What is Soil? Soil Formation Soil Classification Soil Physics Soil Chemistry Living Soil Soil Fertility Soil Management Soil Inventory & Mapping Importance of Soil Soil Composition Soil Biology

For many years, soil was considered simply the loose fraction of the Earth's crust. It was not until the 1880s, that soil was recognized as a natural body - worthy of study in its own right - by the Russian scientist Dokuchaev. Soil is a complex mixture of mineral matter, organic matter and living organisms. Soil is a product of the environment; constantly changing, constantly evolving. Soils develop over time, sometimes very slowly in dry desert areas or more quickly in wet tropical regions. The soil is different from "powdered rock" or "dirt" in that it supports life; in particular, the growth of plants. Soil can be thought of as the "skin" of the land; without it the land would die. Like skin, the soil is constantly being eroded at its surface by wind, water and man's activities, and being renewed at its base by weathering of its parent material. Think of this important resource in three dimensions i.e. soil has depth as well as area. Look at a section through the soil (soil profile) in a road cut. Notice the several layers with different colors. See how the depth of individual layers change from the top to bottom of hills. Why are the layers thicker at the bottom of the hill? Why is the top layer of soil the darkest? The answers to all these questions relate to how the soil has formed. Man's perception of soil differs according to the use of the soil. An engineer sees the soil as a support media for buildings, bridges and highways. A miner sees soil as the overburden that has to be removed to access valuable minerals. A landscaper sees soils as a resource to beautify parks and gardens. The agriculturist and forester as a resource to produce crops and trees. We can apply the traditional sciences of physics, chemistry and biology to study soils. Many scientists have done this over the years. But emerging research is convincing us to change our approach. We are challenged to look at natural systems by thinking of changes and interactions with an integrated approach of all the sciences. Can we study a soil organism without taking into account its environment? Can we study a particle of soil without considering its neighbors in the same aggregate? Clearly, much more knowledge is to be gained if we open our eyes and step out of the barriers that traditional science teaching has created. The Soil Sciences of Physics, Chemistry and Biology attempt to do just this. While concentrating on physical, chemical or biological properties of soils, the interactions and dynamics are not forgotten. Physical Properties Soils are a complex three phase system composed of solids, liquids and gases. The study of the physical behavior of these phases is called Soil Physics and includes: density and porosity texture structure colour waterretention and movement Although most of these properties are inherited from the soil's parent material, with some effort man can adjust some properties to improve or maintain the soil's fertility. The round top structure in the image is typical of a soil high in sodium salts. Crops growing on this soil will have great difficulty penetrating the subsoil with their roots. Chemical Properties Soil Chemistry studies the chemical characteristics of soil which depends on their mineral composition, organic matter and environment. Chemical reactions occur when substances either combine or break apart to form new substances with identifying properties that are different from the original substances. The reactions require energy of some kind (either a gain or loss). New substances may be formed when bonds between atoms or ions are formed, broken or when atoms are rearranged. Ions are atoms which are positively or negatively charged by either losing or gaining electrons. Ions with different charges have an attractive force for each other, while similarly charged ions repel one another. One example of a chemical reaction is hydrogen uniting with oxygen to form water. An understanding of soil chemistry is important in soil formation and fertility. How rocks and minerals breakdown and transform into new compounds is essential to our understanding of weathering and erosion. How mineral nutrients are transformed and bound in soil leads to better fertilization and soil testing techniques. The image is a thin section of soil parent material under a polarized microscope. Note the complex arrangement and size of minerals and the pore structures. Each mineral will have its own rate of solubility and resistance to weathering. For similar minerals, the smaller particles will dissolve faster than larger ones because of increased surface area (per unit mass) exposed to weathering processes. Biological Properties Soil Biology is the study of the living component of soils. Numerous bacteria, fungi, actinomycetes, worms, insects, small rodents and mammals inhabit the soil. Many of these organisms help in maintaining the fertility of the soil by decomposing plant and animal residues which recycle the nutrients. The interaction among various organisms is a fascinating subject in soil science. An example of this interaction is the association of bacteria with plants roots as shown in the image. Often, this association leads to the mutual benefits. Updated Nov 12 2002

The modern classification of soils began with the Russian scientist Dokuchaev in the 1880s. Soil surveys in the US, Europe and Canada began only a few years later. How do we classify soils? We could probably develop many classifications based upon how soils were formed by the environment. could be used for crop production. could be used for building. Today we use a scientific taxonomy based upon the soil's morphology or its (shape and form). From this classification we can interpret important facts relating to crop production, management and so on. However, there are many classification systems used throughout the world. Canada has its own, as does the U.S.A. and the FAO. Fortunately, it is relatively easy to translate from one scheme to the other. The Canadian system (and most others) arranges soils into groups based upon the soil profile characteristics. Why Classify Soil? The most obvious reason is that if one person is studying a soil in one part of the world, are the research results communicated to workers in other parts of the world so that they can apply what has been learned? Classification allows us to communicate our ideas and research about soil and extrapolate them to other similar areas. It also allows us to predict the behavior of soils such as which soils are most subject to flooding or wind erosion? Or where does a city put its garbage dump? Or which soils will be most likely to have a sulfur deficiency?   Soil Profile It is important to think of soils in three dimensions; i.e. the soil has depth. Understanding the soil profile is essential to be able to classify soils. The formation of the layers or soil horizons is a result of the environmental forces that have acted upon the soil during its formation, often for thousands of years. The colour, texture and structure of each horizon and often its chemical characteristics are used to group soils and form the basis of most systems of soil classification.   Soil Zones The Soil Zones of the Canadian Prairies are not found in the Canadian Taxonomy of Soils but nevertheless the broad concept of a soil zone is valid. It enables us to think of soils as a product of the environment and make broad recommendations as to crop production and management. There are many ways to classify soils and there are several systems in use worldwide. Most notable is the U.S system of Soil Taxonomy or "7th approximation" (it underwent 7 "approximations" between 1951 and 1960 before being officially adopted in 1965). This system is used in many countries throughout the world but some countries -- Brazil, Canada, France, Russia -- have developed their own systems. Scientists often report the U.S equivalent classification in scientific reports and publications as well as the local classification, so that their work will have wider appeal. Regardless, all systems recognize the soil as a product of the environment and differ mainly in groupings and horizon definitions. The Canadian Classification of soils organizes or groups soils into a hierarchy of five levels: Order Great Group Subgroup Family Series An important question to ask yourselves is how much area of soil is needed to be able to classify it? Or, how much different does a soil have to be to warrant a different classification? The question is answered, at least in part, by looking at the hierarchy. Soil orders would cover apply to soils over large areas. For example, one order (Chernozemic) covers most of the southern prairies. The northern agricultural areas in the transition zone between prairie and forest are dominated by Luvisolic soils. At the other end of the scale, the lowest member of the hierarchy, the soil series, would apply to small areas dispersed over fields. Updated Nov 12 2002

ABDULLAH R M GHWERE

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