AGRICULTURAL BMPS FOR PHOSPHORUS REDUCTION IN SOUTH FLORIDA

Four sets of eight or twelve 0.7 ha plots, designed for sail and hydra ulic uniformity, were used to screen potential ''Best Management Pract ices'' (BMPs) for reducing total phosphorus (TP) concentrations and lo adings in the Everglades Agricultural Area (EAA) of south Florida. The four production systems and their alternatives (treatments) studied w ere: (I) sugarcane (interspecific hybrids of Saccharum sp,) versus dra ined fallow plots; (2) fast versus slow drainage rates for sugarcane; (3) rice (Oriza sativa L.) in rotation following radishes to serve as a P filter crop versus traditional flooding fallow; and (4) banding ph osphorus (P) fertilizer at 50% of the soil-test recommendation rate fo r cabbage (Brassica oleracea L.) versus full-rate broadcast applicatio ns. The study showed that there were no differences in P concentration s in drainage water between sugarcane and drained fallow fields. Annua l P loading to the plots in rainfall and irrigation water (0.63 kg TP ha(-1)) exceeded the P loading of drainage waters (0.52 kg TP ha(-1) f or sugarcane and 0.59 kg TP ha(-1) for drained fallow plots). Slow dra ined sugarcane plots exhibited significantly higher TP concentrations than the fast drained plots. However, TP loads were significantly high er (0.97 kg ha(-1)) for fast drained plots than for the slow drained p lots (0.67 kg ha(-1)). Rice as a P filter crop following radishes redu ced TP concentrations and loadings. Finally, banding P fertilizer at a reduced rate for cabbage reduced TP concentrations compared to those for broadcasted P at the full recommended level. Total phosphorus load ings in drainage water were 1.17 kg ha(-1) for banded and 1.38 kg ha(- 1) for broadcast treatments. A total of 2.30 kg TP ha(-1) entered the plots in rainfall and irrigation water. All treatment TP loadings leav ing the plots in drainage wafer were close in magnitude to TP loadings to the plots, even under heavy fertilization. This indicates that the EAA system is currently a net assimilator of P.