Soil

What is soil? Made up of weathered rock, air, water and organic matter and supports vegetation.

Why is it important? Plants grow from soil Provides habitat for animals Serves as a filter for water and pollutants

Forming soil Factors in soil type Climate Organisms Topography time Parent material- the rock material from which soil is formed

Soil Horizons As soils form they develop characteristic layers

Soil Horizons Vertical cross section O – few cm thick; organic matter A – AKA topsoil; organic matter and biological activity (roots, bacteria, fungus, animals); zone of leaching (water takes minerals to lower layers) B – AKA subsoil; fewer organisms and less organic layer; zone of accumulation (where minerals deposit) C – lowest soil layer; little organic matter; rock fragments Boundaries are transitional; not sharp

Organisms- bacteria, fungi, insects, animals Decompose leaf litter forming humus Burrowing animals and earthworms churn and mix soils providing space for O2 and water Change atmospheric nitrogen to useable form

Rove beetle Pseudoscorpion Flatworm Centipede Ant Ground beetle Mite Adult fly Roundworms Fly larvae Beetle Mite Springtail Protozoa Millipede Roundworms Bacteria Sowbug Slug Fungi Actinomycetes Snail Mite Earthworm Organic debris

Soil Types Clay – very fine particles (sticky feel) Silt – fine particles (smooth feel) Sand – medium size particles (gritty feel) Gravel – coarse particles Loam – mixture of clay, sand, silt, and humus (spongy feel) Humus – carbon-rich; gives nutrients and a dark color

Increasing percentage sand 100%clay Increasing percentage silt percentage clay 20 40 60 80 100%sand 100%silt Increasing percentage sand sandy clay silty silty clay loam silt sandy clay loamy sand E D A C B

Soil Texture Determines porosity Volume and distance between pores Need fine particles to hold water and coarse particles for air Soil permeability (rate at which water and air move from top to bottom)

Water Water High permeability Low permeability

Infiltration and Leaching Infiltration: downward movement of water Leaching: when nutrients are carried down with the water

Erosion Movement of soil components- mostly surface litter and topsoil Main agents – flowing water (most) and wind Natural and result of humans (farming, logging, construction, overgrazing, off-road vehicles, burning) Effects – loss of fertility, pollutants, sedimentation of waterways

Economic and Ecological Effects – from erosion Loss of plant nutrients Can’t store water Need more fertilizer Increased water runoff Buildup of soil in waterways Desertification