Soil: What is it? Inorganic materials (clay, silt, and sand) weathered from solid rock Living organisms (worms, insects, mites, fungi, …) Decaying organic matter Water air
Soil • Who cares?
Soil • Who cares? • Critical to driving biogeochemical cycles • HNOPS in CHNOPS comes from the soil; YOU come from the soil! • C1480H2960N16O1480P1.8S Air Soil
Soil • How long does it take for soil to form?
Soil • How long does it take for soil to form? • 200-1,000 years for 1 inch of soil
Soil • What influences soil properties?
Soil Profile Dig into the soil and you see the soil’s profile: all the different layers (called horizons) of soil, from the surface litter to the bedrock
Soil Horizons Topsoil Surface Litter Zone of Leaching Subsoil Parent Material Bedrock
Soil • Surface litter: fresh and partly decomposed organic matter • Topsoil: where most living things and nutrients are • Zone of leaching: where dissolved materials from above move down • Subsoil: accumulated materials from above • Parent material: partially broken down rock; source of minerals and inorganic matter in soil • Bedrock: underlying, unweathered rock
Tropical rainforest soil • Have a shallow topsoil layer because of rapid decomposition • Lots of rainfall removes a lot of the silica from the topsoil, but leaves behind metals like aluminum and iron. • If you remove the plants, the topsoil washes away
Tropical rainforest soil • Leaving behind the metal-rich subsoil, which hardens in the sunlight, eventually turning into a hard, red soil/dirt that doesn’t absorb water and can’t support plants • Can grow crops there for 3 yrs or so • Then switch to cattle for another 3-5 yrs • And then land is abandoned
Tropical rainforest soil • So, what is the take-home message? • Where we grow crops is not just determined by climate; soil type must be considered.
Types of soil profiles: • Soils have been cataloged all over the U.S. and most of the world, at this point in time. • See next two slides…
Human impacts on soils • Soil erosion: movement of soil components (esp. topsoil) from one place to another
Types of soil erosion Splash erosion Rill erosion Gully erosion Sheet erosion Figure 8.11
Human impacts on soils • How is soil moved? • 1. Wind • 2. Moving water
Human impacts on soils • What are the rates of soil erosion? • In U.S., for 1/3 of all cropland, erosion rates exceed replacement rates for soil • Amount of topsoil lost in the U.S. each year would fill a dumptruck 3,500 miles long
Human impacts on soils • Where does the soil go? • Oceans • Somewhere else … where it’s not useful as soil anymore...
Human impacts on soils • What factor makes the land more susceptible to erosion? • VEGETATION REMOVAL • Why? • 1. Vegetation (roots) hold the soil in place • 2. Plants slow down wind and running water (less energy)
Human impacts on soils: erosion • Type Tons soil eroded % rain that runs off • Bare soil 41 tons/hectare 30%
Human impacts on soils: erosion • Type Tons soil eroded % rain that runs off • Bare soil 41 tons/hectare 30% • Continuous corn 19.7 tons/hectare 29%
Human impacts on soils: erosion • Type Tons soil eroded % rain that runs off • Bare soil 41 tons/hectare 30% • Continuous corn 19.7 tons/hectare 29% • Continuous wheat 10.1 tons/hectare 23%
Human impacts on soils: erosion • Type Tons soil eroded % rain that runs off • Bare soil 41 tons/hectare 30% • Continuous corn 19.7 tons/hectare 29% • Continuous wheat 10.1 tons/hectare 23% • Rotate corn,wheat, clover 2.7 tons/hectare 14%
Human impacts on soils: erosion • Type Tons soil eroded % rain that runs off • Bare soil 41 tons/hectare 30% • Continuous corn 19.7 tons/hectare 29% • Continuous wheat 10.1 tons/hectare 23% • Rotate corn,wheat, clover 2.7 tons/hectare 14% • Continuousbluegrass 0.3 tons/hectare 12% • Based on 14 years of data from the Missouri Experiment Station, Columbia, Missouri
Human impacts on soils: erosion • So, what was the take-message of that last table?
Human impacts on soils: erosion • So, what was the take-message of that last table? • Amount and type of vegetation affects the amount of erosion of soil that occurs
Human impacts on soils: erosion • What activities lead to soil erosion?
Effects of Soil Erosion • 1. Loss of productivity of the land • Less soil, less nutrients, less water-holding capacity …. Less growth
Effects of Soil Erosion • 2. Increased air and water pollution • From dust in the air and soil in the water...
Effects of Soil Erosion • 3. Increased flooding: due to less water holding capacity of the soil
Effects of Soil Erosion • 4. Increased gullying: thus loss of productive land.
Effects of Soil Erosion • 5. Increased costs due to buying fertilizer, irrigation, etc.
Effects of Soil Erosion • 6. More irrigation leads to salinization of soils and eventually waterlogging (as a farmer attempts to flush out the salts…)
Human impacts on soils: conservation • 1930s dust bowl was a wake-up call (in U.S.) • 1935 Soil Conservation Act established Soil Conservation Service: maintains soils in the U.S. using education, laws, incentives, disincentives...
Chad: The Aboubakar family of BreidjingCampFood expenditure for one week: $1.23 Food United States: The Revis family of North CarolinaFood expenditure for one week: $341.98 From the book, "Hungry Planet"
Food • Malthus, 1700s: • Population is increasing exponentially • Food resources are increasing linearly • ………… BIG problem!
Food • Malthus didn’t/couldn’t anticipate the industrial and green revolutions, which have allowed food resources to increase exponentially for the last few 100 y
Food • BUT • Is this maxed out?
Food: Grain harvests • World grain production has been increasing thru time • But production per person has leveled off, area under production has leveled off, and the grain harvested area per person has decreased
Food • So, do you think we will be able to supply enough food for everyone in the future? • Depends on • Rate of population growth • Ability to increase food availability
Food • Let’s talk about our food for a minute. • What do we eat? • 2 main crops make up 60% of our calories • 1. • 2. • 2 other crops make up most of the rest • 3. • 4. ?