 The top few inches of the earth’s surface that supports plant growth.  Formed from parent material (rocks and minerals) by a process known as weathering.  Productivity can be lost by soil degradation, such as erosion and pollution.

25% water 25% air 40-45% minerals 5-10% organic matter Organic matter is material made from living or once living material.

 Soil is formed from parent material through a process called weathering.  Types of weathering are physical (mechanical) and chemical.  Mechanical/physical:  Plants & animals  Ice wedging  Chemical  water  Acids  oxygen

 Climate  Living organisms  Parent material  Time  How the soil weathered  Topography (the lay of the land)

 Soil has three particle sizes: sand – the largest silt - medium clay – the smallest

 Soil texture is the relative percentage of sand, silt, and clay in a soil sample.  There are 12 soil textures.  Different plants prefer different soil textures.  Different textures have different relationships with water depending on the percentage of particles making up the soil.  Scientists use the soil textural triangle to determine the soil’s texture.

 Sedentary soils are weathered from large patches of bedrock, so they remain in place and don’t really move.  Transported soils occur when particles are transported. colluvial- moved by gravity (landslide, mudslide) alluvial- moved by water (Delta, flood plains) aeolian- moved by wind glacial till- particles moved by glaciers

 OM comes from living matter. Examples of living contributions to soil: Roots Algae Fungi Small animals Insects Slugs Snails Worms Snakes reptiles Examples of non- living contributions to soil: Peat moss Leaf remnants Compost Grass clippings Saw dust manure Dark colored soils indicate greater amounts of OM. Benefits of OM in soil: 1.Makes soil porous. 2.Adds N and other nutrients to soil. 3.Helps hold water. 4.Furnishes food for living organisms. 5.Minimizes leaching. 6.Stabilizes soil structure.

HorizonNameColorsStructureProcess Occuring OOrganicBlack, dark brownLoose, crumbly, well-broken Decomposition ATopsoilDark brown to yellow Loose, crumbly, well-broken Zone of leaching* BSubsoilBrown, red, yellow, gray Larger chunks, dense, cement- like Zone of accumulation CParent material Varies by parent material Dense, rockyWeathering of parent material *Leaching: when materials move through the soil profile; often materials like chemicals and pollutants are carried through the soil profile by water.

Granular Platy Blocky Prismatic/columnar Wedge

 Soils with more sand tend not to bind together and therefore do not show much structural arrangement  Clay give soil more structure  Soil structure is important in the absorption of water and the circulation of air  Structure of the A and B horizons should have medium and large particles for a loose structure that is good for water infiltration, root development, and seed germination.

 Surface material and soil texture will determine how rapidly water flows through the soil profile.  Water that fills up pore spaces between soil particles accumulate below the earth’s surface to create groundwater.  Porosity is a measure of the amount of open space compared to the total volume of rock/soil.  The ability of material to transmit fluid is permeability.  Sandy soils have a greater porosity and therefore a greater permeability than clay and silt. Clay is the least porous and permeable.

 The size, shape, and arrangements of soil particles in a given texture will determine the ability of the soil to retain water.  Large pores conduct water more rapidly than small pores.  Water is more easily removed from large pores than small pores.  In sandy soils, water is lost due to gravity faster than plant roots can access it.

 After water is lost due to gravity, the remaining water is stored under tension in the pores of various sizes.  The smaller the pore, the greater the tension, and the more energy is required to the water.  Water cannot be removed by plants from very small pores.  Hygroscopic water, that which is water closely bound to soil particles, is also not available for plant use.

 Field capacity is water available to plants. It’s about 24 hours after soil saturation, after gravity has set in.  This varies depending on the soil, and can be extended by the irrigation method chosen.  The goal is to allow the plant to get as much water as needed, by altering irrigation to overcome the challenges of the soil texture and weather.  Permanent wilting point is when the point at which water is no longer available to the plant.

SANDFAST SILTMEDIUM CLAYSLOW

 Just below the surface is the zone of aeration.  Below that is zone of saturation.  Below the zone of saturation is the groundwater.  The upper boundary of the zone of saturation is the water table.  The depth of the groundwater/level of the water table varies with the precipitation and climate as well as what gets pumped out and used.  It is essential that the amount pumped out does not exceed nature’s ability to recharge the water source.

 An aquifer is any underground, water-bearing layer that groundwater can flow through.  Aquitards confine the water.