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• 1977; USDA, 1951; and Walsh, 1972). For these reasons, soils with a pH less than 5.0 or greater than 8.5 are typically unsuitable for plant propagation. Conductivity (Salinity). Salinity is normally not measured directly as a soil test. The electrical conductivity (EC) of the soil solution is measured and taken as an indication of salt level. Soluble salts influence the quantity of water available to plants and total dissolved solids concentration in ground water. High salts cause an osmotic pressure barrier to the soil root system interface and inhibit water and nutrient movement into the plant. The tolerance of plants to high soil salt levels is species dependent and has been well documented (USDA, 1969 and Donahue et al., 1977). Salinity levels are most critical during germination and most detrimental in hot dry climates and on south facing slopes than in other landscape positions. Saturation Percentage. Saturation percentage is a useful parameter for detecting low water-holding capacity and clarifying the degree of sodic hazard as indicated by SAR (Merrill et al., 1987). The degree of saturation is highly influenced by the physical properties of the medium. Soils tend to be doughty, coarse textured, and readily leached of nutrients when the water holding capacity at saturation is 25 percent or less. A high saturation percentage (greater than 85 percent) • indicates a fine textured medium with potentially poor air and water permeability characteristics. Particle Size (Texture). Texture refers to the relative proportion of sand, silt, and clay sized particles and generally relatesdirectlytosaturationpercentage. Texture influenceswaterinfiltration and percolation, water and nutrient retention, surface crusting, shrinkage and swelling, frost heaving, compaction, and erodibility. Textural problems are generally encountered when either sand contents approach 85 percent or clay levels are greater than 40 percent. Soils with high silt or very fine sand content are often more susceptible to wind and water erosion. Dominant Water Soluble Cations (Ca. Mg, and Nal. SAR, and ESP. The water soluble Ca, Mg, and Na analyses reveal the type and concentration of salt that exists in solution. The ion concentration is directly proportional to the soil conductivity (USDA, 1969). The ratio of soluble Na to Ca plus Mg, referred to as SAR, is commonly used to predict both chemical and physical properties of growth mediums. The ratio is an indicator of dispersion, flocculation, porosity, infiltration, permeability, erodibility, surface crusting, and seedling emergence. SAR reveals the relative dominance of sodium in the soil water solution whereas ESP reflects the exchangeable • Revised 27 Aug 2002 15