Figure 4. Quadratic-plateau functions describing the relationship between alfalfa yield and normalized difference vegetation index (NDVI) as measured by the GreenSeeker (NDVIGS) and FieldScan (NDVIFS). Canopy reflectance measurements were made 1 d before each of the five harvests during 2005. Observations for a given harvest consist of the mean VI and total plot yield measured from each plot (n = 80).