deficit irrigation cycle. Following study initiation, mowing was only done as needed to minimize any wheel tracking of stressed turf which might affect digital imaging. Te area received approximately 3.0 lbs. (1.361 kg.) of nitrogen annually from a predominantly controlled release granular fertilizer.
Supplemental irrigation needs were determined using a deficit irrigation strategy based on a 70 percent green color threshold (GCT70
). Te deficit irrigation program
began on 30 June 2021, and ended on 13 September 2021. Prior to the deficit irrigation period the entire area was uniformly hydrated via overhead irrigation to maximize the soil water reservoir of this silt-loam soil. Tereafter, the center of each plot was imaged using a digital camera and light box every three to four days depending upon turf response. Images were analyzed for digital green color using a Java-based software program, Turf Analyzer. Once an individual plot fell below the 70 percent green color threshold that plot received .50 inch (1.27 cm.) of water from a hose equipped with a flow meter and the application was split into two .25 inch (.635 cm.) applications approximately 30 minutes apart to prevent runoff and border effects. Te GCT70
threshold was
selected based on previous experience in maintaining a lawn turf at a minimally acceptable level of green color and density. Additionally, visual quality was regularly rated on a 0 to 10 scale where 0=brown, dead turf; 6=minimally acceptable lawn turf; and 10=optimal uniformity, density, and color.
Key Findings
In the second year of the study the supplemental irrigation treatments received 5.3 to 8.6 inches (13.462 to 21.844 cm.) of water (Figure 1). Comparatively, in the first year, supplemental irrigation needs ranged from 7.7 to 8.9 inches (19.558 to 22.606 cm.) of water with only slight differences among treatments. As in year one, the core aeration treatment benefits were negligible and thus data pooled across cultivation. Te non-treated sod and the sod receiving compost only required the most supplemental irrigation (8.6 and 8.3 inches) (21.844 to 21.082 cm.), respectively. Te granular surfactant and surfactant + vermicompost received 7.7 and 7.1 inches (19.558 to 18.034 cm.), respectively. Te most impact occurred in any treatment that had been overseeded with turf-type tall fescue (TTTF) with supplemental irrigation ranging from 5.3 to 6.3 inches (13.462 to 16.002 cm.).
For seasonal turf appearance (April – September) values ranged from 5.3-8.0 (Figure 2). Higher values were associated with any treatment that received compost applications in the early spring, and during the deficit supplemental irrigation phase, those treatments that had been overseeded with TTTF had a higher visual appearance.
12 TPI Turf News September/October 2022
For digital green color during the supplemental irrigation phase values ranged from roughly 80-90 percent at the beginning of the trial with lower values associated with the non-treated sod, vermicompost, or granular surfactant only treatments (Figure 3). Higher values were associated with those treatments containing TTTF overseeding combined with vermicompost and/or a surfactant. All treatments except the TTTF overseeding alone fell below the 70 percent green color threshold approximately 30 days after initiation. In general, those treatments containing TTTF or a surfactant appeared to be more responsive and resilient in terms of summer green color to the supplemental irrigation treatments.
Tis study will be continued in 2022 to determine if there are long term effects and benefits of these cultural inputs on the supplemental irrigation needs of sodded Kentucky bluegrass lawns.
Research plots are shown under the fixed roof rain-out shelter for the project: Determining the Impact of Post-planting Cultural Practices on Sodded Lawn Water Needs in the Cool-Humid Region. Lead researcher for this project is Cale Bigelow, PhD, Purdue University.
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