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Aeration and sand topdressing are important cultural practices for organic matter management on golf course putting greens. Many golf courses lack the budget for applications of new sand topdressing material. A 2-year study was conducted to investigate the effect of recycling sand from hollow-tine aerification cores on a sand-based creeping bentgrass (Agrostis stolonifera) putting green soil properties and playability. Treatments included traditional [T (cores removed and sand topdressed)], verticut [V (cores broken up with verticutter)], and recycle [R (cores recycled using a core recycler)]. There were no differences in root zone organic matter, bulk density, soil porosity, infiltration rates, percent sand recovered during mowing, surface firmness, and ball roll distance between treatments during the study. Immediately after aerification treatments, T had the highest percent green cover (PGC) (38.3%) compared with V (26.9%) and R (26.8%), indicating that T offered the least sand present on the surface. Seven days after treatments, there was no difference in PGC (85.3% to 90.1%), indicating all treatments recovered similarly. Alternative aerification treatments V and R could be useful techniques to minimize or reduce the amount of sand used for backfilling core aeration holes without compromising the putting green soil properties and playability.
Aerification and sand topdressing are important cultural practices to reduce thatch and soil organic matter on golf course putting greens (Christians et al. 2017). However, the cost, dulling of mower blades, and disruption of golfers are some of the reasons golf courses do not apply sand during aeration or infrequently apply sand (Whitlark and Thompson 2019). Skipping an aerification and topdressing application can result in increased thatch buildup and soil organic matter accumulation (Bevard 2011). Furthermore, excessive thatch and soil organic matter can result in decreased water infiltration, localized dry spots, decreased air flow into the root zone, increased pest problems, and reduced pesticide effectiveness (Gaussoin et al. 2013; Landreth et al. 2008). Elevated levels of soil organic matter can also affect the playability of the putting green, which include an increased probability of soft playing conditions, inconsistent green speed, foot printing and golf shoe scuffing, and lack of smoothness (Moeller and Lowe 2016).
Traditionally, aerification and sand topdressing is completed on cool-season grass in the spring and fall. This ensures that the turfgrass is actively growing, which reduces the recovery time (Beard 1973). Aerification in the spring and fall, along with sand topdressing, have been used to manage organic matter accumulation, increase water infiltration, and reduce compaction (Braun et al. 1998; Klingenberg et al. 2013; Schmid et al. 2014b; White and Dickens 1984). In addition, summer cultivation practices can improve soil gas levels, soil hardness, and water infiltration (Bunnell et al. 2001). Furthermore, Cooper and Skogley (1981) reported that monthly topdressing resulted in higher quality turf. Increasing the aerification and topdressing frequency also reduces the organic matter concentration (Schmid et al. 2014a). Atkinson et al. (2012) reported that increasing the number of aerification events and the amount of surface area impacted reduced soil bulk density, surface hardness, and thatch organic matter content. Reducing the frequency of aerification events while still affecting the same amount of surface area did not result in improved soil physical properties, but it did improve visual turf quality and recovery time (Atkinson et al. 2012; Landreth et al. 2008).
Higher organic matter content is found in the portion of soil closest to the surface [0 to 2.5 cm (McClellan et al. 2009)]. Therefore, most of the organic matter in a hollow-tine aerification core is in the portion closest to the surface. Research is needed to see if the lower portion of the core could be returned to the root zone after aerification, which could reduce the amount of sand used for topdressing. Aerification core recycling can be done by using a verticutter to break up the cores, reincorporating a portion of the core back to the soil, or by using a core recycler machine. A core recycler machine collects the cores, transfers them to rotating screens to separate the sand from the organic matter, and then returns the sand back to the surface [Wiedenmann (UK) Ltd, date unknown]. Data are needed to assess how hollow-tine aerification core recycling will affect golf course putting greens. The objective of this study was to evaluate and compare the soil properties and playability of a sand-based putting green subjected to traditional hollow-tine aerification and hollow-tine aerification core recycling.
A 2-year experiment was conducted on a mature (10+ years old) ‘Penncross’ creeping bentgrass (Agrostis stolonifera) putting green starting in 2018 at the Iowa State University Horticulture Research Station (Ames, IA, USA). The putting green root zone consisted of a sand-based root zone that conformed to the U.S. Golf Association (USGA) specifications (USGA 2018). Turfgrass was maintained at a 1/8-inch height of cut, and mowed 6 d per week with a reel mower (John Deere model 2500B; Deere & Co., Moline, IL, USA). Clippings were collected and removed after each mowing. Irrigation was applied to the putting green as needed to prevent drought stress. The putting green also received preventive insecticide and fungicide treatments to minimize turf damage. Plots were fertilized at 3 lb/acre nitrogen with urea (46N–0P–0K) every 14 d throughout the growing season. On average, the initial putting green organic matter content was 4.3%, as determined by loss on ignition (Ball 1964).
Treatments were arranged in a randomized complete block design with three replications. Hollow-tine aerification (Toro Procore model 648; The Toro Co., Bloomington, MN, USA) was applied with a 2-inch by 2-inch spacing and 3/4-inch-diameter tines to a depth of 2 inches to the whole experimental area before sand incorporation treatments. Treatments included the following: traditional (T), removal of the cores and topdressed with sand to fill aeration holes; verticut (V), cores were broken up by verticutting using a riding greens mower (Toro 3100, The Toro Co.) equipped with verticutting reels and dragged back in, excess organic matter removed, and additional sand topdressing was applied as needed to fill the holes; and recycled (R), cores were recycled through a core recycler [Wiedenmann (UK) Ltd, Renfrew, Scotland], and additional sand topdressing was applied as needed to fill the holes. Sand used for backfilling core aeration holes and topdressing conformed to USGA putting greens particle size specifications (USGA 2018). Each experimental unit size was 8 ft by 20 ft and repeated in the same location over time. Treatments were applied on 30 Aug 2018 and 23 Aug 2019.
Soil properties (organic matter, bulk density, porosity, and infiltration rates) were measured before treatments were applied and after turfgrass recovery each year [28 d after treatment (DAT)]. Soil organic matter at a 2-inch depth was determined using the loss on ignition method (Ball 1964). Three soil samples (1.5 inches diameter by 2 inches depth) per treatment were taken to measure the soil organic matter. Soil physical properties were determined using methods similar to Dalsgaard et al. (2020). Three soil cores (2 inches diameter by 6 inches depth) per treatment were taken to measure the bulk density and porosity (Flint and Flint 2002; Grossman and Reinsch 2002). Infiltration rates were determined in the field using double ring infiltrometers (Turf-Tec International, Tallahassee, FL, USA). Three random locations were tested in each plot by using the falling head measurement technique (Klingenberg et al. 2013).
Soil moisture, ball roll distance, surface hardness, and PGC were determined pretreatment; immediately after treatment (posttreatment); and 7, 14, and 21 DAT each year. Soil moisture (volumetric water content) measurements were collected on three locations per treatment by using a time domain reflectance (TDR) sensor (Field Scout TDR 350; Turf-Tec International) with 3-inch tines. Ball roll distance was measured using a modified half-size Stimpmeter with methods similar to Gaussoin et al. (1995) with three rolls per treatment in each direction. Surface firmness values were obtained using a turf firmness meter (Field Scout TruFirm; Turf-Tec International) on three locations per treatment. Digital images were collected using techniques described by Thoms et al. (2011). Digital images were subjected to digital image analysis to determine PGC (Richardson et al. 2001). The percent sand recovered (PSR) in the total clipping weight was calculated 7, 14, and 28 DAT each year.
The experiment was repeated in time. All data collected was subjected to analysis of variance using statistical software (SAS ver. 9.4; SAS Institute Inc., Cary, NC, USA). Treatment mean comparisons were separated using Fisher’s protected least significant difference at the P ≤ 0.05 level.
Treatment means for soil organic matter, bulk density, soil porosity, infiltration rate, soil moisture, PSR, and surface firmness have been combined across years and rating dates due to a nonsignificant interaction with treatment effect (Table 1). Treatments did not have an effect on soil organic matter, bulk density, soil porosity, infiltration rates, soil moisture, PSR, and surface firmness (Table 2). Rootzone organic matter ranged from 4.7% to 5.0%. There was no nontreated control to compare, as T served as the standard cultural practice, so it appears all treatments were able to maintain root zone organic matter. A lack of differences in root zone organic matter indicated that V and R successfully removed the organic matter from the aerification cores before returning the sand to the putting green root zone. This is different from Henry et al. (2021), who reported that the core recycler resulted in a greater organic matter compared with conventional aerification. Bulk density and soil porosity varied from 1.17 to 1.19 g·cm−3 and 0.55 to 0.56 (v/v), respectively. This is consistent with Braun et al. (1998), who found that bulk density was unaffected by aerification or by increasing aerification frequency. Infiltration rates ranged from 3.9 to 4.3 cm·h−1, which indicates that V and R maintained the same infiltration rates as T. Soil moisture ranged from 31.8% to 32.4% (v/v), which indicates that soil moisture was maintained uniform across treatments because the error range of the TDR sensor is ±3%. This result was not unexpected, because the putting green received supplemental irrigation. On average throughout the duration of the study, the PSR in the clippings ranged from 55.5% to 57.8% of the weight of clippings. All treatments received either sand topdressing or recycled sand from the aerification cores with additional topdressing, so this result was not surprising. However, V and R needed less new sand inputs compared with T, as observed by the investigators, which can be estimated to reduce topdressing inputs by roughly 40% [Wiedenmann (UK) Ltd, date unknown]. This result is similar to Henry et al. (2021), who were able to reduce the topdressing rate by 50% using a core recycler. Based on the typical golf course with ≈2.5 acres of putting greens, recycling cores could save on average 653.4 ft3 of topdressing sand per aeration [Whitlark and Thompson 2019; Wiedenmann (UK) Ltd, date unknown]. Surface firmness values varied from 519.3 to 535.0 mm; this small difference indicates a minimal variance in surface firmness between treatments. These results indicate that both, V and R, could be used as an alternative to T to help reduce the input of sand used for backfilling core aeration holes.
A significant rating date-by-treatment interaction was present for PGC, so PGC is presented by rating date (Table 1). Before treatments were applied, there were no differences in PGC (Table 3). Following treatments and dragging the topdressing sand to fill the aeration holes (posttreatment), T had the PGC (38.3%) compared with V (26.9%) and R (26.8%). This difference in PGC may not be of concern because golfers expect putting green damage due to aerification, and they may not be able to tell the difference between 38.3% and 26.8%. The decrease in PGC for V and R relative to T could be due to having greater sand on the surface. as the sand that was recycled contained some moisture as opposed to the dry sand used in the T treatment. Sand with lower moisture has been demonstrated to work into the root zone better than sand with greater moisture (Murphy 2012). Another potential reason for lower PGC for V and R compared with T could be because V and R are more abrasive treatments and may remove or damage more leaf tissue than T. However, by 7 DAT there was no treatment difference for PGC, which ranged from 85.3% to 90.1%. By 14 DAT, the PGC ranged from 98.2% to 98.8% and was fully recovered by 21 DAT. Because there were only treatment differences immediately after treatments and treatments recovered soon after, V and R could possibly be used as an alternative to T and not slow recovery.
A significant year-by-treatment interaction was present for ball roll distance, so ball roll distance is described by year (Table 1). Although there was a treatment-by-year interaction for ball roll distance, there were no treatment differences within each year (data not presented). The treatment-by-year interaction was due to a crossover effect on treatment means (i.e., the treatment with the longest ball roll distance in 2018 had the shortest ball roll distance in 2019). These results, along with the surface hardness, indicate that V and R produce the same putting green playability as T.
Overall, the V and R had the same results as T for root zone organic matter, bulk density, soil porosity, infiltration rate, soil moisture, PSR, surface firmness, and ball roll distance after two aerification events in a 2-year period. The only time T was statistically better than V and R was immediately after treatments, with T having a greater PGC compared with V and R. This indicates that V and R could be useful techniques to minimize or reduce the amount of sand used for backfilling core aeration holes without compromising the putting green soil properties and playability.
Contributor Notes
We thank the U.S. Golf Association and the Iowa Turfgrass Institute for partial financial funding of this experiment.
A.J.L. is the corresponding author: E-mail: alex.lindsey@ufl.edu.
