Figure 1. Drip irrigation lines are installed on the surface of this research plot. Photos by Alex Bach
An increasingly popular method of maintaining turfgrass is subsurface drip irrigation (SDI). Subsurface drip irrigation directly applies water to the soil-root interface using buried driplines, resulting in less water loss through evaporation, wind drift
or runoff than with overhead sprinklers. In golf courses, SDI has been used in tees, bunker faces and some edges of fairways and roughs, with water savings of 50% or more (3, 5). To date, most SDI research in turfgrass has been conducted in sandy
loam soils in the semi-arid, southwestern U.S. and has indicated that turf maintained with SDI was similar to or even better than plots maintained with traditional overhead sprinklers (5-8). However, such research using SDI in other climates and in
fine-textured (silt- or clay-based) soils is lacking.
If SDI is to be installed in lieu of overhead sprinkler systems, one important consideration is to evaluate the effectiveness of using SDI in the establishment of turfgrass from seed, but only a few studies have investigated this (6, 7). Aboveground drip
irrigation (AGD) is similar to SDI except that it rests on the soil surface (Figure 1) and has been suggested as a portable system to enhance the establishment of turfgrass along roadsides (9). However, little research has been conducted to evaluate
the use of AGD in the establishment of turfgrass.
Preparation of the seedbed with cultivation (for example, core aeration or verticutting) is an important consideration when establishing turfgrass. In SDI systems, cultivation has the potential to damage buried driplines if cultivation is deep enough
to nick or penetrate them. Anecdotal reports have indicated that shallow aeration can be successful when using SDI (3). However, to our knowledge, no research has been conducted regarding the effects of cultivation prior to seeding on turfgrass establishment
when using SDI.
Irrigation frequency and the amount of water applied at each irrigation affects the distance that water moves upward and laterally away from the buried driplines in SDI. This water movement may determine the successful convergence of wetting fronts at
the surface between the driplines, as well as whether the surface is maintained wet enough to facilitate turfgrass seed germination.
Covers are frequently used to improve germination and establishment of seeded turfgrass by reducing erosion, retaining soil moisture at the surface via reduced drying rates and modifying the surface temperature. For example, during spring turf establishment,
covers may mitigate low soil temperature extremes that could damage emerging seedlings. To our knowledge, the effects of covers in combination with drip irrigation technologies on the establishment of turfgrass from seed has not been investigated.
Researchers at Kansas State University conducted two studies to determine if the use of SDI and AGD could effectively establish cool-season tall fescue turfgrass from seed comparably to conventional sprinkler irrigation in fine-textured soils in the transition
zone of the U.S. Specific management factors investigated included different cultivation methods for seedbed preparation, water amounts applied per irrigation event, daily irrigation frequencies, and the use of covers and cover type when using SDI
and AGD in fine-textured soils. The two experiments were conducted at the Rocky Ford Turfgrass Research Center at Manhattan, Kan.
Figure 2. Percentage green cover among irrigation treatments during (A) 2019 and (B) 2020. Treatments were overhead sprinkler, aboveground drip (AGD) and subsurface drip irrigation (SDI) applied three times per day (SDI 3×), SDI applied twice per day (SDI 2×), and SDI applied once per day (SDI 1×). On each measurement date, means with the same letter are not significantly different at α = .05.
Experiment 1
The objectives were to investigate the establishment of seeded tall fescue using SDI and AGD compared with overhead sprinklers, core aeration vs. verticutting for seedbed preparation, and various daily irrigation frequencies and water amounts per irrigation
event.
Materials and methods
This study was conducted during the fall of both 2019 and 2020, with seeding dates of Oct. 1 and Sept. 24, respectively. Tall fescue was seeded at a rate of 8 pounds per 1,000 square feet (391 kilograms per hectare). The tall fescue seed blend included
the cultivars Copious, Reunion and Starfire II. The study area was then covered with a 0.5-ounce polyester mesh frost protection blanket to prevent seed movement during potential heavy rain events. The cover was removed when shoots began to appear,
which was approximately one week after seeding, to avoid damage to seedlings when covers were removed. The covers were effective in preventing erosion of seed on plots during rainfall, which prompted a spinoff study (Experiment 2, described below)
to investigate the use of covers in spring seed establishment.
On the day before seeding tall fescue, the two cultivation treatments (core aeration and verticutting) were applied to bare soil to prepare the seedbeds. Core aeration removed 0.5-inch (1.3-centimeter) diameter cores measuring approximately 3 inches (7.6
centimeters) deep and spaced 3 inches apart. Three irrigation treatments were SDI, AGD and traditional overhead sprinklers. Irrigation was applied daily at 150% reference evapotranspiration (ET) as follows: overhead sprinklers — three times
daily at 50% ET per irrigation; AGD — three times daily at 50% ET per irrigation; SDI — one time, two times and three times daily at 150%, 75% and 50% ET per irrigation, respectively. The experiment was arranged in a split-plot complete
block design with irrigation treatments applied to whole plots and cultivation treatments applied to split plots within whole plots.
The driplines in both SDI and AGD systems were pressure-compensating and spaced 18 inches (46 centimeters) apart, with emitters every 12 inches (30 centimeters). Driplines in AGD system rested on the soil surface (Figure 1), while in SDI they were buried
at 6 inches (15 centimeters). Sprinkler irrigation consisted of Hunter I-20 gear-drive rotors. Immediately after seedling emergence and removal of the covers, establishment was evaluated for about the next month with measurements of percentage green
cover using digital images collected with a Nikon D5000 and a lighted camera box, visual turfgrass quality, and normalized difference vegetation index (NDVI) obtained with hand-held and drone-based sensors.
Figure 3. Protective covers were straw blanket (front left), polyester mesh (front middle) and no cover as a control (front right).
Results
Establishment was faster with SDI than AGD or traditional overhead sprinklers, and similar between AGD and overhead sprinklers (Figure 2). By the end of the first month after seeding, green cover and NDVI were up to 25% and 15% greater, respectively,
in SDI than AGD and overhead sprinklers. Furthermore, SDI two times daily at 75% ET replacement per irrigation consistently established tall fescue faster than SDI three times daily at 50% ET per irrigation and, to a lesser degree, than SDI once daily
at 150% ET, which demonstrates the importance of proper irrigation frequency and amounts per irrigation in fine-textured soils when establishing turfgrass from seed with SDI.
Cultivation effects were negligible, indicating seedbed preparation with either verticutting or aeration is appropriate as long as depths of cultivation and driplines are considered to avoid SDI damage (no damage to the SDI system was observed in this
study). Overall, results indicate seeded tall fescue turfgrass can be established with SDI in fine-textured soils in the transition zone climate of Kansas.
Experiment 2
The objectives were to evaluate the effects of polyester mesh and straw blanket covers, and SDI, AGD and overhead sprinkler methods on establishment of seeded tall fescue turfgrass in the spring, when soils were cold.
Materials and methods
This study was repeated twice in the spring of 2020. The same blend of tall fescue described in Experiment 1 was seeded into bare soil on April 9 (Trial 1) and May 2 (Trial 2). Immediately before seeding, the plot area was cultivated with a verticutter.
Urea fertilizer (44% nitrogen, 0% phosphorous, 0% potassium) was applied at a rate of 1 pound per 1,000 square feet (49 kilograms per hectare) approximately three weeks after each trial began.
Two turfgrass cover types were installed immediately after seeding — 0.5-ounce lightweight polyester mesh frost covers (Poly) and straw blankets (Straw) — and uncovered plots (No cover) were used as a control (Figure 3). Covers were removed
immediately after seedling emergence (13 days after seeding in Trial 1 and 12 days after seeding in Trial 2), to avoid damage to seedlings when covers were removed. Irrigation treatments were: 1) SDI; 2) AGD; and 3) overhead sprinkler irrigation (control),
3 times per day for a total of 150% ET daily.
The experiment was arranged in a split-plot design with three irrigation treatments applied to whole plots and three cover treatments applied to split plots within each whole plot. Establishment was evaluated with percentage green cover, visual turfgrass
quality ratings and remote sensing measurements (NDVI), as described in Experiment 1. Day and nighttime seedbed temperatures were measured with soil encapsulated thermocouples (4) and averaged across both trials from 10 a.m. to 6 p.m. (daytime) and
10 p.m. to 6 a.m. CST (nighttime) during the study. Soil surface temperatures were measured only in SDI because of limitations in sensor and data acquisition availability.
Figure 4. Percentage green cover during Trial 1 (A) and Trial 2 (B). Covers included polyester mesh (Poly), a straw blanket (Straw) and an uncovered control (No cover). On each measurement date, means with the same letter were not significantly different at α = .05.
Results
Seeded tall fescue established faster in all irrigation treatments when plots were covered with either Poly or Straw during the first 12-13 days after seeding, as indicated by green cover, ground and drone-based NDVI, and visual turfgrass quality ratings,
in the order of Poly > Straw > No cover in both trials (Figure 4). The initially faster establishment in Poly than Straw was likely caused by a warmer soil surface in Poly than in Straw (and No cover) during the period when covers were installed
(Figure 5), which benefitted seedling emergence under polyester mesh during low spring temperatures. For example, the soil temperature was 57 F (14 C) in Poly compared with 49 F (9.5 C) in Straw and 47.5 F (8.6 C) in No cover; air temperature was
47 F (8.5 C) during the same period (24-hour averages). However, by the end of both trials, establishment was generally similar between Poly and Straw (Figure 4).
Establishment was better in covered (Poly and Straw) than No cover plots because Poly and Straw covers also prevented erosion of the seedbed during rainfall early in both trials (Figure 6). Specifically, during the period when covers were installed in
Poly and Straw plots, the seedbeds in No cover were eroded after 0.71 inches (1.8 centimeters) and 1.6 inches (4.1 centimeters) of rainfall in Trial 1 and Trial 2, respectively.
Leaf burn from nitrogen fertilization was observed in drip irrigation (SGI and AGD) during Trial 2 (Figure 4B; note the decline in green cover late in the study). Trial 2 was conducted later in the spring, when temperatures were higher than in Trial 1.
Leaf burn was significantly less in sprinkler-irrigated plots (data not shown). This indicates a possible limitation to using drip technology in turf that requires further investigation into different types, sources and application rates of nitrogen
fertilizer to minimize leaf burn.
Establishment was similar among all three irrigation treatments (SDI, AGD and overhead sprinklers; data not shown). Although the potential uses for AGD may be more limited than SDI, establishment was acceptable in AGD, and more research is needed into
this method. Overall, the use of protective covers is recommended when establishing turfgrass from seed.
Figure 5. Soil surface temperatures during day (top; A; 10:00-18:00 CST) and night (bottom; B; 22:00-06:00 CST), averaged across both trials. Temperatures were measured during the periods when covers were installed (0 to 12 DAS) and during the first 8 days after covers were removed (13 to 20 DAS). Within each measurement period, means with no letters or the same letter are not significantly different at α = 0.05.
Funding
This work was supported by the Irrigation Innovation Consortium (IIC) and Kansas Turfgrass Foundation.
The Research Says
- Covers improved tall fescue turfgrass establishment in all irrigation treatments.
- In the short run, seedling emergence was faster when using lightweight polyester mesh covers than with straw blankets, but after one month, the turf coverage was similar between the two cover types.
- Improved establishment in covered plots was due to reduced erosion from rainfall during the first week after seeding and higher soil temperatures (polyester mesh covers only) in this spring study.
- Post-emergence applications of granular urea (after covers were removed) caused leaf burn in the second but not the first study, probably because of higher temperatures in the second study.
- Seeded turf establishment was similar among SDI, AGD and traditional overhead sprinkler irrigation treatments.
Figure 6. Turfgrass establishment 14 days after seeding in Trial 2, after removal of covers. No cover plots (3) were clearly eroded by 1.6 inches of rainfall during the first 12 days after seeding, while establishment was better in Poly (1) and Straw (2) because of protection from erosion.
Acknowledgements
The authors appreciate the technical assistance of Wes Dyer and Mu Hong. Full manuscripts of this research are published in two peer-reviewed journals (1, 2).
Literature cited
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Dale Bremer (bremer@ksu.edu) and Cathie Lavis are professors emeriti, Steve Keeley is a professor and department head, and Alex Bach completed his M.S. in the Department of Horticulture and Natural Resources, Kansas State University, Manhattan. Alex Bach is a Landscape Maintenance Manager for The Greensman, Kansas City, Mo.