Soil Salinity Mapping Using Electromagnetic Induction (EM-38) to Provide Input Data for the Csuid-II Model, a Decision Support Tool for Irrigation in Saline Water Reuse Areas.

Soil salinity is a major factor affecting irrigated agriculture in today’s world, especially in arid/ semi-arid regions like the Western San Joaquin Valley of California. In this area both salinity and drainage are limiting factors for agriculture. Soil salinity is a very dynamic property both spatially and temporally. Thus, mapping at field scale requires a rapid and reliable means of taking geospatial measurements. Electromagnetic Induction (EM) survey data and prediction equations relating the apparent electrical conductivity (ECa) measured by the EM-38 to soil salinity (ECe) are important tools to assess the spatial variability of soil salinity in a field. This research is being conducted at the SJRIP (San Joaquin River Improvement Project) facility managed by Panoche Water District (Los Banos, California) where subsurface drainage water is re-used on dedicated cropland (typically sown to forages such as alfalfa (Medicago sativa) and ‘Jose’ tall wheatgrass (Thinopyrum ponticum var. ‘Jose’ (TWG)) to reduce salt loading into the San Joaquin River. EM-38 soil salinity surveys are being conducted in two alfalfa and two tall wheatgrass fields to monitor soil salinity in response to the salinity (EC_w) and volume of applied drainage water. Data will be used for the refinement and validation of a computer model (CSUID-II) which will serve as a decision support tool to optimize soil leaching fractions for irrigation water applications of varying salinity levels, with the overall goal  of improving the sustainability of the forage production under saline irrigation.