http://academic.evergreen.edu/ curricular/ecoag2001/ecoagprgm. htm
Post on 21-Dec-2015
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TRANSCRIPT
Outline
I. Review of approachII. The plantIII. Climate and management to reduce
influence Radiation Circulation Precipitation
Review
Why systems? Allows for general understanding of function
This is transferable place to placeComponents of the system (structure)
change, but the system generally functions similarly at the scale at which we are studying systems
Why are we teaching ecological agriculture this way?
If taught with only structure, and little understanding of the ecosystems underpinnings of function, then farming becomes a “recipe”.
Does this help students develop their decision-making skills?
One needs both the function and the structure.
Complementary approaches
The components present at the particular place are the structure of the agroecosystem
System flows and cycles at the scale that we are learning them describe the general agroecosystem function variations in it may be dictated by structure
What characteristics give structure to an agroecosystem?
The components of the system plants animals sun soil water
nutrients cycle through themenergy flows through them
II. The Plant, basic component of agroecosystem: When you arrive at a place...Observe what plants are native thereFind out what animals were historically there,
particularly what are known as “keystone” species
When you arrive at a potential farm, observe what is growing there now what grows where it is often wet and low, upland what grows on south facing slopes, north
Vegetation can indicate humid and fertile areas
Traditional knowledge identifies weeds or second growth vegetation with good growing conditions for particular crops
Bracken fern indicates
area good for beans
in Costa Rica
General kinds of plants
Annuals- A plant that completes its entire life cycle in one year (from seed to seed in one year) Plants that do not overwinter but spread by seed. Herb, herbaceous
Perennials- A plant that lives for more than two years-- plants that “overwinter”. Woody plants, trees and shrubs
What is the ecological function of a plant? One is to:
Fix carbon from the air into a form of stored chemical energy that is usable by them
CO2 + H2O + light energy C6H12O6 + 6O2 + 6H2O
Glucose is used for energy and building block of cellulose
Herbivores can take advantage of this energy too
Not all plants fix C the same wayC3, C4 and Crassulacean Acid Metabolism (CAM)
C3- CO2 forms a 3-C compound most plants
C4- CO2 forms a 4-C compound, then has source of CO2 off, even if stomata are closed advantage in warm, dry conditions corn, sorghum, sugarcane
CAM- same as C4 but plants let CO2 in at night have closed stomata in the day certain desert-adapted plants
TranspirationThe loss of water vapor
by plant parts, mostly stomata
All life’s processes are dependent on water and transpiration pulls water through the plant
90% of water that flows through plant is transpired
Green revolution vs. traditional grain varietiesPartition more carbon to
seed- from 10-20% in seed of rice
Reduction in stem and leaf
Serious shortage of feed for animals
Less organic matter returned to the soil
Effect on sustainability
Managing the light environmentLight reduced by daylength and cloudsCropping diversity: Humid regions-light management
important, especially where multi-storied systems-- the more stratified the greater challenge for light management
Diverse multistoried systems in tropics are highly productive
Crop selection: C4 plants need high light, e.g. may be more adapted to inland conditions
C3 can take low intensity of light, e.g. coast
Reflective red plastic increases yields Cascadian Home Farm, Rockport, WA
TESC student, Erin Foremen
Responses of plants to temperatureEvery 10° C doubles enzyme activity
increasing temperature increases many activities of a plant Not all enzymes respond in this way (some can take
freezing temperatures to near boiling)
All physiological responses have limits of tolerance for temperature extremes and narrow ranges where function is optimized
Farmers must carefully adapt their practices to the local temperature regime
Knowing one’s place: Likely temperatures and extremes
Extreme temperatures may be more important than the average
Local vegetation can provide indicators for the temperature extremes
Proper selections of crop types and varieties to likely temperatures
Systems can modify temperatures for crops
What is the temperate zone?Temperate zone defined by: Area between Tropic of Cancer 23.5°N to
Arctic circle 66.5 °N Area between Tropic of Capricorn 23.5°S to
Antarctic circle 66.5 °S
Principal Meterological Processes Radiation Circulation Precipitation
Radiation: seasonal changes due to intensity and daylength
In Tropics (between Tropic of Cancer and Capricorn) perpendicular sunlight in area Sunlight in temperate zone slanted at angle-more
perpendicular during N summer, less during N winter causing seasonal temperature effect along with daylength
4x change in radiation from summer to winter in temperate zone vs. only 15% change in radiation in tropics
Radiation: Photoperiod and Daylength
0° latitude = 12.1 hr
25° = 10.6-13.7 hr
45° = 8.7 – 15.7 hrMany temperate zone plants are selected for
photoperiod sensitivity to coordinate with seasonal temperature changes
Radiation: Temperature changes with altitudeChange in temperature with increasing
altitude• 3.6°F/1000ft or 6.5°C/1000m• conversion factor: °C = 5/9 (°F – 32)
As increase in altitude affects crop development
Altitudinal ceiling coffee 1500 m, corn 3000 m
Maritime vs. continental
Water masses are moderators of temperature
“Maritime influence”Not only water but by the temperature of
the water Gulf Stream Japanese current
Mulches can modify extremes of temperatures
Can shade soil May not always be
beneficial- depends on climate
Can change albedo- reflected light
Can add organic matterLiving mulch
plants grown in between crop plants
Corn with living mulch of sub. clover
Preventing frost damage
Mulching, row coversHoop housesIrrigation - evaporation of moisture
transfers heat from soil to evaporated water vapor, which surrounds crop plants
In fruit orchards, smudging and fans keep cold air from settling in depressions
Atmospheric circulation: pattern of wind movement
Hadley cells—0-30°N (and S), 30-60°, 60-90°
– with other circulation patterns causes rainforest at 0° and deserts at 30°
Atmospheric circulation: pattern of wind movement
Coriolis effect causes wind circulation patterns within Hadley cells
– Westerlies- in Temp. zone
– Trade winds- NE in northern hemisphere, SE in Southern hemisphere
PrecipitationPrecipitation temp. zone caused by:
• 1) orographic ppt - rising air hits mountains and cools air, water vapor condenses
• 2) frontal ppt – two fronts collide, one moves up and cools, water vapor condenses
Agroecosystem adaptation to climate
For low input agriculture- adapt plant to place
This involves adaptation to extremes of climate
Microclimate can be modified by management
QuestionsGliessman Ch 3 #1,3, and 4Gliessman Ch 4
How does the type of photosynthetic apparatus allow adaptation to different environments?
As an agroecosystem manager, how can you manage the light environment (both increase and decrease it) for maximum productivity?
Gliessman Ch 5 #1, 4Advanced credit
Gliessman Ch 6 #2, 3, 4 Gliessman Ch 7 #2, 3