Agriculture Reference
In-Depth Information
WHY SOILS?
Throughout history, there have been numerous soil classiÝcations. Our concern is why people
were interested in soils. What was their purpose? Below are four different perspectives, among
many options.
1.
Soil survey. Want to understand soils well enough to predict the consequences of alternative uses
and where they will occur. Because many soil survey programs were initiated in Agriculture
Ministries, there was major emphasis on agriculture and forestry. Those in Ministries of Natural
Resources dealt more with soil as geologic deposits and engineering materials. Today there is a
new emphasis on environmental aspects.
2.
Genesis. Want to understand soils well enough to reveal the genetic relationships among them.
This entails the history of evolution of soils and the pedological development of soil features.
Emphasis has often been on how soil-forming factors and processes have inÞuenced the evolution
and development of the pedosphere.
3.
Use interpretation. Want to understand soils well enough to predict their behavior and response to
management. Emphasis is on the dynamics of current interactions in the environment, with special
emphasis on human-induced changes and expectations. In developing countries, managing soils
is linked to processes of desertiÝcation and the goal of food security.
4.
Correlation. Want to provide a uniform way to link equivalent and near-equivalent soil classes in
different systems together to provide an integrated global overview. Emphasis is on providing a
reference base that reveals the commonality of soils, regardless of their original classiÝcation.
WHAT IS SOIL?
Above are some good reasons to study soils, but what is the userÔs perception of soil, and will
that concept satisfy his or her purpose? What is the universe of soils, what is a population, and
what kind of an individual is needed? As we shall see, there are choices.
1.
Geographic body. Soil is accepted as a function of climate, organisms, relief, parent material, and
time. Because these factors are distributed geographically, so are the functional processes by which
soils occur in landscapes. If observed at points on the landscape, they seem to be individuals; but
if observed in a trench, they are a continuum. A soil has many properties: physical, chemical, and
biological. The evolution of soils and their distribution patterns are of interest: where and why do
the soils occur where they do? Soils, as such, are little geographic bodies; they are polypedons or
their equivalent (Knox, 1965).
2.
Small representative volume. Soil (Jenny, 1963) is conceived as S = f(cl, o, r, p, t). These factors
inÞuence processes that produce properties. There is interest in (a) the factors and how they interact;
(b) the processes that occur and have occurred; (c) the many properties that result from the soil-
forming processes; (d) the sets of properties, how they formed, and how they inÞuence or are
being inÞuenced now. The details of the pedosphere are less important for the primary purpose.
It may be critical, however, for the genetic study of soils as landscapes. Soils are small volumes
with many features; they are pedons or their equivalent.
3.
ProÝle data sets. A soil is a set of propertiesÐphysical, chemical, biologicalÐthat behave or
interact in unique ways with the ambient environment. Based on relationships of properties,
environmental conditions, use, and management, it is possible to predict what will happen and
why. Extrapolation to landscapes is, at some time, necessary, and can build on the knowledge of
others. ProÝles and data sets are the entities of interest.
There is general agreement that all soils (regardless of size or shape) have morphology. This
body or individual requires deÝnition to recognize it either as a member of a population or as a
part of a continuum. Two attributes of interest are the central concept of the individual, and the
boundary limits of the individual. There are options and there are choices.
