BIO103C- Chapter 12 ( Agriculture and the Ecology of Food) Study Guide
Terms in this set (...)
the system of land management used to grow domesticated plants and animals for food, fiber, or energy.
the science that applies knowledge from other fields of study, such as genetics, physiology, chemistry, and ecology, to agriculture.
The period since about 1950 during which global agricultural productivity increased many times over.
Crops and domesticated animals, the physical environment, and other organisms associated with them.
Fraction of total production that can be used by humans
The fraction of energy that the organisms in one trophic level store as biomass and make available to the next trophic level.
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.
A process in which specialized battery in the soil convert NH+ to nitrite (NO2-) and nitrate (NO3-).
Plants in the pea family many of which have nitrogen-fixing nodules.
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.
A nonbiological method of nitrogen fixation adapted to the production of chemical fertilizers.
The uppermost layer of Earth's crust that supports plant growth; a mixture of organic matter and mineral particles.
Mineral particles 0.05-2mm in diameter; the chemical structure of these particles still resembles their parent bedrock.
Mineral particles that have experienced more weathering than sand and that have diameters ranging from 0.002-0.5mm.
Smallest particles of minerals (diameters less than 0.002 mm) that are highly weathered, with unique physical and chemical properties.
The relative amount of sand, slit, and clay in soil.
The distinctive vertical structure of soil layers.
The top layer of natural soil consisting of humus.
Leaves or crop residue and the organic products of their decomposition.
A layer of soil containing a mixture of organic matter and mineral particles.
the subsoil below the A horizon that is especially rich in clay protocols that form the weathering of sand and silt.
The lowest layer of soil or weathering zone
the variety of soil characteristics that support plant growth.
The physical arrangement of soil particles that facilitates aeration, seed;ing emergence, and the growth of roots.
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
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.
Strips of trees planted as windbreaks along the edge of an agricultural field to slow the wind and reduce soil erosion.
Trees planted along the edge of an agricultural field to slow the wind and reduce soil erosion.
An agricultural technique in which an unplowed field is planted using special drills to prevent soil erosion.
Alternating bands of different crops in the same field to bind soil particles in place between the primary crop rows.
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.
Water that flows through the soil as it percolated into the soil, drawn downward by the force of gravity.
Water that is bound to soil particles and cannot be easily used by plants.
Water that is held in the soil by water-to-water hydrogen bonds.
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
The process that occurs when salts contained in irrgation water concentrate and crystallize on the soil surface due to evaporation.
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.
Planting of a single crop species.
The practice of planting multiple crop species in the same field.
(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.
A pesticide that kills a wide variety of organisms.
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.
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.
Foods produced to meet strict standards that limit the use of fertilizers and pesticides.
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
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
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
- 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
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
- Amount of water amount of soil can hold - Depends on soil particle structure
Soil wilting point
- Point where less water available than transpiration rate
- 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
+ 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
- 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
- Produced following standards for pesticide and fertilizer use
• Water important resource for food production • Water footprint - Includes water for production, consumption, and waste • Methods of production vary widely in water use
• Production methods affect public health - E. coli - Melamine contamination • Inspection of imported foods
Choices can reduce environmental impacts and encourage sustainable agriculture