MULTIYEAR RESPONSE OF SUGARCANE TO CALCIUM SILICATE SLAG ON EVERGLADES HISTOSOLS

Plant crops of sugarcane (Saccharum spp.) grown in the Everglades respond to calcium silicate slag. Substantial cost is associated with application of slag. Thus, it is important to know whether yields of successive ratoon crops of sugarcane respond to residual soil Si applied as slag. Our objective was to determine the long-term response of sugarcane grown on a Terra Ceia muck (euic, hyperthermic Typic Medisaprist) at two locations in the Everglades Agricultural Area to slag applied (0, 2.5, 5, 10, 20 Mg ha-1) before either a rice (Oryza sativa L.)/sugarcane rotation or immediately before sugarcane. Slag increased cane and sugar yields as well as tissue Si concentrations. Application of 20 Mg slag ha-1 increased cumulative cane yields as much as 39% and sugar yields as much as 50% over the three crop years. Yield response to slag was generally greater from application immediately prior to sugarcane planting than to the preceding rice rotation crop. Without slag, ratoon yield production decreased as much as 45% in cane and 50% in sugar, whereas with slag, yields decreased only 28% in cane and 29% in sugar. Our data indicate that the critical level for leaf Si may be greater than the previously reported value of 10 g kg-1, and that reduced yields in ratoon crops vs. plant crops were associated with lower Si levels. Consequently, more extensive Si deficiencies may exist in the Everglades than were previously considered. Other yield-limiting factors such as low soil Mg concentrations were also shown to contribute to the decline of sugarcane ratoon yields.