Impact of Soil Temperature on Prizm Zoysiagrass Establishment from Sprigs

Abstract

Zoysiagrasses (Zoysia spp. Willd.) are commonly used on golf course fairways and tees in addition to residential and commercial lawns due to lower input requirements relative to bermudagrass (Cynodon spp.). This has led to increased interest in using zoysiagrass for golf course putting greens; however, zoysiagrass establishment from sprigs is prolonged compared to bermudagrass. Research was conducted in Knoxville, TN to determine the effect of soil temperature on ‘Prizm’ zoysiagrass establishment from sprigs. The study was conducted over replicate experimental runs in separate glasshouses in 2022. Prizm zoysiagrass was exposed to high, medium, and low 5 cm soil temperature treatments, which were imposed via water bath. Over the 49-day study period, the high, medium, and low treatments averaged ~36 °C, ~32 °C, and ~28 °C, respectively. The medium and low treatments averaged 92% turfgrass coverage 49 days after planting (DAP) in run A, which was significantly greater than the high-soil-temperature treatment (70%). In run B, the medium soil temperature achieved 92% turfgrass coverage 44 DAP, which was significantly greater than the low (78%) and high (74%) treatments. Independent of other environmental variables, results from this study imply that an average daily 5 cm soil temperature of approximately 32 °C would likely result in the most rapid establishment of Prizm zoysiagrass from sprigs.

1. Introduction

Zoysiagrass (Zoysia spp. Willd.) is a warm-season, perennial turfgrass that is both stoloniferous and rhizomatous. This species is commonly used in the transition and warm climatic regions of the United States and offers lower input requirements relative to bermudagrass (Cynodon spp.) [1]. However, ultradwarf bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis (Burtt Davy)] is the most widely used warm-season turfgrass for putting greens in areas of the United States where zoysiagrass is adapted [2].

In 1996, ‘Diamond’ zoysiagrass [Zoysia matrella (L.) Merr.] was released for putting green use since it tolerated mowing heights common on putting greens and provided improved shade tolerance relative to bermudagrass [3]. Nonetheless, Diamond has demonstrated prolonged establishment when planted from vegetative sprigs compared to ultradwarf bermudagrass. Briscoe et al. [4] evaluated the establishment of ‘MiniVerde’ ultradwarf bermudagrass and Diamond zoysiagrass from sprigs in the transition zone and concluded that MiniVerde achieved 100% coverage 7 to 35 days earlier than Diamond. Additionally, Zhang et al. [5] compared the vegetative establishment of a Zoysia japonica (Steud.) cultivar and ‘Tifway’ hybrid bermudagrass when planted via sprigs during winter dormancy, spring, and summer. The authors reported that bermudagrass reached full coverage within one season, regardless of planting date, whereas only zoysiagrass planted during dormancy reached full coverage by the end of the first growing season in Arkansas. When ‘Prizm’ zoysiagrass, a recently released Z. matrella cultivar [6], was sprigged at 109 m³ ha⁻¹ throughout spring and summer in Knoxville, TN, plantings in April through June 2020 required ≥85 days to achieve 90% turfgrass coverage; however, plantings in June 2021 achieved 90% turfgrass coverage after ~55 days [7].

Ensuring complete establishment within the first growing season is important to ensure playability throughout the subsequent winter and spring months; however, prolonged establishment also extends course closure, which results in decreased revenue, while golf course maintenance and expenditures continue. Previous research has demonstrated accelerated zoysiagrass establishment from sprigs when increasing sprigging rate [5,8], but increasing nitrogen fertilization had limited effect in hastening establishment [4,8,9,10].

Typically, warm-season turfgrasses are planted in the late spring or early summer months when soil temperatures are conducive for growth [11]. Henry et al. [12] established ‘El Toro’ (Z. japonica) from sprigs or plugs in southern California and observed complete establishment after 3 to 4 months when planting in June compared to 9 and 11 months when planting occurred in September and the following March, respectively. In Indiana and Kentucky, ‘Zenith’ zoysiagrass (Z. japonica) established fastest when seeded from 1 June to 15 June, whereas seedings occurring after 1 July did not reach 95% coverage in the same growing season [13]. Similarly, planting ‘Shadow Turf’ (Z. matrella) from vegetative plugs in June and July led to faster initial establishment than May plantings; nonetheless, planting in May resulted in the greatest turfgrass coverage at the end of the study [14].

Previous research has focused on planting sprigs during the summer months; however, zoysiagrass is well adapted to the subtropical and transition climates in the United States where maximum average soil temperatures are dependent on location and vary from ~27 °C to ~35 °C [15]. Due to differences in soil temperature, varying geographic locations may provide environments more conducive for rapid zoysiagrass establishment from sprigs.

Currently, no optimal soil temperature has been reported for vegetative establishment of warm-season turfgrasses. Planting zoysiagrass sprigs when soil temperatures are optimal may hasten establishment and reduce economic losses from course closure; therefore, the objective of this research was to determine the effect of soil temperature on Prizm zoysiagrass establishment. It was hypothesized that increasing soil temperature would accelerate establishment of Prizm zoysiagrass sprigs.

2. Materials and Methods

2.1. Research Site Management and Treatment Description

This study was conducted in glasshouses at the University of Tennessee (Knoxville, TN, USA) in 2022. Each experimental unit comprised of a 7.6-L bucket (United Solutions, Leominster, MA, USA) with a height of 20 cm and inside diameters at the top and bottom of the bucket of 23 cm and 20 cm, respectively. Each experimental unit was filled with an 80:20 (v:v) mixture of silica sand meeting United States Golf Association (USGA) particle size specifications and sphagnum peat moss to achieve a uniform bulk density of 1.6 Mg m⁻³ [16]. The root zone initially contained 0.8% organic matter.

Two experimental runs were conducted in separate glasshouses during 2022. Under conditions of natural and supplemental light with a 16/8 h day/night photoperiod (PKB, Arize Element L1000 Next-Gen, Current Lighting Solutions, LLC, Cleveland, OH, USA), the average glasshouse temperature in run A was 26.2 °C and 26.6 °C in run B. Over the 49-day study period, plants received an average of 62.4 and 55.0 mol m⁻² day⁻¹ in runs A and B (SQ-500, Apogee Instruments, Inc., Logan, UT, USA).

Individual experimental units were placed in 37.9 L storage totes (Rugged Tote, Centrex, LLC, Findlay, OH, USA) filled with water to create a water bath to maintain consistent soil temperature [17,18] (Figure 1). Treatments included a “high”, “medium”, and “low” 5 cm soil temperature by heating each water bath. To achieve the high soil temperature, two 100 W aquarium heaters (SKU: HGH802, Hygger, Shenzhen Mago Co., Ltd., Shenzhen City, Guangdong Province, China) were placed in each water bath, whereas one aquarium heater was placed in water baths used to impose the medium-soil-temperature treatment. The low-soil-temperature treatment was imposed by filling baths with water devoid of an aquarium heater. In one replication within each glasshouse, the 5 cm soil temperature was recorded with an external temperature sensor (Item #3667-20, Spectrum Technologies, Aurora, IL, USA), and was logged at fifteen-minute intervals with a WatchDog 1000 Series Micro Station (Item #3688WD1, Spectrum Technologies, Aurora, IL, USA). Additionally, 5 cm soil temperature was monitored daily in each experimental unit using digital soil thermometers (#6300; Spectrum Technologies Inc., Aurora, IL, USA). The average 5 cm soil temperature for the high, medium, and low treatments were 36.6 °C, 32.1 °C, and 28.6 °C, respectively, in run A and 36.2 °C, 31.9 °C, and 27.9 °C, respectively, in run B (Figure 2). Water levels were maintained at the top edge of the water bath during each experimental run.

On 13 April 2022, 30.4 g of Prizm zoysiagrass sprigs were planted in each experimental unit, which equated to a sprigging rate of 181 m³ ha⁻¹ using the conversion of 16.6 kg sprigs m⁻³ (D. Doguet, personal communication, 31 March 2022). A companion study revealed a significant positive correlation (p < 0.0001; r = 0.99; GraphPad Prism v. 9.4. GraphPad Software Inc., La Jolla, CA, USA) between increasing sprig material mass and increasing sprig node number. This relationship was used to determine that experimental units in this study were established at approximately 16,146 nodes m⁻² (Figure S1). Sprigs were planted directly on the surface followed by sand topdressing applied to a depth of 3.2 mm. Over the first 14 days after planting, irrigation was delivered 12 times daily, totaling 7 mm d⁻¹. Beginning 14 days after planting through the conclusion of the study, irrigation was applied four times daily, totaling 5 mm d⁻¹. Prior to planting and every two weeks throughout the duration of the experiments, 2.5 g N m⁻² via complete fertilizer (20-20-20) was applied to each individual experimental unit.

2.2. Data Collection and Statistical Analysis

To objectively assess temperature effects on Prizm zoysiagrass establishment, turfgrass coverage was estimated weekly using digital image analysis [19]. The images collected by the digital camera (Canon PowerShot G12, Canon Inc., Melville, NY, USA) were rectangular, but the experimental area was round; therefore, a purple frame was placed in the images to exclude non-experimental area from each image. The frame analysis procedure in TurfAnalyzer [20,21] was then used to evaluate only the experimental area within each image for turfgrass coverage. For each experimental run, weekly assessments of turfgrass coverage lasted approximately 30 min in duration.

This study was a one-factor randomized complete block design with six replications of each soil temperature treatment. Turfgrass coverage was subjected to repeated measures analysis of variance (ANOVA) and a means separation technique (LSMEANS) in PROC GLIMMIX (SAS v. 9.4, SAS Institute Inc., Cary, NC, USA). For all data, slicing was performed in PROC GLIMMIX to identify evaluation dates (days after planting (DAP)) when treatment effects were significant. Treatment means for significant effects were separated using Fisher’s protected LSD (α = 0.05). A significant treatment by experimental run interaction was present; therefore, data for each experimental run will be presented individually.

3. Results and Discussion

The soil temperature-by-DAP interaction significantly affected turfgrass coverage in both run A (p < 0.0001) and run B (p = 0.0006;

Table 1. Analysis of variance testing the main effects and their interactions on turfgrass coverage during experimental run A and B.

Source of Variation	Run A	Run B
	P > F
	Turfgrass coverage
Soil temperature	0.16	0.08
Days after planting (DAP)	<0.0001	<0.0001
DAP × Soil temperature	<0.0001	0.0006

Note. Bolded p values indicate significant higher-order treatment interactions.

). In run A, turfgrass coverage was significantly affected by soil temperature on the final three evaluation dates (

Table 2. Turfgrass coverage of ‘Prizm’ zoysiagrass (Zoysia matrella (L.) Merr.) established in glasshouses in Knoxville, TN. Treatments included high, medium, and low 5 cm soil temperatures, which averaged 36.6 °C, 32.1 °C, and 28.6 °C in run A and 36.2 °C, 31.9 °C, and 27.9 °C in run B. Within evaluation dates, means followed by the same letter are not significantly different according to Fisher’s protected LSD (p ≤ 0.05).

Soil Temperature (°C)	7 DAP †	14 DAP	21 DAP	28 DAP	35 DAP	44 DAP	49 DAP
	Turfgrass coverage (%)
	Run A
High (36.6)	2	6	12	21	48 b	64 b	70 b
Medium (32.1)	0	3	14	36	68 a	82 a	88 a
Low (28.6)	2	4	9	33	77 a	93 a	96 a
	Run B
High (36.2)	3	5	11	24 b	55 b	74 b	87
Medium (31.9)	0	4	10	36 a	75 a	92 a	96
Low (27.9)	1	2	4	18 b	53 b	78 b	91

† DAP, days after planting.

). No differences occurred among treatments until 35 DAP, when the high-soil-temperature treatment resulted in turfgrass coverage values of 48%, 64%, and 70% at 35, 44, and 49 DAP, respectively, which were significantly lower than both the medium and low-soil-temperature treatments. The medium and low-soil-temperature treatments did not significantly differ in turfgrass coverage on any evaluation date, and the treatments averaged 92% turfgrass coverage 49 DAP compared to 70% for the high-soil-temperature treatment.

In run B, the soil temperature-by-DAP interaction significantly affected turfgrass coverage 28, 35, and 44 DAP (Table 2). On all three dates, the medium-soil-temperature treatment resulted in significantly greater turfgrass coverage than both the low and high temperature treatments by ≥12 percentage points. The low- and high-soil-temperature treatments did not differ in turfgrass coverage on any evaluation date within run B. On the final evaluation date (49 DAP), all treatments demonstrated similar turfgrass coverage values.

In both experimental runs, 90% turfgrass coverage was achieved ~44 DAP, which is faster than previously reported for Prizm zoysiagrass establishment. Carr et al. [7] observed 90% turfgrass coverage ≥55 DAP in a field study when the sprigging rate was 109 m³ ha⁻¹; however, the sprigging rate was 181 m³ ha⁻¹ in the present study. Previous research on Diamond reported accelerated establishment when increasing sprigging rate, with 182 m³ ha⁻¹ achieving 90% turfgrass coverage 42 to 49 DAP compared to 70 to 77 DAP when utilizing a sprigging rate of 91 m³ ha⁻¹ [8]. These results denote that increased sprigging rates may be required to reduce establishment duration.

The optimal soil temperature to hasten establishment varied between experimental runs. In run A, the low- and medium-soil-temperature treatments resulted in the fastest establishment of Prizm zoysiagrass, whereas the medium treatment resulted in faster establishment than all other treatments in run B. Increased establishment via the low-temperature treatment in run A may be attributed to increased water bath temperatures beginning 28 DAP (Figure 2). According to continuous soil temperature data in run A, 5 cm soil temperatures averaged 27.7 °C during the first 28 DAP but elevated to 29.8 °C from 29 to 49 DAP. While the average ambient air temperature in each experimental run was similar (26.2 °C and 26.6 °C in run A and run B), run A received greater light quantity (62.4 mol m⁻² day⁻¹) compared to run B (55.0 mol m⁻² day⁻¹). The increased thermal energy from increased light quantity in run A likely increased the temperature of the water baths used to impose the low-soil-temperature treatment.

Another factor contributing to the accelerated establishment for the low-soil-temperature treatment in run A may be the increased diurnal soil temperature amplitude (i.e., difference between daytime maximum and nighttime minimum 5 cm soil temperatures). Across the entire experimental run, the average diurnal soil temperature amplitude for the low treatment was 5.5 °C, which was numerically greater than all other treatments in runs A and B (Figure 2,

Table 3. Average daily maximum, minimum, and amplitude 5 cm soil temperature for soil temperature treatments averaging 36.6 °C, 32.1 °C, and 28.6 °C in run A and 36.2 °C, 31.9 °C, and 27.9 °C in run B. Experimental runs were conducted in glasshouses in Knoxville, TN in 2022.

Soil Temperature (°C)	Average Maximum	Average Minimum	Amplitude (Maximum–Minimum)
	Run A
High (36.6)	38.9	35.3	3.6
Medium (32.1)	33.7	31.2	2.5
Low (28.6)	31.7	26.2	5.5
	Run B
High (36.2)	37.2	35.4	1.8
Medium (31.9)	32.6	31.2	1.4
Low (27.9)	29.3	26.6	2.7

). Ivory and Whiteman [22] observed greater growth rates of tropical pasture grasses when exposed to diurnal temperature amplitude compared to constant temperature. Reduced diurnal temperature amplitude in maize (Zea mays L.), another species in the Poaceae family, linearly increased night respiration and further provided a linear decrease in plant height, total leaf area, and total biomass accumulation [23]. Additionally, goosegrass (Eluesine indica (L.) Gaertn.) has demonstrated increased germination under greater temperature amplitude, where less than 6% germination occurred under constant temperatures of 20 °C, 30 °C, and 35 °C [24]. The results from the present study imply that further research is needed to determine the effects of diurnal ambient and soil temperature amplitude on establishment and growth of zoysiagrass and other warm- and cool-season turfgrass species.

In run B, the medium-soil-temperature treatment resulted in the greatest turfgrass coverage 28 to 44 DAP (Table 2). Soil temperatures averaging approximately 32 °C at a 5 cm depth are limited to the summer months in southeastern United States locations bordering the Gulf Coast and Atlantic Ocean. Soil temperature may be a factor contributing to prolonged establishment, which will become more significant at increasing latitudes. Specifically, 5 cm soil temperatures in Knoxville, TN (35.929° N, 83.949° W) during the summer months rarely average greater than 26 °C [25]. In geographic areas where soil temperatures do not achieve 32 °C, initiating sprigging at the earliest reasonable date may be necessary to ensure complete establishment within the first growing season. Previous research has identified that zoysiagrass planted during the late part of the dormant season in transitional or subtropical regions can achieve full coverage during the first growing season [5].

A consistent result across both experimental runs was prolonged establishment with the high-soil-temperature treatment. While not measured in the current study, elevated temperature from the high-soil-temperature treatment may have increased vapor pressure deficit (VPD), which has a linear relationship with transpiration in warm-season turfgrasses [26]. Increased VPD and transpiration have been shown to reduce rooting percentages of loblolly pine (Pinus taeda L.) stem cuttings [27]. Elevated VPD while establishing zoysiagrass from vegetative sprigs may require adjustments in irrigation practices to reduce transpiration. Additionally, increased nighttime temperatures associated with the high-soil-temperature treatment likely increased respiration, which has negative impacts on plant growth [23]. These combined factors indicate that 5 cm soil temperatures continuously averaging 36 °C will likely not yield rapid establishment of Prizm zoysiagrass.

4. Conclusions

In both experimental runs, 5 cm soil temperatures averaging 32 °C resulted in the most rapid establishment of Prizm zoysiagrass sprigs. Continuous 5 cm soil temperature averaging 36 °C caused prolonged establishment in both experimental runs, potentially due to increased vapor pressure deficit and respiration. Future research should evaluate vegetative zoysiagrass establishment under different average and diurnal soil temperatures to determine if daytime soil temperatures above 36 °C can accelerate establishment if nighttime soil temperatures are reduced. The influence of VPD on the vegetative establishment of zoysiagrass sprigs should also be investigated, as VPD is commonly mitigated when vegetatively propagating horticultural crops.