Study Questions Exam 1, Answered
Soil consists of 2 general solids and 2 general fluids –minerals and organic matter, and
soil solution and air, respectively.
Regolith is all unconsolidated (porous) material lying above rock.
Except for the
uppermost part, the regolith is geologic material.
The upper part (perhaps a meter or
two in depth) that has been altered by soil formation processes is the solum.
O –accumulation of organic matter above mineral soil; A –the uppermost mineral
horizon, characterized by accumulation of organic matter and, therefore, being dark in
color relative the underlying horizons; E –similar to A in texture but lacking accumulated
organic matter so that it is lighter in color than the A; B –horizon underlying A or E,
characterized by accumulation of clay or soluble salts from upper part of profile and
commonly brighter in color than the overlying soil; C –parent material.
Ap –physically altered A horizon, as by plowing (p); Bt –B horizon with sufficient
accumulation of translocated (t) clay to be considered an argillic horizon;
Bg –B horizon
with gley (g) color due to presence of chemically reduced iron (Fe
Mass flow of nutrients to roots with water as it moves to roots, diffusion of nutrients from
a zone of relatively higher concentration away from the root to a zone of lower
concentration near the plant root; and interception by the root system as it grows into a
larger soil volume.
Munsell color chart or book.
Organic matter (see question #3).
Red –the iron-containing mineral hematite (the iron in it is oxidized, Fe
); yellow –the
iron-containing mineral goethite (although the iron is oxidized, this is a hydrated mineral);
gray –chemically reduced iron, indicative of poor aeration (oxygenation, see question #4)
Along the sequence, red to gray, the soil environment is increasingly wetter and more
poorly aerated (oxygenated).
Mottling indicates a somewhat different drainage and
aeration condition than indicated by the dominant color (e.g., gray zones in dominantly
reddish-brown matrix suggest somewhat poor drainage and aeration, whereas zones of
reddish colors in a gray matrix indicate that some parts of the profile are fairly well
drained and aerated).
Very poor drainage and aeration as suggested by the presence of chemically reduced
Sand, 2.000 to 0.0050 mm, silt, 0.050 to 0.002 mm, and clay, < 0.002 mm diameter.
Texture refers to the relative amounts of sand, silt and clay separates.