UC Riverside

Irrigation scheduling based on reference evapotranspiration (ETo) multiplied by a crop coefficient (Kc) is an accepted approach for managing and conserving water applied to turfgrass. However, increasing use of recycled water that is often high in salinity warrants further examination of irrigation practices for turfgrass health and salinity management. A 2-yr study was conducted in Riverside, CA to evaluate the response of perennial ryegrass (Lolium perenne L. `SR 4550') turf to varying quality and quantity of irrigation water. A modified line-source gradient experiment was designed to alternate between distribution of potable and saline water to establish an irrigation salinity gradient (EC ~ 0.6 to 4.2 dS m-1) in between lines. Irrigation was scheduled in four separate irrigation zones perpendicular to the irrigation lines according to 80, 100, 120, and 140% ETo. Changes in turf quality (R2 = 0.30***), cover (R2 = 0.26***), and clipping yield (R2 = 0.08***) were primarily driven by the number of days that the area had been irrigated with saline water. When data were separated by irrigation amount, both time and water quality accounted for 54% and 46% of the variability (P < 0.001) in quality and cover, respectively at 80% ETo. Soil salinity (ECe), and sodium absorption ratio (SAR) were highly correlated with irrigation water quality, but not irrigation amount. Stepwise linear regression revealed that soil ECe at 20-30 cm (P < 0.05), and SAR at 10-20 cm (P < 0.001) and 20-30 cm (P < 0.01) accounted for 43% of the variability in quality and cover in August 2012. In September 2012, soil ECe at 10-20 cm (r = -0.62) and 0-30 cm (r = -0.60) had the highest correlation with turfgrass quality and cover. Regression results revealed that soil ECe at 10-20 cm (P < 0.001) and SAR at 10-20 cm (P < 0.05) accounted for 41% of the variability in quality and cover in September 2012. Our results suggest that perennial ryegrass requires irrigation scheduling above 120% ETo, irrigation water quality below ECw ~ 1.7 dS m-1, and soil salinity (ECe) below 3.8 dS m-1 to maintain acceptable quality and cover for over one year in Riverside, CA.