© 2010 pearson education canada 7 soil resources powerpoint ® slides prepared by stephen turnbull...

© 2010 Pearson Education Canada

7Soil Resources

PowerPoint® Slides prepared by Stephen Turnbull

Copyright © 2013 Pearson Canada Inc.

7-1



Housekeeping Items

• Did anyone go to the lecture on sea-level rise last night?• An interesting resource site to check out is the Global

Footprint Network (http://www.footprintnetwork.org/en/index.php/GFN/)

• The organizer’s founder recently shared the Blue Planet Prize with the co-creator of the ecological footprint concept – Dr. Bill Rees of UBC

• In response to Cameron’s question, it would appear that Earth Overshoot Day is calculated largely on the basis of overuse of renewable resources (forests), replenishable resources (soil, groundwater), and the ability of the biosphere to absorb carbon.



Housekeeping Items

• Clearly, the depletion of non-renewable resources (e.g. fossil fuels, minerals) is not sustainable, but that doesn’t explicitly seem to be part of the calculation, though the production of non-absorbed CO2 is related to fossil fuel combustion.

The Global Footprint Network’sconception of overshoot.



Extra Credit (Voluntary) Homework

• Check out Dirt! The Movie at http://www.truththeory.org/dirt-the-movie/ and write a two-page, single-space handwritten response to it, addressing whatever jumps out at you – things you didn’t know, particularly vivid images, ideas for enhancing and conserving soil, or whatever you like, as long as it’s relevant.

• Try to have it in to me by next Wednesday.



Upon successfully completing this chapter, you will be able to

• Delineate the fundamentals of soil science, including soil-forming processes

• Describe some important properties of soil

• Characterize the role of soils in biogeochemical cycling

• State the importance of soils for agriculture and in supporting plant growth

• Identify the causes and predict the consequences of soil erosion and soil degradation

• Outline the history and explain the basic principles of soil conservation

7-5



7-6



Central Case: Mer Bleue bog

• A 35 km2 protected wetland

• Peat deposits formed over 8000 years are up to 6m thick

• Carbon balance in peat:

- Primary production stores C

- Decomposition releases C

• Interdisciplinary research project studying the influence of climate on carbon balance

“The nation that destroys its soil destroys itself.” – Franklin D. Roosevelt, Former U.S. President

7-7



Soil as a System

Ganaraska wasteland before World War 2Photo courtesy of John Bacher and Ed Borczon



Soil as a system

• Soil consists of mineral matter, organic matter, air, and water

- Dead and living microorganisms, and decaying material

- Bacteria, algae, earthworms, insects, mammals, amphibians, and reptiles

7-9



Soil is a complex, dynamic mixture

• Soil consists of mostly mineral matter with varying proportions of organic matter, the rest is pore space taken up by air, water, and other soil gases

• Parent material = the base geologic material of soil

- Determines the starting composition of the soil

• Organic matter includes living and dead microorganisms as well as decaying plant and animal material

• Water – is not pure, contains dissolved minerals and organics and is important for support of plant growth

• Air – soil air is not the same as air we breathe

• Soil can have an influence on a region’s ecosystem

7-10



Soil formation is slow and complex

• Soil formation begins when parent material is exposed to the effects of the atmosphere, hydrosphere, and biosphere

- Parent material can be lava, volcanic ash, rock, dunes or most commonly, 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

7-11



Soil formation is slow and complex (cont’d)

7-12



Soil formation is slow and complex (cont’d)

• Biological activity includes deposition, decomposition, and accumulation of organic matter

- Humus = a dark, spongy, crumbly mass of material formed by partial decomposition

• Erosion = the dislodging and movement of soil by wind or water

- Occurs when vegetation is absent

- When deposited elsewhere referred to as sediment

7-13



Earth’s Soil Resources

It can take anywhere from 500 to 100 years to produce 1 cm of natural topsoil, depending on local conditions. Much of Canada’s land area was scraped free of soil during the last glaciation by the passage of huge ice masses, which retreated about 10,000 years ago. Today much of interior and northern Canada still lacks soil.

• Given this very long renewal time, is soil truly a renewable resource?

•How should the very long renewal time influence soil management?

weighing

the issues

7-14



A soil profile consists of layers known as horizons

• Horizon = each layer of soil

• Soil profile = the cross-section of soil as a whole

• Topsoil = inorganic and organic material most nutritive for plants

• Leaching = dissolved particles move down through horizons

• Litter = surface deposits of leaves, branches, mosses, animal waste

7-15



A soil profile consists of layers known as horizons (cont’d)• O Horizon – peat deposits

• A Horizon – topsoil

• B Horizon = subsoil, hardpan

• C Horizon = broken parent material

• R Horizon = unaltered parent material

• W Horizon = distinct layer of water in some soils

• Permafrost = some arctic soils contain a perennially frozen layer

7-16



Soils vary in colour, texture, structure, and pH

• Soils are classified into 10 orders based largely on the processes thought to form them

• Soils classified into various categories using properties such as:

- Color

- Texture

- Structure

- pH

7-17



Soils vary in colour, texture, structure, and pH (cont’d)

• Soil color = indicates its composition and fertility

- Black or dark brown = rich in organic matter

- Pale gray or white = indicates leaching

7-18




• Soil texture = the size of particles

- Clay (smallest), silt, sand (largest)

• Loam = soil with an even mixture of the three

- Influences how easy it is to cultivate and let air and water travel through the soil

• Silty soils with medium-size pores, or loamy soils with mixtures of pore sizes are best for plant growth and crop agriculture

7-19




• Soil structure = a measure of soil’s “clumpiness”

- Large clumps can discourage plant roots

- Repeated tilling compacts soil

- Plowpan = a hard layer resulting from repeated plowing that resists water infiltration and root penetration

• Soil pH = influences a soil’s ability to support plant growth

- Soils that are too acidic or basic can kill plants

7-20



Biogeochemical Cycling in Soil

7-21



Soils support plant growth through ion exchange

• Cation exchange = process that allows plants to gain nutrients

- Negatively charged soils hold positive cations of calcium, magnesium, and potassium

• Cation exchange capacity = a soil’s ability to hold cations, preventing them from leaching, thereby increasing their availability to plants

- A useful measure of soil fertility

- Greatest in fine soils, such as clay and organic soils

7-22



Soils support plant growth through ion exchange (cont’d)

• Many pollutants are positively charged, notably heavy metals such as cadmium, lead, and mercury

• These cations are attracted to negatively charged clay and humus particles in soil

- Make it difficult to remediate soil

- Also means they are held in soil instead of being released into aquatic ecosystems

7-23



Soil is a crucial part of the nitrogen cycle

• Nitrogen fixation = inert nitrogen gas from the atmosphere is combined with hydrogen to form ions of ammonium

• Nitrification = specialized bacteria converts ammonium ions into nitrite ions, then by another group of specialized bacteria into nitrate ions

• Denitrification = bacteria convert nitrates in soil or water into gaseous forms of nitrogen

- Carried out by several varieties of bacteria

7-24



Soil is an important terrestrial reservoir for carbon

• Soil plays a crucial role in the global carbon cycle

• Soil represents the largest terrestrial reservoir for carbon

• Main carbon fluxes in which soil is involved are driven by photosynthesis and the production of organic matter, followed by respiration and decay or organic matter

• Decay of soil organic matter produces soil gas that contains carbon

- Carbon dioxide

- Methane

7-25



Soil Degradation: A Global Concern

7-26



Soil degradation: A global concern

7-27



Soil degradation: A global concern

• Soil degradation results from deforestation, agriculture and overgrazing

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

7-28



Regional differences affect soil productivity

• Rainforests have high primary productivity, but the nutrients are in plants, not the soil. If the forests are removed, the soils dry out and cannot readily be regenerated.

• Swidden agriculture = cultivation of a plot for a few years and then letting it regrow into forest

• Temperate grasslands have lower rainfall and less nutrient leaching

7-29



Erosion can degrade ecosystems and agriculture

• Deposition = the arrival of eroded material at its new location

• Flowing water deposits sediment in river valleys and deltas

- Floodplains are excellent for farming

• Erosion occurs faster than new soil is formed

• Erosion increases through: overcultivating fields, overgrazing rangelands, and clearing forested areas

7-30



Soil erodes by several mechanisms

• Wind (aeolian) erosion

• Water erosion (splash, sheet, rill, gully)

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

• Predicting losses by erosion:

- Universal Soil Loss Equation (USLE)

- Wind Erosion Prediction Equation

7-31



Soil erosion is widespread

• Humans are the primary cause of erosion

• 19 billion hectares of croplands worldwide suffer from erosion

• Kazakhstan lost tends of millions of hectares to wind erosion

• Soil degradation over the next 40 years in Africa could reduce crop yields by half

• The on-farm cost of agricultural land degradation in Canada is $670 million per year

7-32



Desertification reduces productivity of arid lands• Desertification

- A loss of more than 10% productivity from erosion, soil compaction, forest removal, overgrazing, salinization, climate change, depletion of water sources

- A type of land degradation

- Affects 1/3 of the planet’s land area

- Most prone areas are arid and semiarid lands

- Climate change could result in displacement of 50 million people in 10 years

7-33



The Dust Bowl was a monumental event in North America (cont’d)

• Native prairie grasses originally held erosion-prone soils in place

• 1879-1929: Widespread cultivation of wheat, and grazing of many thousands of cattle

• Great Depression brought a cycle of poverty and overly intensive agricultural practices

• Dust storms (black blizzards) travelled up to 2000 km

• Lung irritation, dust pneumonia, grasshopper infestations

7-34



The Dust Bowl was a monumental event in North America (cont’d)

7-35



The Soil Conservation Council emerged from the experience of drought

• 1935: Prairie Farm Rehabilitation Administration (PFRA)

• Soil at Risk: Canada’s Eroding Future (1984)

• Soil Conservation Council of Canada

- National plan

- Better public awareness

- Better communication among stakeholders

- Develop policies and production methods

• U.N. Food and Agriculture Organization (FAO)

7-36



Protecting Soils

7-37



Erosion-control practices protect and restore plant cover

• Crop rotation

• Contour farming

• Intercropping and agroforestry

• Terracing

• Shelterbelts

• Reduced tillage

7-38



Crop rotation

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

- Cover crops protect soil

Intercropping

7-39

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



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

Contour Farming Terracing

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

7-40



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

- Alley cropping = shelterbelts + intercropping

Shelterbelts Reduced tillage

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

7-41



Irrigation 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

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

7-42



Irrigation can cause long-term soil problems (cont’d)

• Remedies for correcting salinization once it has occurred:

- Choose crops appropriate for the area

- Irrigate with low-salt water

- Irrigate efficiently

- Drip irrigation targets water directly to plants

7-43



Measuring and regulating soil quality

The government of Canada has adopted comprehensive measures to control air and water quality, and has set legal standards for allowable levels of various pollutants in air and water.

• Could such standards be developed for soil quality?

• If so, what properties should be measured to inform the standards?

weighing

the issues

7-44



The Science Behind The Story: Dark Earth: A New (Old) Way to Sequester Carbon

• Biochar = biomass is reduced to a black, carbon-rich, charcoal-like residue

- Can hold onto plant nutrients thus enhancing fertility of soil

- Also effective at absorbing and holding heavy metals

- May act as a long-term reservoir for carbon

7-45



Other chemicals also contribute to soil contamination

• Fertilizer = substances that contain essential nutrients but over-application can damage soils

• 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 when it gets into the water system

7-46



Other chemicals also contribute to soil contamination (cont’d)

• Nitrogen and phosphorous runoff from farms and other sources can lead to algal blooms

• Nitrates can leach through soil and contaminate groundwater

• Pesticides are another source of soil contamination

• Industrial activity contaminates soil through inappropriate disposal of wastes and improper storage

7-47



Grazing practices can contribute to soil degradation

7-48

Overgrazing is largely responsible for the permanent drying out of parts of the Mediterranean – e.g. Greece and Syria



Conclusion

• The preservation of arable soil is crucial for the maintenance of global food security

• Programs in Canada and worldwide have been successful in reducing topsoil erosion

• However, soil is still being degraded at a rate that threatens the sustainability of the resource

• The role of soil as a reservoir in biogeochemical cycling is also of increasing interest to scientists

7-49



QUESTION: Review

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

7-50



QUESTION: Review

Which horizon is the most valuable for agriculture?

a) A horizon

b) B horizon

c) C horizon

d) R horizon

7-51



QUESTION: Review

Erosion increases through all of the following, except:

a) Excessive tilling

b) Overgrazing

c) Clearing forests

d) All of the above increase erosion

7-52



QUESTION: Review

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

7-53



QUESTION: Weighing the Issues

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

7-54



QUESTION: Weighing the Issues

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

7-55

© 2010 pearson education canada 7 soil resources powerpoint ® slides prepared by stephen turnbull...

Documents