Envirothon Soils SC 2026

Definition: Soil

A mixture of minerals, organic matter, air, and water that forms the top layer of the Earth’s surface and supports animals and life.

45 % mineral particles, 5% organic matter, 25% air, 25% water

Importance of Soil

Supports: plant growth, provides habitats, filters water, carbon cycle, and climate change mitigation.

Basic Soil Properties

Texture, structure, porosity, color, organic matter content, chemistry, pH, nutrient availibility

Diagnostic Significance of Soil Color

1. Drainage class

2. How much organic matter is present

3. Where the soil came from

4. Clues on fertility, drainage, and mineral composition

Munsell Color Book

Munsell Notation is a universal standard for color

• Number and letter symbols represent the hue. 

• Hue represents the dominant color of the soil

• Notation is at the top right of the color book: Y (yellow), R (red),  (green), B (blue), YR (yellow-red)

The number before the slash is the value. 

→ lightness of a color, 0 = pure black; 8 = pure white

→ notation at left side of color book

The number after the slash is the chroma. 

→ intensity of a color, 1 - less intense; 8 = most intense

→ notation at bottom of color book

Color: Weathering

The breakdown of material affects soil color

• Granitic parent material leads to yellow or orange hues

• Volcanic rocks can result in pink, orange, white, or green soils

Color: Oxidation-reduction reactions

Iron can create red or yellow soil when it oxidizes

• Red color indicates well drained soils since Fe is easily oxidized

• Yellow-brown indicates poor drainage

• In anaerobic conditions, iron is reduced to a poor gray color

Color: Organic Matter Decomposition

Decomposing organic matter adds a dark colored humus, which makes your soil appear dark brown or black

Color: Leaching

Downward movement of water can leach out iron and maganese oxides, especially in soils with high percipitation, leading to lighter, bleached colors

The 12 soil orders of taxonomy

Entisols, Inceptisols, Andisols, Mollisols, Alfisols, Spodosols, Ultisols, Oxisols, Gelisols, Histosols, Aridisols, and Vertisols.

Alfisols

•  moderately leached soils that have relatively high fertility

Andisols soils that have formed in volcanic ash

soils that have formed in volcanic ash

soils of arid regions that exhibit subsurface horizon development

Entisols

are soils of recent origin

Gelisols

 soils of very cold climates that contain permafrost within two meters of the surface

Histosols

soils that are composed of mainly organic materials

Inceptisols

soils that exhibit minimal horizon development

Mollisols

 soils of grassland ecosystems

Oxisols

very highly weathered soils that are found primarily in the intertropical regions of the world

Spodosols

acid soils characterized by a subsurface accumulation of humus that is complexed with Al and Fe

Ultisols

strongly leached, acid forest soils with relatively low natural fertility

Veritsols

are clay rich soils that shrink and swell with changes in moisture content

The most common soil orders in SC

Ultisols, Entisols, Inceptisols, Alfisols

Soil Forming Factors

Cl ~ Climate (speeds up or slows down chemical reactions); temperature and precipitation rates affect the rate of weathering and chemical reactions, influencing texture and structure

O ~ Organisms; plants, animals, and microorganisms contribute to soil aggregation and organic matter content, impacting the structure

R ~ Relief (topography); slope and elevation affect erosion and disposition, influencing soil development and structure

P ~ Parent material; the original rock from which the soil forms from determines the initial size distribution of particles, which influences textures

T ~ Time; the length of time the soil has been developing impacts its maturity and the extent of changes in textures and structure

• Human activities such as tillage, compaction, and changes in land cover

  • Tillage: Tillage can damage aggregates and reduce soil structure 

  • Compaction: Heavy machinery and livestock traffic can compact soil, reducing the porosity and altering the structure 

  • Vegetation removal: Loss of vegetation reduces organic matter and the ability of roots to bind soil particles, which impacts structure 

  • Soil Erosion: Removal of topsoil can alter the texture and structure 

Importance of soil forming factors

Soil forming factors are important because they determine characteristics of soil: fertility, structure, ability to support plant life, etc. Understanding soil factors is important to agriculture, land management, and environmental protection

How the soil forming factors influence water retention, nutrients, and erosion: 

• Soils with smaller particles (silt and clay) have a larger surface area and can hold more water

• Clay-rich soils have a higher cation exchange capacity (CEC), which is the soil’s ability to hold positively charged nutrients like nitrogen, phosphorus, and potassium

• Different soils erode at different rates based on how they are made up. Different soil structures have different rates of erosion

Soil forming factors influence the hydrologic and nutrient cycles: 

• Soil texture and structure affect the rate at which water infiltrates into the soil from the surface

• Soil have different water holding capacity 

• Infiltration contributes to groundwater recharge, which is a key part of the hydrologic cycle 

• Soil pH, texture, and organic matter content influence the availability of essential plant nutrients 

• Microorganisms in the soil play a crucial role in decomposing organic matter, releasing nutrients, and transforming them into forms available to plants 

Sand

• the largest particles (0.05 to 2.00), contribute to good drainage and aeration, low water holding capacity 

  • Mostly quartz

  • Low chemical activity

  • Large pore space

  • Low water holding capacity

  • High conductivity

  • “Gritty”

Clay

• the smallest particles (less than 0.002 mm), hold water and nutrients well, but can lead to poor drainage if present in high proportions 

  • Chemically active (neg. charged)

  • High nutrient and water holding capacity

  • Small pore spaces

  • Low conductivity

  • Sticky and plastic

Silt

• intermediate in size (0.002 to 0.05 mm), provides a balance between drainage and water retention, is fertile

  • Low chemical activity 

  • Medium pore spaces

  • Better water holding capacity

  • Smooth and “powdery”

Organic Materials

• contributes to soil’s fertility and aeration, enhances water retention, nutrient availability, and biological activity. Improves soil structure by binding particles together

Blue Ridge Mountains

• 2% of the state 

• Metamorphic rocks (granite gneiss, schist)  

• Soils: loamy - Edneyville, Saluda 

• Westernmost part of the state 

• Features rugged terrain and is home to a variety of ecosystems, like forests and streams 

Piedmont

• A region of rolling hills that is known for its diverse range of soils 

• Major agricultural area in the state 

• 32% of the state 

• Igneous and metamorphic rocks (granite, gneiss, diabase) 

• Sedimentary rocks (Siltstone) 

• Soils: deep, red, clayey, Cecil, Appling, high shrink-swell, Iredell, Brewback

Sand hills

• A distinctive area characterized by sandy soils and pine forests 

• The transitional zone between the piedmont and the coastal plain 

• 15% of the state 

• Eolian sands, ancient river deposits, and weathered clays 

• Sandy to fine-loamy soils - alpin, alley 

Coastal Plain

• A variety of marine sediments are all oriented more or less parallel to the coastline

• The inner coastal plains consist of rolling hills 

• Outer coastal plains consist of flat terraces 

• Vegetation consists of pine-dominated forests with agricultural land interspersed on better-drained sites, hardwood forests along low-gradient streams, and pine forests on less well-drained terraces 

• 50% of the state 

• Marine deposits and river deposits 

• Soils are sandy to clayey, well drained to very poorly drained, dothan (well drained), rains (poorly drained) 

• Benefits of a healthy soil: 

• Supports plant growth 

• Improved water infiltration and retention 

  • Healthy soils hold more water by binding it to organic matter

• Reduced erosion 

• Carbon sequestration 

• Enhances biodiversity 

• Improves air and water quality 

• Reduced reliance on synthetic fertilizers and irrigation 

• Four basic soil health principles to improve soil health and sustainability: 

• Maximizing soil cover (keep the soil covered as much as possible) 

• Minimizing soil disturbance (disturb soils less) 

• Maximizing biodiversity (use plant diversity to increase diversity in the soil)

• Maximize the presence of living roots (keep plants growing throughout the year to feed the soil)

•  Land Capability classification system: 

• Shows the suitability of soils for most kinds of field crops 

• Soils are grouped according to their limitations for field crops, the risk of damage if they are used for crops, and the way they respond to management 

Capability Class

• The broadest groups are designated by the numbers 1 through 8. The numbers indicate greater limitations and narrower choices for practical use 

• Class 1 soils: 

• Soils that have slight limitations that restrict their use

• Example: Sandy and loamy soils

• Class 2 soils: 

• Soils that have moderate limitations that restrict the choice of plants or require moderate conservation practices 

• Example: soils with sandy or loamy sand surfaces up to 20 inches, underlain by sandy loams, sandy clay loams, or clay loams

• Class 3 soils:

• Soils that have severe limitations that restrict the choice of plants or require special conservation practices, or both 

• Example: Neeses loamy sand and Charleston loamy fine sand 

• Class 4 soils: 

• Soils that have very severe limitations that restrict plant choice and require very careful management, or both 

  • Example: sandy loams, fine sandy loams, silt loams, and clay loams

• Class 5 soils: 

• Soils that are subject to little or no erosion but have other limitations are impractical to remove and restrict their use mainly to pasture, rangeland, forestland, or wildlife habitat 

• Example: soils with fragipans or plinthite, which restrict root penetration

• Class 6 soils: 

• Soils that have severe limitations that make them generally unsuitable for cultivation and restrict their use mainly to pasture, rangeland, forestland, or wildlife habitat 

• Example: sandy, loamy, or organic matter content, like soils from Carolina bays and those with more than 10% organic matter

Class 7 soils:

• Soils that have very severe limitations that make them unsuitable for cultivation and that restrict their use mainly to grazing, forestland, or wildlife habitat 

• Example: soils with steep slopes, severe erosion issues, shallow depths to bedrock, or extremely poor drainage 

• Class 8 soils: 

• Soils and miscellaneous areas have limitations that preclude commercial plant production and that restrict their uses to recreational purposes, wildlife habitat, watershed, or esthetic purposes. 

• Example: areas like coastal areas with rocky terrain, marshes, or floodplains

• Capability Subclass 

• Soil groups within one class 

• Designated by adding a small letter e,w,s,or c, to the class numeral, for example, 2e 

• E shows that the main hazard is the risk of erosion unless close-growing plant cover is maintained 

• W shows that water in or on the soil interferes with plant growth or cultivation 

• S shows that the soil is limited mainly because it is shallow, droughty, or stony 

• C is only used in some parts of the United States, shows that the chief limitation is climate that is very cold or very dry 

• In class 1 there are no subclasses because the soils in this class have few limitations 

• Class 5 contains only the subclasses indicated by w,s, or c because the soils in class 5 are subject to little or no erosion 

• Capability Unit

• Soil groups within a subclass 

• The soils in a capability unit are similar enough to be suited to the same crops and pasture plants, to require similar management, and to have similar productivity 

• Generally designated by adding an arabic numeral to the subclass symbol, for example, 2e-4 and 3e-6. These units are not given in all soil surveys 

1. Resource Concerns

Erosion

1. Non-concentrated water erosion

• Water sources that are like stream lets can cause damage if left untreated

2. Wind-erosion

• Transporting soil damage

3. Concentrated water erosion

4. Erosion along bodies of water 

5. Coastal

Compaction

→ Occurs when soil particles are pressed together, reducing pore space between them; a reaction to excess pressure from machinery or animals

Soil Pit/Horizons

O ~ Organisms (decaying leaves, nutrient rich)

A ~ Topsoil (good layer for organisms; minerals and organic matter)

E ~ Eluviated (leeched of clay, minerals, organic matter; concreted sand and silt particles)

B ~  Subsoil (rich in minerals; minerals form above)

C ~ Parent Material

R ~ Bedrock

Soil Structure

Soil structure impacts water movement and well-structured soils facilitate both infiltration (water entry) and percolation (water movement through the soil). 

→ Coarse-textured soils like sand tend to have high infiltration rates but low water retention

→ Fine-textured soils like clay have slow infiltration but high water storage capacity

Well Structured (eg. granular, prismatic, blocky) allow for better water and air movement through interconnected pores

Poorly Structured (platy) can impede water movement due to a lack of interconnected pores

Compacted soils limit water infiltration and movement due to reduced pore space

Sandy soils have large pore spaces, leading to rapid water infiltration but aso rapid drainage, a small capacity for water storage

Clay soils have smaller pore spaces, resulting in high water holding capacity but slow infiltration

Capillary action and Gravity are water movement mechanisms

Good soils structure is crucial for plant growth as it ensures adequate water and air availability to roots

Identify the various types of soil erosion, factors affecting the rate of soil erosion, and best management practices and/or conservation systems used to control soil erosion

• Types of soil erosion: 

  • Water erosion 

    • Sheet

      • A thin layer of soil is uniformly removed from a large area due to flowing water 

    • Rill 

      • Small, ephemeral channels are formed by concentrated water flow on hillsides 

    • Gully 

      • Deep, wide channels are carved by flowing water, often resulting from prolonged severe water erosion 

  • Wind erosion 

    • Wind can sweep away loose soil particles and carry them away which degrades soil 

  • Other types

    • Coastal Erosion

      • Wearing away of soil along coastlines due to waves and currents 

• BMPs to control soil erosion: 

• BMPs to control soil erosion: 

  • Vegetative BMPs

    • Maintain a healthy plant cover 

    • Mulching 

    • Cover crops 

  • Structural BMPs

    • Silt fences 

    • Rain gardens 

    • Riprap 

    • Diversion ditches 

• Factors affecting the rate of soil erosion: 

• Climatic conditions

  • Rainfall 

  • Wind 

  • Temperature 

• Soil properties (type, structure, moisture) 

• Topography (slope and length) 

• Vegetation cover 

• Human activities like agriculture and deforestation 

Explain how composting improves soil health and provide evidence for how composting supports water conservation efforts. 

• How composting improves soil health: 

  • Enhances soil structure 

    • Organic matter helps to bind soil particles together, creating better soil structure and improving aeration 

  • Enhances nutrient availability 

  • Adds organic matter

  • Improves water retention 

  • Increases the number of beneficial microorganisms 

• Evidence for water conservation: 

  • Compost increases the soil’s ability to retain water 

  • Improves soil health and structure

    • Increased water retention 

    • Reduced runoff 

    • Enhanced infiltration 

  • Compost allows plants more access to water which means people have to water less 

  • Helps to mitigate soil erosion. Soil erosion can contribute to water pollution and loss  

Understand the important role soils play in home sewage treatment systems.

• The role soils play in home sewage treatment systems: 

• Act as a physical filter and biological treatment site 

• Physical filter

  • Soil particles (ones with good balance of sand, silt, and clay - loamy soils) filter out larger solids and contaminants from wastewater 

  • Helps prevent pollutants from entering groundwater or surface water 

  • Sandy soils do not offer adequate treatment due to their large particle size 

• Biological Treatment 

  • Soil contains microorganisms that play a vital role in decomposition of organic matter and other pollutants in the wastewater

  • These microbes can remove nitrogen, bacteria, and viruses, which purifies the water before it seeps into the ground

  • Soil type and pH can influence the activity of these microorganisms