Creeping bentgrass putting greens can be a challenge to establish. High-sand-content greens mix, low water-holding capacity, and low initial nutrient content of that greens mix can inhibit rapid establishment.
Because nutrient content can be an issue in putting green establishment, superintendents often apply a range of nutrients or amendments to encourage bentgrass growth. Amendments may include organic sources, which can easily provide many of the needed essential nutrients that might be missing from the high-sand greens mix. Other materials, such as humic acids, may also be added, and this creates a mix of various substances that may or may not enhance bentgrass establishment.
The practice of adding myriad products to promote bentgrass growth led to the research question posed by turfgrass researchers at Penn State University: How do different fertilizer and soil amendment programs affect the establishment of creeping bentgrass?
To answer this question, four fertilization programs were created: (1) add fertilizer (soluble in year 1 and methylene urea in year 2); (2) add surface-applied hydrolyzed poultry meal; (3) add fertilizer (same as Treatment 1) and incorporate humate into the greens mix at construction; and (4) add surface-applied hydrolyzed poultry meal (same as Treatment 2) and incorporate that poultry meal into the greens mix at construction.
The initial putting green was constructed with a 4:1 (sand:peat volume) ratio. Fertilizer materials (surface-applied poultry meal and fertilizer) were all applied at the same nitrogen rate: 1 pound/1,000 square feet (49 kilograms/hectare) in year 1 (applied September, October and November), and 0.5 pound/1,000 square feet (24 kilograms/hectare) in year 2 (May), with 0.25 pound/1,000 square feet (12 kilograms/hectare) every two weeks after that (June-September) (year 2). Collected data included percent bentgrass cover, turfgrass quality, rooting, thatch depth and microbial activity.
For speediest establishment, it was necessary to have surface applications of the soluble inorganic fertilizer (which, in year 1, was a 19N-11P-4K product). This was especially true in the first 35 days of the experiment.
Next, in order of establishment speed, were plots in which humate had been incorporated, followed by those in which poultry meal had been incorporated. When poultry meal was not incorporated and applied to the surface alone, establishment was the slowest at almost every rating date. Establishment was slower because nitrogen from poultry meal becomes available slowly via microbial activity. All treatments had greater than 96% cover at 90 days after seeding.
Incorporating the humate significantly increased root mass, especially when compared with bentgrass from plots in which only the soluble fertilizer had been applied. Treatments with any type of poultry meal inclusion produced bentgrass with intermediate root lengths as compared with the humate + fertilizer (best) and fertilizer alone (worst) treatments. These root-mass differences disappeared as the green aged and were gone by the second year.
Other measured variables (thatch, disease presence) were less affected by treatment or were transitory in nature. The most important factor in the rate of turfgrass establishment was nitrogen availability, and the soluble nitrogen source was needed to supply that nitrogen for immediate use by the growing bentgrass.
Granular humate incorporated at construction increased root length and density, but it did not translate to improved turfgrass quality. Use of soluble nitrogen fertilizer usually did improve turfgrass quality. So, while use of granular humate materials did help root growth, soluble nitrogen fertilizer was needed to get seeded bentgrass growing.
Source: Kaminski, J.E., P.H. Dernoeden and C.A. Bigelow. 2004. Soil amendments and fertilizer source effects on creeping bentgrass establishment, soil microbial activity, thatch, and disease. HortScience 39:620-626.
Beth Guertal, Ph.D., is a professor in the Department of Crop, Soil and Environmental Sciences at Auburn University in Auburn, Ala., and president-elect of the Crop Science Society of America. She is a 20-year member of GCSAA.