Riviera bermudagrass (Cynodon dactylon) is a seeded cultivar released in 2001. This bermudagrass produces a high-quality, moderately fine-textured and dark green turf suitable for golf courses, sports fields and lawns.
Previous research in the southern U.S. region has demonstrated that a late-season nitrogen (N) application on bermudagrass enhances turf color and spring green-up. In these southern U.S. locations, the winter environmental conditions are considered mild and not as cold compared to the transition zone or more northern climates in the U.S. Riviera bermudagrass has demonstrated very good cold tolerance compared to traditional common- and hybrid-types of bermudagrasses, and therefore Riviera is considered suitable for use in the transition zone.
Would late-season N applications improve Riviera bermudagrass color and spring green-up in a transition zone environment with cold winters? Researchers at Kansas State University (Manhattan) evaluated several N fertilizers for their influence on Riviera bermudagrass autumn color and spring green-up during a winter when significant freezing injury occurred.
This field study was conducted on a silty clay loam soil with pH 6.9, on a mature stand of Riviera bermudagrass. The site was mowed two to four days per week with a triplex mower at a height of 0.312 inch (0.792 centimeter).
All N fertilizers were applied as granular products, and the treatments were randomized and replicated according to traditional methods for a turf field study. The N fertilizer treatments were: urea (46% N-0% P2O5-0% K2O); three experimental humic acid and poly-coated fertilizers containing 44% urea-N; six stabilized fertilizers containing 44% urea-N; two poly-coated/sulfur-coated fertilizers with 44% urea-N; and non-fertilized bermudagrass for comparison.
These fertilizer treatments were applied in late August and again about 30 days later in September. All fertilizer treatments were delivered at the rate of 1 pound nitrogen per 1,000 square feet (49 kilograms nitrogen per hectare) for each application timing.
Test plots were evaluated visually for turfgrass color every two weeks beginning in late August at the start of the field study. Plot area with green turf cover was evaluated visually in April and May.
What did the researchers observe? Low monthly air temperatures during the winter months were: 9 F (minus 13 C) in November, 10 F (minus 12 C) in December, minus 6 F (minus 21 C) in January, 5 F (minus 15 C) in February and minus 2 F (minus 19 C) in March. Despite the potential for winter injury from those cold environmental conditions, all N fertilizer applications were positively correlated with turf color ratings in the autumn months and green cover the following spring.
With no fertilizer applied, the bermudagrass had only 10% green cover in May. All 11 fertilizers produced a range of 19% to 44% green cover by early May. Bermudagrass treated with urea only had 30% green cover. When it comes to late-season application of nitrogen fertilizer to bermudagrass, “good old-fashioned” urea alone was as good as those other fertilizers for spring green-up.
In this field study, the observed bermudagrass winter injury was attributed to cold air temperatures and not the fertilizer applications. Keep in mind, this field study was conducted at a site where bermudagrass was contending with very cold, below-freezing air temperatures in the autumn and winter months.
The results of this study indicated a positive correlation between bermudagrass color in October (~autumn season) and green coverage in May (~spring season). The researchers concluded that late summer and/or early autumn N fertilizer applications may have the potential to enhance late-season bermudagrass color and encourage spring green-up with less winter injury in the upper transition zone.
This research was supervised by Jack Fry, Ph.D. He received GCSAA’s Outstanding Contribution Award and recently retired from a distinguished career at Kansas State University. He co-authored “Applied Turfgrass Science and Physiology” (2004), the premier textbook on the topic of turfgrass physiology. More importantly, he is one of the nicest human beings in our turf industry. Best wishes, Dr. Fry!
Source: Goldsby, A., J. Fry and M. Chhetri. 2022. Evaluation of late-season nitrogen source application on autumn color and winter injury of ‘Rivera’ bermudagrass in the upper transition zone of the United States. International Turfgrass Society Research Journal 14:565-568.
Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 24-year member of GCSAA.