Spirea (Spiraea sp.) plants are popular landscape plants in Utah and the Intermountain West United States. Spiraea betulifolia, S. japonica, S. media, S. nipponica, and S. thunbergii were evaluated for salinity tolerance in a greenhouse experiment. Plants were irrigated weekly with a nutrient solution at an electrical conductivity (EC) of 1.2 dS·m−1 (control) or saline solution at an EC of 3.0 or 6.0 dS·m−1 for 8 weeks. At the end of the experiment, all spirea plants survived and retained good visual quality, with average visual scores greater than 4 (0 = dead, 5 = excellent) when irrigated with saline solution at an EC of 3.0 dS·m−1, with the exception of S. thunbergii, which showed slight foliar salt damage and an average visual score of 3.8. When irrigated with saline solution at an EC of 6.0 dS·m−1, all S. thunbergii plants died, S. media exhibited severe foliar salt damage and an average visual score of 1.5, and S. betulifolia, S. japonica, and S. nipponica displayed slight-to-moderate foliar salt damage and average visual scores greater than 3. Regardless of spirea species, shoot dry weight decreased by 20% and 48% when irrigated with saline solution at ECs of 3.0 and 6.0 dS·m−1, respectively, compared with the control. Saline solution at an EC of 3.0 dS·m−1 did not affect net photosynthesis (Pn) of all spirea species except S. nipponica, but saline solution at an EC of 6.0 dS·m−1 decreased the Pn of all species by 36% to 60%. There were 37, 7, 36, 21, and 104 times more sodium (Na+) concentrations in leaf and 29, 28, 28, 13, and 69 times more chloride (Cl−) concentrations in leaf than in the control when S. betulifolia, S. japonica, S. media, S. nipponica, and S. thunbergii were irrigated with saline solution at an EC of 6.0 dS·m−1. Correlation analyses indicated that foliar salt damage and reduced plant growth and photosynthesis were induced mainly by Cl− ions accumulated in the spirea leaves. S. thunbergii was the most sensitive species; it had high mortality and low visual quality at both salinity levels. Spiraea japonica, S. nipponica, and S. betulifolia were relatively more tolerant and had good visual quality at elevated salinity compared with S. media and S. thunbergii. These research results are valuable for growers and landscape professionals during plant selection for nursery production using low-quality water and landscapes in salt-prone areas.
Youping Sun, Liqin Li, Yuxiang Wang, and Xin Dai
Maegen Lewis, Melanie Stock, Brent Black, Dan Drost, and Xin Dai
The demand for locally grown, specialty cut flowers is increasing and now includes nontraditional regions for production, such as the U.S. Intermountain West. The objective of this study was to evaluate snapdragon (Antirrhinum majus L.) as a cool season, cut flower crop in northern Utah, where the high elevation and semiarid climate result in a short growing season with strong daily temperature fluctuations. High tunnel and field production methods were trialed in North Logan, UT (41.77°N, 111.81°W, 1382 m elevation) with cultivars ‘Chantilly’, ‘Potomac’, and ‘Rocket’ in 2018 and 2019. Each year, five to six transplant timings at 3-week intervals were tested, beginning in early February in high tunnels and ending in late May in an unprotected field. Stems were harvested and graded according to quality and stem length. High tunnels advanced production by 5 to 8 weeks, whereas field harvests continued beyond the high tunnel harvests by 2 to 8 weeks. High tunnels yielded 103 to 110 total stems per m2 (65% to 89% marketability), whereas field yields were 111 to 162 total stems per m2 (34% to 58% marketability). Overall, production was the greatest with March transplant timings in the high tunnels and mid-April transplant timings in the field. ‘Chantilly’ consistently bloomed the earliest on 4 and 6 May each year, ‘Potomac’ had the highest percentage of long stem lengths, and ‘Rocket’ extended marketable stem production through July in high tunnels. Selecting optimal transplant dates in the high tunnel and field based on cultivar bloom timing maximizes marketable yields and results in a harvest window lasting 4.5 months.
Yuxiang Wang, Liqin Li, Youping Sun, and Xin Dai
Spirea (Spiraea sp.) plants are commonly used in landscapes in Utah and the intermountain western United States. The relative salt tolerance of seven japanese spirea (Spiraea japonica) cultivars (Galen, Minspi, NCSX1, NCSX2, SMNSJMFP, Tracy, and Yan) were evaluated in a greenhouse. Plants were irrigated with a nutrient solution with an electrical conductivity (EC) of 1.2 dS·m−1 (control) or saline solutions with an EC of 3.0 or 6.0 dS·m−1 once per week for 8 weeks. At 8 weeks after the initiation of treatment, all japanese spirea cultivars irrigated with saline solution with an EC of 3.0 dS·m−1 still exhibited good or excellent visual quality, with all plants having visual scores of 4 or 5 (0 = dead, 1 = severe foliar salt damage, 2 = moderate foliar salt damage, 3 = slight foliar salt damage, 4 = minimal foliar salt damage, 5 = excellent), except for Tracy and Yan, with only 29% and 64%, respectively, of plants with visual scores less than 3. When irrigated with saline solution with an EC of 6.0 dS·m−1, both ‘Tracy’ and ‘Yan’ plants died, and 75% of ‘NCSX2’ plants died. ‘Minspi’ showed severe foliar salt damage, with 32% of plants having a visual score of 1; 25% of plants died. ‘Galen’ and ‘NCSX1’ had slight-to-moderate foliar salt damage, with 25% and 21%, respectively, of plants with visual scores of 2 or less. However, 64% of ‘SMNSJMFP’ plants had good or excellent visual quality, with visual scores more than 4. Saline irrigation water with an EC of 3.0 dS·m−1 decreased the shoot dry weight of ‘Galen’, ‘Minspi’, ‘SMNSJMFP’, and ‘Yan’ by 27%, 22%, 28%, and 35%, respectively, compared with that of the control. All japanese spirea cultivars had 35% to 56% lower shoot dry weight than the control when they were irrigated with saline irrigation water with an EC of 6.0 dS·m−1. The japanese spirea were moderately sensitive to the salinity levels in this experiment. ‘Galen’ and ‘SMNSJMFP’ japanese spirea exhibited less foliar salt damage and reductions in shoot dry weight and were relatively more tolerant to the increased salinity levels tested in this study than the remaining five cultivars (Minspi, NCSX1, NCSX2, Tracy, and Yan).
Haifeng Xing, Julie Hershkowitz, Asmita Paudel, Youping Sun, Ji Jhong Chen, Xin Dai, and Matthew Chappell
Reclaimed water provides a reliable and economical alternative source of irrigation water for landscape use but may have elevated levels of salts that are detrimental to sensitive landscape plants. Landscape professionals must use salt-tolerant plants in regions where reclaimed water is used. Ornamental grasses are commonly used as landscape plants in the Intermountain West of the United States due to low maintenance input, drought tolerance, and unique texture. Six ornamental grass species, including Acorus gramineus (Japanese rush), Andropogon ternarius (silver bluestem), Calamagrostis ×acutiflora (feather reed grass), Carex morrowii (Japanese sedge), Festuca glauca (blue fescue), and Sporobolus heterolepis (prairie dropseed), were evaluated for salinity tolerance. Plants were irrigated every 4 days with a fertilizer solution at an electrical conductivity (EC) of 1.2 dS·m–1 (control) or with a saline solution at an EC of 5.0 dS·m–1 (EC 5) or 10.0 dS·m–1 (EC 10). At 47 days, most species in EC 5 exhibited good visual quality with averaged visual scores greater than 4.6 (0 = dead, 5 = excellent). In EC 10, most A. gramineus plants died, but C. ×acutiflora, F. glauca, and S. heterolepis had no foliar salt damage. At 95 days, C. ×acutiflora, F. glauca, and S. heterolepis in EC 5 had good visual quality with averaged visual scores greater than 4.5. Acorus gramineus, A. ternarius, and C. morrowii showed foliar salt damage with averaged visual scores of 2.7, 3.2, and 3.4, respectively. In EC 10, A. gramineus died, and other grass species exhibited moderate to severe foliar salt damage, except C. ×acutiflora, which retained good visual quality. Plant height, leaf area, number of tillers, shoot dry weight, and/or gas exchange parameters also decreased depending on plant species, salinity level, and the duration of exposure to salinity stress. In conclusion, A. gramineus was the most salt-sensitive species, whereas C. ×acutiflora was the most salt-tolerant species. Festuca glauca and S. heterolepis were more tolerant to salinity than A. ternarius and C. morrowii. Calamagrostis ×acutiflora, F. glauca, and S. heterolepis appear to be more suitable for landscapes in which reclaimed water is used for irrigation. Plant responses to saline water irrigation in this research could also be applied to landscapes in salt-prone areas and coastal regions with saltwater intrusion into aquifers and landscapes affected by maritime salt spray.
B. Shaun Bushman, Lijun Wang, Xin Dai, Alpana Joshi, Joseph G. Robins, and Paul G. Johnson
Much of semiarid western North America is salt affected, and using turfgrasses in salty areas can be challenging. Kentucky bluegrass (Poa pratensis L.) is relatively susceptible to salt stress, showing reduced growth, osmotic and ionic stress, and eventual death at moderate or high salt concentrations. Considerable variation exists for salt tolerance among kentucky bluegrass germplasm, but gaining consistency among studies and entries has been a challenge. In this study, two novel kentucky bluegrass accessions recently reported as salt tolerant (PI 371768 and PI 440603) and two cultivars commonly used as references (Baron and Midnight) were compared for their turf quality (TQ), stomatal conductance (g S), leaf water potential (ψLEAF), electrolyte leakage (EL), and accumulation of inorganic ions under salt stress. TQ, ψLEAF, and EL were highly correlated with each other while only moderately correlated with g S. The tolerant accessions showed higher ψLEAF and lower EL than the cultivars Midnight and Baron at increasing salt concentrations and over 28 days of treatment. The accumulation of sodium (Na) and calcium (Ca) in the leaves was highly correlated and did not vary significantly among the four entries. Genes involved in ion transport across membranes, and in antioxidant activities, were significantly induced on salt stress in the tolerant accessions relative to the susceptible. These data indicate the ability of tolerant accessions to ameliorate oxidative stress and prevent EL, and confirmed the tolerance of germplasm previously reported on while indicating mechanisms by which they tolerate the salt stress.
Shane R. Evans, Kelly Kopp, Paul G. Johnson, Bryan G. Hopkins, Xin Dai, and Candace Schaible
Recent advances in irrigation technologies have led many states to incentivize homeowners to purchase United States Environmental Protection Agency WaterSense-labeled, smart irrigation controllers. However, previous research of smart controllers has shown that their use may still result in excess water application when compared with controllers manually programmed to replace actual water loss. This study compared kentucky bluegrass (Poa pratensis) irrigation applications using three smart irrigation controllers, a conventional irrigation controller programmed according to Cooperative Extension recommendations, and the average irrigation rate of area homeowners in Utah during 2018 and 2019. Of all the controllers tested, the manually programmed controller applied water at amounts closest to the actual evapotranspiration rates; however, smart controllers applied from 30% to 63% less water than area homeowners, depending on the controller and year of the study. Kentucky bluegrass health and quality indicators—percent green cover and normalized difference vegetation indices—varied between years of the study and were lower than acceptable levels on several occasions in 2019 for three of the four controllers tested. Compared with the results of similar studies, these findings suggest that the effects of smart irrigation controllers on turfgrass health and quality may vary by location and over time.