Improving nitrogen management in sugarcane production of the mid-South using remote sensing technology

In Louisiana, current N rate recommendations for sugarcane production are based on multiple year N response trials and refined based on soil and crop variables. Without accounting for current growing conditions, recommendations can potentially lead to over- or under-application of N. The objectives of this research were to 1) determine the ability of an in-season response index value (RINDVI) to estimate sugarcane yield response index (RIHarvest), 2) determine if sugarcane yield potential could be determined using normalized difference vegetative index (NDVI), and 3) estimate the optimum N rate and application timing for sugarcane production in Louisiana. Experiments were established in St. Gabriel and Jeanerette, LA from 2008 through 2011. A GreenSeeker® hand-held optical active sensor was used to obtain NDVI readings for all studies. Fertilizer N was applied as urea ammonium-nitrate (UAN, 32-0-0) at the rate of 0, 45, 90, and 135 kg N ha-1 for most experiments with application timings ranging from early-April through late-May. This study showed that NDVI could be used to accurately estimate both sugarcane RI and yield potential (YP). A RI value was determined using a traditional method, comparing non-limiting N to an unfertilized treatment, and modified method, comparing all N fertilized treatments to an unfertilized treatment. There was a strong relationship between RINDVI and RIHarvest for cane tonnage and sugar yield using both methods. Additionally, NDVI values demonstrated the ability to estimate sugarcane yield potential in-season. This relationship was improved when NDVI was adjusted using climatic variables. An additional study was established to investigate the N rate and application timing on sugarcane production. Fertilizer rate showed a significant positive effect on sugarcane yield for two of three experiments. For these experiments, critical N rates were substantially lower than the current N rate recommendations. The effect of application time was not as pronounced, with only the second stubble sugarcane crop in 2011 showing a significant decrease in sugarcane yield when N fertilization was delayed. Overall, the use of remote sensing principles shows promise in Louisiana sugarcane production. However, limitations such as timing of sensing will need to be overcome prior to implementation