Yumiko Kanke, School of Plant, Environmental, and Soil Sciences, Louisiana State University, Baton Rouge, LA, Brenda Tubana, School of Plant, Environmental, and Soil Sciences, Louisiana State University AgCenter, Baton Rouge, LA, Marilyn Sebial Dalen, School of Plant, Environmental, and Soil Sciences, LSU Agricultural Center - Baton Rouge, Baton Rouge, LA, Josh Lofton, Plant and Soil Science, Oklahoma State University, Stillwater, OK and Howard Viator, Sugar Research Station, LSU AgCenter, St. Gabriel, LA
Since sugarcane is a semi-perennial crop, its nitrogen (N) recommendation is commonly refined based on crop age and soil texture in Louisiana production systems. However, this method can over- or underestimate cane N rate requirements due to temporal and spatial variability. Several researchers have demonstrated the use of mid-season plant N response to refine N rate recommendation. The objective of this study was to evaluate and relate the early-season response to N fertilization (RI) of select agronomic variables (dry biomass, tiller number, and canopy height) to RI of measured sugar yield at harvest of three sugarcane varieties (HoCP 96-540, L 01-283, and L 99-226). A variety x N (0, 45, 90 and 135 kg N ha-1) trial was established at the LSU AgCenter Sugar Research Station in St. Gabriel and New Iberia Research Station in Jeanerette, LA from 2010 to 2012. Biomass, tiller number, and %N were measured once a week for four consecutive weeks from three weeks after N fertilization (WKN). At harvest, sugar yield was collected and its N response was compared with mid-season measured agronomic parameters. Nitrogen response of sugar yield was highly variable and high N supply did not necessarily translate to high sugar yield and vice versa. The positive correlations between N response of agronomic variables (sugar, r = 0.7, and cane, r = 0.69) collected at 5 WKN and N response of sugar and cane yield at harvest were considered notable. Sugar and stalk yield increase due to N was also correlated to RIN% at 4WKN. The findings of this study demonstrated the importance of projecting N response in sugar yield and the potential of using N responses of agronomic variables measured early in the season for refining N rate recommendation.