The Agronomic Use and Application of Canopy Reflectance within the Visible and Near-Infrared Wavebands and its Relation with Nitrogen Fertilization in Energy Cane Production in Louisiana

Spectral vegetation index-based models that are used to estimate yield potential are commonly developed from the relationship between early-season crop canopy reflectance readings and actual yield obtained at harvest. Plant population stand can influence cane yield potential and nutrient requirement. This study was conducted at LSU AgCenter Sugar Research Station in St. Gabriel, LA to evaluate (1) the relation between estimated early season biomass yield and the spectral vegetation indices acquired at the same time, (2) nitrogen (N) response pattern between early-season biomass production and yield at harvest, and (3) the relationship between coefficient of variation (CV) among normalized difference vegetation index (NDVI) readings and stand population of cane planted as whole stalk and billets. Treatments were applied in split plots with a randomized complete block design with four replications. Varieties (Ho 02-113, US 72-114) and N application rates (0, 56, 112, and 224 kg N ha-1) were assigned as main plots and sub-plots, respectively. Another experiment was conducted with planting schemes (whole stalks and billets) and varieties (Ho 02-113, US 72-114, Ho 06-9001, Ho 06-9002, L 01-299, and L 03-371) arranged as main and sub-plots, respectively. Biomass clippings and canopy spectral reflectance readings using Jaz® spectrometer were collected at three, four, and five weeks after N application (WAN). Results showed that early-season biomass yield and its canopy reflectance collected at the same time were correlated. Overall, the relationships between vegetation indices (VIs) and biomass were best described with quadratic model at four WAN. Reflectance from red wavelengths (670 and 690 nm) and VI computed from them consistently performed better than the reflectance from red-edge wavelengths in relating early-season biomass production. Variables collected at four and five WAN showed similar response pattern to variable N rates as with harvest. Under favorable weather, billet-planted cane produced higher initial plant population compared to whole stalk-planted cane in 2013. Negative correlation was found between CV among NDVI and plant population. Coefficient of variation among red-based vegetation indices produced better correlation with plant population than those from different wavelengths. Variety had no effect on canopy spectral reflectance.