Interpretation of salinity and irrigation effects on soybean canopy reflectance in visible and near-infrared spectrum domain
Soil and water salinity can reduce plant growth, affecting yield and quality of agricultural and horticultural crops. This study was designed to measure canopy spectral reflectance of soybean plants under different salinity and irrigation treatments (drip, sprinkler, and furrow), and to relate the reflectance characteristics to salinity-induced alterations in leaf chlorophyll, specific leaf mass, and above-ground biomass. Soybean canopy reflectance was measured with a hand-held Cropscan multispectral radiometer in the visible (460-710 nm) and near-infrared (NIR; 810-950 nm) spectrum domain. Canopy reflectance in the NIR was significantly and consistently reduced by the salinity treatment. The reduction was attributed to increases in specific leaf mass caused by salinity, and can be delineated with the simple ratio vegetation index (SRVI), with 660 and 830 nm as the most sensitive waveband combination. Reflectance in the visible domain did not show a salinity effect nor any correlation to leaf chlorophyll changes from salinity stress. Canopy reflectance in NIR showed the most salinity effect under furrow irrigation where the soybeans were subjected to the most cumulative salinity stress.