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Bernard A. L. Nicoulaud and Arnold J. Bloom

We examined root ammonium absorption by tomato seedlings (Lycopersicon esculentum Mill. `T-5') after first exposure of the roots to ammonium. Some plants received a nutrient medium containing nitrate as the sole N source. In a second treatment, the leaves were sprayed daily with a urea solution, while the roots were in N-free medium. The last two treatments were initially grown in medium that contained ammonium nitrate, but then either were shifted to a N-free medium for 10 days or had their roots excised and were rerooted in N-free medium for 21 days. Root ammonium absorption remained constant after first exposure to ammonium for the plants exposed to nitrate alone, whereas root ammonium absorption declined with time for the other three treatments. These results indicate that for tomato a) ammonium in the rhizosphere does not induce root ammonium absorption and b) some product of ammonium metabolism represses root ammonium absorption.

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Dustin P. Meador and Paul R. Fisher

% conversion of free Cl to chloramines after 0.2 s at pH 7 or 147 s at pH 4 ( White, 1992 ). In horticulture irrigation, water-soluble fertilizer containing ammonium, nitrate, and/or urea N is often supplied in irrigation between 100 and 200 mg·L −1 total N

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Yong-Ping Gao, Hino Motosugi and Akira Sugiura

Abbreviations: A, ammonium; AT, nitrate plus ammonium; T, nitrate. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to

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Christopher S. Imler, Camila I. Arzola and Gerardo H. Nunez

R version 3.5.1 ( R Core Team, 2017 ). Rhizosphere pH data were analyzed using a linear mixed model (see section Rhizosphere pH measurement). Expt. 2: Ammonium uptake effect. After acclimation, plants were transplanted to a split-root hydroponic

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Lijuan Xie, Deying Li, Wenjuan Fang and Kirk Howatt

bentgrass with NIS than with methylated seed oil. Fertilizer salts, such as UAN and ammonium sulfate, often are added to spray solutions with NIS to help increase the activity of foliar-applied herbicides ( Pearson et al., 2008 ). The exact mechanism of

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Elvia Hernández-Gómez, Luis A. Valdez-Aguilar, Ana M. Castillo-González, María T. Colinas-León, Donita L. Cartmill, Andrew D. Cartmill and R. Hugo Lira-Saldívar

( Gerendás et al., 1997 ). Ammonium toxicity has been attributed to reduced proton extrusion at low external pH, acidification of the cytosol, and growing media ( Walch-Liu et al., 2000 ), reduced content of sugars in the roots, and induced deficiency of

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Connie N. Johnson, Paul R. Fisher, Jinsheng Huang, Richard P. Vetanovetz and William R. Argo

the fertilizer; 2) calcium, magnesium, sodium, and potassium are base-forming elements; and 3) ammonium nitrogen is completely nitrified; nitrate nitrogen combined with bases such as sodium or calcium will have a net basic effect ( Pierre, 1933

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Oscar L. Vargas and David R. Bryla

, 1986 ) but typically needs regular applications of N fertilizer to maximize growth and fruit production ( Bañados et al., 2012 ; Hanson and Hancock, 1996 ). The plants acquire primarily the ammonium form of N ( Claussen and Lenz, 1999 ) and, therefore

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Allen V. Barker

Studies were made of ethylene evolution by `Heinz 1350' tomato fruits from plants that had received nitrogen nutrition from ammonium or nitrate salts in soil-based media. Fruits of plants receiving ammonium nutrition had higher ammonium concentrations, higher occurrences of blossom-end rot, and higher rates of ethylene evolution than fruits from nitrate-grown plants. Fruits showing blossom-end rot had higher ammonium concentrations and higher rates of ethylene evolution than normal fruits only if the plants received ammonium nutrition. Ethylene evolution increased as fruits from nitrate-grown plants ripened but without a concurrent increase in ammonium concentrations in the fruits. Ammonium accumulation in fruits apparently induces blossom-end rot and enhances ethylene evolution, but ammonium accumulation does not appear to be a naturally occurring phenomenon in ripening fruits or in fruits that have blossom-end rot arising from other casual factors.

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Allen V. Barker and Kenneth A. Corey

Inhibitors of ethylene synthesis and action were used to alleviate ammonium toxicity in tomato (Lycopersicon esculentum Mill. `Heinz 1350') grown on ammonium-based nutrient solutions. Aminooxyacetic acid and Ag+ were effective in reducing ammonium toxicity, whereas Co+2 and salicylic acid were not. A hypothesis was developed to integrate ammonium accumulation and ethylene biosynthesis into a mechanism for expression of plant injury from environmental stresses.