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Title: Regional-scale Assessment of Soil Salinity in the Red River Valley Using Multi-year MODIS EVI

Author
item LOBELL, D - Stanford University
item LESCH, SCOTT - University Of California
item Corwin, Dennis
item ULMER, M - Natural Resources Conservation Service (NRCS, USDA)
item ANDERSON, K - Natural Resources Conservation Service (NRCS, USDA)
item POTTS, D - Natural Resources Conservation Service (NRCS, USDA)
item DOOLITTLE, J - Natural Resources Conservation Service (NRCS, USDA)
item MATOS, M - Natural Resources Conservation Service (NRCS, USDA)
item BALTES, M - Natural Resources Conservation Service (NRCS, USDA)

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2009
Publication Date: 1/31/2010
Citation: Lobell, D.B., Lesch, S.M., Corwin, D.L., Ulmer, M.G., Anderson, K.A., Potts, D.J., Doolittle, J.A., Matos, M.R., Baltes, M.J. 2010. Regional-scale Assessment of Soil Salinity in the Red River Valley Using Multi-year MODIS EVI. Journal of Environmental Quality. 39(1):35-41

Interpretive Summary: Soil salinity is a major agricultural concern throughout the world, particularly on irrigated lands of arid zone soils. The complex spatial variability of soil salinity has stood as a barrier to its measurement and mapping at field scales and larger spatial extents. Scientists at the USDA-ARS U.S. Salinity Laboratory have developed protocols for mapping soil salinity at field scales using soil sampling directed by geospatial measurements of apparent soil electrical conductivity (ECa) with electromagnetic induction (EMI). Mapping salinity at regional scales remains as a challenge that is best addressed with satellite-based imagery, such as MODIS (Moderate Resolution Imaging Spectroradiometer). A methodology for mapping soil salinity at a regional scale was evaluated using MODIS imagery to characterize spatial variability of salinity over large spatial extents and ECa-directed soil sampling to calibrate MODIS to salinity. The west side of Kittson County, MN (about 240,000 ha), within the Red River Valley (RRV) was used as the study site since recent alterations in weather patterns have caused soil salinity assessment of the RRV to be a top priority by the Natural Resource Conservation Service (NRCS). Multi-year MODIS imagery was used to mitigate the influence of temporally dynamic factors such as climate, pests, disease, and management influences. The most significant observation was that the average of the MODIS enhanced vegetation index (EVI) for a 7-year period exhibited the strongest relationship with soil salinity in all three datasets. The remote sensing methodology showed that soil salinity can be mapped by measuring average MODIS EVI and whether the land qualified for the Conservation Reserve Program (a USDA program that sets aside marginally productive land based on conservation principles). The methodology has the practical simplicity to allow broad application by government agencies, such as NRCS, with minimal cost and has international implications, particularly for use in countries with limited resources. Future work in other counties within the RRV will establish whether the same or similar methodology can be used for the entire 2,400,000 ha of the RRV.

Technical Abstract: The ability to inventory and map soil salinity at regional scales remains a significant challenge to soil, environmental, and natural resource scientists. Previous attempts to use satellite or aerial imagery to assess and map soil salinity have resulted in limited success due, in part, to the inability of the remote sensing methodology to isolate the effects of soil salinity upon vegetative growth from other edaphic, management, meteorological, and biological factors. This study aimed to evaluate the use of MODIS (Moderate Resolution Imaging Spectroradiometer) imagery in conjunction with soil sampling directed by geospatial measurements of apparent soil electrical conductivity (ECa) to assess and map soil salinity at a regional scale (i.e., 10-105 km2) in a parsimonious manner. Correlations with three different soil salinity ground truth datasets differing in scale were made. The west side of Kittson County within the Red River Valley (RRV) of North Dakota and Minnesota was used as the study site since recent alterations in weather patterns have caused soil salinity assessment of the RRV to be a top priority by the Natural Resource Conservation Service (NRCS). Multi-year MODIS imagery was used to mitigate the influence of temporally dynamic factors such as climate, pests, disease, and management influences. The most significant observation was that the average of the MODIS enhanced vegetation index (EVI) for a 7-year period exhibited the strongest relationship with soil salinity in all three datasets. The remote sensing methodology showed that from one-third to one-half of the spatial variability in soil salinity could be captured by measuring average MODIS EVI and whether the land qualified for the Conservation Reserve Program (a USDA program that sets aside marginally productive land based on conservation principles). The methodology has the practical simplicity to allow broad application by government agencies such as NRCS with minimal cost and has international implications, particularly for use in countries with limited resources.