Irrigation Salinity Effects on Tifway Bermudagrass Growth and Nitrogen Uptake

Salinity stress is becoming a more prevalent issue for turf managers due to increased use of recycled water for irrigation. While published data are available on electrical conductivity (EC) thresholds for maintaining adequate turf growth and quality, data are lacking on the relationship between increasing irrigation and/or soil EC and turfgrass nutrient uptake efficiency. The objectives of this greenhouse experiment were to evaluate the effects of five irrigation water sources (reverse osmosis, sodic potable, 2.5 dS m(-1) saline [SA], 5 dS m(-1) SA, and 10 dS m(-1) SA) and two soluble fertilizer N sources (N-15-labeled sources of ammonium sulfate and urea) on Tifway bermudagrass [Cynodon dactylon (L.) Pers. C. transvaalensis Burtt-Davy] growth responses and N uptake efficiency. Results demonstrated that Tifway bermudagrass was capable of tolerating irrigation EC levels up to 5 dS m(-1), which corresponded to final soil EC levels (at 2.5-cm depth) of similar to 2 to 2.6 dS m(-1). However, with 10 dS m(-1) irrigation (corresponding to soil EC levels of similar to 3-5 dS m(-1)), turf quality declined to unacceptable levels and N uptake noticeably declined. Also, under increasing salinity (salinity levels of 2.5, 5, and 10 dS m(-1)), urea produced superior turf quality relative to ammonium sulfate. Collectively, the results indicate that for well-watered, sand-based Tifway bermudagrass, lower N fertilization rates should be considered once irrigation EC levels exceed 5 dS m(-1) or corresponding soil EC levels at the 2.5-cm depth exceed 2 dS m(-1). Although N uptake efficiency of ammonium sulfate was greater than that of urea across all water sources in Year 1, results indicate that urea provided higher turf quality than ammonium sulfate under elevated salinity.