Editor's note: The January "Verdure" column is Dr. Beth Guertal's response to comments she received from her November column about Poa annua.
So, recently I wrote a "Verdure" column that focused on the ways in which we rid ourselves of Poa annua. The article was entirely, 100 percent centered on eliminating Poa annua and viewed Poa annua with the same derision we might heap on cockroaches or toe socks.
A superintendent wrote to let me know that I was coming from the wrong direction, that in many regions Poa annua is viewed as a desirable turfgrass and that the quality of a well-maintained Poa sward is equal to any bermudagrass or bentgrass green. Suitably chastened, I told him I’d find a great article that focused on turfgrass management strategies that keep Poa hanging around, happy and healthy.
That article is a 2007 piece that examined nitrogen rate and form on the quality of a creeping bentgrass (Penn A-4)/annual bluegrass putting green. Conducted by Dr. Maxim Schlossberg of Penn State University, this two-year field study examined annual nitrogen rates of 1.4-8.3 pounds/1,000 square feet (69-402 kilograms/hectare) comprising various ratios of nitrate-nitrogen (NO3-N) to ammonium-nitrogen (NH4-N). Each nitrogen rate was prepared using combinations of ammonium nitrate and calcium nitrate or ammonium sulfate to provide an array of ammonium to nitrate ratios. All nitrogen fertilizer treatments were applied semi-monthly as liquids, and irrigated following application. To ensure sufficiency of calcium and sulfur, gypsum (CaSO4) was applied at 5.9 pounds/1,000 square feet (290 kilograms/hectare) in the fall before each study year.
Collected data included clipping yield/vigor, nutrient content in clippings, color and nitrogen uptake. The researchers evaluated the response of the combined bent/Poa mixture to nitrogen rate and form.