Saoli Chanda1, Marilyn Sebial Dalen2, Suelen Cristina Mendonca Maia3, Payton Dupree4, Brandon White4, Pilatluk Lunliu5 and Brenda Tubana5, (1)Southeast Environmental research Center, Florida International University, miami, FL (2)School of Plant, Environmental, and Soil Sciences, LSU Agricultural Center - Baton Rouge, Baton Rouge, LA (3)Department of Crop Science, College of Agricultural Sciences, São Paulo State University – UNESP, Botucatu, Brazil (4)School of Plant, Environmental, and Soil Sciences, Louisiana State University, Baton Rouge, LA (5)School of Plant, Environmental, and Soil Sciences, LSU AgCenter, Baton Rouge, LA
The application of remote sensing technology to manage nitrogen (N) fertilizer in energy cane production is understudied. A study was initiated in 2012 at the LSU AgCenter Sugar Research Station in St. Gabriel, LA to identify vegetation indices derived from canopy reflectance readings within the red, red-edge, and near infrared (NIR) wavebands that can be used to characterize energy cane biomass and N uptake. A 2 x 4 factorial treatment structure was superimposed on 9 m x three 1.8-m bed plots using a split-plot in randomized complete block design with four replications. The treatments included two energy cane varieties (Ho 02-113 and US 72-114) and four N rates (0, 56, 110, and 224 kg N ha-1). Canopy reflectance readings were collected using a Jaz ® hyperspectral spectrometer (300 to 1100 nm) and 2- and 4-band handheld active sensor from a 1 m2 area of each plot along with chlorophyll readings before biomass cuttings were sampled. Field data collection began three weeks after N fertilization and done once a week for three consecutive weeks. The relationships among measured parameters were evaluated using regression analysis. Chlorophyll readings, N uptake, tiller number, and biomass of US 72-114 variety responded to N fertilizer only at three weeks after application (P<0.05). The relationships of vegetation indices and agronomic parameters were different between the two varieties. The near infrared to red-edge (710 nm) reflectance ratio had a weak positive relationship with biomass of Ho 02-113 (r2=0.22) and N uptake of US 72-114 (r2=0.24) while the normalized difference vegetation index computed from NIR and red reflectance readings had a better association (r2=0.40) with N uptake of both varieties. Thus far, a few vegetation indices have been identified useful for non-destructive characterization of energy cane biomass and N uptake. Future research will focus on building the sensor database and refinement of the relationships among energy cane N-related agronomic parameters and sensor based-vegetation indices.