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Bert M. Cregg and Robert Schutzki

·s −1 and g wv is leaf conductance to water vapor in mmol H 2 O/m −2 ·s −1 . In Aug. 2006, foliar nitrogen was determined for Hydrangea paniculata , Viburnum dentatum , and Viburnum trilobum . Approximately 20 g (fresh weight) of fully

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James A. Hardin, Michael W. Smith, Paul R. Weckler, and Becky S. Cheary

concentration were investigated. Results and Discussion Foliar nitrogen. Foliar N concentration ranged from 1.8% to 3.8% of dry leaf mass across all samples ( Fig. 2 ). Nitrogen levels fell with time ( P < 0.0001) during this study following expected seasonal

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Danijela Janjanin, Marko Karoglan, Mirjana Herak Ćustić, Marijan Bubola, Mirela Osrečak, and Igor Palčić

, utilization, grapevine supply and hence alcoholic fermentation ( Bell and Robson, 1999 ; Christensen et al., 1994 ; Conradie, 1992 ; Holzapfel and Treeby, 2007 ; Schreiber et al., 2002 ). In recent years, foliar nitrogen application occurred as additional

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Frank G. Bethea Jr., Dara Park, Andrew Mount, Nick Menchyk, and Haibo Liu

, M.D. Karcher, D.E. 2011 Foliar nitrogen uptake following urea application to putting green turfgrass species Crop Sci. 51 1253 1260 Stiegler, J.C. Richardson, M.D. Karcher, D.E. Roberts, T.L. Norman, R.J. 2011 Field-based measurement of ammonia

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Kent E. Cushman, William B. Evans, David M. Ingram, Patrick D. Gerard, R. Allen Straw, Craig H. Canaday, Jim E. Wyatt, and Michael M. Kenty

activity of other compounds primarily sold for foliar fertilizer use. Foliar nitrogen products, often composed of a slow-release and proprietary mixture of urea, diurea, or methylene urea, have been reported to slightly increase lint yield of cotton

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B.R. Bondada, J.P. Syvertsen, L. Albrigo, A. Alva, and P. Petracek

Foliar applications of urea nitrogen (N) is a relatively new practice in Florida citrus production resulting from applied research and changes in citrus fertilizer management philosophy. The present study investigated the effect of leaf age and surface morphology on leaf wettability as measured by contact angles, and absorption efficiency of foliar-applied N. Young leaves (0.25 and 1 month) were more efficient than old leaves in the absorption of foliar-applied N. Contact angles of water, urea-, and triazone-N solutions were low in the young leaves. The adaxial surfaces had lower contact angles than abaxial surfaces in each leaf age group. Inefficient N absorption and large contact angles in old leaves (3 and 6 months) were related to surface wax deposition and cuticle thickness, which increased with leaf age. 15N- and 14C-labeled urea are being used to determine precisely how the cuticle and wax affect foliar N absorption in citrus leaves.

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Adriana Beatriz Sanchez-Urdaneta, Raquel Cano-Medrano, and Jorge Rodrl̀guez-Alcazar

The purpose of this research was to investigate the effect of 1% N foliar sprays (0, 2, and 4 sprays at weekly intervals) and girdling (G) on budbreak of three peach advanced selections CP95-1 °C, CP91-8, and CP91-17, and its relationship with both reduced nitrogen (RN) and polyamine contents. Foliar N was applied in July, before flower initiation was detected and girdling was performed 30 days after nitrogen sprays (DAT) The results indicate that 4N+G treatment had the highest content of (RN) with values between 232 and 1000 mg N/g of DW. CP 91-17 and CP95-1 °C selections showed higher RN content than that of CP91-8. Both 2N+G and 4 N+G showed the highest content of putrescine (Put) (908 and 1635 nmol·g-1 FW, respectively). Among peach selections CP91-8 was the one with the highest content of Put. Putrescine content went down as the flower differentiation process evolved. Four N+G treatment promoted budbreak in CP95-1 °C advancing it in 55 days as compared to the control. Budbreak began earlier in the three peach selections treated with 4N+G (11/12/98) followed by 2N+G treatment (7/001/99), and the control (4/02/99). Fruit set was 19%, 12%, and 11% for 4N+G, 2N+G, and control treatments, respectively.

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Robert Wiedenfeld, B. Scully, Marvin Miller, Jonathan Edelson, and Jiandong Wang

Purple blotch (Alternari a porri) and thrips (Thrips tabaci) can seriously reduce yields of short day onions in South Texas. The level of injury caused by these organisms is influenced by the concentration of nitrogen in leaf tissue. Lower levels of tissue nitrogen increase susceptibility to A. porri but decrease susceptibility to thrips. The purpose of this study was to evaluate the effect of tissue N levels on joint susceptibility of 4 onion cultivars to A. porri and thrips. Foliage was fertilized at 0, 4, 8, 12 or 16 lbs N/ac/wk for 6 weeks. Nitrogen concentrations in onion leaves varied over time and by leaf age, but showed very little effect due to foliar fertilization. Significant differences in thrips were noted among cultivars, but not among leaf N concentrations with cultivars. Purple blotch outbreak occurred late in the growing season and was not related to leaf N levels. Total N uptake failed to respond to foliar fertilization, therefore overall use efficiency of the foliar N applied averaged only about 10% relative to the amount taken up in the check plots.

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Anthony S. Davis, Matthew M. Aghai, Jeremiah R. Pinto, and Kent G. Apostol

Because limitations on water used by container nurseries has become commonplace, nursery growers will have to improve irrigation management. Subirrigation systems may provide an alternative to overhead irrigation systems by mitigating groundwater pollution and excessive water consumption. Seedling growth, gas exchange, leaf nitrogen (N) content, and water use were compared between overhead irrigation and subirrigation systems used to produce trembling aspen (Populus tremuloides Michx.) seedlings. After 3 months of nursery culture, subirrigation resulted in a 45% reduction in water use compared with overhead irrigation. At the end of the growing season, subirrigated seedlings had lower net photosynthetic assimilation, stomatal conductance (g S), and leaf area, indicating earlier leaf senescence. However, no significant differences were detected for biomass, leaf N content, height, root-collar diameter, or root volume. Thus, we suggest that subirrigation systems offer promising potential for aspen seedling production when compared with overhead irrigation given the added benefits of water conservation and reduced nutrient runoff. Continuing emphasis on refinement such as determining the plant water requirements based on growth and development as well as container configuration is needed so that the intended benefits of using subirrigation can be realized.

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Bruce L. Dunn and Carla Goad

Leaf nitrogen (N) and contact optical sensor sampling methods vary in the literature. Thus, the objective of this study was to determine the best sampling procedure for correlating leaf N concentration to contact optical sensor readings. To investigate this, fertilizer rates of 0, 5, 10, or 15 g of 16N–9P–12K were applied as a topdress application on ornamental cabbage (Brassica oleracea L.) ‘Tokyo Red’. Soil plant analysis development (SPAD) and atLEAF chlorophyll meters were used every week for 5 weeks starting 30 days after planting. For each pot, SPAD and atLEAF measurements were taken from a single mature leaf from the middle to upper level of the plant at the leaf tip, blade, or base of the leaf not including the midrib. Weekly leaf foliar analysis consisted of collecting either fully developed leaves from a single plant, five plants, or 10 plants per, using only the tip, blade, or base of three leaves for total leaf N concentration per treatment. A significant position affect was seen in both SPAD and atLEAF sensors. For SPAD, sensor readings taken from the tip and blade of a leaf were not significantly different from each other but were significantly different from the base of the leaf. All three positions for atLEAF were significantly different from each other. This indicates that sensor sampling location within a leaf will affect readings. A significant difference was observed among leaf sampling methods. Taking leaf samples from the tip and base had the highest leaf N concentrations and were not significantly different from each other but were significantly different from all other sampling methods, which were not significantly different from each other. Significant correlations were seen among all combinations of sensor positions and leaf N sampling methods except SPAD readings taken from the tip and leaf sampling from a single plant. Highest correlations (r = 0.7 to 0.8) were seen when SPAD readings were taken from the base of the leaf irrespective of leaf sampling method. Based on this experiment, either sensor could be used for correlating leaf N; however, growers should consistently collect sensor readings from the same location on a leaf to achieve consistent values and correlations.