Considerable small-plot research has evaluated sensor-based N fertilization of winter wheat. However, little work has been done using commercial-scale equipment on large plots. The objective of this study was to evaluate the GreenSeeker RT200 for making sensor-based, variable-rate N applications to winter wheat in Virginia. The study was conducted at six sites in the Coastal Plain of Virginia in the spring of 2005. Plot size was 18 m wide by 90 to 150 m long. Topdress N was applied to winter wheat using a Spra-Coupe applicator with an 18-m boom, which was equipped with a GreenSeeker RT200 variable-rate spray system. The experimental design was a RCB that included nine treatments replicated four times. Specific treatments included two variable N rate applications determined using the GreenSeeker, two single N rates based on tissue tests or GreenSeeker-based yield estimates, and a range of five predetermined fixed rates. Results discussed will include grain yield, accuracy of GreenSeeker-based N rates, and our overall assessment of the RT200.
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