ENVIRON 102 Chapter Notes - Chapter 13: Evapotranspiration, Ecological Footprint, Sustainable Agriculture
10 May 2018
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Chapter 13 Agriculture and the Ecology of Food (all)
13.1 Origins and History of Agriculture
Why did Agriculture Begin?: Climate change, cultural progress, and population growth played important
roles in the origins of agriculture.
Agriculture: system of land management used to grow domesticated plants and animals for food,
fiber, or energy
(1) Communities of hunter-gatherers developed language and tools
o Individuals ate wild plants; diet was nutritional and well-balanced
(2) Domestication of plants and animals
o Close of the last ice age brought about agriculture
o Climates were warmer and dry seasons were longer
Evidence suggests change from hunting-gathering lifestyle to farming didn’t improve quality of
human life
o Skeletal evidence shows that hunter-gatherers were taller, better nourished, and longer
living
o Food from farmland is lower nutritional value and agriculture requires more human labor
How did Agriculture Begin?: Humans and their domesticated plants and animals have coevolved.
First signs of agriculture – wheat, barley, peas, lentils, and chickpeas – date back to Mesopotamia
10,000 years ago
Rice cultivation in China 500 years later
Rice and sorghum cultivation in Sahel region in Africa
Agricultural regions in N. and S. America 5000 to 6000 years ago
o Andes Mountains, Native Americans, and central Mexico
Started out with trial and error and then by conscious effort
o Artificial selection of crops that directed evolution
Case study: maize
o Ancestor of maize is believed to be teosinte, a grass that grows in central Mexico
o Humans selected traits that eventually produced the modern corn
12,000 years ago – domestication of animals
o First was the dog – was a source of food but also aided hunting
o Sheep, goats, and pigs domesticated 2000 years later
o Cattle was domesticated 2000 years later – provided meat and labor for agriculture
Animals that humans chose to domesticate had 5 similar characteristics
o Flexible diet, fast rate of growth, ability to breed in captivity, a calm disposition, and
sociality
Domestication of plants and animals was actually a coevolutionary process
o Changes in human behavior and physiology
And Then What? Agricultural History: Technological and cultural innovation have increased agricultural
production and reduced the need for human labor.
Dependence on tools
o Invention of plow
o Sickles, wagons, and irrigation
Food production helped support growing populations
o Ex: town of Ur near the Euphrates River had population of 6,000 people which was
supported for a labor force of 2,500 men and cattle
800-1300 AD: Middles Ages of feudal lords and serfs
o Mediterranean region under Muslim rule – sophisticated water pumping devices, dams,
and reservoirs
1400-1700 AD: discovery of the Americas (new crops), moldboard plow in China, crop rotation
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Industrial Revolution – improved plows and reapers
o Agronomy: science that applies knowledge from fields such as genetics, physiology,
chemistry, and ecology, to agriculture
▪ Ex: understanding of genetics animal and plant breeding
Late 1900s – tractors powered by fossil fuels
Over the past 50 to 60 years – Green Revolution
o Green Revolution: period during which global agricultural productivity has increased many
times over as a result of development of modern fertilizers, herbicides, and pesticides
▪ Synthetic nitrogen fixation via the Haber-Bosch process
o Use of energy from fossil fuels increased productivity
The bigger picture: plants and animals coevolved with human cultures and technologies
13.2 Agroecosystems
Agroecosystems: crops and domestic animals, the physical environments in which they grow, and
the communities of other organisms associated with them
o Depend on energy flow and nutrient cycling
Energetics: Agroecosystems funnel energy into the production of plants and animals that are most useful to
humans.
Green plants – photosynthesis (converting light energy into chemical energy)
Main objective for Agroecosystems – to funnel a major portion of net primary production into
food/fiber for human use
o Key strategy: simplification (ex: growth of single species)
Harvest index: fraction of total population that can be used by humans
o Ex: harvest index of corn is 30 to 50% (only kernel is edible)
Trophic-level efficiency: fraction of energy the animal consumes that is actually stored as biomass
o Most wild animals’ trophic-level efficiency is less than 10%
o Most domestic animals’ trophic-level efficiency is more than 10%
▪ Spend less energy hunting for prey and are enclosed
▪ Food is easily digested
o Ex: 1 unit of deer meat requires 10 units of primary production
Nutrient Cycling: Agroecosystems are prone to nutrient losses.
Nutrient losses from agroecosystems are high for 4 reasons
(1) Harvest: nutrients stores in plant tissues are harvested and removed from the ecosystem
(2) Continual disturbances: plowing causes nutrients to escape into atmosphere
(3) Irrigation: runoff contains nutrients that depletes soil and pollutes streams
(4) Low biodiversity: nutrients and water aren’t absorbed efficiently
Dynamic Homeostasis: Agroecosystems simplicity causes vulnerability.
Dynamic homeostasis: ability of an ecosystem to maintain stable values of key processes
Agroecosystems have low biodiversity which diminished ability for dynamic homeostasis
13.3 The Growth of Crop Plants
Plant Growth and Reproduction: Plants depend on light, water, and essential nutrients.
Energy for plants provided by photosynthesis
o Carbon dioxide enters plants through stomata (pores in leaf surface)
Plants obtain water from soil
o Transpiration: movement of water fro soil to plant to air
o Transports water against force of gravity
o Energy for transportation is provided by diffusion gradient
▪ Gradient between water-saturated air in the spaces between cells in leaves and the
drier air outside
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▪ Depends on amount of moisture in soil and relative humidity in air
▪ Drier the air, the faster the transpiration
Plant growth depends on nutrients – nutrient absorption executed by root hairs
Root growth energy comes from carbohydrates created in leaves
What Are You Eating?: Patterns of growth and reproduction determine the parts of plants that humans use.
Most crop plants were selected because they store carbohydrates, proteins, and oils
Stores in leaves (cabbage, spinach), stems (asparagus, potato), and roots (carrots, radishes)
What Grows Where and Why?: The climate and soil of a region determine which crops can be grown.
Most agriculture takes place in tropical and temperate climate zones
Rainfall
Characteristics of soil – soil moisture and chemistry
The Role of Other Organisms: The growth of crop plants is influenced by the surrounding ecological
community.
Pollination of plant – insects (honeybees)
o Honeybees are threatened by pesticides, bacterial diseases, and infestations of parasitic
mites
Diverse community of soil organisms recycles nutrients
o Earthworms convert agricultural residues into inorganic soil nutrients
▪ Burrows allow air into soil to improve soil quality
o Mites, springtails, beetles, and bacterial break down crop residues and release of nutrients
into the soil
o Fungi release enzymes that break down the cellulose in plant cell walls
▪ Releases the carbon, nitrogen, and other elements in plants
Excessive application of herbicides and fungicides can kill soil organisms
o Results in greater need for artificial cultivation and fertilizers and lower yield
Mycorrhizae: associations between plant roots and specialized fungi
o Fungi transports inorganic nutrients into plants roots
o Plants supply fungi with carbohydrate
Parasites in agroecosystems – roundworms (nematodes), competitors, etc.
13.4 Managing Soil Resources
Soil: mixture of organic matter and mineral particles
o Formed by constant weathering of rocks and addition of organic matter from plants
Soil Origins and Structure: Organic matter and weathered rock form soil.
Mineral particles are classified based on size
From large to small – sand, silt, and clay
Soil texture: relative amounts of sand, silt, and clay in soil
Soil profile: distinctive vertical structure
o From top to bottom: organic matter, mixture of organic matter and weathered mineral
particles, less-weathered rocklike particles
o Horizons: layers in the soil profile
O horizon: leaves and crop residue and humus (organic products of their decomposition)
A horizon: mixture of organic matter and mineral particles
o Upper, humus-rich portion – topsoil
o Contains plant roots
B horizon (aka subsoil): rich in clay particles (formed from sand and silt)
o Accumulation of minerals such as iron and aluminum – red/yellow hue
C horizon (aka weathering zone): bedrock is broken by action of soil water and growth of plant
roots
o Contains particles of rock that are chemically similar to parent rock
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Document Summary
Chapter 13 agriculture and the ecology of food (all) : climate change, cultural progress, and population growth played important roles in the origins of agriculture. Evidence suggests change from hunting-gathering lifestyle to farming didn"t improve quality of. First signs of agriculture wheat, barley, peas, lentils, and chickpeas date back to mesopotamia: food from farmland is lower nutritional value and agriculture requires more human labor. : humans and their domesticated plants and animals have coevolved. Rice cultivation in china 500 years later. Rice and sorghum cultivation in sahel region in africa. Agricultural regions in n. and s. america 5000 to 6000 years ago: andes mountains, native americans, and central mexico. Started out with trial and error and then by conscious effort: artificial selection of crops that directed evolution. Case study: maize: ancestor of maize is believed to be teosinte, a grass that grows in central mexico, humans selected traits that eventually produced the modern corn.
