Remote sensing of sugarbeet canopies for improved nitrogen fertilizer recommendations for a subsequent wheat crop

Rerum to soil of high N, green sugarbeet (Beta vulgaris L.) tops, but not the rerum of low N, yellow to yellow-green tops, reduces the magnitude of N-fertilizer responses for the following crop. Twelve N fertilizer trials with spring wheat (Triticum aestivum L.) were established at sites with late- season 'green' (8 sites) or 'yellow' (4 sites) sugarbeet canopies the previous year. Late-season, aerial color photographs of sugarbeet fields and global positioning system (GPS) technology were used to locate the experimental sites. Based on the soil NO₃-N test customarily used in the Northern Grain Plains, N fertilizer responses were expected at 11 of the 12 sites. However, no significant grain-yield responses were obtained at the eight antecedent 'green' sugarbeet sites. Expected yield and grain-N responses were obtained at the four antecedent 'yellow' sites. In contrast to the usual soil NO₃-test, remote sensing of the previous sugarbeet crop resulted in successful prediction of N-fertilizer responses at all 12 experimental sites. Application of N fertilizer at the 'green' canopy sites increased the likelihood that excess soil NO₃-N would be present after the wheat harvest. A precision farming technique, involving remote sensing of late-season sugarbeet canopies, use of GPS technology, and use of variable rate N-fertilizer application is recommended for a wheat crop following sugarbeet.