Water and Nitrogen Management Effects on Water and Nitrogen Fluxes in Florida Flatwoods

The effects of water and fertilizer best management practices (BMPs) have not been quantified for groundwater nitrogen (N) beneath seepage irrigated vegetable fields with shallow water table environments. This effect was evaluated by a 3-yr study conducted in the Flatwoods of south Florida for watermelon (Citrillus lanatus cv. Mardi Gras and Tri-X 313) and tomato (Solanum lycopersicum cv. BHN 586) using three treatments of water and inorganic fertilizer N (N(fert)) rates: (i) high fertilizer and water rates with seepage irrigation (HR), (ii) recommended fertilizer and water rates (BMP) with seepage irrigation (RR); and (iii) RR with subsurface drip irrigation (RR-SD). These treatments were implemented on six hydraulically isolated plots. The N(fert) rate treatments for high (HR) and recommended (RR and RR-SD) were based on a grower survey and BMP recommendations, respectively. Water applied, water table depth, and soil moisture content were regularly monitored for each treatment. Plant, soil, and groundwater N sampling and analyses were conducted for each season of the 3-yr study. The average water applied in HR (187 cm) was greater than RR (172 cm) and RR-SD (94 cm). Soil N maintained in crop beds for HR was significantly higher than RR and RR-SD. Soil solution analyses showed that N leached beneath HR (112 mg L(-1)) was greater (p = 0.053) than RR (76 mg L(-1)) and RR-SD (88 mg L(-1)). Shallow groundwater concentrations of dissolved inorganic nitrogen (NH(3)-N + NO(3)-N) were higher (p = 0.02) in HR (37 mg L(-1)) compared with RR (15 mg L(-1)) and RR-SD (19 mg L(-1)). Decreased N(fert) and water table levels can improve groundwater quality by reducing N leachate in shallow water table environments with seepage irrigated vegetable production systems.