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<br />. <br /> <br />r or-' <br />-" \ --, <br />W "'-',' <br /> <br />Project Lands <br /> <br />the range of about 36 to 48 inches of the surface. This <br />depresses crop yields substantially, but does not render <br />unsuitable for irrigation. <br /> <br />condi tion <br />t.he lands <br /> <br />ALKALINITY AND SALINITY <br /> <br />No significant. problems from alkaline and saline soils are <br />expected to develop from sustained irrigation on about 78 percent of <br />the irrigable land. These lands, although irrigated in the past under <br />short water supply conditions, have remained free of harmfull accumula- <br />tions of salts and alkali. Under future operations, the quality of <br />water would be equally as good as it has been in the past, and the <br />application of greater supplies would result in greater leaching. <br />Because drainage is adequate, these soils are expected to remain free <br />of harmful accumulations of salts and alkali. <br /> <br />. <br /> <br />Irrigable lands having soils tllat are moderately saline consist <br />of about 22 percent of the total irrigable area. They occur mainly <br />on the low terraces, but small tracts are located on the high terraces <br />and the uplands. The soluble salts, concentrated within the 0.2- to <br />0.5-percent range, occur mainly in the subsoils and substrata. This <br />condition, although prohibiting the attainment of maximum yields, will <br />not limit productivity below the class 2 range. Slightly more than <br />one-third of these lands has the water table level "~thin three to <br />five feet of the surface. By providing adequate drainage and applying <br />timely and ample quanti ties of water, the saline condition can be <br />improved. The saline soils which have developed in the adequately <br />drained areas are instances where the leaching requirement has not <br />been fully met. Irrigation has been practiced long enough, however, <br />to establish a state of equilibri~~ between the water supply and the <br />soil salinity. Thus, the condition is not expected to worsen, and by <br />application of more water with the Narrows Unit in operation, the <br />salinity of these soils could be reduced. <br /> <br />About 19,000 acres or 70 percent, of the Class 6w lands have <br />saline or saline-alkaline soils. Salinization and alkalization have <br />advanced to the point where usually only salt-tolerant crops can be <br />grown. These lands are used almost exclusively for the production of <br />pasture and forage grasses. The lands classed as nonirrigable <br />because of saline or saline-alkaline soils are located mainly on the <br />low terraces. However, some areas of significant size occur on the <br />uplands and small isolated areas on the high terraces. Inadequate <br />drainage is responsible for the salinization and alkalization of the <br />soils. <br /> <br />. <br /> <br />60 <br />