http://academic.evergreen.edu/curricular/ecoag2001/ecoagprgm.htm

Components of place: the plant and climate

Martha Rosemeyer

Ecological Agriculture

October 7, 2003

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

The agroecosystem

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

Photosynthetically active radiation

Red and blue light used

Green light reflected

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

Comparison

C3 vs C4

Net PS rates

double in C4

plants

Carbon can be partitioned differently within the plant

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

Coffee - Musa intercrop

Colombia

Smallholder diverse shaded production system

Cropping systems can modify light

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

Temperature conversion

°C = 5/9 (°F – 32)

0 °C = 32 °F

18 °C = 65 °F

100 °C = 212 °F

Plant’s range of tolerance

Why is it cold in the winter and warm in the summer in the Northern hemisphere?

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

The “spread” of incoming radiation due to earth’s tilt determines seasonality

Seasonal

changes

in distribution

of solar

radiation:

daylength

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

The tilt

Is responsible for: light intensity anddaylength

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

Topographic variation

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

Gerry Malko’s fruit farm in Yakima

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°

Why are temperate zone farmers always looking to the west?

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

Orographic ppt

Frontal precipitation

Corn-bean-squash polyculture can modify microclimate

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

Lec 1: Questions for advanced credit students

What is the name of the watershed we are in?What types of salmon are found in that

watershed?What are the average frost dates?What is the average rainfall? What is its

seasonal pattern (frequency)? Hours of sunlight? Average monthly temperature?