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James E. Altland and Kay Yeon Jeong

Wright (1986) reported that in a 100% pine bark substrate fertilized with ammonium sulfate [(NH 4 ) 2 SO 4 ], ammonium (NH 4 + ) concentration decreased rapidly and nitrate (NO 3 − ) concentration increased when amended with 3 or 6 kg·m −3 DL. In the

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Allen V. Barker, Kathleen M. Ready, and Jinan Feng

Several factors inducing physiological stress in plants were investigated for their effects on foliar ammonium accumulation and ethylene evolution in tomato (Lycopersicon esculentum Mill.). Plants grown on ammonium nutrition (0.015M NH4 +) in solution culture had elevated rates of ammonium accumulation and ethylene evolution relative to plants grown on nitrate nutrition at the same molar concentration. Inhibitors of ethylene action (0.001 mM Ag+) or synthesis (0.01 mM amino-oxyacetic acid) restricted ammonium accumulation and ethylene evolution relative to rates by untreated controls receiving ammonium nutrition. The inhibitors lessened the expression of ammonium toxicity. Stress from salinity, drought, or flooding in soil increased ammonium accumulation and ethylene evolution. Plants infected with root-knot nematode had variable rates of ethylene evolution in response to variations in ammonium accumulation. Ammonium accumulation and ethylene evolution appear to be factors in the expression of physiological stress.

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Donald J. Merhaut and Rebecca L. Darnell

Ammonium and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} uptake and partitioning were monitored in `Sharpblue' southern highbush blueberry plants (Vaccinium corymbosum L. interspecific hybrid) using 10% 15N-enriched N. Shoots and roots were harvested at 0, 6, 12, 24, and 48 hours after labeling. The rate of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\mathrm{-}\mathrm{N}\) \end{document} uptake was higher than that of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\mathrm{-}\mathrm{N}\) \end{document} uptake, averaging 17.1 vs. 8.6 g N/g plant dry weight per hour during the 48-hour period for \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\mathrm{-}\) \end{document} and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\mathrm{-treated}\) \end{document} plants, respectively. At the end of the 48 hours, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\mathrm{-}\mathrm{N}\) \end{document} accumulation averaged 79 mg N/plant compared to 40 mg accumulated by the \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\mathrm{-}\mathrm{N}\mathrm{-treated}\) \end{document} plants. Similarly, the translocation rate of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\mathrm{-}\mathrm{N}\) \end{document} to shoots was higher than translocation of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\mathrm{-}\mathrm{N}\) \end{document} to shoots (7.7 vs. 1.9 g N/g shoot dry weight per hour, respectively) during the 48 hours. Shoot accumulation of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\mathrm{-}\mathrm{N}\) \end{document} averaged 40 mg N/plant at the end of 48 hours, while accumulation in shoots of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\mathrm{-}\mathrm{N}\mathrm{-treated}\) \end{document} plants averaged 10 mg N/plant. Short-term \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} uptake and translocation to shoots appears to be limited relative to \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document} uptake and translocation in southern highbush blueberry when plants are previously fertilized with NH4NO3.

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Sanliang Gu, Porter B. Lombard, and Steven F. Price

One- and two-year-old `Pinot noir' grapevines were irrigated with Hoagland's nutrient solution and shaded with 60% shade cloth to investigate the effect of shading on inflorescence necrosis (IN), tissue ammonium, and nitrate status. Shading increased IN, tissue ammonium, and nitrate concentrations of laminas, petioles, and rachis in two-year-old vines. IN was positively correlated with tissue ammonium and nitrate levels. In one-year-old vines, tissue ammonium and nitrate concentrations were increased by shading in most tissues except for nitrate in tendrils and old roots. Tissue ammonium correlated with nitrate concentration in various tissues after anthesis in one-year-old vines and in laminas, petioles, fruit, and rachis of two-year-old vines. Elevated tissue ammonium in rachis has been suggested as a possible cause of IN.

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Charles F. Mancino and Joseph Troll

Combining frequent N applications and irrigations for turfgrasses grown in sandy soils is a common occurrence on golf course putting greens. A greenhouse study was conducted to determine leaching losses of nitrate and ammonium nitrogen from `Penncross' creeping bentgrass (Agrostis palustris L.) growing on an 80 sand:20 peat soil mixture following frequent, moderately heavy irrigations and light or moderate N fertilizer applications. Nitrogen sources included calcium nitrate, ammonium nitrate, ammonium sulfate, urea, urea formaldehyde and isobutylediene diurea. Application levels were 9.76 kg N/ha per 7 days and 19.52 kg N/ha per 14 days for 10 weeks. Irrigation equivalent to 38 mm·week-1 was applied in three equal applications. Overall, 46% of the applied water leached. Total leaching losses were <0.5% of the applied N. Nitrate represented the major portion of the leached N, with ammonium losses being negligible. There were no differences between sources when applied at these levels. In a second study, a single 48.8 kg N/ha application resulted in higher leaching losses of N, but only calcium nitrate and ammonium nitrate had total losses > 2% (2.80% and 4.13%, respectively, over an n-day period). Nitrate concentrations were found to exceed 45 mg·liter-1 for ammonium nitrate.

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JiWeon Lee and Paul V. Nelson

Tomato `Marglobe' seed were sown on germination paper in enclosed plastic dishes in a growth room Ammonium was more toxic when applied as the single salt, ammonium sulfate, than when applied as part of a complete Hoagland solution. The lowest toxic ammonium levels were for the single salt 1.5 mM and for the complete solution 4.5 mM. Symptoms included reduced length of primary and particularly lateral roots, reduced numbers of root hairs, and chlorosis, distortion, and slower development of cotyledons. Tomato `Marglobe' seedlings were also grown in 288 cell plug trays in a substrate of 3 sphagnum peat moss and 1 perlite containing no N, P, or K but amended with dolomitic limestone to pH 6.0 They were fertilized every third watering with 4 mM NH4 + NO3, 0.4 mM PO4, and 1.2 mM K from 15 to 28 days after sowing and at double this concentration from 29 to 42 days. A zero leaching percentage was practiced. Ammoniacal-N comprised 25, 50, or 75% of total N. There were no effects of ammonium on root or shoot weights, height or appearance of plants through this period. Plant growth was limited throughout this period by N stress in accordance. with commercial practice. After 42 days N stress was alleviated by again doubling the nutrient solution concentration and applying it with every watering. Ammonium toxicity developed with symptoms of shorter plant height, general chlorosis of lower leaves, and necrosis of the base of lower leaves.

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Linda L. Taylor, Alexander X. Niemiera, Robert D. Wright, Gregory K. Evanylo, and Wade E. Thomason

N from ammonium sulfate [(NH 4 ) 2 SO 4 ], phosphorus from phosphoric acid (H 3 PO 4 ), potassium from potassium chloride (KCl) and micronutrients from Peters Special S.T.E.M (Peters Fertilizer Products, Allentown, PA; 15 mg·L −1 ). The fertilizer

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D. Savvas, H.C. Passam, C. Olympios, E. Nasi, E. Moustaka, N. Mantzos, and P. Barouchas

Two successive lettuce crops were grown in spring 2005 in a completely closed hydroponic system. The ratio of ammonium to total nitrogen (Nr) in the fresh nutrient solution (FNS) introduced into the closed system to compensate for plant uptake was 0, 0.1, 0.2 and 0.3 on a molar basis. In all Nr treatments, the concentrations of total N, K, Ca, Mg, P, and micronutrients in the FNS were identical, but that of SO4 2– increased as Nr increased, to compensate electrochemically for the enhanced NH4 + and decreased NO3 supply. The highest fresh and dry weights per plant were attained with the highest ammonium supply (Nr = 0.3) but, even when no NH4 + was included in the FNS as an N source, the plants were healthy without apparent nutritional disorders. The ammonium concentration in the drainage solution dropped to nearly zero in all treatments some days after the initiation of recycling, which implies a preferential uptake of NH4-N over NO3-N. The root zone pH, as indicated by the values measured in the drainage solution, decreased slightly as Nr increased, and ranged from 6.5 to 8.0 in all treatments. The leaf K, Ca, Mg, and Fe concentrations were not influenced, whereas those of P, Mn, Zn, and Cu were enhanced by the increasing NH4 + supply. The increased ammonium supply did not enhance the utilization of N in plant metabolism, although it reduced the nitrate concentration of the internal leaves in the early spring experiment. The leaf micronutrient concentrations were clearly more than critical levels even when NO3 was the sole N source for lettuce, whereas the P concentration approached the lowest critical level when Nr was 0 or 0.1. The stimulation of lettuce growth as Nr was increased to 0.3 may be a consequence of enhanced P uptake resulting from better control of pH in the root zone.

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Harvey J. Lang and George C. Elliott

Effects of medium, NH4: N03, ratio, and N fertilizer rate on the development of NH4 oxidation in soilless potting media were evaluated. In two separate experiments, NH4 oxidizing activity increased to a maximum (4 to 6 weeks of cropping) and then dropped off sharply. Ammonium oxidation activity varied significantly among types of soilless potting media. Media fertilized with 1 NH4-N: 3 N03-N had higher rates of NH4 oxidation than media fertilized with ratios of either 1:1 or 3:1. Nitrogen fertilization at 15 mm gave consistently higher oxidation rates than fertilization at 30 mm. In general, media samples that had been cropped with plants had higher nitrifying activity than unplanted samples. Ammonium oxidation rate over all observations was significantly correlated with medium pH (r = 0.50). pH values above 6.8 were necessary but not completely sufficient for relatively high rates of NH4 oxidation. Rates of oxidation were insignificant with pH values <5.6.

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Kevin R. Kosola* and Rebecca L. Darnell

Cultivated Vaccinium species (e.g. highbush blueberry, Vaccinium corymbosum, or cranberry, V. macrocarpon) commonly require acidic soil (pH 4.5 to 5.5) for optimum growth. Under these conditions, ammonium (NH4 +) is the dominant form of inorganic N. In contrast, V. arboreum, the sparkleberry can tolerate higher-pH mineral soils, where nitrate (NO3 -) is typically the predominant inorganic N form. This tolerance may be related to increased ability to acquire and utilize NO3—N. Measurements of 15NO3 - and 15NH4 + influx kinetics in excised roots of V. arboreum, V. corymbosum, and V. macrocarpon did not support this hypothesis. NO3 - influx kinetics measured from 10 micromolar to 200 micromolar NO3 - were similar among all three species. NO3 - influx was consistently lower than NH4 + influx at all concentrations for all three species.