Irrigation of High Maintenance Turf Using the Arizona Department of Water Resources Water Duty: Evaluation of Turf Performance and the Potential for Soil Salinization

Water is an essential resource that requires careful management at all golf courses located in southern Arizona. The Arizona Department of Water Resources, through its enforcement of irrigation water duties, is forcing the golf industry to reduce water usage. The objective of this study was to evaluate turfgrass performance and the potential for soil salinization, when high maintenance desert turf systems are irrigated in accordance with the present Tucson area water duty of 1.4 ha-m/ha/yr (4.6 ac-ft/ac/yr). Two large weighing lysimeters supporting year-round turf systems consisting of bermudagrass (Cynodon dactylon x transvalensis (L.) pers.) overseeded with intermediate ryegrass (Lolium multiflorum x perenne) were irrigated at rates not to exceed the ADWR water duty using either low salinity (EC = 0.25 dS/m) groundwater or higher salinity effluent water (EC = 1.0 dS/m). Irrigation treatments were initiated in August 1997 and continued through September 1998 and consisted of applying water daily at rates set by applying appropriate crop coefficients to values of reference evapotranspiration generated by an on-site weather station. Soil moisture and salinity regimes were monitored weekly using the lysimeter subsurface sampling system and time domain reflectometry (TDR). Water percolating below the root zone was quantified and sub-sampled to facilitate assessment of leaching fractions and total lysimeter salt balance. For the year ending 30 Sept. 1998, each lysimeter received —1729 mm (68 in.) of water comprised of 1296 mm (51 in.) of irrigation water and 433 mm (17 in.) of precipitation. Turfgrass evapotranspiration (ET) totaled 1419 mm (56 in.) for the lysimeter irrigated with groundwater (east lysimeter) and 1466 mm (58 in.) for the lysimeter irrigated with effluent (west lysimeter). Approximately 421 and 311 mm of drainage water was removed from the east and west lysimeters, respectively, establishing leaching fractions of 0.24 in the east lysimeter and 0.18 in the west lysimeter. Salts accumulated in both lysimeters over the course of the study; however, the substantial amount of drainage did not allow for salts to accumulate to harmful levels. Turfgrass performance, as quantified by turf quality and growth was acceptable or better during most months of the study. Crop coefficients (Kcs) were slightly higher than previous years, however, Kcs compared favorably to previous research at the study site. Summer Kcs averaged 0.79 and were significantly higher than winter Kcs that averaged 0.73. Turf irrigated with effluent produced better quality turf and used slightly more water than turf irrigated with groundwater. These data indicate that the present ADWR water duty of 1.4 ha-m/ha/yr (4.6 acre-ft/acre/yr) is adequate to replace turfgrass evapotranspiration and provide for leaching of salts when rainfall exceeds normal amounts, assuming no water loss due to irrigation and plumbing inefficiencies.hydrology collectio