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R. Kasten Dumroese

Juniperus scopularum Sarg. (Rocky Mountain juniper) and Potentilla fruticosa L. `Gold Drop' (gold drop potentilla) plants grown in containers had similar or better morphology, higher nitrogen concentrations and contents, and higher N-use efficiency when grown with liquid fertilizer applied at an exponentially increasing rate as compared to the same amount of N applied via controlled-release fertilizers. More importantly, plants grown with a half-exponential rate were similar to those grown with controlled-release fertilizer but with a higher N-use efficiency, indicating that this type of fertilization may be a method for reducing the amounts of applied nutrients in nurseries and subsequent nutrient discharge.

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Jeremy R. Pinto, Rhiannon A. Chandler, and R. Kasten Dumroese

Pale purple coneflower [Echinacea pallida (Nutt.) Nutt.] was grown within three container volumes (90, 105, and 340 cm3) under subirrigation and overhead irrigation treatments. Subirrigated coneflowers showed increased seedling quality with more biomass (14%), better nitrogen use efficiency (13%), greater nitrogen content (N; 11%), more height (15%), and lower mortality compared with overhead-irrigated seedlings. Plants also showed increasing height, biomass, and N content with increasing container volume. Overhead irrigated coneflowers had more leachate compared with subirrigated seedlings, which produced none. Leachate electrical conductivity and N were monitored throughout the growing season and decreased at similar rates, whereas subirrigation effluent levels remained constant. Subirrigation offers a viable alternative to traditional overhead irrigation systems by producing this native plant with equal or better quality without discharging potentially harmful leachate into the environment.

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Olga A. Kildisheva, R. Kasten Dumroese, and Anthony S. Davis

The results of a series of experiments involving a variety of dormancy-breaking treatments indicate that Munro's globemallow [Sphaeralcea munroana (Douglas) Spach] seeds are physically dormant, possess a cap-like structure in the occlusion of the water gap, which inhibits imbibition, and can be artificially dislodged through boiling water scarification. The highest germination capacity (93%) was achieved by mechanical scarification of previously stored seeds. Exogenous application of a gibberellin solution and cold stratification failed to enhance germination compared with scarification alone, indicating an absence of additional dormancy types. These results should improve the usefulness of this drought-tolerant perennial for landscaping and restoration given its effectiveness in soil stabilization, tolerance to a variety of soil types, extreme temperatures, and ecological importance.

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R. Kasten Dumroese, Robert L. James, and David L. Wenny

Inoculum of Douglas fir root diseases caused by the fungi Fusarium and Cylindrocarpon is carried from crop to crop in reused containers. Soaking containers for 90 seconds in 80 °C water removed ≈99% of Fusarium and 100% of Cylindrocarpon inoculum between growing cycles. Overall seedling growth was also improved: seedlings grown in containers soaked between growing cycles were 10% taller and had 20% more biomass than seedlings grown in nonsoaked containers. We obtained a 13% increase in the number of deliverable seedlings from containers soaked in hot water between crops, from the use of copper coated containers, or from both practices combined.

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R. Kasten Dumroese, Douglass F. Jacobs, and Anthony S. Davis

Restoration of Acacia koa A. Gray (koa) forests on degraded sites in Hawaii is important for conservation of rare, endemic plants and animals and is often accomplished by planting nursery-grown seedlings. To be successful after outplanting, koa seedlings must access sufficient nutrients from the soil and outcompete other vegetation. Forming symbiotic associations with nitrogen-fixing microorganisms may help alleviate inherent nutrient deficiencies found on volcanic sites, but interactions between inoculation and fertilization during production of koa seedlings are not well studied. Under operational nursery conditions, we fertilized koa seedlings at six controlled-release fertilizer (CRF) rates (ranging from 0 to 11.9 kg·m−3 Osmocote Plus 15N–9P–12K), which were also either inoculated with a locally collected source of nitrogen-fixing Bradyrhizobium spp. or not. Fertilized seedlings were significantly larger than the control; on average, fertilized seedlings were 300% taller and had 180%, 700%, and 350% more root-collar diameter, shoot biomass, and root biomass, respectively. Nitrogen (N) concentration was 23% to 119% greater in fertilized seedlings than nonfertilized seedlings. Inoculation with Bradyrhizobium had no significant affect on seedling characteristics except for root N concentration, which was 8% higher for inoculated seedlings. Fertilizer rate and inoculation interacted to significantly affect nodule number and nodule biomass/seedling. With inoculation, we observed an increase in nodule number (16.5 to 25.5) and biomass (5.8 mg to 11.7 mg) with fertilizer rate up to 4.7 kg·m−3 but a decline to nearly zero at the highest rates. Without inoculation, nodule formation was scarce (3.2 nodules/seedling or less) and only observed when CRF was 2.3 kg·m−3 or less. Our results suggest that high rates of fertilization and successful nodulation are not mutually exclusive nursery practices. Concurrent use of fertilization and inoculation in the nursery may provide opportunity to produce larger seedlings that have high potential to reduce the time needed to achieve canopy closure and thereby help achieve restoration objectives.

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R. Kasten Dumroese, Jasmine L. Williams, Jeremiah R. Pinto, and Peng Zhang

Our objective was to evaluate oxyfluorfen for control of birdseye pearlwort (Sagina procumbens L.) in a bareroot nursery crop of western larch (Larix occidentalis Nutt.) seedlings. Oxyfluorfen applied at rates up to 0.56 kg a.i./ha in a split-plot experiment with combinations and frequencies of pre- and postemergence sprays gave minimal control of birdseye pearlwort. Although preemergence rates 0.42 kg a.i./ha or greater reduced western larch emergence 10% compared with the control, final seedling inventory was similar for rates 0.42 kg a.i./ha or less. Seedlings receiving 0.42 kg a.i./ha or greater grew 30% more biomass than those that received 0.28 kg a.i./ha or less. When applied postemergence, oxyfluorfen reduced the number of larch seedlings at final inventory 9% and those seedlings had 20% less biomass than the control. Oxyfluorfen applied preemergence increased the amount of bare soil (reduced the weed canopy) throughout the production cycle compared with the control but even the most efficacious treatment combinations still had birdseye pearlwort canopy coverage 63% or greater.

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Robert R. Tripepi, Mary W. George, R. Kasten Dumroese, and David L. Wenny

European birch (Betula pendula Roth) seedlings (1+ 0 plugs) were planted in a container growth medium amended with 0, 1.2, 2.4, or 3.6 kg/m3 of a commercial hydrogel and watered either daily or once every 3 or 5 days. When hydrogel was incorporated in the growth medium, shoot and root dry weights and lea area were reduced by 19, 29 and 18%, respectively, compared to controls. Shoot height, stem diameter and shoot:root ratio were unaffected by hydrogel amendment rate. Compared to seedlings in polymer-amended media, plants growing in medium without hydrogel had significantly lower stomata1 conductance and transpiration on fewer than 25% of the measurement dates. Irrigation frequency significantly affected all plant growth Indices and stomata1 parameters; seedlings irrigated daily grew the most and had the highest stomata1 conductance and transpiration. Although polymer-amended media held more water than the medium without hydrogel at all measured tensions, this moisture was retained in the expanded gel rather than being available for plant uptake at higher tensions. The hydrogel appeared to have little benefit for container production of birch.