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

This study investigated how spring nitrogen (N) application affects N uptake and growth performance in tall bearded (TB) iris ‘Immortality’ (Iris germanica L.). Container-grown iris plants were treated with 0, 5, 10, 15, or 20 mm N from 15NH4 15NO3 through fertigation using a modified Hoagland’s solution twice a week for 6 weeks in Spring 2013. Increasing N rate increased plant height, total plant dry weight (DW), and N content. Total N content was closely related to total plant DW. The allocation of N to different tissues followed a similar trend as the allocation of DW. In leaves, roots, and rhizomes, increasing N rate increased N uptake and decreased carbon (C) to N ratio (C/N ratio). Leaves were the major sink for N derived from fertilizer (NDFF). As N supply increased, DW accumulation in leaves increased, whereas DW accumulation in roots and rhizomes was unchanged. This indicates increasing N rate contributed more to leaf growth in spring. Nitrogen uptake efficiency (NupE) had a quadratic relationship with increasing N rate and was highest in the 10 mm N treatment, which indicates 10 mm was the optimal N rate for improving NupE in this study.

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Tongyin Li, Guihong Bi, Richard L. Harkess, Geoffrey C. Denny, Eugene K. Blythe and Xiaojie Zhao

One-year-old liners of Encore® azalea ‘Chiffon’ (Rhododendron sp.) were transplanted in Apr. 2013 into two types of one-gallon containers: black plastic container and paper biodegradable container. Azalea plants were fertilized with 250 mL of nitrogen (N) free fertilizer solution twice weekly plus N rate of 0, 5, 10, 15, or 20 mm from ammonium nitrate (NH4NO3). All plants were irrigated with the same total volume of water through one or two irrigations daily. Plant growth and N uptake in response to N fertilization, irrigation frequency, and container type were investigated. The feasibility of biodegradable paper containers was evaluated in 1-year production of Encore® azalea ‘Chiffon’. Paper biocontainers resulted in increased plant growth index (PGI), dry weights (leaf, stem, root, and total plant dry weight), leaf area, and root growth (root length and surface area) compared with plastic containers using N rates from 10 to 20 mm. Biocontainer-grown plant had more than twice of root length and surface area as plastic container–grown plant. Leaf SPAD reading increased with increasing N rate from 0 to 20 mm. One irrigation per day resulted in greater PGI, root dry weight, root length, root surface area, and root N content than two irrigations per day. Higher tissue N concentration was found in plants grown in plastic containers compared with those grown in biocontainers when fertilized with 15 or 20 mm N. However, N content was greater for plants grown in biocontainers, resulting from greater plant dry weight. The combinations of plastic container and one irrigation per day and that of 20 mm N and one irrigation per day resulted in best flower production, 21.9 and 32.2 flowers per plant, respectively. Biocontainers resulted in superior vegetative growth of azalea plant compared with plastic containers with sufficient N supply of 10, 15, and 20 mm.

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Tongyin Li, Guihong Bi, Genhua Niu, Susmitha S. Nambuthiri, Robert L. Geneve, Xueni Wang, R. Thomas Fernandez, Youping Sun and Xiaojie Zhao

The performance of biocontainers as sustainable alternatives to the traditional petroleum-based plastic containers has been researched in recent years due to increasing environmental concern generated by widespread plastic disposal from green industry. However, research has been mainly focused on using biocontainers in short-term greenhouse production of bedding plants, with limited research investigating the use of biocontainers in long-term nursery production of woody crops. This project investigated the feasibility of using biocontainers in a pot-in-pot (PIP) nursery production system. Two paper (also referred as wood pulp) biocontainers were evaluated in comparison with a plastic container in a PIP system for 2 years at four locations (Holt, MI; Lexington, KY; Crystal Springs, MS; El Paso, TX). One-year-old river birch (Betula nigra) liners were used in this study. Results showed that biocontainers stayed intact at the end of the first growing season, but were penetrated to different degrees after the second growing season depending on the vigor of root growth at a given location and pot type. Plants showed different growth rates at different locations. However, at a given location, there were no differences in plant growth index (PGI) or plant biomass among plants grown in different container types. Daily water use (DWU) was not influenced by container type. Results suggest that both biocontainers tested have the potential to be alternatives to plastic containers for short-term (1 year) birch production in the PIP system. However, they may not be suitable for long-term (more than 1 year) PIP production due to root penetration at the end of the second growing season.