WATER AND NITROGEN MANAGEMENT OF SUGARCANE GROWN ON SANDY, HIGH-WATER-TABLE SOIL

Little information exists regarding water and N fertilizer management for sugarcane (Saccharum spp.) production on Florida's high-water-tabl e sandy soils. We hypothesized that sugar yield and N-use efficiency w ould be affected by water table depth and N fertilizer application tim ing. Sugarcane (cv. CP 72-1210) was grown in >1-ha plots for three sea sons on Basinger sand (siliceous, hyperthermic Spodic Psammaquent) to determine the effects of water table depth (0.46 vs. 0.57 m), N fertil ization frequency (13 vs. 7 split applications ;for 3 yr, at 224 kg N ha(-1) yr(-1)), and Mg fertilizer rate (0 vs. 60 kg Mg ha(-1) yr(-1)) on cane and sugar yields. Annual mean high- and low-water-table differ ences were 0,13, 0.11, and 0.10 m, resulting in a 0.2 to 1.4 J kg(-1) difference in soil water matric potential at middle of the root zone, and a 0.02 to 0.11 m(3) m(-3) difference in soil water concentration i n the top 0.30 m. Three-gear mean yields for low vs. high water table were 73.7 vs. 67.9 t sugarcane ha(-1) and 9.23 vs. 8.51 t sugar ha (1) . High vs. low N fertilization frequency yielded 75.0 vs. 66.5 t sugar cane ha(-1) and 9.41 vs. 8.33 t sugar ha(-1). There were no water leve l x N fertilization frequency interactions. Where mean Mehlich 1 extra ctable Mg was 25 mg kg(-1), Mg fertilization did not affect yield, sug gesting that this Mg level should be classified in the unresponsive (' 'high'') range. Although increasing N fertilization frequency increase s the fertilization program cost, its use is justified by increased su gar yield.