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Salt Chemistry Effects on Indirect Field Salinity Assessment in the Arkansas River Valley, Colorado by Curtis Cooper (USDA Graduate Fellow, Colorado State University) and Grant Cardon (Extension Soil Specialist, Utah State University) influences the EC /calcium relationship above an EC of approximately 3.0 dS m-1. The chloride relationship to EC is also unclear, presum ably due to the different hydrological regimes on how the soils were "salted up." In fields in which the salt source is from the top down it is expected that chlo- Data for the baseline chemistry are currently being analyzed, but preliminary results reveal that there are re- lationships between extract water electrical conductivity (EC) and the sodium concentrations (Figure 2), which is also true for the magnesium, and sulfate concentrations. This relationship is not found in the calcium concentra- tions in the extract waters. It is surmised that this is because CaSO4 (typically as gypsum) and CaCO3 (typi- cally as calcite) are slightly to limited in their solubili- ties in near neutral pH conditions (Figure 2). However, some soils also appear to have a reserve of calcium attached either to colloids or in the soil solution that Pore water extract waters were sampled from the Research Station in Rocky Ford, CO. Irrigation was ap- plied on Day 0, and with in -situ extractions occurring on Days 1 — 4. Pore waters were sampled through multiple tubes each with a ceramic cup at either 1, 2, 3, and 4 foot depths using suction induced with a pump. Sample waters were not available at the 3 and 4 foot depths on Day 1. In Figure 3. the irrigation water sodium concen- tration and the saturated paste extract concentrations are presented as reference points. A combination of leach- ing, dilution of the pore waters and the movement of the wetting front through the soil profile are shown in Fig- ure 3. These data are also paired with EM -38 measure- ments which suggest that there is a change in the overall bulk conductivity as the wetting front expands through the soil profile. Multiple extracts of a single soil sample were completed in January 2005. This sample was repeatedly processed in a manner equivalent to all the other soil samples for saturated paste extracts. The chemical results of the repeated testing are in Figure 4. From these results the initial flush of sodium from the soil and a subsequent