NITROGEN FERTILIZATION OF SUGARCANE ON A SANDY SOIL: I. YIELD AND LEAF NUTRIENT COMPOSITION

The determination of optimum N fertilization rates for sugarcane (Saccharum spp. hybrids) on Florida sandy soils has been limited to a few studies. The objective of this study, conducted during 1999-2003 at the Southwest Florida Research and Education Center, UF-IFAS, at Immokalee, FL (27°25 ' N, 81°25 ' W), was to determine the response of sugarcane cultivar CP 78-1628 grown on a sandy soil to varying N rates. Three rates of N fertilizer (170, 280, and 390 kg N ha-1 yr-1) were evaluated. The N fertilizer rates were surface applied next to the row in four split applications at 8-wk intervals between March and September. Sugarcane leaf samples were collected for nutrient analysis from each plot, between May and October. Samples were taken 4.5 and 4.0 wk following the latter three split applications of fertilizer in the first ratoon and second ratoon crops, respectively. Nitrogen concentration was obtained in Kjeldahl digests. Phosphorus, K, Ca, Mg, Zn, Mn, Cu, Fe, B, and Na were determined by ashing ground samples, dissolving the ash in HCl and filtering. Concentrations of elements in the filtrate were determined at the Analytical Research Laboratory (ARL), UF-IFAS, at Gainesville, FL, by inductively coupled plasma (ICP) or atomic absorption spectrophotometry (AAS) in combination with colorimetric analysis for P. Leaf macro and micronutrient concentrations were not affected by the N rates. Sugarcane and sugar yields also were not affected by N fertilizer rates greater than 170 kg N ha-1 yr-1. Only stalk weight in the second ratoon crop approached a significant slope for N rate (g stalk-1 = 0.51 kg N ha-1 yr-1 + 515; r2 = 0.25, P = 0.096)