Soil Science Explained: Definition and Key Disciplines

Soil science comprises six well-defined and developed disciplines, and the scope of soil science is manifested through these disciplines. Soil science is the scientific study of soil as a natural resource on the Earth's surface, encompassing pedology (which focuses on soil genesis, classification, and mapping), as well as the physical, chemical, biological, and fertility properties of soil, and their relationship to soil management for crop production.

Soil fertility: refers to the nutrient-supplying properties of soil.

Soil chemistry: pertains to the chemical constituents, chemical properties, and chemical reactions within the soil.

Soil physics: involves the study of the physical properties of soil.

Soil microbiology: deals with microorganisms, including their population, classification, and role in transformation.

Soil conservation: focuses on the protection of soil against physical loss through erosion or chemical deterioration, which involves excessive loss of nutrients by natural or artificial means.

Pedology: concerned with the genesis, survey, and classification of soil.

Components of Soil and Their Percentages

Component                                  Percentages

Mineral matter                          45%

Organic matter                           5%

Soil water is 25%

The basic components of soil are minerals, organic matter, water, and air. The typical soil consists of approximately 45% mineral, 5% organic matter, 20-30% water, and 20-30% air. These percentages are only generalizations at best. In reality, the soil is very complex and dynamic.

Soil is a natural body comprising mineral and organic constituents, which are organized into horizons. These horizons are typically unconsolidated and vary in depth, exhibiting differences among themselves and compared to the underlying parent material. These differences encompass morphology, physical composition, chemical properties, overall composition, and biological characteristics.

Soil represents the unconsolidated mineral matter found on the Earth's surface. It undergoes the influence of genetic and environmental factors, including parent materials, climate (in terms of moisture and temperature effects), macro and microorganisms, as well as topography. These influences act over time, culminating in the development of a distinct product known as 'soil.' This soil material diverges from its source material in numerous physical, chemical, biological, and morphological properties and characteristics.

Importance of Soils in Agriculture

Soil is a medium for plant growth, a habitat for different species, a filtration system for surface water, and the maintenance of atmospheric gases. Soil sustains life by providing food in the form of essential minerals and nutrients; water and air to support the survival and growth of plants, worms, fungi, and bacteria.

Soil not only absorbs valuable water and prevents evaporation from the surface but also initiates crop growth, the production of bio-materials, anchors roots, and enables the transport of water and nutrients to the soil interface and the roots of plants.

Soil filters water, aiding in the regulation of the Earth's temperature and crucial greenhouse gases. It also serves as the foundation for basic ecosystem functions promoted by advances in natural resource and environmental sciences.

The study of soil resources is critical for the environment, food production, and fiber production. Understanding techniques to improve soil conservation, such as cover crops, crop rotation, planted windbreaks, and conservation tillage, which affect both soil fertility and erosion, is also important.

Soil plays an important role in the farm ecosystem by providing nutrients essential for the growth of agricultural and horticultural crops. Fertile soil is rich in nutrients and highly suitable for agriculture, serving as the primary nutrient base for healthy crops. Rich soil contains a pH and primary plant nutrients like nitrogen, phosphorus, and potassium due to its previous or decaying content of organic matter, along with minor nutrients that aid in plant growth.

Some of the functions associated with soil include nutrient cycling, water regulation, an ecological role in providing a plant growth medium, recycling organic wastes and nutrients, modifying the atmosphere, regulating water supply and purification, serving as a habitat for soil organisms, and participating in other normal processes that occur in the ecosystem to benefit water quality, food production, and flood control, thus improving the economy and quality of life.

Important benefits of soil include its role as a natural protector of seeds and plants, the dispersal and germination of seeds within the soil ecosystem, a physical support system for plants, and the retention and delivery of nutrients to crops.

Approaches to Soil Study

Parent Material:

Parent material refers to the upper portion of the regolith. It consists of unconsolidated mineral materials that have undergone chemical weathering processes, and it serves as the initial stage of soil formation.

Parent material plays a pivotal role in soil development, and it can consist of both mineral rock and organic matter. Soil formation begins when parent rock material is exposed to the atmosphere, or when organic matter and minerals are deposited on the Earth's surface.

Classification of Soil:

Soil classification primarily relies on its texture, categorizing it into three primary groups based on particle size: small (clay), medium (silt), and large (sand). Additionally, soils are classified into three major types based on the agents involved in the weathering processes.

Weathering of Rocks and Minerals:

Weathering is the process of disintegration and decomposition of rocks and minerals due to both physical agents and chemical processes. This process leads to the formation of regolith or unconsolidated residues, either on the Earth's surface or above solid rocks.

Weathering essentially involves the breakdown of solid rocks into parent material, which is crucial in soil formation.

The Sequence of Processes in Soil Formation:

Soil formation encompasses a series of processes, beginning with the weathering of rocks and minerals. This leads to the production of regolith or parent material, which eventually transforms into genuine soil through soil-forming processes.

Soil minerals, derived from parent materials through weathering and natural erosion, form the foundation of soil. Various factors and processes, including water, wind, temperature changes, gravity, chemical interactions, living organisms, and pressure differences, contribute to the breakdown of parent materials.

Processes of Weathering (Soil Formation):

a). Physical Weathering of Rocks:

Physical weathering involves the disintegration of rocks into smaller pieces without creating new substances. Factors such as rock permeability, temperature variations, and mineral characteristics impact this process. For example, porous sandstone weathers more readily than solid basalt, and temperature fluctuations contribute to rock surface weakening.

b). Chemical Weathering of Rocks:

Chemical weathering occurs through various chemical processes, leading to the breakdown of minerals and rocks. The surface area of rocks plays a crucial role in the effectiveness of chemical weathering. Factors like hydration, hydrolysis, water action, freezing, alternate wetting and drying, wind action, solutions, carbonization, oxidization, and reduction influence chemical weathering.

To sum it up, chemical weathering involves the destruction of primary minerals and the production of secondary minerals. In sedimentary rocks, weathering initially targets weak bonding agents, such as iron oxide, freeing particles for further weathering.

c). Biological Weathering of Rocks:

In contrast to physical and chemical weathering, biological weathering is facilitated by living agents, which both decompose and disintegrate rocks and minerals. The environmental context significantly influences biological processes.

Animals, including humans, contribute to weathering through activities such as rock cutting for construction. Many animals, such as birds, insects, and worms, create holes in rocks, accelerating weathering. In tropical regions, ants, termites, and their activities, including acid secretion, play a vital role in rock disintegration.

Roots of plants create cracks and joints in rocks

Roots of plants, including trees, penetrate cracks and joints in rocks, exerting disruptive forces as they grow. Microorganisms, including bacteria, mosses, fungi, and actinomycetes, play a critical role in nutrient extraction, decomposition, and soil formation.

These organisms interact with the breakdown of plant and animal remains, releasing organic molecules and carbon dioxide, which contribute to mineral breakdown and soil development.

Conclusion

Soil science is a multidisciplinary field that delves deep into the intricate world beneath our feet. It encompasses pedology, soil fertility, soil chemistry, soil physics, soil microbiology, and soil conservation, each shedding light on different aspects of this vital natural resource. As we've explored the components of soil and the factors influencing its formation, it becomes evident that soil is far from static; it's a dynamic and complex entity shaped by geological, environmental, and biological forces over time.

The importance of soils in agriculture, ecosystem functions, and environmental sustainability cannot be overstated. Soil provides the essential foundation for plant growth, nutrient cycling, water regulation, and habitat for countless organisms. It is a silent partner in the global effort to feed the world's population and maintain the delicate balance of our planet's ecosystems.

As we move forward in our understanding of soil science, it is imperative that we continue to explore innovative approaches to study soil, nurture its fertility, and protect it from degradation. Our ability to implement sustainable practices in agriculture and land management, guided by the principles of soil science, will be crucial in ensuring the health of our soils and the well-being of future generations.