WEEK ONE LECTURE NOTES
CHAPTER ONE - INTRODUCTION
The soil is a "collection of three-dimensional, natural bodies on the earth's surface that has been subjected to and influenced by the genetic and environmental factors of parent material, climate, organisms and topography all acting over a period of time and producing a product - soil - that differs from which it was derived in many physical, chemical, biological and morphological properties and characteristics."
I. PEDOLOGY - recognized subfield or area of specialization of soil science which studies the soil and its weathering profile - (Division S-5 of Soil Science Society of America Journal)
A. From Greek
words:
pedos ---->
ground
logos ----> science
B. Subdivisions of Pedology
1. Genesis - the soil is a product of factors and processes of soil formation
2. Classification - categorization of soils into groups according to their physical, mineralogical and chemical properties - The term Soil Taxonomy when used in this course refers to the USDA Soil Classification system developed in the United States and widely used throughout the world
3. Morphology - description of the properties of soil horizons in a profile
4. Survey - field mapping; the determination of soil types and their pattern on the landscape
5. Characterization - measurement of soil properties using laboratory analysis
6. Interpretations - predicts how a soil responds to land use and management
II. CONCEPTS OF SOIL GENESIS
A. Pedogenic processes that are active in soils today have been operating over time
B. The soil profile is the result of many reactions and processes that have proceeded simultaneously in both the present and past
C. Distinctive combinations of geological materials and processes produce distinctive soils
D. The five soil forming factors (cl, o, r, p, t) provide the energy to drive the pedogenic processes within the soil
E. Present day soils may carry the imprint of pedogenic and glacial processes not presently active at a site
F. A succession of different soils may have taken place at a particular location as soil forming factors have changed
G. The time scale for soil formation is much shorter than the geologic time scale but much longer than the age of most biological species
H. Complexity of soil genesis is more common than simplicity
I. Soils are natural sites for the formation of clay minerals
J. An understanding of soil genesis is useful in classification and mapping
K. Knowledge of soil genesis is basic to understanding the impact of human use and management
III. SOILS AS AN OPEN SYSTEM (fig.1.9)
IV. BASIC PRINCIPLES OF SOIL CLASSIFICATION
A. Whenever two objects are compared with one another, either critically or casually, they are being distinguished one from the other, and are in effect, being classified. The nature and extent of the real and significant differences that exist between the two objects will become more or less apparent depending upon the observational skill of the observer and upon their fundamental knowledge of the objects. The process of classification involves the formation of classes by grouping the objects on the basis of their common properties. In any system of classification, those groups about which the greatest number of things can be stated for the chosen objective are generally the best and the most useful classification groupings. A classification system is an organization of the knowledge of the moment.
B. We classify soils for the following purposes:
1. To organize our
knowledge about soils
2. To
provide an organizational chart or map of the world of soils as we perceive it -
the soil survey
3. To
develop principles and guidelines for proper use and
management:
a. to predict
behavior
b. to identify best
uses
c. to estimate
productivity
d. to identify potential
problems
4. To
facilitate easier transfer of information and technology
5. To provide a basis
for research and
experimentation
6. To
understand relationships among individuals of the
population
C. Attributes of a good soil taxonomic system:
1. Definition of a class
or taxon should carry as nearly as possible the same meaning to each
user
2. Should be a
multicategoric system
(hierarchy)
a. lower levels - narrowly defined - large number of differentiating
characteristics
b. higher levels - broadly defined - few soil properties are used
to differentiate
3. Classes
or taxa should be concepts of real bodies of soil that exist in
nature
4. Must be
capable of providing for all the soils observed in a
landscape
5. Differentiating
characteristics should be properties that are observable in the field or
quantitatively measured by reliable
techniques
6. The system
should be capable of modification to incorporate new knowledge with a minimum of
disturbance
7. The criteria
used should keep undisturbed and cultivated soils in the same taxa.
D. Definition of terms:
1. Class or taxon - a group of individuals or other units that are similar in selected properties (characteristics) and distinguished from all other classes of the same population by differences in these properties
2. Population - all the individuals of a natural population collectively
3. Category - a grouping of classes (taxa) formed at about the same level of classification produced by differentiation within the population being categorized. It includes the entire population.
4. Pedon - the smallest volume for which one should describe and sample the soil to represent the nature and arrangement of its horizons. It has three dimensions. Its lower limit extends downward to the depth of plant roots or the lower limit of the genetic horizons. Its lateral dimensions are large enough to represent the nature of the horizons and their variability. The minimum lateral cross section ranges from one to ten square meters.
5. Polypedon or soil individual - it is the smallest natural body that can be defined as a thing complete in itself. It consists of more than one contiguous pedons all of which are within a defined range of soil properties. It is the link between the pedon and the taxonomic unit (the soil series).
6. Mapping unit - constructed during the course of a soil survey to identify populations of taxonomically identified soil individuals within an area of land. A taxon name is commonly used as part of the mapping unit name.
7. Soil profile - vertical cut that exposes the horizons for examination or sampling
8. Soil solum - genetic horizons that have undergone alteration by pedogenic processes
9. Control section - portion of the pedon used for the family category in Soil Taxonomy
