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pH ranging from 7.5 to 8.4 contain alkaline earth carbonates and may be alkali. Soils <br /> with a pH greater than 8.5 are nearly always alkali and contain a large percentage of <br /> alkline-earth carbonates (USDA, 1951 and USDA, 1969). Soils with pH less than 5.0 usually <br /> contain solubilized aluminum and excessive amounts of other heavy metal trace elements <br /> which are soluble under acid conditions. Total nutrient availability is greatest for <br /> neutral to slightly acid soils within a pH range of 6.5 - 7.0 (Donahue at al ., 1977; USDA, <br /> 1951; and Walsh, 1972). For these reasons, soils with a pH less than 5.0 or greater than <br /> 8.5 are typically unsuitable for plant propagation. <br /> Conductivity (Salinity). Salinity is normally not measured directly as a soil test. The <br /> electrical conductivity (EC) of the soil solution is measured and taken as an indication <br /> of salt level . Soluble salts influence the quantity of water available to plants and <br /> total dissolved solids concentration in ground water. High salts cause an osmotic <br /> pressure barrier to the soil root system interface and inhibit water and nutrient movement <br /> into the plant. The tolerance of plants to high soil salt levels is species dependent and <br /> has been well documented (USDA, 1969 and Donahue et al ., 1977). Salinity levels are most <br /> critical during germination and most detrimental in hot dry climates and on south facing <br /> slopes than in other landscape positions. <br /> Saturation Percentage. Saturation percentage is a useful parameter for detecting low <br /> water-holding capacity and clarifying the degree of sodic hazard as indicated by SAR <br /> (Merrill et al ., 1987). The degree of saturation is highly influenced by the physical <br /> properties of the medium. Soils tend to be droughty, coarse textured, and readily leached <br /> of nutrients when the water holding capacity at saturation is 25 percent or less. A high <br /> saturation percentage (greater than 85 percent) indicates a fine textured medium with <br /> potentially poor air and water permeability characteristics. <br /> Particle Size (Texture). Texture refers to the relative proportion of sand, silt, and <br /> clay sized particles and generally relates directly to saturation percentage. Texture <br /> influences water infiltration and percolation, water and nutrient retention, surface <br /> crusting, shrinkage and swelling, frost heaving, compaction, and erodibility. Textural <br /> problems are generally encountered when either sand contents approach 85 percent or clay <br /> levels are greater than 40 percent. Soils with high silt or very fine sand content are <br /> 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 /> 6-1-17 Revised 04/11/88 <br />