|CLARKE, THOMAS - 5344-20-10
|Pinter Jr, Paul
Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 10/15/2001
Publication Date: 10/21/2001
Technical Abstract: Plant response to nutrient availability manifests itself as shifts in spectral reflectance resulting from changing chlorophyll concentration. Reflectance at the far-red wavelength of 720nm was normalized to the near-infrared reflectance at 790nm to produce a signal sensitive to canopy chlorophyll content. However, the range of possible signal responses is proportional to the amount of vegetation in the sensors' field of view. It is necessary to have some measure of canopy cover in order to evaluate the signal response in terms of actual crop condition. Therefore a two-dimensional approach was used, with canopy density estimated by red and near-infrared reflectances providing one dimension and the chlorophyll signal response as the other dimension. This Planar Domain method, previously found effective for cotton and wheat, was tested on a differentially irrigated and fertilized broccoli crop in the 2000/2001 growing season. The Canopy Chlorophyll Content Index was successful in distinguishing the low nitrogen plots at 36% plant cover, while a Normalized Difference Vegetation Index was unable to fully discriminate between treatments until twenty-eight days later, one week before harvesting began.