Phosphorus Concentrations in Drainage Water in the Everglades Agricultural Area

Phosphorus in drainage water leaving the Everglades Agricultural Area (EAA) in southern Florida is alleged to be contributing to the accelerated eutrophication of Lake Okeechobee and the degradation of the Water Conservation Areas and the Everglades National Park ecosystems. Agricultural “best management practices” (BMPs) offer a means for achieving reductions in P in drainage water. Prior to developing and implementing BMPs, it is necessary to establish baseline EAA P concentrations. Baseline total P (TP) and total dissolved P (TDP) concentrations for various crop and field conditions in the EAA were determined. Thirty-six 0.7-ha plots were installed at four locations. Average TP and TDP concentrations were derived from 6 to 30 drainage events for each of five conditions between November 1988 and December 1989: sugarcane (Saccharum spp.), radish (Raphanus sativus L.), and cabbage (Brassica oleracea L.) production fields, flooded fallow fields, and drained fallow fields. Baseline TP and TDP concentrations for main farm canals and rainfall were also determined. Average TP concentrations ranged from 0.25 mg L⁻¹ for radishes to 1.03 mg L⁻¹ during the drain-down of flooded fallow plots. Total dissolved P concentrations ranged from 48 to 80% of TP. Main farm canal TP concentrations averaged 0.16 mg L⁻¹. Total P concentrations in rainfall averaged 0.07 mg L⁻¹ Total P in drainage water during 1989 for sugarcane, cabbage, and drained fallow fields were 0.72, 1.38, and 0.59 kg ha⁻¹, respectively. During the radish season, drainage water TP loading was 0.8 kg ha⁻¹. Flooded fallow fields after radishes yielded a TP loading rate of 3.82 kg ha⁻¹. Total P loading to the fields from rainfall averaged 0.70 kg ha⁻¹. Total dissolved P loading rates ranged from 25 to 60% of TP. Potential areas for BMP development and implementation for P concentration and loading reduction in the EAA include drainage rate, volume, and timing management, fertilizer use reduction, and enhanced crop rotation strategies. Florida Agric. Exp. Stn. Journal Series no. R-00906.