Site-Specific Management of Nitrogen Fertilizer in Louisiana Sugarcane Production System.

The implementation of site-specific nitrogen (N) management in sugarcane production in Louisiana requires a decision tool which can account both within-field and year-to-year variation in crop growth factors. An on-site, sensor-based N decision tool has been recently developed which derived N recommendation based on sugarcane yield potential and estimate of plant-available N at the time of fertilization. A large-scale field demonstration study was established in 2013 at three locations in south Louisiana to evaluate the performance of three different N fertilizer recommendation systems: (1) farmer’s standard practice, (2) based on yield goal and soil test nitrate, and (3) sensor-based N decision tool using yield, net return to N fertilizer, and unit of N used/unit of cane tonnage produced as performance metrics. A separate study was also established to evaluate the effect of different sources (urea, ammonium nitrate, and urea-ammonium nitrate solution - surface and subsurface applied) of N applied at different rates (0, 45, 90, and 134 kg N ha^-1) on cane productivity and soil inorganic N content. Treatments from all these tests were replicated. Across sites, sensor-based N decision tool consistently obtained higher net return than the farmer’s standard practice averaging $145 ha^-1. The N recommendation based on yield goal and soil test nitrate earned the highest net return of $551 ha^-1 in one site, but lost $57 ha^-1 on another site. For two sites, the amount of N used for every cane tonnage produced was recorded to be the lowest for sensor-based N decision tool. The concentrations of nitrate and ammonium within the 30-cm soil sampling depth highly varied among N sources 21 days after application. Our results have demonstrated that the both yield goal-soil test nitrate and sensor-based N decision tool are viable approach for site-specific N management in sugarcane production in Louisiana.