Reducing Drainage Phosphorus Loads through Rice Cultivation in South Florida.

Phosphorus concentration is an important factor of farm drainage water in the Everglades Agricultural Area in south Florida and rice cultivation may reduce P concentration through plant uptake and particulate settling. This two-year study is  conducted to assess the impacts of four water management schemes on outflow water quality, rice yield, and rice water weevil infestation. Four water level treatments: 15 cm continuous flood, 15 cm continuous flood with midseason drawdown, 5 cm continuous flood, and 5 cm continuous flood with midseason drawdown, and two rice cultivars: Cheniere and Taggart, are tested in a 2.4 ha split-plot experimental design with four replications. Phosphorus (P) concentration is measured in water samples of inflows and outflows of each experimental plot. First year results have shown the highest P concentration reduction (58%) in 15 cm continuous flood and lowest reduction (39%) is in 5 cm midseason drawdown, with an overall average reduction of 46%. Rice grain yield was not significantly different between treatments; average yield was 4.6 Mg ha^-1. Rice water weevil larval density in the 15 cm flood was significantly higher (39%) than 5 cm flood. First year results show that growing flooded rice under shallow water level appears to improve water quality and reduce rice water weevil infestation. A single midseason drawdown can potentially be used to conserve 3600 m³ ha^-1 of water per day without significantly decreasing rice yields and water quality.