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• is greatest for neutral to slightly acid soils within a pH range of 6.5 - 7.0 (Donahue et al., 1977; USDA, <br />1951; and Walsh, 1972). For these reasons, soils with a pH less than 5.0 or greater than 8.5 are <br />typically unsuitable for plant propagation. <br />Conductivity (Salinitvl. Salinity is normally not measured directly as a soil test. The electrical <br />conductivity (EC) of the soil solution is measured and taken as an indication of salt level. Soluble <br />salts influence the quantity of water available to plants and total dissolved solids concentration in <br />ground water. High salts cause an osmotic pressure barrier to the soil root system interface and <br />inhibit water and nutrient movement into the plant. The tolerance of plants to high soil salt levels is <br />species dependent and has been well documented (USDA, 1969 and Donahue et al., 1977). Salinity <br />levels are most critical during germination and most detrimental in hot dry climates and on south <br />facing slopes than in other landscape positions. <br />Saturation Percentaae. Saturation percentage is a useful parameter for detecting low water-holding <br />capacity and clarifying the degree of sodic hazard as indicated by SAR (Merrill et al., 1987). The <br />degree of saturation is highly influenced by the physical properties of the medium. Soils tend to be <br />• doughty, coarse textured, and readily leached of nutrients when the water holding capacity at <br />saturation is 25 percent or less. A high saturation percentage (greater than 85 percent) indicates a <br />fine textured medium with potentially poor air and water permeability characteristics. <br />Particle Size (Textural. Texture refers to the relative proportion of sand, silt, and clay sized particles <br />and generally relates directly to saturation percentage. Texture influences water infiltration and <br />percolation, water and nutrient retention, surface crusting, shrinkage and swelling, frost heaving, <br />compaction, and erodibility. Textural problems are generally encountered when either sand contents <br />approach 85 percent or clay levels are greater than 40 percent. Soils with high silt or very fine sand <br />content are often more susceptible to wind and water erosion. <br />Dominant Water Soluble Cations (Ca. Mg. and Na). SAR. and ESP. The water soluble Ca, Mg, <br />and Na analyses reveal the type and concentration of salt that exists in solution. The ion <br />concentration is directly proportional to the soil conductivity (USDA, 1969). The ratio of soluble Na <br />to Ca plus Mg, referred to as SAR, is commonly used to predict both chemical and physical properties <br />of growth mediums. The ratio is an indicator of dispersion, flocculation, porosity, infiltration, <br />• Revised 9/99 2.04.6-14 <br />