Soil Formation, Erosion and Conservatio

n

Soil Profile O Horizon – “Organic” HUMUS: detritus, leaf

litter and other organic material lying on the surface.

dark because of the decomposition.

decompose into nutrients that enrich the soils.

Soil Profile A Horizon – “Topsoil” darker than the lower

layers. loose and crumbly

with varying amounts or organic matter.

most productive layer of soil.

Soil Profile B Horizon – “Subsoil” Light colored, dense,

and low in organic matter.

materials leached and eluviated from the topsoil accumulate here.

Soil Profile C Horizon –

“Weathered Parent Material”

transition area between soil and parent material.

Partially disintegrated parent material.

mineral particles. less organic/living matter.

Soil Advancement

Differentiate among the terms accumulation of humus, leaching, eluviation and capillary

action.

Humus is the accumulation of dead and decayed plant and animal matter that makes up the organic nature of soil. Occurs where there is substantial plant and animal growth.

Leaching is the process where nutrients are washed down through the soil with the movement of liquids/water soluble minerals down the soil profile. Occurs where there is substantial rainfall.

Differentiate among the terms accumulation of humus, leaching, eluviation and capillary

action.

Eluviation is the lateral or downward movement of (solids / insoluble minerals) clay and other fine materials in suspension. Occurs where there is substantial rainfall.

Capillary action results when water molecules are attracted to clay particles and drawn upward through the soil profile. Occurs where it is substantially dry.

Soil formation is slow and complex

• Parent material = the base geologic material of soil

- Lava, volcanic ash, sedimentary rock, dunes

- Bedrock = the continuous mass of solid rock comprising the Earth’s crust

• Weathering = the physical, chemical, or biological processes that break down rocks to form soil

- Physical (mechanical) = wind and rain, no chemical changes in the parent material

- Chemical = substances chemically interact with parent material

- Biological = organisms break down parent material

Weathering produces soil

FIGURE 7.2

Soil: The foundation for feeding a growing population

• Land devoted to agriculture covers 38% of Earth’s land surface

• Agriculture = practice of raising crops and livestock for human use and consumption

• Cropland = land used to raise plants for human use

• Rangeland or pasture = land used for grazing livestock

• Soil = a complex plant-supporting system consisting of disintegrated rock, organic matter, water, gases, nutrients, and microorganism

Population and consumption degrades soil

• Feeding the world’s rising human population requires changing our diet or increasing agricultural production

• We must find ways to improve the efficiency of food production; the key is how – biotech or intensive organic? There's a big debate on this...

• Mismanaged agriculture turns grasslands into deserts, removes forests, diminishes biodiversity, and pollutes soil, air, and water. Is it possible to create agricultural systems that support biodiversity and that enhance ecosystems? Have been examples in the past?

We lose 5-7 million hectares of productive cropland annually

Soil degradation has many causes

• Soil degradation results from deforestation, agriculture and overgrazing

• Over the past 50 years, soil degradation has reduced global grain production by 13%

FIGURE 7.7

7-14

Tillage (Ploughing)

According to Wikipedia, tillage has the following benefits:

It loosens and aerates the soil which in turn facilitates deeper penetration of roots. A drawback is the compaction of the lower layers of soil.

It helps in the growth of microorganisms present in the soil and thus, maintains the fertility of the soil, though fertility can decline as microorganisms' boom period after tilling is followed by a bust period. It is debatable whether worms benefit or suffer from tillage

It helps in the mixing of organic matter (humus)and nutrients evenly throughout the soil.

It is used for destroying weeds. The downside is that it also compacts the soil

and promotes erosion.

Traditional vs. Industrial agriculture

FIGURE 7.9

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Traditional vs. Industrial agriculture• Traditional agriculture = biologically powered

agriculture, using human and animal muscle power

- Subsistence agriculture = families produce only enough food for themselves

- in between are cultures where farmers support a hierarchy of rulers and craftspeople

• Industrialized agriculture = using large-scale mechanization and fossil fuels to boost yields

- Also uses pesticides, irrigation and fertilizers

- Monocultures = uniform planting of a single crop

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Soil degradation: problems and solutions• Problems

- Erosion

- Desertification

- Salinization

- Chemical loading

- Compaction

- Overgrazing

• Solutions

- Soil conservation

- Restoring plant cover

- Preventing salinization

- Better fertilization practices

- Better grazing practices

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Soil erodes by two main methods

• Wind (aeolian) erosion• Water erosion (splash, sheet, rill,

gully)-Rill erosion moves the most topsoil, followed by sheet and splash erosion

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Four kinds of water erosion

GullyFIGURE 7.11

Splash Sheet Rill

7-20

Fertilizers boost yields but can be overapplied• Fertilizer = substances that contain essential

nutrients

• Inorganic fertilizers = mined or synthetically manufactured mineral supplements

• Organic fertilizers = the remains or wastes of organisms

- manure, crop residues, fresh vegetation

- Compost = produced when decomposers break down organic matter

- Not perfect [can also contribute to eutrophication]

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Environmental effects of over-fertilizing

FIGURE 7.17

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Grazing practices can contribute to soil degradation

FIGURE 7.18

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Effects of overgrazing can be striking

Ungrazed plot Grazed plot

70% of the world’s rangeland is classified as degradedFIGURE 7.19

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Irrigation: boosts productivity but can cause long-term soil problems

• Irrigation = Artificially providing water to support agriculture

• Waterlogging = over-irrigated soils which suffocates roots

• Salinization = the buildup of salts in surface soil layers. Can also be caused by excessive fertilization.

Salinization inhibits production of 20% of all irrigated cropland, costing more than $11 billion/year

FIGURE 7.16

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Farmers can protect soil against degradation in various ways

• Crop rotation

• Contour farming

• Intercropping and agroforestry

• Terracing

• Shelterbelts

• Reduced tillage7-26

Crop rotation

• Crop Rotation = alternating the crops grown field from one season or year to the next

- Cover crops protect soil

• Contour Farming = plowing furrows sideways across a hillside, perpendicular to its slope, to prevent rills and gullies

Contour farming

FIGURE 7.14

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• Terracing = level platforms are cut into steep hillsides, forming a “staircase” to contain water

• Intercropping = planting different types of crops in alternating bands or other spatially mixed arrangements to increase ground cover

Terracing Intercropping

FIGURE 7.14

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• Shelterbelts or Windbreaks = rows of tall, perennial plants are planted along the edges of fields to slow the wind

Shelterbelts Reduced tillage

• Reduced Tillage = furrows are cut in the soil, a seed is dropped in and the furrow is closed

FIGURE 7.14

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- Alley cropping = shelterbelts + intercropping

Plant cover reduces erosion

• Eroding banks along creeks and roadsides are stabilized by planting plants to anchor soil

• China has the world’s largest tree-planting program (monoculture)

- Slows erosion

- Forests are not ecologically functionalFIGURE 7.15

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Salinization is easier to prevent than to correct

• Choose crops appropriate for the area

• Irrigate with low-salt water

• Irrigate efficiently

- Drip irrigation targets water directly to plants

FIGURE 7.16

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How would you farm?

You are a farmer with land on both sides of a steep ridge. You want to plant one crop on the sunny and windy south slope and a crop that needs irrigation on the north slope.

• What types of farming techniques might maximize conservation of your soil?

• What other factors might you want to know about before you decide to commit to one or more methods?

7-32

Which process transports soluble inorganic matter downward through the soil?

A) accumulation of humusB) capillary actionC) eluviationD) leaching

Which term refers to the process by which particles of insoluble inorganic matter are transported downward through the soil?

(A) accumulation of humus(B) capillary action(C) eluviation(D) leaching

Which refers to the upward movement of soluble material through the soil by water?

(A) capillary action(B) eluviation(C) erosion(D) leaching

Which term refers to the process by which minerals and dissolved salts are transported upward through the soil?

(A) accumulation of humus(B) capillary action(C) eluviation(D) leaching

Traditional subsistence agriculture uses all of the following, except:

a) Animal power

b) Irrigation

c) Irrigation water

d) Fossil fuels

7-35

Physical weathering is characterized by:

a) The chemical interaction of water with parent material

b) Organisms breaking down parent material

c) Wind or rain breaking down parent material

d) The dislodging or movement of soil by wind

7-36

a) Which horizon is the most valuable for agriculture?

a) A horizon

b) B horizon

c) C horizon

d) R horizon

FIGURE 7.37-37

Erosion increases through all of the following, except:

a) Excessive tilling

b) Overgrazing

c) Clearing forests

d) All of the above increase erosion

7-38

Which sustainable farming method involves planting rows of trees along field edges to slow the wind?

a) Terracing

b) Crop rotation

c) Shelterbelts

d) Contour farming

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7-40

Should developed nations fund reforestation projects in developing nations to combat erosion and deforestation?

a) Absolutely, developing nations are facing a crisis

b) No, not with money, but developed nations could give advice

c) No, developed nations had to solve their problems, let the others solve their own problems

d) I don’t care, it doesn’t really affect me

7-41

Should the Canadian government provide farmers with financial incentives to use technologies such as no-till farming and crop rotation?

a) Absolutely, farmers may be more likely to switch to these techniques

b) Yes, but farmers must put any money received into the farm

c) No, it’s not the government’s job to interfere with farming practices

d) I don’t care, it doesn’t really affect me