Identification of saline soils with multiyear remote sensing of crop yields
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Soil salinity is an important constraint to agricultural sustainability, but accurate information on its variation across agricultural regions and its impact on regional crop productivity are difficult to obtain. We evaluated the relationships between remotely sensed wheat (Triticum aestivum L.) yields and salinity in an irrigation district in the Colorado River Delta region. The goals of this study were to: (i) document the relative importance of salinity as a constraint to regional wheat production; and (ii) develop techniques to accurately identify saline fields. Estimates of wheat yield from 6 yr of Landsat data agreed well with ground-based records on individual fields (R-2 = 0.65). Salinity measurements on 122 randomly selected fields revealed that average 0- to 60-cm, salinity levels > 4 dS m(-1) reduced wheat yields, but the relative scarcity of such fields resulted in < 1% regional yield loss attributable to salinity. Moreover, low yield was not a reliable indicator of high salinity, because many other factors contributed to yield variability in individual years; however, temporal analysis of yield images derived from remote sensing data showed that a significant fraction of fields exhibited consistently low yields during the 6-yr period. A subsequent survey of 60 additional fields, half of which were consistently low yielding, revealed that this targeted subset had significantly higher salinity at 30- to 60-cm depth than the control group (P = 0.02). These results suggest that consistently low yields are an indicator of high subsurface salinity, and that multiyear yield maps derived from remote sensing therefore hold promise for mapping salinity across agricultural regions.
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