In‐Season Prediction of Sugarbeet Yield, Quality, and Nitrogen Status Using an Active Sensor

Abstract

Nitrogen fertilizer management of sugarbeet (Beta vulgaris L.) continues to increase in importance with rising fertilizer costs and industry payments weighted toward crop quality. Our objective was to evaluate the use of an optical sensor for assessment of in‐season sugarbeet N status, yield, and quality prediction and total N in foliage on the day of harvest. Six N fertilizer treatments, from 0 to 225 kg N ha−1, were applied at three sites in Michigan in 2006 and four sites in 2007. Normalized difference vegetative indices (NDVIs) were measured at four growing degree day (GDD) intervals in 2006, five intervals in 2007, and at harvest in both years with a red‐band active sensor. Leaf biomass and root yield were determined at harvest, and root samples were collected for determination of sucrose content and clear juice purity. The NDVI readings were useful for differentiating control treatments from fertilized plots but were not able to identify a yield response threshold until late in the season. Midseason 1200 to 1400 GDD, 1900 to 2300 GDD, and harvest NDVI values were strongly related to recoverable white sucrose per area (R2 = 0.89, 0.87, and 0.80, respectively). Harvest NDVI was strongly related to sugarbeet vegetation total N (R2 = 0.87). Active sensing during the growing season shows promise as a means to estimate root yield and recoverable sugar in sugarbeet fields. Sensing on the day of harvest may improve rotational N management by providing an indication of N return to the cropping system.