Chapter10: Agriculture

Chapter 10: Farming: Conventional
and Sustainable Practices
10.1 Resources For Agriculture
• Soils are complex ecosystems
• Healthy soil fauna can determine soil fertility
• Your food comes mostly from the A horizon
Soil Formation
Young Soils
• Strongest Influence Is Parent Material
Mature Soils
• Strongest Influences: Climate, Vegetation,
Never Safe From Weathering
Soil Formation Processes
Leaching from Surface
• K, Mg, Na
• Ca
• Si
• Al, Fe
Accumulation beneath Surface
• Al, Fe in Humid Climates
• Ca in Arid Climates
• Clay (Mechanical Movement)
Soil Horizons and Profiles
• Soil Horizons
– Layers in Soil
– Not Deposited, but Zones of Chemical Action
• Soil Profile
– Suite of Layers at a Given Locality
• Some CSI myths
– You can’t generally identify a soil from surface
– You can’t generally pinpoint a location from a soil
Principal Soil Horizons
• O: Organic (Humus)
– Often Absent
• A: Leaching
– K, Mg, Na, Clay
• B: Accumulation
– Absent in Young
– Distinct in Old Soils
– Al, Fe, Clay (Moist)
– Si, Ca (Arid)
• C: Parent Material
Limits of Soil Formation
• Balance Between:
– Downward Lowering of Surface
– Downward Migration of Horizons
• If erosion rapid or soil evolution slow, soils
may never mature beyond a certain point.
– Soils on Steep Slopes
– Soils in Arid or Cold Climates
• Extremely ancient soils may have lost
everything movable
Soil Classification
• May be the most difficult classification problem in
• Varied Bases for Classification
– Age
– Parent Material
– Climate and Drainage
• Multiple Objectives
– Scientific
– Agricultural
– Engineering
"The 7th Approximation"
• U.S. Soil Conservation Service
• 12 Soil Orders
"The 7th Approximation"
Degree of Weathering and B Horizon Development
Moderate Large
Aridisols 10,000 yrs. 100,000 y 1 m.y.
Inceptisols Alfisols
Spodosols Ultisols
100 years 1000 yrs. Mollisols
Soils Defined by Special Constituent Materials
Volcanic Ash
Peat, Organic Matter
“Self-Mixing” Clay Soils
Soils on Permafrost
Mollisols Feed The World
Aridisol, Kuwait
Soils of the U.S.
Oxisol, California (a Paleosol)
Soils and Organisms
Earthworms (not always good?)
– Aerate and Mix Soil, but….
– In northern U.S. and Canada, most are exotic
– Consume Organic Matter
10.2 Ways We Use And Abuse Soils
Arable land is unevenly distributed
Soil losses reduce farm production
Wind and water move most soil
Deserts are spreading around the world
The Counterfeit Paradise
• Year-round growing season – but --• Tropical Soils are nutrient poor
• Tropical ecosystems ruthlessly recycle
• Agriculture rapidly depletes nutrients
– Slash and burn agriculture
– Need for Fertilizer for intensive agriculture
– Hardpan development
10.3 Water And Nutrients
• All plants need water to grow
• Plants need nutrients, but not too much
– "Brawndo's got what plants crave. It's
got electrolytes"
• Farming is energy-intensive
– Global Food Production = 6 x 1015 cal/yr = 25 x
1018 J/yr
– Global Energy Use = 474 × 1018 J/yr
Farming is energy-intensive
• Global Food Production = 6 x 1015 cal/yr = 25 x
1018 J/yr
• Global Energy Use = 474 × 1018 J/yr
• Direct Agricultural Energy Use = 1% of Total or
about 5 x 1018 J/yr
• By Some Estimates We Use More Energy Than
We Get Out
• We Cannot Grow Enough Crops to replace
Fossil Fuels
10.4 Pests And Pesticides
• People have always used pest controls
• Modern pesticides provide benefits, but also
create problems
– Kill beneficial organisms
– Toxic to humans
– Resistance
• There are many types of pesticides
People have always used pest controls
People have always used pest controls
10.5 Environmental Effects Of Pest
• Pesticides accumulate in remote places
• Many pesticides cause human health
• Hormone Disruptors
• “Organic” Pest Control Can Backfire
– Mongooses in Hawaii to Control Rats
– Cane Toads in Australia to Control Beetles
– Mosquito Fish (Worldwide)
10.6 Organic And Sustainable
What does “organic” mean?
Careful management can reduce pests
Useful organisms can help us control pests
Integrated Pest Management uses a
combination of techniques
10.7 Soil Conservation
Contours reduce runoff
Ground cover protects soil
Reduced tillage leaves crop residue
Low-input agriculture can be good for farmers
and their land
• Consumers’ choices play an important role
Natural and Human Processes
• Most human processes are “natural”
• What’s unnatural:
– Rate of human processes
– Scale of human processes
– We Now Move More Material Than Natural
Soil Depletion
• Wind
• Water
• Remedies
– Windbreaks
– Contour plowing
– Strip Cropping
– No-till Agriculture
Contour Plowing
Strip Cropping

similar documents