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<br />-') <br /> <br />~ <br />00 <br />~ <br />-~ <br /> <br />is gypsum in the soil. This water can be used on coarse textured (sandy) <br />or organic soi Is that take waters wel!." <br />Rhodes (1972) pointed out the need to adjust the calcuation of ESP, <br />Exchangeable Sodium Percentage, for ionic strength and furthermore the ESP at <br />the base of the root system should be considered at var'rous leaching ratios. <br />Table 2 presents the factors in this calculation. If one utilizes the limit <br />of ESP promulgated by the California CommIttee of Consultants, i.e., 9 as a <br />critical value at which severe permeability problems develop, the leaching ratio <br />of 30% should be used until the TDS exceeds 1,100 ppm and then 4~!o should be <br />used. <br /> <br />Table 2. Calculation of Exchangeable Sodium Percentage in soils at the surface <br />and at the base of the root zone with 10, 20, 30, and 4~!o leaching ratios. <br />After Rhodes (1972). <br /> <br /> Palk <br />TDS (pK2-pKe) p(Ca+Mg) P(HCI3) pHc <br />900 2.29 2.42 2.515 7.225 <br />1000 2.325 2.38 2.505 7.21 <br />1100 2.335 2.34 2.495 7.17 <br />1200 2.345 2.31 2.485 7.14 <br />1300 2.354 2.29 2.480 7.12 <br />1400 2.362 2.25 2.470 7.08 <br />pHc = (pKz-pKe) + p(Ca+Mg) + palk <br />ESPs = SARlw I + (8.4 - pHe) <br />TDS SAR ESP3 ES P b 1 0 ESPb20 ESPb30 ESPb40 <br />900 3.36 7.31 15.06 9.94 7.53 6.07 <br />1000 3.46 7.57 15.59 10.29 7.80 6.28 <br />1100 3.90 8.70 17.92 11.83 8.96 7.22 <br />1200 4.17 9.42 19.40 12.81 9.70 7.82 <br />1300 4.43 10.10 20.81 13.74 10.40 8.38 <br />1400 4.68 10.86 22.37 14.76 11.19 9.01 <br /> <br />However, McNeal et a1. (1966) showed that swelling would be minor at the <br />ESP 22 and 1400 ppm concentration of this study, Quirk (1955) agrees. In <br />his diagram separating stable permeability and decreasing permeability the <br />highest ESP values at 10% leaching fall within the stable permeability area. <br />It is concluded that if the ion mixes are not changed from their potential <br />values, permeability will not be greatly effected by sodium. <br />Bicarbonate Hazard <br /> <br />Eaton (1950) introduced the <br />RSC = (C03= + HCO;] <br /> <br />residual sodium carbonate (RSC) <br />- [Ca++ + Mg++] in meq/I. <br /> <br />10 <br />