Factors Affecting Soil Factors Affecting Soil FormationFormation

Ag IAg I

Northshore HighNorthshore High

Soil Formation TermsSoil Formation Terms• Topography – the slope of the ground

surface as determined by features such as mountains, hills, plains, etc.

• Weathering – the process by which rocks and minerals are changed to soils.

• Soil formation – process by which rocks and minerals are changed to soil over a period of time.

• Rock – solid & massive materials composed of one or more minerals.

Soil Formation TermsSoil Formation Terms

• Mineral – chemical compound neither animal nor vegetable; results from inorganic processes of nature.

• Loess – silty, floury material laid down by wind (fine soil particles)

• Alluvium – soil material laid down by running water in the flood plains or bottomlands of rivers and streams.

What affects soil formation?What affects soil formation?• Soil characteristics develop as a result of

their origin and environment. Soil begins as a particular rock material and develops slowly over many years. Each soil is a product of a combination of the following factors.– Parent material– Climate– Living organisms (biota)– Topography– Time

Parent MaterialParent Material• Alluvium – finely pulverized rock laid down

by running water. Mostly silt and clay particles with some sand.

• Marine Deposits – finely pulverized rock laid down under sea. This material has been thrust up by shifts in the earth’s crust.

• Loess – silty, floury material laid down by winds. Mostly silt and clay with little or no sand.

ClimateClimate

• Physical weathering – results from mechanical agents, such as heating & cooling, freezing & thawing, &/or abrasion.– Materials are still the same at the molecular

level.– Materials are classified by the way they have

been moved or scattered

ClimateClimate• Chemical weathering – Results from the

action of water, oxygen, & carbon dioxide on the rocks.– Carbon dioxide mixed with rain water forms a

weak acid, speeding up the weathering of parent material.

– Materials that have been chemically weathered are no longer the same at the molecular level.

• Example – Clay has been synthesized into something physically and chemically different from the parent rock.

ClimateClimate

•Climate is the single most important factor affecting soil formation.

BiotaBiota• Biota is made up of living organisms such

as plants, animals, insects, bacteria, & fungi.– Plants have the most important affect

because they determine the type & amount of organic matter.

– Animals & insects mix and aerate the soil as well as add organic matter.

– In the US, organic matter in the soils increases as you move north &/or east. Why?

TopographyTopography

• Topography refers to the “lay of the land” or the angle & length of the slope.

• It affects soil formation because it influences runoff, drainage, & erosion.

• It also may affect the type & amount of plant growth (biggest factor in determining type & amount of organic matter)

TopographyTopography

• Steep slopes– High runoff rates– Less water infiltration– Fewer plant forms– Less organic matter– Increased erosion– Thinner surface soil– Slower formation/development

TopographyTopography

• Level to Gentle slope– Little runoff– Increased water infiltration– Faster plant growth leading to more organic

matter– Less erosion– Deeper surface soil– Faster formation/development

• Excessive water can slow development

TimeTime

• As soon as material has become loose enough to hold enough water, air, and nutrients for plant growth, it is considered a soil.– Soil formation/development may take place

over several centuries or just a few days.

TimeTime

• Young soils– Volcanic or alluvial in origin– Have greater fertility– Have poorly developed profiles– Usually they are highly productive.– Where are the youngest soils in Louisiana

located?

TimeTime

• Old soils– Have well developed soil profiles– Have an increased clay content– More acid pH– Nutrients are leached– Lower fertility & productivity than younger

soils.

Student ActivityStudent Activity

• For next class period, bring in a soil sample in a ziplock bag.– On the bag mark your name, where you

collected the sample, and what horizon it came from

– I will keep the samples for other activities in this unit.

– 10 BONUS POINTS to all who participate!