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Nitrate accumulation in hydroponically-grown lettuce cultivars and relationship to nitrogen supply

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Title: Nitrate accumulation in hydroponically-grown lettuce cultivars and relationship to nitrogen supply
Author(s): Al-Redhaiman, Khalid Nasser
Doctoral Committee Chair(s): Swiader, John M.
Department / Program: Agriculture, AgronomyNatural Resources & Environmental Science
Discipline: Horticulture
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: Ph.D.
Genre: Dissertation
Subject(s): Agriculture, Agronomy Biology, Plant Physiology
Abstract: The research in this thesis is made up of three related experiments, each concerned with nitrate (NO$\sb{3-})$ accumulation and reduction in hydroponically-grown lettuce (Lactuca sativa L.), and its relationship to various aspects of N supply, including solution NO$\sb{3-}$ concentration, the nitrate:ammonium solution ratio, and the interaction between solution flow rate and NO$\sb{3-}$ fertilization level.In the first experiment, significant effects from both solution NO$\sb{3-}$ rate and genotype influenced tissue NO$\sb{3-}$ concentrations. A sustained concentration of 1.0 mM NO$\sb{3-}$ in solution was adequate to support lettuce growth, as there was very little response in either fresh or dry shoot weight with increasing NO$\sb{3-}$ supply up to 5.0 and 15.0 mM NO$\sb{3-}.$ In leaves, NRA showed a curvilinear response to increasing solution NO$\sb{3-}$ rates, with highest NRA at 5.0 mM solution NO$\sb{3-}.$ At low levels of solution N supply (0.5 and 1.0 mM NO$\sb{3-})$ just about all the N in the leaves of each cultivar was in reduced form, however, as the solution NO$\sb{3-}$ rate increased to 5.0 and 15.0 mM, RN/TN values decreased, and differences among cultivars for in situ NO$\sb{3-}$ assimilation became greater, with RN/TN values higher romaine cultivars than in butterhead cultivars.In the second experiment, tissue NO$\sb{3-}$ concentrations in hydroponically-grown lettuce were reduced significantly with increasing NH$\sb{4+}$:NO$\sb{3-}$ ratios in the nutrient; however, effects of mixed-N nutrition on plant growth response varied considerably, depending on cultivar. With increasing solution NH$\sb{4+}$:NO$\sb{3-}$ ratios up to 50:50 (in a 15.0 mM N solution), shoot NO$\sb{3-}$ concentrations in romaine lettuce at full head development were reduced approximately 58% (52% on a fresh weight basis), while shoot dry weights increased 46% (28% fresh weight). In butterhead cultivars, a solution NH$\sb{4+}$:NO$\sb{3-}$ ratio of 50:50 decreased shoot NO$\sb{3-}$ concentrations 58% (54% fresh weight basis), but shoot growth was also reduced 9% (15% fresh weight basis). In both leaves and roots, NRA decreased with increasing proportion of NH$\sb{4+}$ in the nutrient solution, beginning at a solution NH$\sb{4+}$:NO$\sb{3-}$ ratio of 25:75 in leaves, and 0:100 NH$\sb{4+}$:NO$\sb{3-}$ in roots.In the third experiment, significant interactions between solution flow rate and NO$\sb{3-}$ supply affected shoot NO$\sb{3-}$ concentrations. At 0.5 mM solution NO$\sb{3-},$ leaf NO$\sb{3-}$ concentrations increased with increasing solution flow rate up to 1000 ml min$\sp{-1},$ and then tended to either level off or decrease slightly. In plants supplied with 10.0 mM NO$\sb{3-},$ leaf NO$\sb{3-}$ levels were relatively unaffected by solution flow rate. Lettuce shoot weights increased with increasing solution flow rate up to 1000 ml min$\sp{-1}$ at the Low NO$\sb{3-}$ supply, and up to 25 ml min$\sp{-1}$ in plants grown with 10.0 mM NO$\sb{3-}.$ Both actual and potential NRA in leaves was unaffected by solution flow rate. Although actual NRA in leaves was significantly higher at 10.0 mM solution NO$\sb{3-}$ than at 0.5 mM NO$\sb{3-},$ there was little or no effect of NO$\sb{3-}$ supply rate on potential NRA in leaves. (Abstract shortened by UMI.)
Issue Date: 1996
Type: Text
Language: English
URI: http://hdl.handle.net/2142/19271
ISBN: 9780591087642
Rights Information: Copyright 1996 Al-Redhaiman, Khalid Nasser
Date Available in IDEALS: 2011-05-07
Identifier in Online Catalog: AAI9702438
OCLC Identifier: (UMI)AAI9702438
 

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