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Presentation on theme: "7-1."— Presentation transcript:

1 7-1

2 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 ( 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.

3 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’s conception of overshoot.

4 Extra Credit (Voluntary) Homework
Check out Dirt! The Movie at 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.

5 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

6 7-6

7 Central Case: Mer Bleue bog
“The nation that destroys its soil destroys itself.” – Franklin D. Roosevelt, Former U.S. President 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

8 Soil as a System Ganaraska wasteland before World War 2 Photo courtesy of John Bacher and Ed Borczon

9 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

10 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

11 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

12 Soil formation is slow and complex (cont’d)

13 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

14 Earth’s Soil Resources
weighing the issues 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?

15 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

16 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

17 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

18 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

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

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

21 Biogeochemical Cycling in Soil

22 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

23 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

24 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

25 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

26 Soil Degradation: A Global Concern

27 Soil degradation: A global concern

28 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%

29 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

30 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

31 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

32 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

33 Desertification reduces productivity of arid lands
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

34 The Dust Bowl was a monumental event in North America (cont’d)
Native prairie grasses originally held erosion-prone soils in place : 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

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

36 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

37 Protecting Soils 7-37

38 Erosion-control practices protect and restore plant cover
Crop rotation Contour farming Intercropping and agroforestry Terracing Shelterbelts Reduced tillage 7-38

39 Intercropping Crop rotation
Crop Rotation = alternating the crops grown field from one season or year to the next Cover crops protect soil Intercropping = planting different types of crops in alternating bands or other spatially mixed arrangements to increase ground cover

40 Contour Farming Terracing
Contour Farming = plowing furrows sideways across a hillside, perpendicular to its slope, to prevent rills and gullies Terracing = level platforms are cut into steep hillsides, forming a “staircase” to contain water 7-40

41 Reduced tillage Shelterbelts
Shelterbelts or Windbreaks = rows of tall, perennial plants are planted along the edges of fields to slow the wind Alley cropping = shelterbelts + intercropping Reduced Tillage = furrows are cut in the soil, a seed is dropped in and the furrow is closed

42 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

43 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

44 Measuring and regulating soil quality
weighing the issues 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?

45 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

46 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

47 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

48 Grazing practices can contribute to soil degradation
Overgrazing is largely responsible for the permanent drying out of parts of the Mediterranean – e.g. Greece and Syria

49 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

50 QUESTION: Review Physical weathering is characterized by:
The chemical interaction of water with parent material Organisms breaking down parent material Wind or rain breaking down parent material The dislodging or movement of soil by wind Answer: c 7-50

51 QUESTION: Review Which horizon is the most valuable for agriculture?
A horizon B horizon C horizon R horizon Answer: a 7-51

52 QUESTION: Review Erosion increases through all of the following, except: Excessive tilling Overgrazing Clearing forests All of the above increase erosion Answer: d 7-52

53 QUESTION: Review Which sustainable farming method involves planting rows of trees along field edges to slow the wind? Terracing Crop rotation Shelterbelts Contour farming Answer: c 7-53

54 QUESTION: Weighing the Issues
Should developed nations fund reforestation projects in developing nations to combat erosion and deforestation? Absolutely, developing nations are facing a crisis No, not with money, but developed nations could give advice No, developed nations had to solve their problems, let the others solve their own problems I don’t care, it doesn’t really affect me Answer: any 7-54

55 QUESTION: Weighing the Issues
Should the Canadian government provide farmers with financial incentives to use technologies such as no-till farming and crop rotation? Absolutely, farmers may be more likely to switch to these techniques Yes, but farmers must put any money received into the farm No, it’s not the government’s job to interfere with farming practices I don’t care, it doesn’t really affect me Answer: any 7-55

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