Nitrogen and Water Stress Impacts Hard Red Spring Wheat (Triticum aestivum) Canopy Reflectance

Remote sensing has been proposed as a method for implementing an inseason spring wheat (Triticum aestivum) nitrogen (N) fertilization program. However, in fields where yields are influenced by both water and N stress, accurate N recommendations require that that the N and water stress signals be separated from each other. The objective of this study was to determine the impact of water and N stress on canopy reflectance and the ability of vegetation (NDVI, GNDVI, and BNDVI), and chlorophyll (CGreen and CRedEdge) indices to separate water and N stress. A split-plot experiment containing four blocks was conducted in 2002, 2003, and 2005 at Aurora South Dakota. The treatments were two soil moisture regimes and four N rates. Canopy reflectance was measured with a handheld multispectral radiometer at Haun 2, 4-4.5, 6, and 10-10.2. Canopy reflectance was measured in 16 different bands. Remote sensing-based prediction models for yield, yield loss due to N stress, yield loss for water stress, and protein were developed. Yield loss due to N stress decreased with increasing N, while yield loss to water stress had the opposite relationship. Protein concentration generally increased with N. The remote sensing models for protein and yield loss due to N stress explained more of the variability than the yield model at Haun 4-4.5 and Haun 6. These data suggest that canopy reflectance can be used to separate N and water stress signals in hard red spring wheat.