Red Edge as a Potential Index for Detecting Differences in Plant Nitrogen Status in Winter Wheat

Under certain conditions normalized difference vegetative index (NDVI) has low sensitivity; therefore red-edge position (REP) has been tested as an alternative vegetative index. The objective of this study was to determine if REP could be useful for detecting differences in N status for winter wheat compared to NDVI. A spectrometer, and the SPAD meter were used to measure N status. Sensitivity to plant N response and different growth stages was found for NDVI and REP, but NDVI sensitivity tended to decrease as N rate increased and REP sensitivity tended to increase with increased N rate and advancing growth stage. Both NDVI and REP were linearly correlated at all growth stages (r2 = 0.85). REP and SPAD meter readings were highly correlated (r2 = 0.62) as were NDVI and SPAD (r2 = 0.56). Overall, REP and NDVI sensitivity at high plant biomass were similar for winter wheat.