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MONITORING SALINITY STRESSED SPINACH VIA SPECTRAL REFLECTANCE MESUREMENTS

Extensive research has been carried out using hand-held radiometers, aerial platforms and satellites to observe water and nitrogen status of vegetation. Salinity detection using remote sensing attracted scientist’s attention in the past three decades, however, their work often focused on detection of salt affected soils. Real time detection of salt affected crops is important as well. It is considered an uncharted research area especially for vegetables given that most experiments focus on major crops (cotton, wheat, etc.). The main objective for this study was to investigate the potential usefulness of growing-season spectral measurements to detect and monitor salinity stress effects on spinach. Spinach plants were planted in twelve 1x1 meter plots that had 4 salinity treatments (equivalent to yield reductions of 0, 10, 25 and 50%), three replicates each. A hand-held radiometer with filters in the visible and infrared parts of the electromagnetic spectrum was used to monitor salt affected spinach plants. Spectral indices; salinity stress index (SSI) and normalized difference vegetation index (NDVI), as well as spectral reflectance at different wavelengths ranging between 510 nm and 1480 nm were used to monitor salinity stress effects on spinach. SSI indicated salinity very well only in the middle of the growing season. Although water and nitrogen were adequately applied, the independence of SSI from the effects of other growth retardation sources can not be confirmed. Reflectance at 750 nm was superior to all the tested reflectance factors and indices in monitoring salinity. Reflectance at 1000 nm comes in the second place among all the tested reflectance factors in differentiating salinity treatments. There are advantages of using reflectance at 750 nm and 1000 nm for monitoring salinity stressed spinach. Also, they may be integrated with 660 nm, 760 nm and 1480 nm bands to develop new indices.