Abstract

Controlled application of agricultural nitrogen (N) has recently become a focus of remote sensing technology research. Escalating energy and fertilizer prices along with the potential of adverse environmental impacts have forced growers to consider technologies that deliver nutrients in a more effective way. Assessing leaf and canopy chlorophyll (chl) contents can provide an indirect measure that expresses the condition of the crop’s environment. Nitrogen content at the scale of the leaf and the entire canopy will have a strong association to chl content at that same scale. Therefore, N stresses can be inferred through changes in chl content. Remote sensing is rapidly becoming recognized as a tool that has the potential to quickly assess chl content over a large area at both the leaf and canopy scale non-destructively. These studies examined the relationship of corn (Zea mays L.) leaf and canopy spectral response to chl and N content. The effects of N stress on leaf and canopy spectra, chl content, and N content were examined. Nitrogen stress will visibly present itself through the degradation of chl content. Chlorophyll content and N content continue to exhibit a strong relationship throughout the vegetative stages of growth for both measurement scales. As a result, instruments that measure chl content can also be used to estimate N content.

A variety of spectral indices have been introduced for the purpose of quantifying plant status. A few of these indices were selected for these studies and evaluated for their ability to assess N stress. The indices selected were those that utilize the chl spectral reflective segments of the spectrum (green, and red edge). These regions show more promise than do the chl absorbance segments of the spectrum (blue, and red).

Our results suggest that instrumentation that measures spectral reflectance holds promise for the assessment of chl and N stress at both the canopy and leaf level. The ability to non-destructively measure chl content or N content in real time will be useful in agricultural N management. Additional investigation is needed for the design and construction of active systems that can implement the functions presented.