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<br />RESOURCE USE <br /> <br />For <br /> <br />CROPLAND AND PASTURELAND PRODUCTION <br /> <br />Description of Area: <br /> <br />Virgin Valley Sub evaluation Unit, Arizona, Nevada, Utah <br /> <br />Parameters <br /> <br />Unit <br /> <br />Present <br />Conditions <br /> <br />Future Conditions <br />Plazmin<> Alternatives <br />Future I I <br />Without 1 2 <br /> <br />The salinity hazard associated with Alternative 2 should result in less than <br />five percent yield reduction of alfalfa, under steady state conditions, assuming <br />all the applied water has an electrical conductivity of 3.5 mmho/cm. This salinity <br />is representative of the maximum levels, which occur under low flow conditions <br />during the summer months, and was used to assess the maximum potential effects of <br />salinity on crop growth. Below are average soil water electrical conductivity and <br />associated yield reduction for alfalfa for the management options given in Table 8. <br />The electrical conductivities were calculated using the composition of the irrigation <br />water reported by USGS for August 24, 1176 (Ca - 30.9; Mg - 5.8; Na - 7.4; K - 0.6; <br />C1 - 6.5; RCO - 5.2; S04 - 33.3 meq L- ) and leaching fractions, corrected for <br />runoff, ca1cutated from water balance data reported in Table 8. The high calcium <br />and sulfate concentrations reduce the salinity hazard of this water because of gypsum <br />precipitation. <br /> <br />~~ <br /> <br />CALCULATED SOIL WATER ELECTRICAL CONDUCTIVITIES AND <br />ASSOCIATED YIELD REDUCTION FOR ALFALFA <br /> <br /> Future Without <br />Factor Salinity Program Alternative 1 Alternative 2 <br /> 1./ <br />Leaching fraction 0.55 0.38 0.22 <br />Average root zone <br />Salinity (mmho/cm) (1) 3.8 4.3 5.0 <br />Projected yield <br />reduction (%) (2) 0 1 4 <br /> <br />"l-. <br />,(, <br /> <br />':.... <br />.;;}; <br /> <br />1/ Leaching fraction equals seasonal deep percolation divided by the quantity, <br />seasonal gross application minus seasonal net runoff. <br /> <br />SOURCE: Page A-12, Oster, J. D., U.S. Salinity Laboratory Correspondence. <br />1981., <br />(1) Oster, J. D., and J. D. Rhoades, 1977 (see Bibliography). <br />(2) Maas, E. V. and G. J. Roffman, 1977 (see Bibliography). <br /> <br />A-12 <br /> <br />. ~ r t", 0 <br />o 'J (, ..,. ,j J <br />