Improving Nitrogen Management Strategies in Louisiana Sugarcane Production Systems.

Proper nitrogen (N) management is essential to optimize crop production. This study was conducted to evaluate different N fertilizer management strategies to improve N use efficiency and yield in sugarcane production in Louisiana. The experiment was arranged in a randomized complete block design with four replications consisted of different N rates (0, 45, 90, and 135 kg N ha^-1) and sources (urea-46%N, ammonium nitrate [AN]-34% N, and UAN solution-32% N [dribbled and knifed-in]) as treatments. Sensor readings were taken to validate the sugarcane yield potential prediction and response index (RI) models based on normalized difference vegetation index (NDVI). Soil nitrate(NO₃^-) and ammonium (NH₄⁺) at 0-15 and 15-30 cm depths were also measured at different days after N fertilization (DANF). At the grand growth stage, plots which were knifed-in with UAN showed a more even distribution of NO₃^- and NH₄⁺ compared to urea- and AN-treated plots for both depths. The highest sugarcane yield was achieved from plots treated with 90 kg N ha^-1 as UAN knife-in and 135 kg N ha^-1 as AN. Our results also showed that both yield potential prediction models established in 2012 and 2015 could be used to estimate sugar and cane yield using NDVI readings collected at 21 (r²=0.30 and r²=0.51) and 60 (r²=0.41 and r²=0.52) DANF, respectively. Both RI and modified RI models demonstrated a better level of precision when RI was predicted at 60 DANF (r²=0.30) for both cane and sugar yield compared to 21 DANF (r²=0.15). The outcomes of this study demonstrated the effectivity of UAN knife-in as N source and validate the current N rate recommendation for sugarcane. Several limitations of the models used for predicting the components of remote sensor-based N recommendations for Louisiana sugarcane production were revealed and should be addressed in future studies.