Let’s Get Down and Dirty!

I

APES

Soil is a mixture of eroded rock, mineral nutrients, decaying organic matter, water, air, and living organisms

5 Soil Forming Factors

• Parent material• Climate• Living organisms• Topography• Time

Soil texture is an important soil characteristic that drives crop production and field management. The textural class of a soil is

determined by the percentage of sand, silt, and clay.

Soil texture determines the rate at which water drains through a saturated soil; water moves more freely through sandy soils than it does through clayey soils.

Silty clay – rolls into a ball; dark in color

Mature soils are arranged in a series of zones called

soil horizons

Most mature soils have at least three of the possible

horizons

In forests you will find the O Horizon (surface litter layer)

Topsoil layer (humus)

Subsoil layer (inorganic matter)

Parent material (inorganic matter)

The A and O Horizons is where the interaction with bacteria, fungi, earthworms, and small worms take place

Fertile soil that produces high crop

yields has a thick topsoil layer with

lots of humus

Dark brown or black topsoil is nitrogen rich and high in organic matter

Gray, bright yellow, or red topsoil is low in organic matter and needs Nitrogen enrichment

It can take 200 to 1000 years to develop an inch of topsoil

Soil permeability is a measurement of the rate water moves through soil. Soil permeability is governed by the makeup of the soil. Sandy and rocky soils have a high rate of soil permeability, while clay types of soils have a low rate. The rate of soil permeability can affect engineering and planning for structures such as sewer systems and earthen dams. It also is used to determine footings in buildings to prevent settling.

Porosity is the open space between soil grains. Soil scientists use porosity measurements to determine how effectively air and water move through the subsurface. Large pore spaces within a soil column help promote infiltration allowing the water to uptake into the root system of plants without mounding and becoming boggy.

There are three ways that wetland soils may filter contaminants from water:

Physical filtration occurs when moving water containing suspended sediments floods a wetland. Often, the water’s movement is slowed, perhaps even to a stand still. Sediments then settle out of the water.

Biological filtration occurs with nitrates. In the case of NO3-, anaerobic bacteria use the nitrate molecule as their final electron acceptor, reducing it to N2 gas or various nitrogen oxides (also gases). This process is especially important when agricultural fields are adjacent to waterways.

Chemical filtration occurs because wetland soils are often high in CEC (cation exchange capacity). Positively charged particles are selectively removed from the water.

Soil Problems• Acidic soil – decrease uptake of nutrients

• add lime and organic fertilizer

• Alkaline soil -western and southwestern United States• Add sulfur – converted by bacteria to sulfuric acid

• Soil erosion• Sheet erosion• Rill erosion• Gully erosion

Soil removed in uniform layer; slowest moving water

at top of hill

Flowing water coalesces into small channels; tiny

gullies form

Channels coalesce into larger channels; water increases

velocity and volume; erodes into larger gully

Gully Erosion

Harmful Effects of Soil Erosion

• Loss of soil fertility• Loss of ability to hold water• Pollutes water, kills fish and shellfish• Clogs irrigation ditches, boat channels• Fills lakes and reservoirs with silt

Providence Canyon resulted from poor farming practices – Lumpkin, GA

Global Soil Erosion

• Topsoil is eroding faster than it forms on about one third of the world’s croplands

• 15% of land scattered across the globe are too eroded to grow crops because

• Overgrazing (35%)• Deforestation (30%)• Unsustainable farming (28%)

Global Soil Erosion

• About 40% of world’s land used for agriculture is seriously degraded by

• Erosion• Salinization• Waterlogging

• Soil degradation has reduced food production on about 16% of world’s cropland

Practices That Leave Soil Vulnerable to Desertification

• Overgrazing on fragile arid and semi-arid land• Deforestation without reforestation• Surface mining without reclamation• Irrigation techniques that lead to increase erosion• Salt buildup from irrigation• Farming on land with unsuitable terrain or soils• Soil compaction by farm machinery and cattle

Symptoms of Desertification

• Loss of native habitat• Increased erosion• Salinization• Lowering of water table• Reduced surface water supply

Consequences of Desertification

• Worsening drought• Famine• Declining health standards• Environmental refugees

Which of the following ecosystems best characterizes a thick O horizon?

A. ChaparralB. DesertC. GrasslandD. Semi-desertE. Taiga

Which of the following ecosystems best characterizes a thick O horizon?

A. ChaparralB. DesertC. GrasslandD. Semi-desertE. Taiga

How does soil compaction affect the use of the land?

A. Compacted soils have negligible effects on land use.B. Compacted soils help reduce the threat of invasive

species taking over.C. Although compacted soils reduce the flow of water

through the soil, there is an increase in the availability of oxygen.

D. Soil compaction helps to keep the topsoil from eroding.

E. Compaction reduces space between soil particles, obstructing the flow of gases, nutrients, and water through the soil.

How does soil compaction affect the use of the land?

A. Compacted soils have negligible effects on land use.B. Compacted soils help reduce the threat of invasive

species taking over.C. Although compacted soils reduce the flow of water

through the soil, there is an increase in the availability of oxygen.

D. Soil compaction helps to keep the topsoil from eroding.

E. Compaction reduces space between soil particles, obstructing the flow of gases, nutrients, and water through the soil.

Deforestation, overgrazing, and the overworking of soil for crop production can lead to which of the following>

A. SalinizationB. MonocultureC. DesertificationD. Increased crop rotationE. Depletion of aquifers

Deforestation, overgrazing, and the overworking of soil for crop production can lead to which of the following?

A. SalinizationB. MonocultureC. DesertificationD. Increased crop rotationE. Depletion of aquifers

Soil Conservation

• Conservation tillage farming (no till)

• Terracing• Contour farming• Strip cropping

• Alley cropping• Gully reclamation• Windbreaks or

shelterbreaks• Land classification

No till farming or Minimum tillage farming

Terrace Farming

Strip Cropping – a row of crop such as corn alternates in strips with another crop, such as grass-legume mixture,

that completely covers the soil

Alley cropping or agroforestry – several crops are planted together in strip or alleys

between shrubs and trees

Windbreaks or shelterbreaks – reduce wind erosion (retain soil moisture, fuelwood, and provide a habitat

Restoring Soil FertilityOrganic Fertilizers

Restoring Soil Fertility

Commercial Inorganic Fertilizer

Green Manure – plowing into soil plants currently growing

Composting

Restoring Soil Fertility

Restoring Soil Fertility

Crop Rotation – plant areas or strips with nutrient-depleting crops (tobacco, corn, and cotton deplete soil of nitrogen) one year and the

next year they plant the same areas with legumes

Not crop rotation – center pivot irrigation

Which of the following factors did NOT contribute to the Dust Bowl in the United States?

A. No-till agricultureB. Removal of vegetative coverC. Soil erosionD. DesertificationE. Drought

Which of the following factors did NOT contribute to the Dust Bowl in the United States?

A. No-till agricultureB. Removal of vegetative coverC. Soil erosionD. DesertificationE. Drought

If you were to practice crop rotation which of the following crops would be best for you rotate with corn?

A. TobaccoB. CottonC. MaizeD. SoybeansE. Sugarcane

If you were to practice crop rotation which of the following crops would be best for you rotate with corn?

A. TobaccoB. CottonC. MaizeD. SoybeansE. Sugarcane

Questions?