Leaf chlorophyll content (μg cm -2 ) is an important variable for agricultural remote sensing because of its close relationship to leaf N content. Th e objectives of this study were to develop and test a new index, based on red, green and blue bands, that is sensitive to differences in leaf chlorophyll content at leaf and canopy scales. We propose the triangular greenness index (TGI), which calculates the area of a triangle with vertices: (λr, Rr), (λg, Rg), and (λb, Rb), where λ is the wavelength (nm) and R is the refl ectance for bands in red (r), green (g), and blue (b) wavelengths. Th e TGI was correlated with chlorophyll content using a variety of leaf and plot refl ectance data. Generally, indices using the chlorophyll red-edge (710-730 nm) had higher correlations with chlorophyll content compared to TGI. However, correlations between TGI and chlorophyll content were equal to or higher than broad-band indices, when leaf area index (LAI) was >2. Simulations using the Scattering by Arbitrarily Inclined Leaves (SAIL) canopy model indicate an interaction among TGI, LAI, and soil type at low LAI, whereas at high LAI, TGI was only aff ected by leaf chlorophyll content. Th e TGI could be used with low-cost sensors, such as commercially-available digital cameras, for N management by remote sensing.

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This study assessed whether vegetation indices derived from broadband RapidEye TM data containing the red edge region (690-730 nm) equal those computed from narrow band data in predicting nitrogen (N) status of spring wheat (Triticum aestivum L.). Various single and combined indices were computed from in-situ spectroradiometer data and simulated RapidEye TM data. A new, combined index derived from the Modified Chlorophyll Absorption Ratio Index (MCARI) and the second Modified Triangular Vegetation Index (MTVI2) in ratio obtained the best regression relationships with chlorophyll meter values (Minolta Soil Plant Analysis Development (SPAD) 502 chlorophyll meter) and flag leaf N. For SPAD, r 2 values ranged from 0.45 to 0.69 (p,0.01) for narrow bands and from 0.35 and 0.77 (p,0.01) for broad bands. For leaf N, r 2 values ranged from 0.41 to 0.68 (p,0.01) for narrow bands and 0.37 to 0.56 (p,0.01) for broad bands. These results are sufficiently promising to suggest that MCARI/MTVI2 employing broadband RapidEye TM data is useful for predicting wheat N status.