Many golf courses use spray applications of fertilizer for a significant portion of the total annual nitrogen applied to putting greens. A USGA-sponsored research project at the University of Arkansas evaluated the efficiency of this practice under golf course field conditions. An additional study evaluated different inorganic and organic formulations of fertilizers marketed for spray applications.
In the first study, the scientists measured the seasonal uptake of foliar-applied nitrogen (N) by ‘Penn A1’ creeping bentgrass and ‘TifEagle’ ultradwarf bermudagrass managed as putting greens. Urea was spray-applied monthly, May through September, at rates of 0.1 lbs. N per 1000 ft 2 and 0.25 lbs. N per 1000 ft2. Both grasses absorbed urea rapidly, with 24 to 67 percent of the fertilizer nitrogen entering the foliage within one hour following the spray application. The peak uptake by leaves was generally observed at four hours after the nitrogen was sprayed onto putting greens. The amount foliage absorbed was significantly reduced at higher nitrogen application rates for both grasses. When averaged across all sampling times and nitrogen rates, foliar absorption percentages were similar between the two species, ranging from 36 to 69 percent for creeping bentgrass and 38 to 62 percent for bermudagrass.
In the second study, the researchers evaluated different formulations on inorganic and organic nitrogen. The common fertilizers included urea, ammonium sulfate, and potassium nitrate, while the organic forms included three amino acids (glycine, L-glutamic acid, and L-proline). All treatments were applied to a ‘Penn G2’ creeping bentgrass putting green at 0.1 lbs. N per 1000 ft 2 in September and October, as well as in June the following year. Foliar uptake within eight hours after application ranged from 31 to 56 percent of the nitrogen applied. The nitrogen source had a significant effect on the amount of nitrogen recovered in grass leaves and shoots. Potassium nitrate absorption was lower than the other inorganic forms tested. The other forms of nitrogen were similar in their ability to supply nitrogen to the grass foliage, including the organic-nitrogen amino acid compounds. Urea was the best form of nitrogen when considering cost, efficiency, and potential for causing damage to the putting greens.
J. Chris Stiegler, Michael D. Richardson, Douglas E. Karcher, Trenton L. Roberts, and Richard J. Norman. 2013. Foliar Absorption of Various Inorganic and Organic Nitrogen Sources by Creeping Bentgrass. Crop Science, 53:1148-1152.