MODELING OF SUGARBEET QUALITY VARIABLES FROM CANOPY SPECTRAL INDICES IN A FERTILITY TRIAL
Sugarbeet quality varies inversely with N fertility, while gross yield varies positively with N. Existing models of 
yield from remotely sensed data do not consider crop quality. A fertility trial was used as the basis for a canopy reflectance 
study to correlate quality variables to canopy characteristics. Sugarbeet canopy reflectance and radiance were measured with 
a portable spectroradiometer, and from airborne images of the trial plots. Canopy data were collected five times from early 
August to early October of 1999. Linear regression models were used to correlate canopy indices to sugarbeet quality 
variables on each date. Both a green NDVI and the conventional NDVI indices showed strong correlation to recoverable 
sucrose concentration in sugarbeet roots. Correlations to harvest quality in October were highest in spectral measurements 
taken in early to mid–August. Other quality variables including root concentrations of sodium, potassium, and amino–N were 
poorly correlated to spectral properties of the canopy. The results suggest that a single image of a field in August could provide 
spatial indication of variability in root quality.