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Guillermo Cardoso, Roger Kjelgren, Teresa Cerny-Koenig, and Rich Koenig

Low water landscapes are increasing popular and important in the urban areas of the Intermountain West (IMW). Perennial wildflowers are an essential part of low water landscapes, and are a dominant plant type in IMW native habitats. We compared pot-in-pot (PIP) vs. conventional above-ground (CAG) production of six IMW native wildflower species, Mirabilismultiflora, Aquilegia caerulea, Penstemon palmeri, Polemonium foliosissimum, Sphaeralcea grossularifolia, and Penstemonstrictus in #1 (4-L) containers. Media temperature, container-plant water loss, stomatal conductance, and growth were measured during two production cycles per year over 2 years. Growing medium temperatures in the PIP system averaged 10 °C cooler than in the CAG system. Consistent with cooler growing media, overall water loss of PIP-grown plants averaged 10% lower than plants grown in the CAG production system. Lower growing media temperatures apparently affected transpiration, as stomatal conductance was about 60% higher in the PIP system as compared to the CAG-grown plants. The integrated effect of lower growing media temperatures on plant performance resulted in about one-third greater top and root growth for plants growing in the PIP system compared to those in the CAG system. Pot-in-pot production may be an economically suitable nursery system for producing IMW native perennial wildflowers by reducing water loss and enhancing growth.

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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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Nickolee Zollinger, Teresa Cerny-Koenig, Roger Kjelgren, Rich Koenig, and Kelly Kopp

Although salinity is becoming an increasing concern for landscape plants in many areas of the West, few studies have been carried out to evaluate salinity responses of ornamental plants, especially herbaceous perennials. We investigated salinity tolerance of four traditionally grown and four Intermountain West native ornamental herbaceous perennials. Penstemo×mexicali `Red Rocks', Leucanthemum×uperbum `Alaska', Echinacea purpurea, Lavandula angustifolia, Geranium viscosissimum, Eriogonum jamesii, Penstemon palmeri, and Mirabilismultiflora were irrigated with water containing a mixture of 2 CaCl2: 1 NaCl at salinity levels of 0.33 (tap water control), 2.2, 5.4, and 8.3 dS·m-1 for 8 weeks. Growth, visual quality, and gas exchange were assessed. Mirabilis multiflora and L.×uperbum `Alaska' showed high salt tolerance based on visual quality. No noticeable leaf necrosis was observed for either species at any salinity level. However, over the 8-week period, growth rates for L. superbumwere reduced by 35%, 58%, and 72% compared to the control for the 2.2, 5.4, and 8.3 dS·m-1 salinity levels, respectively. The decrease in growth did not reduce visual quality. Growth rates for M. multiflora were slightly higher than the control for the 2.2 and 5.4 dS·m-1 salinity levels and dropped about 20% at the highest salinity level. Echinaceapurpureashowed the lowest tolerance to salinity, as evidenced by substantial margin burn at all salinity levels as well as high mortality; all plants in the highest salinity treatment died.

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Nickolee Z, Roger Kjelgren, Teresa Cerny-Koenig, Rich Koenig, and Kelly Kopp

We investigated drought responses of Echinacea purpurea, Gaillardia aristata, Lavandula angustifolia, Leucanthemum ×uperbum `Alaska', Penstemonbarbatus`Rondo', and Penstemo×mexicali `Red Rocks' established in a 10-gal pot-in-pot system in northern Utah. Plants were irrigated at frequencies of 1, 2, or 4 weeks between June and Sept. 2004. Osmotic potential, gas exchange, visual quality, leaf area, and dry biomass were assessed. In a confined root zone, P. barbatusshowed the greatest tolerance to drought, avoiding desiccation by increasing root: shoot ratio and decreasing transpiration as water became more limiting. Plants maintained high visual quality throughout the study and experienced little wilt, burn, or dieback. However, P. barbatus above-ground biomass was reduced by 15% for the 2-week treatment and by 40% for the 4-week treatment. Alternatively, G. aristata and L. superbum displayed drought avoidance mechanisms, dying back when water was limiting and resprouting after they were watered. Above-ground biomass declined by 50% and 84% for G. aristata and 47% and 99% for L. superbum, respectively, for the 2- and 4-week treatments. Root mass was affected similarly for both species. However, transpiration remained high for all treatment levels. Leaf burn and reduction in above- and below-ground biomass were also evident for E. purpurea at the 2- and 4-week treatments, but results were not as pronounced as for G. aristata and L. superbum. Overall, P. barbatusexhibited the greatest drought tolerance while maintaining an acceptable appearance. G. aristata, contrary to expectations, did not exhibit drought tolerance with a confined rooting volume, suggesting that it avoids drought in landscapes by means of deep rooting.