| Section S | S index | 611-619 of 1376 terms |
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soft rimeA white, opaque coating of fine rime deposited chiefly on vertical surfaces, especially on points and edges of objects, generally in supercooled fog. On the windward side, soft rime may grow to very thick layers, long feathery cones, or needles pointing into the wind and having a structure similar to that of frost.
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soft waterWater without significant hardness, that is, low (< 60 mg/l) in concentration of magnesium or calcium salts.
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soil airThe air and other gases in spaces in the soil; specifically, that which is found within the zone of aeration. The aeration of soil by exchange with the free air above is a continuing process, but is accelerated by pressure and temperature changes (see normal aeration). The composition of soil air is modified by bacterial activity and by chemical processes due to the action of oxygen and carbon dioxide in the presence of soil moisture. Generally speaking, soil air contains more carbon dioxide than does free air. In addition to the gases originating in the soil, the following may be present in the soil atmosphere in measurable quantities: ammonia, hydrogen sulfide, methane, and other hydrocarbons resulting from decay of organic materials. Traces of helium, radon, thoron, and actinon from radioactive processes also diffuse through the soil layers into the atmosphere by the process of exhalation.
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soil creepSlow downhill movement, usually over relatively short distances, of near-surface masses of soil and loose rock material on hillslopes under the influence of gravity, soil dynamics (shrink– swell or freeze–thaw action), and soil-water movements. Same as surficial creep.
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soil moisture contentThe amount of water in an unsaturated soil, expressed as a volume of water per unit volume of porous media, or as a mass of water per unit oven-dry mass of soil.
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soil moisture deficitThe difference between the amount of water actually in the soil and the amount of water that the soil can hold. The amount of water the soil can hold is generally called field capacity, which is the amount of water that remains after gravitational forces have drained water from the soil macropores. See field water-holding capacity, gravitational water.
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soil moisture profileA graph of soil water content as a function of depth in the soil.
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soil moisture tensionA measure of the amount of work that must be done (suction that would need to be applied) to move water in the soil. Also the energy of retention at the outer edge of the moisture film of the soil particles. Tensions are generally expressed in pascals, bars, or atmospheres. See water potential.
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