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<br /> <br />Table 2.3. Results of studies of drainage water salt concentrations. <br /> <br />Reference <br /> <br />Ayars, J. E. <br />1976 <br /> <br />Brown, Kirl< W. <br />et al. 1978 <br /> <br />o <br /> <br />Carter, et al. <br />1979 <br /> <br />Period of <br />data <br />1975 <br /> <br />1974 and 1975 <br /> <br />2 years <br />(1973C74) <br /> <br />Crops <br />grown <br />Alfalfa, <br />wheat, and <br />crested <br />Wheat <br />grass <br /> <br />Rice <br /> <br />Not <br />Cropped <br /> <br />Soil type <br /> <br />Grand Valley <br />soils <br /> <br />Beauroont <br />clay soil <br />(Typic <br />pelludert) <br /> <br />Pott neuf <br />silt loam <br /> <br />Depth of <br />drains <br />Approximately <br />3 meters <br /> <br />Surface <br />runoff <br /> <br />Variable <br /> <br />SEE€ <br /> <br />Results <br /> <br />lDeation <br /> <br />Salt concentration of the leachate Grand Valley, <br />at the bottom of the soil profile Colorado <br />is llidependent of the volume of <br />water. 'I'ffi profile at the beginning <br />and end of gro<oing season show the <br />concentration of salt in the profile <br />below the root zone relatively con- <br />stant. This region acts as a buffer <br />and causes salt concentration of the <br />rettn:n flCM to be relatively constant. <br />i.e. reduction in salt loading is <br />directly proportional to reductions <br />in the volume of return flow. <br />fIOO(Ij,i"ater was not percolatlligtliroiigll Texas <br />the soil profile. The salts were <br />evidently adsorbed and not readily <br />solubilized. i.e. the soil served <br />IIDre as a sink than a source. <br /> <br />Salt in Salt in <br />Year Irrigation irrigation return <br />Technique water flow <br />Kg/be Kg/ha <br /> <br />1974 ltlpounded 528 559 <br />1974 Continuous 993 575 <br />1975 ltlpounded 428 433 <br />1975 Continuous 712 587.9 <br /> <br />(i) Since rrore salt-bearing water is <br />added to the continuous flow plots <br />than is raroved in the outflow during <br />the growing season. it is apparent <br />that this managaIE!1t practice could <br />lead to excess salt in the soil <br />during years which do not receive <br />1Il.lch rainfall between gro<oing seasons <br />(ii) Concentration of salts in the <br />outflow frcm the plots were less and <br />the water would roc>re easily t:J:eet <br />rigi..d water quality standarda. <br />(1) Once residual salts are ramved <br />by irrigation. there is no rapid <br />salt accurru1ation to high concen- <br />trations from dissolving minerals. <br />when lands are no longer irrigated. <br />(2) The quantity of salt outflow <br />from soils. after residual salts are <br />renuved, depends almJst entirely <br />upon the aIOO1mt of leaching water <br />passing through the soil. With less <br />water passing through the soil, smaller <br /> <br />Twinfal~ <br />Idaho <br />