Site descriptions and data collected.

The experiment was conducted in Summer 2015 at university research facilities in Baton Rouge, LA; Starkville, MS; Stillwater, OK; and Lexington, KY [U.S. Department of Agriculture (USDA) hardiness zones 9A, 8A, 7A, and 6B, respectively]. The soil at the Burden Center (Louisiana State University) was an Olivier silt loam [fine-silty, mixed, thermic, Typic Fragiudalf; pH: 7.3; 88 lb/acre phosphorus (P); 473 lb/acre potassium (K)]. The soil at the R.R. Foil Research Center (Mississippi State University) was a Marietta fine sandy loam (fine-loamy, siliceous, Fluvaquentic Eutrochrept; pH: 5.7; 329 lb/acre P; 341 lb/acre K). The soil at the OSU Turfgrass Research Center (Oklahoma State University) was a Norge loam (fine-silty, mixed, active, thermic Udic Paleustolls; pH: 7.2; 144 lb/acre P; 263 lb/acre K). The site was modified in 2009, and U.S. Golf Association (USGA) specification sand (U.S. Golf Association, 2004) was added and mixed to the top 20 cm of the soil profile. A soil sample was collected on 15 July 2015, and the soil texture was classified as a sandy loam according to the USDA soil textural triangle (U.S. Department of Agriculture, 2016) and consisted of 72.5% sand, 13.8% silt, and 13.8% clay. The soil at the A.J. Powell, Jr. Turfgrass Research Center (University of Kentucky) was a Maury silt loam (fine, mixed, mesic, typic Paleudalf; pH: 5.2; 448 lb/acre P; 318 lb/acre K). ‘Latitude 36’ hybrid bermudagrass sprigs for all locations were donated by Winstead Turf Farms, Arlington, TN.

Plots were established during the second week of July at all locations with the exception of Louisiana, where the study was established during the third week of July. Whole plots measured 12 × 10 ft. Granular fertilizer was applied at planting at rates of 0, 11, 22, and 44 lb/acre N with 13N–5.7P–10.8K, and then weekly at the same rates using urea (46N–0P–0K) until plots were established (≈90% groundcover measured by digital image analysis). Bermudagrass was hand-sprigged at rates of 200, 400, 600, and 800 bu/acre to cover the spectrum between low, high, and commonly recommended sprigging rates (Han and Huckabay, 2008; Relf, 2009; Samples and Sorochan, 2007). Plots were rolled after sprigging to increase sprig to soil contact, and oxadiazon (Ronstar G; Bayer Crop Science, Research Triangle Park, NC) was applied over the sprigs at a rate of 150 lb/acre. ‘Latitude 36’ was chosen for this study because of it being a new, yet highly used cultivar that exhibits excellent turf-quality characteristics, as well as its suitability to be grown at all locations of this study (Morris, 2013). Photos were taken weekly with a light box and digitally analyzed with SigmaScan Pro (Systat Software, San Jose, CA) using methods described by Richardson et al. (2001) to objectively measure plot cover. Plots were mowed twice per week with a rotary mower set at 2 inches with clippings returned. Irrigation was supplied as needed to prevent wilt. No pesticide applications were performed during the experimental period.

Statistical analysis.

The experimental design was a split-plot with four replications nested at each location. The fixed effects of sprig and N rates were the main plots and subplots, respectively. The dependent variable bermudagrass coverage was recorded weekly (Blouin et al., 2011). Rather than looking for differences across locations, the statistical design was selected to find general trends in bermudagrass establishment requirements across the southern region of the United States during suitable environmental conditions for establishing bermudagrass. Statistical analysis of bermudagrass coverage data was performed using the mixed procedure in SAS (version 9.4; SAS Institute, Cary, NC) with weekly bermudagrass coverage analyzed over time using repeated measures analysis. Means for the dependent variable bermudagrass coverage were separated according to Fisher’s least significant difference (LSD) at P ≤ 0.05 when the fixed effects of sprig rate, N rate, or week were significant at P ≤ 0.05.

The influence of nitrogen on establishment rate.

The single effects of sprig rate, nitrogen rate, and week as well as the interactions of N rate by week and sprig rate by week were all significant (α = 0.05) with regard to turfgrass coverage (Table 1). In general, as N rate increased from 0 to 44 lb/acre, bermudagrass coverage increased concurrently over the establishment period (Table 2). Interestingly, all N rates resulted in ≈90% coverage within 4 WAP indicating the aggressiveness of ‘Latitude 36’ compared with ‘Tifsport’ and ‘Tifway’ hybrid bermudagrass that typically take 5 to 7 weeks to achieve full coverage (Guertal and Hicks, 2009). Although N rate was statistically significant at almost every observation date, differences were slight (i.e., <4% difference in plot cover between high and low N rates at 4 WAP) and likely not relevant for the practitioner. In a similar work examining the effect of N and sprigging rates, Guertal and Evans (2006) also reported that increasing N rates up to 33 lb/acre N improved the establishment of ‘TifEagle’ hybrid bermudagrass. It has also been reported that shoot density of ‘Tifsport’ and ‘Tifway’ hybrid bermudagrass increased as N rates increased up to 68 lb/acre N (Guertal and Hicks, 2009). However, they found that increased shoot density did not result in an overall increase in percent cover.

Table 1.

Type 3 fixed effects for ‘Latitude 36’ hybrid bermudagrass cover affected by sprig and nitrogen (N) rates and time (weeks) at four locations in 2015.

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Table 2.

Effect of nitrogen (N) rate on ‘Latitude 36’ hybrid bermudagrass cover across four sprigging rates over a 6-week observation period at four locations during Summer 2015.

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In the current study, the results align with N rates reported by Johnson [1973 (44 lb/acre N per month)] rather than those of Guertal and Hicks (2009) [(271 lb/acre N per month)] when evaluating bermudagrass propagation by sprigs. Because all but the lowest N rate reached ≥90% coverage within 4 WAP, the use of additional N may not be warranted, especially if mitigation of potential offsite N pollution is a concern. Reduction in N rates from 44 to 11 or 22 lb/acre is supported from an economical and environmental standpoint, but also when considering that unfertilized plots exhibited improvements in coverage at each observation date with ≥90% coverage 5 WAP, the benefits of high N rates are questionable.

Sprig rate affects establishment rate.

The more important factor to accelerate bermudagrass establishment appears to be sprig rate (Table 3). The effect of sprig rate on turfgrass cover showed that increasing rates not only resulted in higher initial coverages but also maintained higher coverages until all sprig rates resulted in full coverage 6 WAP. For example, sprigs planted at the lowest rate of 200 bu/acre had initial coverage of 19.9% and achieved >90% cover 5 WAP compared with the highest sprig rate of 800 bu/acre which had 41.8% initial coverage and 95.4% cover within 4 WAP. This increase in bermudagrass coverage may be attributed to increased plant survival after planting, the possibility of a mulching effect retaining moisture in the soil, and a greater interception and use of applied N. However, as is the case with N, excessive sprigging rates do not necessarily provide proportional benefits. For example, sprigging rates of 400 and 600 bu/acre resulted in coverages of 91.3% and 94.1%, respectively, at 4 WAP compared with the highest sprig rate of 800 bu/acre at 95.4% cover. The influence of sprig rate on bermudagrass establishment may be more pronounced for slower-growing bermudagrass cultivars.

Table 3.

Effect of sprigging rate on ‘Latitude 36’ hybrid bermudagrass cover across four nitrogen rates over a 6-week period at four locations during Summer 2015.

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Turf managers are commonly under pressure to establish turfgrass surfaces as quickly as possible. Decreasing the duration of establishment not only shortens the period turfed areas cannot be used but can also potentially reduce offsite sediment loading and P losses (Mostaghimi et al., 1994). Therefore, if the goal of a turf manager is to accelerate bermudagrass coverage, on finely textured soils, it is recommended for them to increase sprig rate and apply 11 to 22 lb/acre N per week until established. However, increasing sprigging rate over 600 bu/acre results in only slight increases in cover during the establishment period and does not reduce time to full cover. As long as temperatures are suitable for bermudagrass growth and finer textured soils are used, results should be similar to those found in this study, regardless of location.

Units

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