Characterization of water and nitrogen stresses in wheat leaves by the visible and near-infrared reflectances Conference Paper uri icon

abstract

  • Dryland wheat of semi-arid areas is significantly affected by water and nitrogen availability since deficiency in these resources creates stress, reduces the chlorophyll content in the leaves, and damages the yield production. The objective of the current research was to characterize wheat stresses caused by the lack of nitrogen fertilization on one hand, and water on the other hand. This objective was implemented by measuring the spectral reflectance of wheat plants in different growth conditions, in the leaf level. The reflectance was measured in the spectral range of 400-1100 nm by a Licor LI-1800 high spectral resolution spectroradiometer, equipped with an integrating sphere. We aimed to examine spectral vegetation indices that would be sensitive to changes in bio-physiological variables that were measured in parallel: chlorophyll, nitrogen, and water contents in the leaves, and hence serve as indicators to the wheat stress. The following indices were applied to the spectral data: Normalized Differences Vegetation Index (NDVI), Green-NDVI, Normalized Differences Greenness Index (NDGI), Red-edge-position, Normalized Pigment Chlorophyll Index (NPCI), Pigment Simple Ratio (PSR), and the ratios R695/R420, R695/R760, and R970/R900 (where R is the reflectance of the respective wavelength). The sensitivity of these indices was estimated by correlating the spectral data with the bio-physiological variables. We found that the green range of the electromagnetic spectrum (around 550 nm) is the most sensitive for the nitrogen wheat stress while the NIR range of the spectrum between 700 to 1100 nm is not sensitive for water stress as a whole, although it includes one of the water absorbance bands (970 nm). It is assumed that this region was affected by differences in the leaf size and structure that occur due to nitrogen treatments. We also found that the red region (680-700 nm) is sensitive to nitrogen stress and water content. We improved the sensitivity to water status by using a water absorption wavelength in the ratio R970/R900, instead of the entire NIR region. In summary, we conclude that using the green range and water absorption wavelengths in different indices enables the user to distinguish between nitrogen and water stresses.

publication date

  • January 1, 2003