Geoscience Reference
In-Depth Information
ural bodies, created through consistent and orderly interactions with formative envir-
onmental factors, that will be emphasized here.
Before turning to the influences producing different soils, two points need to be
made. First, it must be appreciated that there are other approaches to soil classifica-
tion. Valid single-purpose or general classifications, and soil distribution maps, can
be produced solely from observed data. Such systems do not require reference to, or
presumptions about, relationships between soil units and environmental controls. The
data can be individual soil properties, for example, surface soil acidity, texture, or or-
ganic matter content. Soils are then just grouped into classes based on ranges of the
property used. This is often the course used to define soils in biological studies. Al-
ternatively, the data can be compiled for many variables, determined at more than one
depth. These data can be analysed by computer classifications that allocate each re-
corded individual soil into a statistically determined group. Such methods simply ac-
cept that the soil categories are valid if they are found to be useful for a particular
purpose. There are different opinions among protagonists of the traditional and nu-
meric schools concerning the principles and practice of soil classification. However, it
is generally accepted that both approaches have their value. The numerical approach
can be tailored to specific management issues more readily than can the general-pur-
pose approach of the environmentally based schemes. These latter, on the other hand,
with their linked galleries of classes at different levels of division, can round out the
geographic picture; they can show relationships between the physical and biological
worlds, and indicate the role of soils as a natural resource. The traditional classifica-
tions have survived criticism and remain continuously in active development and use,
ever since their origins a century or so ago in the work of pioneering scientists, not-
ably the Russian, V. V. Dokuchaev.
