Soil Composition and Its Importance in the Ecosystem PDF

Integrated Science Chapter 3 Soil Soil Composition and Its Importance in the Ecosystem Ms. Israa Hassan  Soil is not merely clay underfoot; it is a complex system composed of essential components. It is the upper, loose layer that covers the Earth's crust, formed through weathering and c...

Integrated Science Chapter 3 Soil Soil Composition and Its Importance in the Ecosystem Ms. Israa Hassan  Soil is not merely clay underfoot; it is a complex system composed of essential components. It is the upper, loose layer that covers the Earth's crust, formed through weathering and crumbling of various types of rocks (igneous, sedimentary, and metamorphic) by physical and environmental factors. Soil formation is a continuous yet slow process, evolving over tens of thousands of years. It occurs through weathering processes that fragment and decompose rocks via physical, chemical, or biological means. 1.Physical Weathering – Physical weathering results from the fragmentation of rocks due to temperature fluctuations, repeated freezing and thawing of water in rock cracks, and mechanical forces. – Wind, water currents, and gravity also play significant roles in breaking down rocks into smaller particles. 2. Chemical Weathering – In chemical weathering, mineral components in rocks decompose when they react with water, air, or other chemicals, altering their composition. – This process involves minerals reacting and changing chemically, leading to soil formation. 3. Biological Weathering – Biological weathering occurs when living organisms, such as animals and plants, contribute to the breakdown of rocks. – For instance, digging animals allow water and air to penetrate rocks, and plant roots expand into rock cracks, causing them to fracture and break apart.  Soil composition includes mineral particles, organic matter, water, and air, each playing an essential role in supporting life. It is crucial to understand soil's physical and chemical properties to appreciate its importance in ecosystems. 1. Minerals Minerals are the largest component of soil, mainly silicate minerals. They are categorized into two main types: Primary minerals: Formed by the fragmentation of rocks through physical factors; they tend to be irregular in shape and size and are typically coarse. Secondary minerals: Produced through chemical and biological weathering of primary minerals, and are generally more stable. 2. Organic Matter Organic matter consists of the remains of plants and animals like insects, earthworms, and microorganisms (e.g., fungi and bacteria). This mixture, known as humus, influences the chemical, physical, and biological properties of soil. Sources of organic matter include fertilizers, plant crop residues, and living components such as insects, fungi, and parasites. 3. Water Water occupies the pores within soil, serving as a critical component for nutrient transportation to plants and soil organisms. It aids biological and chemical decomposition processes. Soil's water retention capacity depends on soil grain size and temperature; for example, clay soils retain water more effectively than sandy soils. 4. Gases The exchange of atmospheric gases occurs within the pores of the soil, including: Oxygen: Vital for the respiration of plant roots and soil microorganisms. Carbon dioxide and nitrogen: Essential for organisms like nitrogen-fixing bacteria that contribute to plant growth.  The soil profile is a vertical section of soil that displays its different major horizons or zones. The thickness of these layers varies based on factors such as: The type of bedrock from which the soil formed. The influence of organisms and climate. The time the bedrock has been exposed to weathering. 1.Horizon A (Soil Surface) – Consists mainly of plant remains and is rich in humus. – Contains nutrients, organic matter, and biological activity. – Most plant roots, earthworms, insects, and microorganisms are active here. – It is darker in color due to organic matter. 2. Horizon B (Subsoil Surface) – Contains clay-rich soil and is often less fertile than Horizon A. – Retains more moisture, has a lighter color, coarser texture, and less biological activity. 3. Horizon C (Parent Rock) – Composed of rocky material from which Horizons A and B were formed. – Plant roots do not penetrate this layer.  Soils differ in properties based on composition and environment, with main types including clay, sandy, and alluvial (silt) soils. 1.Clay Soil – Made up of fine sediments with very small spaces between particles. – Dense and poorly ventilated but has a high water retention capacity. – Drains poorly, retaining moisture for long periods; expands when wet and shrinks when dry, leading to cracks. 2. Sandy Soil Composed of coarse sandy deposits with large pores between particles. Well-ventilated and has low water retention; water drains quickly, making it quick to dry. Generally unsuitable for agriculture without regular irrigation and is often subject to erosion. 3. Alluvial Soils (Silt Soils) A mixture of clay, sand, and silt particles with moderate aeration. High water retention capacity, making it moisture-retentive yet prone to weakness when waterlogged. Has average drainage and high fertility, making it ideal for cultivation.  Soil's Essential Role in Ecosystems Soil is a vital component of the ecosystem, supporting numerous environmental processes that sustain life. Key roles include: 1. Supporting Plant Growth Soil supplies essential nutrients like nitrogen, phosphorus, and potassium necessary for plant growth. It provides stability by anchoring roots, preventing plants from falling or shifting. Soil retains water, making it available to plants as needed. 2. Regulating the Water Cycle Soil absorbs and stores rainwater, which supports plants during dry periods. As water percolates through soil layers, the soil acts as a natural filter, removing impurities and pollutants before the water reaches groundwater. 3. Nutrient Cycling Soil contains microorganisms like bacteria and fungi that decompose dead organic matter, converting it into nutrients usable by plants. 4. Supporting Biodiversity and Ecological Balance Soil serves as a habitat for various organisms like worms, insects, bacteria, and fungi. These organisms help with decomposition, nitrogen fixation, and aeration. Soil promotes plant biodiversity, creating a suitable environment for diverse plant species, which supports wildlife. 5. Climate Regulation Healthy soils help mitigate climate change by sequestering carbon (absorbing carbon dioxide) and reducing greenhouse gases in the atmosphere. Soil conservation and reclamation of degraded soils help reduce greenhouse gas emissions. Soil regulates temperature by absorbing and storing heat during the day and releasing it at night, helping to moderate temperature fluctuations. 6. Maintaining Earth's Structure and Preventing Erosion Plants growing in soil help stabilize it, preventing erosion by wind or water. Healthy soils with plant cover prevent desertification and land degradation Soil is an essential element of life, not only supporting plants but also contributing to crucial ecological processes. Each type of soil has unique properties, making it suitable for specific uses and crops. More than a physical medium, soil is a living, dynamic system that supports ecosystem balance and life's sustainability on Earth. Research and Investigation Activity 1: Analyzing Soil Samples 1.Collect soil samples from different areas and analyze their composition (mineral content, organic matter, moisture, and air). 2.Compare their physical characteristics and see how these properties affect plant growth. 1.Texture Observation: Touch and feel the soil to describe its texture. 2.Water Retention Test: Pour water over each sample and observe how much water is retained. 3.Drainage Test: Measure how fast water drains through the soil samples. Research and Investigation Activity 2: Investigating the Influence of Soil on Plant Growth 1.Plant seeds in different soil types (sand, clay, and loam) and observe plant growth over two weeks. 2.Record plant height, leaf color, and germination rate in each soil type. 3.Use the results to draw conclusions about which type of soil best supports plant growth.