Environmental Engineering Reference
In-Depth Information
4.5.3 Conditions for Measuring Soil Color
Ideally, soil color should always be read on a ped (clump of soil) interior, immediately
after excavation, in a moist state and under direct natural light. Soil is not smeared
prior to reading soil color. Hydric soils, especially when they are saturated, may
change color quickly upon exposure to oxygen. Therefore, it is important to describe
the colors soon after excavation. If the soil does change color with time, you should
also record the color of the soil once it has changed and the amount of time that has
passed since excavation.
Although it is best to describe soil color moist, often a hydric soil is saturated and
thus it is impossible to acquire a moist sample while in the field. In this case
documentation that the soil color was read under saturated conditions is made
and a sample may be collected and let dry to a moist state before soil color is
read again. A saturated soil may change color as it dries indicating a reduced matrix
(Fe is reduced in situ). Changing moisture content may affect soil value, while a
change due to oxidation or reduction of Fe will most likely produce a change in
chroma and confirms a reduced matrix (reduced Fe was present). If the change in
color is only due to moisture state and not Fe reduction, then the moist color only
needs to be recorded. However, if it is in fact a reduced matrix both colors and the
fact the matrix is reduced should be noted.
Soil color should be read under full natural light with the color book facing the
sun at a 90
angle. It is best to do this during mid-day when the sun is high. If soil
color is read in a forest, the color should be read in a spot where the sun is shining
through the canopy. Morning and evening sunlight makes it much more difficult to
distinguish between different colors, especially in the winter.
4.5.4 Describing Soil Colors
Multiple colors are often present in a single horizon or layer of a hydric soil. The
color pattern is critical to many of the Field Indicators. Therefore, when describing
soil colors it is important to document the pattern of colors according to the
following parameters.
4.5.4.1 Matrix Color
The matrix color (dominant color) is the color that occupies the greatest volume
of the layer (Fig.
4.5
). If there are multiple colors that appear to be equally
dominant, the soil is described as having a mixed matrix.
