Impact of fertilizer calendar blackout restrictions and recycled wastewater irrigation on St. Augustinegrass lawns: I. Turfgrass performance and tissue nutrition

Abstract Florida's urban landscapes increasingly rely on recycled wastewater (RWW) for irrigation and concomitantly face restrictive fertilizer blackout periods to address concerns about nonpoint source pollution. A 2‐year field study was conducted in Davie, FL, to evaluate the performance of CitraBlue St. Augustinegrass ( Stenotaphrum secundatum [Walter] Kuntze) under RWW versus canal water (CW) irrigation, three nitrogen (N) rates (0, 98, and 196 kg N ha − 1 year − 1 ), and seasonal fertilizer blackout restrictions. RWW irrigation acted as a significant nutrient source, maintaining acceptable turf quality (>6) and greater percent green cover even in nonfertilized controls, whereas nonfertilized CW turfgrass failed to meet acceptable quality standards. Sensor data (normalized difference vegetation index and dark green color index) corroborated visual ratings, showing that RWW consistently enhanced turf color and density compared to CW, particularly during the first year. Volumetric water content was ∼20% greater in RWW turfgrass compared to CW turfgrass, likely due to altered soil chemistry from dissolved solutes or increased electrical conductivity in the RWW source. Tissue analysis revealed that RWW increased leaf nitrogen (N), potassium (K), magnesium (Mg), and boron (B) concentrations. Notably, the 98 kg N ha − 1 year − 1 rate was generally sufficient to maintain quality in CW turfgrass, performing similarly to the 196 kg rate. Fertilizer blackout scheduling led to no impact on turf performance. Results indicate that nutrient‐laden RWW can effectively offset fertilization requirements for CitraBlue, and current N recommendations may be reduced without sacrificing landscape aesthetics in south Florida.