Sites
Trial sites are located in Arizona, California, Oregon, Utah, and Washington.
| Site | Location | USDA Zone | Sunset Zone | Annual Precipitation (in.) | Soil Type |
|---|---|---|---|---|---|
| Oregon State University, North Willamette REC | Aurora, OR | 8b | 6 | 41.84 | Willamette silt loam |
| University of Arizona | Tucson, AZ | 9b | 12 | 11.92 | Glendale silt loam |
| University of California, Davis | Davis, CA | 9b | 14 | 19.66 | Yolo silty clay loam |
| University of California, South Coast REC | Irvine, CA | 10a | 22 | 14.42 | San Emigdio fine sandy loam |
| University of Washington | Seattle, WA | 8b | 5 | 37.13 | Not determined |
| Utah State University | Logan, UT | 6a | 2B | 18.53 | Millville silt loam |
Experimental Design
At all sites plants were evaluated outdoors over two growing seasons. The standard site design utilized a grid pattern with plants spaced 2 meters (6.56’) apart in rows spaced 2 meters (6.56’) apart in full sun conditions with the fields covered with an organic mulch to suppress weeds and conserve soil moisture. At selected sites plants may have been evaluated in other conditions such as being grown under 50% shade cloth to replicate part sun conditions or in fields with 3 meter (9.84’) spacing to accommodate larger plant sizes.
Irrigation Practices
At all sites plants were irrigated with a single point-source pressure-compensating emitter and drip ring that encircled the plant in an effort to distribute water evenly around the root zone. Plant Available Water (PAW) for each site was obtained from US Geological Survey data via soilweb.ucdavis.edu. Evapotranspiration (ETo) data for each site was obtained via a regional or statewide weather station network for each site, e.g. California Irrigation Management Information System (CIMIS). Plants were irrigated regularly during their first growing season to minimize stress and fully establish the root system in the native soil. During this establishment period plants were irrigated when 25% of PAW was removed as estimated by daily ETo values, note: a coefficient of 80% was used to modify ETo.
During the deficit season plants were irrigated to when 50% of PAW was removed as measured by daily ETo data. Treatments were imposed by applying a coefficient to ETo with 3 treatments being applied, equal to 80%, 50%, and 20% of ETo. With this methodology the amount of water applied at each irrigation, equal to 50% of PAW, is constant while the frequency and number of irrigations will vary. The 80% treatment reduces daily ETo values the least meaning this treatment will show more ET is lost each day resulting in the fastest drawdown of soil moisture of all treatments. Thus the 80% treatment will receive irrigations the most frequently of all 3 treatments and consequently will have the most irrigations and water applied over the deficit season.
Data Collection & Analysis
Unique to ornamental plants, the element that people “harvest” is appearance. As a result researchers collected aesthetic quality ratings monthly during the deficit season, assessing foliage quality, floral quantity, disease tolerance, pest resistance, vigor and overall appearance (oa) on a 1-5 scale. Plant length, width, and height was measured monthly during the deficit season to determine if there was a significant size difference between treatments.
In analyzing the data researchers seek to determine if there is a significant difference in overall appearance ratings, the metric which best captures the performance of the plant, and pgi results between the treatments over the deficit season. To minimize landscape water-use, researchers will recommend the lowest irrigation treatment with acceptable aesthetic quality.