Question

List six factors that control soil characteristics and briefly discuss each one.

Short answer

The six factors that control soil characteristics are climate, organisms, relief, parent material, time, and human activity.

Step-by-step solution

Climate

Climate affects soil formation by influencing the rate of weathering of parent material. Temperature and precipitation determine the rate of chemical and physical weathering, organic matter decomposition, and leaching. For example, warm, wet climates promote rapid soil formation.

Organisms

Organisms, including plants, animals, and microorganisms, contribute organic material to the soil. Plant roots can interact with soil by anchoring soil particles, breaking down rock, and creating organic acids that enhance weathering. Microorganisms decompose organic matter, enriching the soil with nutrients.

Relief (Topography)

Topography influences water drainage and retention, affecting soil moisture and erosion. Soils on steep slopes tend to be thinner due to erosion, whereas soils in low-lying areas may accumulate more organic material and be deeper due to sediment deposition.

Parent Material

Parent material refers to the original rock or sediment from which the soil develops. It provides the mineral composition and initial structure for the soil. Different types of parent material (like volcanic ash or limestone) contribute different minerals and chemistry to the soil.

Time

Time allows for the natural processes of weathering, organic matter accumulation, and horizon development to occur. Older soils are often more developed, with well-defined horizons, but they may also be more leached and weathered compared to younger soils.

Human Activity

Human activities such as agriculture, grazing, deforestation, and urbanization can significantly alter soil structure, composition, and fertility. These activities can cause erosion, compaction, and changes in water and nutrient cycles, impacting soil health and productivity.

Key concepts

Soil Formation

Soil formation is a fascinating process where various factors contribute to creating the earthy mix we rely on for agriculture and natural ecosystems. Over time, rocks and organic matter break down to form soil. There are several key players in this process: climate, organisms, relief, parent material, time, and human activity.
Climate plays a significant role by affecting the rate at which weathering and organic matter decomposition occur. Wetter and warmer climates generally speed up soil development. Organisms, such as plants and microorganisms, help by adding organic material and nutrients to the soil.
Relief, or the lay of the land, dictates how water moves and drains. This affects erosion and soil thickness. Parent material provides the foundational minerals and initial composition, setting the stage for soil characteristics. Time allows these processes to evolve, resulting in soil with distinct layers or horizons. Human activities also impact soil formation through practices that replenish or deplete nutrients.

Weathering

Weathering is the breakdown of rocks and minerals into smaller particles, an essential part of soil formation. There are two main types of weathering: physical and chemical.

• Physical weathering involves breaking down rocks into smaller pieces without changing their chemical composition. This can happen through processes like freezing and thawing, root growth, or abrasion from wind and water.
• Chemical weathering changes the chemical composition of rocks and minerals. Water and gases can react with minerals, leading to decay and dissolution. For example, carbonic acid in rain can dissolve limestone over time.

Weathered material from these processes eventually combines with organic matter to form soil, offering varying nutrients based on the original parent materials.

Organic Matter Decomposition

Organic matter decomposition is crucial for soil fertility and structure. It involves the breakdown of plant and animal residues into simpler substances.
Decomposition is driven by microorganisms, like bacteria and fungi, which break down complex organic compounds into humus, a sticky, nutrient-rich component of soil. This process releases valuable nutrients such as nitrogen, phosphorus, and potassium into the soil.
Humus plays several roles in soil health:

• Enhances nutrient availability by holding essential minerals.
• Improves soil structure by binding soil particles together.
• Increases water retention, which is beneficial for plants in dry periods.

As organic matter decomposes, it not only supplies nutrients but also boosts the soil's ability to support plant growth.

Topography

Topography refers to the shape and features of the Earth's surface and strongly influences soil characteristics. It affects how water moves across the landscape, impacting erosion and drainage patterns.
In hilly or mountainous regions, soil tends to be thinner due to erosion, as rainwater flows downhill, washing away soil particles. On flat or gently sloping land, water may accumulate, leading to deeper, richer soils that can develop thick layers of organic material.
Topography also affects microclimatic conditions, like sunlight exposure and temperature variations, which can influence vegetation types and growth rates, further affecting soil development.
Understanding topography helps in land use planning and management, ensuring sustainable agriculture and natural resource conservation.