Soil Taxonomy is a comprehensive system developed by the United States Department of Agriculture (USDA) for classifying soils. It is a hierarchical system consisting of six levels of classification: Order, Suborder, Great Group, Subgroup, Family, and Series. Each level is based on specific soil properties and characteristics that reflect the soil’s genesis, morphology, and behavior.
Key Facts
- Classification Levels: Soil Taxonomy consists of six levels of classification, from most general to specific: Order, Suborder, Great Group, Subgroup, Family, and Series.
- Parameters Considered: Soil Taxonomy classifies soils based on various parameters, including depth, moisture, temperature, texture, structure, cation exchange capacity, base saturation, clay mineralogy, organic matter content, and salt content.
- Soil Orders: There are 12 soil orders in Soil Taxonomy, which represent the top hierarchical level of classification. Each order has specific properties that reflect major differences in soil genesis.
- Soil Types: Soil Taxonomy classifies soils into different types, such as Alfisols, Andisols, Aridisols, Entisols, Gelisols, Histosols, Inceptisols, Mollisols, Oxisols, Spodosols, Ultisols, and Vertisols.
- Purpose: Soil Taxonomy serves several purposes, including providing a connotative naming system for remembering soil properties, understanding soil relationships within and between areas, communicating concepts of soils and soil properties, and projecting soil experience from one area to another.
Parameters Considered in Soil Taxonomy
Soil Taxonomy considers various parameters to classify soils, including:
- Depth: The depth of the soil profile, including the thickness of horizons and layers.
- Moisture: The soil’s moisture regime, such as udic (moist), aridic (dry), or aquic (wet).
- Temperature: The soil’s temperature regime, such as frigid (cold), mesic (moderate), or thermic (warm).
- Texture: The relative proportions of sand, silt, and clay particles in the soil.
- Structure: The arrangement of soil particles into aggregates, such as granular, blocky, or prismatic.
- Cation Exchange Capacity (CEC): The ability of the soil to hold positively charged ions (cations) on its exchange sites.
- Base Saturation: The percentage of CEC occupied by basic cations (calcium, magnesium, potassium, and sodium).
- Clay Mineralogy: The types and proportions of clay minerals present in the soil.
- Organic Matter Content: The amount of organic matter in the soil, which influences its fertility and structure.
- Salt Content: The concentration of soluble salts in the soil, which can affect plant growth and soil properties.
Soil Orders
Soil Taxonomy classifies soils into 12 orders, which represent the highest level of classification. Each order has specific properties that reflect major differences in soil genesis. The 12 soil orders are:
- Alfisols: Soils with clay accumulation in the subsoil and a moderate to high base saturation.
- Andisols: Soils formed from volcanic ash and characterized by high organic matter content and poorly crystalline minerals.
- Aridisols: Dry soils with low organic matter content and limited leaching.
- Entisols: Young soils with minimal horizon development and no diagnostic subsurface horizons.
- Gelisols: Soils with permafrost within 2 meters of the surface or gelic materials within 1 meter.
- Histosols: Organic soils with more than 20% organic matter content.
- Inceptisols: Young soils with some horizon development but lacking diagnostic subsurface horizons.
- Mollisols: Dark-colored soils with high organic matter content and a mollic epipedon.
- Oxisols: Highly weathered soils with low nutrient availability and a high content of iron and aluminum oxides.
- Spodosols: Acidic soils with an accumulation of organic matter and iron and aluminum oxides in the subsoil.
- Ultisols: Acidic soils with low base saturation and an argillic or kandic horizon.
- Vertisols: Clay-rich soils with high shrink-swell potential and deep cracks.
Soil Types
Within each soil order, Soil Taxonomy further classifies soils into different types, called soil series. A soil series is a group of soils that have similar properties, including texture, mineralogy, drainage, and landform. Soil series are named after a geographic location where they were first identified.
Purpose of Soil Taxonomy
Soil Taxonomy serves several purposes:
- Connotative Naming System: It provides a connotative naming system for remembering soil properties, making it easier for soil scientists and land managers to communicate about soils.
- Understanding Soil Relationships: It helps in understanding the relationships between soils within and between areas, allowing for the transfer of knowledge and experience from one area to another.
- Communication: It facilitates communication among soil scientists, land managers, and other stakeholders, enabling a common understanding of soil properties and behavior.
- Projecting Soil Experience: It allows for projecting soil experience from one area to another, aiding in the management and use of soils for various purposes, such as agriculture, forestry, and engineering.
References:
- Soil Taxonomy: A Basic System of Soil Classification for Making and Interpreting Soil Surveys, Second Edition. United States Department of Agriculture, Natural Resources Conservation Service. (https://www.nrcs.usda.gov/sites/default/files/2022-06/Soil%20Taxonomy.pdf)
- Soil Taxonomy. Natural Resources Conservation Service, United States Department of Agriculture. (https://www.nrcs.usda.gov/resources/guides-and-instructions/soil-taxonomy)
- USDA Soil Taxonomy. Wikipedia. (https://en.wikipedia.org/wiki/USDA_soil_taxonomy)
FAQs
What is Soil Taxonomy?
Soil Taxonomy is a comprehensive system developed by the United States Department of Agriculture (USDA) for classifying soils. It is a hierarchical system consisting of six levels of classification, from most general to specific: Order, Suborder, Great Group, Subgroup, Family, and Series.
What parameters are considered in Soil Taxonomy?
Soil Taxonomy considers various parameters to classify soils, including depth, moisture, temperature, texture, structure, cation exchange capacity, base saturation, clay mineralogy, organic matter content, and salt content.
What are the 12 soil orders in Soil Taxonomy?
The 12 soil orders in Soil Taxonomy are:
- Alfisols
- Andisols
- Aridisols
- Entisols
- Gelisols
- Histosols
- Inceptisols
- Mollisols
- Oxisols
- Spodosols
- Ultisols
- Vertisols
What is the purpose of Soil Taxonomy?
Soil Taxonomy serves several purposes, including:
- Providing a connotative naming system for remembering soil properties
- Understanding soil relationships within and between areas
- Facilitating communication among soil scientists, land managers, and other stakeholders
- Projecting soil experience from one area to another
What are soil types in Soil Taxonomy?
Within each soil order, Soil Taxonomy further classifies soils into different types, called soil series. A soil series is a group of soils that have similar properties, including texture, mineralogy, drainage, and landform. Soil series are named after a geographic location where they were first identified.
How many levels of classification are there in Soil Taxonomy?
There are six levels of classification in Soil Taxonomy: Order, Suborder, Great Group, Subgroup, Family, and Series.
What is the highest level of classification in Soil Taxonomy?
The highest level of classification in Soil Taxonomy is Order. There are 12 soil orders, each representing a major group of soils with distinct properties and characteristics.
What is the lowest level of classification in Soil Taxonomy?
The lowest level of classification in Soil Taxonomy is Series. A soil series is a group of soils that have similar properties, including texture, mineralogy, drainage, and landform. Soil series are named after a geographic location where they were first identified.