Horizon “O”: Organic Layer All soils do not have this Found beneath vegetation Contributes OM to all other layers Horizon “A”: Topsoil Other than location, no “official” or regulated definition Critical to plant growth Critical to landscape success Should be removed prior to construction and stock piled on site Horizon “B”: Subsoil (a transition zone) Much of the exposed soil in areas where construction has occurred May contain accumulated soluble salts beneath cultivated areas Horizon “C”: Parent Material Little or no soil development. Usually contains various sized rocks Horizon “D”: Bedrock You Get What You Pay For Soil Horizons What is Topsoil? Poison Hemlock!
Physical Properties Soil Horizons Soil Texture, Consistency, & Structure Soil Compaction (Bulk Density) Soil Moisture Chemical Properties pH Cation Exchange Capacity (CEC) Biological Properties Microorganisms bacteria fungi (e.g. mycorrhizas) protozoa nematodes Macroorganisms arthropods earthworms nematodes Decomposition / Nutrient Recycling Aeration Aggregation (e.g. “microbial glue”) Biological Chemical Physical Soil Properties: SOIL TEXTURE pH CEC SOIL MOISTURE SQUIRMEES SOIL STRUCTURE They Are Not Independent!
Topsoil A: Subsoil B: Parent Material C: Bedrock D: Trouble on the Horizon Organic O: Squeeze Play! Note: Topsoil Remains, but it is compressed COMPACTION!
Trouble on the Horizon Compaction
Characteristics of Soil Compaction: • Impermeable (hard!) soil: • High resistance to water penetration and movement (low infiltration and drainage) • High resistance to root penetration • Low Water Holding Capacity • Low Oxygen Holding Capacity
Root Needs • Water • Warmth • Oxygen [O]: the #1 element needed for root health • 25% of the soil volume • At 5%, root growth stops • At 2%, roots decline and die
Mineral Particles: 45% Mineral Particles: 75% Air: 25% Air: 12% Water: 25% Organic Matter: 5% Water: 12% Organic Matter: 1% Soil Structure and Compaction Good Soil Structure Poor Soil Structure Soil Pores Soil Pores
Your Soil May Not be Compacted Several Soil Problems Mimic the Characteristics of Soil Compaction
Topsoil A: Subsoil B: Parent Material C: Bedrock D: Trouble on the Horizon Organic O: Gone in 60 Seconds Exposed Subsoil: Mimics Compacted Soil!
Trouble on the Horizon Topsoil Removed Topsoil Stockpiled
Trouble on the Horizon Only 2-3” of topsoil returned!
Topsoil A: Compaction Zone Subsoil B: Parent Material C: Bedrock D: Subsurface Plow Compaction Zone: Organic O:
Topsoil A: Compaction Zone Subsoil B: Parent Material C: Bedrock D: Subsurface Tilling Compaction Zone: Organic O:
Subsurface Rototiller Compaction Zone Front Tines Weight Weight Rear Tines
Built on a Farm Field? Plowing: Washing-Out Clay Particles
“False” Clay-Layer Horizon Illuviation: Deposition of Particles in Lower Level Eluviation: Downward Movement of Soil Particles by Water Clay Particles
Topsoil A: Clay Layer Subsoil B: Parent Material C: Bedrock D: Perched Water Table: “False” Clay-Layer Horizon: MORE WATER WATER Organic O:
Topsoil A: Clay Layer Subsoil B: Parent Material C: Bedrock D: "Upside-Down Soils: Acts Like Compacted Soil! Organic O:
“Upside-Down” Soils: Lower layers are brought to the surface
Clay Layer Subsoil B: Parent Material C: Bedrock D: "Upside-Down Soils: Note: some topsoil may remain beneath the false clay layer
Dealing With a False Clay Layer and/or a Subsurface Compaction Zone: Subsoiler
Other Soil Perspectives A really big guy? …or just a small shovel?