Envirothon

Soil

Topics• Soil • Soil Formation• Soil Texture• Soil Color• Organic Matter• pH• Salinity• Soil Air• Compaction/Shrink-Swell• Drainage• Erosion• Soil Surveys-How to Use Them• References

Typical Loamy Soil

Air

Water

Mineral

Organic

Typical Clayey Soil

Air

Water

Mineral

Organic

Typical Sandy Soil

Air

Water

Mineral

Organic

Forming Factors

• Climate

• Living Organisms

• Parent Material

• Topography

• Time

Climate

• Most influential factor• Temperature and

precipitation in particular

• Determines the nature and speed of formation

• High Heat, High humidity, abundant rain=a lot of power

Living Organisms

• Plants and animals• Grasses vs trees• Microorganisms

Parent Material

• Geology • Gulf Coast was a

fluvial deltaic system• Soils are derived from

loamy and clayey sediments

• About 14,000 years old

Topography

• Nearly level • Slope occurs along

drainage

Time

• Soils on flood plains and coast line are youngest

• Stable landscapes have older soils

• Takes about 500 years to form an inch of soil from hard parent material

Texture

• USDA• % of Sand,

Silt and Clay• Key factor

chemically and physically

Clayey Soils

• High Shrink-Swell• High Organic Content• High Water Holding

Capacity• Agriculturally

productive• Difficult to work with

Sandy Soil

• High pore space• Low organic matter• Low fertility• Low water holding

capacity• Easy to work with

Loamy Soil

• Wide array of soils• Low to High Fertility• Low to High Organic

content• Low to High Water

Holding Content• Moderate to work with

Soil Color

• Dark=high organic content

• Light=low organic content

• Red, yellow, brown is well drained

• Gray could mean excessive wetness

Dark= High Organic

• Most clayey soils in our area are dark and have high organic content

Light=Low organic content

• <1 percent• Most loamy and

sandy soils in our area are low in organic content

Well Drained

• High on the landscape

• Ridges and sloping areas

• Yellow, red or brown• Black is usually well

drained

Gray Could be Wet

• Gray surface• Contains mottles

(oxidized or reduced iron)

• Concave landscape• Wet soils could be

associated with wetlands!

Organic Matter

• Accumulation of partially decomposed plant and animal residues

• Loosens soil• Nutrient source for

plants• Increases water

holding capacity• Food for microbes

Soil Organic Matter

• Highest in the surface where the majority of biotic activity occurs

• Important to stockpile surface layer

• Easily destroyed when disturbed

Increasing Organic Content

• Warm and humid conditions are ideal for microorganisms

• Constant struggle• Leave grass

clippings, leaves, and twigs

• Add mulch

Organic Matter Considerations

• Carbon to Nitrogen ratio

• Microbes use nitrogen to eat carbon

• Could cause nitrogen difficiency in plants

• Add nitrogen fertilizer• Will correct over time • Use good compost

Soil pH

• Ideal pH range is 5.5 to 7.5• pH >8.5 could mean high salt

content• pH<4 Aluminum and Iron

toxicity• pH meters • Add lime for soils less than 5.5

and sulfur for soils above 7.5• Local soils are in good pH

range• Best to not get too worried

about changing pH

Salinity

• A localized problem on Gulf Coast

• Almost all soils have some salinity

• Causes soil to become hard

• Damages roots and stunts plants

• Damages steel

Soil Air

• Well aerated soils support better plant growth

• Mechanical aerator

• Incorporate organic matter into the soil for a long term solution

Soil Compaction

• Occurs in high traffic areas

• Occurs when soils are manipulated when wet

• Plowing or incorporating organic matter decreases compaction

• Minimize hazard of compaction by having a good thick layer of mulch on surface

Shrink and Swell

• All clayey soils do it• swell when wet and

shrink when dry• $$$$$ to fix damage

Soil Drainage Classes• Very poorly Drained-Water is at or near the surface

during much of the growing season• Poorly drained-The soil is wet at shallow depths

periodically during the growing season or remains wet for long periods.

• Somewhat Poorly drained-The soil is wet at a shallow depth for significant periods during the growing season.

• Moderately Well drained-Water is removed from the soil somewhat slowly during some periods of the year

• Well drained-Water is removed from the soil readily, but not rapidly.

• Somewhat Excessively Drained-Water is removed from the soil rapidly.

• Excessively Drained-Water is removed from the soil very rapidly.

Drainage

• Poorly drained soils are gray with oxidized iron zones

• Concave landscapes• Usually have water

loving plants

Drainage

• Well drained are brown, yellow or red and most black soils

• Convex landscapes• Avoid making

depressions if you want the soil to stay well drained

Erosion

• Soil moved by wind or water

• Occurs in high traffic areas where surface vegetation is gone

• Areas with more than 3 percent slope are susceptible

• Mulch and terraces (anything to slow wind and water down)

Soil Surveys

• An inventory of soils that includes maps, interpretative tables, and soil descriptions for use in general land use planning

Using a Soil Survey

• Locate your area of interest in the soil map section

• Identify all of the soil map unit symbols at your area of interest

How to Use Soil Surveys

• Go to the table that contain the information you seek

• Find your map unit symbol and then find the land use practice

• Table provides information on suitability for that soil for that particular land practice

References

• The Nature and Properties of Soils, by Nyle C. Brady

• http://soils.usda.gov/

• http://www.tx.nrcs.usda.gov/

• http://soildatamart.nrcs.usda.gov/

• http://soilcrop.tamu.edu/

Contacts

• USDA-Natural Resources Conservation Service – Rosenberg=281-232-6898 ext 3– Angleton=979-849-6820– Temple State Soils Staff=254-742-9850– Rosenberg Soil Survey Office=281-232-4668

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