Submitted to: Nitrogen Environment and People Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: April 18, 2001
Publication Date: N/A
Technical Abstract: Mapping the spatial variability of within-field crop nitrogen status is essential for better nitrogen management using site-specific variable-rate application technology. Reflectances from multispectral and hyperspectral remotely sensed images are correlated with expressions of crop nitrogen status such as leaf chlorophyll content, leaf nitrogen content, leaf area index, and percent crop cover. Multispectral approaches emphasize linear combinations of broad spectral bands (known as vegetation indices) and hyperspectral approaches analyze reflectance signatures from narrow spectral bands. Active system approaches with laser-induced fluorescence imaging spectrometers have also yielded data that are highly correlated with leaf nitrogen and leaf chlorophyll. Impediments to adoption of these remote sensing approaches include sensitivity of passive reflectance data to other characteristics of the crop and the low signal to noise of fluorescence data in daylight. If used as a basis for nitrogen management, erroneous information can lead to applications of excess nitrogen fertilizer, thus contributing to non-point-source pollution. Additionally, information on crop nitrogen status from remote sensing may be available only after the window of time when sidedress nitrogen treatments can be applied. Thus, remote sensing solutions to mapping crop nitrogen status clearly require attention to issues of optimization before application.