Relationships Between Spectral Reflectance and Agronomic Parameters in Three Different Sugarcane Varieties.

Remote sensing technology is a useful tool to investigate spatial and temporal variability in crop and field for better nutrient management. The distinct differences in geometrical structure among sugarcane varieties may alter the ability of spectral reflectance in estimating biomass or N uptake. Variety x N trials were established in 2009 in St. Gabriel and Jeanerette, LA to evaluate the changes on canopy reflectance in relation to sugarcane biomass production and N uptake at different N application rates, and to establish the quantitative relationships of spectra vegetation indices to agronomic parameters of sugarcane varieties with different canopy structure. Treatments included three cane varieties L99-226, L 01-283 and HoCP 96-540, and four N rates at 0, 45, 90 and 134 kg ha^-1. Canopy reflectance readings and biomass were collected at three sampling dates: 3^rd, 4^th and 5^th week after spring N fertilization. The relationships between spectral reflectance and agronomic parameters were different among varieties. Spectral reflectance of variety which has planophile canopy (droopy) structure  had weak relationships to both biomass and N uptake compared with variety which has erectophile canopy (erect) structure. The sensitivity of spectral reflectance with changing agronomic parameters tends to decrease as plant biomass production increases.