RS 478: Lecture 10 Topsoil in Restoration
• A major limitation in many restoration projects is lack of suitable soil for plant
growth which can be due to:
o Loss of soil due to intentional removal or erosion
o Contamination of soil due to human pollution or mineral weathering
o Naturally poor soils that is difficult to establish plants on.
• Soil Horizons: A layer of soil, approximately parallel to the surface, having
distinct characteristics produced by soil forming processes. Used to classify the
soil and make interpretations
• O- horizon: Organic layers of decaying plant and animal tissue (must be greater
than 12-18 % organic carbon, excluding live roots).
• A - Horizons (topsoil): Mineral horizon at or near the surface in which an
accumulation of humified organic matter is mixed with the mineral material.
o Ap - Plowed A horizon
o Ab - buried horizon.
• E – Horizons: Eluvial horizons: Mineral horizon where the main feature is loss of
silicate clay, iron, aluminum.
• B - Horizons (subsoil): mineral horizon
• C - Horizon/Layers (substratum): The un-weathered geologic material the soil
formed in. Shows little or no sign of soil formation.
• Soils can tell the ecological history of a site
• Topsoil = O and A horizon, (the good stuff on top)
Review Question: Which soil horizon is typically considered topsoil?
ü A and O
• Why is topsoil important?
o Makes for a good seedbed, Organic matter, Soil Biota, Plant nutrients,
Plant Propagules (seeds/roots)
• It improves seedbed characteristics: Enhances proper seed burial and therefore
ensures good seed-soil contact and provides for unrestricted root development
• The presence of OM in topsoil influences the nutrient status and physical
properties of soil. • Disturbance can remove OM, adding OM can renew a soil with respect to
nutrients, structure, and microbes.
• Soil Biota – topsoil can be a primary source in restoration. Critical for
decomposition and nutrient cycling. Critical for plants that require specific
o Plant Nutrients – topsoil can be a primary source in restoration. Other
soil horizons may contain lesser amounts