Quantifying Nitrogen Content in Wheat in Mediterranean Environments Using Spectral Vegetation Indices.

This study was conducted to study the usefulness of vegetation indices (VIs) for the estimation of canopy nitrogen (N) and chlorophyll (CHL) content at two different developmental stages (stem elongation Z 30 and anthesis Z 65). Additionally, the influence of LAI, scale at which the indices are developed (leaf vs. canopy), and geographic location on the estimation of canopy N and chlorophyll content were evaluated. Data were collected from two rainfed field sites cropped to wheat, one in Southern Italy (Foggia) and the other in the south eastern Australia (Horsham). Perpendicular Vegetation Index (PVI) showed the highest coefficient of determination against plant N (%) (r² = 0.81; standard error (s.e.) = 0.41%; p<0.001). Whereas, Canopy Chlorophyll Content Index (CCCI) was best correlated with plant N (g N m^-2) (r² = 0.73; s.e. = 0.603; p<0.001). LAI influenced the performance of the VIs causing loss of sensitivity for LAI values higher than 3. The geographical location influenced mainly simple ratio or normalized indices, while indices that contain red-edge wavelengths were less affected.