BIO103C- Chapter 12 ( Agriculture and the Ecology of Food) Study Guide

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Terms in this set (...)

agriculture
the system of land management used to grow domesticated plants and animals for food, fiber, or energy.
agronomy
the science that applies knowledge from other fields of study, such as genetics, physiology, chemistry, and ecology, to agriculture.
Green Revolution
The period since about 1950 during which global agricultural productivity increased many times over.
agroecosystem
Crops and domesticated animals, the physical environment, and other organisms associated with them.
harvest index
Fraction of total production that can be used by humans
trophic-level efficiency
The fraction of energy that the organisms in one trophic level store as biomass and make available to the next trophic level.
nitrogen fixation
A process in which atmosphere N2 is converted to NH3; most nitrogen fixation is carried out by nitrogen-fixing bacteria, which convert N2 to NH3 and then into nitrogen-containing organic molecules, such as amino acids and nucleic acids.
nitrification
A process in which specialized battery in the soil convert NH+ to nitrite (NO2-) and nitrate (NO3-).
legumes
Plants in the pea family many of which have nitrogen-fixing nodules.
denitrification
Nitrogen in soil and water is returned to the atmosphere; specialized bacteria convert NO3- to N2 gas. The total nitrogen in Earth's organisms, soils, and waters is determined by the balance between nitrogen fixation and denitrification.
Haber-Bosch process
A nonbiological method of nitrogen fixation adapted to the production of chemical fertilizers.
soil
The uppermost layer of Earth's crust that supports plant growth; a mixture of organic matter and mineral particles.
sand
Mineral particles 0.05-2mm in diameter; the chemical structure of these particles still resembles their parent bedrock.
slit
Mineral particles that have experienced more weathering than sand and that have diameters ranging from 0.002-0.5mm.
clay
Smallest particles of minerals (diameters less than 0.002 mm) that are highly weathered, with unique physical and chemical properties.
texture
The relative amount of sand, slit, and clay in soil.
soil profile
The distinctive vertical structure of soil layers.
O horizon
The top layer of natural soil consisting of humus.
humus
Leaves or crop residue and the organic products of their decomposition.
A horizon
A layer of soil containing a mixture of organic matter and mineral particles.
B horizon
the subsoil below the A horizon that is especially rich in clay protocols that form the weathering of sand and silt.
C horizon
The lowest layer of soil or weathering zone
soil fertility
the variety of soil characteristics that support plant growth.
tilth
The physical arrangement of soil particles that facilitates aeration, seed;ing emergence, and the growth of roots.
contour farming
A soil-conserving agricultural technique used in hilly terrain in which plowing occurs along the contour of the land, rather than up and down hills
terracing
An agricultural technique used on steep mountain slopes in which a series of wide steps are cut into the slope. this helps to retain water and limit runoff in sites that would otherwise be very difficult to cultivate.
shelterbelts
Strips of trees planted as windbreaks along the edge of an agricultural field to slow the wind and reduce soil erosion.
windbreaks
Trees planted along the edge of an agricultural field to slow the wind and reduce soil erosion.
no-till
An agricultural technique in which an unplowed field is planted using special drills to prevent soil erosion.
intercropping
Alternating bands of different crops in the same field to bind soil particles in place between the primary crop rows.
cover crops
crops such as winter wheat or rye that are planted to hold soils that would otherwise lie exposed to the weather between seasons, reducing the risk of erosion.
gravitional water
Water that flows through the soil as it percolated into the soil, drawn downward by the force of gravity.
hygroscopic water
Water that is bound to soil particles and cannot be easily used by plants.
capillary water
Water that is held in the soil by water-to-water hydrogen bonds.
field capacity
The amount of water that a given volume or weight of soil can hold against the force of gravity.
soil wilting point
The point at which there is no longer enough water in the soil for plants to replace the water that is being lost to transpiration.
potential evapotranspiration (PET)
Estimated water evaporated and transpired from a hypothetical agricultural field
soil salinization
The process that occurs when salts contained in irrgation water concentrate and crystallize on the soil surface due to evaporation.
drip irrigation
A system that provides water to plants through pipes with small openings at the base of each plant that feed water to the root zone.
monocultures
Planting of a single crop species.
interplanting
The practice of planting multiple crop species in the same field.
polyculture
(see intercropping)
Alternating bands of different crops in the same field to bind soil particles in place between the primary crop rows.
genetically modified organism (GMO)
An organism whose DNA has been altered by the insertion of a gene from a different species into the organism's cells.
broad-spectrum pesticide
A pesticide that kills a wide variety of organisms.
biomagnification
the process by which the concentration of a toxin increases at each higher level of a food web.
biological pest control
the use of predators and parasites to manage pests.
pheromone
Volatile chemical signals used to send a message from one individual organism to another.
integrated pestmanagement (IPM)
The effective combination of all three kinds of pest control- chemical, biological, and cultural- carefully designed to minimize environmental damage.
organic foods
Foods produced to meet strict standards that limit the use of fertilizers and pesticides.
Food security
Physical, social, and economic access to sufficient, safe, and nutritious food to meet dietary needs and food preferences needed for an active and healthy life (as defined by the Untied Nations' Food and Agriculture Organization.)
Origins and History of Agriculture
+Agriculture originated independently in several places as a consequence of climate change, cultural process, and human population growth.
+Humans, crop plants, and domestic animals have coevolved.
Agroecosystems (Key point)
agricultural ecosystems depend on energy flow and nutrient cycling following the same principles as natural ecosystems.
The Growth of Crop Plants
+Plant growth and reproduction depend on adequate light, water, and nutrients.
+Differences in range of tolerance for environmental factors determine when and where different crop plants grow best.
Managing Soil Resources
+Soil structure organic matter and nutrient content influence the growth of crop plants.
+Unlike natural ecosystem, agroecosystem lack processes to sustain soil fertility.
+ Soil conservation practices include limiting soil exposure and disturbance as well as diversifying crops.
Water and Agriculture
+Soil texture and organic matter determine the amount of water that a soil can hold against the force of gravity.
+Irrigation has allowed expansion of agriculture in arid regions, but it creates important environmental challenges.
Livestock in Agroecosystems
Domesticated animals in agroecosystems prevent several environmental challenges, including land for and range, waste disposal, and disease.
Managing Competiors and Pests
Pesticides are used to control populations of weeds, pests, and disease organisms that compete for the food in agroecosystems.
Managing Genetic Resources
Selective breeding, clothing, and genetic engineering have produced very productive strains of domestic plants and animals, but they have also diminished genetic diversity.
The Ecology of Eating
the ecological impacts of our eating habits are determined by whether our diet emphasizes plants or meat, how our food is grown, and where our food comes from.
Agronomy (key point)
- Brings in multiple disciplines to improve agriculture
Agroecosystems
• Nutrient cycling
- Agroecosystems are prone to nutrient loss
1. Harvest
+ Biomass removed from system
2. Continual disturbance
+ Soil more vulnerable to erosion
3. Irrigation
+ Leaching
4. Low biodiversity
+ Composed of a few species
Agroecosystems
• Nitrogen
1. Most abundant element
2. Small amounts in crust
3. Microorganisms transform nitrogen gas to usable forms
4. Plants modify to create essential compounds • Amino acids
• Nucleic acids
Nitrogen cycles rapidly between atmosphere and biosphere:
1. Nitrogen enters biosphere by nitrogen fixation
• Bacteria convert N2 to NH3 and then other molecules
• Small amount by lightning
2. Soil bacteria carry out nitrification
• Makes nitrogen available to other organisms
3. Denitrification
• Bacteria transform nitrates to N2 gas
Agroecosystems (key point)
• Phosphorus is abundant in crust but absent from atmosphere
• Organisms use phosphorus as phosphate (PO4)
• Must be weathered out of sedimentary rock
• Limiting factor in marine production
Agroecosystems
• Human impacts
1. Humans have increased rate of nitrogen fixation
2. Haber-Bosch process
• Nonbiological method of nitrogen fixation
• Source of chemical fertilizer
3. Increased N and P production advanced agricultural production
4. Excess N and P may act as pollutants
5. Aquatic ecosystems extremely sensitive
• Eutrophication and dead zones
Agroecosystems
• Dynamic homeostasis
- Ability of system to maintain stable values
- Net primary production
Agroecosystems
• Nutrient cycles
1. Nitrogen
2. Phosphorus
3. Potassium
4. Micronutrients
• Iron, magnesium, and others
Agroecosystems
• Issues
(1) Nutrient loss
• Harvest
• Continual disturbance
• Irrigation
(2) Low biodiversity
• Monocultures
Agroecosystems
• Solutions
- Mimic natural systems
Plant requirements for photosynthesis essential:
1. Light
2. Water
3. Essential nutrients
- Nitrogen
- Phosphorus
- Potassium
Plants selected for storage of carbohydrates, proteins, and oils:
1/ Portion of plant we consume tends to be rich in one of these
2/ Leaves
• Lettuce, spinach, cabbage, onions
3/ Stem
• Potatoes, celery, asparagus
4/ Roots
• Carrots, beets, turnips
5/ Fruits
• Peppers, apples, squash
Most agriculture occurs in tropical and temperate zones
- Tolerance of temperature and rainfall determine where a crop may be grown
- Plants vary in soil needs
- Usually matches climate/soil where the crop evolved
Role of other organisms
- Crops are influenced by surrounding organisms
Many crops require pollination
- Bees and other pollinators
Soil organisms recycle nutrients and maintain soil
- Worms, insects, bacteria, fungi
The Growth of Crop Plants
• Role of other organisms
• Many crops require pollination
• Soil organisms recycle nutrients and maintain soil
• Pests and pathogens
Soil (key point)
- Mixture of minerals, organic matter, water, air, and organisms
• Minerals
1/ Sand
• Particles 0.05-2 mm
• Chemical structure resembles that of parent material
2/ Silt
• Particles 0.002-0.5 mm
3/ Clay
• Particles less than 0.002 mm
Soil horizons
- Layers of the soil
O horizon (key-point)
• Humus—leaves or crop residues
A horizon (key-point)
• Mixture of organic matter and minerals
B horizon (key-point)
• Subsoil—rich in clay from sand and silt weathering
C horizon (key-point)
• Lowest layer
• Bedrock broken up
Follow soil horizons layer (top->bottom):
1. O horizon
2. A horizon
3. B horizon
4. C horizon
Determined by soil characteristics
- Availability of nutrients
- pH
- Amount of aeration
- Overall soil structure
Managing Soil Resources
• Soil fertility refers to ability of soil to support plant growth
Managing Soil Resources
• Soil conservation
1. Agroecosystems lack many of the processes that maintain soil fertility
- Accumulation of topsoil
2. Water erosion
- Problematic on exposed soil - Cover crops
Four basic principles for soil conservation
- Keep soil covered
- Minimally disturb soil
- Keep plant growth year round
- Diversify crops/cover crops
Amount of water soils hold depends on soil texture and organic matter
1. Gravitational water
- Water that flows through soil
2. Hygroscopic water
- Water bound to soil particles
3 Capillary water
- Water held in micropores
Water is essential to plant growth
- Water availability determined by rainfall and soil factors
Field capacity
- Amount of water amount of soil can hold - Depends on soil particle structure
Soil wilting point
- Point where less water available than transpiration rate
Irrigation
- First used 5,000 years ago
- Water diversion and pumping has allowed crops to be grown were water is limited
Conserving water in agroecosystems
1• Alternative methods - Drip irrigations
2• Plant-breeding programs
- Developing new breeds of crops that use less water
3• Planting alternative crops - Jojoba
Livestock in Agroecosystems
• Domestic animals
• Significant portion of agriculture
• 20% of Earth's pasture for animals
• 30% of crops for animal feed
• Trophic-level efficiency varies by species
Trophic-level efficiency (key-point)
- Most domestic animals are herbivores
- Efficiency depends on ability to break down cellulose
- Ungulates most efficient
• Cattle, sheep, goats, and pigs
- Horses have simpler digestive tracts
• A pasture can support twice as many cattle as horses
Environmental impacts
+ Waste management
1. Manure is rich in nutrients
2. Some pathogen concern
3. Methane production
- Livestock accounts for 5% of global warming
- Possible energy source
Land use
- Forests and habitats cleared for grazing
Transmission of disease
- Coevolution of flu virus
- E. coli
Managing Genetic Resources
• Humans dependent on a handful of crop species
• Species extremely productive from breeding, hybridization, and cloning
• Genetic diversity reduced
• Older varieties have greater genetic diversity
- More resistant to change
• Current efforts to maintain and improve genetic diversity ongoing
Genetically modified organisms
1- Improve yields
2- Improve disease and pest resistance
• BT corn
3- Addition of nutrients
• Golden rice
4- Controversy still abounds in general public
• Philosophical concerns
• Labeling
Competitors and pests are a major issue
- 42% of all crops are lost to pests and disease
Chemical pest control
- Effective, yet some threats to human health
• Biomagnification - DDT
Biological pest control
- Use of predators and parasites to control pests
Agroecosystem management of pests
- Managing crop environment can reduce pests - Government regulation reduces pest import
- Crop rotation
- Mechanical methods for weed/pest control
Integrated pest management (IPM) -key point
- Uses chemical, biological, and cultural pest control to minimize crop loss
The Ecology of Eating
• Diet determines significant portion of ecological footprint
• Meat consumption increases footprint
• Food miles
- Distance food travels before consumption
• Processing and storage
Organic foods
- Produced following standards for pesticide and fertilizer use
Hidden water
• Water important resource for food production
• Water footprint
- Includes water for production, consumption, and waste
• Methods of production vary widely in water use
Food safety
• Production methods affect public health
- E. coli
- Melamine contamination
• Inspection of imported foods
Choices can reduce environmental impacts and encourage sustainable agriculture
- Reduce food waste
- Eat more plant-based foods - Eat local foods
- Eat fresh foods
- Eat seasonally
- Choose sustainable products - Ask questions
Sustainable agriculture
- Aims to provide future generations with high level of food with minimal environmental cost
- Must conserve resources and habitat
Food distribution
- Major obstacle to ending hunger
Which of the following traits have made certain wild plants good candidates for domestication?
limited seed dispersal
The move from hunter-gatherers to purposefully planning cultivation of crops first began in ________.
Mesopotamia
Compared to most natural ecosystems, agroecosystems are particularly fragile because __________.
they have much less biodiversity
Most crops cannot grow in ________.
water logged soil
According to this data depicting the climate limits of specific crops, corn, an important food crop, grows best in the ________ biome.
temperate forest
The primary cause of soil erosion is ________.
over cultivation
The two main processes that form soil are __________.
the weathering of bedrock and the decomposition of organic materials near the soil surface
Moisture content, pH, and aeration are factors that greatly influence __________.
soil fertility
Water diversion and irrigation has allowed humans to grow crops in areas where natural supplies have been limited. A major challenge that exists in these regions has been ________.
salinization of soils
As water percolates into soil, __________.
hygroscopic water clings to soil particles because of hydrogen bonds between water and soil particles
The wastes from a dairy farm with 700 cows__________.
contribute to global warming and are equivalent to the septic waste produced by a population of about 10,000 people
Which of the following is a concern people have about genetically modified organisms?
It can lead to herbicide resistance.
Managing crop competitors and pests have been challenging to agronomists for centuries. One approach, integrated pest management, ________.
combines chemical pesticides with biological control techniques
To best reduce the environmental impact of agriculture, consumers should choose __________.
foods that are in season
A pheromone is a ________.
species-specific chemical attractant
________ is defined as physical, social, and economic access to sufficient, safe, and nutritious food to meet dietary needs and food preferences needed for an active and healthy lifestyle.
Food security
Which of the following is the greatest obstacle to feeding all of Earth's people?
equitable food distribution