Ingrid Elizabeth Hersh, The Pennsylvania State University, 116 Agricultural Sciences & Industries Building, University Park, PA 16802 and Maxim J. Schlossberg, Penn State University, Dept. Crop & Soil Sciences, 116 ASI, University Park, PA 16802-3504.
Canopy phytotoxicity/desiccation resulting from foliar application of N fertilizer to golf greens can reduce aesthetic value, but is generally temporary under typical mowing frequencies. The objective of this study was to determine the efficacy of a follow-up foliar iron application in ameliorating such phytotoxic damage. Phytotoxicity was induced on Penn A-4 and Penn G-2 creeping bentgrass (Agrostis palustris L.) putting greens following foliar N applications of ammonium nitrate (NH4NO3), ammonium sulfate (NH4)2SO4, or urea (NH2)2CO; at 9.8, 19.5, or 29.3 kg ha-1 sprayed in volumes of either 407.5 or 815 L ha-1. Approximately 4 hours after treatment (HAT), soluble iron (FeCl2·4H2O) was applied at 1.2 kg ha-1 in a strip to half of all N fertilized plots. Digital images were collected 24 and 96 HAT and used to determine rel. dark green color index (rDGCI) of each strip plot. Clipping yields were collected across the 0 or 1.2 kg Fe strip plots, 168 HAT. The iron main effect significantly improved rDGCI 24 and 96 HAT across all initial N fertilizer sources or rates. However, rDGCI was significantly affected by interactions between N treatment source, rate, and follow-up iron treatment. The application of iron more effectively reversed severe phytotoxic damage associated with ammonium nitrate or ammonium sulfate than urea treatments. From 24 to 96 HAT, plots receiving higher N rates demonstrated greater improvement in rDGCI than plots treated at lesser rates. Statistical exceptions to this trend were plots fertilized with the N urea source. At all rates, N levels in clippings showed significantly less N recovery in urea treated plots compared to those treated with alternative N sources. Ammonia volatilization likely resulted from foliar applications of urea made during high temperature periods. In summary, foliar Fe treatment proved to be an effective ameliorant of bentgrass putting green phytotoxicity.