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Hadi Susilo, Ying-Chun Peng, Shui-Cheng Lee, Yu-Chun Chen, and Yao-Chien Alex Chang

when studying use of N fertilizer using traditional methods. Nitrogen-14 and nitrogen-15 ( 15 N) are the two stable isotopes of N with atmospheric natural abundances of 99.6337% and 0.3663%, respectively. The latter is an important tracer element in

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Hadi Susilo, Ying-Chun Peng, and Yao-Chien Alex Chang

Phalaenopsis orchid is a slow-growing crop that responds slowly to fertilization. In this study, we used 15N-labeled Johnson’s solution to investigate the accumulation and use of fertilizer nitrogen (N) during the vegetative and reproductive growth stages of Phalaenopsis Sogo Yukidian ‘V3’ with a focus on the nitrogen source for inflorescence development. Labeling of fertilizer applied to mature plants 6 weeks before forcing or at 6 weeks into forcing showed that in the inflorescence, the ratio of N derived from fertilizer applied 6 weeks before forcing to the N derived from fertilizer applied 6 weeks into forcing was 31% to 69%, which shows the importance of newly absorbed fertilizer for supplying the N needed for inflorescence development. The fate of fertilizer N applied during the small, medium, or large plant stage of vegetative Phalaenopsis Sogo Yukidian ‘V3’ was traced separately with 15N-labeling. The capacity of the plant to accumulate N after fertilizer application was different during the various stages of vegetative growth, with large plants having more N storage capacity as a result of their greater biomass. However, the percentage of the accumulated N that was later allocated to the inflorescence was similar regardless of the stage of fertilizer application: of the fertilizer N absorbed during various stages of the vegetative period, 6% to 8% was allocated to the inflorescence at the visible bud stage. This result highlights the mobility of N stored early on within the plant. By calculation, of the total N in the inflorescence at the visible bud stage, the N absorbed during the small, medium, and large plant stages contributed 7%, 11%, and 25%, respectively, whereas N applied after spiking made up the other 57%. This result indicates that both N stored during the vegetative stage and N applied during the reproductive stage contribute significantly to inflorescence development.

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Hadi Susilo and Yao-Chien Alex Chang

Plants of Phalaenopsis orchid are known for their great resilience and ability to flower under less than ideal conditions, including long periods without fertilization. Significant nutrient storage is thought to account for this characteristic; however, the use of stored nutrients in Phalaenopsis has not been fully studied. We used 15N-labeled Johnson’s solution to trace the use of stored nitrogen (N) and recently absorbed fertilizer N in Phalaenopsis given various fertilizer levels during forcing. By separately labeling fertilizer N applied to Phalaenopsis Sogo Yukidian ‘V3’ plants 6 weeks before and 6 weeks into forcing, we found in the inflorescence that the ratio of N derived from fertilizer applied 6 weeks before forcing to the N derived from fertilizer applied 6 weeks into forcing was 43% to 57%. With 90% reduction in fertilizer concentration during the reproductive stage, the ratio increased to 89% to 11%, indicating that stored N becomes a significant N source for inflorescence development when fertility becomes limited. Reducing fertilizer level during the reproductive stage from full-strength Johnson’s solution down to zero decreased the dry weight of newly grown leaves, reduced the number of flowers from 10.8 to 8.9, and slightly increased the time required between initiation of forcing and anthesis. However, the overall effect of reduced fertilization on the growth and flowering of Phalaenopsis Sogo Yukidian ‘V3’ plants in this study was slight, because under little or no fertilization, more stored N was mobilized and this was sufficient to meet most of the N demand for inflorescence development.

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Richard C. Rosecrance, Steve A. Weinbaum, and Patrick H. Brown

The interrelationships between crop load, root growth, and nutrient uptake in mature, pistachio trees were examined in this study. Nutrient uptake was determined during the spring, summer, and fall using labeled nitrogen (15N) and boron (10B) and by differences in whole-tree accumulation between tree harvests for other nutrients (e.g., P, K, Ca, Zn). Nitrogen and boron uptake were double in fruiting compared with nonfruiting trees in the spring. Most of the labeled N was found in the developing fruits and leaves. Total labeled N recovery during the spring flush period, however, was low, indicating that much of the N in the fruit came from N reserves from within the tree rather than uptake from the soil. In contrast, significant amounts of N were taken up from the soil during the summer uptake period. Thus, our data support the hypothesis that sink demand (i.e., fruit development) conditions N uptake in pistachio. The relationship between root growth and N uptake was also examined in this study. Root observation chambers were constructed, and root growth determined by tracing roots growing up against the glass windows. Root length, root growth rate, relative root growth rate, and total tree fine root weight were all greater in nonfruiting compared to fruiting trees during the fruit development period (late May to mid-July). Surprisingly, fruiting trees had less root growth, but greater N uptake than nonfruiting trees during this period. This evidence suggests that N uptake is decoupled from root growth in mature pistachio trees.

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Samuel Y.C. Essah, Jorge A. Delgado, Merlin Dillon, and Richard Sparks

these effects. Units Literature cited Clark A. 2007 Managing cover crops profitably. 3rd ed. Sustainable Agriculture Network, Beltsville, MD Collins, H.P. Delgado, J.A. Alva, A.K. Follett, R.F. 2007 Use of nitrogen-15 isotopic techniques to estimate

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Yang Fang, Jeffrey Williamson, Rebecca Darnell, Yuncong Li, and Guodong Liu

and carbohydrates Tree Physiol. 22 1297 1303 Danso, S.K. Bole, J.B. Zapata, F. 1983 A guide to the use of Nitrogen-15 and Radioisotopes in studies of plant nutrition, calculations and interpretation of data. IAEATECDOC-288. IAEA, Vienna. 10 May 2017

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Ariana P. Torres and Roberto G. Lopez

the following (mg·L −1 ): 100 nitrogen, 15 phosphorus, 84 potassium, 34 calcium, 14 magnesium, 0.5 iron, 0.25 manganese and zinc, 0.13 boron and copper, and 0.05 molybdenum (Peters Excel© Cal-Mag© 15N-2.2P-12.5K; The Scotts Co., Marysville, OH

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Joan R. Davenport, Robert G. Stevens, Kelly M. Whitley, and Tanya Winkler

Kessavalou, A. Doran, J.W. Powers, W.L. Qian, J.H. Kettler, T.A. 1996 Bromide and nitrogen-15 tracers of nitrate leaching under irrigated corn in central Nebraska J. Environ. Qual. 25 1008 1014 Kohne, J.M. Gerke, H.H. 2005 Spatial and temporal dynamics of

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Ursula K. Schuch, Jack J. Kelly, and Trent Teegerstrom

. Plants were fertigated once every 12 d at a rate of 510 mg·L −1 nitrogen (15N–12.9P–12.5K plus micronutrients; Scotts Miracle-Gro Products, Marysville, OH). Annuals were maintained for 33 d and perennials for 118 d. Senescent flower stalks of angelita

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Joji Muramoto, Richard F. Smith, Carol Shennan, Karen M. Klonsky, James Leap, Miriam Silva Ruiz, and Stephen R. Gliessman

-based agroecosystems? A review Nutr. Cycl. Agroecosyst. 72 101 120 Crozier, C.R. King, L.D. Volk, R.J. 1998 Tracing nitrogen movement in corn production systems in the North Carolina Piedmont: A nitrogen-15 study Agron. J. 90 171 177 Cutcliffe, J.A. 1971 Effects of