干旱区生态环境知识资源中心

Dryland wheat of semi-arid areas is significantly affected by water and nitrogen availability since deficiency in these resources creates a stress status over the crop, reduce the chlorophyll content in the leaves, and damage 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 integrated sphere. We aimed to create spectral vegetation indices that would be sensitive to changes in 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: NDVI, Green-NDVI, NDGI, and the ratios R695/R420, R695/R760, and R970/R900 (where R is the reflectance of the marked wavelength). The sensitivity of these indices was estimated by correlating the spectral data with the bio-physiological variables that were taken in parallel. 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 is sensitive for both nitrogen and water stresses. We improved the sensitivity to water status by using a water absorption wavelength in the ratio R970/R900, instead of the entire NIR region. Therefore, using the green range and water absorption wavelengths in different indices, enables the user to distinguish between these two types of stress.