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• <br />SATURATED SOIL PASTE FOR THE DETERMINATION <br />OF WATER SOLUBL35 (Na, Ca, A1g and K) pH <br />ELECTRICAL CONDUCTIVITY AND SATUP.ATION <br />(USDA Handbook 60 - Modified) <br />Procedure: <br />1. Weigh 25.0 g of soil into a solo cup (3e oz.). <br />2. With a mohr pipet, add deionized water to prepare the <br />saturated soil paste. Record the amount of water required <br />to reach saturation. <br />Note: A saturated paste glistens as it reflects light, <br />flows slightly when the container is tipped and <br />the paste slides freely and cleanly off the spatula <br />for all materials except soils that are of high <br />clay content. <br />3. After mixing, the sample should set for 1 hour and the <br />criteria for saturation is rechecked. <br />NOTE: Free water should not collect on the surface, nor <br />should the paste stiffen. If the paste stiffens or <br />loses its glisten add more water and remix. Record <br />the amount of additional caater added. <br />n <br />1J <br /> <br />4. Check pH of the paste using a glass electrode and record <br />the data. <br />5. After running pH, transfer the paste to a Gouche crucible <br />with a glass fiber filter paper in the bottom. <br />6. Apply vacuum and collect 2 ml of extract from the saturated <br />paste. This may require considerable time. <br />7. Run electrical conductivity on this extract, using 1 ml of <br />extract and the micro cell for the Wheatstone Bridge. <br />8. An aliquot of extract is diluted to volume with a 18 <br />La~~ background.* <br />9. Frepare blank by adding only the LaC1. <br />10. Measure Na, Ca, Mg and K directly on the Atomic Absorption <br />Spectrophotometer and recor3 the absorbance. <br />11. fieq [•7eiyht: <br />Na 23.0 Mg 12.2 <br />Ca 20.0 K 39.1 <br />* The dilution required will change for every sample, <br />however, a SOOX and a 50X dilution will cover a majority <br />of all samples. <br />NOTE: Samples, Standards and Blanks need a 18 La€~ background. <br />6-99 <br />