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Estimating Yields of Salt- and Water-Stressed Forages with Remote Sensing in the Visible and Near Infrared

USDA-ARS George E. Brown, Jr. Salinity Laboratory, 450 West Big Springs Road, Riverside, CA 92507

View larger version (30K): [in a new window]   Fig. 1. Spectra obtained from 350 to 1000 nm averaging canopy reflectance over high and low salinity and evapotranspiration (ET) treatments for (a) wheatgrass and (b) alfalfa. Both salinity and drought reduced reflectance in the near-infrared (NIR) region.

View larger version (27K): [in a new window]   Fig. 2. Spectra obtained from 350 to 700 nm averaging canopy reflectance for wheatgrass and alfalfa for (a) high and low evapotranspiration (ET) and (b) over high and low salinity. Both salinity and drought increased reflectance in the visible region except for alfalfa where nitrogen concentrations confounded the "green peak" (550 nm).

View larger version (16K): [in a new window]   Fig. 3. A significant increase in tissue nitrogen with salinity was found for alfalfa but not wheatgrass. The effect of water stress on N content was not significant for either species (data not shown).

View larger version (40K): [in a new window]   Fig. 4. Coefficients of determination (r2) for the linear relationships between canopy reflectance at each wavelength and total fresh weight biomass for (a) wheatgrass and (b) alfalfa, total cumulative evapotranspiration for (c) wheatgrass and (d) alfalfa, and the integrated electrical conductivity of the irrigation water for (e) wheatgrass and (f) alfalfa.

View larger version (26K): [in a new window]   Fig. 5. The fitted estimate of yield and the coefficient of determination of a multiple linear regression model composed of two vegetative indices, Onecartwr and the inverse of Readthr. Coefficients provided from this fit were applied to predict yield of other harvests under similar environmental conditions.

View larger version (25K): [in a new window]   Fig. 6. The results of predicting yield from a multiple linear regression model when applied to forage production under simultaneous water and salinity stress for wheatgrass and alfalfa on a "prior" harvest period (a and b) and a "post" harvest period (c and d) with species-dependent coefficients.