Transcript Food and Agriculture

Food and Agriculture
How to feed the ever expanding
population
Currently 5.8 billion
30 years 12 billion
Modern methods in Agriculture
• Green Revolution
• Blue Revolution
What’s needed to grow food?
• soil - the outer weathered layer of
the earth's crust.
• Water
• Light
• nutrients
Soil contains both Biotic and
Abiotic Components
• Topsoil is the upper 1 ft of land that is
usable for plant growth
• Composition is clay:sand:silt defines the
character of the soil
• Topsoil varies in different Biomes
– Grasslands are the riches
– Tropical Rainforest are some the poorest
BIOTIC
ABIOTIC
HUMUS
SILT (0.02-0.05mm)
Insect,
Worms
Nematodes
Bacteria
Protista
Symbiotes
Sand (0.05-2 mm)
Clay (<0.02 mm)
Charged
organic matter - typically about
1% in nature
litter - partially decayed organic matter on
the soil surface.
humus - highly decomposed, fine,
amorphous organic matter in the soil.
Functions of Organic Matter:
1) stabilizes soil structure
2) increases water retention and availability
3) increases drainage and aeration
4) increases cation exchange capacity
5) supplies nutrients upon decay
(only if low C:N ratio)
6) stabilizes pH
7) food source for microorganisms
• Bacteria and Fungi Decompose Organic
Matter
• Micorrhizal Symbiotes (tree and fungi)
enhance mineral uptake into plants
• Worms, Nematode and Insects
decompose organic matter and aerate the
soil
Soil Horizon
A Horizon or topsoil
- highly weathered
- abundant life, therefore, high in organic
matter
- dark colored
plow pan - a compacted impermeable
layer in the A horizon due to
repeated plowing or tilling
(approx. 6" deep)
B Horizon or subsoil
- less weathered; higher in clay
- less life, therefore, low in organic matter
- lighter colored
clay pan - impermeable layer high in clay.
hard pan - impermeable layer high in iron.
C Horizon or parent material
- little weathered
- little life, except deep rooted plants and
little to no organic matter
D Horizon or bedrock
- rock base
TYPICAL AGRICULTURAL SOIL
Agriculturally productive soil is a balanced mixture of
sand, silt, and clay.
Riches farming soils:
grasslands (Mollisols)
deciduous forest (Alfisols)
Land Degradation
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Overgrazing
Deforestation
Agricultural activities
Overexploitation
Industrialization
water and wind
are the main
agents of erosion
Trees and Ground Cover
Prevent erosion.
Why has 100 years of farming in the U.S.
resulted in a loss of ½ of all cropland?
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Row crops
Deep plowing
Heavy herbicide use (no ground cover)
Machine made gullies
Chemical fertilizer
No rotation of crops
monoculture
• 72% of all fresh water (rivers, lakes and
ground water) is used for irrigation
• Over-watering leads to
– Loss of Oxygen
– Salinization
Fertilizers Provide Inorganic Nutrients
• Major: N, K, P, C, Mg,S
• Applied Fertilizer
– 1950: 20 kg/ha
– 1990: 91kg/ha
Phosphates and nitrates from farm field and cattle
feed lots are aquatic pollutant.
Alternative Ways to Fertilize
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Manure
Crop residues
Ashes
Composted refuse
Green manure
– *nitrogen fixing crops
Climate: The greenhouse effect
• Increasing CO2 increases productivity