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<br />" .J ,"'''- <br /> <br />000281 <br />reduced crop yields. Now, we have formal data that substantiate the severity and extent ofthe <br /> <br />problemsl' <br /> <br />Since 1999, personnel from Colorado Stat~ University have cbllected extensive data. <br /> <br />throughout the irrigated area from Manzanola to Adobe Creek in western Bent County, <br /> <br />monitoring more than 100 observation wells in a region representing about 130,000 acres. <br /> <br />During the irrigation season, readings are taken weekly to detennine the depth to the water table <br /> <br />and the salinity of the ground water. These results showed the electrical conductivity (BC), used <br /> <br />to measure salinity, ranged from an average on.5 dS/m in 1999 down to 3,1 dS/m in 2001. <br /> <br />Unfortunatelv. crop Yields. on the maior field crops start to substantially decline when soil salinity <br /> <br />measures about 2.0 dS/m or higher. <br /> <br />Surface-water salinity has also been measured weekly throughout most of the season at <br /> <br />more than 170 locatiotis incltlding several different points down the Arkansas River, in siX major <br /> <br />canals, in 12 dTainage ditches, and ill two reservoirs. The average salinity 'of the water in the <br /> <br />irrigation canals was 0.93 dS/m in 1999 and 1.12 dS/m in 2000 indicating low to moderate <br /> <br />restriction in use for irrigation. However, the salinity of the water in the river was found to <br /> <br />increase as it progressed downstream. This is due to surface salt pickup as the water flowed over <br /> <br />the land, concentration of salts in return flows due to evapotranspiration, and pickup of <br /> <br />subsurface salts dissolved as the water passed through the soil and back to the river. <br /> <br />Soil salinity was measured in early June and mid-August on 68 fields in 1999, 77 in 2000 <br /> <br />and 80 in 2001, using electromagnetic induction probes. More than 6,000 soil samples were <br /> <br />collected to calibrate the probes. Average soil salinity was estimated as 2.8 dS/m in 1999 and 2.0 <br /> <br />dS/m in 2000. In 1999, crop yield reduction on corn and alfalfa due to salinization was estimated <br /> <br />to range between 0 and 75% on fields spread over the test area and averaged about lO%. <br />