleced minerals 33 3.5 Nutrient solution by variety interaction effects on bulb ash 35 VII LIST OF ABBREVIATIONS ALS Advanced Life Support AOAC Association of Analytical Chemists B Boron C Celsius Ca Calcium Ca(N03)2 Calcium Nitrate CELSS Controlled Ecological Life Support System CI Chlorine CO Colorado CT Connecticut Cu Copper CUSO4 Cupric Sulfate d Day dap Days After Planting DRV Daily Reference Value Fe Iron FeS04 Iron Sulfate GLM General Linear Model H3BO3 Boric Acid ha Hectare VIII HCI Hydrochloric Acid JSC Johnson Space Center K Potassium KNO3 Potassium Nitrate KOH Potassium Hydroxide LaCb Lanthanum Chloride Lat. Latitude LLMPD Longest Leaf Midpoint Diameter Long. Longitude MA Massachusetts Mg Magnesium MgS04 Magnesium Sulfate Mn Manganese MnCl2 Manganese Chloride Mo Molybdenum MS Mississippi N Nitrogen Na EDTA Sodium Ethylenediamineteraacetic acid Na Sodium Na2Mo04 Sodium Molybdate NaCI Sodium Chloride NASA National Aeronautics and Space Administration IX NH4*-N Ammonium Nitrate NH4H2PO Ammonium Phosphate Ni Nickel NJ New Jersey NOa" Nitrate OH Ohio P Phosphorus PVC Polyvinyl Chloride RDI Recommended Daily Intake S Sulphur s Second SAS Statistical Analysis Software TX Texas U.S. United States Zn Zinc ZnS04 Zinc Sulfate CHAPTER I LITERATURE REVIEW Introduction During extended space missions such as Mars exploration, or establishing bases on the lunar surface, humans will continue to need food, water, and air (Lawson, 2003). It is not practical or economical to re-supply basic life support elements from Earth for these long duration missions (Lawson, 2003). The National Aeronautics and Space Administration (NASA) needs to develop systems that produce food, purify the water supply, regenerate oxygen and remove undesirable components of the air (Lawson, 2003). In the late 1980s, NASA developed a regenerative life support system to develop systems for long- term space flight (Barta & Henninger, 1996). The purpose of the controlled ecological life support system (CELSS) program is to develop a large-scale integrated testing bed for plant growth with physiochemical life support subsystems that would provide oxygen and food production for astronauts (Barta & Henninger, 1996). Plant growth in controlled environments can be optimized by closely controlling environmental light intensity, photoperiod, temperature, and nutrient solution composition. Scientists and engineers specializing in food production and processing and human nutrition within the Advanced Life Support (ALS) program comprised a list of candidate crops for development as food crops (Lawson, 2003). Candidate crops need to be highly productive over a short time period, contain high nutritional value, and be waste limiting (Lawson, 2003). The candidate crop list was to be limited in order to maximize the degree to which the readiness technology level of each individual crop could be improved. Among the list of candidate crops identified for space vehicle food systems was the onion (Allium cepa L.) (Table 1.1) (Lawson, 2003). Onion is one of the least studied of the 15 ALS baseline crops. The onion is a good candidate crop because of its high productivity of edible biomass; furthermore, the carbohydrate storage bulb structure facilitates studies of source sink relationships in regulating plant response to environmental conditions. Onion has unusual morphology, growth characteristics, and biochemical composition including essential oils, secondary metabolites, and nutritive phytochemicals. The data collected would fill gaps in the knowledge of the physiology and the controlled environmental production of onion. Onions Onions are in the genus Allium, in the Alliaceae family (Maynard & Hochmuth, 1997). Onion ranks among the most important vegetable crops worldwide, with a production of 37 million tons in 1998 (Goldman & Schroek, 2001). The onion trails only tomato (Lycopersicon esculentum Mill.), potato (Solanum tuberosum L.), and lettuce (Lactuca sativa L.) in value among all vegetable crops in the U.S. The U.S. is the third largest onion producer in the world, with 3 million tons produced on approximately 64,751 ha in 1998 and a value of $830 million (Schroek & Goldman, 2001). The annual value of the U.S. onion crop is $800 million at the farm level, and roughly $3-4 billion at retail (National Onion Association, 2001) average annual onion consumption is approximately 6.2 kg of onions per person worldwide (National Onion Association, 2001). Beneficial Components Onions contain a flavonoid (antioxidant compound) called quercetin, which delays oxidative damage to cells and other bodily tissues (National Onion Association, 2001). Quercetin is the most abundant flavonoid in the human diet, and is mainly found in onions (Duthie & Dobson, 1998). Onions contain the highest amount of quercetin among commonly
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