Submitted to: Proceedings of the International Salinity Forum
Publication Type: Proceedings
Publication Acceptance Date: 4/11/2005
Publication Date: 4/25/2005
Citation: Poss, J.A., Russell, W.B., Grieve, C.M. 2005. Remote sensing canopy reflectance of salinized and deficit irrigated alfalfa and wheatgrass. In: Proceedings of the International Salinity Forum, Managing Saline Soils and Water: Science, Technology, and Soil Issues. April 25-27, 2005. Riverside, CA pp:367-370. Interpretive Summary: Alfalfa and wheatgrass are two important forages that can be utilized in areas where soil salinity is a limitation to crop productivity. The ability to monitor or evaluate the efficiency of cropping production systems in saline areas can be dramatically improved by applying remote sensing principles to these important crops. Remotely-sensed ground-based spectral reflectance of salinized and drought stressed alfalfa and wheatgrass canopies at individual wavelengths ranging from the violet visible portion of the electromagnetic spectrum (350nm) to the infrared (2500nm) were used to calculate vegetative indices that are significantly correlated with these stress factors in these crops. Four vegetative indices from a group of over 60 evaluated were selected and used to develop a model predicting fresh weight biomass production of each forage under varying levels of salinity and water stress. A multiple linear regression model was developed and calibrated for each forage independently that significantly explained the variation in yields for both forages when subjected to salinity and water stress. The spectral regions of interest were in the visible red and green portion of the spectrum and in the near-infrared. The vegetative indices were of two types: normalized difference vegetation index (NDVI) and a derivative-based red-edge position pseudo-absorbance index. Plant physiological variables percent N, relative water content, an chlorophyll a&b pigment concentrations were also significantly related to indices under salinity and water stress for each crop independently. Leaf area index was successfully characterized for both species together with one vegetative index: either a single ratio vegetation index (SRVI) or the derivative-based red-edge position pseudo-absorbance index.
Technical Abstract: Remote sensing studies in agriculture have devoted little attention to salinity stress detection in plants. To evaluate the ability of remotely-sensed ground-based spectral reflectance information to characterize salinized and drought stressed alfalfa and wheatgrass production, a study was designed to vary and control salinity and water stress and quantify the canopy spectral reflectance properties. Four levels of applied water based on ratios of baseline evapotranspiration for a well-water control (ETR 1.25, 1.00,0.75, and 0.50) were applied with water qualities ranging from 2 to 28 dS/m. Alfalfa and wheatgrass canopy reflectance was measured at individual wavelengths ranging from the violet visible portion of the electromagnetic spectrum (350nm) to the infrared (2500nm) and the data used to calculate vegetative indices. Four indices that were deemed biologically relevant were applied to a multiple linear regression model to related with yields of alfalfa and wheatgrass crops. The model was able to explain from 41 to 95% of the variation in yields with remotely sensed indices. Other relationships between crop chlorophyll a&a concentrations, relative water content, and leaf area index changes associated with water and salinity stress were also significantly detected with remote sensing techniques. Remote sensing of water and salinity stress effects on alfalfa and wheatgrass forage production is a viable tool. Further research to refine this techonology for generally applicability, information extraction, and crop independence is needed to expand the utility of remote sensing crops in saline areas.