A Visual Method of Calibrating Nitrogen Need, Tied to Season NDVI Values.

A Visual Method of Calibrating Nitrogen Need, Tied to Season NDVI Values
For Corn and Winter Wheat

Y. Kanke, D.B. Arnall, D. Edmonds, B. England, B. Desta, and W.R. Raun

Recent advancements in sensing technologies have assisted in determining plant and soil conditions for increasing nitrogen use efficiency (NUE). The chlorophyll meter (Minolta, SPAD) has provided a good indicator of nitrogen status in actively growing plants. On the go sensing systems commercially available today can provide site-specific N management resulting in increased nitrogen use efficiency.  GreenSeeker^tm is a real time plant reflectance NDVI sensor developed by Ntech Inc. This optical sensor is used to determine plant responses stimulated by N fertilization. However, there are still limitations to extend these technologies due to high-costs, time restraints, or educational limitations. Visual evaluation of cereal crop growth, specifically symptoms of early season chlorosis has been used for centuries as a means of determining the need for added fertilizer N. The objective of this study was to establish a visual method of calibrating nitrogen need, tied to NDVI values for winter wheat, and corn. Long-term winter wheat and corn experiments were sampled with a wide range of preplant N rates.  Each corn or wheat plot was evaluated over various growth stages using a Minolta SPAD 502 chlorophyll meter, an Ocean Optics USB4000 spectrometer, hand-held GreenSeeker^tm, and digital camera. All measurements were taken from 1 meter square areas for winter wheat and 1m of row for corn.  Results from this work will include the correlation of NDVI, spectrometer, and chlorophyll meter data, in addition to the generation of printed templates with defined colors that can be used to decipher N needs, and back calibrated to NDVI and chlorophyll meter readings.