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<br />I\) <br />(;J <br />00 <br />I\) <br /> <br />some slopes up to three percent. Geographically, the valley <br />rests in a U-shaped trough, cut into Cretaceous shale and <br />I imestone bedrock. <br /> <br />Most of the i rri gated so i 15 are ",e II su i ted to a '" i de range <br />of crops including the high value cash crops. The soils <br />vary from 10'" to high in "'ater intake, ",ater holding <br />capacity, permeability, and ",ater erosion ",hich magnifies <br />the need for proper management. <br /> <br />PROBLEMS <br /> <br />The Lower Arkansas River in Colorado, according to the <br />Cooperative Extensi"on, is the most saline stream of its size <br />in the United States. The average sal inity levels of canal <br />systems east of Pueblo increase from 300 ppm Total Dissolved <br />So lids <TDS) to over 4,000 ppm TDS near the state line. <br />Shallow wells in the area have simi lar TDS concentrations. <br />Water containing more than 2,000 ppm TDS has often been <br />assumed to be unsuitable for irrigation, but such waters <br />have been used in the Arkansas Valley for many years. <br />Approximately two thirds of the 290,000 acres of irrigated <br />land is being irrigated ",ith Class C4 ",ater, the U.S. <br />Sal inity Laboratory's highest sal inity hazard <br />classifi'cation. High sediment and salinity problems were <br />identified In the Colorado Nonpoint Assessment report for <br />this reach of the river. <br /> <br />The Patterson Hollo", Hydrologic Unit Area obtains water from <br />the Rocky Ford Highl ine, Oxford, Otero, Rocky Ford, and <br />Cat Ii n Cana Is. These cana I s divert ",ater form the Arkansas <br />R i ,ve r be for e the wa t e r qua lit y i nth e r i ve r has .d e t e r i 0 rat e d <br />significantly. The quality of the water diverted averages <br />about 500 ppm TDS in these canals. <br /> <br />The Arkansas River downstream from the project area has a <br />salinity concentration of approximately 2,500 ppm TDS. <br />Salinity levers therefore change rapidly in this 25 mile <br />reach of the river. <br /> <br />The soi 15 in the area are well suited to all locally adapted <br />crops. The loamy soils management problems include <br />maintaining good tilth and getting good distribution of <br />irrigation water. Management of irrigation water on slopes <br />greater than one percent is needed to reduce erosion and <br />loss of plant nutrients and pesticides. <br /> <br />The soi Is are calcareous <br />genera II y I eached out of <br />prof i I es are more sandy. <br />depth beginning at three <br /> <br />throughout the i r prof i Ie with sa Its <br />the surface layers. The lower <br />Some areas have I imestone at a <br />and one half feet. <br /> <br />7 <br />