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Vincent A. Fritz and Carl J. Rosen

Recent adoption of a raised bed production system for improved drainage on muck soils prompted experimentation to improve N use efficiency. The established methods of N fertilization was to simply broadcast 908 kg·ha–1 of 10–26–27 prior to planting in single rows. The raised bed production system results in a concentrated rooting zone directly underneath the raised bed. A system that places the N fertilizer within the root zone of influence at a peak time of crop utilization would increase N use efficiency, reduce fertilizer costs, and promote appropriate environmental stewardship. The use of a spoke wheel injector to sidedress N fertilizer effectively reduced total fertilizer costs by half, while producing onion yields equal to or greater than the established broadcast method under the raised bed production system. In addition, the use of the spoke wheel injector was not intrusive to the integrity of the raised bed, which allowed realization of benefits from using raised beds for the entire growing season.

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S.B. Phillips, J.G. Warren, and G.L. Mullins

Previous work suggests that `Beauregard' sweetpotato [Ipomoea batatas (L.) Lam.] has a much lower N requirement than other common cultivars. Over the past 10 years, `Beauregard' has become the premier sweetpotato cultivar grown in Virginia; however, N fertilizer recommendations have not been reassessed to consider the potentially lower N requirement of `Beauregard'. The objectives of this study were to evaluate the effects of N rate and application timing on root yield, quality, and N use efficiency for `Beauregard' sweetpotato production in Virginia. A field study was conducted each year from 2000 to 2002 at the Eastern Shore Agricultural Research and Extension Center, Painter, Va. Nitrogen fertilizer was applied at rates of 28, 56, and 84 kg·ha-1 either before transplanting, 2 to 3 weeks after transplanting (WAT), or 4 to 5 WAT. A check treatment that received no N fertilizer was also included. Optimum N rates varied annually; under normal precipitation, root yield was greatest at the 28-kg·ha-1 rate, while 56 kg·ha-1 was required for maximum yield in wet conditions. Of note is that this range of rates is considerably lower than the current N recommendation for Virginia sweetpotato production (56 to 84 kg·ha-1). Delaying N application until 2 to 3 WAT further increased marketable root yield compared with applying N before transplanting or 4 to 5 WAT. Crude protein and N uptake increased with increasing N rate up to 84 kg·ha-1; however, N use efficiency was highest (67%) when 28 kg·ha-1 was applied 2 to 3 WAT.

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Dan Drost, Rich Koenig, and Terry Tindall

Nitrogen (N) losses can be substantial in furrow-irrigated onions (Allium cepa L.). Polymer-coated urea (PU) may reduce N losses and result in an increase in productivity. In this study, we investigated the effects of different rates and blends of urea and PU on onion yield and N use for two cropping seasons. Nitrogen was applied at 112, 168, and 224 kg·ha-1 as PU or urea. In addition, three PU/urea blends equal to 224 kg·ha-1 of N were compared. Plant growth and N concentration, soil nitrate concentrations, and bulb yield were evaluated each year. Onion yield decreased by 95 Mg·ha-1 for each 25% increase in the proportion of urea in the fertilizer blends. Reducing the N rates from 224 to 112 kg·ha-1 had minimal effect on bulb yield when all the fertilizer was supplied by urea. A reduction of N applied from 224 to 168 kg·ha-1 had little effect on yield, although a further reduction to 112 kg·ha-1 did significantly reduce bulb yield when the entire N was supplied from PU. Nitrogen source and rate had no effect on bulb maturity and only minor effects on leaf area and storage potential. Soil sampling indicated that more N was retained in PU-treated onion beds than in urea-treated beds, which improved nitrogen use efficiency. In addition, N use efficiency improved when there was more PU in the blend and when PU was compared with urea at the same rate. We conclude that the use of PU can dramatically improve N use efficiency and productivity in direct-seeded onions.

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Sameh Sassi-Aydi, Samir Aydi, and Chedly Abdelly

The nitrogen (N) requirement of legumes can be met by inorganic N assimilation and symbiotic N2 fixation. Both N assimilation routes have diverse influences on drought tolerance because of the differences in the use of energy and the reduction in power characteristics of those pathways. We investigated N nutrition under osmotic stress and likely criteria conferring tolerance to osmotic stress in common bean. Osmotic stress tolerance in a drought-sensitive common bean cultivar (Coco blanc) was compared with beans relying on N nutrition, N2 fixation, or fertilization with urea. Osmotic stress was applied by means of 25 (mild stress), 50 (moderate stress), or 75 (severe stress) mm mannitol for 15 days. At the end of the stress period, relative water content, total N contents, total soluble sugars, total chlorophyll, total protein, and potassium were assayed. Urea-fed plants grew better and had better tolerance to osmotic stress. This was attributed to maintaining higher N use efficiency, better leaf hydration, and adequate osmoregulation.

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Dharmalingam S. Pitchay, Jonathan M. Frantz, James C. Locke, Charles R. Krause, and George C. J. Fernandez

not uncommon under intensive greenhouse production systems. The N use efficiency is critical in determining N supply rate, which ultimately can reduce input costs while protecting the environment from N deposition ( Good et al., 2004 ). In greenhouse

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M. Lenny Wells

– Y n )|/( Y n – 1 + Y n )], where n is number of years and Y is tree yield for the corresponding year ( Conner and Worley, 2000 ; Pearce and Dobersek-Urbanc, 1967 ). Agronomic N use efficiency ( AE N ), defined as pecan yield per unit N applied

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Silvia Jiménez Becker, Maria Teresa Lao, and Mari Luz Segura

models that allow the prediction of nitrogen nutritional needs of Dieffenbachia amoena to increase the N use efficiency in a recycled system. To achieve these aims, N uptake has been correlated to climate parameters such as temperature (T), vapor

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Carolyn F. Scagel, Guihong Bi, Leslie H. Fuchigami, and Richard P. Regan

assessed using ANOVA in a full factorial design with cultivar, N05 rate, and W05 treatment as main effects. The influence of irrigation frequency on relationships between N05 rate and N uptake (N uptake efficiency) and N uptake and growth (N use efficiency

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M. Lenny Wells

yield for the corresponding year ( Pearce and Dobersek-Urbanc, 1967 ). Agronomic N use efficiency, defined as pecan yield per unit of N applied, was determined by dividing yield (kg·ha −1 ) by the total amount of fertilizer N applied (kg·ha −1 ) per

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Desire Djidonou, Xin Zhao, Eric H. Simonne, Karen E. Koch, and John E. Erickson

grown with drip irrigation in Florida sandy soils; and 2) characterize the influence of grafting with vigorous rootstocks on irrigation water and N use efficiency under these conditions. Materials and Methods Grafting and transplant production. The field