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Soil Erosion

Honors: Planet in Crisis

Alexis Bury

on 28 March 2013

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Transcript of Soil Erosion

Bull photo credit Nasa / Goddard Space Flight Center / Reto Stöckli By Alexis Bury
Honors Seminar: Planet in Crisis
March 25th 2013 Soil Erosion If this... Can do this... What will this do? The Solution The Problem The Science "A nation that destroys
its soils, destroys itself."
President Roosevelt The Science Behind the Soil What is Soil? 1st: Organic Matter = Glue Energy source
Soil biota
Facilitates formation of soil aggregates
Increase soil porosity and structure
Improve infiltration
Improve nutrient cycling Ideal concentration = 100 tons per hectare
Concentrated at upper layers
Where most erosion occurs
Therefore susceptible
Average national loss of 17 tons per ha per yr tranlsates to 2 tons of organic matter This... Is transformed into this... By these... 2nd: Soil Biota Large portion of organic matter
Recycle basic nutrients required by plants
Carbon, Nitrogen, etc
Erosion decrease diversity and abundance of biota
BUT... Straw-mulching increases biota 300% In one hectare, there is on average... 1000 kg arthropods 1000 kg earthworms 150 kg protozoa 150 kg algae 1700 kg bacteria 2700 kg fungi 3rd: Inorganic Matter Eroded bedrock Sand Silt Clay Higher degrees of erosion Sand percolates well
Clay swells when wet
Best soil
1/3 sand
1/3 silt
1/3 clay What is
Erosion? Removal of earth’s surface
Exposed rock
Removes topsoil
Most bio activity
Degrades soil structure Removes nutrients
Reduced plant productivity
Pollute streams
Natural and artificial fertilizer Stuff taken away holds 3x more nutrients than stuff remaining Erosion Algal blooms Lake eutrophication What Causes
Erosion? Water Ice Wind Snow How does
Occur? The force behind a raindrop hitting bare soil is that of a bullet
Bare soil loses particles 123x faster than land covered with sod
Particles loosened Tossed into air
Particles travel
Africa -> Brazil
China -> Hawaii Plant residues can slow erosion
Crop residues removed and burned for fuel
60% in China
90% in Bangladesh Carried away
Streams, valleys, lakes, sewers, etc.
Leaves behind desert-like landscape
Difficult for plants to grow Types of Erosion Sheet Gully Rill What Makes Erosion Detrimental? Natural part of Rock Cycle Igneous Sedimentary Metamorphic Water erosion causes
Losses of nutrient and substrate on-site
Loss of agricultural productivity
Build up of sediment downstream
Ecological disruption
Clogging of reservoirs Reduce infiltration rates
Soil become water logged
Degraded structure = Decreased water holding capacity Plant
Cover Slows water as it flows over land
Allows for water to sink in
Roots hold soil in place
Reduce momentum of falling raindrop
Water storage
Instead of flowing downhill and eroding, water is sucked up by plants
1 tree = difference between a flood and no flood Erosion Prevention Contour Plowing Wind Breaks Overall:
Inhibit water runoff
and encourage
water infiltration Strip Cropping Extensive Plant Cover In fields and
river banks High Humus Content Controlled Grazing Practices Preserve Wetlands Crop Rotation Decreased or No Tilling Accelerated by... Overstock + overgrazing
Removes ground cover
Excess plowing
Not rotating crops
Not planting across contour Each year, 75 billion metric tons of soil are removed from the land by wind and water erosion During the last 40 years, 1/3 of the world's arable land has been lost by erosion Population increasing Per capita
decreasing To support a diverse diet, each person requires need 0.5 ha of arable land, but only 0.27 is available
(6 billion people) Most from land farmed with unsustainable farming practices What are some sustainable vs. unsustainable farming practices? Potential to create pollution and health problems
Destroy natural habitats Fertilizers + Pesticides + Irrigation
offset deleterious effects of erosion 90% US cropland losing soil
above sustainable rate 54% US cropland
overgrazed In the Past
50 Years... Average farm increased in size from 90 to 190 hectares
Remove grass strips, shelter belts, hedgerows
Crop specialization
Heavy machines
Start to use slopes because we are running out of land
More easily eroded
Remove plant residues = 10 Hectacres Food and Agriculture Organization reports that the per capita production of grains, which make up 80% of the world's food supply, has been declining since 1984 Soil Forms Slowly Take 200-1000 years to form 2.5 cm (1 in) of topsoil under cropland conditions
longer under pasture
US loses 2.5 cm every 16.5 years
Loss 17 times rate of formation
US topsoil depth 1776 =23 cm
After 200 years farming = 15 17 tons of soil per ha per year lost due to water and wind erosion
75 mm water
2 tons org matter
15 kg of available N
soil depth 1.4mm
soil biota population diminished
Total: 8% reduction in crop productivity over 1 year Water and nutrient loss has the greatest impact on crop productivity over long term
(50-75% of the reduced productivity) Contriute to high energy consumption and unsustainable agricultural systems
6% of nation's energy consumption
10% used to offset losses of nutrients, water and crop productivity due to erosion-
1,600,000 kcal of fossil energy per ha per year Erosion causes
$44 billion
in damages
per year Many more... Case Study: The Dust Bowl Crop failure
+ Drought
= Dust storms 1930's Discussion Consequences Guatemala Virginia, USA Applachian Mountains, West Virginia, USA Champaign, IL, USA Dead Zone, Gulf of Mexico Eagle City, Oklahoma, USA What words come to mind when you think of soil?

(no need to be scientific) Sources http-//soils.usda.gov/sqi/publications/files/sq_two_1.pdf.pdf
Soil Quality Resource Concerns: Soil Erosion
Soil Erosion
Amplification of the North American ‘‘Dust Bowl’’ drought through human-induced land degradation
Causes of the Dust Bowl
The Phoenix Dust Storm and the Dust Bowl—Caused by Humans? Are we in danger of a second Dust Bowl?
Is it worth the time and man-hours to enact erosion prevention efforts even if it saves so much money?
What does this mean for jobs? 1 hectare = 10,000 meters = 100 x 100 Reactions? Let's start with a question... Do you see evidence of soil erosion around you? 100 m 100 m Brown or Red = Exposed soil
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