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Remote Sensing Maps Salinity In Red River Valley

A USDA scientist has led efforts to develop a new method for using remote sensing to assess soil salinity. This could give land managers worldwide a regional-scale tool for measuring and inventorying soil salinity in fields where salt buildup lowers crop yields.  

Dennis Corwin, a soil scientist with the USDA's Agricultural Research Service (ARS)  led a team that used Moderate Resolution Imaging Spectroradiometer (MODIS) imagery to assess and map soil salinity across approximately 741,300 acres of North Dakota's and Minnesota's Red River Valley. Increased soil salinity levels in this region have been linked to higher water tables caused by management and precipitation changes over the past 20 years.

The team compared two vegetation indices:  the normalized difference vegetation index (NDVI) and the enhanced vegetation index (EVI).  Both indices were developed using seven years of vegetation reflectance data obtained with MODIS imagery.

The team also collected soil samples from 60 fields across three counties in the Red River Valley to see how strongly field-scale soil saline levels correlated with the EVI and NDVI indices.  

The researchers found that 21% to 37% of the variability in soil salinity levels could be correlated with EVI.  Then they added another factor into their estimates:  whether the land qualified for the Conservation Reserve Program (CRP), a federal program that sets aside marginally productive land for conservation purposes.  They found that 34% to 53% of the variability in soil salinity could be correlated to EVI and whether land was eligible for CRP inclusion.  

Results from this research, which were published in the Journal of Environmental Quality, provide the NRCS with an easy and reliable tool for mapping soil salinity over regions that span from hundreds of thousands to millions of acres.