REFLOOD TIMING FOR RATOON RICE GROWN ON EVERGLADES HISTOSOLS

Rice (Oryza sativa L.) ratooning is commonly practiced in the Everglad es Agricultural Area of southern Florida, yet optimum length of the dr ained period between main and ratoon crops has not been determined. Re search was conducted to determine the effect of length of drain period at main-crop harvest on ratoon rice productivity on an Everglades His tosol. Our research was conducted in 250-L (0.95 m height, 0.58 m i.d. ) custom-made water control lysimeters filled with a Pahokee muck soil (euic, hyperthermic Lithic Medisaprist). Ratoon reflood timing treatm ents were 0, 5, 15, 25, 35, and 45 d drained beginning at main-crop ma turity. Ratoon-crop grain yield exhibited a significant quadratic resp onse to length of drain period with maximum grain yield produced at 28 d drained. Ratoon panicle number was not affected by reflood timing, but quadratic responses to length of drain period were observed for gr ain number and 1000-grain weight. We propose that the resultant effect of reflood timing on ratoon grain yield was the combined responses to increasing mineral N supply and increasing water stress associated wi th delayed reflooding. For drained durations <28 d, the beneficial eff ects of increased mineral N supply resulting from organic matter oxida tion resulted in a net increase in ratoon-crop yield. Conversely, for drained periods >28 d, the detrimental impact of prolonged water stres s dominated the response to reflood timing and ratoon rice yields decl ined.