SUGARCANE RESPONSES TO N FERTILIZER APPLICATION ON CLAY SOILS

Sugarcane fertilization practices have been developed for the Rio Grande Valley of Texas based on numerous studies; however, few have been conducted on clay soils. Nitrogen has been found to be the primary nutrient needed, and responses to N fertilization have been limited in the plant-cane crop and increase incrementally in succeeding ratoons to its highest level in the second and following ratoons. This study was conducted to evaluate the effect of rate and timing of N fertilizer application on sugarcane growth, and to determine optimum fertilization practices for sugarcane yield on clay soils. As in previous studies, responses to N application did not occur in the plant cane crop, but were observed in the first through third ratoons. Increasing rate of N application improved stalk population, stalk growth rate, leaf area index, cane yield and sugar yield. Early N application resulted in depletion of available N before full growth potential had been reached, possibly to microbial immobilization or leaching. Late fertilizer application caused a loss of early growth, an effect that was mostly, but not entirely, compensated for by later growth. Soil NO3 -N levels varied little even though yield responses to N fertilization indicated that there were some dramatic differences in soil N availability and residual levels. Increasing N application had detrimental effects on sugarcane juice quality, but the magnitude of the effects were small compared to increasing cane growth responses, therefore sugar yield continued to increase as N application increased. Early fertilizer application resulted in lower sugar yield due to lower cane yield, while late fertilizer application resulted in lower sugar yields due to lower juice quality rather than any loss in growth. Nitrogen fertilizer application to sugarcane on clay soils in subtropical South Texas is not required on plant cane crops, and should be at least at or above the level of 224 kg ha -1 used in this study in ratoon crops. Timing of a single application should be in March or April, or split into 2-3 applications on clay soils. YIELD COMPONENTS OF SUGARCANE SUBJECTED TO FLOOD AT PLANTING 1 C.W. Deren and R.N. Raid University of Florida/IFAS Everglades Research and Education Center Belle Glade, FL 33430 cwd@gnv.ifas.ufl.edu