DEFINITION OF SOIL
Soil may be defined as: “A dynamic natural body on the surface of the earth in which plants grow, composed of mineral and organic materials and living forms.”
“Soil is a natural body developed by natural forces acting upon natural materials. It is usually differentiated into horizons from mineral and organic constituents of variable depth which differ from the parent material below in morphology, physical properties, and constituents, chemical properties and composition, and biological characteristics.”
“Soil is the more or less loose and crumbly part of the outer earth crust in which, by means of their roots, plants find foot-hold and nourishment as well as all other conditions essential to their growth.”
“Soll is the upper a most weathered layer of the earth’s crust, which consists of rocks that have been reduced to small fragments and have been more or less changed chemically together with the remains of plants and animals that live on it and in it.”
Soil science: The the science dealing with soil as a natural resource on the surface of the earth, including, Pedology (soil Genesis, classification, and mapping) and the physical, chemical, biological, and fertility properties of soils and these properties in relation to their management for crop production.
SCOPE OF SOIL SCIENCE
Soil science has six well-defined and developed disciplines. The scope of soil science is reflected through these disciplines.
1 Soil fertility: it denotes the status of a soIl concerning the amount and availability of elements to a plant necessary for its growth. Soil fertility, therefore, refers to the nutrient-supplying properties of the soil. it is best to understand considering (i) the nutrient requirement of plants; (ii) the supply of nutrients by the soil, (iii) ways in which nutrients are lost from the soil, and (iv) methods by which sol fertility may be maintained or restored. White, soil productivity is the capacity of a soil, in its natural environment, to produce crops under a specified system of management, and expressed in terms of yield. In the definition, specifications are necessary, since no soil can produce all crops with equal success nor can a single system of management produces the same effect on all soil.
2 Soil chemistry: It is a division of soil science concerned with the chemical constituents, chemical properties, and soil chemical reactions. it is the study of the chemical composition of soil concerning crop needs.
3 Soil physics: Soil physics is a division of soil science that involves the study of the physical properties of soil. Soil is a complex system and is made up of solid, liquid, and gaseous materials. The chemical and physical relationships among solid, liquid, and gaseous phases are affected not only by their own respective properties but also by temperature, pressure, and light.
4 Soil microbiology: Soll microbiology is the science, which deals with the microscopic population of the soil, its role in various transformations, and its importance in plant nutrition and crop production. Soil microbiology is concerned not only with the enumeration and classification of soil-inhabiting microorganisms but also with measurements of their activities in the soil. These activities are like the decomposition of organic substances that are present in the soil or that find their way into the soil, with the production of ammonia, nitrates, fixation of nitrogen, and numerous such transformations.
5 Soil conservation: it is a division of soil science dealing with the protection of soil against physical loss by erosion or against chemical deterioration; that is excessive loss of nutrients by either natural or artificial means. It deals with a combination of all management and land-use methods, which conserve the soil against degradation or deterioration by natural or human-induced factors. It is the management of the soil to produce high yields and, at the same time, protect it from degradation.
6 Pedology: The science dealing with the genesis, survey and classification and the laws of the geographic distribution of soils as a body in nature.
THE APPROACHES OF SOIL STUDY
Historic development of science gives out two concepts of soil study. One treats soil as a natural body, the weathered and synthesized product of nature. While other treat soil as a medium for plant growth, these conceptions lead to the two approaches that can be used in studying soils, Pedological and Edaphological.
Pedologlcal approach; The origin of the soil, its classification, and its description is examined in pedology (from the Greek word pedon, which means soil or earth. Pedology is the study of the soil as a natural body and does not focus primarily on the soil’s immediate practical use. A pedologist study examines and classifies soils as they occur in their natural environment.
Edaphological approach: Edaphology (from the Greek word edaphos, which means soil or ground) is the study of soil from the standpoint of higher plants. Edaphologists consider the various properties of soils in relation to plant production. They are practical and have the production of food and fiber as their ultimate goal. To achieve that goal, Edaphologists must determine the reasons for variation in the productivity of soils and find means of conserving and improving production.