Factors Affecting Soil Formation

Soil formation is a complex process influenced by various factors that interact to create diverse soil profiles. These factors, often referred to as the “five factors of soil formation,” include parent material, climate, topography, organisms, and time.

Parent Material

Parent material refers to the material from which soil develops. It can be rock that has decomposed in place or material deposited by wind, water, or ice. The character and chemical composition of the parent material play a crucial role in determining soil properties, especially during the early stages of development.

Coarse-grained parent materials composed of minerals resistant to weathering tend to produce coarse-textured soils, while fine-grained soils develop from unstable minerals that readily weather. Parent material composition also impacts soil chemistry and fertility. Materials rich in soluble ions, such as calcium, magnesium, potassium, and sodium, are easily dissolved in water and made available to plants. In contrast, materials low in soluble ions can lead to acidic soils unsuitable for agriculture.

Climate

Climate, particularly temperature and precipitation, strongly influences soil formation. Energy and precipitation drive physical and chemical reactions on the parent material. Climate also determines vegetation cover, which in turn affects soil development. Precipitation influences horizon development factors, such as the translocation of dissolved ions through the soil. Over time, climate becomes a primary influence on soil properties, while the influence of parent material diminishes.

Topography

Topography, encompassing slope angle and length, has a significant impact on soil formation. It determines water runoff and affects microclimate, which in turn influences vegetation. Water moving across the surface can strip away parent material, impeding soil development. Erosion is more pronounced on steeper, unvegetated slopes.

Slope angle and length affect runoff generated by rainfall. As water moves downslope, it accumulates, increasing in volume and velocity. This leads to increased erosion near the base of the slope, preventing the formation of well-developed soils.

Topography also influences soil texture. Larger particles, like sand, are deposited closer to the base of the slope, while finer particles, like clay, are carried further away. As a result, coarse-textured soils tend to be found near the base of the slope, while fine-textured soils are located further away.

Organisms

Organisms, including plants and animals, play a vital role in soil development and composition. They add organic matter, aid decomposition, weathering, and nutrient cycling. The richness and diversity of soil organisms and plant life are closely tied to climate.

Nutrient cycling involves the exchange of nutrients between organisms and soils. Broadleaf deciduous trees, like oak and maple, have high nutrient demands and create surface litter rich in nutrients when leaves die and fall to the forest floor. Decomposition of the litter releases nutrients back into the soil for the tree to take up, maintaining high levels of soluble bases and nutrients in the soil.

In contrast, pine trees generally have low nutrient demands. The decaying litter that falls to the forest floor is poor in nutrients. As a result, little cycling of soluble nutrients occurs, leading to acidic soil conditions.

Soil organisms also contribute to weathering. The decomposition of pine needles creates a weak acid that can strip soluble ions from the soil. Burrowing animals create passageways through the soil, aerating it and allowing water to infiltrate. They also help translocate materials and fertilize the soil at depth.

Time

Time is a crucial factor in soil formation. Over time, weathering processes continue to act on soil parent material, breaking it down and decomposing it. Horizon development processes differentiate layers in the soil profile by their physical and chemical properties. As a result, older, more mature soils have well-developed sequences of horizons, though some may undergo so much weathering and leaching that visually distinct layers may be hard to see.

Climate interacts with time during soil development. Soil development proceeds much more rapidly in warm and wet climates, reaching a mature status sooner. In cold climates, weathering is impeded, and soil development takes much longer.

In conclusion, soil formation is a complex process influenced by the interaction of five key factors: parent material, climate, topography, organisms, and time. These factors give soil profiles their distinctive character and determine their suitability for various agricultural and environmental purposes.

References:

1. University of Minnesota Extension. (2018). Five factors of soil formation. Retrieved from https://extension.umn.edu/soil-management-and-health/five-factors-soil-formation
2. Ritter, M. E. (2022). 11.5: Factors affecting soil development. In The Physical Environment: An Introduction to Physical Geography (pp. 333-336). LibreTexts. Retrieved from https://geo.libretexts.org/Bookshelves/Geography_(Physical)/The_Physical_Environment_(Ritter)/11%3A_Soil_Systems/11.05%3A_Factors_Affecting_Soil_Development
3. Landcare Research. (n.d.). Factors affecting soil formation. Retrieved from https://soils.landcareresearch.co.nz/topics/understanding-soils/how-do-soils-form/factors-affecting-soil-formation/

FAQs

What is soil formation?

Soil formation is the process by which soil develops from parent material, such as rock or deposited material. It is influenced by various factors that interact over time to create distinct soil profiles.

What are the five factors of soil formation?

The five factors of soil formation are:

1. Parent material: the material from which soil develops, such as rock or deposited material
2. Climate: temperature, precipitation, and other climatic factors
3. Topography: the shape and slope of the land
4. Organisms: plants, animals, and microorganisms that live in the soil
5. Time: the length of time over which soil-forming processes have been acting

How does parent material affect soil formation?

Parent material influences soil properties such as texture, chemistry, and fertility. Coarse-grained parent materials produce coarse-textured soils, while fine-grained materials produce fine-textured soils. Parent material composition also affects soil chemistry and the availability of nutrients for plants.

How does climate affect soil formation?

Climate, particularly temperature and precipitation, influences soil formation by driving physical and chemical reactions on the parent material. Climate also determines vegetation cover, which in turn affects soil development. Warmer and wetter climates promote rapid soil formation, while colder and drier climates slow down the process.

How does topography affect soil formation?

Topography, including slope angle and length, affects soil formation by influencing water runoff and erosion. Steeper slopes are more prone to erosion, which can strip away parent material and impede soil development. Water runoff can also transport soil particles, leading to the formation of different soil textures and profiles.

How do organisms affect soil formation?

Organisms, including plants, animals, and microorganisms, play a vital role in soil formation. They contribute organic matter, aid decomposition, weathering, and nutrient cycling. Plant roots help break down rocks and create channels for water infiltration. Soil organisms also help aerate the soil and improve its structure.

How does time affect soil formation?

Time is a crucial factor in soil formation. Over time, weathering processes continue to act on parent material, breaking it down and decomposing it. Horizon development processes differentiate layers in the soil profile by their physical and chemical properties. As a result, older, more mature soils have well-developed sequences of horizons.