SOIL SURVEY

- :180-Permeability, soil - The ease with which gasses, and liquids pass through a bul kmass of soil or a layer of soil . Because different soil horizons vary i npermeability, the particular horizon should be designated .pH, soil - The negative logarithm of the hydrogen-ion activity of a soil . Thedegree of acidity (or alkalinity) of a soil as determined by means of aglass, quinhydrone, or other suitable electrode or indicator at a specifie dmoisture content or soil-liquid ratio, and expressed in terms of the pH scale .Plastic limit (Atterberg limit) - The water content corresponding to an arbitrar ylimit between the plastic and the semisolid states of consistency of a soil .Plasticity number (plasticity index) - The numerical difference between the liqui dand the plastic limit . The plasticity index gives the range of moistur econtents within which a soil exhibits plastic properties .Profile, soil - A vertical section of the soil through all its horizons and extendin ginto the parent material .Reaction, soil - The degree of acidity or alkalinity of a soil, which is usuall yexpressed as a pH value . Descriptive terms commonly associated with certai nranges in pH are : extremely acid,9 .0 .Regolith - The unconsolidated mantle of weathered rock and soil material on th eearth's surface .Regosolic - An order of soils having no horizon development, or development o fthe A and B horizons insufficient to meet the requirements of the other orders .Relief - The elevations or inequalities of the land surface when considered collectively.Residual material - Unconsolidated and partly weathered mineral materials forme dby the desintegration of consolidated rock in place .Runoff - The portion of the total precipitation on an area that flows away throug hstream channels . Surface runoff does not enter the soil . Groundwaterrunoff or seepage flow from groundwater enters the soil before reaching th estream .