Spatial Variation of Soil Salinity in the Mexicali Valley, Mexico: Application of a Practical Method for Agricultural Monitoring Gabriel Judkins • Soe Myint Received: 24 September 2010 / Accepted: 22 May 2012 / Published online: 29 June 2012 Ó Springer Science+Business Media, LLC 2012 Abstract The degradation of irrigated lands through the process of soil salinization, or the buildup of salts in the soil, has hampered recent increases in agricultural pro- ductivity and threatens the sustainability of large-scale cultivation in critical agricultural regions of the world. Rapid detection of soil salinity on a regional basis has been identified as key for effective mitigation of such land degradation. The ability to detect regional patterns of soil salinity at an accuracy sufficient for regional-scale resource management is demonstrated using Landsat 5 Thematic Mapper (TM) imagery. A case study of the Mexicali Valley of Baja California, Mexico was selected due to the region’s agricultural significance and concern for future soil salinity increases. Surface soil salinity was mapped using geore- ferenced field measurements of electrical conductivity (EC), collected concurrently with Landsat 5 TM imagery. Correlations between EC measurements and common indices derived from the satellite imagery were used to produce a model of soil salinity through regression analy- sis. Landsat band 7, TNDVI, PCA 1, Tasseled Cap 3 and Tasseled Cap 5 were found to offer the most promising correlations with surface soil salinity. Generally low levels of soil salinity were detected, however, distinct areas of elevated surface salinity were detected at levels potentially impacting sensitive crops cultivated within the region. The difficulty detecting low levels of salinity and the mid-range spatial resolution of Landsat 5 TM imagery restrict the applicability of this methodology to the study of broad regional patterns of degradation most appropriate for use by regional resource managers. Keywords Remote sensing  Soil salinization  Land degradation  Agriculture  Produce  Onion  Mexico Introduction The contribution of irrigation to the expansion and increased productivity of the world’s agriculture has been significant as over 40 % of the food and fiber crops are currently cultivated on irrigated lands occupying only 17 % of the world’s agri- cultural land area (Rhoades 1990; Scheumann 1997). Meeting future demands of a growing and increasingly affluent pop- ulation for year-round access to fresh produce will require an even greater contribution from irrigation, particularly in arid regions as their climates are favorable for winter produce cultivation (Redman 1999). However, irrigated agricultural lands face a number of challenges including rising capital costs, relatively low food prices, and the degradation of land and water resources (Scheumann 1997). One of the most significant threats to the future productivity of irrigated agri- culture is the degradation of irrigated soils through the process of soil salinization. Already, one out of five hectares of irri- gated land is affected by soil salinization, stagnating the productivity of the world’s agriculture since as much land is lost to degradation as is being gained through the opening of new irrigated lands (Rhoades 1990; Postel 1999). Soil sali- nization is a land degradation problem specifically affecting the critical agricultural regions of the Lower Colorado River area of the U.S. and Mexico, where two-thirds of the agri- cultural land within this region is believed to be afflicted to varying degrees (Postel 1999). G. Judkins (&) Department of Geoscience, University of Nevada Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154-4010, USA e-mail: gabriel.judkins@unlv.edu; gabejudkins@gmail.com S. Myint School of Geographical Sciences and Urban Planning, Arizona State University, Tempe, AZ, USA 123 Environmental Management (2012) 50:478–489 DOI 10.1007/s00267-012-9889-3