Changes in Soil Inorganic Nitrogen, Leaf Tissue Nitrogen, Yield and Primary Components of Sugarcane in Response to Varying Source and Rate of Nitrogen Fertilizer.

Louisiana is one of the few sugarcane-producing states in the US and has the largest production area with more than 170,000 hectares. The common source of nitrogen (N) fertilizer in the region is urea-ammonium nitrate (UAN, 28-32% N) solution and little is known about the performance of other N sources. The study was established in 2013 at LSU AgCenter Sugar Research Station in St. Gabriel, LA to evaluate the effect of different N sources (urea-46%N, ammonium nitrate (AN)-34%N, polymer-coated urea (PCU), and UAN solution-32% N (dribbled and knifed-in) applied at different rates (0, 45, 90, and 134 kg N ha^-1) on sugarcane productivity, and soil inorganic N content. Soil samples (30-cm depth), leaf tissue samples and sensor readings were collected at one, two, four, and eight weeks after N fertilization (WANF). In 2014, the application of UAN (knife-in) at 90 kg N ha^-1 increased cane tonnage by 3 Mg ha^-1 and sugar yield by 335 kg ha^-1 compared to the check plot. Reduction in theoretical recoverable sugar was observed for plots which received higher N rates (90 or 134 kg N ha^-1) using urea, AN, and PCU. In 2015 across sampling dates, soil inorganic (nitrate + ammonium) content and NDVI readings significantly increased with increasing N rates. At one WANF, urea and AN-treated plots had higher inorganic N content (+71 kg N ha^-1) than those plots treated with UAN and PCU. At two WANF, UAN-dribbled-treated plots produced almost 10 kg N ha^-1 more than urea-treated plots. On the other hand at four WANF, PCU-treated-plot maintained the highest amount of inorganic N content (40 kg N ha^-1) compared to all N-treated plots. This study showed a significant positive response on yield and quality of sugarcane using UAN knife-in as a source of N application in Louisiana production system.