Question

What is the basis of the Soil Taxonomy system? How many soil orders, suborders, great groups, subgroups, families, and series are there?

Short answer

The Soil Taxonomy system is based on soil properties, formation processes, and distribution patterns. There are 12 soil orders. Each order has various suborders, which are further divided into great groups, subgroups, families, and series. The exact number of these categories varies as they account for local variations.

Step-by-step solution

Understanding the Basis of Soil Taxonomy

The Soil Taxonomy system is a taxonomic classification system for soils. It's based on soil properties, formation processes, and distribution patterns. It's primarily used in the United States, but is also applied worldwide.

Identifying Soil Orders

Soil orders are the highest level of classification in the soil taxonomy. There are 12 soil orders: Alfisols, Andisols, Aridisols, Entisols, Gelisols, Histosols, Inceptisols, Mollisols, Oxisols, Spodosols, Ultisols, and Vertisols.

Detailing Suborders

Each soil order is further divided into suborders. The suborders are based on properties that influence soil forming factors or soil use. There are various suborders in each soil order, hence the total number differs.

Explaining Great Groups, Subgroups, Families, and Series

Great groups distinguish soils based on the arrangement of horizons and other developmental characteristics. Each great group is divided into subgroups. The soil family category is used to separate soils based on physical and chemical properties, while the series is used to refine the Soil Taxonomy further, accounting for local variations within a family. As with suborders, the exact number of great groups, subgroups, families, and series varies.

Key concepts

Soil Orders

In the Soil Taxonomy system, soil orders represent the most fundamental level of classification. There are 12 distinct soil orders, each named after specific characteristics and formation processes. These orders are crucial for understanding broad aspects of soil composition and functionality.

• Alfisols: Known for their fertility and typically found in temperate regions.
• Andisols: Originate from volcanic ash and have unique properties like high phosphorus fixation capacity.
• Aridisols: Characteristic of arid regions with limited moisture, often featuring salt accumulations.
• Entisols: Recently formed soils with minimal horizon development.
• Gelisols: Found in cold environments, often with permafrost.
• Histosols: Rich in organic matter, commonly found in wetlands.
• Inceptisols: Young soils with more horizon development than Entisols.
• Mollisols: Known for their thick, dark, and fertile surface horizon.
• Oxisols: Highly weathered, often found in tropical regions with poor fertility.
• Spodosols: Found under coniferous forests, possessing distinctive horizons from organic matter and aluminum accumulation.
• Ultisols: Weathered soils found in humid climates, slightly less fertile than Alfisols.
• Vertisols: Contain high clay content, causing them to shrink and swell dramatically with moisture changes.

Understanding these soil orders enables scientists and land managers to predict how soils in an area might behave or respond to land-use changes.

Soil Classification

Soil classification in the Soil Taxonomy system is an organized way to explore the diversity of soils by examining specific attributes. This classification provides a framework for identifying and comparing soil types, essential for agricultural planning, environmental management, and scientific research. The system divides soils into orders, suborders, great groups, subgroups, families, and series. This multi-tiered structure, similar to biological taxonomy, allows detailed categorization based on a series of increasing specific attributes.

• Suborders: Refine the broad categories of orders, focusing on moisture and temperature regimes or vegetation type.
• Great Groups: Consider the presence of specific horizons and their arrangements.
• Subgroups: Show deviations from typical characteristics of a great group.
• Families: Group soils based on similar physical and chemical characteristics, like texture or mineralogy.
• Series: Represent the most specific category, often based on localized soil properties and conditions.

This classification helps in managing soil resources efficiently and understanding how different soils can affect plant growth and environmental interactions.

Soil Properties

Soil properties are integral to the Soil Taxonomy classification, offering insights into both physical and chemical characteristics that define different soil types. These properties include texture, structure, color, depth, pH, organic matter content, and nutrient availability. Each property plays a significant role in determining the soil's utility for agriculture, construction, and ecology.

• Texture: Determined by the proportion of sand, silt, and clay particles, affecting drainage and nutrient retention.
• Structure: Refers to how soil particles bind together, impacting aeration and water movement.
• Color: Offers clues about organic content and nutrient availability.
• pH Level: Indicates the acidity or alkalinity, influencing nutrient solubility.
• Organic Matter: Enhances soil fertility by retaining moisture and providing nutrients.

Understanding these properties is crucial for effective soil management and use, as they determine the soil's ability to support plant life and other ecosystem services.

Soil Formation Processes

The development of soil from parent material involves intricate soil formation processes, which include weathering, organic matter addition, and horizon development. These processes result in the diverse characteristics observed in soils around the world.

• Weathering: Breakdown of parent material into smaller particles via physical, chemical, or biological means.
• Organic Matter Accumulation: Addition of decomposed plant and animal matter to soil, enhancing fertility.
• Horizon Development: Formation of distinct horizontal layers within the soil profile. Each layer, or horizon, has unique properties based on the accumulation or leaching of materials.
• Leaching: The process by which water removes soluble substances from soil, often leading to the depletion of nutrients in some horizons.
• Clay Translocation: Movement of clay particles from upper to lower horizons, impacting soil texture and structure.

These formation processes define the distinct behaviors and properties of different soils, reflecting the climatic, biological, topographical, and parent material influences. Understanding these processes is key to predicting soil responses to environmental or management changes.