Chapter 15- Soil Resources

Ecological Succession

Soil

• The thin surface layer of the Earth’s crust consisting of mineral and organic matter that has been modified by weather, wind, water, and organisms.

Soil

• Weathering processes (biological, chemical, & physical) break parent material (rock) into smaller & smaller particles.

Soil

• Topography affects soil deposition . Steep slopes have little or no soil. Erosion, gravity, & runoff.

• Slopes and valleys aid in soil formation & give rise to pioneer organisms.

• Soil is made up of 4 distinct parts-minerals (45%), organic matter (5%),water (25%), and air (25%)

Soil• Organic portion of soil is made up of leaf

and plant litter

• Humus: a mixture of organic material that binds nutrient mineral ions and holds water.

• Detritivores like Earthworms, termites, and ants help to breakdown humus.

• Humus persists in agricultural soil for about 20 years.

Soil• Pore spaces: Occupy about 50% of a soils volume

and can be filled with H2O (soil H2O) or air (soil air).

• Soil air is found in larger pores.

• Soil H2O is found in smaller pores (0.05mm).

Soil Water• Leaching: the removal of dissolved materials from

soil by the percolating of water downward.

• Illuviation: The deposition of leached material into lower layers of soil.

• Illuvial materials include: Fe, & Al compounds, humus, and clay.

Soil Air• Contains less O2 and more CO2 compared to

atmospheric air. (due to cellular respiration).

Soil Horizons• Horizontal layers of organized soil.

• A soil profile is a vertical section from surface to parent material.

E-horizon develops if leaching is severe.

Soil Organisms• Castings are produced ad digested soil passes

through the intestine of an Earthworm.

• Mycorrhizae: root fungus that lives in symbiosis with vascular plants (Tracheophytes).

• Mycelium: threadlike body of the fungus that brings nutrients and water to the roots of the plant. In turn the fungus receives glucose from the plant via photosynthesis.

Earthworm Castings

Earthworm Dissection

Nutrient Cycling

• The pathways of various nutrient minerals or elements from the environment. Decomposition, assimilation, absorption

Soil Texture

• The texture of a soil is determined by the percentages of particles like sand, silt, & clay that it contains.

Soil Ions

• Soil minerals are often present in charged versions called ions.

• Loam: an ideal agricultural soil that has an optimum combination of soil particle sizes.

• Soil quality is greatly affected by the pH level, and the hydrogen ion concentration.

Soil Groups

• Spodosols: have distinct layers (usually caused by colder climate, ample precipitation, & good drainage. Often found in coniferous forests.

Soil Groups

• Alfisols: temperate deciduous forests produce this soil group. Brown to gray A-horizon, enough precipitation to wash clay and soluble nutrients into the B-horizon.

• Maintained by detritus (leaf litter, twigs, acorn shells.

Soil Groups

• Mollisols: temperate semi-arid grasslands.

• Have a thick, dark brown to black A-horizon rich in Humus.

• Low precipitation so minerals stay in upper levels due to a lack of leaching.

• Most of the world’s grain crops are grown in/on mollisols.

Aridosol- Not much organic matter

Oxisol- Low in nutrients. Found in tropical rainforests.

Soil Erosion

• The wearing away of the soil by wind and water.

Mineral Depletion of Soil

Soil Conservation Techniques

• Conservation tillage- Leave scrap behind!

• No-tillage (Very narrow seed rows)

• Crop rotation

• Contour plowing

• Strip cropping

• Terracing

• Composting