Douglas L. Kieffer, Spectrum Technologies, Inc., Plainfield, IL and Harold F. Reetz Jr., 107 S. State Street, Suite 300, Reetz Agronomics, LLC, Monticello, IL
One parameter used to help compute sidedress nitrogen recommendations is leaf greenness, which is a proxy for chlorophyll content, and thus plant nitrogen status. There are a number of optical tools that use pre-selected wavelengths of light in the red and infrared bands and generate a greenness index (SPAD number, NDVI, ...). Recent work has shown that color images taken with digital cameras can be processed with PC-based software to produce a Dark Green Color Index (DGCI) that correlates well with existing indexes. Proper color processing requires a neutral (pink background) with yellow and green color standards to properly account for different light levels. The GreenIndex system adapts this technology as an App for the iPod, iPhone, iPad. DGCI results are available immediately and can be geo-referenced using the device’s internal GPS receiver. Data transfer is accomplished via an attached e-mail file. The GreenIndex provides a relatively low cost alternative for estimating relative N status of plants. The resulting DGCI can be calibrated to guide sidedress and other in-season supplemental N fertilizer applications.