Impact of fertilizer calendar blackout restrictions and recycled wastewater irrigation on St. Augustinegrass lawns: II. Nutrient concentration in leachate and soil accumulation

Abstract

Proper management of St. Augustinegrass grown on Florida's sandy soils is critical for water quality protection, yet interactions between municipal fertilizer blackout ordinances, recycled wastewater (RWW) irrigation, and newer cultivars remain understudied. RWW often contains elevated nutrients that may inadvertently contribute to leaching, which is relevant within the realm of nutrient restriction strategies. This 2‐year field study conducted in Davie, FL, evaluated the interactive effects of irrigation source, nitrogen rates (0, 98, and 196 kg N ha ^{− 1} year ^{− 1} ), and blackout scheduling on nutrient leaching and soil nutrient accumulation in CitraBlue St. Augustinegrass. Leachate was extracted weekly via suction lysimeters and analyzed for oxidized nitrogen (NO _x ─N), nitrite, ammonium, and orthophosphate. Results identified irrigation source as a primary driver of nutrient export. RWW supplied more than 188 kg N ha ^{− 1} year ^{− 1} from irrigation alone and increased NO _x ‐N leaching two‐ to threefold relative to canal water. RWW was the sole source of orthophosphate input in this study. Additionally, RWW significantly increased soil phosphorus (P), sodium (Na), and calcium (Ca) accumulation. Notably, blackout scheduling failed to reduce total nutrient export. Under this scheduling, applications at 196 kg N ha ^{− 1} year ^{− 1} triggered peaks in ammonium and nitrite losses. Conversely, the 98 kg N ha ^{− 1} rate minimized leaching comparable to controls even under blackout scheduling. This study demonstrates that nutrient‐rich RWW is a primary driver of nitrogen and phosphorus presence in leachate and that blackout period fertilization at 196 kg N ha ^{− 1} year ^{− 1} can induce increases in nitrite and ammonium concentration in leachate.