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Xiaojie Zhao, Guihong Bi, Richard L. Harkess, and Eugene K. Blythe

The form of nitrogen (N) in fertilizer can influence plant growth, nutrient uptake, and physiological processes in the plant. However, few studies have been conducted on the effects of N form on tall bearded (TB) iris (Iris germanica L.). In this study, five NH4:NO3 ratios (0:100, 25:75, 50:50, 75:25, and 100:0) were applied to investigate the response of TB iris to different N form ratios. NH4:NO3 ratios in fertilizer did not affect the leaf, root, and rhizome dry weight, or total plant dry weight. Plant height and SPAD reading were affected by NH4:NO3 ratios in some months, but not over the whole growing season. Neither spring nor fall flowering was influenced by NH4:NO3 ratios. Across the whole growing season, leachate pH was increased by higher NH4:NO3 ratios. At the end of the growing season, concentrations of phosphorous (P), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu) in leaf; calcium (Ca), magnesium (Mg), Mn, boron (B) in root; and N, P, Mg, Fe, Mn, and Zn in rhizome tissues were affected by NH4:NO3 ratios. Greater NH4:NO3 ratios increased the uptake of Fe, Mn, and Zn. The net uptake of N was unaffected by NH4:NO3 ratios, which indicates TB iris may not have a preference for either ammonium or nitrate N.

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

One deciduous cultivar of Rhododendron L., Gibraltar (AZ), and two evergreen cultivars, P.J.M. Compact (PJM) and English Roseum (ER), were grown in containers for 1 year to determine the effects of irrigation frequency during container production on plant performance the next spring when the plants were transplanted into the landscape. While in the containers, each cultivar was irrigated once or twice daily, using the same amount of water per day, and fertilized with complete nutrient solutions containing 0, 35, 70, or 140 mg·L−1 nitrogen (N). Three months after transplanting into the landscape, nutrient uptake, growth, and flowering were evaluated. In general, the effects of irrigation frequency in containers on performance in the landscape differed between the deciduous cultivar and the evergreen cultivars. In AZ, less frequent irrigation in containers had a pre-conditioning effect that resulted in greater vegetative growth in the landscape but less reproductive growth. In contrast, less frequent irrigation reduced vegetative growth of evergreen cultivars in the landscape and improved flowering. Different growth responses to irrigation frequency between deciduous and evergreen cultivars appeared to be related to differences in timing of nutrient uptake and mobilization. In the deciduous cultivar, less frequent irrigation increased nutrient reserves and improved the ability of the plants to absorb and use nutrients after transplanting, but in the evergreen cultivars, it generally decreased nutrient uptake after transplanting. Less frequent irrigation also altered plant attributes that are important to consumers, including developing a sparser canopy in ER and a fuller canopy in PJM, and producing more but smaller inflorescences in both cultivars. Landscape performance was related to plant nutrition in containers; however, irrigation frequency in containers disrupted relationships between nutrition and performance in all three cultivars. Our results indicate that irrigation frequency during container production of Rhododendron results in a tradeoff between vegetative and reproductive growth the next spring when the plants are in the landscape.

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

The influence of fall sprays with urea on the uptake of nutrients other than nitrogen (N) was assessed using 1-year-old container-grown Rhododendron L. (Rhododendron ‘H-1 P.J.M’) and azalea (Rhododendron ‘Cannon's Double’) grown with different rates of N. Plants were grown with a complete fertilizer containing different N rates from May to Sept. 2004 sprayed or not with urea in the fall of 2004 and grown with a complete fertilizer containing different N rates in the spring of 2005. Urea sprays altered uptake of nutrients other than just N although fertilizer application with other nutrients ceased before plants were sprayed with urea. Across a wide range of plant sizes and N status, urea sprays increased net phosphorus (P), copper (Cu), and manganese (Mn) uptake and decreased net potassium (K) and magnesium (Mg) uptake during the year of urea application. Spraying plants with urea altered nutrient demand and storage in different plant structures during the winter. For azalea, urea sprays increased P demand by roots, Mn demand by 2004 stems, and Cu demand by stems. Urea also decreased storage of K in roots and 2004 stems of azalea and Mg in roots. For rhododendron, urea sprays increased P demand by 2003 stems and 2004 leaves and Mn demand by 2004 leaves. Urea sprays also decreased storage of K and Mg in 2004 leaves of rhododendron. For both cultivars, urea sprays increased mobilization of iron (Fe) from storage and demand for Fe in stems. Spraying Rhododendron with urea in the fall altered uptake and demand for certain nutrients during the following spring. Urea sprays in the fall of 2004 increased uptake and possibly demand for P, K, and sulfur during the spring of 2005 for both cultivars, the uptake of calcium by rhododendron, and the uptake of Mg and Mn by azalea. Our results indicate that when growers spray plants with urea in the fall, spring fertilizer practices may need to be modified to account for increased uptake or demand of certain nutrients.

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Xiaojie Zhao, Guihong Bi, Richard L. Harkess, Jac J. Varco, Tongyin Li, and Eugene K. Blythe

Tall bearded (TB) iris (Iris germanica L.) has great potential as a specialty cut flower due to its fragrance and showy, multicolor display; however, limited research has been reported on optimal nitrogen (N) nutrient management for TB iris. The objectives of this study were to investigate the effects of N fertilizer rate on plant growth and flowering of ‘Immortality’ iris and determine the influence of both stored N and spring-applied N fertilizer on spring growth and flowering. On 14 Mar. 2012, rhizomes of ‘Immortality’ iris were potted in a commercial substrate with no starter fertilizer. Plants were fertigated with 0, 5, 10, 15, or 20 mm N from NH4NO3 twice per week from 28 Mar. to 28 Sept. 2012. In 2013, half of the plants from each of the 2012 N rate were supplied with either 0 or 10 mm N from 15NH4 15NO3 twice per week from 25 Mar. to 7 May 2013. Growth and flowering data including plant height, leaf SPAD, number of fans and inflorescence stems, and length of inflorescence stem were collected during the growing season. Plants were harvested in Dec. 2012 and May 2013 to measure dry weight and N concentration in leaves, roots, and rhizomes. Results showed higher 2012 N rates increased plant height, leaf SPAD reading, and number of inflorescence stems at first and second blooming in 2012. Greater 2012 N rates also increased plant dry weight and N content in all structures, and N concentration in roots and rhizomes. Rhizomes (58.8% to 66.3% of total N) were the dominant sink for N in Dec. 2012. Higher 2012 N rates increased plant height, number of fans, and the number of inflorescence stems at spring bloom in 2013. In May 2013, N in leaf tissue constituted the majority (51% to 64.3%) of the total plant N. Higher 2012 N rates increased total dry weight, N concentration, and N content in all 2013 15N rates; however, leaf dry weight in all plants was improved by 2013 15N rate. Percentage of tissue N derived from 2013 15N (NDFF) decreased with increasing 2012 N rate. New spring leaves were the dominant sink (56.8% to 72.2%) for 2013 applied 15N. In summary, ‘Immortality’ iris is capable of a second blooming in a growing season, this second blooming dependent on N fertilization rate in current year. A relatively high N rate is recommended to produce a second bloom.

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Pinghai Ding, Shufu Dong, Lailiang Cheng, Guihong Bi, and Leslie H. Fuchigami

Near-infrared (NIR) reflectance spectroscopy was used to determine the chemical composition of fruit and nut trees. Potted almond and bench-grafted Fuji/M26 trees were fertigated during the growing season with different N levels by modifying the Hoagland to create different levels of nitrogen and carbohydrates in plant tissues during dormancy. Dried, ground, and sieved shoot, shank, and root samples were uniformly packed into NIR cells and scanned with a Foss NIRSystem 6500 monochromator from 400 to 2500 nm. Statistical and multiple linear regression methods were used to derive a standard error of performance and the correlation between NIR reading and standard chemical composition analysis (anthrone, Kjedahl and Ninhydrin methods for carbohydrate, total N, and amino acid analysis, respectively) were determined. The multiple determination coefficients (R 2) of apple and almond tissues were 0.9949 and 0.9842 for total nitrogen, 0.9971 and 0.9802 for amino acid, and 0.8889 and 0.8687 for nonstructural carbohydrate, respectively.

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

The influence of nitrogen (N) fertilizer application on plant allocation, uptake, and demand for other essential nutrients was evaluated from May 2005 to Feb. 2006 in evergreen Rhododendron ‘P.J.M. Compact’ (PJM) and ‘English Roseum’ (ER) and deciduous Rhododendron ‘Gibraltar’ (AZ) grown in containers filled with soilless substrate. Net nutrient uptake and losses were calculated using piecewise regression and uptake efficiency, root absorption capacity, aboveground demand, nutrient use efficiency, and uptake ratios between N and other nutrients (N ratios) were calculated using net uptake between harvest dates. Nitrogen application increased uptake rate of all nutrients, enhanced late-season uptake of many nutrients, and increased the rate of nutrient loss during the winter. Nutrient uptake often occurred as late as November in plants grown with N but was usually undetectable after September in plants grown without additional N fertilizer. Nutrient losses during the winter were not always associated with biomass loss and were related to differences in preferential nutrient allocation to different structures and the plant's ability to export nutrients before biomass loss. Plants with a greater potential for rapid growth were more capable of later-season nutrient uptake than plants with slower growth rates. Nitrogen availability altered N ratios indicating that when adding N to container-grown Rhododendron, fertilizers with higher ratios of N/phosphorus (PJM, AZ), N/calcium (PJM, ER), N/boron (PJM AZ), N/copper (PJM, ER), and N/iron (PJM, ER) and lower ratios of N/potassium (PJM, ER, AZ), N/sodium (PJM, ER, AZ), N/calcium (AZ), N/boron (ER), N/manganese (AZ), and N/zinc (ER) may be needed to optimize growth and minimize nutrient inputs. Increasing N availability altered uptake efficiency, root absorption capacity, aboveground demand, and nutrient use efficiency for several nutrients, indicating that changes in N management practices need to consider how altering N application rates may influence the plant's ability to take up and use other nutrients. This information can be used to develop fertilizer formulations to minimize excess application of nutrients and to evaluate the potential effects of altering N management practices on use of production resources. Our results indicate that nutrient management strategies for perennial crops such as Rhododendron need to take into consideration not only the nutrient demand for current growth, but also how to optimize nutrient availability for uptake that contributes to future growth potential and end-product quality.

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

Growth, nitrogen (N) uptake, and N storage were assessed in transplanted 1-year-old rhododendron liners. Two evergreen cultivars, Rhododendron ‘P. J. Mezitt Compact’ (PJM) and R. ‘English Roseum’ (ER), and one deciduous cultivar, R. ‘Gibraltar’ (AZ), were transplanted into 1-gal. pots and given liquid fertilizer with (+N) or without (–N) N. Increased N availability increased growth after July (ER, PJM) or August (AZ), and resulted in three to five times more total biomass. Biomass continued to increase after stem elongation and leaf production ceased. Nitrogen uptake was correlated with growth of all plant structures on AZ, whereas N uptake was only correlated with stem and leaf growth on evergreen cultivars. The rate of N uptake was highest before July for AZ (1.9 mg·d−1) and in August and September for the evergreen cultivars (≈5 mg·d−1). Thirteen percent to 16% of total N uptake from between May and February occurred after N fertilization ceased at the beginning of September. Plants contained the most N in October (AZ), November (PJM), or December (ER). Biomass loss after November accounted for a loss of 14% to 48% of the maximum total plant N content. Nitrogen demand by roots and stems increased from May to February in all cultivars. The role of new and old leaves in N storage on evergreen cultivars varied with cultivar and time. Differences in N storage between the evergreen cultivars occurred primarily in their roots and leaves. Over the winter, PJM stored more N in its roots, whereas ER stored more N in its leaves. Changes in N concentrations and contents in different plant structures after November indicate that, during early winter, N stored in other structures moves to roots and old stems of PJM, old stems of ER, and roots and new and old stems of AZ. These results suggest that fertilizer application strategies for transplanted liners of these cultivars should include low N availability after transplanting followed by high N availability in mid to late summer. This type of strategy will not only improve N uptake efficiency from fertilizer, but also will minimize N loss from the containers. The results also demonstrated that N uptake in the autumn may play an important role in supplementing plant N reserves required for growth during the next season as well as for balancing N losses incited by leaf abscission, root turnover, and maintenance functions that occur over winter.

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

The influence of irrigation frequency (same amount of water per day given at different times) on nutrient uptake of container-grown evergreen Rhododendron ‘P.J.M. Compact’ (PJM) and ‘English Roseum’ (ER) and deciduous Rhododendron ‘Gibraltar’ (AZ) grown with different rates of nitrogen (N) fertilizer was evaluated. Increased N application rate increased nutrient uptake and plant dry biomass. Irrigation frequency did not significantly influence total plant dry biomass; however, more frequent irrigation decreased net uptake of several nutrients including phosphorus (P), boron (B), and manganese (Mn) uptake in all cultivars; potassium (K), copper (Cu), and zinc (Zn) uptake in AZ and ER; sulfur (S) uptake in ER and PJM; and iron (Fe) uptake in AZ. Additionally, more frequent irrigation of evergreen cultivars increased calcium (Ca) uptake. Covariate analyses were used to compare nutrient uptake among cultivars and irrigation treatments after accounting for the variability in nutrient uptake attributable to differences in biomass and N uptake. For most nutrients, the influence of irrigation frequency on uptake was partially attributable to differences in biomass and N uptake. After accounting for the variability in nutrient uptake associated with biomass or N uptake, increased irrigation frequency decreased P, S, B, Cu, and Mn uptake only in ER and increased Ca uptake in the two evergreen cultivars. Differences in nutrient uptake among cultivars in response to irrigation treatments were related to water and N availability during production and their combined influence on water stress, nutrient uptake, and biomass partitioning. Estimates of nutrient demand and uptake efficiency using nutrient concentrations and ratios are discussed in relation to nutrient management differences for different cultivars and irrigation treatments.

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Tongyin Li, Guihong Bi, Richard L. Harkess, Geoffrey C. Denny, and Carolyn Scagel

Plant growth, water use, photosynthetic performance, and nitrogen (N) uptake of ‘Merritt’s Supreme’ hydrangea (Hydrangea macrophylla) were investigated. Plants were fertilized with one of five N rates (0, 5, 10, 15, or 20 mm from NH4NO3), irrigated once or twice per day with the same total daily amount of water, and grown in either a paper biodegradable container or a traditional plastic container. Greater N rate generally increased plant growth index (PGI) in both plastic and biocontainers. Leaf and total plant dry weight (DW) increased with increasing N rate from 0 to 20 mm and stem and root DW were greatest when fertilized with 15 mm and 20 mm N. Plants fertilized with 20 mm N had the greatest leaf area and chlorophyll content in terms of SPAD reading. Container type had no influence on DW accumulation or leaf area. N concentrations (%) in leaves, roots, and the entire plant increased with increasing N rate. N concentrations in roots and in the entire plant were lower in biocontainers compared with plastic containers. Greater N rate generally increased daily water use (DWU), and biocontainers had greater DWU than plastic containers. The 20 mm N rate resulted in the highest net photosynthetic rate measured on 11 Sept. and 22 Sept. (65 and 76 days after treatment). Net photosynthetic rate (measured on 8 Oct.) and stomatal conductance (g S) (measured on 27 Aug., 22 Sept., and 8 Oct.) were lower in biocontainers compared with plastic containers. Two irrigations per day resulted in higher substrate moisture at 5-cm depth than one irrigation per day, and slightly increased PGI on 19 Aug. However, irrigation frequency did not affect photosynthetic rate, g S, or N uptake of hydrangea plants except in stems. Considering the increased water use of hydrangea plants when grown in the paper biocontainer and lower plant photosynthesis and N uptake, the tested paper biocontainer may not serve as a satisfactory sustainable alternative to traditional plastic containers.

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

The influence of irrigation frequency (same amount of water per day given at different times) and nitrogen (N) fertilizer rate on water stress [stomatal conductance (g S)], N uptake, and growth (biomass) of container-grown evergreen Rhododendron ‘P.J.M. Compact’ and ‘English Roseum’ and deciduous Rhododendron ‘Gibraltar’ was evaluated. Both N deficiency and high N rate increased water stress. Water stress was greatest in plants fertilized with the highest N rate and g S of plants grown with the higher N rates changed more in response to water deficits resulting from irrigation treatments and seasonal climatic changes. Watering plants more frequently decreased water stress of plants fertilized with higher N rates and altering irrigation frequency had little impact on alleviating water stress of N-deficient plants. Increasing irrigation frequency decreased N uptake efficiency (N uptake per gram N applied), increased N use efficiency (growth per gram N uptake) and altered biomass allocation with little influence on total plant biomass. Response of biomass allocation to N rates was similar among cultivars and response of biomass allocation to irrigation frequency varied among cultivars. Altering irrigation frequency changed either the availability of N in the growing substrate or the ability of roots to absorb N. Our results indicate that transitory increases in plant water stress can alter N uptake, N use, and plant form without detectable changes in total plant biomass.