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Agricultural Pacific West Area Research Service U.S. Salinity Laboratory 450 W. Big Springs Road Riverside, CA 92507-4617 Tel. 909-369-4867 Fax. 909-342-4962 Email. Jrhoades@ussl.ars.usda.gov November 8, 1996 Jim Valli8nt Regional Irrigation Specialist Colorado State University 411 North 10th Street Rocky Ford, CO 81067 Dear Jim: Please find enclosed a summary of the mobile-assessment and laboratory analysis results- for the fields involved in what Scott called the "Colorado Expedition" trip. Also enclosed is a table of analytical data for the soil samples we collected. We normally would not do so much laboratory work, but we did this time to make sure you got some good data/results-since the fields were drier than we like them to be for our instrumental measurements. A few comments about the analytical results: Sulphate is the dominant anion; the cations are mixed and generally in the order: Na>Mg>Ca. Boron is low and not a problem; nor is pH. Now a few comments about the results given in the "Expedition Report". Average soil salinity levels(about 5.7-8.0)are high enough in field #1 to reduce the yield of crops like beans, alfalfa, clover, fescue, milkvetch, maize(forage), sudangrass(forage), trefoil and other such sensitive and moderately sensitive crops and forages-especially those grown for vegatative- growth. However, the observed levels should not cause undue yield-losses for more salt-tolerant crops like wheat, sugarbeets, barley, maize(grain), tall wheatgrass, sorghum(grain), etc. The above conclusion assumes irrigation by flood techniques is used (as was the case for this field) with reasonably good irrigation management during the seedling establishment period to obtain satisfactory stand using whatever water has been being used there. This conclusion is based on the observation of the levels of soil salinity that have resulted from the use of that water and on the salt-tolerance data of the USSL. It precludes the use of sprinkler-irrigation-since this could introduce foliar-salt/uptake problems, as discussed next in terms of the other fields. The levels of salinity within field #1 are rather uniform as fields go, as you can see in Tables I & 5 and in Figures 6 & 10. The levels of SAR in the soil are not overly high; I would not expect a serious ~.odicity-related problem in this field, especially given the corresponding salinity levels and fact thatthe field is furrow-irrigated. Soil salinity levels in field #2 are sufficiently high to limit crop production to only salt- tolerant crops such as barley, sugarbeets, rye, bermudagrass, etc. (The mean EC, is essentially 10